EP4719990A1

EP4719990A1 - Method for polymorph control in pcc precipitated from cacl 2 with na2co3

Info

Publication number: EP4719990A1
Application number: EP24730245.8A
Authority: EP
Inventors: Christian SANTNER; Michael Pohl
Original assignee: Omya International AG; EasyMining Sweden AB
Current assignee: Omya International AG; EasyMining Sweden AB
Priority date: 2023-05-31
Filing date: 2024-05-28
Publication date: 2026-04-08
Also published as: WO2024246045A1; CN121219238A

Abstract

The present invention relates to a process for producing a scalenohedral PCC product, to a scalenohedral PCC product obtainable by the inventive process as well as to the use of the inventive scalenohedral PCC product in polymer applications, paper coating applications, paper making, paints, coatings, sealants, adhesives, feed, pharmaceuticals, concrete, cement, cosmetics, water treatment, engineered wood applications, plasterboard applications, packaging applications, catalysis, gas treatment applications and/or agricultural applications.

Description

Method for polymorph control in PCC precipitated from CaCh with Na2CC>3

Technical Field of the Invention

Background of the Invention

In the recent years calcium carbonate has found a wide array of uses across many fields. For example, calcium carbonate is one of the most widely used minerals in the paper, plastic, paint and coating industries both as a filler and, due to its white colour, as a coating pigment. In the paper industry calcium carbonate is valued for its high brightness, opacity and gloss and is commonly used as a filler to make bright opaque paper. In addition, calcium carbonate is frequently used as an extender in paints and is also used as a filler in adhesives, sealants and plastics. High grade calcium carbonate has also found uses in formulations of pharmaceuticals or in foods. In addition to that calcium carbonate is also often used in catalysis applications, gas treatment applications, water treatment and/or agricultural applications.

Calcium carbonate is known to exist as natural occurring minerals as well as synthetically produced products. Ground calcium carbonate (GCC) is a calcium carbonate obtained from natural sources and processed through a wet and/or dry treatment step. Precipitated calcium carbonate (PCC) is a synthesized material obtained from a precipitation reaction. While naturally occurring ground calcium carbonate (GCC) is usually used as a filler in many applications, synthetically manufactured precipitated calcium carbonate (PCC) may be tailor-made, especially with respect to its morphology or particle size, allowing PCC to fulfil additional functions.

Generally, one way to produce precipitated calcium carbonate commercially is by calcining crude limestone to obtain quicklime. Water is then added to yield an aqueous suspension of calcium hydroxide (“milk of lime”) (this reaction is shown in reaction (1)), and carbon dioxide is reintroduced into this slurry to precipitate the calcium carbonate (this reaction is shown in reaction (2)).

(1) CaO + H₂O — > Ca(OH)₂ + heat

(2) Ca(OH)₂ + CO₂ ->• CaCO₃ + H₂O + heat

The product of this process is known as precipitated calcium carbonate (“PCC”). The resulting aqueous suspension, or slurry, of calcium carbonate may be used as it is or further processed (e.g., dewatered, ground, deagglomerated, etc.) to form a dry product. Depending on the exact reaction conditions the precipitation reaction is capable of producing calcium carbonate with different characteristics. US5811070A discloses a process for producing precipitated calcium carbonate particles, the process comprising the steps of introducing carbon dioxide into a milk of lime containing a first reagent to prepare an aqueous suspension containing calcium carbonate particles of 0.4 pm in average size, adding a milk of lime into the aqueous suspension, and continuously reacting a carbonated solution containing a second reagent with the aqueous suspension.

EP1631525A1 discloses a process for the preparation of platy precipitated calcium carbonate comprising the steps of providing a suspension of calcium hydroxide, carbonating the suspension of calcium hydroxide, adding a polyacrylate to the suspension prior to the completion of carbonation to precipitated platy calcium carbonate.

US2006/0196836 A1 describes a process for treating seven types of saline waters. The process includes the steps of contacting the water with a first reagent comprising a source of calcium ions selected from calcium oxide and calcium hydroxide to form a first solid product which is recovered. The process includes a further step of subjecting at least a portion of the partially processed water to at least partial evaporation so as to promote the formation of a precipitate and a mother liquor. The precipitate is recovered as a second product.

Technical Problems

However, in the known process of reaction step (1), merely calcium oxide is used as source for producing the calcium hydroxide, also known as “milk of lime”, and afterwards the precipitated calcium carbonate. Furthermore, in reaction step (2) carbon dioxide is introduced into this slurry to precipitate the calcium carbonate. Nowadays, it is often desirable to use different calcium sources to be more flexible and especially at least one source that is different to calcium oxide and the milk of lime. Additionally, the use of carbon dioxide, which is a gas, often results in significantly more complex and more expensive equipment. Also processes which have an increased carbon dioxide footprint are unfavourable and are often rejected by manufacturers.

Furthermore, due to the ongoing preferences for ecological and environmentally friendly products, it is preferred that the educts can be prepared or obtained from recovered materials such as waste materials.

In addition to that monitoring and controlling of the above reaction is often difficult and, therefore, sometimes unwanted morphologies or even mixtures of different morphologies are obtained. However, this is disadvantageous since in many fields tailor-made precipitated calcium carbonate (PCC), especially with respect to its morphology and sometimes also particle size or surface area is needed to fulfil additional functions.

Therefore, there is a continuous need for processes providing precipitated calcium carbonate products, that overcome at least one of the above mentioned disadvantages and especially for processes that allow the control of the morphology of the precipitated calcium carbonate product.

Object of the Invention

Accordingly, it is an objective of the present invention to provide a process for producing a precipitated calcium carbonate product which has a defined morphology, namely a process for producing a scalenohedral PCC product. The scalenohedral PCC exhibit clusters (rosettes) of triangular-shaped crystals emanating from a central core. Another object of the present invention is to provide a process for producing precipitated calcium carbonate that uses different calcium sources. In particular, it is an object of the present invention to provide a process for producing precipitated calcium carbonate that uses at least one calcium source that is different to calcium oxide and milk of lime.

Furthermore, it is another object of the present invention to provide a process for producing a precipitated calcium carbonate product that is inexpensive, easy to handle and easily adaptable. Especially it is desirable that the process for producing a precipitated calcium carbonate product has a reduced carbon dioxide footprint and uses no carbon dioxide containing compound, especially no gaseous carbon dioxide. Furthermore, it is desirable that no toxic or harmful chemicals are used or obtained as by-products.

The foregoing and other objects are solved by the subject-matter as defined herein in the independent claims.

According to one embodiment of the present invention a process for producing a scalenohedral PCC product is provided, the process comprising the steps of a) providing at least one calcium compound selected from the group consisting of calcium oxide powder, calcium hydroxide powder and calcium hydroxide suspension; b) providing a calcium chloride solution, wherein the solution comprises 0.5 to 270 g/l of calcium; c) mixing the at least one calcium compound of step a) and the calcium chloride solution of step b) in any order, wherein the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture is in the range from 7:93 to 80:20; d) adding to the mixture obtained in step c) a sodium carbonate source selected from sodium carbonate or a mixture consisting of at least 70 wt.-% sodium carbonate and up to 30 wt.-% sodium bicarbonate at a temperature from 30 to 70 °C and at a pH value from 9.5 to 13.5, wherein the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1.00:1.00 to 1.00:1.30.

The inventors surprisingly found that by the above process it is possible to control the morphology of the precipitated calcium carbonate and to obtain a scalenohedral PCC product. Furthermore, the inventors found that in addition to calcium oxide or milk of lime calcium chloride can be used as further calcium source. Additionally, the inventors surprisingly found that no carbon dioxide containing compound, especially no gaseous carbon dioxide has to be used in the inventive process to obtain the scalenohedral PCC product. Rather a sodium carbonate source selected from sodium carbonate or a mixture consisting of at least 70 wt.-% sodium carbonate and up to 30 wt.-% sodium bicarbonate is sufficient to produce the scalenohedral PCC product at the above mentioned temperature and pH value. Therefore, the inventive process has a reduced carbon dioxide footprint, and is inexpensive, easy to handle and easily adaptable. In this process no chemicals are used that are toxic or harmful to the user. Furthermore, the by-products obtained in this process are also not toxic or harmful and might even be recovered for later use such as, for example, sodium chloride.

According to another embodiment of the present invention a scalenohedral PCC product obtainable according to the process of the present invention is provided.

According to another embodiment of the present invention the inventive scalenohedral PCC product obtainable according to the process of the present invention is used in polymer applications, paper coating applications, paper making, paints, coatings, sealants, adhesives, feed, pharmaceuticals, concrete, cement, cosmetics, water treatment, engineered wood applications, plasterboard applications, packaging applications, catalysis, gas treatment applications and/or agricultural applications.

Advantageous embodiments of the present invention are defined in the corresponding subclaims.

According to one embodiment of the present invention, the at least one calcium compound of step a) is a calcium hydroxide powder or a calcium hydroxide suspension, preferably a calcium hydroxide suspension and preferably the calcium hydroxide suspension has a solids content of from 5 to 50 wt.-%, based on the total weight of the calcium hydroxide suspension, preferably from 7 to 47 wt.-% and most preferably from 9 to 45 wt.-%.

According to another embodiment of the present invention, the at least one calcium compound of step a) is in form of calcium hydroxide particles having a volume median particle size cfeo(vol) from 0.05 to 25 pm, preferably from 0.2 to 10 pm, more preferably from 0.4 to 5 pm, and most preferably from 1 .0 to 3.5 pm, and/or a volume-based particle size cfoo(vol) from 0.15 to 75 pm, preferably from 1 to 30 pm, more preferably from 1 .5 to 15 pm, and most preferably from 2 to 10 pm.

According to another embodiment of the present invention, the calcium chloride solution of step b) comprises 1 .0 to 200 g/l of calcium, preferably 2.0 to 150 g/l, more preferably 3.0 to 100 g/l and most preferably 5.0 to 50 g/l.

According to another embodiment of the present invention, the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture in step c) is in the range from 10:90 to 70:30, preferably from 15:85 to 50:50, more preferably from 20:80 to 40:60 and most preferably is about 25:75.

According to another embodiment of the present invention, the temperature in step d) is from 40 to 60 °C and more preferably from 45 to 50 °C and/or wherein the pH value is from 10.0 to 13.0 and more preferably 10.5 to 12.0.

According to another embodiment of the present invention, to the mixture obtained in step c) the sodium carbonate source is added in at least two portions, wherein the first portion contains 0.01 to 5 wt.-% of the total amount of the sodium carbonate source and is added in form of a solution comprising 5 to 20 g/l of the sodium carbonate source, preferably wherein the first portion of the sodium carbonate source in step d) contains 0.1 to 4.0 wt.-% of the total amount of the sodium carbonate source, more preferably 1 .0 to 3.0 wt.-% and most preferably 1 .5 to 2.5 wt.-% and/or is added in form of a solution comprising 7 to 17 g/l of the sodium carbonate source, preferably 8 to 15 g/l.

According to another embodiment of the present invention, the remaining sodium carbonate source after the first portion is added in one portion as second portion and/or wherein the remaining sodium carbonate source after the first portion is added as solid and/or the sodium carbonate source is sodium carbonate.

According to another embodiment of the present invention, the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1 .00:1 .00 to 1 .00:1 .20, more preferably from 1 .00:1 .00 to 1 .00:1 .10 and most preferably in an amount of about 1 .00:1 .05.

According to another embodiment of the present invention, the process further comprises a step e) of adding to the mixture obtained in step c) an additive, preferably a dispersing agent and/or a nucleation agent such as sucrose or citrate and most preferably sucrose.

According to another embodiment of the present invention, the process further comprises a step f) of separating the scalenohedral PCC product from the aqueous suspension obtained in step d) and preferably step f) is done by solvent evaporation and/or pressure filtration and/or wherein the process further comprises a step g) of drying the scalenohedral PCC product after step d) or after step f), if present, at a temperature in the range from 60 to 120 °C, preferably from 80 to 110 °C, most preferably from 95 to 105°C, preferably until the moisture content of the scalenohedral PCC product is less than 1 wt.-%, based on the total weight of the dried scalenohedral PCC product.

According to another embodiment of the present invention, the calcium chloride solution in step b) is a waste material, preferably obtained from a recycling process and more preferably from an aqueous phosphor recycling process and/or wherein the calcium chloride solution comprises further salts, preferably selected from the group consisting of magnesium salts, sodium salts and potassium salts and most preferably is selected from the group consisting of magnesium chloride, sodium chloride and potassium chloride.

According to another embodiment of the present invention, the calcium chloride solution in step b) comprises magnesium salts and preferably the solution comprises 5 to 200 mg/l of magnesium, more preferably 5 to 100 mg/l and most preferably 5 to 50 mg/l.

