WO2020128021A1

WO2020128021A1 - Particles comprising hydroxyapatite, process for making and their use

Info

Publication number: WO2020128021A1
Application number: PCT/EP2019/086762
Authority: WO
Inventors: Thierry Delplanche; Beatrice Ortego; Michel Caprasse
Original assignee: Solvay Sa
Priority date: 2018-12-20
Filing date: 2019-12-20
Publication date: 2020-06-25

Abstract

Solid particles which comprises a hydroxyapatite and secondary particles. The hydroxyapatite and secondary particles may form agglomerates and/or coreshells in which the hydroxyapatite is in a shell that covers at least partially the secondary particles. The hydroxyapatite may be calcium-deficient, may be a modified hydroxyapatite onto which an additive is deposited and/or a hydroxyapatite composite into which an additive is incorporated or embedded. Preferred processes for making the solid particles may comprise: an acid attack of a Ca source with phosphoric acid at an acidic pH to make brushite followed by an alkaline maturation step to convert brushite to hydroxyapatite and using a source of secondary particles in the first step and/or in the second step to make the solid particles. The secondary particles may comprise water-insoluble chemical substance(s), such as preferably calcium carbonate, silica, alumina, a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.7 and/or a bone char, more preferably calcium carbonate and/or bone char. An adsorbent comprising said solid particles and use thereof in removing contaminants from a fluid.

Description

Particles comprising hydroxyapatite process for making and their use

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to European application No.

18214577.1 filed December 20, 2018, the whole content of this application being incorporated herein by reference for all purposes.

TECHNICAL FIELD

The invention relates to solid particles comprising hydroxyapatite and secondary particles, a process for producing them and their use in removing contaminants from a fluid.

BACKGROUND ART

It is common to treat various sources of waste effluents in order to remove contaminants. Examples of sources of waste effluents for treatment include water sources such as surface water, ground water, and industrial aqueous waste streams.

The problems posed by the impact of heavy metals in the environment are well known. Numerous industrial processes release liquid or gaseous effluents that are heavily loaded with heavy metals, in particular heavy metal soluble salts, such as cationic form salts. The expression "heavy metals" is understood to mean metals whose density is at least equal to 5 g/cm³, and also beryllium, arsenic, selenium, and antimony, in accordance with the generally accepted definition (Heavy Metals in Wastewater and Sludge Treatment Processes; Vol I, CRC Press Inc; 1987; page 2). Lead or cadmium are particularly significant examples, given their harmful effect on the human body. Nickel is another example thereof due to its allergenic effect.

Wastewater treatment is one of the most important and challenging environmental problems. For example, in the coal -based power generation, using wet scrubbers to clean flue gas is becoming more popular worldwide in the electrical power industry. While wet scrubbers can greatly reduce air pollution, toxic metals in the resulting wastewater present a major environmental problem. The industry is preparing to invest billions of dollars in the next decade to meet ever-more stringent environmental regulations; unfortunately, a cost-effective and reliable technology capable of treating such complicated wastewater is still being sought after. Hydroxyapatite is an adsorbent mainly used for trapping and

immobilizing metals within its structure from contaminated effluents, particularly aqueous effluents. Cationic species such as zinc, copper and lead are preferentially trapped over anionic species such as arsenate (As04), selenate (Se04), or molybdate (Mo04). Furthermore, hydroxyapatite does not exhibit a high affinity for mercury despite being in cationic form. As a result, the use of hydroxyapatite cannot be an all-in-one solution for removing the main contaminants from a wastewater effluent to meet the environmental regulations for safe discharge.

Additionally, it is believed that a large portion of the hydroxyapatite present in hydroxyapatite particles is not used to trap and immobilize metals as the metals do not have access to the hydroxyapatite located inside the particles. Thus there is an inefficient use of the hydroxyapatite in the form of particles.

There is a need for a solid hydroxyapatite-based adsorbent effective on treating effluents for example of industrial origin and also applicable to water purification in general to remove anionic and cationic species of contaminating elements, but for which there is a more efficient use of the hydroxyapatite in the adsorbent.

It is thus useful to develop a material capable of absorbing and retaining large amounts and varieties of contaminants for treating industrial effluents such as wastewaters originating from treatment plants before the release thereof into the natural environment, or even the treatment of natural aquifer waters, some of which are naturally loaded with contaminants and in particular Cd, Cr, Ni, Zn, and As.

SUMMARY OF INVENTION

A first aspect according to the present invention relates to solid particles comprising which comprises a hydroxyapatite and secondary particles.

The solid particles may be in the form of coreshells and/or agglomerates. The hydroxyapatite and secondary particles may form agglomerates and/or the hydroxyapatite may be in a shell that covers at least partially the secondary particles.

The hydroxyapatite may be calcium-deficient, may be a modified hydroxyapatite onto which an additive is deposited and/or a hydroxyapatite composite into which an additive is incorporated or embedded.

The secondary particles may comprise water-insoluble chemical substance(s), such as preferably calcium carbonate, silica, alumina, a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.7 and/or a bone char, more preferably calcium carbonate and/or bone char.

It has been surprisingly found that such solid particles which contain hydroxyapatite and secondary particles can be used as an adsorbent for removal of contaminants from a fluid. In particular, these solid particles which contain hydroxyapatite and secondary particles have an improved removal efficiency with respect to metals and non-metals from water compared to hydroxyapatite particles.

An embodiment of the first aspect according to the present invention relates to solid particles comprising :

- agglomerates of a hydroxyapatite and secondary particles.

Another preferred embodiment of the first aspect according to the present invention relates to solid particles comprising :

- a core; and

- a shell comprising a hydroxyapatite, in which the shell covers at least partially the secondary particles (serving as particle core).

The secondary particles or core may comprise water-insoluble chemical substance(s) in solid form.

As used herein, the water solubility is a measure of the amount of chemical substance that can dissolve in water at 25°C. A water-insoluble chemical substance(s) has a water solubility of less than 500 mg/L, preferably less than 200 mg L, at 25°C.

The secondary particles or core may comprise:

• a substance that contains Ca but no P, such as calcium carbonate, · a substance that does not contain Ca nor P, such as silica, alumina,

• a substance that contains Ca and P, such as a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.7 or a bone char, or

• combinations thereof

The secondary particles or core preferably comprises calcium carbonate, silica, alumina, bone char, or any combination thereof, more preferably comprises calcium carbonate and/or a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.67 or a bone char.

In some embodiments, the secondary particles or core are preferably made from or contains a solid calcium source which is used to synthesize the hydroxyapatite which then forms a shell at least partially covering the secondary particles or core comprising unreacted calcium source. Accordingly, a preferred embodiment of the first aspect of the present invention relates to coreshell solid particles comprising :

- a core containing calcium carbonate; and

- a shell comprising a hydroxyapatite, said shell covering at least partially the core.

Accordingly, another embodiment of the first aspect according to the present invention relates to solid particles comprising :

- agglomerates of a hydroxyapatite and secondary particles of calcium carbonate. The solid particles may have an overall Ca:P molar ratio of at least 1.75, preferably at least 1.8, more preferably at least 1.9, yet more preferably at least 2. The particles may have an overall Ca:P molar ratio of at most 12, preferably at most 10, more preferably at most 6.

Accordingly, another embodiment of the first aspect of the present invention relates to coreshell solid particles comprising :

- a core containing bone char; and

- agglomerates of a hydroxyapatite and secondary particles of bone char.

The particles may have an overall Ca:P molar ratio of at least 1.55, preferably at least 1.6. The particles may have an overall Ca:P molar ratio of at most 1.9, preferably at most 1.8, more preferably at most 1.75.

In the solid particles, the hydroxyapatite agglomerated with secondary particles may be a calcium-deficient hydroxyapatite, preferably a hydroxyapatite with a Ca/P molar ratio more than 1.5 and less than 1.67.

When the secondary particles or core do not comprise Ca, such as silica, alumina, the solid particles may have an overall Ca:P molar ratio of at least 1.55, preferably of at least 1.6 and/or at most 2.0, preferably of at most 1.8, more preferably of at most 1.7.

When the secondary particles or core include Ca but no P, such as calcium carbonate, the solid particles may have an overall Ca:P molar ratio of at least 1.75, preferably at least 1.8, more preferably at least 1.9, yet more preferably at least 2.

When the secondary particles or core comprises both Ca and P with a molar ratio Ca/P of about 1.55 to 1.7, such as bone char, the solid particles may have an overall Ca:P molar ratio of at least 1.55, preferably of at least 1.6 and/or at most 1.9, preferably of at most 1.8, more preferably of at most 1.7.

A particular preferred process for making the solid particles, comprises: an acid attack of a Ca source with phosphoric acid at an acidic pH to make brushite followed by an alkaline maturation step to convert brushite to hydroxyapatite and using a source of secondary particles in the first step and/or in the second step to make the solid particles.

The solid particles may be in the form of coreshells and/or agglomerates.

A first advantage of the solid particles in the present invention is in their use as an adsorbent to remove contaminants from a fluid ; there is an improved removal efficiency with respect to metals and non-metals from a fluid compared to similar particles comprising at least about 90% hydroxyapatite throughout the particles.

A second advantage of the present invention is a lower cost

hydroxyapatite-based material and a lower-cost process for making

hydroxyapatite-based material to be used as adsorbents. In particular, the secondary particles or core can be selected from various low cost sources of preferably water-insoluble substances. Since the adsorption phenomenon primarily takes place at the surface of the adsorbent particles, the production of these solid particles permits to maintain or even increase the adsorption performance while reducing the cost of production because one can select low- cost secondary particles that may or may not participate in the adsorption process. For example a hydroxyapatite having a high BET specific surface area can be optimally used in the solid particles while a low-cost substance such as low BET specific surface area hydroxyapatite (such as bone char) or calcium carbonate can be used in the secondary particles or core.

In some embodiments, the solid particles may comprise, based on the total weight of dry matter:

- at most 85wt%, advantageously at most 70wt%, and more advantageously still at most 65wt% of hydroxyapatite; and

- at least 25wt%, advantageously at least 30wt% of hydroxyapatite.

- more than 7wt%, advantageously more than 20wt%, advantageously more than 25wt% secondary particles such as calcium carbonate; and - at most 75wt%, advantageously at most 70% secondary particles such as calcium carbonate.

In some embodiments, the solid particles may further comprise, based on the total weight of dry matter:

- at least lwt%, advantageously at least 2wt% of water; and

- at most 10t% water, advantageously at most 9wt% water.

In some embodiments when the solid particles comprise coreshells, the shell may further comprise calcium carbonate.

In some embodiments, the solid particles may be essentially free of a calcium phosphate compound other than a hydroxyapatite, preferably essentially free of a calcium phosphate compound selected from the group consisting of monocalcium phosphate monohydrate, dicalcium phosphate dihydrate, dicalcium phosphate anhydrous, and octacalcium bis(hydrogen phosphate)

tetrakisphosphate pentahydrate.

In some embodiments, the solid particles may have a BET surface area of more than 60 m²/g and preferably up to 180 m²/g.

In some embodiments, the solid particles may have a pore volume of from 0.3 cm³/g up to 0.45 cm³/g.

In some embodiments, the hydroxyapatite in the solid particles may be a modified hydroxyapatite onto which at least one additive is deposited on the hydroxyapatite.

In some embodiments, the hydroxyapatite in the solid particles may be a hydroxyapatite composite wherein the at least one additive is incorporated or embedded into the hydroxyapatite. In such instance, the at least one additive comprises copper or derivatives thereof, iron or derivatives thereof (such as iron hydroxide, zero-valent iron, FeOOH, iron oxide), a metal sulfide, and/or activated carbon.

A second aspect of the present invention relates to a process for making the solid particles according to any embodiment described herein in relation to the first aspect of the invention. The solid particles may be in the form of coreshells and/or agglomerates.

The process comprises two steps: a first step (acid attack) of a Ca source with a source of phosphate at an acidic pH to make a calcium phosphate structure (other than hydroxyapatite) followed by a second step (alkaline maturation) to convert, with a source of hydroxide, the calcium phosphate structure to hydroxyapatite and using a source of secondary particles in the first step and/or in the second step to make coreshells and/or agglomerated solid particles.

The Ca source to make the calcium phosphate structure is preferably calcium carbonate.

The source of phosphate is preferably phosphoric acid.

The calcium phosphate structure (other than hydroxyapatite) is preferably brushite.

The source of hydroxide is preferably calcium hydroxide.

The source of secondary particles comprises water-insoluble substances, such as preferably calcium carbonate, silica, alumina, and/or a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.67 and/or a bone char.

In preferred embodiments, the process comprises:

- in a first acid attack step, calcium-containing particles (a Ca source) and phosphoric acid are mixed in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of from 1.2 to 12, preferably from 1.7 to 11, more preferably from 1.9 to 10, and reacting the calcium-containing particles with said phosphoric acid at a pH of between 4 and 7, in order to obtain a suspension (A) of calcium phosphate and calcium carbonate,

wherein the calcium-containing particles contain calcium carbonate, preferably contain >70 wt% calcium carbonate, more preferably contain >90 wt% calcium carbonate, most preferably contain >95 wt% calcium carbonate; and

- in a second alkaline maturation step, adding to the suspension (A) a calcium compound comprising hydroxide ions in order to increase the pH to at least 7 and at most 10.5 to obtain a suspension (B) of the solid particles having an overall Ca/P molar ratio of at least 1.7, preferably at least 1.8, more preferably at least 1.9 and at most 12, preferably at most 8, more preferably at most 6.

In this preferred embodiment, the calcium-containing particles used in the first step comprises calcium carbonate and serve not only as a Ca source to make brushite but also as source of secondary particles.

In yet another preferred embodiments, the process comprises:

- in a first acid attack step, calcium-containing particles and phosphoric acid are mixed in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of less than 1.2 and more than 0.9, preferably from 0.95 to 1.1, and reacting the calcium-containing particles with said phosphoric acid at a pH of between 3 and 7, in order to obtain a suspension (A) of brushite, wherein the calcium-containing particles contain calcium carbonate, preferably contain >70 wt% calcium carbonate, more preferably contain >90 wt% calcium carbonate, most preferably contain >95 wt% calcium carbonate; and

- in a second alkaline maturation step, adding, to the suspension (A), calcium- containing particles and calcium hydroxide ions in order to increase the pH to at least 7 and at most 10.5 to obtain a suspension (B) of the solid particles having an overall Ca/P molar ratio of at least 1.75, preferably at least 1.8, more preferably at least 1.9 and at most 12, preferably at most 8, more preferably at most 6.

In this preferred embodiment, the calcium-containing particles used in the first and second step is the same and comprises calcium carbonate, and serve not only as a Ca source to make brushite in the first step but also as source of secondary particles in the second step.

In yet other preferred embodiments, the process comprises:

- in a first acid attack step, calcium-containing particles and phosphoric acid are mixed in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of less than 1.2 and more than 0.9, preferably from 0.95 to 1.1, and reacting the calcium-containing particles with said phosphoric acid at a pH of between 3 and 7, in order to obtain a suspension (A) comprising brushite,

- in a second alkaline maturation step, adding, to the suspension (A) calcium hydroxide ions in order to increase the pH to at least 7 and at most 10.5 to obtain a suspension (B) of the solid particles; and

- further adding a source of secondary particles in the first and/or second steps, wherein the source of secondary particles comprises or is a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.67 or a bone char.

In preferred embodiments of the process, the calcium compound comprising hydroxide may comprise or consist essentially of calcium hydroxide.

A third aspect of the present invention relates to the use of the solid particles as adsorbent for removing from a fluid at least a portion of a contaminant or a method for removing from a fluid at least a portion of a contaminant using the solid particles as adsorbent. In particular embodiments of the third aspect of the present invention, the contaminants may be selected from the group consisting of Al, Ag, As, B, Ba,

Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hg, Hf, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr. The solid particles are particularly suitable as adsorbent for removing from a fluid at least a portion of Cd, Cr, Ni, Zn, and/or As from a fluid, such as a water effluent.

Such use or method may comprise contacting the solid particles according to any of the first aspect of the present invention with said fluid for a time sufficient to remove at least a portion of the element, preferably Cd, Cr, Ni, Zn, and/or As, from the fluid.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying methods or processes or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions or methods or processes do not depart from the spirit and scope of the invention as set forth in the appended claims.

DEFINITIONS

Unless otherwise specified, all reference to percentage (%) herein refers to percent by weight.

As used herein, a“high BET specific surface area” represents a BET specific surface area of more than 60 m²/g and preferably up to 200 m²/g, more preferably up to 180 m²/g.

As used herein, a“low BET specific surface area” represents a BET specific surface area of at most 60 m²/g, preferably of at most 50 m²/g.

