EP3523247A1

EP3523247A1 - Method for producing zincate crystals of at least one metal, and/or a metalloid and/or a lanthanide, and the applications thereof

Info

Publication number: EP3523247A1
Application number: EP17786982.3A
Authority: EP
Inventors: François Lacoste; Valentin LAIR; Julien THIEL; Samy HALLOUMI
Original assignee: Easyl SA
Current assignee: Easyl Zinc
Priority date: 2016-10-05
Filing date: 2017-10-05
Publication date: 2019-08-14
Also published as: FR3056980B1; MA46456A; WO2018065735A1; FR3056980A1

Abstract

The invention relates to a method for producing zincate crystals from a least one element other than zinc (Zn), marked "A", independently selected from a metal, a metalloid or a lanthanide, with the exception of zincate crystals that only comprise calcium (Ca) as element A, said method comprising at least the following steps: suspending different starting reactants comprising at least a source of the zinc element with a degree of oxidation +2 and a source of said A element(s) with a degree of oxidation from 1 to 6, in a liquid medium, so as to form a suspension called "starting suspension"; grinding said starting suspension at an ambient temperature lower than or equal to 50°C, in a three-dimensional microbead grinder in a liquid medium during a residence time of 15 min or less; recovering, at the outlet of said three-dimensional microbead grinder, a suspension called "end suspension" comprising said starting reactants in the activated form or zincate crystals of said A element(s), which are generally in a hydrated form; and if necessary, the calcination of said end suspension when it comprises said starting reactants in the activated form so as to obtain generally non-hydrated zincate crystals of said A element(s).

Description

Process for producing zincate crystals of at least one metal, and / or a metalloid and / or a lanthanide, and their applications

TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention relates to a method for producing zincate crystals of at least one metal and / or one metalloid and / or one lanthanide.

In particular, the present invention relates to a process for manufacturing crystals of these various zincates, in particular implementing a micromilling step in a three-dimensional microbead mill in a liquid medium (usually water) carried out in a very short time and without heating. particular. This micromilling step also makes it possible to facilitate a possible calcination step that can be performed later.

The crystals of the various zincates obtained with the aforementioned process can be used to produce catalysts, materials having dielectric properties, photocatalysis or photoluminescence, chemical absorbents or antibacterial agents.

BACKGROUND

There exist in the state of the art various methods for preparing homogeneous mixtures of zincate powder of at least one other chemical element, which is generally selected from metals, metalloids or lanthanides.

One distinguishes a chemical approach and a mechano-synthesis approach. These two approaches generally implement, as starting reagents, a zinc oxide and an oxide of the other chemical element, or one of their precursors.

In particular, the preparation of zincate crystals by chemical means consists first of all in preparing the starting reagents, in mixing them as homogeneously as possible and in calcining the mixture thus obtained so as to carry out the combination reaction.

The mixture of the raw materials can be carried out dry. In this case, the imperfect homogeneity of the mixture is compensated by long-term calcination, of the order of several hours and at a high temperature (the temperatures regularly exceed 1200 ° C.) in order to give the necessary time for carrying out the reaction by solid diffusion. Despite these extreme conditions, the end product is usually not completely transformed. It is then necessary to carry out one or more additional calcination cycles before arriving at a sufficiently pure final product. The mixture of the raw materials can also be carried out in a liquid medium (aqueous solution), in order to give, after drying, a more homogeneous powder which will subsequently be calcined at high temperature in the presence of CO ₂ (the recommended temperature is generally greater than 1250 ° C). As an example, the publication of H. G McADIE, "The Pyro-synthesis of Strontium Zincate": Journ. Inorg. nucl. Chem: Vol. 28 (1966); 2801-2809, describes the preparation of strontium zincate crystals from a solution of zinc acetate and strontium acetate.

In order to further improve the homogeneity of the mixture comprising the starting reagents, many authors use the "Sol-Gel" method. This method consists in preparing an alcoholic solution, for example in ethanol, zinc acetate and the salt of the other chemical element, and in gelling it before calcining it. Thus Linhua Xu describes in his publication "Optical and structural properties of ZnO / MgO composite thin films prepared by sol-gel technique: Journ. of Alloys and Compounds ": Vol. 548 (2013); 7-12, the preparation of magnesium zincate crystals.

However, the disadvantages of all these methods of zincate preparation chemically are the cost of raw materials, the complexity of a preparation in several stages and the gas pollution released during the calcination.

Another approach is thus to prepare the zincate crystals of another element and in particular the mixing step mentioned above, by mechano-synthesis.

This method consists of generally dry milling (non-liquid medium) starting reagents in the form of powder in a bowl, steel or agate, with balls whose diameter is generally of the order of 10 mm and at then carry out a calcination step.

Evvgenii Avvakumov's book entitled "Soft Mechano Chemical Synthesis" published in 2001 by Kluwer Académie Publishers "gives examples of preparations that make it possible to obtain, by mechanical synthesis and after calcination, numerous oxide ceramics, in particular aluminates and silicates. or titanates. This process thus uses starting reagents in the form of powder, so as to perform dry grinding. In particular, it is specified in Chapter 5 of this work that it is necessary to carry out the partial dehydration of the starting reagents when these are in hydrated form, such as in the form of hydroxide, in order to "activate" The starting mixture.

By way of example, T. Santhaveesuk et al., In the publication "Ethanol sensing properties of Zn ₂ Ti0 ₄ particles", published in 2015 in the journal Ceramics International Volume 41, describe the manufacture by mechanical synthesis of titanium zincate of the empirical formula Zn ₂ TiO ₄ , this compound may especially be used as a gaseous ethanol detector. According to this publication, titanium zincate is prepared in the following manner: zinc oxide and titanium oxide are dry milled in a mortar for 2 hours; the dry mixture obtained is inserted for 24 hours in a rotary ball mill at a speed of between 200 rpm and 400 rpm in the presence of ethanol; four washes are then carried out before drying the mixture 24h at 80 ° C; finally, a calcination is carried out at 1000 ° C. for 6 hours. Thus, the steps necessary to prepare the titanium zincate according to this publication are numerous and also very long, with elementary times of up to 24 hours.

US 2014/176285 discloses a ferrite ceramic composition comprising at least Fe, Mn, Cu, Zn, Mg and Ni. In particular, the manufacturing method described in this document comprises the mixture of various source reagents of Fe, Mn, Cu, Zn, Mg, Ni, such as Fe ₂ O ₃ , Mn ₂ O ₃ , CuO, ZnO, MgO and NiO in specific proportions, then their calcination. The mixing step is carried out in a ball mill (PSZ balls) in aqueous phase (with pure water).

EP 2623480 discloses a sintered composite material, as well as its method of manufacture. The method comprises in particular a step of premixing a source of Ti with a source of AI, a calcination step; a step of mixing with zinc oxide, a molding step and a sintering step. According to Example 1, the premixing step can be done in a dry-lease mix and the step of mixing with zinc oxide in a wet-phase ball mill. ("Wet lease millet"). The grinding time is not indicated.

The publication of Adriana D.Ballarini et al. "Characterization of ZnAI ₂ 0 ₄ obtained by different methods and used as catalytic support of Pt", Catal Lett (2009) 129: 293-302, relates to the synthesis of ZnAl ₂ 0 ₄ by various techniques, including the mechanical technique. wet environment synthesis (HMS). In particular, in the experimental part, it is indicated that the HMS method consists in: mixing by grinding γ-ΑΙ ₂ 0 ₃ with ZnO at a molar ratio ΖηΟ / γ-ΑΙ ₂ 0 ₃ of 1.05 mol in order to obtain a fine powder; adding water to obtain a paste which is milled for 24 hours at room temperature in a ball mill (140 mL Teflon cylindrical bottle containing 13 mm diameter zirconia beads which is rotated at 200 rpm); drying the resulting paste at 110 ° C for 6 hours; and calcining at 900 ° C for 12 h.

The publication of Huabin Yang et al. "Calcium zincate synthesized by ballasting as a negative material for secondary alkaline batteries", Journal of the Electrochemical Society, 151 (12) A2126-A2131 (2004), describes two methods for preparing calcium zincate, a first method by chemical and a second by mechano-synthesis. The second method by mechano-synthesis consists of mixing in a ball mill "Fritsch planetary lease miller - P6", Ca (OH) ₂ with ZnO in an aqueous medium with 10 or 20 mm beads for 9 hours (speed of 300 Rotations per minute). Thus, the second approach to preparing zincate crystals of another element also has several disadvantages. Firstly, the necessary duration of the grinding is relatively long (it lasts most often several hours). Then, the capacity of the mills is generally limited to a few tens of grams (low productivity) and is thus difficult to transfer to the industrial scale.