According to another embodiment of the present invention, the obtained scalenohedral PCC product i) has a specific surface area from 0.1 to 25.0 m²/g, preferably from 0.5 to 20.0 m²/g, and most preferably from 1 .0 to 15.0 m²/g, measured using nitrogen and the BET method according to

ISO 9277:2010 and/or ii) is in form of particles having a volume-based median particle size cfeo(vol) from 0.05 to 10 pm, preferably from 0.2 to 8 pm, more preferably from 0.4 to 5 pm, and most preferably from 1 .0 to 3.5 pm, and/or iii) is in form of particles having a volume-based top cut particle size cfo8(vol) from 0.15 to 20 pm, preferably from 1 to 15 pm, more preferably from 1 .5 to 10 pm, and most preferably from 2 to 8 pm and/or iv) has an ISO brightness (R457) of at least 90 %, preferably at least 92 %, more preferably at least 95 %, and most preferably at least 97 %; and/or v) a yellowness index (Yl) of below 2, preferably below 1 .8, more preferably below 1 .6 and most preferably of from 0.5 to 1 .5 and/or vi) comprises at least 80 wt.-% scalenohedral PCC, based on the total dry weight of the scalenohedral PCC product, preferably 90 wt.-% and most preferably 95 wt.-% and 20 wt.-% or less aragonite, based on the total dry weight of the scalenohedral PCC product, preferably 10 wt.-% or less and most preferably 5 wt.-% or less.

It should be understood that for the purpose of the present invention, the following terms have the following meaning:

A “calcium carbonate-comprising material” in the meaning of the present invention is a mineral material or a synthetic material having a content of calcium carbonate of at least 80 wt.-%, preferably 85 wt.-%, more preferably 90 wt.-%, and most preferably 95 wt.-%, based on the total weight of the calcium carbonate-comprising material.

“Natural ground calcium carbonate” (GCC also known as GNCC) in the meaning of the present invention is a calcium carbonate obtained from natural sources, such as limestone, marble, or chalk, and processed through a wet and/or dry treatment such as grinding, screening and/or fractionating, for example, by a cyclone or classifier.

“Precipitated calcium carbonate” (PCC) in the meaning of the present invention is a synthesized material, that can generally be obtained by precipitation following a reaction of carbon dioxide and calcium hydroxide (hydrated lime) in an aqueous environment (milk of lime) or by precipitation of a calcium and a carbonate source in water. Additionally, precipitated calcium carbonate can also be the product of introducing calcium and carbonate salts, calcium chloride and sodium carbonate, for example, in an aqueous environment. PCC may be vaterite, calcite or aragonite or a mixture thereof. PCCs are described, for example, in EP2447213A1 , EP2524898A1 , EP2371766A1 , or WO2013/142473A1 .

“Scalenohedral PCC” in the meaning of the present invention is PCC in the form of calcite, which has a trigonal structure with a scalenohedral crystal habit. The scalenohedral PCC exhibit clusters (rosettes) of triangular-shaped crystals emanating from a central core.

“Calcium oxide” in the meaning of the present invention is a chemical compound having the formula CaO and consisting of calcium ions and oxide ions.

“Calcium hydroxide” in the meaning of the present invention is a chemical compound having the formula Ca(OH)2 and consisting of calcium ions and hydroxide ions.

“Calcium chloride” in the meaning of the present invention is a chemical compound having the formula CaCh and consisting of calcium ions and chloride ions.

“Sodium carbonate” in the meaning of the present invention is a chemical compound having the formula Na2COs and consisting of sodium ions and carbonate ions. It is also known as washing soda, soda ash and soda crystals. “Sodium bicarbonate” in the meaning of the present invention is a chemical compound having the formula NaHCCh and consisting of sodium ions and bicarbonate ions. It is also known as baking soda or bicarbonate of soda.

Throughout the document the “particle size” of particulate materials other than the obtained scalenohedral PCC product and the calcium hydroxide herein is described by its distribution of particle sizes c/x(wt). Therein, the value c/_x(wt) represents the diameter relative to which x % by weight of the particles have diameters less than c/_x(wt). This means that, for example, the cbo(wt) value is the particle size at which 20 wt.% of all particles are smaller than that particle size. The cfeo(wt) value is thus the weight median particle size, i.e. 50 wt.-% of all particles are smaller than that particle size and the cfoo(wt) value, is the particle size at which 90 wt.-% of all particles are smaller than that particle size. The weight-based median particle size cfeo(wt) and the weight-based particle size cfoo(wt) are measured by the sedimentation method, which is an analysis of sedimentation behaviour in a gravimetric field. The measurement is made with a Sedigraph™ 5120 of Micromeritics Instrument Corporation, USA. The method and the instrument are known to the skilled person and are commonly used to determine particle size distributions. The measurement is carried out in an aqueous solution of 0.1 wt.-% N34P2O7. The samples are dispersed using a high speed stirrer and sonication.

The “particle size” of the obtained scalenohedral PCC product and the calcium hydroxide herein is described as volume-based particle size distribution c/_x(vol). Therein, the value c/_x(vol) represents the diameter relative to which x % by volume of the particles have diameters less than c/_x(vol). This means that, for example, the c/2o(vol) value is the particle size at which 20 vol.% of all particles are smaller than that particle size. The cfeo(vol) value is thus the volume median particle size, i.e. 50 vol.% of all particles are smaller than that particle size, the cfoo(vol) value is thus the value at which 90 vol.% of all particles are smaller than that particle size and the cfo8(vol) value, referred to as volume-based top cut, is the particle size at which 98 vol.% of all particles are smaller than that particle size. Volume median particle size dso was evaluated using a HELOS Particle size analyzer and the Software WINDOX of Sympatec GmbH. The particle size of the obtained scalenohedral PCC product is measured in water and the particle size of the calcium hydroxide is measured in ethanol p.a. The cfeo, doo or do& value, measured using a HELOS Particle size analyzer and the Software WINDOX of Sympatec GmbH, indicates a diameter value such that 50 %, or 90 %, or 98 % by volume, respectively, of the particles have a diameter of less than this value. The raw data obtained by the measurement are analysed using the Mie theory, with a particle refractive index of 1 .57 and an absorption index of 0.005. Alternatively a Malvern Mastersizer 3000 Laser Diffraction System can be used.

Throughout the present document, the term “specific surface area” (in m²/g), which is used to define functionalized calcium carbonate or other materials, refers to the specific surface area as determined by using the BET method (using nitrogen as absorbing gas). The BET method is well known to the skilled man (ISO 9277:2010). The total surface area (in m²) of the filler material is then obtained by multiplication of the specific surface area and the mass (in g) of the corresponding sample.

The term “brightness” as used in the context of the present invention is a measurement of the percentage of diffuse light reflected from a powder tablet produced from the PCC product. A brighter PCC product reflects more diffuse light. As used herein, brightness of the PCC product may be measured at a wavelength of light of 457 nm (R457) and is specified in percent.

The “yellowness index (Yl)” as used in the context of the present invention is measured according to DIN 6167. The yellowness index (Yl) is a number calculated from spectrophotometric data that describes the change in colour of a test sample from clear or white to yellow.

For the purpose of the present invention, the term “viscosity” or “Brookfield viscosity” refers to Brookfield viscosity. The Brookfield viscosity is for this purpose measured by a Brookfield DV-II+ Pro viscometer at 25 °C ± 1 °C at 100 rpm using an appropriate spindle of the Brookfield RV-spindle set and is specified in mPa s. Based on his technical knowledge, the skilled person will select a spindle from the Brookfield RV-spindle set which is suitable for the viscosity range to be measured. For example, for a viscosity range between 200 and 800 mPa s the spindle number 3 may be used, for a viscosity range between 400 and 1 600 mPa s the spindle number 4 may be used, for a viscosity range between 800 and 3200 mPa s the spindle number 5 may be used, for a viscosity range between 1 000 and 2 000 000 mPa s the spindle number 6 may be used, and for a viscosity range between 4 000 and 8 000 000 mPa s the spindle number 7 may be used.

For the purpose of the present invention, the “solids content” of a liquid composition is a measure of the amount of material remaining after all the solvent or water has been evaporated. If necessary, the “solids content” of a suspension given in wt.-% in the meaning of the present invention can be determined using a Halogen Moisture Analyzer HR73 from Mettler-Toledo (7 = 160 °C, automatic switch off 3, standard drying) with a sample size of 5 to 20 g.

Unless specified otherwise, the term “drying” refers to a process according to which at least a portion of water is removed from a material to be dried such that a constant weight of the obtained “dried” material at 160 °C is reached. The term “dry” material or “dry” composition, is understood to be a material/composition having less than 1 .0 % by weight of water relative to the material/composition weight. The % water is determined using a Halogen Moisture Analyzer HR73 from Mettler-Toledo (7 = 160 °C, automatic switch off 3, standard drying) with a sample size of 5 to 20 g.

A “powder” in the meaning of the present invention is a dry material which is in the form of particles.

A “suspension” or “slurry” in the meaning of the present invention comprises undissolved solids and liquid, and optionally further additives, and usually contains large amounts of solids and, thus, is more viscous and can be of higher density than the liquid from which it is formed.

Where the term “comprising” is used in the present description and claims, it does not exclude other elements. For the purposes of the present invention, the term “consisting of’ is considered to be a preferred embodiment of the term “comprising of’. If, hereinafter, a group is defined to comprise at least a certain number of embodiments, this is also to be understood to disclose a group, which preferably consists only of these embodiments.

Where an indefinite or definite article is used when referring to a singular noun, e.g. “a”, “an” or “the”, this includes a plural of that noun unless something else is specifically stated.

Terms like “obtainable” or “definable” and “obtained” or “defined” are used interchangeably. This e.g. means that, unless the context clearly dictates otherwise, the term “obtained” does not mean to indicate that e.g. an embodiment must be obtained by e.g. the sequence of steps following the term ‘obtained” even though such a limited understanding is always included by the terms “obtained” or ‘defined” as a preferred embodiment.

Detailed description of the invention

The inventive process for producing the scalenohedral PCC product comprises the steps of a) providing at least one calcium compound selected from the group consisting of calcium oxide powder, calcium hydroxide powder and calcium hydroxide suspension; b) providing a calcium chloride solution, wherein the solution comprises 0.5 to 270 g/l of calcium; c) mixing the at least one calcium compound of step a) and the calcium chloride solution of step b) in any order, wherein the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture is in the range from 7:93 to 80:20; and d) adding to the mixture obtained in step c) a sodium carbonate source selected from sodium carbonate or a mixture consisting of at least 70 wt.-% sodium carbonate and up to 30 wt.-% sodium bicarbonate at a temperature from 30 to 70 °C and at a pH value from 9.5 to 13.5, wherein the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1 .00:1 .00 to 1 .00:1 .30.

In the following preferred embodiments of the inventive process for producing the scalenohedral PCC product will be set out in more detail. It is to be understood that these embodiments and details also apply to the inventive products and uses thereof.

Process step a)

In step a) of the process of the present invention at least one calcium compound selected from the group consisting of calcium oxide powder, calcium hydroxide powder and calcium hydroxide suspension is provided.

The calcium oxide powder of step a) can be obtained by calcining a calcium carbonate containing material. Calcination is a thermal treatment process applied to calcium carbonate containing materials in order to bring about a thermal decomposition resulting in the formation of calcium oxide and gaseous carbon dioxide. Calcium carbonate containing materials which may be used in such a calcinations process are those selected from the group comprising precipitated calcium carbonates; natural calcium carbonate containing minerals such as marble, limestone and chalk, and mixed alkaline earth carbonate minerals comprising calcium carbonate such as dolomite, or calcium carbonate rich fractions from other sources. It is also possible to subject a calcium carbonate containing waste material to a calcination process in order to obtain a calcium oxide containing material.

Calcium carbonate decomposes at about 1000 °C to calcium oxide (commonly known as quicklime). The calcination step may be carried out under conditions and using equipment well-known to the person skilled in the art. Generally, calcination may be carried out in furnaces or reactors (sometimes referred to as kilns) of various designs including shaft furnaces, rotary kilns, multiple hearth furnaces, and fluidized bed reactors. The end of the calcination reaction may be determined, e.g. by monitoring the density change, the residual carbonate content, e.g. by X-ray diffraction, or the slaking reactivity by common methods.

According to one embodiment of the present invention, the calcium oxide containing material is obtained by calcining a calcium carbonate containing material, preferably selected from the group consisting of precipitated calcium carbonate, natural calcium carbonate minerals such as marble, limestone and chalk, mixed alkaline earth carbonate minerals comprising calcium carbonate such as dolomite, and mixtures thereof and most preferably by calcining a natural calcium carbonate mineral such as marble, limestone and chalk.