As used herein, the water solubility is a measure of the amount of chemical substance that can dissolve in water at 25°C. A water-insoluble chemical substance(s) has a water solubility of less than 500 mg/L, preferably less than 200 mg/L, at 25°C.

“Fresh” material or sorbent denotes a material which has not been in contact with contaminants, whereas“spent” material denotes a material which has already been in contact with contaminants. As used herein, the term“upstream” refers to a position situated in the opposite direction from that in which the fluid to be treated flows.

As used herein, the term“downstream” refers to a position situated in the same direction from that in which the fluid to be treated flows.

As used herein, the terms“% by weight”,“wt%”,“wt. %”,“weight percentage”, or“percentage by weight” are used interchangeably.

As used herein, the term“dry matter” refers to a material which has been subjected to drying at a temperature of 105°C for at least 1 hour.

As used herein, the term“precursor of the additive” refers to a compound that is converted to the additive. For example a copper salt like copper chloride can be converted to, at least in part, copper sulfide during the making of a modified hydroxyapatite in the solid particles.

In the present specification, the choice of an element from a group of elements also explicitly describes :

- the choice of two or the choice of several elements from the group,

- the choice of an element from a subgroup of elements consisting of the group of elements from which one or more elements have been removed.

In addition, it should be understood that the elements and/or the characteristics of a composition, a method, a process or a use, described in the present specification, can be combined in all ways possible with the other elements and/or characteristics of the composition, method, process, or use, explicitly or implicitly, this being without departing from the context of the present specification.

In the passages of the present specification that will follow, various embodiments or items of implementation are defined in greater detail. Each embodiment or item of implementation thus defined can be combined with another embodiment or with another item of implementation, this being for each mode or item unless otherwise indicated or clearly incompatible when the range of the same parameter of value is not connected. In particular, any variant indicated as being preferred or advantageous can be combined with another variant or with the other variants indicated as being preferred or advantageous.

In the present specification, the description of a range of values for a variable, defined by a bottom limit, or a top limit, or by a bottom limit and a top limit, also comprises the embodiments in which the variable is chosen, respectively, within the value range : excluding the bottom limit, or excluding the top limit, or excluding the bottom limit and the top limit. In the present specification, the description of several successive ranges of values for the same variable also comprises the description of embodiments where the variable is chosen in any other intermediate range included in the successive ranges. Thus, for example, when it is indicated that "the magnitude X is generally at least 10, advantageously at least 15", the present description also describes the embodiment where : "the magnitude X is at least 11", or also the embodiment where : "the magnitude X is at least 13.74", etc.; 11 or 13.74 being values included between 10 and 15.

The term "comprising" includes "consisting essentially of and also "consisting of.

In the present specification, the use of "a" in the singular also comprises the plural ("some"), and vice versa, unless the context clearly indicates the contrary. By way of example, "a material" denotes one material or more than one material.

If the term "approximately" or“about” is used before a quantitative value, this corresponds to a variation of ± 10 % of the nominal quantitative value, unless otherwise indicated.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS SOLID PARTICLES

The first aspect according to the present invention relates to solid particles comprising which comprises a hydroxyapatite and secondary particles.

- agglomerates of a hydroxyapatite and secondary particles. A preferred embodiment of the first aspect according to the present invention relates to solid particles comprising :

- a core; and

The secondary particles or core may comprise water-insoluble chemical substance(s). As used herein, the water solubility is a measure of the amount of chemical substance that can dissolve in water at 25°C. A water-insoluble chemical substance has a water solubility of less than 500 mg/L, preferably less than 200 mg/L, at 25°C.

The secondary particles or core preferably originates from a source of particles that have a BET specific surface area lower than the hydroxyapatite.

The secondary particles or core may comprise a substance having a low BET specific surface area, i.e., of 60 m²/g or less.

The secondary particles or core may comprise:

• a substance that contains Ca but no P, such as calcium carbonate,

• a substance that does not contain Ca nor P, such as silica, alumina,

· combinations thereof

The secondary particles or core preferably comprise calcium carbonate and/or a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.67 or a bone char.

“Bone char” (also called“bone charcoal”) refers to a porous, black, granular material produced by charring animal bones. Its composition varies depending on how it is made. Bones (especially cow bones) are heated in a sealed vessel at up to 700 °C (1,292 °F); a low concentration of oxygen is maintained during heating, as oxygen content affects the quality of the bone char product, particularly its adsorption capacity. Most of the organic material in the bones is driven off by heat. Bone char generally contains 7-10% carbon.

A bone char typically comprises from 55 to 90 wt% hydroxyapatite.

A bone char to be used as source of secondary particles or core generally has a low BET specific surface area. The hydroxyapatite in the solid particles preferably has a higher BET specific surface area than the bone char.

A bone char represents a low-cost source of secondary particles. The solid particles according to the invention in general comprise, based on the total dry matter weight,

- at most 95wt%, advantageously at most 85wt%, and more advantageously still at most 75wt% of hydroxyapatite; and/or

- at least 25wt%, advantageously at least 30wt% of hydroxyapatite.

The solid particles preferably comprise, based on the total weight of the hydroxyapatite and the secondary particles:

- from 25 to 85 wt%, preferably from 30 to 80 wt%, more preferably from 35 to 70 wt% of the hydroxyapatite and

- from 15 to 75 wt%, preferably from 20 to 70 wt%, more preferably from 30 to

65 wt%, of the secondary particles.

When the secondary particles or core comprise Ca and P with a molar ratio

Ca/P of about 1.5 to 1.7, such as bone char, the solid particles may have an overall Ca:P molar ratio of at least 1.55, preferably of at least 1.6 and/or at most 2.0, preferably of at most 1.8, more preferably of at most 1.7.

The weight ratio of the hydroxyapatite to secondary particles or core in the solid particles may be generally equal to or greater than 0.25, preferably equal to or greater than 0.3, more preferably equal to or greater than 0.4, yet more preferably equal to or greater than 0.6, and/or less than 12, more preferably less than 10, yet more preferably less than 8, most preferably less than 3.

One particular embodiment of the first aspect according to the present invention relates to coreshell solid particles comprising :

- a core containing calcium carbonate; and

- a shell comprising a hydroxyapatite, in which the shell covers at least partially the core.

Another particular embodiment of the first aspect according to the present invention relates to agglomerated solid particles comprising : - agglomerates of calcium carbonate (as secondary particles) and the

hydroxyapatite.

These coreshell or agglomerated solid particles have an overall Ca:P molar ratio of at least 1.75, preferably at least 1.8, more preferably at least 1.9, yet more preferably at least 2. These coreshell or agglomerated solid particles may have an overall Ca:P molar ratio of at most 12, preferably at most 10, more preferably at most 6.

Another particular embodiment of the first aspect according to the present invention relates to coreshell solid particles comprising :

- a core containing bone char; and

Another particular embodiment of the first aspect according to the present invention relates to agglomerated solid particles comprising :

- agglomerates of bone char (as secondary particles) and the hydroxyapatite.

These coreshell or agglomerated solid particles preferably have an overall Ca:P molar ratio of at least 1.55, preferably at least 1.6, and/or at most 1.9, preferably at most 1.8.

In preferred embodiments, the solid particles have a mean diameter D50 of which is greater than 10 pm, in general at least 20 pm, or even at least 25 pm, or even at least 30 pm, or even at least 35 pm, and/or preferably less than 1000 pm, or even less than 800 pm, or even less than 500 pm.

In some preferred embodiments, the solid particles have a mean diameter D50 from 20 microns to 60 microns. The mean particles size D50 is the diameter such that 50 % by weight of the particles have a diameter less than said value.

The particle size measurement may be measured using laser diffraction, such as using a Beckman Coulter LS 230 laser diffraction particle size analyser (laser of wavelength 750 nm) on particles suspended in water and using a size distribution calculation based on Fraunhofer diffraction theory (particles greater than 10 pm) and on Mie scattering theory (particles less than 10 pm), the particles being considered to be spherical.

In additional embodiments, the solid particles have a BET specific surface area of at least 60 m²/g, preferably of at least 90 m²/g, more preferably of at least 100 m²/g, yet more preferably of at least 110 m²/g.

In additional embodiments, the solid particles have a BET specific surface area of at most 180 m²/g, preferably of at most 170 m²/g. In additional embodiments, the solid particles have a total pore volume of at least 0.25 cm³/g, or at least 0.30 cm³/g, or at most 0.45 cm³/g, or at most 0.4 cm³/g.

A calcium phosphate (‘CaP’) compound such as the hydroxyapatite in the solid particles can be detected using Scanning Electron Microscopy (SEM) with backscattered electron detector (BED) such as on a JCM-6000 PLUS SEM from JEOL. A calcium phosphate particle will appear white in contrast to grey-coloured particles that do not contain CaP compounds. This SEM technique with BED detector can be used to identify the hydroxyapatite in the resulting solid particles. If the secondary particles also contain a calcium phosphate compound (such as bone char), it may be difficult to differentiate between these two CaP compounds, unless they have different shapes. The hydroxyapatite may be in the form of particles that comprise plate-like crystallites, of thickness of a few nano-meters (nm) on their surface, with the sharp edges of plate-like crystallites associated with the hydroxyapatite structure. The bone char will appear like irregular-shaped particles, generally having been subjected to grinding. An example of such hydroxyapatite shape was shown in WO2015/173437.

The term "apatite" denotes a family of mineral compounds, the chemical formula of which can be written in the following general form:

MIO(X0₄)₆Y2

In this formula, M generally represents a divalent cation (M²⁺), X0₄ a trivalent anionic group (X0₄ ³ ) and Y a monovalent anion (U ).

Calcium phosphate hydroxyapatite Caio(P0₄)₆(OH)₂ crystallizes in the space group of the hexagonal system. This structure consists of a close-packed quasi-hexagonal stack of X0₄ groups, forming two types of parallel tunnels.

The existence of these tunnels gives apatites chemical properties akin to those of zeolites. Vacancies may also be created either by the departure of anions and cations, or by the presence of cations or anions of different valency. Apatites therefore appear to be particularly stable structures which may tolerate large gaps in their composition.

Hydroxyapatite should not be confused with tricalcium phosphate (TCP), which has a similar weight composition: Ca₃(P0₄)_2. The Ca/P molar ratio of TCP is 1.5 whereas it is 1.67 for hydroxyapatite. Industrial apatites sold as food additives or mineral fillers are, as a general rule, variable mixtures of TCP and hydroxyapatite. Other salts of calcium and phosphate, including TCP, do not have the same properties as hydroxyapatite. Although TCP can also react with heavy metals, hydroxyapatite is more advantageous as it can enclose metals in the form of an insoluble, and therefore relatively inert, matrix.

The hydroxyapatite in the solid particles may be deficient in calcium compared to a stoichiometric hydroxyapatite with a Ca/P molar ratio of 1.67. The Ca/P molar ratio of the calcium-deficient hydroxyapatite is preferably more than 1.5 and less than 1.67, more preferably with a Ca/P molar ratio more than 1.54 and less than 1.65.

In preferred embodiments, the solid particles comprise a shell of a calcium- deficient hydroxyapatite, preferably with a Ca/P molar ratio more than 1.5 and less than 1.67.

In some embodiments when the secondary particles or core does not comprise calcium and P, the solid particles may comprise a calcium-deficient hydroxyapatite with a Ca/P of less than 1.67 and has an overall Ca/P molar ratio is about the same as the calcium-deficient hydroxyapatite.

In some embodiments when the secondary particles or core comprises calcium and no P, the solid particles may comprise a calcium-deficient hydroxyapatite with a Ca/P of less than 1.67 but has an overall Ca/P molar ratio higher than the calcium-deficient hydroxyapatite, preferably of at least 1.75. In more preferred embodiments, the calcium-deficient hydroxyapatite may have a Ca/P molar ratio of about 1.55-1.59, while the solid particles may have an overall Ca/P molar ratio of at least 1.75, preferably at least 1.8, more preferably at least 1.9, yet more preferably at least 2 and/or an overall Ca:P molar ratio of at most 12, preferably at most 10, more preferably at most 6.

Calcium may be present in another form (other than the hydroxyapatite) in the solid particles. Calcium carbonate may be present in solid particles when in coreshell form, preferably in the core and optionally in the shell.

Bone char as another form of Ca may be present in the secondary particles or cores of solid particles.

In some embodiments with solid particles in coreshell form, the shell may further comprise calcium carbonate. When the shell and the core both comprise calcium carbonate, more than 50% of the weight of the CaC03, preferably more than 55% of the weight of the CaC03, is present in the core.

When solid particles comprises calcium carbonate, the weight ratio of the calcium-deficient hydroxyapatite to calcium carbonate in the solid particles is generally equal to or greater than 0.4, preferably equal to or greater than 1, more preferably equal to or greater than 2, and/or less than 20, more preferably less than 12, more preferably less than 6.

Generally, when the solid particles comprises a calcium compound but no P in the secondary particles, because of this other form of Ca in the solid particles, the solid particles may have an overall Ca/P molar ratio higher than the calcium-deficient hydroxyapatite present in the solid particles. For that reason, in some embodiments, even though the calcium-deficient hydroxyapatite may have a Ca/P molar ratio less than 1.67, the entire solid particles may have a Ca/P molar ratio more than 1.75, however it is generally not more than 12.

Other salts of calcium and phosphate, including TCP, do not have the same properties as hydroxyapatite or a hydroxyapatite-like structure. Although TCP can also react with metals, a hydroxyapatite of Ca/P=1.67 as well as a calcium- deficient hydroxyapatite (1.5 < Ca/P < 1.67) are more advantageous because they can enclose or entrap metals in an insoluble form, and therefore relatively inert, matrix.

When the secondary particles does not comprise calcium nor phosphate such as silica, alumina, the solid particles may have an overall Ca/P molar ratio from about 1.55 to about 1.8, preferably from 1.55 to 1.67.

In some embodiments, the solid particles may further comprise: water, of the order of from 0 to 20 wt%, advantageously from 1 % to 20 wt%, more advantageously from 2 % to 10 wt%, based on the total weight of dry matter further comprising, based on the total weight of dry matter:

In some embodiments, the solid particles may comprise water, of the order of from 5 wt% to 20 wt%, advantageously from 6 wt% to 20 wt%, based on the total weight of dry matter.

In preferred embodiments, the solid particles may comprise, based on the total weight of dry matter,

- at least lwt%, advantageously at least 2wt% of water; and/or

- at most 10t% water, advantageously at most 9wt% water.

The solid particles may further comprise, based on the total weight of dry matter, calcium dihydroxide Ca(OH)₂ from 0 to 4 %, or more advantageously from 0 to 1 wt%, or alternatively more than 0 wt% but at most 4 wt%, or from 1% to 4wt%.

The solid particles may further comprise, based on the total weight of dry matter, less than 1 wt% of calcium dihydroxide Ca(OH)₂, preferably less than 0.5 wt% calcium dihydroxide, more preferably less than 0.3 wt% calcium

dihydroxide, even more preferably less than 0.2 wt% calcium dihydroxide, or even less than 0.1 wt% Ca(OH)_2.

In some embodiments, the solid particles are substantially free of calcium dihydroxide (i.e., less than 0.1 wt% Ca(OH)₂).

The solid particles may additionally contain residual compounds or impurities originating from raw materials used and/or intermediates in its manufacture, such as: sands or clays; these residual constituents or impurities are in general less than 2% by weight based on the total weight of dry matter.

In some embodiments, the solid particles contains less than 10 wt% of tricalcium phosphate (TCP) or preferably excludes TCP.

Preferably, the solid particles are essentially free (e.g., less than 0.5 wt%) of a calcium phosphate compound other than a hydroxyapatite, preferably essentially free of a calcium phosphate compound selected from the group consisting of monocalcium phosphate monohydrate, dicalcium phosphate dihydrate, dicalcium phosphate anhydrous, and octacalcium bis(hydrogen phosphate) tetrakisphosphate pentahydrate.

In preferred embodiments, the solid particles do not contain an organic polymer crosslinked network, for example created by in-situ polymerization of at least one polymer during the synthesis of the hydroxyapatite.

In some embodiments, the solid particles may exclude a polymer, such as may exclude chitosan and/or a polyvinyl alcohol.

In preferred embodiments, the solid particles are inorganic.

In other embodiments, the solid particles contain less than 1 wt% organics. In some embodiments, the solid particles may exclude bone char.

In some embodiments, the solid particles may further include bone char.

In some embodiments, the solid particles may be substantially free of carbon, i.e., less than 0.5 wt% of carbon.

In preferred embodiments, the solid particles may further include from 1 to 30 wt% activated carbon, preferably from 2 to 20 wt% activated carbon, more preferably from 3 to 15 wt% activated carbon.