Finally, it is also described in the prior art to carry out the calcination step under pressure.

For example, V. Solozhenko et al. in the publication ("High-pressure formation of Mg _x Zn _1-x solid solutions with solid rock structure", published in 2006 in Solid State Communications 138) propose to manufacture crystals of magnesium zincate, gross formula Mg _x Zn _1-x O with 0 <x <1 according to this method. Magnesium zincate has particular applications in the field of photoluminescence.

In particular, the authors propose mixing zinc oxide ZnO and magnesium oxide MgO, and then calcining this mixture at temperatures above 1200 ° C. and under a pressure of 4.4 GPa.

However, this process suffers because it requires a number of steps, high temperatures over long times and the need for pressurization.

Also known from the state of the art, the publication of N. Kislov et al.

"Optical absorption red and blue shifts in ZnFe ₂ 0 ₄ nanoparticles", Materials Science and Engineering B 153 (2008) 70-77 which describes a method of reducing the particle size of ZnFe ₂ 0 ₄ via a ball mill.

There is thus a real need for a new process for manufacturing zincate crystals of at least one other chemical element, such as a metal, a metalloid or a lanthanide which allows the manufacture of such crystals in a rapid manner (by opposition to what is currently proposed in the state of the art), while reducing the risks of pollution and manufacturing costs, thus making the process usable on an industrial scale.

The object of the present invention is, therefore, to provide a new zincate manufacturing process of at least one other element avoiding, at least in part, the aforementioned drawbacks.

In particular, the object of the present invention is to propose a new process for manufacturing crystals of different zincates that is simple to implement and industrially exploitable (that is, does not require a too high number of steps) while decreasing the times requiring a particular heating, and not requiring special pressurization. OBJECT OF THE INVENTION

For this purpose, the subject of the present invention is a method for manufacturing crystals (hydrated or not) of zincate of one or more element (s) other than zinc (Zn), noted "A" independently selected from a metal, a metalloid or a lanthanide, with the exception of zincate crystals comprising as element A only calcium (Ca), said process comprising at least the following steps:

(1) suspending separate starting reagents comprising at least: a source of the zinc element which has a degree of oxidation +2 and a source of said element or elements A which has a degree of oxidation ranging from 1 to 6, in a liquid medium, such as water, so as to form a suspension called "starting suspension", the mass concentration of starting reactants being between 10 g / L and 1000 g / L, preferably between 50g / L and 800g / L, and particularly between 100g / L and 600g / L;

(2) grinding said starting suspension at an ambient temperature of less than or equal to 50 ° C., preferably less than or equal to 35 ° C., in a three-dimensional microbead mill in a liquid medium for a residence time less than or equal to 15 min, preferably less than or equal to 1 minute, and especially ranging from 5 to 25 seconds and in particular from 10 to 20 seconds;

(3) recovering from said three-dimensional microbead mill a suspension called "final suspension" comprising said starting reagents in activated form or zincate crystals of said at least one A-element generally in hydrated form;

(4) optionally, drying or concentrating the final suspension obtained at the end of step (3), so as to obtain a powder or a concentrate comprising, respectively, said starting reagents in the form of activated or said crystals, generally in hydrated form, zincate said element (s) A;

(5) the calcination of said final suspension obtained at the end of step (3) when it comprises said starting reagents in activated form, or of the powder or concentrate obtained at the end of step (4) when it comprises said starting reagents in activated form, so as to obtain crystals, generally non-hydrated, of zincate of said element (s) A.

According to the invention, the starting suspension comprises at least two starting reagents. Therefore, the source of the aluminum element and the source of said element or elements A are distinct.

In general, these starting reagents for obtaining zincate crystals of one or more element (s) A are non-nanometric and non-heat-sensitive. According to the invention, "an ambient temperature of less than or equal to 50 ° C" comprises the following values: 50; 49; 48; 47; 46; 45; 44; 43; 42; 41; 40; 39; 38;

37; 36; 35; 34; 33; 32; 31; 30 ; 29; 28; 27; 26; 25; 24; 23; 22; 21; 20; 1 9; 18;

17; 16; 15; 14; 13; 12; 1 1; 10; etc. or any intervals between these values.

Also, according to the invention, "a residence time of less than or equal to 15 minutes" comprises the following values: 15 min; 14 min; 13 min; 12 min; 1 1 min; 10 minutes ; 9 min; 8 min; 7 min; 6 min; 5 min; 4 min; 3 min; 2 min ; 1 min; 55 sec; 50 sec; 45 sec;

40 sec; 35 sec; 30 sec; 25 sec; 20 sec; 15 sec; 10 sec; 5 sec; etc. or any intervals between these values.

Similarly, "an oxidation level of 1 to 6" includes the following oxidation states: 1, 2, 3, 4, 5, 6 and any ranges between these values.

Generally, the calcination step (5) is carried out at a temperature of between 400 ° C. and 1500 ° C., preferably between 700 ° C. and 1250 ° C. for a duration preferably ranging from 15 min to 3 h, in particular from 30 minutes to 1 hour 30 minutes.

For the purposes of the invention, the mass concentration of the starting reagents corresponds to the mass of the source of the zinc element + the mass of the source of the said chemical element (s) A on the volume of the liquid medium.

In general, the final suspension comprises starting reagents in activated form when these are insoluble in the liquid medium. Also, the final suspension preferably comprises said zincate crystals of said element (s).

A being generally in hydrated form when the starting reagents are at least partially soluble in the liquid medium, such as water.

For the remainder of the description, unless otherwise specified, the indication of a range of values "from X to Y" or "between X and Y" in the present invention means as including the X and Y values. Moreover, the sign "<" means strictly inferior and the sign ">" means strictly superior, while the sign

"<" And ">" means respectively "less than or equal to" and "greater than or equal to".

The zincate crystals of one or more element (s) A obtained after calcination of the aforementioned process can be used to manufacture luminescent materials in the ultraviolet range, electrodes for supercapacitors, catalysts, photocatalytic materials, dielectric ceramics, photoluminescent materials, gas detectors such as ethanol, absorbents for azo dyes, or antibacterial agents. DETAILED DESCRIPTION OF THE INVENTION

The invention will be better understood and other objects, details, characteristics and advantages thereof will appear more clearly on reading the following description of exemplary embodiments, with reference to the appended figures in which:

- Figure 1 shows a sectional view along the longitudinal axis XX of a three-dimensional microbeads mill in the liquid phase, according to an alternative embodiment suitable for implementing the method according to the invention;

FIG. 2 represents sectional views along the axis XX and the axis AA, of liquid-phase three-dimensional microbead grinder variants according to FIG. 1 in which: (a) the agitator is in disks, (b) agitator has fingers and (c) the grinding chamber is annular;

FIG. 3 is an X-ray diffractometry (XRD) spectrum of magnesium zincate crystals obtained according to the process of the invention, using the following parameters: starting suspension comprising 600 g / L of ZnO + Mg (OH) raw materials ₂ , a flow rate of the starting slurry in the mill of 30L / h, a bead diameter of 500 μηη and a calcination temperature of 1200 ° C for 1 hour;

FIG. 4 is an X-ray diffractometry (XRD) spectrum of magnesium zincate crystals obtained according to the process of the invention using the following parameters: starting suspension comprising 600 g / l of ZnO + Mg (OH) raw materials ₂ , a flow rate of the starting slurry in the mill of 30L / h, a bead diameter of 500 μηη and a calcination temperature of 900 ° C for 1 hour;

FIG. 5 is an X-ray diffractometry (XRD) spectrum of magnesium zincate crystals obtained according to the process of the invention, using the following parameters: starting suspension comprising 600 g / l of ZnO + Mg (OH) raw materials ₂ , a flow rate of the starting slurry in the mill of 30L / h, a bead diameter of 500 μηη and a calcination temperature of 1050 ° C for 1 hour;

FIG. 6 is an X-ray diffractometry (XRD) spectrum of titanium zincate crystals obtained according to the process of the invention, using the following parameters: starting slurry comprising 300 g / l of ZnO + TiO ₂ raw materials, a flow rate of the starting slurry in the mill of 30L / h, a bead diameter of 500 μηη and a calcination temperature of 1050 ° C for 1 hour;

FIG. 7 is an X-ray diffractometry (XRD) spectrum of iron zincate crystals obtained according to the process of the invention, using the following parameters: starting suspension comprising 300 g / l of ZnO + FeOOH raw materials, a flow rate of the starting slurry in the mill of 30L / h, a bead diameter of 500 μηη and a calcination temperature of 1200 ° C for 1 hour;

FIG. 8 is a scanning electron microscope (SEM) micrograph of hydrated strontium zincate crystals obtained according to the method of the invention, using the following parameters: starting slurry comprising 100 g / l of ZnO + Sr raw materials ( OH) ₂ -8H ₂ O, a flow rate of the starting slurry in the mill of 30L / h and a bead diameter of 500 μηη (no calcination step);

FIG. 9 is an X-ray diffractometry (XRD) spectrum of the strontium zincate crystals obtained according to the method of the invention, using the same parameters as those described in FIG. 8 above.