For reasons of efficiency, it is preferred that the calcium oxide powder has a minimum calcium oxide content of at least 75 wt.-%, preferably at least 90 wt.-%, and most preferably 95 wt.-%, based on the total weight of the calcium oxide powder. According to one embodiment, the calcium oxide powder consists of calcium oxide.

The calcium oxide powder can consist of only one type of calcium oxide powder. Alternatively, the calcium oxide powder can consist of a mixture of two or more types of calcium oxide powders.

The calcium oxide containing material is ground before use to obtain crushed calcium oxide particles or the calcium oxide powder. In general, the dry grinding step may be carried out with any conventional grinding device, for example, under conditions such that comminution predominantly results from impacts with a secondary body, i.e. in one or more of: a ball mill, a rod mill, a vibrating mill, a roll crusher, a centrifugal impact mill, a vertical bead mill, an attrition mill, a pin mill, a hammer mill, a pulveriser, a shredder, a de-clumper, a knife cutter, or other such equipment known to the skilled man. It is also common that such a calcium oxide containing material undergoes a beneficiation step after grinding such as magnetic separation to remove impurities.

According to one embodiment of the present invention the crushed calcium oxide is in form of particles having a weight median particle size cfeo(wt) from 20 to 100 mm, preferably from 20 to 90 mm, and most preferably from 20 to 70 mm. Such crushed calcium oxide is also known as lump lime to the skilled person and is commercially available.

According to another embodiment of the present invention the crushed calcium oxide is in form of particles having a weight median particle size cfeo(wt) from 0.5 to 20 mm, preferably from 1 to 20 mm. Such crushed calcium oxide is also known as pebble lime to the skilled person and is commercially available.

According to another embodiment of the present invention the calcium oxide powder is in form of particles having a weight median particle size cfeo(wt) from 0.05 to 90 pm, preferably from 0.05 to 50 pm. According to another embodiment of the present invention the calcium oxide powder is in form of particles having a weight median particle size cfeo(wt) from 0.05 to 25 pm, preferably from 0.2 to 10 pm, more preferably from 0.4 to 5 pm, and most preferably from 1 .0 to 3.5 pm.

Additionally or alternatively the calcium oxide powder is in form of particles having a particle size cfoo(wt) from 0.15 to 75 pm, preferably from 1 to 30 pm, more preferably from 1 .5 to 15 pm, and most preferably from 2 to 10 pm.

According to one embodiment of the present invention the calcium oxide powder of step a) consists of calcium oxide and is in the form of particles having a weight median particle size cfeo(wt) from 0.05 to 25 pm, preferably from 0.2 to 10 pm, more preferably from 0.4 to 5 pm, and most preferably from 1 .0 to 3.5 pm and a particle size cfoo(wt) from 0.15 to 75 pm, preferably from 1 to 30 pm, more preferably from 1 .5 to 15 pm, and most preferably from 2 to 10 pm.

The calcium hydroxide powder and calcium hydroxide suspension of step a) can be prepared by mixing water and a calcium oxide containing material. Preferably the calcium oxide containing material and the water are mixed in a weight ratio from 1 :1 to 1 :12 (e.g., in a weigh ratio from 1 :3 to 1 :12 or from 1 :5 to 1 :10).

The reaction of the calcium oxide containing material with water results in the formation of a milky calcium hydroxide suspension, better known as milk of lime. Said reaction is highly exothermic and is also designated as “lime slaking” in the art.

The temperature of the water, which is used to slake the calcium oxide containing material, is adjusted to be in the range from more than 0°C and less than 100°C. In other words, the water that is used to slake the calcium oxide containing material is adjusted to a temperature range, in which the water is in liquid form. Preferably, the temperature of the water is adjusted to be from 1 °C to 70°C, more preferably from 2°C to 50°C, even more preferably from 30°C to 50°C, and most preferably from 35 to 45°C.

According to a preferred embodiment, the “lime slaking” is performed under mixing, agitation, or stirring, for example, mechanical stirring. Suitable process equipment for mixing, agitation or stirring is known to the skilled person.

The progress of the slaking reaction may be observed by measuring the temperature and/or conductivity of the reaction mixture. It can also be monitored by turbidity control. Alternatively or additionally, the progress of the slaking reaction can be inspected visually.

According to a preferred embodiment of the present invention, the calcium hydroxide suspension has a solids content of from 5 to 50 wt.-%, based on the total weight of the calcium hydroxide suspension, preferably from 7 to 47 wt.-% and most preferably from 9 to 45 wt.-%.

Additionally or alternatively, the calcium hydroxide suspension has a Brookfield viscosity from 1 to 1000 mPa s at 25°C, more preferably from 5 and 800 mPa s at 25°C, and most preferably from 10 and 500 mPa s at 25°C. According to one embodiment, the Brookfield viscosity is measured at 100 rpm.

According to one embodiment the calcium hydroxide is separated from the water of the calcium hydroxide suspension. Separation may take place by any conventional means of separation known to the skilled person, for example, mechanically and/or thermally. Examples of mechanical separation processes are filtration, e.g. by means of a drum filter or filter press, nanofiltration, or centrifugation. An example for a thermal separation process is a concentrating process by the application of heat, for example, in an evaporator.

After separation, the calcium hydroxide can be dried in order to obtain a calcium hydroxide powder. Drying can take place at a temperature in the range from 60 to 120 °C, preferably from 80 to 100 °C, preferably until the moisture content of the calcium hydroxide powder is less than 1 wt.-%, based on the total weight of the dried calcium hydroxide. The drying can, for example, include thermal drying and/or drying at reduced pressure using equipment such as an evaporator, a flash drier, an oven, a spray drier and/or drying in a vacuum chamber. The drying step f) can be carried out at reduced pressure, ambient pressure or under increased pressure. The skilled person can choose the drying time dependent on the equipment, the water content and the intended use.

For reasons of efficiency, it is preferred that the calcium hydroxide powder has a minimum calcium hydroxide content of at least 75 wt.-%, preferably at least 90 wt.-%, and most preferably 95 wt.-%, based on the total weight of the calcium hydroxide powder. According to one embodiment, the calcium hydroxide powder consists of calcium hydroxide.

The calcium hydroxide powder can consist of only one type of calcium hydroxide powder. Alternatively, the calcium hydroxide powder can consist of a mixture of two or more types of calcium hydroxide powders.

According to a preferred embodiment the calcium hydroxide powder is in form of particles having a volume median particle size cfeo(vol) from 0.05 to 25 pm, preferably from 0.2 to 10 pm, more preferably from 0.4 to 5 pm, and most preferably from 1 .0 to 3.5 pm.

Additionally or alternatively the calcium hydroxide powder is in form of particles having a volume-based particle size cfoo(vol) from 0.15 to 75 pm, preferably from 1 to 30 pm, more preferably from 1 .5 to 15 pm, and most preferably from 2 to 10 pm.

According to a preferred embodiment of the present invention the calcium hydroxide powder of step a) consists of calcium hydroxide and is in the form of particles having a volume median particle size cfeo(vol) from 0.05 to 25 pm, preferably from 0.2 to 10 pm, more preferably from 0.4 to 5 pm, and most preferably from 1 .0 to 3.5 pm and a volume-based particle size cfoo(vol) from 0.15 to 75 pm, preferably from 1 to 30 pm, more preferably from 1 .5 to 15 pm, and most preferably from 2 to 10 pm.

Process step b)

In step b) of the inventive process a calcium chloride solution is provided, wherein the solution comprises 0.5 to 270 g/l of calcium.

The calcium chloride solution of step b) can be obtained by dissolving calcium chloride in water. According to a preferred embodiment of the present invention, the calcium chloride solution is an aqueous solution and the solvent consists only of water.

Alternatively the solvent comprises water and in addition thereto minor amounts of at least one water-miscible organic solvent selected from the group comprising methanol, ethanol, acetone, acetonitrile, tetrahydrofuran and mixtures thereof. If the solution comprises water and at least one water-miscible organic solvent, the at least one water-miscible organic solvent is present in an amount of from 0.1 to 40.0 wt.-% preferably from 0.25 to 30.0 wt.-%, more preferably from 0.5 to 20.0 wt.-% and most preferably from 1 .0 to 10.0 wt.-%, based on the total weight of the solvent.

The calcium chloride solution of step b) comprises 0.5 to 270 g/l of calcium. According to a preferred embodiment of the present invention the calcium chloride solution of step b) comprises 1.0 to 200 g/l of calcium, preferably 2.0 to 150 g/l, more preferably 3.0 to 100 g/l and most preferably 5.0 to 50 g/l, like in a range of 15 to 50 g/l or 25 to 50 g/l. According to another embodiment of the present invention the calcium chloride solution comprises the calcium chloride in an amount from 0.1 to 60 wt.-%, based on the total weight of the aqueous solution, preferably in an amount from 0.3 to 50 wt.-%, more preferably in an amount from 0.5 to 36 wt.-%, even more preferably in an amount of 0.8 to 22 wt.-%, and most preferably in an amount from 1 .4 to 12 wt.-%.

The calcium chloride solution of step b) can be obtained by dissolving calcium chloride in water. Alternatively the calcium chloride solution of step b) is obtained from a waste material. For example, the calcium chloride solution can be obtained from a recycling process. Recycling processes that provide calcium chloride solutions are known to the skilled person. According to a preferred embodiment the recycled calcium chloride solution is obtained from an aqueous phosphor recycling process.

According to another embodiment of the present invention the calcium chloride solution of step b) comprises further salts, preferably selected from the group consisting of magnesium salts, sodium salts and potassium salts and most preferably is selected from the group consisting of magnesium chloride, sodium chloride and potassium chloride.

The additional salts may be each present in the calcium chloride solution in an amount from 10 to 500 mg/l of magnesium, sodium, and potassium, more preferably 15 to 300 mg/l and most preferably 15 to 200 mg/l.

According to a preferred embodiment of the present invention the calcium chloride solution of step b) comprises magnesium salts. For example, the calcium chloride solution comprises, preferably consists of water, calcium chloride and magnesium salts. According to a preferred embodiment, the calcium chloride solution of step b) comprises magnesium salts and preferably the solution comprises 5 to 200 mg/l of magnesium, more preferably 5 to 100 mg/l and most preferably 5 to 50 mg/l.

Process step c)

In step c) of the present invention the at least one calcium compound of step a) and the calcium chloride solution of step b) are mixed in any order. The molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture is in the range from 7:93 to 80:20.

According to one embodiment of the present invention, step c) comprises the steps of providing the at least one calcium compound of step a) and then adding the calcium chloride solution of step b). According to another embodiment of the present invention, step c) comprises the steps of providing the calcium chloride solution of step b) and then adding the at least one calcium compound of step a).

The second component may be added in one portion or may be added in several equal or unequal portions, i.e. in larger and smaller portions.

Additional water may be added to the obtained mixture of step c).

The mixing or contacting or combining of the at least one calcium compound of step a) and the calcium chloride solution of step b) can be accomplished by any conventional means known to the skilled person. Preferably, mixing may be carried out using a wet mill, a mixing tank, a feeding pump or a flotation agitator. The mixing may be carried out at room temperature, or at other temperatures. According to one embodiment the mixing may be carried out at a temperature from 5 to 80°C, preferably from 10 to 70°C and most preferably from 20°C to 65°C, or at other temperatures. For example, the mixing may be carried out at 60°C ±2°C. Heat may be introduced by internal shear or by an external source or a combination thereof.

The mixing step can be performed, for example, for at least 30 seconds, for at least 1 minute, 2 minutes, 5 minutes, 10 minutes, 30 minutes, 1 hour, 2 hours, 12 hours or 1 day. The skilled person can choose the mixing time dependent on the equipment and the solids content.

According to one embodiment of the present invention, the mixture obtained in step c) is ground during and/or after step c). The grinding step can be carried out with any conventional grinding device, for example by e.g. using a ball mill, a centrifugal impact mill, a vertical bead mill, or an attrition mill. However, any other device that is able to grind the mixture obtained in step c) during and/or after method step c) may be used.

The solids content of the mixture obtained in step c) can be adjusted by the methods known to the skilled person. To adjust the solids content of the mixture, the suspension may be partially or fully dewatered by a filtration, centrifugation or thermal separation process. Alternatively, water may be added to the mixture until the desired solids content is obtained. According to one embodiment of the present invention, the mixture has a solids content of from 5 to 50 wt.-%, based on the total weight of the mixture, preferably from 7 to 47 wt.-% and most preferably from 9 to 45 wt.-%.

Additionally or alternatively, the mixture has a Brookfield viscosity from 1 to 1000 mPa s at 25°C, more preferably from 5 and 800 mPa s at 25°C, and most preferably from 10 and 500 mPa s at 25°C. According to one embodiment, the Brookfield viscosity is measured at 100 rpm.