In some embodiments, the hydroxyapatite in the solid particles is a hydroxyapatite composite wherein at least one additive is incorporated or embedded into the hydroxyapatite. The hydroxyapatite composite in the solid particles may comprise more than one additive. In such embodiments, a first additive may serve as support for a second additive.

In some embodiments, the additive or precursor thereof may be in the form of a solid before it is added at the beginning or during the (second) alkaline maturation step of the process for making the solid particles.

In some embodiments, the additive or precursor thereof may be in the form of a solid before it is added to at least one of the first and second steps of the two-step process of making the solid particles.

The hydroxyapatite composite preferably comprises a weight ratio of hydroxyapatite to additive (HAP: A) of from 1:0.01 to 1 :0.5. That is to say, when lOOg of hydroxyapatite in the composite, a minimum of 1 g of additive is present and/or a maximum of 50 g is present in the composite. The weight ratio of is preferably at least 1 :0.02 or at least 1 :0.03. The weight ratio of is preferably at most 1 :0.3, more preferably at most 1 :0.25. The hydroxyapatite composite may comprise a weight ratio of hydroxyapatite to additive (HAP: A) of from 1 :0.01 to 1 :0.5, preferably from 1 :0.02 to 1 :0.4 or from 1 :0.03 to 1 :0.4, more preferably from 1 :0.04 to 1 :0.3, yet more preferably from 1 :0.05 to 1 :0.25, yet even more preferably from 1 :0.05 to 1 :0.20.

A range of 5 to 20 g additive per 100 g of hydroxyapatite is particularly suitable.

The hydroxyapatite composite may comprise at least 2 wt%, or at least 3 wt%, or at least 4 wt%, or at least 5 wt%, of the additive based on the total weight of dry matter.

The hydroxyapatite composite may comprise at most 50 wt%, or at most

40 wt%, or at most 30 wt%, or at most 20 wt% of the additive based on the total weight of dry matter.

For the hydroxyapatite composite, the at least one additive may comprise copper or derivatives thereof, iron or derivatives thereof (such as iron hydroxide, zero-valent iron, FeOOH, iron oxide), a metal sulfide, and/or activated carbon.

For the hydroxyapatite composite, the at least one additive or a precursor thereof may be added prior to or during the hydroxyapatite synthesis. The additive may be added in the form of a precursor, and this precursor takes the form of the additive during the synthesis of the solid particles for the additive to be present in the final composition of the composite. For example, a precursor of the additive may be a salt of a metal, and during the synthesis of the composite, the salt of a metal is converted to an hydroxide or oxihydroxide of the metal to generate the additive in the hydroxyapatite composite.

Hydroxyapatite composite with activated carbon in the shell

In some embodiments, the hydroxyapatite comprises or is a hydroxyapatite composite and the additive in the hydroxyapatite composite may comprise or consists of at least one activated carbon.

The hydroxyapatite composite may comprise at least 2 wt%, or at least 3 wt%, or at least 4 wt%, or at least 5 wt%, of at least one activated carbon based on the total weight of dry matter.

The hydroxyapatite composite may comprise at most 50 wt%, or at most

40 wt%, or at most 30 wt%, or at most 20 wt% of at least one activated carbon based on the total weight of dry matter.

Activated carbon may originate from various sources. It can be produced from carbonaceous source materials such as bamboo, coconut husk/shell, willow peat, wood, coir, lignite, coal, petroleum coke, and/or petroleum pitch.

In preferred embodiments, the activated carbon used as additive is in a powder form. Its average particle size is generally in size of less than 1 mm. Preferred average particle size for activated carbon may be at most 500 microns, preferably at most 400 microns, or at most 300 microns, or at most 200 microns, or at most 100 microns, or at most 80 microns, or at most 60 microns. Generally, the average particle size for activated carbon may be at least 5 microns, or at least 10 microns.

In particular embodiments, the average particle size for activated carbon is preferably within +/- 50% of the average particle size of the solid particles which are to be synthesized in the presence of this activated carbon.

In particular preferred embodiments, the average particle size for activated carbon is preferably less than the average particle size of the solid particles which are to be synthesized in the presence of this activated carbon.

The activated carbon may be selected based at least on the following criteria: the activated carbon yields a pH of at least 5 when dispersed in a suspension at 0.3 wt% in deionized water for 5 hours.

When the additive comprises an activated carbon or blend of two or more activated carbons, the activated carbon or blend of two or more activated carbons is selected so that a 0.3 wt% dispersion of the activated carbon(s) in deionized water provides a pH of 5 or more. If the selected activated carbon yields a pH of less than 5 when dispersed in a suspension at 0.3 wt% in deionized water for 5 hours, then a blend with another more-alkaline activated carbon may be used in the additive to provide a pH of 5 or more.

The activated carbon may comprise a pore volume of at least 0.25 cm³/g, preferably at least 0.35 cm³/g, more preferably at least 0.4 cm³/g.

The activated carbon may have a BET surface area of at least 500 m²/g, preferably at least 750 m²/g.

The activated carbon may have a unique distribution of pore sizes that contributes to the ability of the composite to remove specific contaminants from aqueous systems. In one embodiment, the activated carbon has a porosity of at least about 0.25 cm³/g. The pores diameter of the activated carbon may be at least about 10 and at most about 500 A (Hg intrusion porosimetry, such as using a Micromeritics model AutoPore-II 9220 porosimeter). In another embodiment, the activated carbon has a porosity of at least about 0.4 cm³/g in pores diameter of at least about 10 and at most about 500 A.

In preferred embodiments, the hydroxyapatite is a hydroxyapatite composite wherein activated carbon is incorporated or embedded into the hydroxyapatite during the synthesis of the solid particles.

In the making of a hydroxyapatite composite comprising activated carbon, because the activated carbon is added prior to or during the synthesis of the hydroxyapatite structure (for example during the alkaline maturation step), the solids associated with the activated carbon are linked to the hydroxyapatite structure via cohesive forces, because they are not released from the solid particles after being submerged under agitation in deionized water, or if the activated carbon is released, its release is less than what would occur with a same amount of the activated carbon not in the solid particles.

In some embodiments, the activated carbon has been subjected to a treatment prior to being used into the synthesis of the solid particles. Such treatment may enhance the sorption capability of the activated carbon and/or modify the porosity of the activated carbon.

For example the activated carbon may be impregnated by sulfur to enhance the sorption of mercury cations. An example of such sulfur-impregnated activated carbon is MerSorb® from NUCON International.

In another treatment example, the activated carbon may be subjected to an acid treatment such as with nitric acid. Yet in another treatment example, the activated carbon may be subjected to steam, generally to impact its porosity.

In some embodiments, the activated carbon is not treated with acid prior to being used into the synthesis of the solid particles.

In some embodiments concerning the formulation of the solid particles, the additive may exclude activated carbon.

Hydroxyapatite composite with iron or derivatives thereof in the shell

In some embodiments, the hydroxyapatite comprises or is a hydroxyapatite composite and the additive in the hydroxyapatite composite may comprise or consists of at least one iron-containing additive.

The iron-containing additive preferably is in the form of metal of oxidation state 0, salt, oxide, oxyhydroxide, or hydroxide, preferably in the form of metal of oxidation state 0, oxide, oxyhydroxide, or hydroxide. The iron in the additive may be of oxidation state 0, 2 or 3. The iron-containing additive is preferably inorganic. If the additive comprises an iron salt, the iron salt is preferably inorganic.

The additive may comprise or consist of an iron oxide. The iron oxide may be iron(III) oxide or ferric oxide of formula FeaCri, iron(II) oxide (FeO), or ΪGoh(II,III) oxide (FesCri). The additive may comprise or consist of Fe3C>4.

When the additive comprises iron, the additive more preferably comprises iron(III) hydroxide, and/or iron(III) oxyhydroxide. Iron(III) hydroxide has the chemical formula Fe(OH)3. Iron(III) oxyhydroxide has the chemical formula FeOOH.

The iron may be added during the synthesis of the hydroxyapatite in the form of an iron precursor such as a salt. A suitable precursor of iron may be iron chloride, iron nitrate, iron sulfate, or any combination thereof. A base (source of OH ) is generally added to this iron precursor to generate iron(III) hydroxide or oxyhydroxide.

Modified hydroxyapatite or hydroxyapatite composite with a metal sulfide in the shell

The hydroxyapatite in the shell may be a modified hydroxyapatite onto which a metal sulfide is deposited on the hydroxyapatite or a hydroxyapatite composite wherein a metal sulfide is incorporated or embedded into the hydroxyapatite.

To enhance the sorption of the hydroxyapatite-based solid particles towards a large spectrum of contaminants and in particular Hg, it has been found that the hydroxyapatite activity can be supplemented by adding a metal sulfide to yield a hydroxyapatite-based material with an improved adsorption affinity and/or efficiency with respect to metals such adsorption affinity and/or efficiency being the same or greater than that of an unmodified hydroxyapatite structure, that is to say, which is not modified or incorporated with a metal sulfide.

In some preferred embodiments, the metal sulfide may be deposited on the hydroxyapatite, preferably in the form of particles, to form a modified hydroxyapatite material. In such instance, the metal sulfide is preferably formed from two precursors/sources. One precursor provides the metal‘Me’ in the metal sulfide and the other precursor provides the‘sulfide’ in the metal sulfide. By “deposited” it is meant that the metal sulfide may be coated onto the

hydroxyapatite surface, or otherwise associated with the hydroxyapatite structure via cohesive forces. This deposition is carried out after the hydroxyapatite is formed in the shell of the particles.

In other preferred embodiments, the metal sulfide may be incorporated or embedded into the hydroxyapatite, preferably in the form of particles, to form a hydroxyapatite composite in the shell. In instances of when forming a composite, the metal sulfide is preferably used‘as is’ and may be sourced from a

commercially available metal sulfide or may be formed separately before being mixed with, incorporated or embedded into the hydroxyapatite.

The modified hydroxyapatite or composite in the shell preferably has a molar ratio of S:Me which is at most twice the stoichiometric ratio of S per Me in the metal sulfide (also referred to a“equivalent” ratio), preferably at most the stoichiometric ratio of S per Me in the metal sulfide, more preferably at most 0.85 eq. S per metal, more preferably at most 0.7 eq. S per metal.

In preferred embodiments, the metal Me in the metal sulfide is selected from the group consisting of iron (Fe), cobalt (Co), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb), antimony (Sb), and any combination of two or more thereof, preferably selected from the group consisting of iron (Fe), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), antimony (Sb), and any combination of two or more thereof; more preferably selected from the group consisting of iron (Fe), copper (Cu), zinc (Zn) and any combination of two or more thereof; most preferably selected from the group consisting of copper (Cu), zinc (Zn), and any combination thereof.

As used herein, the term“MeS” for the metal sulfide is used generically and refers to any form of the metal sulfide and not limited to an equimolar formula with a S:Me=l. For example when copper is the metal Me,“MeS” may encompass CuS and/or CU2S. When antimony Sb is the metal Me,“MeS” may encompass Sb2S3. When iron is the metal Me,“MeS” may encompass the following : pyrite (FeS2, cubic), marcasite (FeS2, orthorombic), greigite (Fe3S4, cubic), smythite (FegSn, hexagonal), mackinawite (FeSi__x, 0<x<0.07, tetragonal), pyrrhotite (Fei__xS, 0<x<0.125, monoclinic and hexagonal) and/or trolite (FeS, hexagonal).

In some embodiments according to the present invention in which the solid particles further comprises a metal sulfide, the solid particles may have plate-like hydroxyapatite crystallites, of thickness of a few nano-meters (nm) on their surface, which may be coated by smaller particles of the metal sulfide or into which smaller particles of the metal sulfide are embedded into the

hydroxyapatite. The smaller particles of the metal sulfide are likely associated with the hydroxyapatite structure via cohesive forces.

In some embodiments according to the present invention, the

hydroxyapatite-based material in the shell of the particles may comprise two distinct types of solids, a first type associated with the hydroxyapatite structure with plate-like crystallites, of thickness of a few nano-meters (nm) on their surface, and another type of solid associated with the metal sulfide. These distinct types of solids are preferably interdispersed.

In the making of a hydroxyapatite composite comprising a metal sulfide, because the metal sulfide is added prior to or during the synthesis of the hydroxyapatite structure (for example during the alkaline maturation step), the particulates associated with the metal sulfide are associated with the

hydroxyapatite structure via cohesive forces, because they are not released from the solid particles after being submerged under agitation in deionized water, or if the metal sulfide is released, its release is less than what would occur with a same amount of the metal sulfide which would not be in the solid particles. PROCESS OF MAKING THE SOLID PARTICLES

A second aspect of the present invention relates to a process for producing the solid particles comprising a hydroxyapatite and secondary particles, which includes using separate sources of calcium and phosphate to form a

hydroxyapatite. The solid particles may be in the form of agglomerates and/or coreshells, in which the hydroxyapatite is in a shell at least partially covering a secondary particle (serving as core).

A particular preferred embodiment of this aspect of the present invention relates to a process for producing the solid particles, which includes using separate sources of calcium and phosphate to form a shell comprising a hydroxyapatite and covering at least partially secondary particles containing calcium carbonate and/or bone char.

The secondary particles or core may comprise water-insoluble chemical substance(s) in solid form. As used herein, a water-insoluble chemical substance(s) has a water solubility of less than 500 mg/L, preferably less than 200 mg/L, at 25°C.

The secondary particles or core may comprise a chemical substance having a low BET specific surface area, i.e., of 60 m²/g or less.

The secondary particles or core preferably comprises calcium carbonate, silica, alumina, bone char, and /or combinations thereof, more preferably comprises calcium carbonate and/or bone char.

The process, generally referred to as the“2-step” process, comprises two steps:

- an acid attack step of calcium-containing particles with a source of phosphate to convert some of the Ca from the calcium-containing particles to solid calcium phosphate and to obtain a suspension (A), then

an alkaline maturation step with a source of hydroxide, such as lime, added to the suspension (A) to form a hydroxyapatite from the solid calcium phosphate.

The process further comprises adding secondary particles in the first step and/or second step. The formed hydroxyapatite may form agglomerates with the secondary particles or may form a shell on top of the secondary particles that remain undissolved and/or unreacted during the process.

During the first step of the 2-step process for making the solid particles, the calcium phosphate compounds formed in the suspension (A) may be a mixture of monocalcium phosphate (MCP) having the weight formula Ca(H₂P0₄)₂, of dicalcium phosphate (DCP) having the weight formula CaHPCL, or the hydrate thereof, brushite, having the weight formula CaHP0_4.2H₂0, and of octacalcium having the weight formula Ca₈H₂(P0₄)_6.6.5H₂0. The Ca/P molar ratios are respectively for these compounds: 0.5 (MCP), 1.0 (DCP and brushite), 1.33 (octacalcium). In order to promote, in the first (acid attack) step of the 2-step process, the formation of MCP and DCP, the calcium-containing particles in the first step under acidic pH preferably comprises calcium carbonate, and the source of phosphate is phosphoric acid (H₃PO₄). Specifically, this makes it possible to obtain a rapid attack of the calcium carbonate and a rapid degassing of the CO₂.

In the 2-step process for making the solid particles of the present invention, phosphoric acid is preferred as source of phosphate in the first step due to its greater availability and lower cost compared to dihydrogen and monohydrogen phosphate salts.

During the first step of the 2-step, the calcium phosphate compound preferably formed in the suspension (A) is dicalcium phosphate (DCP) dihydrate: brushite, having the weight formula CaHP0_4.2H₂0.

The source of hydroxide is preferably calcium hydroxide.

The source of secondary particles may comprise at least one water- insoluble substance, preferably comprise or is calcium carbonate, silica, alumina, and/or a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.67 and/or a bone char.

In some preferred embodiment, the added secondary particles may be calcium carbonate particles which are added in excess compared to the stoichiometric ratio of Ca:P (1.67) to make a hydroxyapatite, so that some CaC03 particles remain at the end of the 2-step process. Therefore a portion of the calcium carbonate particles are used as reactant for the acid attack while another portion is used as secondary particles. The calcium carbonate particles that are remaining after the acid attack and/or those that are added at the beginning of the alkaline maturation step thus provide calcium carbonate- containing secondary particles with which the hydroxyapatite can form agglomerates and/or onto which the hydroxyapatite can form a shell in the second (alkaline maturation) step.

It is to be noted that when calcium carbonate particles added in excess in the first step to serve as secondary particles, it is likely that part of the surface of these particles will be subjected to the acid attack, but there would not be sufficient amount of acid to completely dissolve and convert these particles into the solid calcium phosphate. On the other end, when calcium carbonate particles added in excess in the second step to serve as secondary particles, it is likely that these particles will remain intact and form agglomerates and/or cores to a hydroxyapatite shell.