The Applicant has endeavored to develop a new method for manufacturing zincate crystals of one or more chemical element (s) other than zinc (Zn), noted "A" adapted to be implemented on an industrial scale and simple to implement.

In particular, the zincate crystals comprising as element A only calcium (Ca) are excluded from the invention.

According to the invention, the other element (s) A (noted for example Ai, A ₂ , A _n ) suitable for the process of the invention are independently selected from a metal, a metalloid or a lanthanide.

According to a first embodiment, the process according to the invention makes it possible to manufacture zincate crystals of a single element A. According to this mode, the crystals thus obtained (after calcination) can satisfy the following general formula: Zn _x A _y OHz, with 0 <x <1, 0 <y <1, 5 and z is preferably 0 and may correspond to the crystals of formulas: ZnLi ₆ 0 ₄ , Nai ₀ Zn ₄ O ₉ , BaZnO ₂ , ZnCr ₂ 0 ₄ or ZnCu ₂ 0 ₄ .

According to a second embodiment, the method according to the invention makes it possible to manufacture zincate crystals of several elements A, denoted "A1", "A2", "An", etc. According to this mode, the crystals thus obtained (after calcination) may for example satisfy the following general formula: A1 _v (Zn _x A2 _w ) 0 ₃ , with 0 <x <1; 0 <v ≤ 1 and 0 <w <1. Advantageously, according to this mode, w = (1 -x) and / or v = 1. Even more advantageously, v = 1, x = 1/3 and w = 1-x = 2/3. Thus, the following crystals can be obtained according to the process of the invention after calcination: Ba (Zn _1/3 Nb _2/3) 03, Ba (Zn _1/3 Ta _2/3) 03, Sr (Zn _1/3 Nb _2/3) 03, Sr (Zn _1/3 Nb _2/3) 03, Ca (Zn _1/3 Nb _2/3) 03 or

For this, the method for manufacturing the crystals (hydrated or not) of zincates of said element (s) "A" comprises at least the following steps:

(1) suspending at least one source of the zinc element which has a degree of oxidation +2 and at least one source of said element or elements A which presents a degree of oxidation ranging from 1 to 6, in a liquid medium, such as water, so as to form a suspension called "starting suspension", the mass concentration of the starting reagents being between 10 g / L and 1000 g / L, preferably between 50 g / L and 800 g / L, and particularly between 100 g / L and 600 g / L;

(3) the recovery at the outlet of said three-dimensional micro-bead mill of a suspension called "final suspension" comprising, depending on the nature of the starting reagents and the liquid medium, said starting reagents in activated form or zincate crystals of said one or more (s) A elements are generally in hydrated form;

(4) optionally, drying or concentrating the final suspension obtained at the end of step (3), so as to obtain a powder or a concentrate comprising, respectively,

said starting reagents in activated form, or

said crystals, generally in hydrated form, of zincate of said element (s) A;

Thus, depending on the nature of the starting reagents and the liquid medium, it is possible to obtain, according to a first variant of the process according to the invention, zincate crystals of the element A or elements directly at the end of the stage. grinding (3), namely in a single step not requiring special heating and in a very short time (in general, a single passage in the grinder is sufficient).

This first variant is in particular carried out when the starting reagents are at least partially soluble in the liquid medium and they are furthermore capable of performing an acid-base reaction. Without being bound by any theory, the Applicant has discovered that when an acid-base reaction can take place in the three-dimensional micro-bead mill, then there was formation of crystals from the grinding step (3) and that it was therefore not necessary to carry out a calcination step in order to obtain zincate crystals of the element A.

By way of example, this first variant can be implemented when the source of element A or elements has a basic character and is, for example, in the form of hydroxide and that the liquid medium is water. In this case, in general, the source of the zinc element, such as ZnO, will react in water with the source of the element A in hydroxide form and thus allow a synthesis reaction of the zincate crystals during the grinding step. Indeed, according to this variant, the final suspension resulting from step (3) comprises zincate crystals or elements A, including crystals in hydrated form. This variant has been illustrated in Example F ° of the experimental part described below which describes the production of hydrated crystals of strontium zincate SrZn (OH) ₄ -H ₂ O by performing only steps (1) to (4). ) of the process of the invention from ZnO and Sr (OH) ₂ in water as starting reagents.

Of course, other syntheses of hydrated zincate crystals are possible by carrying out this first variant of the process, such as the production of hydrated barium zincate crystals such as BaZn (OH) ₄ .H ₂ 0 or sodium hydrous crystals such as Na ₂ Zn (OH) ₄ .

Also, it is of course possible to carry out a calcination step:

- Of said final suspension obtained at the end of step (3) when it comprises said zincate crystals of said element (s) A in hydrated form or,

the powder or concentrate obtained at the end of step (4) when it comprises said zincate crystals of said element (s) in hydrated form,

so as to obtain unhydrated crystals of zincate of said element (s)

AT.

Indeed, this calcination step (5), which is not mandatory to obtain crystals according to this first embodiment, however, makes it possible to manufacture zincate crystals or elements A in non-hydrated form.

According to a second variant, especially when the source of the zinc element and the source of the element (s) A are insoluble in the aqueous medium, zincate crystals are not obtained directly after step (3). ; a calcination step is then necessary in order to finish the combination reaction Zinc + element (s) A in the form of crystals.

However, at the end of the grinding step (3) according to the invention, the starting reagents were mixed so intensely that they are said to be "activated", ie the source of the zinc element is mixed with very homogeneous and intimate manner with the source of the element A. Without being bound here also by any theory, it would seem that the grinding in the three-dimensional microbead mill according to the invention and this, even for a duration less than 15 min or 20 s and at room temperature, would cause a change in the surface of the starting reagents, or even disorders in the crystal lattice or crystal defects. However, the Applicant has discovered that when Starting reagents are in "activated" form, this facilitates the subsequent calcination step. It has indeed been found that the calcination step was much shorter and did not require as high a temperature as the calcination steps described in the processes of the prior art.

For example, when the source of the zinc element and the source of the element (s)

A does not form an acid-base reaction in the liquid medium (water) or that the source of the element A does not have a basic character in the liquid medium (as is the case for the example D ° described in the experimental part below), then the starting reagents are in "activated" form at the end of the grinding step (3) according to the invention.

Generally, the calcination step (5) is carried out at a temperature of between 400 ° C. and 1500 ° C., preferably between 700 ° C. and 1250 ° C. for a duration preferably ranging from 15 minutes to 3 hours, in particular from 30 minutes to 1 hour 30 minutes.

Thus, the Applicant has developed a general process which, unexpectedly, makes it possible to manufacture zincate crystals of one or more elements A in a very short time (reaction time less than or equal to 15 minutes and in general, less than or equal to 1 minute), in only one or two steps (grinding step followed, if necessary a calcination step). In particular, the first grinding stage is in particular carried out at room temperature (the process does not require a particular heating step before proceeding with the calcination), and this with energy and water (liquid medium) consumptions minimum (non-polluting), with excellent performance.

As will be demonstrated in the tests below, the process of the invention also makes it possible to obtain, surprisingly, zincate crystals of excellent quality, namely very pure and of fine and well controlled particle size distribution.

The method according to the invention also has the advantages of having a very low cost (the raw materials used are indeed widely available, non-polluting and inexpensive) and to have excellent reproducibility, which makes it more unique processes described in the prior arts. The method according to the invention also has the advantage of being able to be implemented continuously. However, these characteristics are important for an application on an industrial scale.