According to another preferred embodiment of the present invention, the mixture obtained in step c) has a temperature from 40 to 75 °C and more preferably from 45 to 70 °C.

According to another preferred embodiment of the present invention, the mixture obtained in step c) has a pH value from 7.0 to 13.0, preferably from 10.0 to 13.0 and more preferably 10.5 to 12.0.

The at least one calcium compound of step a) and the calcium chloride of step b) are mixed in step c) in an amount such the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture is in the range from 7:93 to 80:20. Preferably the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture in step c) is in the range from 10:90 to 80:20 (e.g., from 15:85 to 80:20), preferably from 10:90 to 70:30 (e.g., from 15:85 to 70:30), more preferably from 15:85 to 50:50 (e.g., from 15:85 to 40:60), even more preferably from 20:80 to 40:60 and most preferably is about 20:80 or about 25:75.

Process step c) can be carried out in form of a batch process, a semi-continuous or a continuous process.

Process step d)

In step d) of the present invention to the mixture obtained in step c) a sodium carbonate source is added at a temperature from 30 to 70 °C and at a pH value from 9.5 to 13.5. The sodium carbonate source is selected from sodium carbonate or a mixture consisting of at least 70 wt.-% sodium carbonate and up to 30 wt.-% sodium bicarbonate. Furthermore the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1 .00:1 .00 to 1 .00:1 .30.

In step d) of the present invention to the mixture obtained in step c) a sodium carbonate source is added, wherein the sodium carbonate source is selected from sodium carbonate or a mixture consisting of at least 70 wt.-% sodium carbonate and up to 30 wt.-% sodium bicarbonate.

According to one embodiment of the present invention the sodium carbonate source consists only of sodium carbonate. “Sodium carbonate” in the meaning of the present invention is a chemical compound having the formula Na2COs and consisting of sodium ions and carbonate ions. It is also known as washing soda, soda ash and soda crystals.

According to another embodiment of the present invention the sodium carbonate source is a mixture consisting of at least 70 wt.-% sodium carbonate and up to 30 wt.-% sodium bicarbonate, based on the total dry weight of the sodium carbonate source. “Sodium bicarbonate” in the meaning of the present invention is a chemical compound having the formula NaHCCh and consisting of sodium ions and bicarbonate ions. It is also known as baking soda or bicarbonate of soda. For example, the sodium carbonate source is a mixture consisting of 72.0 wt.-% to 99.0 wt.-% sodium carbonate and 28.0 wt.-% to 1 .0 wt.-% sodium bicarbonate, based on the total dry weight of the sodium carbonate source, preferably from 75.0 wt.-% to 90.0 wt.-% sodium carbonate and 25.0 wt.-% to 10.0 wt.-% sodium bicarbonate, and most preferably from 78.0 wt.-% to 85.0 wt.-% sodium carbonate and 22.0 wt.-% to 15.0 wt.-% sodium bicarbonate.

According to a preferred embodiment of the present invention the sodium carbonate source consists only of sodium carbonate.

The sodium carbonate source can be in dry form, for example in form of a powder or can be in form of a solution, for example in form of an aqueous solution. In case the sodium carbonate source is in form of a solution, the sodium carbonate solution comprises the sodium carbonate source in an amount from 1 .0 to 30 wt.-%, based on the total weight of the sodium carbonate solution, for example in an amount from 5.0 to 25 wt.-%, even more preferably in an amount from 10 to 20 wt.-%, for example in an amount from 15 wt.-% ± 2 wt.-%. Alternatively the sodium carbonate source is in form of a solution and comprises the sodium carbonate source in an amount from 1 .0 to 30 g/l, for example in an amount from 3.0 to 25 g/l, even more preferably in an amount from 5.0 to 20 g/l, for example in an amount from 15 g/l ± 2 g/l.

The sodium carbonate source may be added in one portion or in several portions, for example in two, three or four portions. The portions may be equal or different.

According to one embodiment the sodium carbonate source is added in one portion. For example, the sodium carbonate source consists only of sodium carbonate, preferably in the form of a dry powder and is added in one portion in step d).

According to another preferred embodiment the sodium carbonate source is added in two portions. Preferably, the first portion contains 0.01 to 5 wt.-% of the total amount of the sodium carbonate source, more preferably 0.1 to 4.0 wt.-%, even more preferably 1 .0 to 3.0 wt.-%, and most preferably 1 .5 to 2.5 wt.-%. Additionally or alternatively, the first portion is added in form of a solution comprising 1 .0 to 30 g/l of the sodium carbonate source, preferably 3.0 to 25 g/l, even more preferably 5.0 to 20 g/l, even more preferably 7 to 17 g/l, and most preferably 8 to 15 g/l of the sodium carbonate source.

According to a preferred embodiment the sodium carbonate source is added in at least two portions, wherein the first portion contains 0.01 to 5 wt.-% of the total amount of the sodium carbonate source, preferably 0.1 to 4.0 wt.-%, more preferably 1 .0 to 3.0 wt.-%, and most preferably 1 .5 to 2.5 wt.- %, and is added in form of a solution comprising 5 to 20 g/l of the sodium carbonate source, preferably 7 to 17 g/l, and most preferably 8 to 15 g/l.

The remaining sodium carbonate source can be added after the first portion in one portion as second portion or in several portions, for example in two, three or four portions. These portions may be equal or different. Additionally or alternatively, the remaining sodium carbonate source can be added afterthe first portion as solid or as solution and preferably is added as solid.

According to a preferred embodiment, to the mixture obtained in step c) the sodium carbonate source is added in at least two portions, wherein the first portion contains 0.01 to 5 wt.-% of the total amount of the sodium carbonate source and is added in form of a solution comprising 5 to 20 g/l of the sodium carbonate source, preferably wherein the first portion of the sodium carbonate source in step d) contains 0.1 to 4.0 wt.-% of the total amount of the sodium carbonate source, more preferably 1 .0 to 3.0 wt.-%, and most preferably 1 .5 to 2.5 wt.-% and/or is added in form of a solution comprising 7 to 17 g/l of the sodium carbonate source, preferably 8 to 15 g/l, and the remaining sodium carbonate source after the first portion is added in one portion as second portion and the remaining sodium carbonate source after the first portion is added as solid. Preferably the sodium carbonate source is sodium carbonate.

In step d) of the present invention to the mixture obtained in step c) the sodium carbonate source is added at a temperature from 30 to 70 °C. According to a preferred embodiment, the temperature in step d) is from 40 to 60 °C and more preferably from 45 to 50 °C. It will be apparent to the skilled person that the initial temperature of the mixture obtained from step c) is not necessarily the same one as the temperature of the mixture prepared in step d). However, if the temperature of the mixture obtained in step c) is below 30 °C or above 70 °C, it has to be cooled or heated before the calcium carbonate source in step d) is added. The skilled person knows how to adjust the temperature of the mixture obtained in step c), for example by cooling with cooling pipes or by external heating.

Furthermore, if the sodium carbonate source is added in at least two portions, the temperature when the first portion is added and the temperature when the second portion is added may be different or the same and preferably are the same.

According to one embodiment of the present invention, the sodium carbonate source is added in form of a solution in step d), and the temperature of the solution is adjusted to be in the range from more than 10°C and less than 90°C. Preferably, the temperature of the sodium carbonate is adjusted to be from 30°C to 70°C, more preferably from 40°C to 60°C, and most preferably from 45°C to 50°C.

The skilled person knows how to control the temperature during step d), for example by cooling with cooling pipes or by external heating. In step d) of the present invention to the mixture obtained in step c) the sodium carbonate source is added at a pH value from 9.5 to 13.5. According to a preferred embodiment, the pH in step d) is from 10.0 to 13.0 and more preferably from 10.5 to 12.0.

It will be apparent to the skilled person that the initial pH of the mixture obtained from step c) is not necessarily the same one as the pH of the mixture prepared in step d). However, if the pH of the mixture obtained in step c) is below 9.5 or above 13.5, it has to adjusted before the calcium carbonate source in step d) is added. The skilled person knows how to adjust the pH of the mixture obtained in step c), for example by diluting the mixture with water.

Furthermore, if the sodium carbonate source is added in at least two portions, the pH when the first portion is added and the pH when the second portion is added may be different or the same and preferably are the same.

According to one embodiment of the present invention, the sodium carbonate source is added in form of a solution in step d), and the pH of the solution is adjusted to be in the range from 9.5 to 13.5, preferably from 10.0 to 13.0, and more preferably from 10.5 to 12.0.

The skilled person knows how to control the pH during step d), for example by diluting the mixture with water.

According to a preferred embodiment of the present invention, the temperature in step d) is from 40 to 60 °C, and more preferably from 45 to 50 °C, and the pH value is from 10.0 to 13.0, and more preferably 10.5 to 12.0.

The calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1 .00:1 .00 to 1 .00:1 .30. Preferably, the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1 .00:1 .00 to 1 .00:1 .20, more preferably from 1.00:1 .00 to 1 .00:1.10 and most preferably in an amount of about 1 .00:1 .05.

More precisely, the total amount of the calcium ions of the calcium oxide powder or the calcium hydroxide powder or the calcium hydroxide suspension of step a) and the calcium chloride solution of step b) and the total amount of carbonate ion of the sodium carbonate or the mixture of sodium carbonate and sodium bicarbonate is in a molar ratio (Ca²⁺:CC>3² ) in the range from 1 .00:1 .00 to 1.00:1.30, preferably from 1.00:1.00 to 1.00:1.20, more preferably from 1.00:1.00 to 1.00:1.10 and most preferably from about 1 .00:1 .05.

The inventors surprisingly found that by the above process it is possible to control the morphology of the precipitated calcium carbonate and to obtain a scalenohedral PCC product.

According to one embodiment of the present invention, the scalenohedral PCC product obtained in step d) has a specific surface area from 0.1 to 25.0 m²/g, preferably from 0.5 to 20.0 m²/g, and most preferably from 1 .0 to 15.0 m²/g, measured using nitrogen and the BET method according to ISO 9277:2010. Additionally or alternatively, the scalenohedral PCC product obtained in step d) is in form of particles having a volume-based median particle size cfeo(vol) from 0.05 to 10 pm, preferably from 0.2 to 8 pm, more preferably from 0.4 to 5 pm, and most preferably from 1 .0 to 3.5 pm.

Additionally or alternatively, the scalenohedral PCC product obtained in step d) is in form of particles having a volume-based top cut particle size cfo8(vol) from 0.15 to 20 pm, preferably from 1 to 15 pm, more preferably from 1 .5 to 10 pm, and most preferably from 2 to 8 pm.

Additionally or alternatively, the scalenohedral PCC product obtained in step d) has an ISO brightness (R457) of at least 90%, preferably at least 92%, more preferably at least 9 %, and most preferably at least 97% measured according to ISO 2469:2014.

Additionally or alternatively, the scalenohedral PCC product obtained in step d) has an yellowness index (Yl) of below 2, preferably below 1 .8, more preferably below 1 .6 and most preferably of from 0.5 to 1 .5 measured according to DIN 6167.

Additionally or alternatively, the scalenohedral PCC product obtained in step d) comprises at least 80 wt.-% scalenohedral PCC, based on the total dry weight of the scalenohedral PCC product, preferably 90 wt.-% and most preferably 95 wt.-%. Scalenohedral (PCC) precipitated calcium carbonate according to the present invention is in the form of calcite, which has a trigonal structure with a scalenohedral crystal habit. The scalenohedral PCC exhibit clusters (rosettes) of triangularshaped crystals emanating from a central core.

Additionally or alternatively, the scalenohedral PCC product obtained in step d) comprises 20 wt.-% or less aragonite, based on the total dry weight of the scalenohedral PCC product, preferably 10 wt.-% or less and most preferably 5 wt.-% or less. Aragonite in the meaning of the present invention is an orthorhombic structure with typical crystal habits of twinned hexagonal prismatic crystals, as well as a diverse assortment of thin elongated prismatic, curved bladed, steep pyramidal, chisel shaped crystals, branching tree, and coral or worm-like forms.

According to another embodiment the scalenohedral PCC product obtained in step d) comprises at least 80 wt.-% scalenohedral PCC, based on the total dry weight of the scalenohedral PCC product, preferably 90 wt.-% and most preferably 95 wt.-% and 20 wt.-% or less aragonite, based on the total dry weight of the scalenohedral PCC product, preferably 10 wt.-% or less and most preferably 5 wt.-% or less. According to a preferred embodiment of the present invention the scalenohedral PCC product obtained in step d) consists only of scalenohedral (PCC) precipitated calcium carbonate.