In some embodiments, the process may further include addition of an additive during the synthesis of the hydroxyapatite to form a hydroxyapatite composite or after the synthesis of the solid particles to modify the

hydroxyapatite present in the solid particles.

In a particular embodiment when calcium-containing secondary particles are added in the first step to serve as a source of Ca to make brushite and also as a source of secondary particles, the process comprises:

- an acid attack of the calcium-containing particles (an excess of which is used so that not all of the calcium-containing particles react with phosphoric acid) with phosphoric acid to at least partially dissolve Ca from the calcium- containing particles and to convert some of the Ca to brushite and to obtain a suspension (A), and then

- an alkaline maturation step with lime (Ca(OH)₂) to form, from the brushite, a hydroxyapatite that forms a shell on top of calcium-containing particles that remain at least partially undissolved and/or unreacted with the acid.

When calcium carbonate-containing particles are added in the first step to serve as a source of Ca to make brushite and also as a source of secondary particles, the process preferably comprises:

- in a first acid attack step, calcium-containing particles and phosphoric acid are mixed in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of from 1.2 to 12, preferably from 1.7 to 11, more preferably from 1.9 to 10, and reacting the calcium-containing particles with said phosphoric acid at a pH of between 4 and 7, in order to obtain a suspension (A) of calcium phosphate and calcium carbonate,

- in a second alkaline maturation step, adding to the suspension (A) a calcium compound comprising hydroxide ions in order to increase the pH to at least 7 and at most 10.5 to obtain a suspension (B) of the solid particles having an overall Ca/P molar ratio of at least 1.7, preferably at least 1.8, more preferably at least 1.9 and at most 12, preferably at most 8, more preferably at most 6. When calcium carbonate-containing particles are added in the first step to serve as a source of Ca to make brushite and also calcium-containing particles are added in the second step to serve as source of secondary particles, the process preferably comprises:

- in the first acid attack step, calcium carbonate-containing particles and phosphoric acid are mixed in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of from 1.2 to 12, preferably from 1.7 to 11, more preferably from 1.9 to 10, and reacting the calcium carbonate-containing particles with said phosphoric acid at a pH of between 4 and 7, in order to obtain a suspension (A) comprising brushite,

wherein the calcium carbonate-containing particles preferably contain >70 wt% calcium carbonate, more preferably contain >90 wt% calcium carbonate, most preferably contain >95 wt% calcium carbonate;

- in the second alkaline maturation step, adding to the suspension (A) calcium- containing particles (such as calcium carbonate and/or bone char) to serve as source of secondary particles and a source of hydroxide ions (such as calcium hydroxide) in order to increase the pH to at least 7 and at most 10.5 to obtain a suspension (B) of the solid particles having an overall Ca/P molar ratio of at least 1.7, preferably at least 1.8, more preferably at least 1.9 and at most 12, preferably at most 8, more preferably at most 6.

When the secondary particles comprise Ca, generally the number of moles of phosphate used in the process is less than what the stoichiometric molar ratio of 1.67 would require compared to the number of moles of Ca used, preferably at least 10% less, more preferably at least 15% less, yet more preferably at least 20% less, most preferably at least 30% less, and up to 90% less, preferably at most 85% less, more preferably at most 80% less, yet more preferably at most 70% less, than the number of moles per moles of Ca used in the synthesis. In preferred embodiments, the number of moles of phosphate used in the process is at least 30% less and at most 70% less than what the stoichiometric molar ratio of 1.67 would require compared to the number of moles of Ca used that would be required to achieve an overall Ca/P ratio of 1.67.

In a preferred embodiment of the 2-step process of the present invention, the calcium-containing particles used as secondary particles in the first and/or second step(s) advantageously comprise calcium carbonate, preferably 70 wt% calcium carbonate, more preferably >90 wt% calcium carbonate, most preferably >95 wt% calcium carbonate. The calcium-containing particles comprise more advantageously a limestone, or a mixture of limestone and calcium oxide or hydroxide. More advantageously, the calcium-containing particles are in the form of powder or aqueous suspension of powder, and the powder has a mean particle size of less than 300 pm.

In another preferred embodiment of the 2-step process of the present invention, the calcium-containing particles used as secondary particles in the first and/or second step(s) advantageously comprise bone char, preferably 70 wt% bone char, more preferably >90 wt% bone char, most preferably >95 wt% bone char.

It is advantageous in the 2-step process for the calcium-containing particles be in the form of a powder or aqueous suspension of powder, and to have a small particle size. It is recommended that the mean diameter of the particles of the powder be less than 300 pm, advantageously less than 200 pm and preferably less than 100 pm. The mean diameter in question is the D50, that is to say the diameter such that 50% by weight of particles have a diameter less than said value.

In another embodiment of the 2-step process of the present invention, the secondary particles in the first and/or second step(s) do not contain calcium.

They may contain for example silica, alumina, or another water-insoluble chemical substance not containing calcium.

In the process for making the solid particles according to the invention, in the first step (acid attack) in the 2-step process, the overall Ca/P molar ratio based on the amounts of reactant used (e.g., calcium carbonate, phosphoric acid and calcium hydroxide) is in particular from 1.2 to 12, preferably from 1.7 to 11, more preferably from 1.9 to 10.

In some instances of coreshell solid particles, some of the calcium carbonate from the initial calcium-containing particles may be found at the surface and/or in the shell of the coreshell particles. Indeed it is possible for the formed hydroxyapatite not to cover the entire surface of the core. In this case, the shell may comprise the formed hydroxyapatite and also some of the calcium carbonate which remains unreacted and undissolved from the initial calcium- containing particles. The remaining calcium carbonate may be intermixed or agglomerated with the hydroxyapatite.

In the present invention, in the first step of the 2-step process, the calcium- containing particles and the phosphoric acid (H3PO4) are in general reacted for at least 0.1 hour, preferably at least 0.5 hour. It is not useful to react the calcium- containing particles and the phosphoric acid over excessively long durations.

Advantageously, the calcium-containing particles and the phosphoric acid in the 2-step process are reacted for at most 4 hours, more advantageously at most 2 hours, or even at most 1 hour. For example, a duration of 1 hour at pH 5 already enables a good reaction of the calcium and the phosphate ions, and makes it possible to sufficiently release the CO2 when the calcium-containing particles comprising calcium carbonate are used, before moving on to the second step.

In the 2-step process according to the present invention, in the (second) alkaline maturation step, the suspension (B) in general has a Ca/P molar ratio of at least 1.7, preferably at least 1.8, more preferably at least 1.9 and of at most 12, preferably at most 8, more preferably at most 6.

In the present invention, it is advantageous, in the second step of the 2-step process, for the calcium compound used that comprises hydroxide ions, to be calcium hydroxide.

In the process for making the solid particles, in general, the stirring and the density of suspension (B), in the (second) alkaline maturation step and advantageously also of suspension (A) in the first step in the 2-step process, are adjusted in order to avoid the appearance of a calcium phosphate gel having a viscosity of at least 200 cps. The viscosity of the composite suspension (B) in the (second) alkaline maturation step is typically about 10 cps (mPa.s). Specifically, the production of a gel, even in the presence of the (second) alkaline maturation step, results in solid particles of small particle size being produced, with weight- average D50 values of less than 10 pm, which is a disadvantage for certain applications for treatment of liquid effluents such as those that use a sludge blanket.

The suspended solids density of the suspension (A) in the first step is in general at most 25% by weight.

The suspended solids density of the suspension (B) in the (second) alkaline maturation step is in general at most 35%, preferably at most 25% by weight.

The suspended solids density of the suspension (A) and or of the suspension (B) is advantageously at least 5 wt%, more advantageously at least 10 wt%. A preferred range of suspended solids density of the suspension (B) in the (second) alkaline maturation step is from 10 wt% to 25 wt%. It has been indeed observed that a too low density of suspension decreases the efficacy of the produced reactant particles in heavy metal adsorption. Moreover a too low density of suspension induces longer time of water separation when decantation or filtration is used in the process.

In the process of the present invention, the stirring of the suspension during the first and (second) alkaline maturation steps corresponds generally to a stirring dissipated energy in the reactors volume of at least 0.2 and at most 1.5 kW/ m³, preferably at least 0.5 and at most 1.0 kW/ m³.

In a first embodiment of the present invention, the first step in the 2-step process is carried out at a temperature of less than 50°C, preferably at a temperature of at most 45°C, or at a temperature of at most 40°C, more preferably at a temperature of at most 35°C. This makes it possible to obtain, at the end of the (second) alkaline maturation step, solid particles of large to medium particle size and having a high specific surface area.

It is generally advantageous for the (second) alkaline maturation step to be carried out at a temperature of at least 45°C, preferably of at least 50°C, more preferably of at least 55°C, or of at least 60°C, or of at least 80°C, and/or of at most 90°C. Specifically, this makes it possible to rapidly convert the calcium phosphate intermediate compound of low Ca/P ratio (such as brushite) formed in the first step into a hydroxyapatite of higher Ca/P ratio, with a good fixation of the hydroxide ions, and to more rapidly consume the phosphates from the solution of the suspension (B). Advantageously, the (second) alkaline maturation step is carried out for a duration of at least 0.5 hour.

In general, the addition of the calcium compound comprising hydroxide ions in order to set the pH of the (second) alkaline maturation step, to obtain the suspension (B) of particles having an overall Ca/P molar ratio of at least 1.7, preferably at least 1.8, more preferably at least 1.9 and at most 12, preferably at most 8, more preferably at most 6, lasts no more than 6 hours, advantageously no more than 4 hours, or no more than 3 hours; at higher temperature such as at 50 or at 60°C a duration of generally one to 2.5 hours may be sufficient, as at 40°C the duration for alkaline compound addition to set the pH of the (second) alkaline maturation step is generally longer: and about 2.5 to 3.5 hours may be needed.

Preferably, the addition of the calcium compound comprising hydroxide ions is stopped when the pH remains at the set value for at least 15 minutes.

It is to be understood that the time for reaction in the (second) alkaline maturation step is generally dependent of the end pH of the (second) alkaline maturation step, and it may be impacted by the size of the equipment that is used to make the solid particles. It was observed for example that, when using the same temperature for the (second) alkaline maturation step, for a 3-L or 5-L reactor, the reaction time needed to reach the pH of about 8 to 9 in the second step was generally from 1 hour to 3 hours, whereas in a 200-L reactor, the reaction time needed to reach the pH of about 8 to 9 in the second step was generally from 2 hours to 6 hours

The addition of calcium hydroxide for setting the pH of the (second) alkaline maturation step provides both hydroxide ions and additional source of calcium to adjust the overall Ca/P ratio.

About from 65 to 95% of the moles of Ca used in the process to make the solid particles are preferably used in the first step of the process, depending on the overall Ca/P molar ratio of at least 1.70 which is desired in the solid particles.

In comparison, for a similar process in which an overall Ca/P ratio of 1.67 is desired to form hydroxyapatite particles (non-coreshell where the

hydroxyapatite is distributed throughout the particles), about 59-61% of the moles of Ca used in the process are used in the first step of the process.

In a particular preferred embodiment, the process for making the solid particles takes place in two steps, the first step called "phosphoric acid attack" and the second step is called "lime maturation". The first step includes the decarbonation of calcium carbonate by the addition of phosphoric acid. Carbonic acid formed by this acid attack decomposes into water and carbon dioxide, as soon as the maximum solubility of CO₂ in the aqueous phase is reached. Calcium hydrogenphosphate (CaHP0_4.2H₂0, also known as brushite) formed in the first step of the 2-step process has a Ca/P molar ratio of 1. In the second step "lime maturation", the addition of lime (Ca(OH) ₂) to the brushite contributes the calcium necessary to approach a stoichiometric hydroxyapatite which is formed with the calcium in the surface of the calcium-containing particles. This addition of lime also allows the addition of hydroxide anions necessary for the structure of the hydroxyapatite and the neutralization of H ⁺ hydrogenphosphate .

This technique has the advantage that it allows the synthesis of

hydroxyapatite as a shell on a core of calcium carbonate particles from relatively inexpensive reagents, compared to other methods, and uses relatively mild conditions of synthesis (temperature and pH). This allows also to reduce the overall cost of production as it is believed that most of the secondary particles is not used in the adsorption process for removing contaminants. Forming coreshell solid particles from calcium carbonate particles retaining a calcium carbonate core thus saves raw material cost in using less phosphoric acid than what would be required if more than 90%, preferably more than 92%, of the calcium carbonate particles would be reacted to form non-coreshell particles, comprising about 90 wt% or more hydroxyapatite distributed throughout the particles with a few wt% of calcium carbonate in the particles.

Therefore, the number of moles of phosphate used in the process compared to the number of moles of Ca is less than what would be require to achieve the stoichiometric molar ratio of 1.67. The number of moles of phosphate used in the process preferably at least 10% less, more preferably at least 15% less, yet more preferably at least 20% less, most preferably at least 30% less, and up to 90% less, preferably at most 85% less, more preferably at most 80% less, than the number of moles per moles of Ca used in the synthesis that would be required to achieve an overall Ca/P ratio of 1.67. In preferred embodiments, the number of moles of phosphate used in the process is at least 30% less and at most 70% less than what the stoichiometric molar ratio of 1.67 would require compared to the number of moles of Ca used.

In this particular preferred embodiment of the process, the first step is to attack calcium carbonate with phosphoric acid at a temperature of from 20 to 25°C to make a brushite type structure as a layer on top of a core of calcium carbonate (secondary particles). At the end of the addition of acid, the second step is initiated by heating the mixture up to at least 50°C. A suspension of Ca(OH)₂ (such as 25 wt%) is then added to maintain the pH of the suspension at a maximum value, for example 9. The second step preferably uses an overall Ca/P molar ratio of at least 1.70. The goal of this second step is to convert the brushite type structure created in the first step to a hydroxyapatite structure in the second step.

During the synthesis of apatite structure and more precisely during the second step corresponding to the addition of the hydroxide ions, the pH becomes alkaline and can reach a value of at least 7.01 to a maximum of 10.5, and this addition of the hydroxide ions becomes more difficult, if not impossible without raising the pH too much. This moment is called "plateau".

The process may include a separation step to remove solid particles from a suspension fluid such as water. Hence the process may include a dewatering step which increases the solids content. The separation may comprise for example filtration, such as, but not limited to, in a filter press, centrifuge filter, or rotating filter.

Optionally, in the process of making the solid particles according to the present invention, at the end of the (second) alkaline maturation step, the suspension (B) comprises an aqueous solution (C) and solid particles, and - in a third step, a portion of the aqueous solution (C) is separated from the suspension (B) in order to obtain an aqueous suspension (D) comprising at least 18% and at most 50% of particles, or in order to obtain a wet solid (D¹) comprising at least 50% and at most 80% of composite particles, or a pulverulent solid (D") comprising at least 80% and at most 95% of composite particles and at least 5% and at most 20% of water.

The process may exclude a separation step.

The suspension from the lime maturation step may be dried.

In some embodiments, the process for making the solid particles may further comprise drying the recovered material at a temperature between 50 to 180°C, preferably from 80 to 130 °C, or more preferably from 90 to 120 °C, most preferably from 95 to 115 °C.

Drying may comprise any suitable technique suitable for decreasing the water content of the recovered solid particles such as, but not limited to, spray drying, flash drying, and/or drying in a fluidized bed.

In some embodiments, the suspension from the lime maturation may be sent directly to a flash drier in which the water evaporates onto heated surfaces such as rotating hollow disks connected to a common axis through which saturated steam at regulated pressure is internally fed in the disks assembly axis to heat the disks’ surface. The suspension is splashed on the external surfaces (two faces) of the disks. A portion of the solids stayed on the disks surfaces and the excess dropped into a recirculation tank. The solids on the disks surface dried by water evaporation, and dry solids are separated from the disks surfaces with a scrapper.

Drying may be carried out in an inert atmosphere or in the presence of an inert gas, such as containing or consisting of nitrogen (N2).

Process for making a hydroxyapatite composite in the solid particles

An embodiment of the process for making the solid particles includes steps for making a hydroxyapatite composite wherein the at least one additive is incorporated or embedded into the hydroxyapatite formed in the shell of the solid particles. The process for producing solid particles comprising a hydroxyapatite composite in the shell may include forming the hydroxyapatite from the separate sources of calcium and phosphate in the“2-step” process as described previously, and further include the addition of at least one additive or a precursor thereof during the hydroxyapatite synthesis.

The at least one additive may include copper, iron or derivatives thereof, activated carbon, and/or a metal sulfide incorporated or embedded into the hydroxyapatite.