Furthermore, despite the many studies conducted on the synthesis of zincate crystals, none have suggested the aforementioned method and in particular a grinding step in a three-dimensional microbead mill from a starting suspension comprising at least one zinc source having a +2 oxidation state and a source of said element or elements A having an oxidation state ranging from 1 to 6, or one of their precursors and this, in an excess of liquid medium such as water. However, obtaining zincate has many industrial applications.

By way of example, titanium zincate may be used as a pigment for painting or may be used in the fields relating to catalysis, semiconductor or gas detector. In general, the different applications of zincate crystals are known to those skilled in the art.

Description of the three-dimensional ball mill

To better understand the process that is the subject of the invention, a three-dimensional microbead mill capable of obtaining an intimate and homogeneous mixture of a suspension comprising either the starting reagents in activated form or the zincate crystals thereof. or said elements A, will first be described below with reference to Figures 1 and 2.

As illustrated in FIG. 1, a three-dimensional micro-bead mill 1 comprises at least:

a stationary grinding chamber 2 of generally cylindrical shape extending along a longitudinal axis XX, said chamber 2 being at least partially filled with said microbeads (not shown) and comprises: at a first end 3 at least one inlet 5 for introducing said starting suspension, and at a second end 4, an outlet 6 having a separating means 7 adapted to evacuate the suspension formed in said chamber 2; and

an agitator 8, disposed in the stationary grinding chamber 2, in the form of an elongated rod along the longitudinal axis XX, said stirrer 8 being able to set in motion the microbeads / starting suspension assembly.

In particular, the inlet 5 is generally connected to a peristaltic pump (not shown). This pump makes it possible to bring the initial suspension, for example contained in a container, such as a tank, inside the grinding chamber 2 via the inlet 5. The pump also allows, during the operation of the three-dimensional crusher, to bring this starting suspension according to a certain flow rate that is adjustable, hereinafter called "flow rate". This flow rate further forms a current in the grinding chamber 2 for driving the starting suspension from the inlet 5 to the outlet 6.

The outlet 6 of the grinding chamber 2 comprises in particular the separation system 7 of the microspheres of the final suspension comprising an intimate and homogeneous mixture of the raw materials. This separation means 7 may be a sieve whose orifices have a smaller dimension than that of the microbeads or a separation slot whose width is also adapted to retain the microbeads within the chamber 2. The inner wall 9 of the grinding chamber 2 comprises, according to a first embodiment, a smooth internal surface. However, according to an alternative embodiment that will be described below, it can be arranged on the inner surface 9 fingers 1 1.

As mentioned above, inside the grinding chamber 2 is arranged the stirrer 8 which, in addition to the flow rate, also allows the start of movement of the suspension.

In particular, the agitator 8 is able to rotate about the X axis via a rotary shaft (14, FIG. 2) to impart a vortex movement to the starting suspension within the grinding chamber 2 and thereby perform a stirring intense between this starting suspension and the microbeads present in the chamber 2 along the inner wall 9 of this chamber 2.

In particular, the mill via its rotary shaft 14 has a rotation speed greater than or equal to 100 revolutions per minute, advantageously greater than or equal to 1000 revolutions per minute (rpm), preferably greater than or equal to 2000 revolutions per minute and typically greater than or equal to 2500 rpm.

For the purposes of the invention, "a rotational speed greater than or equal to 100 revolutions per minute" includes the following values: 100; 150; 200; 250; 300; 350; 400; 450, 500; 550; 600; 650, 700; 750; 800; 850; 900, 950; 1000; 1,100; 1200; 1300; 1400; 1500; 1600; 1700; 1800; 1900; 2000; 2100; 2200; 2300; 2400; 2500; 2600; 2700; 2800; 2900; 3000; 3100; 3200; 3300; 3400; 3500; 3600; 3700; 3800; 3900; 4000, 4500; 5000; 5500; 6000; etc., or any intervals between these values.

In general, the mill has a rotation speed ranging from 1000 rpm to 5000 rpm, in particular from 1500 rpm to 4500 rpm, preferably from 2000 rpm to 4000 rpm and typically from 2800 to 3200 rpm.

In order to improve this stirring, the stirrer 8, just like the internal wall 9 of the chamber 2, can have various possible configurations represented for example in FIG. 2.

According to a first configuration illustrated in FIG. 2a, the stirrer 8 comprises, along its elongated rod, disks 10, arranged perpendicular thereto. Their number can vary from 2 to 8, preferably from 2 to 5. These discs 10 allow on the one hand, to improve the grinding of the starting suspension by stirring the microbeads further and on the other hand, to accelerate the reaction time.

According to a second configuration illustrated in FIG. 2b, the stirrer 8 may also comprise along its stem one or more perpendicularly arranged disks 10 which are furthermore capable of cooperating with fingers 1 1 arranged perpendicularly with respect to the internal wall 9 of the chamber 2. A finger is in particular in the form of a ring which extends perpendicularly from of the wall 9. For this configuration, the disks 10 and the fingers 1 1 are staggered, namely the disks 10 and the fingers January 1 are alternately arranged in the chamber 2. In addition, the thickness of the 8 is increased relative to the previous configuration (Figure 2a) so that the periphery of the discs 10 is close to the inner wall 9 and that of the fingers 1 1 is close to the periphery of the rod of the stirrer 8. Thus, in this configuration, the volume of the chamber is reduced compared to the previous configuration, thus allowing a better mixing between the starting suspension, the microbeads and the inner wall 9 of the chamber 2.

The volume of the chamber 2 can be further reduced as shown in FIG. 2c. In this configuration, the agitator 8 has an external diameter slightly smaller than the internal diameter of the chamber 2, thus forming a small volume annular chamber 12 disposed between the outer wall of the stirrer 8 and the inner wall 9 of the chamber 2 The microbeads (not shown) are arranged in this annular chamber 12. During operation of this configuration, the starting suspension is introduced through the inlet 5 with a certain flow rate, which will then travel through the annular chamber 12 to the exit 6 while being brewed by the microbeads.

In general, the mill suitable for carrying out the process according to the invention comprises a grinding chamber having a diameter of 75 mm to 300 mm for a length of 80 mm to 900 mm and an agitator having a size ranging from 65 mm to 260 mm. . Thus, the volume of the grinding chamber varies from 0.35 L to 600 L, preferably from 0.35 L to 400 L, and typically from 0.35 L to 62 L.

For the purposes of the invention, "a volume of the grinding chamber ranging from 0.35 L to 600 L" comprises the following values: 0.35; 0.5; 0.8; 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 15; 20; 25; 30 ; 35; 40; 45; 50; 55; 60; 65; 70; 80; 85; 90, 100; 1 10; 120; 130; 140; 150; 160; 170; 180; 190; 200; 210; 220; 230; 240; 250; 260; 270; 280; 290; 300; 350; 400; 450; 500; 550; 600 etc., or any interval between these values.

The geometry of the grinding chamber and the stirrer may be adjusted by those skilled in the art depending on the amount of reactants initially introduced, as well as the desired reaction time. For example, it is also possible that the grinding chamber 2 comprises an accelerator to improve the grinding of the starting suspension.

In addition, the microbeads housed in the grinding chamber 2 and suitable for the process according to the invention are substantially spherical in shape and have an average diameter of less than or equal to 5 mm, generally ranging from 0.05 mm to 4 mm, of preferably from 0.2 to 3 mm, in particular from 0.3 to 2 mm, and typically of the order of 0.5 to 1 mm. Preferably, the diameter of the microbeads is less than or equal to 1 mm and is typically of the order of 0.05 mm to 1 mm. They are preferably selected from microbeads having a high hardness and relatively resistant to abrasion.

In particular, the microbeads have a Vickers hardness measured according to the EN ISO 6507-1 standard greater than or equal to 900 HV1, preferably ranging from 900 HV1 to 1600 HV1, typically ranging from 1000 to 1400 HV1 and especially from the order of 0.05 mm to 1 mm.

For the purposes of the invention, "a Vickers hardness greater than or equal to 900 HV1" comprises the following values: 900; 910; 920; 930; 940; 950; 960; 970; 980; 990; 1000; 1010; 1020; 1030; 1040; 1050; 1060; 1070; 1080; 1090; 1000; 1 1 10; 1120; 1,130; 1,140; 1,150; 1,160; 1,170; 1,180; 1,190; 1200; 1300; 1400; 1500; 1600; 1700; etc., or any intervals between these values.

Advantageously, they have a high real density. In general, the microbeads according to the invention have a real density greater than or equal to 2 g / cm ³ , in particular ranging from 2 to 15 g / cm ³ , preferably from 3 to 12 g / cm ³ , and typically from 4 to at 10 g / cm ³ .