According to one embodiment of the present invention, the obtained scalenohedral PCC product i) has a specific surface area from 0.1 to 25.0 m²/g, preferably from 0.5 to 20.0 m²/g, and most preferably from 1 .0 to 15.0 m²/g, measured using nitrogen and the BET method according to

According to one more specific embodiment of the present invention, the obtained scalenohedral PCC product has an ISO brightness (R457) of at least 90 %, preferably at least 92 %, more preferably at least 95 %, and most preferably at least 97 %; and a yellowness index (Yl) of below 2, preferably below 1 .8, more preferably below 1 .6 and most preferably of from 0.5 to 1 .5.

According to one more specific embodiment of the present invention, the obtained scalenohedral PCC product

- has a specific surface area from 0.1 to 25.0 m²/g, preferably from 0.5 to 20.0 m²/g, and most preferably from 1 .0 to 15.0 m²/g, measured using nitrogen and the BET method according to

ISO 9277:2010 and

- is in form of particles having a volume-based median particle size cfeo(vol) from 0.05 to 10 pm, preferably from 0.2 to 8 pm, more preferably from 0.4 to 5 pm, and most preferably from 1 .0 to 3.5 pm, and

- has an ISO brightness (R457) of at least 90 %, preferably at least 92 %, more preferably at least 95 %, and most preferably at least 97 %; and

- a yellowness index (Yl) of below 2, preferably below 1 .8, more preferably below 1 .6 and most preferably of from 0.5 to 1 .5.

As already set out above, the inventors surprisingly found that by the above process it is possible to control the morphology of the precipitated calcium carbonate and to obtain a scalenohedral PCC product.

Furthermore, the inventors found that in addition to calcium oxide or milk of lime, calcium chloride can be used as further calcium source.

Additionally, the inventors surprisingly found that no carbon dioxide containing compound, especially no gaseous carbon dioxide has to be used in the inventive process to obtain the scalenohedral PCC product. Rather a sodium carbonate source selected from sodium carbonate or a mixture consisting of at least 70 wt.-% sodium carbonate and up to 30 wt.-% sodium bicarbonate is sufficient to produce the scalenohedral PCC product at the above mentioned temperature and pH value. The process for producing these particles is an easy and quick process and the obtained product is affordable and especially easy to handle. The process can be performed in standard equipment without significant burden for humans and environment. Furthermore, the inventive process has a reduced carbon dioxide footprint, and is inexpensive, easy to handle and easily adaptable. Additionally in the inventive process no chemicals are used that are toxic or harmful to the user. Furthermore, the by-products obtained in this process are also not toxic or harmful and might even be recovered for later use such as, for example, sodium chloride.

Additional process steps

The process of the present invention can comprise additional process steps.

According to another embodiment of the present invention the process further comprises a step e) of adding an additive to the mixture obtained in step c).

According to one embodiment the additive added in step d) is a dispersing agent.

Conventional dispersing agents known to the skilled person can be used. The skilled person will choose the dispersing agent dependent on his equipment and the intended use of the scalenohedral PCC.

A suitable dispersing agent may be selected from polyphosphates, and is in particular a tripolyphosphate. Another suitable dispersing agent may be selected from the group comprising homopolymers or copolymers of polycarboxylic acid salts based on, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid or itaconic acid and acrylamide or mixtures thereof. The homopolymers or copolymers of polycarboxylic acid salts can be fully or partially neutralized, for example, at least 70 %, or at least 80% or at least 90 % of the acid groups are neutralized. Neutralizing means that the protons of the carboxylic acids are exchanged with another cation such as sodium and/or calcium cations. According to a preferred embodiment, the homopolymers or copolymers of polycarboxylic acid salts are fully neutralized and most preferably are fully neutralized with sodium and/or calcium ions. Homopolymers or copolymers of acrylic acid are especially preferred. Most preferred are homopolymers or copolymers of acrylic acid that are fully neutralized with sodium and/or calcium ions. The weight average molecular weight Mw of such products is preferably in the range from 2 000 to 15 000 g/mol, with a weight average molecular weight M_w from 3 000 to 7 000 g/mol or 3 500 to 6 000 g/mol being especially preferred. According to an exemplary embodiment, the dispersing agent is sodium polyacrylate having a weight average molecular weight Mw from 2 000 to 15 000 g/mol, preferably from 3 000 to 7 000 g/mol, and most preferably from 3 500 to 6 000 g/mol.

According to one embodiment the additive added in step d) is a nucleation agent.

Conventional nucleation agents known to the skilled person can be used. The skilled person will choose the nucleation agent dependent on his equipment and the intended use of the scalenohedral PCC.

A suitable nucleation agent may be selected from sucrose, sugar alcohols, citrate or citric acid and most preferably may be sucrose. According to one embodiment of the present invention the process further comprises a step e) of adding an additive to the mixture obtained in step c), preferably a dispersing agent and/or a nucleation agent such as sucrose or citrate and most preferably sucrose.

According to a preferred embodiment, the scalenohedral PCC product is separated from the obtained suspension, for example by filtration. Afterwards a dispersant may be added to the filter cake, preferably in form of a solution or dispersion. The skilled person knows how to filter and redisperse the scalenohedral PCC product and will chose the dispersant and separation method dependent on his equipment and the intended use.

The aqueous suspension obtained after step d) may be further processed, e.g., the scalenohedral PCC product may be separated from the aqueous suspension and/or subjected to a drying step.

According to one embodiment, the process of the present invention further comprises a step f) of separating the scalenohedral PCC product from the aqueous suspension obtained in step d). Thus, a process for producing a scalenohedral PCC product may comprise the following steps: a) providing at least one calcium compound selected from the group consisting of calcium oxide powder, calcium hydroxide powder and calcium hydroxide suspension; b) providing a calcium chloride solution, wherein the solution comprises 0.5 to 270 g/l of calcium; c) mixing the at least one calcium compound of step a) and the calcium chloride solution of step b) in any order, wherein the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture is in the range from 7:93 to 80:20; d) adding to the mixture obtained in step c) a sodium carbonate source selected from sodium carbonate or a mixture consisting of at least 70 wt.-% sodium carbonate and up to 30 wt.-% sodium bicarbonate at a temperature from 30 to 70 °C and at a pH value from 9.5 to13.5, wherein the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1 .00:1 .00 to 1 .00:1 .30 and e) separating the scalenohedral PCC product from the aqueous suspension obtained in step d).

The scalenohedral PCC product obtained from step d) may be separated from the aqueous suspension by any conventional means of separation known to the skilled person. According to one embodiment of the present invention, in process step e) the scalenohedral PCC product is separated mechanically and/or thermally. Examples of mechanical separation processes are filtration, e.g. by means of a drum filter or filter press, nanofiltration, or centrifugation. An example for a thermal separation process is a concentrating process by the application of heat, for example, in an evaporator. According to a preferred embodiment, in process step e) the scalenohedral PCC product is separated by solvent evaporation and/or pressure filtration.

After separation, the scalenohedral PCC product can be dried in order to obtain a dried scalenohedral PCC product. According to one embodiment, the process of the present invention further comprises a step f) of drying the scalenohedral PCC product after step d) or after step e), if present, at a temperature in the range from 60 to 120 °C, preferably from 80 to 110 °C, most preferably from 95 to 105 °C, preferably until the moisture content of the scalenohedral PCC product is less than 1 wt.-%, based on the total weight of the dried scalenohedral PCC product. Thus, a process for producing a scalenohedral PCC product may comprise the following steps: a) providing at least one calcium compound selected from the group consisting of calcium oxide powder, calcium hydroxide powder and calcium hydroxide suspension; b) providing a calcium chloride solution, wherein the solution comprises 0.5 to 270 g/l of calcium; c) mixing the at least one calcium compound of step a) and the calcium chloride solution of step b) in any order, wherein the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture is in the range from 7:93 to 80:20; d) adding to the mixture obtained in step c) a sodium carbonate source selected from sodium carbonate or a mixture consisting of at least 70 wt.-% sodium carbonate and up to 30 wt.-% sodium bicarbonate at a temperature from 30 to 70 °C and at a pH value from 9.5 to 13.5, wherein the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1 .00:1 .00 to 1 .00:1 .30 and e) separating the scalenohedral PCC product from the aqueous suspension obtained in step d) and f) drying the scalenohedral PCC product.

In general, the drying step f) may take place using any suitable drying equipment and can, for example, include thermal drying and/or drying at reduced pressure using equipment such as an evaporator, a flash drier, an oven, a spray drier and/or drying in a vacuum chamber. The drying step f) can be carried out at reduced pressure, ambient pressure or under increased pressure. For temperatures below 100 °C it may be preferred to carry out the drying step under reduced pressure. The drying step can be performed, for example, for at least 30 seconds, for at least 1 minute, 2 minutes, 5 minutes, 10 minutes, 30 minutes, 1 hour, 2 hours, 12 hours or 1 day. The skilled person can choose the drying time dependent on the equipment, the water content and the intended use.

According to one embodiment, in process step f) the scalenohedral PCC product is dried until the moisture content of the scalenohedral PCC product is less than or equal to 1 .0 wt. %, based on the total weight of the dried scalenohedral PCC product, preferably less than or equal to 0.5 wt. %, and more preferably less than or equal to 0.2 wt. %.

According to another embodiment, the process of the present invention further comprises a step g) of treating the surface of the scalenohedral PCC product obtained in step d) and/or step e) and/or step f). Thus, a process for producing a scalenohedral PCC product may comprise the following steps: a) providing at least one calcium compound selected from the group consisting of calcium oxide powder, calcium hydroxide powder and calcium hydroxide suspension; b) providing a calcium chloride solution, wherein the solution comprises 0.5 to 270 g/l of calcium; c) mixing the at least one calcium compound of step a) and the calcium chloride solution of step b) in any order, wherein the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture is in the range from 7:93 to 80:20; d) adding to the mixture obtained in step c) a sodium carbonate source selected from sodium carbonate or a mixture consisting of at least 70 wt.-% sodium carbonate and up to 30 wt.-% sodium bicarbonate at a temperature from 30 to 70 °C and at a pH value from 9.5 to 13.5, wherein the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1 .00:1 .00 to 1 .00:1 .30 and e) separating the scalenohedral PCC product from the aqueous suspension obtained in step d) and f) drying the scalenohedral PCC product and g) treating the surface of the obtained scalenohedral PCC product.

In general, the treatment step g) may take place using any suitable treatment agent, for example hydrophobic agents such as fatty acids. Such hydrophobic agents like stearic acid and palmitic acid are known to the skilled person and are commercially available. The surface treatment of the scalenohedral PCC product may affect the rheological properties of that material.

The process of the present invention can be carried out in form of a batch process, a semi- continuous or a continuous process. According to a preferred embodiment of the present invention, the inventive process is carried out in form of a batch process.

According to an exemplified embodiment of the present invention, the process for producing a scalenohedral PCC product may comprise the following steps: a) providing at least one calcium compound that is a calcium hydroxide suspension and has a solids content of from 5 to 50 wt.-%, preferably from 9 to 45 wt.-%; and the calcium hydroxide particles have a volume median particle size cfeo(vol) from 0.05 to 25 pm, preferably from 1 .0 to 3.5 pm; b) providing a calcium chloride solution, wherein the solution comprises 0.5 to 270 g/l of calcium, preferably 5.0 to 50 g/l; c) mixing the at least one calcium compound of step a) and the calcium chloride solution of step b) in any order, wherein the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture is in the range from 7:93 to 80:20; d) adding to the mixture obtained in step c) a sodium carbonate source which is sodium carbonate at a temperature from 30 to 70 °C and at a pH value from 9.5 to 13.5, wherein the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1 .00:1 .00 to 1 .00:1 .30 and e) optionally separating the scalenohedral PCC product from the aqueous suspension obtained in step d) and f) optionally drying the scalenohedral PCC product.

According to another exemplified embodiment of the present invention, the process for producing a scalenohedral PCC product may comprise the following steps: a) providing at least one calcium compound that is a calcium hydroxide suspension and has a solids content of from 5 to 50 wt.-%, preferably from 9 to 45 wt.-%; and the calcium hydroxide particles have a volume median particle size cfeo(vol) from 0.05 to 25 pm, preferably from 1 .0 to 3.5 pm; b) providing a calcium chloride solution, wherein the solution comprises 0.5 to 270 g/l of calcium, preferably 5.0 to 50 g/l; c) mixing the at least one calcium compound of step a) and the calcium chloride solution of step b) in any order, wherein the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture is in the range from 7:93 to 80:20; d) adding to the mixture obtained in step c) a sodium carbonate source which is a sodium carbonate solution at a temperature from 30 to 70 °C and at a pH value from 9.5 to 13.5, wherein the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1 .00:1 .00 to 1 .00:1 .30 and e) optionally separating the scalenohedral PCC product from the aqueous suspension obtained in step d) and f) optionally drying the scalenohedral PCC product.