The addition is preferably carried out during the synthesis of the solid particles, particularly when the calcium phosphate intermediate(s) obtained in the first step are converted to hydroxyapatite in the second step.

The plateau described earlier is preferably where the additive is added out at one time, although the addition of additive may be carried out in several increments.

However, it is to be understood that the addition of the additive in the

(second) alkaline maturation step may be carried out during the same period of time when the hydroxide ions are added (that is to say, before the pH plateau is reached), such as a one-time addition, in several increments, or in a continuous manner.

A preferred embodiment of the process for producing a hydroxyapatite composite in the solid particles according to the present invention, in the“2-step process”, comprises:

- in a first acid attack step, the calcium-containing particles and phosphoric acid are mixed in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of from 1.2 to 12, preferably from 1.7 to 11, more preferably from 1.9 to 10, and reacting the calcium-containing particles with said phosphoric acid at a pH of between 4 and 7, in order to obtain a suspension (A) of calcium phosphate and calcium carbonate,

- further adding at least one additive in the first step, in the second step, or in both in the first and second steps.

When the additive is added in the first step, it may be added at the beginning of the first step before the reaction takes place, during the reaction, or after the reaction is completed in the first step (this being preferred).

It is envisioned that the additive may be added not all at once, for example in at least two portions, for example a first portion in the first step and another portion in the second step.

It is also envisioned that two or more additive may be added. In an example, a first additive is added in the first step and a second additive is added in the second step. Alternatively, the first and second additive may be added in the first step or in the second step.

In some embodiments, the additive may be in the form of a solution or a slurry before it is added to at least one of the first and second steps of the 2-step process.

In preferred embodiments, the additive may be in the form of a solid before it is added to at least one of the first and second steps of the 2-step process.

In such embodiments, when the D50 particle size of the solid additive is greater than 100 microns, the process for making the composite may further include grinding or milling the additive solid to achieve a D50 less than 100 microns or less than 90 microns, preferably less than 75 microns, or more preferably less than 63 microns, before the resulting powder is added to at least one of the first and second steps of the synthesis.

In some embodiments when the additive may be in the form of a powder (either sold‘as is’ or ground before use), the process may further include sieving the powder of the additive to remove large particles, such as those exceeding a size of 100 microns, or exceeding a size of 90 microns. For example, the powder of the additive which passes through a sieve No. 170 (under ASTM El 1) equivalent to a size of less than 90 microns, or through a sieve No. 200 (under ASTM El 1) equivalent to a size of less than 75 microns, or through a sieve No. 230 (under ASTM El 1) equivalent to a size of less than 63 microns can be added to at least one of the first and second steps of the 2-step process.

Moreover the hydroxyapatite composite comprising the additive, when made in the two-step process using the first step at low temperature (less than 40°C, preferably 20-25°C), and the second step made at higher temperature (more than 40°C, or of at least 50°C, or of at least 60°C), has shown particularly high specific surface and particular high adsorption capacity of metals.

Advantageously, the addition of the additive or a precursor thereof may be carried out once the addition of hydroxide ions for setting the pH of the (second) alkaline maturation step is completed.

Alternatively, the addition of the additive or a precursor thereof may be carried out before or during the addition of hydroxide ions for setting the pH of the (second) alkaline maturation step.

The additive needs to be present during the hydroxyapatite synthesis but its addition does not have to necessarily take place at the time of the hydroxyapatite synthesis. The additive or a precursor thereof may be added prior to the plateau in the (second) alkaline maturation step, or even before the conversion of the low Ca/P calcium-phosphate compound (such as brushite of Ca/P = 1), either used as a source of calcium and phosphate formed in the first step in the 2-step process, to the hydroxyapatite structure formed in the (second) alkaline maturation step. For example, the additive or a precursor thereof may be added before the addition of the hydroxide ions is initiated in the (second) alkaline maturation step. The additive or a precursor thereof may be added even during the first step, particularly if the additive or precursor thereof is compatible with the pH condition of the first step, which is generally less than 7, or less than 6.5, or even less than 6.“Compatible” here means that the additive or precursor thereof added in the first step is not degraded/reacted or otherwise rendered ineffective as an additive for making a hydroxyapatite composite in the (second) alkaline maturation step.

Process for making a modified hydroxyapatite in the shell

An embodiment of the process for making the solid particles may include steps for making a modified hydroxyapatite in the shell wherein the at least one additive is deposited onto the hydroxyapatite in the shell.

The at least one additive may include copper, iron or derivatives thereof, and/or a metal sulfide incorporated or embedded into the hydroxyapatite.

In such instance, the solid particles may be removed from the solution to generate wet particles that can then be dispersed into water or aqueous solution in which the additive or a precursor thereof may be added. Alternatively, the suspension containing the solid particles obtained at the end of the synthesis may be used“as is” and the additive or a precursor thereof may be added to that suspension.

An embodiment of the process for making the solid particles comprises:

- making a suspension of solid particles in water;

- contacting the solid particles in the suspension with the additive or a precursor thereof;

- separating the particles from the suspension after contacting with additive or a precursor thereof;

- washing the separated particles with water; and

- recovering the washed particles to form the modified hydroxyapatite

comprising the additive on the shell of the solid particles.

In some embodiments, the suspension of the solid particles comprises from 25 to 200 g, from 50 to 150 g, of dry matter per liter of water.

As used herein, the term“precursor of the additive” refers to a compound that is converted in the modified hydroxyapatite material to the additive. For example a copper salt like copper chloride can be converted to, at least in part, copper or copper oxide or copper sulfide during the making of the modified hydroxyapatite in the shell of the solid particles.

The precursor may comprise a salt of the additive.

Process for making a modified hydroxyapatite with metal sulfide in the shell

When the solid particles comprise a modified hydroxyapatite wherein the at least one metal sulfide is deposited (coated) onto the hydroxyapatite, an embodiment of the process for making the solid particles comprises:

- making a suspension of solid particles in water;

- contacting the solid particles in the suspension with a precursor of the metal

(Me);

- contacting the solid particles in the suspension with a source of S² or HS , preferably thiourea, thioamides, thiols, H₂S, NaHS or Na₂S, more preferably NaHS, during or after the contacting step with said metal precursor, to achieve a molar ratio S:Me which is at most 2, preferably at most 1, more preferably at most 0.85, yet more preferably at most 0.7;

- separating the particles from the suspension after contacting with the source of S² or HS ;

- washing the separated particles with water; and

- recovering the washed particles to form the modified hydroxyapatite

comprising a sulfide of said metal (MeS) on the shell of the solid particles. In some embodiments, the suspension of the solid particles comprises from 25 to 200 g, from 50 to 150 g, of dry matter per liter of water.

It can be envisioned that two or more metal precursors may be used in the process. In an example, a first metal precursor may be added in the first contacting step and a second metal precursor is added in the second contacting step with the source of S² or HS . Alternatively, the first and second metal precursors may be used together during the same contacting step with the solid particles in the suspension.

If two different metals Me’ and Me” are used in the process for making the solid particles comprising the modified hydroxyapatite, it may be envisioned that a Me’ precursor and a Me” precursor may be added in the contacting step with the solid particles. Alternatively, the Me’ precursor may be added in the first contacting step with the solid particles in the suspension and the Me” precursor may be added in the second contacting step with the source of S² or HS .

The metal precursor may be organic or inorganic.

In preferred embodiments, the metal precursor is inorganic.

In preferred embodiments, the precursor of the metal Me may comprise, or consist essentially of, a salt of the metal, preferably an inorganic salt of the metal, more preferably a chloride, nitrate or sulfate salt of the metal, yet more preferably a chloride or nitrate salt of the metal.

In some embodiments, the precursor of the metal may be used in dissolved form, in gas form, in solid form or in suspended form (such as a slurry).

In some embodiments, the process comprises adding the metal precursor in the form of a solution or a slurry to the suspension.

In preferred embodiments when the metal precursor is water-soluble, the precursor of the metal may be dissolved into water prior to adding it the suspension for contacting the solid particles.

In some embodiments, the process for making the modified hydroxyapatite comprises adding the metal precursor in the form of a solid to the suspension.

In some embodiments when the D50 particle size of the solid metal precursor is greater than 100 microns, the process for making the modified hydroxyapatite may further include grinding or milling the solid metal precursor to achieve a D50 less than 100 microns or less than 90 microns, preferably less than 75 microns, or more preferably less than 63 microns, to achieve a powder which is then added to the suspension. In some embodiments, when the metal precursor may be in the form of a powder (either sold‘as is’ or ground before use), the process for making the modified hydroxyapatite in the solid particles may further include sieving the powder of the Me precursor to remove large particles, such as those exceeding a size of 100 microns, or exceeding a size of 90 microns. For example, the powder of the Me precursor which passes through a sieve No. 170 (under ASTM El 1) equivalent to a size of less than 90 microns, or through a sieve No. 200 (under ASTM El l) equivalent to a size of less than 75 microns, or through a sieve No. 230 (under ASTM El 1) equivalent to a size of less than 63 microns can be added to the suspension.

In some embodiments, the process comprises adding the metal precursor in the form of a gas.

The source of S² or HS used during the making of the modified hydroxyapatite in the solid particles may include an inorganic or organic sulfide, hydrosulfide, disulfide, or polysulfide. The source of S² or HS preferably comprises or consists of an alkali metal hydrosulfide such as NaHS or an alkali metal sulfide such as Na2S, or gaseous H₂S, more preferably comprises or consists of NaHS. Suitable organic sulfides may include thiols, thioamides (e.g., thioacetamide‘TAA’), thiourea, ... When the source of S² or HS includes gaseous ¾S, the gaseous source of S² or HS may be bubbled through the suspension. The gas may be recovered and recycled to the suspension.

In some embodiments, less than 100% of the S in the source of S² or HS is converted to the metal sulfide MeS. Other species of sulfur present in the modified hydroxyapatite in the solid particles may be in the form of sulfate / sulfite and/or S°.

The contacting with the source of S² or HS is preferably carried out after the contacting with the metal precursor. There may be a separation between the two contacting steps, but preferably there is no separation between the two contacting steps.

In preferred embodiments in the process for making the modified hydroxyapatite in the solid particles, when contacting with the source of S² or HS is carried out after the contacting with the metal precursor, the water from the suspension is preferably not removed from the suspension and the solid particles contacted with the metal precursor are not washed before the contacting with the source of S² or HS . In alternate embodiments although not preferred, the contacting with the source of S² or HS may be carried out at the same time as the contacting with the metal precursor.

The contacting step with the metal precursor is preferably performed by mixing the suspension containing the solid particles with the metal precursor.

The contacting step with the metal precursor is preferably carried out at a temperature from 10 to 50°C, preferably from 15 to 35°C, more preferably from 18 to 25 °C, most preferably at ambient temperature.

The time period for contacting with the metal precursor is preferably at least 10 minutes, or at least 30 minutes, and/or up to 5 hours, more preferably from 1 hour to 3 hours.

The contacting step with the metal precursor is preferably carried out at a pH from 4 to 10, preferably a pH from 4 to 8.

The contacting step with the source of S² or HS is preferably performed by mixing the suspension containing the solid particles with the source of S² or HS .

The contacting step with the source of S² or HS is preferably carried out at a temperature from 10 to 50°C, preferably from 15 to 35 °C, more preferably from 18 to 25 °C, most preferably at ambient temperature.

The time period for contacting with the source of S² or HS is preferably at least 10 minutes, or at least 30 minutes, and/or up to 5 hours, more preferably from 1 hour to 3 hours.

The contacting step with the source of S² or HS is preferably carried out at a pH from 4 to 10, preferably a pH from 4 to 8.

At least a portion of the metal precursor is converted to the metal sulfide during the contacting step with the source of S² or HS in order for the metal sulfide to be present in the modified hydroxyapatite.

In some embodiments, during the contacting with the source of S² or HS , a portion of the metal from the metal precursor is precipitated with S² or HS to form MeS (see reaction I) in the modified hydroxyapatite, while another portion of Me which is not precipitated into MeS is present in a cationic form, preferably Me²⁺’ and/or in the metallic form (Me⁰) in the modified hydroxyapatite. The metallic form (Me⁰) may be formed via a redox reaction with S² or HS (e.g., see reaction II with HS ). The reduction would generate solid metallic form (Me⁰) and solid sulfur.

Reaction I : Me²⁺ + HS MeS + H⁺ Reaction II : Me²⁺ + HS Me_soiid + S_soiid + H⁺

The likelihood of the formation of the metal sulfide in the modified hydroxyapatite is dictated by the precipitation equilibrium (pKs). However depending on the redox potential of the metal cation /metal pair (Me²⁺/Me_soiid), there may be a competing side reaction which may direct some of the source of S² and HS to the formation of Me_soiid and S _solid during the contacting step with the source of S² and HS .

For illustration, TABLE 1 provides the precipitation equilibrium (pKs) of various metal sulfides and TABLE 2 provides the redox potentials of various Me²⁺/Me_soiid pairs compared to the S/H₂S and S/HS pairs. For iron, TABLE 2 further includes the redox potential for the pair Fe³⁺/Fe²⁺.

TABLE 1 : Precipitation equilibrium (pKs) of various metal sulfides

TABLE 2 : Redox potentials

The formation of solid metallic form (Me⁰) in the modified hydroxyapatite such as via Reaction II is not desirable because it reduces the metal availability to form the metal sulfide.

In some embodiments, it is preferable to avoid oxidative conditions when the metal precursor and the source of S² or HS are contacting. In some instances the suspension may be kept under an inert atmosphere, or an inert gas (such as nitrogen gas N₂) may be bubbled through the suspension.

When the metal sulfide is deposited on the hydroxyapatite, the metal sulfide is preferably coated at least a portion of the surface of the modified hydroxyapatite in the shell of the solid particles. ADSORBENT OR REACTANT

Another aspect of the present invention relates to an adsorbent or reactant for removal of contaminants, such as Al, Ag, As, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hf, Hg, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, particularly Cd, Cr, Ni, Zn, and/or As, from a fluid such as a water or gas effluent, comprising :

- the solid particles according to any embodiment of the invention described herein ; or

- two or more types of solid particles according to any embodiment of the invention described herein, wherein the solid particles may have different overall Ca/P ratios and/or wherein one type of solid particles has a

hydroxyapatite composite or a modified hydroxyapatite and the other type of solid particles does not include a hydroxyapatite composite or a modified hydroxyapatite.

The adsorbent or reactant may be in the form of a powder or an aqueous suspension.

AQUEOUS SUSPENSION

Another aspect of the present invention also relates to an aqueous suspension comprising the solid particles according to the various embodiments of the present invention.

The aqueous suspension may comprise at least 0.01wt%, preferably at least 0.03wt% or at least 0.05 wt%, or at least 0.1 wt%, and/or at most 30wt%, preferably at most 20wt%, more preferably at most 10wt%, yet more preferably at most 8 wt%, most preferably at most 6 wt%, of the soild particles according to any embodiment of the invention described herein. The solid particles are preferably obtained by the different processes of making described herein.

In preferred embodiments, the suspension comprises from 0.01 wt% to 10 wt%, preferably from 0.02 wt% to 8 wt or from 0.03 wt% to 6 wt% of the solid particles.

The solid particles is preferably obtained by the different processes of making as described herein.

The shell of the solid particles may include :

- a hydroxyapatite (without additive),

- a modified hydroxyapatite wherein the at least one additive is deposited onto the hydroxyapatite, and/or - a hydroxyapatite composite wherein the at least one additive is incorporated or embedded into the hydroxyapatite.

The shell of the solid particles may further include calcium carbonate.

The aqueous suspension may be effective for treating a fluid contaminated by at least one element such as Al, Ag, As, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hf, Hg, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr.

In alternate embodiments, the present invention also relates to an aqueous suspension (D) comprising at least 25%, preferably at least 40% and at most 50% of solid particles obtained by the present process, or to a wet solid (D¹) comprising at least 50% and at most 80% of particles obtained by the present processes, or a pulverulent solid (D") comprising at least 70%, preferably at least 80%, and at most 95% of particles and at least 5% and at most 20% of water. USE OF THE SOLID PARTICLES

Another aspect of the present invention also relates to the use of the solid particles or the adsorbent or reactant comprising the solid particles according to any embodiment of the invention described herein, for removing contaminants, e.g., metals and non-metals, from a fluid, such as a water or gas effluent, particularly removing Cd, Cr, Ni, Zn, and/or As from a water effluent.

The present invention also relates to a method for treating a fluid to be treated such as a water or gas effluent or for removing one or more other contaminants from a fluid to be treated, for example contaminants in the form of metals, non-metals, their cations and/or oxyanions, or their respective oxyanions, comprising contacting the solid particles or the adsorbent or reactant comprising at least one type of solid particles with the fluid to be treated to remove at least a portion of one or more other contaminants from the fluid.