Thus, the microbeads according to the invention may be ceramic microspheres, (zirconium oxide Zr0 ₂ , zirconium silicate ZrSiO ₄ ); steel microbeads, tungsten carbide microbeads, glass microbeads or a combination thereof.

Preferably, the microbeads are ceramic because they do not generate pollution by their wear.

In particular, the microbeads are made of zirconium oxide.

Optionally, the zirconium oxide microbeads may be stabilized by another oxide, such as cerium oxide, yttrium oxide and / or silicon.

By way of examples, the following compositions, summarized in Table 1 below, are suitable for forming the microbeads according to the invention:

Microbead Composition Hardness HV1 Density Actual Manufacturer (g / cm ³ )

- 12% Si0 ₂ ,

- 5% Al ₂ 0 ₃ and

- 4% Y ₂ 0 ₃

Silicate microspheres of>800> 6.5 Saint-Gobain zirconium ZrSi0 ₄ (Rimax Ceramic

Beads)

Glass microbeads 500> 3,76 -

Steel microbeads 700> 7.7 -

Table 1

Generally, the microbeads suitable for the process of the invention are not glass or exclusively glass.

In particular, the microbeads represent, in volume, relative to the total volume of the stationary chamber 2 from 50% to 85%, preferably from 55% to 70%.

Within the meaning of the invention, "a volume of 50 to 85%" comprises the following values: 50; 55; 60; 65; 70; 75; 80; 85; etc., or any intervals between these values.

By way of example, the three-dimensional wet-phase microbead mill suitable for carrying out the process according to the invention may correspond to grinders marketed by the WAB companies, Dyno-Mill range: Multi Lab, ECM and KD, NETZCH Company, by example LABSTAR LS1, or Alpine Hosokawa, for example, Agitated Media Mill AHM. Description of the process according to the invention

The manufacturing method according to the invention will now be described more explicitly below.

As indicated above, the production of zincate crystals of one or more element (s) A according to the invention comprises firstly (1) a starting reactive slurrying step. The latter comprise at least: a source of zinc having a +2 oxidation state and at least one source of said element or elements A having a degree of oxidation ranging from +1 to +6. The suspension obtained is hereinafter referred to as "starting suspension".

The starting suspension is conventionally prepared by mixing the starting reagents with the liquid medium in a suitable device, such as a vessel or tank, equipped with a stirring system (such as a magnetic stirrer, stirring blades). agitation, etc.). The device and the stirring system may be adapted by the skilled person depending on the amount of crystals of different zincates or elements A to be manufactured.

As mentioned above, according to the first variant or the second variant embodiment, the liquid medium may be chemically inert or not. In particular, according to the first embodiment, the liquid medium, such as water (H ₂ 0) may react with the starting reagents and in particular the source of the element A or elements having a basic character (if it is for example in the form of a hydroxide) and form an acid-base reaction with the source of the zinc element (as ZnO).

However, most often, the liquid medium is chemically inert, ie it does not react with the source of zinc and the source of the element or elements A. This corresponds to the second variant of the process of the invention (the starting reagents its insoluble in the liquid medium, so at the end of the grinding step, a final suspension is obtained comprising the starting reagents in activated form).

The liquid medium will generally be water (H ₂ 0). However, the liquid medium may also correspond to an organic solvent, such as methanol or isopropanol.

In general, this step (1) is carried out in a large excess of liquid medium (water). Indeed, the mass concentration of starting reagents (source of the zinc element + source of said chemical element (s) A) is between 10 g / l and 1000 g / l, preferably between 50 g / l and 800 g / l, and particularly between 100g / L and 600g / L.

This excess of liquid medium makes it possible in particular to improve the synthesis of the zincate crystals of the element (s) A (first variant) or to improve the activation of the starting reagents within the mill by allowing an intense mixing (second variant embodiment ). Indeed, an excess of liquid medium promotes the setting in motion of the microspheres of the mill for better grinding of the starting suspension.

Preferably, the source of the zinc element and the source of the element (s) A are mixed in the starting slurry in a stoichiometric proportion. It is of course possible to deviate substantially from this stoichiometric proportion if, for example, a composition containing an excess of one of the reactants is desired and come within the scope of the process of the invention.

Generally, the molar ratio (Zn): (the element or elements A) ranges from 0.001 to 10, in particular ranges from 0.01 to 5.

By way of example, the source of the zinc element having a +2 oxidation state is generally chosen from one or more of the following compounds: zinc oxide (ZnO), zinc peroxide (ZnO ₂ ), zinc hydroxide (Zn (OH) ₂ ) and zinc carbonate (ZnCO ₃ ) or a precursor thereof.

Preferably, the source of the zinc element is chosen from: zinc oxide (ZnO), zinc hydroxide (Zn (OH) ₂ ), zinc carbonate (ZnCO ₃ ) or a precursor thereof.

Even more preferably, the source of the zinc element is chosen from: zinc oxide (ZnO). In general, the source of said element (s) A is in the form of an oxide, a dioxide, a peroxide, a hydroxide, a di- or trihydroxide, a hydroxide oxide, carbonate, or a precursor thereof.

As mentioned above, the element or elements A are independently selected from a metal, a metalloid or a lanthanide, "A" being however different from zinc and also different from Ca when it is not combined with another element A .

Said element (s) A may be chosen in particular from:

alkali metals: lithium (Li), sodium (Na), cesium (Cs); the following alkaline earth metals: magnesium (Mg), strontium (Sr), barium (Ba), calcium (Ca);

the following transition metals: titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), niobium (Nb), molybdenum (Mo), cadmium (Cd), hafnium (Hf), tantalum (Ta);

the following poor metals: aluminum (Al), gallium (Ga), indium (In); bismuth (Bi);

the following metalloids: silicon (Si), boron (B);

the following lanthanides: lanthanum (La); and

one of their combinations.

In general, the element (s) A are independently selected from: Fe, Mg, Ni, Ti, Sr, Ba, Al. In particular, Fe, Mg, Ni and Ti are preferred.

Thus, within the meaning of the invention, the source of the element (s) A may be chosen from:

LiOH, Li ₂ CO ₃ or a precursor thereof, so in particular to obtain, after calcination, lithium zincate crystals of formulas: ZnLi ₂ 0 _2, ZnLi ₆ 0 ₄ , Li ₄ ZnO ₃ or Zn ₄ Li ₁₀ O ₉ ;

NaOH, Na ₂ CO ₃ , Na ₂ O or a precursor thereof, so in particular to obtain, after calcination, sodium zincate crystals of formulas: Na ₂ Zn ₂ O ₃ , Na ₂ ZnO ₂ or Nai _O Zn ₄ O ₉ ;

CCs ₂ 0 ₃ , Cs (OH) -yH ₂ O or a precursor thereof, so in particular to obtain, after calcination, cesium zincate crystals of formulas Cs ₂ ZnO ₂ ;

- MgO, Mg (OH) ₂ , MgCO ₃ , C ₄ Mg ₄ O ₁₂ -H ₂ MgO ₂ -xH ₂ 0 or one of their precursors so as to obtain, in particular after calcination, magnesium zincate crystals corresponding to the general formula Zn _x Mg _1-x O, where 0 has a value strictly greater than 0 and strictly less than 1 (namely 0 <x <1), such that Zn _1/3 Mg _2/3 0 or else, Zn _1/2 Mg _1/2 0; CaO, CaCO ₃ , Ca (OH) ₂ or one of their precursors, provided that, after calcination, crystals of calcium zincate Ca [Zn (OH) ₃ ] ₂ ; Sr (OH) ₂ , SrO, SrC0 ₃ or SrO ₂ , or one of their precursors, so as to obtain at the end of step (3) SrZn (OH) ₄ .H ₂ O and after calcination (at the result of step 5) strontium zincate crystals can meet the general formula Zn _x Sr _1-x O, where 0 has a value strictly greater than 0 and strictly less than 1, such as Zn _1/2 Sr _1/2 0 is ZnSr0 ₂ ;

BaO, BaO ₂ , BaCO ₃ , Ba (OH) ₂ or one of their precursors, so as to obtain at the end of step (3) Ba ₂ Zn (OH) ₂ .H ₂ O and after calcination ( after step 5) barium zincate crystals may have the general formula Zn _x _Bai-x O, where x has a value strictly greater than 0 and strictly less than 1, such as Zn _1/3 Ba _2/30 ;

TiO, TiO ₂ , H ₂ TiO ₃ or one of their precursors, so in particular to obtain, after calcination, titanium zincate crystals of formulas: Zn ₂ TiO _4, ZnTi ₃ 0 ₈ or ZnTi0 ₃ ; according to this mode, the following reaction can take place

ΖηΟ + 2 ΤΊ0 ₂ → Ζη ₂ ΤΊ0 ₄ .