According to an exemplified embodiment to the mixture obtained in step c) the sodium carbonate source is added in at least two portions, wherein the first portion contains 0.01 to 5 wt.-% of the total amount of the sodium carbonate source and is added in form of a solution comprising 5 to 20 g/l of the sodium carbonate source, preferably 1 .0 to 3.0 wt.-% and is added in form of a solution comprising 8 to 15 g/l of the sodium carbonate source, and the remaining sodium carbonate source after the first portion is added in one portion as second portion and is also in form of a solution.

According to another exemplified embodiment of the present invention, the process for producing a scalenohedral PCC product may comprise the following steps: a) providing at least one calcium compound that is a calcium hydroxide suspension and has a solids content of from 5 to 50 wt.-%, preferably from 9 to 45 wt.-%; and the calcium hydroxide particles have a volume median particle size cfeo(vol) from 0.05 to 25 pm, preferably from 1 .0 to 3.5 pm; b) providing a calcium chloride solution, wherein the solution comprises 0.5 to 270 g/l of calcium, preferably 5.0 to 50 g/l; c) mixing the at least one calcium compound of step a) and the calcium chloride solution of step b) in any order, wherein the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture is in the range from 7:93 to 80:20; d) adding to the mixture obtained in step c) a sodium carbonate source which is a mixture consisting of at least 70 wt.-% sodium carbonate and up to 30 wt.-% sodium bicarbonate at a temperature from 30 to 70 °C and at a pH value from 9.5 to 13.5, wherein the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1 .00:1 .00 to 1 .00:1 .30 and e) optionally separating the scalenohedral PCC product from the aqueous suspension obtained in step d) and f) optionally drying the scalenohedral PCC product.

Products and their use

According to one embodiment of the present invention a scalenohedral PCC product is provided, which is obtained by the process comprising the steps of: a) providing at least one calcium compound selected from the group consisting of calcium oxide powder, calcium hydroxide powder and calcium hydroxide suspension; b) providing a calcium chloride solution, wherein the solution comprises 0.5 to 270 g/l of calcium; c) mixing the at least one calcium compound of step a) and the calcium chloride solution of step b) in any order, wherein the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture is in the range from 7:93 to 80:20; d) adding to the mixture obtained in step c) a sodium carbonate source selected from sodium carbonate or a mixture consisting of at least 70 wt.-% sodium carbonate and up to 30 wt.-% sodium bicarbonate at a temperature from 30 to 70 °C and at a pH value from 9.5 to 13.5, wherein the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1.00:1.00 to 1.00:1.30.

Furthermore, the process may comprise the step e) of adding to the mixture obtained in step c) an additive, preferably a dispersing agent and/or a nucleation agent such as sucrose or citrate and most preferably sucrose.

Furthermore, the process may comprise the step f) of separating the scalenohedral PCC product from the aqueous suspension obtained in step d) and preferably step f) is done by solvent evaporation and/or pressure filtration and/or the step g) of drying the scalenohedral PCC product after step d) or after step f), if present, at a temperature in the range from 60 to 120 °C, preferably from 80 to 110 °C, most preferably from 95 to 105°C, preferably until the moisture content of the scalenohedral PCC product is less than 1 wt.-%, based on the total weight of the dried scalenohedral PCC product.

By the inventive process a scalenohedral PCC product is obtained. According to a preferred embodiment the obtained scalenohedral PCC product comprises at least 80 wt.-% scalenohedral PCC, based on the total dry weight of the scalenohedral PCC product, preferably 90 wt.-% and most preferably 95 wt.-%. Scalenohedral (PCC) precipitated calcium carbonate according to the present invention is in the form of calcite, which has a trigonal structure with a scalenohedral crystal habit. The scalenohedral PCC exhibit clusters (rosettes) of triangular-shaped crystals emanating from a central core.

According to another preferred embodiment the obtained scalenohedral PCC product comprises 20 wt.-% or less aragonite, based on the total dry weight of the scalenohedral PCC product, preferably 10 wt.-% or less and most preferably 5 wt.-% or less. Aragonite in the meaning of the present invention is an orthorhombic structure with typical crystal habits of twinned hexagonal prismatic crystals, as well as a diverse assortment of thin elongated prismatic, curved bladed, steep pyramidal, chisel shaped crystals, branching tree, and coral or worm-like forms.

According to a preferred embodiment of the present invention, the obtained scalenohedral PCC product comprises at least 80 wt.-% scalenohedral PCC, based on the total dry weight of the scalenohedral PCC product, preferably 90 wt.-% and most preferably 95 wt.-% and 20 wt.-% or less aragonite, based on the total dry weight of the scalenohedral PCC product, preferably 10 wt.-% or less and most preferably 5 wt.-% or less.

According to one embodiment of the present invention the obtained scalenohedral PCC product consists only of scalenohedral (PCC) precipitated calcium carbonate.

According to one embodiment of the present invention, the scalenohedral PCC product obtained in step d) has a specific surface area from 0.1 to 25.0 m²/g, preferably from 0.5 to 20.0 m²/g, and most preferably from 1 .0 to 15.0 m²/g, measured using nitrogen and the BET method according to ISO 9277:2010.

Additionally or alternatively, the scalenohedral PCC product obtained in step d) is in form of particles having a volume-based median particle size cfeo(vol) from 0.05 to 10 pm, preferably from 0.2 to 8 pm, more preferably from 0.4 to 5 pm, and most preferably from 1 .0 to 3.5 pm.

According to another embodiment of the present invention the scalenohedral PCC product obtained in step d) has an ISO brightness (R457) of at least 90%, preferably at least 92%, more preferably at least 9 %, and most preferably at least 97% measured according to ISO 2469:2014.

According to another embodiment of the present invention the scalenohedral PCC product obtained in step d) has a yellowness index (Yl) of below 2, preferably below 1 .8, more preferably below 1.6 and most preferably of from 0.5 to 1.5 measured according to DIN 6167.

According to a preferred embodiment of the present invention the obtained scalenohedral PCC product i) has a specific surface area from 0.1 to 25.0 m²/g, preferably from 0.5 to 20.0 m²/g, and most preferably from 1 .0 to 15.0 m²/g, measured using nitrogen and the BET method according to ISO 9277:2010 and/or ii) is in form of particles having a volume-based median particle size cfeo(vol) from 0.05 to 10 pm, preferably from 0.2 to 8 pm, more preferably from 0.4 to 5 pm, and most preferably from 1 .0 to 3.5 pm, and/or vi) comprises at least 80 wt.-% scalenohedral PCC, based on the total dry weight of the scalenohedral PCC product, preferably 90 wt.-% and most preferably 95 wt.-% and 20 wt.-% or less aragonite, based on the total dry weight of the scalenohedral PCC product, preferably 10 wt.-% or less and most preferably 5 wt.-% or less.

According to another preferred embodiment of the present invention the obtained scalenohedral PCC product i) has a specific surface area from 0.1 to 25.0 m²/g, preferably from 0.5 to 20.0 m²/g, and most preferably from 1 .0 to 15.0 m²/g, measured using nitrogen and the BET method according to ISO 9277:2010 and ii) is in form of particles having a volume-based median particle size cfeo(vol) from 0.05 to 10 pm, preferably from 0.2 to 8 pm, more preferably from 0.4 to 5 pm, and most preferably from 1 .0 to 3.5 pm, and vi) comprises at least 80 wt.-% scalenohedral PCC, based on the total dry weight of the scalenohedral PCC product, preferably 90 wt.-% and most preferably 95 wt.-% and 20 wt.-% or less aragonite, based on the total dry weight of the scalenohedral PCC product, preferably 10 wt.-% or less and most preferably 5 wt.-% or less.

ISO 9277:2010 and

The inventors of the present invention surprisingly found that the precipitated calcium carbonate product obtained by the process according to the present invention has improved properties. More precisely, the precipitated calcium carbonate product has a controlled morphology, namely the obtained precipitated calcium carbonate product is a scalenohedral PCC product. Furthermore, in the inventive process according to the present invention no carbon dioxide containing compound, especially no gaseous carbon dioxide has to be used and, therefore, the obtained scalenohedral PCC product has a reduced carbon dioxide footprint, which is nowadays becoming increasingly important. Furthermore the inventive process is very economic and ecologic. Additionally, in this process no chemicals are used that are toxic or harmful to the user. Furthermore, the byproducts obtained in this process are also not toxic or harmful and might even be recovered for later use such as, for example, sodium chloride.

The inventors surprisingly found that the scalenohedral PCC product obtained by the process of the present invention can be used in polymer applications, paper coating applications, paper making, paints, coatings, sealants, adhesives, feed, pharmaceuticals, concrete, cement, cosmetics, water treatment, engineered wood applications, plasterboard applications, packaging applications, catalysis, gas treatment applications and/or agricultural applications. It is especially favourable to use the scalenohedral PCC product obtained by the process of the present invention in fields where a defined morphology of the filler or pigment is required.

Brief Description of the drawings

Figure 1 is a SEM photograph of example 1 , showing the morphology of the obtained precipitated calcium carbonate product obtained by the comparative process.

Figure 2 is a SEM photograph of example 2, showing the morphology of the obtained precipitated calcium carbonate product obtained by the inventive process.

Figure 3 is a SEM photograph of example 3, showing the morphology of the obtained precipitated calcium carbonate product obtained by the inventive process.

Figure 4 is a SEM photograph of example 4, showing the morphology of the obtained precipitated calcium carbonate product obtained by the inventive process.

Figure 5 is a SEM image of the product obtained by example 5 showing PCC crystals with a scalenohedral morphology.

Figure 6 is a SEM image of the product obtained by example 6 showing PCC crystals with a scalenohedral morphology.

Figure 7 is a SEM image of the product obtained by example 7 showing PCC crystals with a scalenohedral morphology.

Figure 8 is a SEM image of the product obtained by example 8 showing PCC crystals with a scalenohedral morphology.

Figure 9 is a SEM image of the product obtained by example 9 showing PCC crystals with a scalenohedral morphology.

Figure 10 is a SEM image of the product obtained by reference example 1.

Figures 11A and 11 B shows SEM images of the product obtained by reference example 2 in two different magnifications.

The scope and interest of the invention will be better understood based on the following examples which are intended to illustrate certain embodiments of the invention and are non-limitative. Examples

1. Measurement methods

Particle size distribution

The volume median grain diameter is determined by the laser diffraction method. This method is based on the deflection of a laser beam by an ensemble of particles dispersed in either a liquid or an air stream. The angles of diffraction or scattering angles are characteristic of the particle size. Volume-based median particle size cfeo(vol), and the particle size cfoo(vol) and the volume-based top cut particle size cfo8(vol) was evaluated using a HELOS Particle Size analyser and the Software WINDOX of Sympatec GmbH. The cfeo(vol), or cfoo(vol) or cfo8(vol) value indicates a diameter value such that 50 %, or 90 % or 98 % by volume, respectively, of the particles have a diameter of less than this value. The raw data obtained by the measurement was analyzed using the Mie theory, with a particle refractive index of 1 .57 and an absorption index of 0.005. The methods and instruments are known to the skilled person and are commonly used to determine particle size distributions of fillers and pigments. The particle size of the obtained scalenohedral PCC product is measured in water and the particle size of the calcium hydroxide is measured in ethanol p.a. .

The weight median grain diameter cfeo(wt) and the weight-based particle size cfoo(wt) was determined by the sedimentation method, which is an analysis of sedimentation behaviour in a gravimetric field. The measurement is made with a Sedigraph™ 5120, Micromeritics Instrument Corporation. The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement is carried out in an aqueous solution of 0.1 wt% N34P2O7. The samples were dispersed using a high speed stirrer and supersonicated.

The processes and instruments are known to the skilled person and are commonly used to determine grain size of fillers and pigments.

X-ray diffraction (XRD)

XRD experiments are performed on the samples using rotatable PMMA holder rings. Samples are analysed with a Bruker D8 Advance powder diffractometer obeying Bragg 's law. This diffractometer consists of a 2.2 kW X-ray tube, a sample holder, a 0-0-goniometer, and a VANTEC- 1 detector. Nickel-filtered Cu-Ka radiation is employed in all experiments. The profiles are chart recorded automatically using a scan speed of 0.7° per min in 20. The resulting powder diffraction pattern can easily be classified by mineral content using the DIFFRACsuite software packages EVA and SEARCH, based on reference patterns of the ICDD PDF 2 database.