The present invention also relates to a method for removing Cd, Cr, Ni, Zn, and/or As from a water effluent, in which the solid particles or the adsorbent or reactant comprising the solid particles according to any embodiment of the invention described herein contacts the effluent to remove at least a portion of removing Cd, Cr, Ni, Zn, and/or As.

In preferred embodiments, the solid particles are dispersed into a water effluent to form a suspension of from 0.01 wt% to 10 wt%, preferably from 0.02 wt% to 8 wt or from 0.03 wt% to 6 wt%.

The present invention also relates to a method for purifying a substance contaminated by metallic and/or non-metallic contaminants, according to which the substance is brought into contact with the solid particles according to any embodiment of the present invention, whether it be in the form of the suspension or a wet solid or a dry solid, in order that at least a portion of the contaminants, are removed from the substance by the solid particles.

In the purification or removal method according to the invention, the contaminated substance, fluid, or effluent may be a flue gas containing metallic and/or non-metallic contaminants such as Al, Ag, As, Ba, Be, Bi, Ce, Co, Cd,

Cu, Cr, Fe, Hf, Hg, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti,

U, V, Y, Zn, and/or Zr, preferably Cd, Pb, Zn, Hg, Se, and/or As and according to which the solid particles or an adsorbent comprising at least one type of solid particles, whether it be in the form of the suspension or a wet solid or a dry solid , is dispersed in the flue gas, the flue gas being at a temperature of at least 100°C, or of at least 120°C, or of at least 150°C, and preferably not more than 1100°C, or of at most 300°C, of at most 250°C, or of at most 200°C, the resulting mixture then being subjected to a separation in order to obtain resulting spent solids and a flue gas partially purified of at least one contaminant selected from Cd, Cr, Ni, Zn, and/or As and optionally of other metallic and/or non-metallic elements.

In the purification or removal method according to the invention, the contaminated substance or effluent may be a liquid effluent containing contaminants, such as: Al, Ag, As, B, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, F, Fe, Hf, Hg, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, preferably Cd, Cr, Cu, Hg, Ni, Pb, and/or Zn, whether these elements may be in the form of cations and/or anions, such as oxyanions, according to which the solid particles or an adsorbent material or reactant comprising solid particles (preferably in suspension form) is mixed into the liquid effluent for a sufficient time such that the solid particles adsorb at least a portion of the metallic and/or non-metallic contaminants, and the mixture is subjected to a clarification in order to produce a liquid partially purified of metallic and/or non- metallic contaminants, on the one hand, and spent solid particles loaded with metallic and/or non-metallic contaminants, that are removed from the liquid effluent. Preferably, the solid particles are used with the liquid effluent in a contact reactor, such as a sludge blanket reactor or a fluidized bed. The contact time between the solid particles or the adsorbent / reactant containing solid particles and the liquid effluent is in general at least one minute, advantageously at least 15 minutes, more advantageously at least 30 minutes, even more advantageously at least one hour. In one particularly advantageous embodiment of the invention, the liquid effluent is introduced into a sludge blanket contact reactor in which the solid particles or the adsorbent / reactant containing the solid particles is present at a weight concentration of at least 0.01% by weight, preferably at least 0.03 wt%, more preferably at least 0.05 wt% and in general at most 10% by weight, preferably at most 8 wt%, more preferably at most 6 wt%;a liquid is recovered as overflow from the sludge blanket reactor; a flocculant is added to the recovered liquid in order to form a mixture comprising the spent solid particles or the adsorbent containing them entrained out of the contact reactor and flocculated; said mixture is then introduced into a settling tank where the mixture is separated into:

- the liquid partially purified of metallic and/or non-metallic contaminants, and said liquid is recovered as overflow from the settling tank,

- and into an underflow from the settling tank comprising flocculated and settled particles of spent solid particles recovered as underflow from the settling tank.

At least one portion of the underflow from the settling tank containing flocculated and settled solid particles may be recycled to the sludge blanket contact reactor. The effectiveness of the treatment of metallic elements and/or non-metallic elements may be monitored by comparing the concentrations of these elements upstream (in the liquid effluent) and downstream of the purification unit (in the partially treated liquid), for example by an automatic analyser or by sampling and analysis. The solid particles charge of the contact reactor is in general regularly renewed in portions. For example, by partial purging of the spent solid particles or the adsorbent containing them loaded with metallic and/or non-metallic elements at the underflow from the settling tank, and by adding fresh solid particles or adsorbent containing them to the contact reactor. Such a method thus ensures a "chemical polishing" of the liquid effluent. The treatment method is particularly advantageous in the case where the liquid partially purified of metallic elements and/or non-metallic elements is then treated in a biological treatment plant producing sewage sludges. This makes it possible to reduce the concentrations of such elements of said sewage sludges and to reutilize them, for example in agriculture or in land development.

In the purification method according to the invention, the contaminated fluid or substance may be a solid residue or a soil contaminated by Hg and other metallic elements such as Al, Ag, As, B, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, F, Fe, Hf, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, preferably Cd, Cr, Ni, Zn, and/or As, according to which the solid particles or the adsorbent / reactant containing the solid particles (for example in the form of an aqueous suspension of solid particles or wet solid particles or dried solid particles) are injected into the solid residue or the soil in the vicinity of other metallic and/or non-metallic elements for a sufficient contact time so that the solid particles adsorb at least a portion of the Cd, Cr, Ni, Zn, and/or As and optionally other metallic and/or non-metallic elements.

In particular the present invention relates to the following embodiments: ITEM 1. Coreshell solid particles for removing contaminants from a fluid, comprising :

- a core containing calcium carbonate; and

- a shell comprising a hydroxyapatite,

said shell covering at least partially the core,

said particles having an overall Ca:P molar ratio of at least 1.75, preferably at least 1.8, more preferably at least 1.9, yet more preferably at least 2.

ITEM 2. The particles according to ITEM 1, having an overall Ca:P molar ratio of at most 12, preferably at most 10, more preferably at most 6.

ITEM 3. The particles according to ITEM 1 or 2 wherein the hydroxyapatite in the shell is a calcium-deficient hydroxyapatite, preferably a hydroxyapatite with a Ca/P molar ratio more than 1.5 and less than 1.67.

ITEM 4. The particles according to any of ITEMS 1 to 3, comprising, based on the total weight of dry matter:

- at least 25wt%, advantageously at least 30wt% of hydroxyapatite.

ITEM 5. The particles according to any of ITEMS 1 to 4, comprising, based on the total weight of dry matter:

- more than 7wt% calcium carbonate, advantageously more than 20wt% calcium carbonate, advantageously more than 25wt% calcium carbonate; and

- at most 75wt% calcium carbonate, advantageously at most 70% calcium carbonate.

ITEM 6. The particles according to any of ITEMS 1 to 5, further comprising, based on the total weight of dry matter:

- at least lwt%, advantageously at least 2wt% of water; and

- at most 10t% water, advantageously at most 9wt% water.

ITEM 7. The particles according to any of ITEMS 1 to 6, wherein the shell further comprises calcium carbonate. ITEM 8. The particles according to any of ITEMS 1 to 7, being essentially free of a calcium phosphate compound other than a hydroxyapatite, preferably essentially free of a calcium phosphate compound selected from the group consisting of monocalcium phosphate monohydrate, dicalcium phosphate dihydrate, dicalcium phosphate anhydrous, and octacalcium bis(hydrogen phosphate) tetrakisphosphate pentahydrate.

ITEM 9. The particles according to any of ITEMS 1 to 8, having a BET surface area of more than 60 m²/g and preferably up to 180 m²/g and/or having a pore volume of from 0.3 cm³/g up to 0.45 cm³/g.

ITEM 10. The particles according to any of ITEMS 1 to 9, wherein the hydroxyapatite in the shell is a modified hydroxyapatite onto which at least one additive is deposited on the hydroxyapatite.

ITEM 11. The particles according to any of ITEMS 1 to 10, wherein the hydroxyapatite is a hydroxyapatite composite wherein the at least one additive is incorporated or embedded into the hydroxyapatite.

ITEM 12. The particles according to ITEM 10 orl 1, wherein the at least one additive comprises copper or derivatives thereof, iron or derivatives thereof (such as iron hydroxide, zero-valent iron, FeOOH, iron oxide), a metal sulfide, and/or activated carbon.

ITEM 13. A process for making the coreshell particles according to any of ITEMS 1 to 12, the process comprising:

- in a second alkaline maturation step, adding to the suspension (A) a calcium compound comprising hydroxide ions in order to increase the pH to at least 7 and at most 10.5 to obtain a suspension (B) of the coreshell particles having an overall Ca/P molar ratio of at least 1.7, preferably at least 1.8, more preferably at least 1.9 and at most 12, preferably at most 8, more preferably at most 6. ITEM 14. Process according to the preceding ITEM, wherein the calcium- containing compound comprises or consists essentially of calcium hydroxide. ITEM 15. Use of the coreshell particles according to any of ITEMS 1 to 12 for removing from a fluid at least a portion of an element selected from the group consisting of Al, Ag, As, B, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hg, Hf, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, preferably for removing Cd, Cr, Ni, Zn, and/or As from a fluid, such as a water effluent,

comprising contacting the coreshell particles with said fluid for a time sufficient to remove at least a portion of the element, preferably Cd, Cr, Ni, Zn, and/or As, from the fluid.

ITEM 16. Coreshell solid particles for removing contaminants from a fluid, comprising :

- a core containing water-insoluble chemical substance(s) in solid form, preferably comprising calcium carbonate, silica, alumina, a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.67 or a bone char, or any combination thereof, more preferably comprising calcium carbonate and/or a bone char; and

- a shell comprising a hydroxyapatite,

said shell covering at least partially the core.

ITEM 17. Coreshell particles according to ITEM 16, having a BET surface area of more than 60 m²/g and preferably up to 180 m²/g and/or having a pore volume of from 0.3 cm³/g up to 0.45 cm³/g.

ITEM 18. Coreshell particles according to any of ITEMS 16 or 17, wherein the hydroxyapatite in the shell is a modified hydroxyapatite onto which at least one additive is deposited on the hydroxyapatite and/or wherein the hydroxyapatite is a hydroxyapatite composite wherein the at least one additive is incorporated or embedded into the hydroxyapatite.

ITEM 19. Coreshell particles according to ITEM 18, wherein the at least one additive comprises copper or derivatives thereof, iron or derivatives thereof (such as iron hydroxide, zero-valent iron, FeOOH, iron oxide), a metal sulfide, and/or activated carbon.

ITEM 20. Process for making the coreshell particles according to any of ITEMS 16-19, comprising:

a first step (acid attack) of a Ca source with a source of phosphate at an acidic pH to make a calcium phosphate structure (other than hydroxyapatite); a second step (alkaline maturation) to convert, with a source of hydroxide, the calcium phosphate structure to hydroxyapatite; and

using a source of core particles in the first step and/or in the second step to make the coreshell particles with a shell comprising a hydroxyapatite and covering at least partially the core.

ITEM 21. Process for making the coreshell particles according to ITEM 20, wherein the Ca source to make the calcium phosphate structure comprises calcium carbonate; the source of phosphate is phosphoric acid; wherein the calcium phosphate structure (other than hydroxyapatite) comprises brushite; the source of hydroxide is calcium hydroxide; and the source of core particles is preferably calcium carbonate, silica, alumina, and/or a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.67 or a bone char.

ITEM 22. Process according to ITEM 20 or 21, wherein the calcium- containing compound comprises or consists essentially of calcium hydroxide. ITEM 23. Adsorbent comprising the coreshell particles according to any of ITEMS 1 to 12 or ITEMS 15-19 for removing from a fluid, such as a water effluent, a contaminant, preferably selected from the group consisting of Al, Ag, As, B, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hg, Hf, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, more preferably selected from the group consisting of Cd, Cr, Ni, Zn, and/or As.

ITEM 24. Use of the coreshell particles according to any ITEMS 1 to 12 or ITEMS 15-19 as an adsorbent for removing from a fluid, such as a water effluent, at least a portion of a contaminant, preferably selected from the group consisting of Al, Ag, As, B, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hg, Hf, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, more preferably selected from the group consisting of Cd, Cr, Ni, Zn, and/or As.

ITEM 101. Solid particles, comprising :

- a hydroxyapatite ; and

- secondary particles containing water-insoluble chemical substance(s) in solid form, preferably comprising calcium carbonate, silica, alumina, a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.67 or a bone char, or any combination thereof, more preferably comprising calcium carbonate and/or a bone char; and

wherein the hydroxyapatite and secondary particles form agglomerates and/or coreshells in which a shell comprising the hydroxyapatite covers at least partially the secondary particles that serves as particle cores. ITEM 102. Solid particles according to ITEM 101, wherein the secondary particles comprises calcium carbonate, and wherein the solid particles have an overall Ca:P molar ratio of at least 1.75, preferably at least 1.8, more preferably at least 1.9, yet more preferably at least 2 and/or of at most 12, preferably at most 10, more preferably at most 6.

ITEM 103. Solid particles according to ITEM 101 or 102, comprising, based on the total weight of dry matter:

- at least 25wt%, advantageously at least 30wt% of hydroxyapatite.

ITEM 104. Solid particles according to any of ITEMS 101 to 103, comprising, based on the total weight of dry matter:

- more than 7wt% calcium carbonate, advantageously more than 20wt% calcium carbonate, advantageously more than 25wt% of secondary particles; and - at most 75wt% calcium carbonate, advantageously at most 70% secondary particles.

ITEM 105. Solid particles according to any of ITEMS 101 to 104, comprising particles in the form of coreshells in which a shell comprising the hydroxyapatite covers at least partially the secondary particles, and wherein the shell further comprises calcium carbonate.

ITEM 106. Solid particles according to ITEM 101, wherein the secondary particles comprises bone char, and wherein the particles have an overall Ca:P molar ratio of at least 1.55, preferably at least 1.6, and/or of at most 1.9, preferably at most 1.8, more preferably at most 1.75.

ITEM 107. Solid particles according to ITEM 101 or 102 wherein the hydroxyapatite is a calcium-deficient hydroxyapatite, preferably a

hydroxyapatite with a Ca/P molar ratio more than 1.5 and less than 1.67.

ITEM 108. Solid particles according to any of ITEMS 101 to 107, being essentially free of a calcium phosphate compound other than a hydroxyapatite, preferably essentially free of a calcium phosphate compound selected from the group consisting of monocalcium phosphate monohydrate, dicalcium phosphate dihydrate, dicalcium phosphate anhydrous, and octacalcium bis(hydrogen phosphate) tetrakisphosphate pentahydrate.

ITEM 109. Solid particles according to any of ITEMS 101 to 108, having a BET surface area of more than 60 m²/g and preferably up to 180 m²/g and/or having a pore volume of from 0.3 cm³/g up to 0.45 cm³/g. ITEM 110. Solid particles according to any of ITEMS 101 to 109, wherein the hydroxyapatite is a modified hydroxyapatite onto which at least one additive is deposited on the hydroxyapatite and/or wherein the hydroxyapatite is a hydroxyapatite composite wherein the at least one additive is incorporated or embedded into the hydroxyapatite.

ITEM 111. Solid particles according to ITEM 110, wherein the at least one additive comprises copper or derivatives thereof, iron or derivatives thereof (such as iron hydroxide, zero-valent iron, FeOOH, iron oxide), a metal sulfide, and/or activated carbon.

ITEM 112. Process for making the solid particles according to any of

ITEMS 101 to 111, comprising:

using a source of secondary particles in the first step and/or in the second step to make the solid particles.

ITEM 113. Process for making the solid particles according to ITEM 112, wherein the Ca source to make the calcium phosphate structure comprises calcium carbonate; the source of phosphate is phosphoric acid; wherein the calcium phosphate structure (other than hydroxyapatite) comprises brushite; the source of hydroxide is calcium hydroxide; and the source of secondary particles is preferably calcium carbonate, silica, alumina, and/or a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.67 or a bone char.

ITEM 114. Process according to any of claims ITEMS 102 to 105 & 107 to 111, the process comprising:

wherein the calcium-containing particles contain calcium carbonate, preferably contain >70 wt% calcium carbonate, more preferably contain >90 wt% calcium carbonate, most preferably contain >95 wt% calcium carbonate; wherein at least a portion of calcium-containing particles serves as secondary particles; and

ITEM 115. Process according to ITEM 114, wherein the calcium- containing compound comprises or consists essentially of calcium hydroxide.