Cr0 ₃ , Cr ₂ 0 ₃ , Cr ₂ (CO ₃ ) ₃ , Cr (OH) 3 or one of their precursors so as to obtain in particular chromium zincate crystals of formulas: ZnCr ₂ 0 ₄ or ZnCrO ₄ ;

Mn (OH) ₃ , Mn (OH) ₂ , MnO, Mn ₂ 0 ₃ or a precursor thereof, in particular to obtain manganese zincate crystals of formula ZnMn ₂ 0 ₄ ;

Fe ₂ O ₃ , FeO (OH), Fe (OH) ₃ , FeCO ₃ , Fe ₃ O ₄ or a precursor thereof, so as to obtain, in particular after calcination, iron zincate crystals corresponding to the formula ZnFe ₂ O ₄ ;

CoO, Co ₃ O ₄ , Co ₂ O ₃ , CoCO ₃ , Co (OH) ₂ , or one of their precursors _, so as to obtain, in particular after calcination, cobalt zincate crystals corresponding, for example, to the formula ZnC0 ₂ 0 ₄ (provided of course that the source of calcium is mixed with a source of another element A);

NiO, Ni ₂ O ₃ , Ni (OH) ₂ , NiO (OH), NiCO ₃ or a precursor thereof _, so in particular to obtain, after calcination, nickel zincate crystals corresponding to the general formula Ni _x Zn _1-x O, where x has a value strictly greater than 0 and strictly less than 1 (namely 0 <x <1), preferably 0.7 <x <1, or correspond to ZnNi ₂ 0 ₄ ;

Cu (OH) ₂ , CuCO ₃ , CuO, Cu ₂ O or a precursor thereof _, so as to obtain, in particular after calcination, copper zincate crystals corresponding, for example, to the formula ZnCu ₂ O ₄ ; - Zr (OH) ₄ , Zr (OH) ₂ CO ₃ -ZrO ₂ , ZrO ₂ , or one of their precursors, so in particular to obtain, after calcination, zirconium zincate crystals of formula ZrZn ₂ 0 ₄ ;

Nb ₂ 0 ₅ , Nb (OH) ₅ , NbO ₂ , or one of their precursors, so in particular to obtain, after calcination, niobium zincate crystals of formula

ZnNb ₂ 0 ₆ ;

Mo0 ₃ , MoO <, or one of their precursors, so in particular to obtain, after calcination, molybdenum zincate crystals of formula MoZnO ₄ ; Cd (OH) ₂ , CdO, CdC0 ₃ or a precursor thereof, so in particular to obtain after calcination of cadmium zincate crystals of formula

ZnCd0 ₂ ;

- Ta (OH) ₅ , Ta ₂ 0 ₅ or a precursor thereof, so in particular to obtain after calcination of tantalum zincate crystals of formula ZnTa ₂ 0 ₆ ;

- Al (OH) ₃ , AlO (OH), Al ₂ O ₃ or a precursor thereof, so in particular to obtain after calcination of aluminum zincate crystals of formula

ZnAl ₂ O ₄ ;

Ga (OH) ₃ , Ga ₂ O ₃ or a precursor thereof, so in particular to obtain, after calcination, gallium zincate crystals of formula ZnGa ₂ O ₄ ;

ln (OH) ₃ , ln ₂ 0 ₃ or one of their precursors, so in particular to obtain, after calcination, indium zincate crystals of formula Znln ₂ 0 ₄ ;

Sn (OH) ₂ , SnO ₂ , SnO or one of their precursors, so in particular to obtain after calcination tin zincate crystals of formulas: Zn ₂ Sn0 _4, ZnSn ₂ 0 ₄ or ZnSn0 _3.

- La ₂ 0 _3, La ₂ (C0 ₃₎ _3, La (OH) ₃ or a precursor thereof, in particular so to obtain, after calcination zincate crystals of lanthanum formula:

ZnI_a ₂ 0 _4;

- Si0 ₂ , H ₂ SiO ₃ or a precursor thereof, so in particular to obtain after calcination of silicon zincate crystals of formula: Zn ₂ SiO _4;

- or one of their combinations.

For the purposes of the invention, "precursor" means any chemical compound, which in contact with water, moisture and / or air (C0 ₂ , etc.) can synthesize the aforementioned compounds. By way of example, Li ₂ O ₂ (peroxide) makes it possible to form lithium hydroxide LiOH by reacting with water. The precursors thus include, for example, the following compounds: Li ₂ O / Li ₂ O ₂ / Na ₂ O ₂ / MgO ₂ , etc.

In general, the sources of zinc and element A or elements are in the form of powder.

For example, zinc oxide suitable for the present invention is also in powder form and generally has a lower particle size or equal to 100 μηι, preferably less than or equal to 50 μηι. Preferably, the size of the particles is greater than or equal to 0.01 μηι, in particular greater than or equal to 10 μηι, such that greater than or equal to 20 μηι. Zinc oxide of CAS number: 1314-13-2 and marketed for example by AMPERE Industrie, of purity greater than or equal to 99.9%, is suitable for carrying out the process of the invention.

The source of the element A or elements is also in the form of powder. In general, the particle size is less than or equal to Ι ΟΟμηη, in particular less than or equal to 50 μηη and preferably less than or equal to 20 μηη. Thus, it is not necessary for the source of element A to be at the nanoscale.

For example, the magnesium hydroxide that is suitable for the present invention preferably has a particle size of less than or equal to 100 μηη and preferably less than or equal to 50 μηι, and in particular the particle size ranges from 0.01 μπΊ to 20 μηη. . The magnesium hydroxide of CAS number 1309-42-8, and sold for example by the company Toplus Inc., of purity greater than or equal to 99%, is suitable for carrying out the process of the invention.

Preferably, the source of zinc and the source of the element (s) A have a high purity, in general greater than or equal to 90%, in particular greater than or equal to 95% and typically greater than or equal to 99%, or even greater than or equal to at 99.9%.

Once the initial suspension is prepared, it is brought to the three-dimensional micro-bead mill 1 generally via the adjustable-rate peristaltic pump via the inlet 5. The peristaltic pump makes it possible to continue the mixing of the suspension In addition, as indicated above, this pump makes it possible to introduce the starting suspension into the chamber 2 with a controlled flow rate.

Generally, the starting suspension is introduced at a flow rate greater than or equal to 10 L / h.

For the purposes of the invention, "a flow rate greater than or equal to 10 L / h" comprises the following values: 10 L / h; L / h; 20 L / h; L / h; L / hr; L / h; 40 L / h; 45 L / h; 55 L / h; 60 L / h; 65 L / h; 70 L / h; 80 L / h; 85 L / h; 90 L / h; 95 L / h; 100 L / h; 1 L / h; 120 L / h; 130 L / h; 140 L / h; 150 L / h; 50 L / h; 55 L / h; 60 L / h; 65 L / h; 70 L / h; 75 L / h; 80 L / h; 85 L / h; 90 L / h; 95 L / h; 100 L / h; 105 L / h; 1 L / h; 1 L / hr; 120 L / h; 125 L / h; 130 L / h; 135 L / h; 140 L / h; 145 L / h; 150 L / h; 155 L / h; 160 L / h; 165 L / h; 170 L / h; 175L / h; 180 L / h; 200 L / h; 300 L / h; 400 L / h; 500 L / h; 600 L / h; 700 L / h; 800 L / h; 900L / h; 1 m ³ / h; 2 m ³ / h; 3 m ³ / h; 4 m ³ / h; 5 m ³ / h; 6 m ³ / h; 7 m ³ / h; 8 m ³ / h; 9 m ³ / h; 10 m ³ / h; 1 m ³ / h; 12 m ³ / h; 13 m ³ / h, 14 m ³ / h, 15 m ³ / h etc., or any intervals between these values. In particular, the starting suspension is introduced at a flow rate ranging from 10 to 130 L / h, preferably from 20 to 100 L / h and typically from 30 to 90 L / h.