Quantitative analysis of diffraction data refers to the determination of amounts of different phases in a multi-phase sample and has been performed using the DIFFRACsuite software package TOP AS. In detail, quantitative analysis allows to determine structural characteristics and phase proportions with quantifiable numerical precision from the experimental data itself. This involves modelling the full diffraction pattern using the Rietveld approach such that the calculated pattern(s) duplicates the experimental one. BET Specific surface area (SSA)

The specific surface area is measured via the BET method according to ISO 9277:2010 using nitrogen, following conditioning of the sample by heating at 250°C for a period of 30 minutes. Prior to such measurements, the sample is filtered within a Buchner funnel, rinsed with deionised water and dried overnight at 90 to 100°C in an oven. Subsequently, the dry cake was ground thoroughly in a mortar and the resulting powder placed in a moisture balance at 130°C until a constant weight is reached.

Viscosity measurement

The Brookfield viscosity is measured by a Brookfield DV-II+ Pro viscometer at 25 °C ± 1 °C at 100 rpm using an appropriate spindle of the Brookfield RV-spindle set and is specified in mPa s. A spindle was selected from the Brookfield RV-spindle set which was suitable for the viscosity range to be measured. For a viscosity range of < 200 mPa s the spindle number 2 was used, for a viscosity range between 200 and 800 mPa s the spindle number 3 was used, for a viscosity range between 400 and 1 600 mPa s the spindle number 4 was used, and for a viscosity range between 800 and 3 200 mPa s the spindle number 5 was used.

Suspension/solution pH measurement

The pH of a suspension or solution is measured at 25°C using a Mettler Toledo Seven Easy pH meter and a Mettler Toledo InLab® Expert Pro pH electrode.

A three point calibration (according to the segment method) of the instrument is first made using commercially available buffer solutions (from Aldrich) having pH values of 4, 7 and 10 at 20°C.

The reported pH values are the endpoint values detected by the instrument (the endpoint being the point when the measured signal differs by less than 0.1 mV from the average over the last 6 seconds).

Suspension conductivity measurement

The conductivity of a suspension is measured at 25°C using Mettler Toledo Seven Multi equipped with the corresponding Mettler Toledo conductivity expansion unit and a Mettler Toledo InLab® 730 conductivity probe, directly following stirring this suspension at 1.500 rpm using a pendraulic tooth disk stirrer.

The instrument is first calibrated in the relevant conductivity range using commercially available conductivity calibration solutions from Mettler Toledo. The influence of temperature on conductivity is automatically corrected by the linear correction mode.

Measured conductivities are reported for the reference temperature of 20°C. The reported conductivity values are the endpoint values detected by the instrument (the endpoint is the point when the measured conductivity differs by less than 0.4 % from the average over the last 6 seconds).

Moisture content measurement

The obtained sample is measured with a Halogen Moisture Analyzer HR73 from Mettler- Toledo at 7 = 160 °C. The moisture content of a sample is measured by determining the weight of the sample (between 5 to 20 g) and then quickly heating the sample by the integral halogen dryer unit. During the heating the moisture vaporizes and the instrument continuously determines the weight of the sample and displays the loss of moisture. On completion of drying when the weight of the sample does not change anymore, the moisture content of a sample is displayed as the final result.

Brightness measurement and yellowness index

The pigment brightness and yellowness index (Yl) of the obtained particles were measured using an ELREPHO 45 OX from the company Datacolor according to ISO 2469:2014 and DIN 6167, respectively. The obtained values are reported as ISO brightness R457 in %.

The samples were dried in an oven at 105°C to a residual moisture content of < 0.5 % by weight and the resulting powder was treated to deagglomerate the powder particles. From 12 g of said powder a tablet was pressed via application of 4 bar pressure for 15 s. The resulting powder tablet with a diameter of 45 mm was then subjected to the measurement.

In the present measurement the yellowness index was measured via measuring the reflectance of the obtained precipitated calcium carbonate product, the illuminant used being D 65 and the standard observer function being 10°.

The Yellowness Index according to DIN 6167 is calculated as follows: where X, Y, and Z are the CIE Tristimulus values and the coefficients depend on the illuminant and the observer function as indicated in the Table below:

2. Examples

Used Materials and Equipment

Calcium chloride solution (CaCh) for Examples 1 to 4: obtainable from Solvay with a sheds quality from 77 - 80%

Calcium chloride solution (CaCh) for Examples 5 to 9: brine solution containing CaCL obtained from a (aqueous phosphor) recycling process (Ca²⁺ concentration of about 42 g/L)

Sodium Carbonate (Na2COs): obtainable from Solvay under the trade name Soda Solvay Light Calcium oxide (CaO): obtainable from the Polish lime quarry Lhoist Bukowa

Example 1 - Comparative Example

This comparative example demonstrates a method for producing precipitated calcium carbonate (PCC) from a brine solution containing calcium chloride (CaCh). The process involves a reaction of calcium chloride with sodium carbonate, which yields precipitated calcium carbonate. The process of precipitating calcium carbonate was carried out in a cylindrical stainless steel reactor with a double jacket, having a capacity of 1000 liters. The reactor was equipped with a high shear impeller powered by a 55 kW motor, which operated at 1480 revolutions per minute and utilized a stator rotor principle. Additionally, pH and conductivity probes were installed in the reactor to monitor the suspension throughout the process.

400 liter of a CaCh containing solution/brine which features a concentration of dissolved Ca²⁺ of 42 g/l were taken. This solution/brine was transferred into an high shear reactor. The temperature of the reaction mixture was adjusted to 50 °C.

During the initial nucleation phase of the reaction, 1100 g/min of sodium carbonate powder (Na2COs) were added to the mixture. This process was performed constantly and under vigorous agitation in a high shear reactor for a duration of 40 minutes. Then the addition was stopped. This means that a total mass of 44 kg of dry Na2COs was added to the mixture, which corresponds to a stoichiometric ratio of 1 :1 between calcium (Ca²⁺) and carbonate ions (CO3² ).

The obtained suspension of structured precipitated CaCCh was dewatered and the brine mother liquor was exchanged with fresh water on a washing filter known to the skilled person in the art (e.g. vacuum rotary- or band filter with washing zone).

The washed filter cake was redispersed with fresh water to obtain an aqueous slurry of structured precipitated CaCCh with 17% solids content, an electrical conductivity of about 299 pS/cm and a pH of 10.5 (25°C).

Optionally the PCC slurry can be dried on a spray-dryer to obtain a structured precipitated CaCOs powder with about 0.2 % residual moisture.

Example 2 - Inventive Example

The following illustrative example of the invention involves the preparation of scalenohedral precipitated calcium carbonate from a calcium chloride (CaCh) containing brine solution. Said process involved the reaction of calcium chloride and calcium hydroxide with Na2COs into precipitated calcium carbonate. Example 2 was carried out in a similar manner as Example 1 , except that prior to the addition of Na2CC>3, calcium hydroxide was added to the brine solution.

A slurry of calcium hydroxide was prepared. 7.8 kg of quicklime (CaO) from Poland were added to 62 liters of tap water in a stirred reactor. The water temperature was adjusted to 50°C before adding the quicklime. The slaking process was carried out for 40 minutes under continuous stirring. The resulting slurry, known as "milk of lime," was screened through a 100 pm screen. The solids content of the milk of lime after slaking was 14.7% w/w.

To produce a lime milk with a particle size cfeo(vol) of 2.5 pm, the lime milk from the previous step has been wet-ground in an agitated bead mill with a specific energy input of about 30 kWh/DTO. The resulting lime milk was screened through a 45 pm mesh size to remove any larger particles. The particle size cfeo(vol) was measured with Helos Sympatec using ethanol.

In order to initiate the process, 400 liters of a brine solution containing CaCh were transferred into a high shear reactor. The solution had a concentration of dissolved Ca²⁺ of 42 g/l. 72 kg of the produced lime milk was added to the solution under agitation, in an amount that corresponds to 25% of Ca²⁺ coming from Ca(OH)2 seeds and 75 % of Ca²⁺ coming from the dissolved CaCh in the brine. Next, 31 g of Sucrose were added to the reaction mixture under agitation, which corresponds to 0.1 % dry sucrose to dry CaO in mixture. The temperature of the mixture was adjusted to approximately 50 °C.

During the initial phase of the reaction, 1466 g/min of sodium carbonate powder (Na2COs) were added to the mixture. This process was performed constantly and under vigorous agitation in a high shear reactor for a duration of 40 minutes. Then the addition was stopped. This means that a total mass of 58.6 kg of dry Na2COs was added to the mixture, which corresponds to a stoichiometric ratio of 1 :1 between calcium (Ca²⁺) and carbonate ions (CO3² ).

Dewatering, washing, redispersion and characterization of the obtained precipitated calcium carbonate was carried out as stated above in example 1 .

Example 3 - Inventive Example

Example 3 was carried out in a similar manner as Example 2, except that sodium carbonate (Na2COs) was dosed in liquid form within 20 minutes instead as a dry powder.

To the reaction mixture, under vigorous agitation of high shear reactor, 11 .6 l/min of an aqueous solution of Na2COs that has been highly diluted to 1 % w/w and that has been adjusted to about 50°C temperature were constantly added as first portion. The addition has been stopped after 5 minutes, which corresponded to a total volume of aqueous solution of Na2COs of 58 liter and coincides to 1 wt.-% of the total amount of sodium carbonate.

Subsequently, under vigorous agitation of high shear reactor, 22.4 l/min of an aqueous solution of Na2CO3 that has been diluted to 15% w/w and that has been adjusted to about 50 °C temperature were added constantly to the reaction mixture as second portion. The addition was stopped after 15 minutes, which corresponded to a total volume of aqueous solution of Na2COs of 336.6 liter and coincides to 99 wt.-% of the total amount of sodium carbonate. The total Na2COs corresponds to a stoichiometric ratio of 1 :1 between calcium (Ca²⁺) and carbonate ions (CO3² ).

Example 4 - Inventive Example

Example 4 was carried out in a similar manner as Example 2, except that sodium carbonate powder (Na2COs) was dosed in mixture with sodium bicarbonate powder (NaHCCh).

1638 g/min of a homogenous mixture containing 80 wt.-% of sodium carbonate powder (Na2COs) and 20 wt.-% sodium bicarbonate powder were added to the reaction mixture. This process was performed constantly and under vigorous agitation in a high shear reactor for a duration of 40 minutes. Then the addition was stopped. This means that a total mass of 65.5 kg of dry Na2COs was added to the mixture, which corresponds to a stoichiometric ratio of 1 :1 between calcium (Ca²⁺) and carbonate ions (CO3² ), and the addition was stopped.

Dewatering, washing, redispersion and characterization of the obtained precipitated calcium carbonate was carried out as stated above in example 1 . Example 5 - Inventive Example

A slurry of calcium hydroxide ("milk of lime") was prepared as follows: 500 g of quicklime (CaO) from Bukowa, Poland were added to about 4 liters of tap water in a stirred reactor. The resulting slurry was screened through a 100 pm screen. To produce a lime milk with a particle size cfeo(vol) of about 1 pm, the lime milk from the previous step has been wet-ground in an agitated bead mill (Dynomill with Cermil 0.45 mm grinding media) with a volume flow of 30 L/h. The resulting lime milk was screened through a 45 pm mesh size. The particle size cfeo(vol) was measured with Helos Sympatec using ethanol.

In order to initiate the process, 6 liters of a brine solution containing CaCh (obtained from an aqueous phosphor recycling process) were transferred into a high shear reactor. 875 g of the produced lime milk was added to the solution under agitation, in an amount that corresponds to 20% of Ca²⁺ coming from the lime milk (Ca(OH)2) and 80 % of Ca²⁺ coming from the dissolved CaCh in the brine (total Ca²⁺ cone, after addition of lime milk: 38.2 g/L). Next, 0.44 g of sucrose was added to the reaction mixture under agitation, which corresponds to 0.1 % dry sucrose to dry CaO in the mixture. The temperature of the mixture was adjusted to approximately 50 °C.

During the initial phase of the reaction, 41 g/min of sodium carbonate powder (Na2COs) was added to the mixture. This process was performed constantly and under vigorous agitation in a high shear reactor for a duration of 20 minutes. Then the addition was stopped. This means that a total mass of 825 g of dry Na2COs was added to the mixture, which corresponds to a stoichiometric ratio of 1 :1 between calcium (Ca²⁺) and carbonate ions (CO3² ).

The obtained suspension of structured precipitated CaCCh was dewatered and the brine mother liquor was exchanged with fresh water on a washing filter known to the skilled person in the art (e.g. vacuum rotary- or band filter with washing zone). The washed filter cake was redispersed with fresh water to obtain an aqueous slurry of structured precipitated CaCCh with an electrical conductivity of less than 500 pS/cm.

Example 6 - Inventive Example

Example 6 was carried out in a similar manner as Example 5, except that the sodium carbonate powder (Na2COs) was dosed for 23 minutes to provide a total mass of 948 g of dry Na2CC>3, which corresponds to a stoichiometric ratio of 1 :1 .15 between calcium (Ca²⁺) and carbonate ions (CO3² ).