ITEM 116. Process for making the solid particles according to any of

ITEM 101 to 111, the process comprising:

- in a first acid attack step, calcium-containing particles and phosphoric acid are mixed in water, and reacting the calcium-containing particles with said phosphoric acid, in order to obtain a suspension (A) comprising brushite, wherein the calcium-containing particles contain calcium carbonate, preferably contain >70 wt% calcium carbonate, more preferably contain >90 wt% calcium carbonate, most preferably contain >95 wt% calcium carbonate; and

- in a second alkaline maturation step, adding to the suspension (A) calcium hydroxide ions in order to increase the pH to at least 7 and at most 10.5 to obtain a suspension (B) of the solid particles,

wherein a source of the secondary particles is used in the first step and/or second step; and

wherein the source of secondary particles comprises water-insoluble chemical substance(s) in solid form, preferably comprising calcium carbonate, silica, alumina, a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.67 or a bone char, or any combination thereof, more preferably comprising calcium carbonate and/or a bone char.

ITEM 117. Process according to ITEM 116, wherein the calcium- containing particles and phosphoric acid are mixed in the first step to obtain a Ca/P molar ratio of from 0.9 to 1.1.

ITEM 118. Use of the Solid particles according to any of ITEM 101 to 111 as an adsorbent for removing from a fluid, such as a water effluent, at least a portion of a contaminant, preferably selected from the group consisting of Al, Ag, As, B, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hg, Hf, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, more preferably selected from the group consisting of Cd, Cr, Ni, Zn, and/or As.

EXAMPLES

The examples, the description of which follows, serve to illustrate the invention.

In these examples the pH measurements were made using a WTW Sentix 41 electrode (pH 0-14, temperature: 0 °C-80 °C), a pH meter WTW pH3110. The calibration of the equipment was made using three buffer solutions: at pH 4.0 (batch Dulco test-0032) Prominent, a WTW pH 7.0 (WTW D-82362) and at pH 10.01 Hach (cat 27702). Note: If multiple sample measurements were to be made with the same electrode, the electrode was rinsed with deionized water between each measurement.

The measurement of the residual water was performed using an infrared analyser Ref. MA150C from Sartorius. For this, 1.0 to 2.0g of sample are dried at 105 °C till a constant weight is obtained during at least 5 minutes.

The particle size measurement was carried out on a Beckman Coulter LS 230 laser diffraction particle size analyser (laser of wavelength 750 nm) on particles suspended in water and using a size distribution calculation based on Fraunhofer diffraction theory (particles greater than 10 pm) and on Mie scattering theory (particles less than 10 pm), the particles being considered to be spherical.

The BET specific surface area and pore volume were determined by gas adsorption on a Micromeritics ASAP2020 machine. Before the analysis, the samples (0.7 to 1 g) are pretreated under vacuum at 250°C until a stable vacuum of 4-5 pbar has been achieved. The measurements were carried out using nitrogen as adsorbent gas at 77°K via the volumetric method, according to the ISO 9277: 2010 standard (Determination of the specific surface area of solids by gas adsorption - BET method). The BET specific surface area was calculated in a relative pressure (P/P0) range varying from around 0.05 to 0.20.

The following chemicals in TABLE 3 were used in the examples that follow. TABLE 3

Example 1 (not in accordance with the invention)

Preparation of hydroxyapatite material

A hydroxyapatite material HAP was made under similar conditions as those described in example lb of WO2015/173437 patent application.

In the first step, a mass of a suspension of limestone CaCCri in water was added a mass of a phosphoric acid solution in baffled 5 -liter reactor. The mixture was stirred generally at 20-30°C with a rotational speed of 700 ppm using a 4-blade impeller. The goal of this first step was to attack the limestone to make a brushite type structure.

At the end of the addition of acid, the second alkaline maturation step was initiated by heating the suspension up to about 50°C. A mass of a suspension of Ca(OH)₂ was then added to maintain the pH of the suspension at a maximum 10. The goal of this second step was to convert the brushite type structure created in the first step to a hydroxyapatite structure in the second step.

After the reaction time, the suspension was continually stirred at half the stirring speed than was used in the first step to allow it to cool down to room temperature (20-25°C).

For Example 1, the calculated Ca/P from the amount of the reactants used in the synthesis was 1.67.

The aqueous suspension was filtered under pressure with a 0.45-micron paper filter to achieve a wet solid.

The various proportions of the reactants : CaCCri, H₃PO₄, Ca(OH)₂ are provided in TABLE 4. The estimated overall Ca/P¹ molar ratios calculated from the amounts of reactants used in the 1^st and from the amounts of reactants used in both the 1^st and 2^nd steps are also provided in TABLE 4. The initial and final pH, the temperature range, and the time of reaction for the 1^st step, as well as the percentage of moles of Ca used in the first step compared to the total amount of moles of Ca used in both steps are provided in

TABLE 5

The initial and final pH, the temperature range, and the time of reaction for the 2^nd step, the resulting % solids in the suspension obtained at the end of the 2^nd step, and the dry matter (wt% DM) in the collected solids are provided in

TABLE 6

For the measure of the dry mater content for each material sample, 2-3 g of a sample was dried for 3 hours, stirring every 30 minutes in an oven at 80°C to obtain a representative homogeneous sample; and the dry matter content (wt% DM) of the dried sample was determined using a moisture meter such as a thermal balance sold by Sartorius.

Examples 2-5 (in accordance with the invention) Preparation of solid particles with hydroxyapatite:

adding extra CaCC>3 as“secondary particles” in the first step

Four (4) hydroxyapatite materials : HAP-1, HAP-2a, HAP-2b and HAP-3 were made under similar conditions as those described in Example 1, except that the amount of phosphoric acid was reduced in the first step to increase the overall molar Ca/P ratio of the material obtained. The calculated Ca/P from the amount of the reactants used in the synthesis of Examples 2 to 5 was varied from 1.93 to 5.64. Because the amount of Ca used in the preparation was higher than the stoichiometric ratio 1.67 for hydroxyapatite, not all of the limestone particles were converted to an apatite structure. A portion of the CaCCri particles used as raw material remained unconverted leaving a CaCCri core. The synthesis was carried out in the same 5 -liter reactor using the same stirring speed and the same temperatures for the first and second steps (room temperature for the acid attack step and about 50°C for the lime maturation step).

The various proportions of the reactants : CaCCri, H₃PO₄, Ca(OH)₂ are provided in TABLE 4. The calculated Ca/P¹ molar ratios calculated from the amounts of reactants used in the 1^st and after the 2^nd step are also provided in TABLE 4

The initial and final pH, the temperature range, and the time of reaction for the 1^st step, as well as the percentage of moles of Ca used in the first step compared to the total amount of moles of Ca used in both steps are provided in

TABLE 5 The initial and final pH, the temperature range, and the time of reaction for the 2^nd step, the resulting % solids in the suspension obtained at the end of the 2^nd step, and the dry matter (wt% DM) in the collected solids are provided in

TABLE 6

Example 6 (in accordance with the invention)

Preparation of solid particles with hydroxyapatite composite material: adding extra CaCC>3 as“secondary particles” in the first step

One (1) hydroxyapatite material (HAP-2c) were made under similar conditions as those described in Example 4 (HAP-2b) with the calculated Ca/P from the amount of the reactants used in the synthesis being 2.7, except that an activated carbon Pulsorb C was added during the 2^nd step.

The various proportions of the reactants : CaC03, H₃PO₄, Ca(OH)₂,

Pulsorb C (“AC”) are provided in TABLE 4. The calculated Ca/P¹ molar ratios calculated from the amounts of reactants used in the 1^st and after the 2^nd step are also provided in TABLE 4.

TABLE 5

TABLE 6

TABLE 4

molar Ca/P¹ = calculated from the added reactants TABLE 5

TABLE 6

Example 7

Porosity and particle size of Examples 1-6

The porosity characteristics were determined after a heat treatment (drying) at 110 °C under vacuum overnight (about 16 hours). The BET specific surface area was determined by gas adsorption on a Micromeritics ASAP2020 machine. The particle size measurement was carried out on a Beckman Coulter LS 230 laser diffraction particle size analyser (laser of wavelength 750 nm

The BET specific surface area and mean particles size D50, D10 for the Examples 1-6 can be found in TABLE 7. TABLE 7

Example 8

Composition of Examples 1-6 after drying

The composition of the materials of Examples 1-6 was determined by thermogravimetric analysis (TGA). TGA is a method of thermal analysis in which the weight of a sample is measured over time as the sample is heated at a constant rate, in this case heated from 35 to 250 °C at a rate of 10°C/min. This measurement provides information about the decomposition of the sample.

The composition of the materials of Examples 1-6 based on TGA analysis as well as the overall molar ratio Ca/P of the resulting particles which was calculated from the weight % measured by TGA analysis can be found in

TABLE 8

molar Ca/P = calculated from the weight % measured by TGA analysis AC = Activated Carbon

Example 9 (in accordance with the invention)

Water treatment testing of materials of Examples 1-6 9.1. Cationic standard test testing for water treatment on selected metallic cations 9.1.1 Preparation of mother solutions for each metallic cation:

A mother solution for each of the metals from the following metal salts containing M = Cd, Cr, Cu, Mn, Ni, Pb, Zn, Hg, as shown in TABLE 9 is prepared by adding the salt of each metal in deionized water to reach 1 g M/L content.

TABLE 9

* MW = molecular weight

9.1.2 Preparation of a standard solution for the cationic standard test:

A standard solution containing 5 mg/L (5 ppm) of cations for Cd, Cr, Cu,

Mn, Ni, Pb, Zn and 1 mg/L (1 ppm) Hg cation was prepared from the 7 mother solutions as follows: with the aid of a micropipette, add 5 mL of each of the mother liquors containing Cd, Cr, Cu, Mn, Ni, Pb, Zn and 1 mL of the mother liquor containing Hg into a flask and add water to reach a total volume of 1 liter. 3 A.3 Measure of the dry mater content for each material sample for the standard test:

Dry approximately 2-3 g of an apatic material sample for 3 hours, stirring every 30 minutes in an oven at 80°C to obtain a representative homogeneous sample ; and

- Determine the dry matter content (wt% DM) of the dried sample using a mosture meter such as a thermal balance sold by Sartorius.

3 A.4 Steps for the cationic standard test on performance evaluation :

- Take a 100-ml initial sample from the standard solution at time 0 (before adding the apatic material to start the test) - Measure the mass of the wet material sample (not dried) in order to achieve a suspension containing 0.03 wt% of dry matter in a given volume of the standard solution in a container using the following formula: Mass (wet sample)

- Shake the suspension mechanically for 1 hour in the container at 250 rpm;

- Take a 100-ml sample from the suspension after 1 hour and filter it on a 0.45- pm filter to remove solids;

- Stabilize the two 100-ml samples taken at time = 0 and time = 1 hour by adding 1 ml of concentrated nitric acid (65% HNO₃); and

- Send to ICP-OES for analysis to determine the contents of metals: Cd, Cr, Cu, Mn, Ni, Pb, Zn, Hg.

9.1.5 Method ICP-EOS :

Scandium (as internal standard) and optionally gold (to stabilize Hg when Hg determination is required) to an aliquot of each water sample which is slightly acidified with concentrated nitric acid. The solution is then brought to volume with ultrapure water in order to obtain a 5-time dilution. The final diluted solution typically contains 2% to 5% HNO3, 1 or 2 mg/1 scandium and, where appropriate, 1 or 2 mg/1 gold.

The determination of contents of specific elements such Cd, Cr, Cu, Mn,

Ni, Pb, Zn, Hg in the water samples are done by ICP-OES (Inductively Coupled Plasma - Optical Emission Spectrometry) with axial and observation of the plasma and CCD detector. The solutions to be measured are nebulized and transported in the plasma with argon as a carrier gas. In the plasma, the different elements emit light with a wavelength specific to each element and with an intensity directly proportional to their concentration.

The measurements of the emitted light intensity by each element used in the standard test are evaluated against an external calibration established between 0 and 5 mg/1 for each element to be measured. This calibration consists of seven (7) solutions: a calibration blank and six (6) solutions of increasing

concentrations (0.1 mg/1, 0.2 mg/1, 0.5 mg/1, 1 mg/1, 2 mg/1 and 5 mg/1 of each element). All the calibration solutions also contain the same concentration of HNO3, scandium and gold as the diluted sample solutions.

9.2 Results of the cationic standard test for Examples 1-6 The cationic standard test was carried out with the materials of Examples 2-6 and the HAP of Example 1. The % removal for the 7 metallic cations after one hour are provided in TABLE 10.

For the hydroxyapatite material HAP of Example 1 (control), the best removal efficiency (>99%) was with Cu and Pb cations, and the least removal efficiency was with Hg and Ni cations.

For Cd, the removal efficiency compared to 75% with the hydroxyapatite material HAP (Ex 1 control) was :

increased with all of the coreshell Examples 2-6, the best performance being obtained with the materials with the measured Ca/P molar ratios of from 2.43 to 5.15.

For Cr, the removal efficiency compared to 95% with the hydroxyapatite material HAP (Ex 1 control) was :

all improved to 99-100% with all of the materials of Examples 2-6, the best performance being obtained with the materials with the measured

Ca/P molar ratios of from 2.40 to 5.15.

For Cu, the removal efficiency compared to 99% with the hydroxyapatite material HAP (Ex 1 control) was :

about the same with all of the materials of Examples 2-6.

For Hg, the removal efficiency compared to 20% with the hydroxyapatite material HAP (Ex 1 control) was :

improved (44%) with the coreshell material of Example 2 : HAP- 1 with the measured Ca/P molar ratio of 1.81;

slighlty improved (23-27%) with the materials of Examples 3, 4, 6 : HAP- 2a, HAP- 2b, HAP- 2cwith the measured Ca/P molar ratio of about 2.4-

2.47; and

decreased with the coreshell material of Example 5: HAP- 3 with the measured Ca/P molar ratio of 5.15.

For Ni, the removal efficiency compared to 19% with the hydroxyapatite material HAP (Ex 1 control) was :

improved (35-48%) with all of the materials of Examples 2-6 with the measured Ca/P molar ratio of from 1.81 to 5.15.

For Pb removal, the removal efficiency compared to 99% with the hydroxyapatite material HAP (Ex 1 control) was :

- the same (99%) with all of the materials of Examples 2-6. For Zn, the removal efficiency compared to 75% with the hydroxyapatite material HAP (Ex 1 control) was :

increased (95-97%) with all of the materials of Examples 2-6. TABLE 10

For all of the 5 coreshell hydroxyapatite materials of Examples 2-6, the removal rate for Cd, Cr, Ni and Zn was greatly improved compared to the control hydroxyapatite (Example 1).

Comparing the performance of the coreshell hydroxyapatite materials of Examples 2-6, the best increase in removal efficiency was observed with

Example 4 HAP- 2b and Example 6 (HAP- 2c with a composite of

hydroxyapatite and activated carbon), which demonstrated an increased removal rate for Cd, Cr, Hg, Ni, and Zn.

9.3 Anionic standard test for performance evaluation on selected metallic anions

9.3.1 Preparation of mother solutions for each metallic anion:

A mother solution for each of the metals from the following metal salts containing M = Arsenic(V), Molybdenum(VI), Selenium(VI) and Vanadium(V), as shown in TABLE 11 was prepared by adding the salt of each metal in deionized water to reach 1 g M/L content. TABLE 11

* MW = molecular weight

9.3.2 Preparation of a standard solution for the anionic standard test:

A standard anionic solution containing 1 mg/L (1 ppm) of anions for As

(V), Mo (VI), Se (VI) and V (V), was prepared from the 4 mother solutions as follows: with the aid of a micropipette, add 1 mL of each of the 4 mother liquors containing As (V), Mo (VI), Se (VI) and V (V) into a flask and add water to reach a total volume of 1 liter.

9.3.3 Measure of the dry mater content for each material sample for the standard test:

- Dry approximately 2-3 g of a composite sample for 3 hours, stirring every 30 minutes in an oven at 80°C to obtain a representative homogeneous sample ; and

- Determine the dry matter content (wt% DM) of the dried sample using a moisture meter such as a thermal balance sold by Sartorius.

9.3.4 Steps for the anionic standard test on performance evaluation :

- Take a 100-ml initial sample from the standard solution at time 0 (before adding the apatic material to start the test)

- Measure the mass of the wet material sample (not dried) in order to achieve a suspension containing 0.5 wt% of dry matter in a given volume of the standard solution in a container using the following formula:

Mass (wet sample)

- Shake the suspension mechanically for 1 hour in the container at 250 rpm;

- Take a 100-ml sample from the suspension after 1 hour and filter it on a 0.45- mih filter to remove solids; - Stabilize the two 100-ml samples taken at time = 0 and time = 1 hour by adding 1 ml of concentrated nitric acid (65% HN03); and

- Send to ICP-OES as described in Section 6b.5 for analysis to determine the contents of the following metals: As (V), Mo (VI), Se (VI) and V (V).