Of course, the flow rates may vary depending on the size of the three-dimensional micro-bead mill used to carry out the process. For example, for a three-dimensional microbead mill having a stationary chamber 2 of 0.5L volume, the flow rate may be of the order of 40 to 150L / h, such as about 45 L / h; while for larger mills having in particular a stationary chamber 2 of 60L, the flow rate may be of the order of 2 to 15 m ³ / h, such as about 4 m ³ / h.

Once the starting suspension is introduced into the chamber 2, the grinding step (2) begins.

Under the effect of the current created by the flow rate, the starting suspension traverses the stationary chamber 2 of the inlet 5 to the outlet 6, while being set in motion by the stirrer 8 which allows intense mixing of this suspension with the microbeads and, if necessary, with the disks 10, the fingers 1 1, etc., along the inner wall 9 of the chamber 2.

The rotational speed of the stirrer may for example vary from 4 to 20 pi rad / s, preferably from 4 to 8 pi rad / s.

According to the invention, "a rotation speed ranging from 4 to 20 pi rad / s" comprises the following values: 20; 19; 18; 17; 16; 15; 14; 13; 12; 1 1; 10; 9; 8; 7; 6; 5; 4 and any intervals between these values.

The residence time of the starting suspension is less than or equal to 15 min, preferably less than or equal to 1 minute, and goes especially in the mill from 5 to 25 seconds and in particular from 10 to 20 seconds. It is in fact inherent to the apparent volume of the balls and the flow of passage.

For example, if the total apparent volume of the beads is 270 cm ³ (bulk density beads 3.7 g / cm ³ ) for a chamber volume of 360 cm ³ and the rate of introduction of the suspension is of 30 L / h, or 8.3 cm ³ / s, then the residence time of the suspension in the chamber 2 is estimated at about 1 1 seconds. Therefore, the residence time can be advantageously adjusted, for example by controlling the apparent density of the microbeads, as well as the flow rate.

By "apparent volume" is meant the volume of microbeads including interstitial air between the beads. Bulk density is the ratio of microbead mass to apparent volume.

In addition, by varying the size of the microbeads and the flow rate, more or less fine crystals can be obtained. For example, a finer grinding can be obtained if the flow rate of the starting suspension is slowed down. The grinding step can be carried out in continuous mode or discontinuous mode in one or more passes (pendulum or recirculation mode).

When it is carried out in batch mode, the number of passages of the so-called initial suspension may be from 1 to 10, preferably from 1 to 5 (ie, after a first pass, the suspension is recovered at the outlet 6 and reinjects it again, thanks to the pump, into the chamber 2 via the inlet 5 to allow a second passage). In particular, the number of passages of the starting suspension is 1.

Indeed, the Applicant has noticed that a single passage through the microbead mill, despite a very short residence time, was sufficient to carry out the process according to the invention and to allow the synthesis of crystals, hydrated or not, of zincate. or A elements.

Thus, this grinding step will preferably be performed in continuous mode.

Advantageously, this grinding step takes place at an ambient temperature of less than or equal to 50 ° C., that is to say, most often at an ambient temperature ranging from 15 ° C. to 45 ° C., in particular from 18 ° C. to 35 ° C., and in general is of the order of 20 ° C to 25 ° C. Indeed, this step according to the invention does not require any particular heating in order to obtain, either at the end of the recovery step (3), or at the end of the calcination step (5), zincate crystals. In particular, the starting / starting suspension reagents are introduced into the mill at room temperature (generally around 20-25 ° C.). However, depending on the starting reagents used, an exothermic reaction may take place during this grinding stage and the temperature rises slightly (generally the outlet temperature of the mill is less than or equal to 50 ° C. VS).

Once the grinding step (2) has been performed, the output recovery of said three-dimensional microbead mill is carried out with a final suspension comprising:

most of the crystals, most often hydrated, of zincate or elements A (especially when the starting reactants are in stoichiometric proportion and they make it possible to form an acid-base reaction with the liquid medium), of purity and very satisfactory size (first embodiment);

either the starting reagents in activated form (second variant embodiment). As mentioned above, the microgrinding performed in step 2, even if it does not directly allow the synthesis of zincate crystals according to this mode, however, allows to activate the starting reagents, which will allow by the subsequently to facilitate the calcination step and thus the synthesis of the crystals during this last step.

Optionally, following the recovery step (3), said final suspension described above is concentrated or dried, so as to obtain respectively a powder or a crystal concentrate (generally hydrated) of zincates of said element (s) A or a powder or a concentrate of starting reagents in activated form.

According to an embodiment characteristic, the final suspension can be dried in the open air.

According to another characteristic embodiment, the final suspension may be dried by drying or by calcination, such as at a temperature of 50 to 400 ° C for 1 to 4 hours.

The dried or concentrated product is generally stored until used as an aqueous paste or mixed with a solvent. It can also be dried and stored in a sealed container.

If necessary, following the recovery step (3) or following the drying step (4), one proceeds to the calcination (5) of said final suspension described above.

For this, the final suspension recovered after step (3) or the powder or concentrate recovered after step (4) is placed in crucibles, which may be porcelain or alumina, and then calcined (5) in an oven, for example a stationary oven or a passage oven. This calcination step generally takes place at a temperature between 400 ° C. and 1500 ° C., preferably between 500 ° C. and 1400 ° C., and particularly between 600 ° C. and 1250 ° C .; for a period of time for example between 30 minutes and 4 hours, preferably between 30 minutes and 1 hour 30 minutes.

By way of example, the calcination temperatures for the elements A below may be as follows (indicative data):

^* Minimum recommended calcination temperature

Those skilled in the art will be able to adapt the calcination temperature according to the nature of the element A and crystals that wish to be manufactured. Also, the minimum temperature is given as an indication, and will depend on the type of calcination furnace, or the presence of moisture during calcination.

The process according to the invention thus makes it possible to manufacture zincate crystals of the element (s) A.

In particular, according to the first embodiment variant, the calcination of said final suspension obtained at the end of step (3) when it comprises said zincate crystals of said element (s) A in hydrated form or, of the powder or concentrate obtained at the end of step (4) when it comprises said crystals of zincate of said one or more elements A in hydrated form, makes it possible to form non-hydrated crystals of zincate of said element (s) A.

Also, according to the second embodiment variant, the calcination of said final suspension obtained at the end of step (3) when it comprises said starting reagents in activated form, or of the powder or concentrate obtained (e.g. ) at the end of step (4) when it (it) comprises said starting reagents in activated form, can form crystals, generally non-hydrated, zincate said element (s) A.

According to one embodiment, the crystals thus obtained (after calcination) can meet the following general formula: Zn _x A _y O, where 0 <x <1 and 0 <y <1, 5 and may correspond to the crystals of the formulas: ZnLi ₆ 0 ₄ , Nai ₀ Zn ₄ O ₉ , BaZnO ₂ , ZnCr ₂ 0 ₄ or ZnCu ₂ O ₄ .

Preferably according to this mode, y = 1 _-x and the zincate crystals obtained correspond to the following general formula: Zn _x Y _1-x O with 0 <x <1 (discrete values, or continuous ranges depending on the nature of A). The following elements A in particular make it possible to form zincate crystals forming part of this general formula: Ba, Cd, Sr, Mg, Ti, Ni.

For example, in a non-exhaustive list, the following stoichiometries can be found (Table 2):

Table 2

According to a second embodiment, the method according to the invention makes it possible to manufacture zincate crystals of several elements A, denoted "A1", "A2", "An", etc. According to this mode, the crystals thus obtained (after calcination) may for example satisfy the following general formula: A1 _v (Zn _x A2 _w ) 0 ₃ , with 0 <x <1; 0 <v≤1 and 0 <w <1. Advantageously, according to this mode, w = (1 -x) and / or v = 1. Even more advantageously, v = 1, x = 1/3 and w = 1-x = 2/3. Thus, the following crystals can be obtained according to the process of the invention after calcination: Ba (Zn _1/3 Nb _2/3) 03, Ba (Zn _1/3 Ta _2/3) 03, Sr (Zn _1/3 Nb _2/3) 03, Sr (Zn _1/3 Ta _2/3) 03, Ca (Zn _1/3 Nb _2/3) 03 or

The present invention also relates to the use of the zincate crystals of said element or elements A obtained according to the process for producing catalysts, materials having dielectric properties, photo catalysis or photoluminescence, chemical absorbents or antibacterial agents.