Example 7 - Inventive Example

Example 7 was carried out in a similar manner as Example 5, except that the sodium carbonate powder (Na2COs) was dosed for 26 minutes to provide a total mass of 1072 g of dry Na2CO3, which corresponds to a stoichiometric ratio of 1 :1 .3 between calcium (Ca²⁺) and carbonate ions (CO3² ). Example 8 - Inventive Example

A slurry of calcium hydroxide ("milk of lime") was prepared as follows: 2000 g of quicklime (CaO) from Bukowa, Poland were added to about 16 liters of tap water in a stirred reactor. The resulting slurry was screened through a 100 pm screen. To produce a lime milk with a particle size cfeo(vol) of about 1 pm, the lime milk from the previous step has been wet-ground in an agitated bead mill (Dynomill with Cermil 0.45 mm grinding media) with a volume flow of 30 L/h. The resulting lime milk was screened through a 45 pm mesh size. The particle size cfeo(vol) was measured with Helos Sympatec using ethanol.

In order to initiate the process, 3 liters of a brine solution containing CaCh (obtained from an aqueous phosphor recycling process) were transferred into a high shear reactor. 3370 g of the produced lime milk was added to the solution under agitation, in an amount that corresponds to 67% of Ca²⁺ coming from the lime milk (Ca(OH)2) and 33% of Ca²⁺ coming from the dissolved CaCh in the brine (total Ca²⁺ cone, after addition of lime milk: 64.3 g/L). Next, 0.53 g of sucrose was added to the reaction mixture under agitation, which corresponds to 0.1 % dry sucrose to dry CaO in the mixture. The temperature of the mixture was adjusted to approximately 50 °C.

During the initial phase of the reaction, 50 g/min of sodium carbonate powder (Na2COs) was added to the mixture. This process was performed constantly and under vigorous agitation in a high shear reactor for a duration of 20 minutes. Then the addition was stopped. This means that a total mass of 1000 g of dry Na2COs was added to the mixture, which corresponds to a stoichiometric ratio of 1 :1 between calcium (Ca²⁺) and carbonate ions (CO3² ).

Example 9 - Inventive Example

Example 9 was carried out using the same lime milk as described in Example 8.

In order to initiate the process, 3 liters of a brine solution containing CaCh (obtained from an aqueous phosphor recycling process) were transferred into a high shear reactor. 6988 g of the produced lime milk was added to the solution under agitation, in an amount that corresponds to 80% of Ca²⁺ coming from the lime milk (Ca(OH)2) and 20% of Ca²⁺ coming from the dissolved CaCh in the brine (total Ca²⁺ cone, after addition of lime milk: 127.3 g/L). Next, 0.87 g of sucrose was added to the reaction mixture under agitation, which corresponds to 0.1 % dry sucrose to dry CaO in the mixture. The temperature of the mixture was adjusted to approximately 50 °C.

During the initial phase of the reaction, 83 g/min of sodium carbonate powder (Na2COs) was added to the mixture. This process was performed constantly and under vigorous agitation in a high shear reactor for a duration of 20 minutes. Then the addition was stopped. This means that a total mass of 1660 g of dry Na2COs was added to the mixture, which corresponds to a stoichiometric ratio of 1 :1 between calcium (Ca²⁺) and carbonate ions (CO3² ). The obtained suspension of structured precipitated CaCCh was dewatered and the brine mother liquor was exchanged with fresh water on a washing filter known to the skilled person in the art (e.g. vacuum rotary- or band filter with washing zone). The washed filter cake was redispersed with fresh water to obtain an aqueous slurry of structured precipitated CaCCh with an electrical conductivity of less than 500 pS/cm.

Table 1 : Physical data of precipitated calcium carbonates (PCCs) obtained in Examples 1 to 4

The inventors showed that by the inventive process it is possible to control the morphology of the obtained precipitated calcium carbonate product. In the inventive examples 2 to 4 scalenohedral PCC product is obtained whereas in the comparative example 1 vaterite is obtained as can be seen from table 1 and figure 1 .

Table 2: Physical data of precipitated calcium carbonates (PCCs) obtained in Examples 5 to 9

*0.6% of Portlandite (Ca(OH)2) as trace impurity

SEM images of the products of inventive examples 5 to 9 show a scalenohedral crystal morphology as can be seen from Figures 5 to 9.

Reference example 1

As a reference example, a precipitated calcium carbonate was prepared following the working protocol of Example 10 of US 2006/019.6836 A1 with the exception that the reverse osmosis (RO) concentrate was simulated by a comparable, but synthetically prepared, solution with the following ion concentrations:

18 mg/L of Mg (from 150.3 mg/L MgCh x 6H2O)

90 mg/L of Ca (from 330.1 mg/L CaCh x 2H2O)

11600 mg/L bicarbonate (from 16.0 g/L of NaHCOs)

0.1 mg/L sulfate (from 0.26 mg/L Mg(SO4) x 7H2O)

11300 mg/L chloride (from 18.3 g/L NaCI)

Total dissolved solid content: 34 g/L. The reactions were carried out in a lab reactor. The pH of the second reaction was decreasing when the CaCh solution (18 wt.%) was added to a final value of 7.2, contrary to the specification of Example 10 in the US patent which states that the pH in the second reaction is resulting to a pH value of 10.2 to 10.5.

The final product obtained in reference example 1 had a fine, blocky, prismatic calcite shape with a dso (Sedigraph) of 2,94 pm and a SSA of 5.3 m²/g. The purified product contained 100% calcite according to geochemical analysis (XRD). A SEM image of the final product obtained in reference example 1 is shown Fig. 10. Reference example 2

As another reference example, a precipitated calcium carbonate was prepared following the working protocol of Example 11 of US 2006/019.6836 A1 with the exception that the reverse osmosis (RO) concentrate was simulated by a comparable, but synthetically prepared, solution with the following ion concentrations:

3700 mg/L sodium (from 1 .2 g/L NaCI)

74 mg/L potassium (from 141 .2 mg/L KCI)

120 mg/L magnesium (from 698.7 mg/l MgCh X 6H2O)

49 mg/L calcium (from 179.7 mg/L CaCh X 2H2O)

8540 mg/L bicarbonate (from 11 .8 g/L NaHCOs)

144 mg/L sulfate (from 369.5 mg/L Mg(SO4) x 7H2O)

550 mg/L chloride

Total dissolved solid content: 13.2 g/L.

The reactions were carried out in a lab reactor. The final product of the second reactor obtained in reference example 2 had a coarse, blocky, prismatic calcite shape with a dso (Sedigraph) of 6.8 pm and a SSA of 1 .6 m²/g. The purified product contained 100% calcite according to geochemical analysis (XRD). A SEM image of the final product obtained in reference example 2 is shown Fig. 11 .

Claims

1 . Process for producing a scalenohedral PCC product, the process comprising the steps of a) providing at least one calcium compound selected from the group consisting of calcium oxide powder, calcium hydroxide powder and calcium hydroxide suspension; b) providing a calcium chloride solution, wherein the solution comprises 0.5 to 270 g/l of calcium; c) mixing the at least one calcium compound of step a) and the calcium chloride solution of step b) in any order, wherein the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture is in the range from 7:93 to 80:20; d) adding to the mixture obtained in step c) a sodium carbonate source selected from sodium carbonate or a mixture consisting of at least 70 wt.-% sodium carbonate and up to 30 wt.-% sodium bicarbonate at a temperature from 30 to 70 °C and at a pH value from 9.5 to 13.5, wherein the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1.00:1.00 to 1.00:1.30.

2. The process according to claim 1 , wherein the at least one calcium compound of step a) is a calcium hydroxide powder or a calcium hydroxide suspension, preferably a calcium hydroxide suspension and preferably the calcium hydroxide suspension has a solids content of from 5 to 50 wt.- %, based on the total weight of the calcium hydroxide suspension, preferably from 7 to 47 wt.-% and most preferably from 9 to 45 wt.-%.

3. The process according to any of the preceding claims, wherein the at least one calcium compound of step a) is in form of calcium hydroxide particles having a volume median particle size cfeo(vol) from 0.05 to 25 pm, preferably from 0.2 to 10 pm, more preferably from 0.4 to 5 pm, and most preferably from 1 .0 to 3.5 pm, and/or a volume based particle size cfoo(vol) from 0.15 to 75 pm, preferably from 1 to 30 pm, more preferably from 1 .5 to 15 pm, and most preferably from 2 to 10 pm.

4. The process according to any of the preceding claims, wherein the calcium chloride solution of step b) comprises 1 .0 to 200 g/l of calcium, preferably 2.0 to 150 g/l, more preferably 3.0 to 100 g/l and most preferably 5.0 to 50 g/l.

5. The process according to any of the preceding claims, wherein the molar amount of the at least one calcium compound of step a) to calcium chloride of step b) in the obtained mixture in step c) is in the range from 10:90 to 70:30, preferably from 15:85 to 50:50, more preferably from 20:80 to 40:60 and most preferably is about 25:75.

6. The process according to any of the preceding claims, wherein the temperature in step d) is from 40 to 60 °C and more preferably from 45 to 50 °C and/or wherein the pH value is from 10.0 to 13.0 and more preferably 10.5 to 12.0.

7. The process according to any of the preceding claims, wherein to the mixture obtained in step c) the sodium carbonate source is added in at least two portions, wherein the first portion contains 0.01 to 5 wt.-% of the total amount of the sodium carbonate source and is added in form of a solution comprising 5 to 20 g/l of the sodium carbonate source, preferably wherein the first portion of the sodium carbonate source in step d) contains 0.1 to 4.0 wt.-% of the total amount of the sodium carbonate source, more preferably 1 .0 to 3.0 wt.-% and most preferably 1 .5 to 2.5 wt.-% and/or is added in form of a solution comprising 7 to 17 g/l of the sodium carbonate source, preferably 8 to 15 g/l.

8. The process according to claim 7, wherein the remaining sodium carbonate source after the first portion is added in one portion as second portion and/or wherein the remaining sodium carbonate source after the first portion is added as solid and/or wherein the sodium carbonate source is sodium carbonate.

9. The process according to any of the preceding claims, wherein the calcium comprising materials of step a) and b) in combination and the sodium carbonate source of step d) have a calcium ion to carbonate ion molar ratio (Ca²⁺:CC>3² ) in the range from 1 .00:1 .00 to 1 .00:1 .20, more preferably from 1 .00:1 .00 to 1 .00:1 .10 and most preferably in an amount of about 1 .00:1 .05.

10. The process according to any of the preceding claims, wherein the process further comprises a step e) of adding to the mixture obtained in step c) an additive, preferably a dispersing agent and/or a nucleation agent such as sucrose or citrate and most preferably sucrose.

11 . The process according to any of the preceding claims, wherein the process further comprises a step f) of separating the scalenohedral PCC product from the aqueous suspension obtained in step d) and preferably step f) is done by solvent evaporation and/or pressure filtration and/or wherein the process further comprises a step g) of drying the scalenohedral PCC product after step d) or after step f), if present, at a temperature in the range from 60 to 120 °C, preferably from 80 to 110 °C, most preferably from 95 to 105°C, preferably until the moisture content of the scalenohedral PCC product is less than 1 wt.-%, based on the total weight of the dried scalenohedral PCC product.

12. The process according to any of the preceding claims, wherein the calcium chloride solution in step b) is a waste material, preferably obtained from a recycling process and more preferably from an aqueous phosphor recycling process and/or wherein the calcium chloride solution comprises further salts, preferably selected from the group consisting of magnesium salts, sodium salts and potassium salts and most preferably is selected from the group consisting of magnesium chloride, sodium chloride and potassium chloride.

13. The process according to any of the preceding claims, wherein the calcium chloride solution in step b) comprises magnesium salts and preferably the solution comprises 5 to 200 mg/l of magnesium, more preferably 5 to 100 mg/l and most preferably 5 to 50 mg/l.

14. The process according to any of the preceding claims, wherein the obtained scalenohedral PCC product i) has a specific surface area from 0.1 to 25.0 m²/g, preferably from 0.5 to 20.0 m²/g, and most preferably from 1 .0 to 15.0 m²/g, measured using nitrogen and the BET method according to

15. A scalenohedral PCC product obtainable according to any one of claims 1 to 14.

16. Use of a scalenohedral PCC product according to claim 15 in polymer applications, paper coating applications, paper making, paints, coatings, sealants, adhesives, feed, pharmaceuticals, concrete, cement, cosmetics, water treatment, engineered wood applications, plasterboard applications, packaging applications, catalysis, gas treatment applications and/or agricultural applications.