9.4. Results of the anionic standard test for Examples 1-6

The anionic standard test (see Section 9.3) was carried out with Examples 1-6. The % removal for the 4 metallic anions during the anionic standard test after 1 hour are provided in TABLE 12.

TABLE 12

The removal % (77 to 91%) for As (V) with the materials of Examples 2-6 was improved compared to the removal (55%) obtained with the apatite material (Example 1- control).

For the other anions Mo (VI), Se (VI) and V (V) though, the materials of Examples 2-6 did not improve the removal. To the contrary for Vanadium (V), the removal % decreased as the measured Ca/P ratio and amount of CaC03 increased in the materials of Examples 2-6.

Example 10 (in accordance with the invention)

Preparation of solid particles comprising hydroxyapatite:

adding CaCC>3 as“secondary particles” in the second step

One hydroxyapatite material : HAP-4 was made under similar conditions as those described in Example 1, except that the extra amount of calcium carbonate was added at the beginning of the second step to increase the overall molar Ca/P ratio of the material obtained (instead of using this extra amount in the first step). The amounts of calcium carbonate (limestone particles) and phosphoric acid used in the first step were such to achieve an initial Ca/P ratio =

1 : 1 to make a brushite structure in the first step, and the amount of calcium carbonate (limestone particles) and the calcium hydroxide (lime) added to the second step resulted in a calculated final Ca/P to be about 3.4. Because the amount of Ca used in the preparation was higher than the stoichiometric ratio 1.67 for hydroxyapatite, not all of the limestone particles were converted to an apatite structure and a portion of the CaCCri particles used as raw material remained unconverted leaving CaCCri particles in the solid particles obtained after the second step.

The synthesis was carried out in the same 5-liter reactor using the same stirring speed and the same temperatures for the first and second steps (about room temperature for the acid attack step (1^st step) and about 50°C for the lime maturation step (2^nd step).

Half of the suspension made in the first step containing brushite was used in the second step to make this hydroxyapatite material Example 10. The second step was carried out 72 hours after the first step was performed. The other half of the suspension made in the first step of Example 10 was used to make solid particles comprising hydroxyapatite composite described in Example 11 below.

The main difference between the synthesis of material Example 10 compared to the materials Examples 2-5 is that excess calcium carbonate particles (meaning an amount more than what would be required to achieve a stoichiometric hydroxyapatite of Ca/P=1.67) that served as secondary particles for the materials were added at the beginning of the second step after the brushite material was formed in the first step. For the materials Examples 2-5, the excess calcium carbonate particles that served as secondary particles for these materials were added at the beginning of the first step before the brushite material was formed

The various proportions of the reactants : CaCCri, H₃PO₄, Ca(OH)₂ used to make material Example 10 are provided in TABLE 13. The calculated Ca/P¹ molar ratios calculated from the amounts of reactants used in the 1^st and after the 2^nd step are also provided in TABLE 13.

The initial and final pH, the temperature range, and the time of reaction for the 1^st step, as well as the percentage of moles of Ca used in the first step compared to the total amount of moles of Ca used in both steps are provided in TABLE 14. The initial and final pH, the temperature range, and the time of reaction for the 2^nd step are provided in TABLE 15. TABLE 13

*half of the suspension of the first step was used in the 2^nd step molar Ca/P¹ = calculated from the added reactants

TABLE 14

TABLE 15

Example 11 (in accordance with the invention) Preparation of coreshell hydroxyapatite composite material

One (1) hydroxyapatite material (HAEMc) was made under similar conditions as those described in Example 10 (HAP-4) with the calculated Ca/P from the amount of the reactants used in the synthesis being 3.6, except that an activated carbon from Jacobi was added during the 2^nd step to achieve 10 wt% activated carbon in the composite material. The other half of the suspension made in the first step of Example 10 was used to make the solid particles comprising a hydroxyapatite composite material. Similarly to Example 10, excess calcium carbonate particles were added at the beginning of the second step to serve as secondary particles for the material Example 11 after the brushite material was formed in the first step.

The various proportions of the reactants : CaCC^, H3PO4, Ca(OH)₂, Jacobi activated carbon (“AC”) for the composite material Example 11 are provided in TABLE 16. The calculated Ca/P¹ molar ratios calculated from the amounts of reactants used in the 1^st and after the 2^nd step are also provided in TABLE 16. The initial and final pH, the temperature range, and the time of reaction for the 1^st step, as well as the percentage of moles of Ca used in the first step compared to the total amount of moles of Ca used in both steps was already provided in TABLE 14. The initial and final pH, the temperature range, and the time of reaction for the 2^nd step are provided in TABLE 17.

TABLE 16

TABLE 17

The main difference between the synthesis of composite material Example

11 compared to the composite material Example 6 is that calcium carbonate particles that served as secondary particles were added at the beginning of the second step after the brushite material was formed in the first step.

Examplea 12-13 (in accordance with the invention) Preparation of solid particles comprising hydroxyapatite:

adding CaCC>3 particles or bone char particles as“secondary particles” in the second (lime maturation) step

One hydroxyapatite material Example 12: HAP-5a was made under similar conditions as those described in Example 10 using limestone particles as secondary particles at the beginning of the 2^nd step (lime maturation). Another hydroxyapatite material Example 13: HAP-5b was made under similar conditions as those described in Example 10 except that bone char particles were added as secondary particles at the beginning of the 2^nd step (lime maturation) for Example 13: HAP-5b instead of the limestone secondary particles that were used in Example 12: HAP-5a.

As in Example 10, the amounts of calcium carbonate (limestone particles) and phosphoric acid used in the first step (acid attack) were such to achieve an initial Ca/P ratio = 1 : 1 to make a brushite structure in the first step.

The amount of the extra calcium carbonate particles and the calcium hydroxide (lime) added to the second step resulted in a calculated final Ca/P ratio of about 3.3 for Example 12: HAP-5a.

The amount of bone char particles and the calcium hydroxide (lime) added to the second step resulted in an estimated final Ca/P ratio to be about 1.7 for Example 13: HAP-5b. The purity in hydroxyapatite of the bone char was estimated to be about 90% hydroxyapatite. The bone char particles contained components other than hydroxyapatite, notably calcite (about 5 wt% calcium carbonate). The bone char particles contained a very low BET specific surface area hydroxyapatite (less than 3 m²/g).

Half of the suspension made in the first step containing brushite was used in the second step to make the hydroxyapatite material Example 12 using calcium carbonate as secondary particles. The other half of the suspension made in the first step was used to make the other hydroxyapatite Example 13 using bone char as secondary particles.

The second step was carried out 24 hours after the first step was performed.

The various proportions of the reactants : CaCCri, H₃PO₄, Ca(OH)₂, bone char (“BCH”) for the composite materials Examples 12 and 13 are provided in TABLE 18. The Ca/P¹ molar ratios calculated from the amounts of reactants used in the 1^st and after the 2^nd step are also provided in TABLE 18. The initial and final pH, the temperature range, and the time of reaction for the 1^st step, as well as the percentage of moles of Ca used in the first step compared to the total amount of moles of Ca used in both steps was already provided in TABLE 19. The initial and final pH, the temperature range, and the time of reaction for the 2^nd step are provided in TABLE 20.

TABLE 18

*half of the suspension of the first step was used in the 2^nd step to make

HAP-5a and the other half was used to make HAP-5b

molar Ca/P¹ = calculated from the added reactants

** assuming that the bone char contained about 90wt% hydroxyapatite (Caio(P04)6(OH)₂) and 5wt% CaCC^.

TABLE 19

TABLE 20

Example 14

Porosity and particle size of Examples 10-13

The porosity characteristics were determined after a heat treatment (drying) at 110 °C under vacuum overnight (about 16 hours). The BET specific surface area (m²/g) and pore volume (cm³/g) were determined by gas adsorption on a Micromeritics ASAP2020 machine. The particle size measurement was carried out on a Beckman Coulter LS 230 laser diffraction particle size analyser (laser of wavelength 750 nm).

The BET specific surface area, pore volume, and mean particles size D50 for the Examples 10-13 can be found in TABLE 21.

TABLE 21

Example 15

Composition of Examples 10-13 after drying The composition of the materials of Examples 10-13 was determined qualitatively by XRD. The residual quantity of calcium carbonate was determined by thermogravimetric analysis (TGA). TGA is a method of thermal analysis in which the weight of a sample is measured over time as the sample is heated at a constant rate, in this case heated from 35 to 250 °C at a rate of 10°C/min. This measurement provides information about the decomposition of the sample.

The composition (e.g., residual calcium carbonate) of the materials of Examples 10-13 based on XRD and TGA analysis can be found in TABLE 22.

TABLE 22

* measured by TGA*

molar Ca/P = calculated from the weight % measured by TGA analysis

AC = Activated Carbon

Example 16 (in accordance with the invention)

Water treatment testing of materials of Examples 10-13

The cationic standard test described in Example 9 was carried out with the materials of Examples 10-13. The % removal for the 7 metallic cations is provided in TABLE 23. TABLE 23

For the coreshell hydroxyapatite materials of Examples 10-11, the removal rate for Cr, Ni and Zn was greatly improved compared to the control hydroxyapatite (Example 1). For the coreshell hydroxyapatite materials of Examples 11 and 13, the removal rate for Hg was improved compared to the control hydroxyapatite (Example 1).

Comparing the performance of the coreshell hydroxyapatite materials of Examples 10-13, the best increase in removal efficiency was observed with Example 11 (HAP- 4c with a composite of hydroxyapatite and activated carbon), which demonstrated an increased removal rate for Cr, Cu, Hg, Ni, and Zn.

The disclosure of all patent applications, and publications cited herein are hereby incorporated by reference, to the extent that they provide exemplary, procedural or other details supplementary to those set forth herein.

Should the disclosure of any of the patents, patent applications, and publications that are incorporated herein by reference conflict with the present specification to the extent that it might render a term unclear, the present specification shall take precedence.

In the present application, where an element or component is said to be included in and/or selected from a list of recited elements or components, it should be understood that in related embodiments explicitly contemplated here, the element or component can also be any one of the individual recited elements or components, or can also be selected from a group consisting of any two or more of the explicitly listed elements or components. Any element or component recited in a list of elements or components may be omitted from such list.

Further, it should be understood that elements, embodiments, and/or features of processes or methods described herein can be combined in a variety of ways without departing from the scope and disclosure of the present teaching, whether explicit or implicit herein.

Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the preferred embodiments of the present invention.

While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of systems and methods are possible and are within the scope of the invention.

Claims

1. Solid particles, comprising :

- a hydroxyapatite ; and

- secondary particles containing water-insoluble chemical substance(s) in solid form, preferably comprising calcium carbonate, silica, alumina, a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.67 or a bone char, or any combination thereof, more preferably comprising calcium carbonate and/or a bone char; and wherein the hydroxyapatite and secondary particles form agglomerates and/or coreshells in which a shell comprising the hydroxyapatite covers at least partially the secondary particles that serves as particle cores.

2. Solid particles according to claim 1, wherein the secondary particles comprises calcium carbonate, and wherein the solid particles have an overall Ca:P molar ratio of at least 1.75, preferably at least 1.8, more preferably at least 1.9, yet more preferably at least 2 and/or of at most 12, preferably at most 10, more preferably at most 6.

3. Solid particles according to claim 1 or 2, comprising, based on the total weight of dry matter:

- at least 25wt%, advantageously at least 30wt% of hydroxyapatite.

4. Solid particles according to any of claims 1 to 3, comprising, based on the total weight of dry matter:

- more than 7wt% calcium carbonate, advantageously more than 20wt% calcium carbonate, advantageously more than 25wt% of secondary particles; and

- at most 75wt% calcium carbonate, advantageously at most 70% secondary particles.

5. Solid particles according to any of claims 1 to 4, comprising particles in the form of coreshells in which a shell comprising the hydroxyapatite covers at least partially the secondary particles, and wherein the shell further comprises calcium carbonate. 6. Solid particles according to claim 1, wherein the secondary particles comprises bone char, and wherein the particles have an overall Ca:P molar ratio of at least 1.55, preferably at least 1.

6, and/or of at most 1.9, preferably at most

I.8, more preferably at most 1.75.

7. Solid particles according to claim 1 or 2 wherein the hydroxyapatite is a calcium-deficient hydroxyapatite, preferably a hydroxyapatite with a Ca/P molar ratio more than 1.5 and less than 1.67.

8. Solid particles according to any of claims 1 to 7, being essentially free of a calcium phosphate compound other than a hydroxyapatite, preferably essentially free of a calcium phosphate compound selected from the group consisting of monocalcium phosphate monohydrate, dicalcium phosphate dihydrate, dicalcium phosphate anhydrous, and octacalcium bis(hydrogen phosphate) tetrakisphosphate pentahydrate.

9. Solid particles according to any of claims 1 to 8, having a BET surface area of more than 60 m²/g and preferably up to 180 m²/g and/or having a pore volume of from 0.3 cm³/g up to 0.45 cm³/g.

10. Solid particles according to any of claims 1 to 9, wherein the hydroxyapatite is a modified hydroxyapatite onto which at least one additive is deposited on the hydroxyapatite and/or wherein the hydroxyapatite is a hydroxyapatite composite wherein the at least one additive is incorporated or embedded into the hydroxyapatite.

11. Solid particles according to claim 11, wherein the at least one additive comprises copper or derivatives thereof, iron or derivatives thereof (such as iron hydroxide, zero-valent iron, FeOOH, iron oxide), a metal sulfide, and/or activated carbon.

12. Process for making the solid particles according to any of claims 1 to

I I, comprising: a first step (acid attack) of a Ca source with a source of phosphate at an acidic pH to make a calcium phosphate structure (other than hydroxyapatite); a second step (alkaline maturation) to convert, with a source of hydroxide, the calcium phosphate structure to hydroxyapatite; and using a source of secondary particles in the first step and/or in the second step to make the solid particles.

13. Process for making the solid particles according to Claim 12, wherein the Ca source to make the calcium phosphate structure comprises calcium carbonate; the source of phosphate is phosphoric acid; wherein the calcium phosphate structure (other than hydroxyapatite) comprises brushite; the source of hydroxide is calcium hydroxide; and the source of secondary particles is preferably calcium carbonate, silica, alumina, and/or a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.67 or a bone char.

14. Process according to any of claims 2 to 5 & 7 to 11, the process comprising:

- in a first acid attack step, calcium-containing particles and phosphoric acid are mixed in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of from 1.2 to 12, preferably from 1.7 to 11, more preferably from 1.9 to 10, and reacting the calcium-containing particles with said phosphoric acid at a pH of between 4 and 7, in order to obtain a suspension (A) of calcium phosphate and calcium carbonate, wherein the calcium-containing particles contain calcium carbonate, preferably contain >70 wt% calcium carbonate, more preferably contain >90 wt% calcium carbonate, most preferably contain >95 wt% calcium carbonate; wherein at least a portion of calcium-containing particles serves as secondary particles; and

15. Process according to the preceding claim, wherein the calcium- containing compound comprises or consists essentially of calcium hydroxide.

16. Process for making the Solid particles according to any of claims 1 to 11, the process comprising: - in a first acid attack step, calcium-containing particles and phosphoric acid are mixed in water, and reacting the calcium-containing particles with said phosphoric acid, in order to obtain a suspension (A) comprising brushite, wherein the calcium-containing particles contain calcium carbonate, preferably contain >70 wt% calcium carbonate, more preferably contain >90 wt% calcium carbonate, most preferably contain >95 wt% calcium carbonate; and

- in a second alkaline maturation step, adding to the suspension (A) calcium hydroxide ions in order to increase the pH to at least 7 and at most 10.5 to obtain a suspension (B) of the solid particles, wherein a source of the secondary particles is used in the first step and/or second step; and wherein the source of secondary particles comprises water-insoluble chemical substance(s) in solid form, preferably comprising calcium carbonate, silica, alumina, a calcium phosphate with a Ca/P molar ratio from 1.5 to 1.67 or a bone char, or any combination thereof, more preferably comprising calcium carbonate and/or a bone char.

17. Process according to the preceding claim, wherein the calcium- containing particles and phosphoric acid are mixed in the first step to obtain a Ca/P molar ratio of from 0.9 to 1.1.

18. Use of the Solid particles according to any of claims 1 to 11 as an adsorbent for removing from a fluid, such as a water effluent, at least a portion of a contaminant, preferably selected from the group consisting of Al, Ag, As, B,

Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hg, Hf, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, more preferably selected from the group consisting of Cd, Cr, Ni, Zn, and/or As.