For example, ZnTiO ₃ titanium zincate can be used as an absorbent for azo dyes, or as an antibacterial agent, as mentioned in the publication "Synthesis, structural characterization of nano ZnTi0 ₃ ceramic: an effective azo dye adsorbent and antibacterial agent Published by RS Raveendra et al., In the Journal of Asian Ceramic Societies 2 (2014), 357-365; Also, A. Stoyanova et al. recall that ZnTi0 ₃ can also be used as a dielectric material, as photocatalytic material, or catalyst, in their publication entitled "Synthesis, photocatalytic and antibacterial properties of nanosized ZnTi0 ₃ powders obtained by different sol-gel methods" published in 2012 in the "Digest Journal of Nanomaterials and Biostructures »Volume 7.

Similarly, for example, nickel zincate Ni _0.7 Zn _0.3 O is contemplated as the electrode material for supercapacities, as reported by KK Upadhyay et al., In the publication "Hydrothermally grown Ni _0.7 Zn _0.3 O directly on carbon fiber paper substrate as an electrode material for energy storage application "published in 2016 in the" International Journal of Hydrogen Energy ".

EXAMPLES

The description of the tests below is given by way of purely illustrative and nonlimiting example.

Characterization

✓ MEB

Scanning electron microscopy (SEM) was performed on a Zeiss EVO MA 15 device, in secondary electrons and backscattered (chemical contrast) with a primary beam of 5 to 20 kV.

✓ DRX

X-ray diffractometry (XRD) spectra were collected with a D8 ADVANCE Series II diffractometer sold by Bruker using CuKal radiation (0.15406 nm) according to the Bragg-Brentano configuration.

The detector used is a LynxEye 1 D detector from Bruker. The opening angle of the detector is 3 ° (150 bands).

The XRD measurements were performed between 10 ° and 140 ° (at 2 ° scale) with a step of 0.008 ° (1 s / step). B ° Procedure for the preparation of the tested samples

Equipment

The tests were carried out in a three-dimensional Dyno Mill MultiLab micro-bead mill from Willy A. Bachofen AG which contains 1 KG of microbeads.

The microbeads are made of zirconium oxide and have a diameter of 0.5 mm.

The characteristics of the microbeads used for the tests are summarized in Table 3 below:

Table 3

Microbeads of 500 μηη are marketed under the brand name Zirmil® Y Ceramic Beads by Saint-Gobain.

The crushing chamber of the mill has a capacity of 309 ml and is filled, by volume, relative to its total volume and depending on the tests, 80% of the microbeads described above.

In operation, the microbeads are agitated by an agitator at a rotation speed of 2890 rpm. The agitator further comprises two polyurethane mixing discs of 64mm diameter.

Raw materials

For the tests, the raw materials of departure are:

zinc oxide (ZnO) having a purity greater than or equal to 99% marketed by A.M.P.E.R.E. Industry;

the source of the metallic element A is chosen from:

magnesium hydroxide (Mg (OH) ₂ ) of purity greater than or equal to 99% marketed by Toplus Inc;

titanium dioxide (TiO ₂ ) of 98.5% purity marketed by the company Univar;

o strontium hydroxide octohydrate (Sr (OH) ₂ -8H ₂ O) of purity greater than or equal to 98% marketed by Chongquing Hua'nan Sait Chemical Co, LTD;

iron oxide hydroxide (FeOOH) with a purity greater than or equal to 99% marketed by the company Boss Chemical Industry Co, LTD. General procedure implemented for the tests:

To perform each test below, the following steps are performed: - a starting slurry is prepared (1) in a beaker from the zinc oxide and the mineral source of the metallic element, in stoichiometric proportion, in a liquid phase (water), then the starting slurry is stirring with a magnetic stirrer;

it is then fed, via a peristaltic pump with an adjustable flow rate to the Dyno Mill MultiLab mill described above: the throughput rate in the mill can reach 60 l / h;

- The starting suspension is then ground in the three-dimensional mill (2) having microbeads of 0.5 mm in diameter for a certain time (which depends on the flow rate of the starting suspension) at room temperature (20-25 °). C), thus making it possible, at the outlet of the mill, to obtain an intimate and homogeneous mixture of the initial reactants;

then, generally speaking, a final suspension comprising either the activated starting reagents or the zincate crystals of the element A or elements (generally in hydrated form) is recovered (3);

- Then, this final suspension is dried (4) in an oven at 80 ° C for 1 hour;

- Finally, the final dried suspension thus obtained is calcined (5) at a temperature between 700 ° and 1200 ° C, in a stationary oven. The duration of the calcination is fixed at 1 h.

for ranges of continuous stoichiometry such as 0.65 <x <1, using the hydroxide as the mineral source of the metallic element (FIGS. 3, 4 and 5)

The aim of this example is to obtain magnesium zincate crystals Mg _× Zn _{1 ×} O on values of the continuous x value ranges. Specifically, over the range of x ranging from 0.65 to 1, the following compositions: Mg ₀ 65 d _0, 35O, MgO 7 ₅ mg _0, 250, or Mg _0.88 d _0, I2O, can be performed.

The crystals of magnesium zincate were synthesized according to the general procedure mentioned above, with initial suspensions containing 600 g of reagents (ZnO + Mg (OH) ₂ ) per liter of solvent (water), with a single passage in the grinder at a flow rate of 30 l / h, and using in particular the following calcination parameters (Table 4):

Table 4 Referring to Figure 3, we see that the lines of the XRD spectrum obtained for magnesium zincate Mg _0, 65Zn _0, 35O are very close to those of the reference spectrum of the Mg _0.68 Zn _0, 32O, known to those skilled in the art (according to JCPDS 04-019-1259), both for their angular positions and for their relative intensities. It should however be noted that the cards known to those skilled in the art are not complete on the continuous range studied in this example. Thus, a slight adjustment of the mesh parameters was necessary to adapt the existing plug. This approach appears consistent because the lines of the DRX spectrum confirm the presence of a single compound.

We note the presence of the three main peaks (crystallographic planes [1 1 1],

[200] and [220]) at respectively 36.7217 42.658 ° and 61.913 °. In addition, all other significant peaks are present at the predicted angles, such as 74.195 °; 78.099 °; 108.842 °; with substantially the expected intensities.

Referring to Figure 4, we see that the lines of the XRD spectrum obtained for magnesium zincate Mg _0.75 Zn _0, 2 ₅ O are consistent with those of the Mg in the reference spectrum _0.75 Zn _0, ₅ O 2, known to those skilled in the art (according to JCPDS 04-06-7454), both in their angular positions as their relative intensities. So :

we note the presence of the three main peaks (crystallographic planes [1 1 1], [200] and [220]), respectively at 36.7777 42.724 ° and 62.014 °,

- all other significant peaks are present at the predicted angles, such as

78.236; 109.077; 74.322 °; with substantially the expected intensities. Referring to Figure 5, we see that the lines of the XRD spectrum obtained for magnesium zincate Mg _0.88 Zn _0, I2O are in accordance with those of the reference spectrum of the Mg _0.88 Zn _0, I2O, known to those skilled in the art (according to JCPDS 04-019-1257), both for their angular positions and for their relative intensities. So :

we note the presence of the three main peaks (crystallographic planes [1 1 1], [200] and [220], respectively 36.7807 42.727 ° and 62.019 °,

- all other significant peaks are present at the predicted angles, such as 78.242 °; 109.089 °; 126.331 °, with substantially the expected intensities.

These three XRD spectra also show that the samples analyzed have excellent purity. Indeed, no contamination is listed:

- the main peaks of ZnO (according to JCPDS 04-003-2106), which are at 31, 7667 34,4197 36,2517 56,591 ° do not appear there;

the main peaks of Mg (OH) ₂ (according to JCPDS 04-01 1 -5938), which are at 37.9847 18.5807 50.815 ° do not appear there either;

- the main peaks of MgO (according to JCPDS 04-010-4039), which are 42.8887 62.266 ° do not appear either. In conclusion, the process of the invention makes it possible to easily obtain highly pure magnesium zincate crystals, Mg _× Zn _1-x O for continuous stoichiometry ranges, for example for 0.65 <x <1, and , using a hydroxide as the mineral source of the metallic element

D Characterization of titanium zincate crystals Zn 3 TiCl 4 obtained using a dioxide as a mineral source of the metallic element

The crystals of titanium zincate were synthesized according to the general procedure mentioned above, with initial suspensions containing 300 g of reagents (ZnO + TiO ₂ ) per liter of solvent (water), with two successive passes in the mill at a rate 30L / h. The calcination was carried out at 1050 ° C for 1 hour.

Referring to FIG. 6, it can be seen that the lines of the XRD spectrum obtained for titanium zincate Zn ₂ TiO ₄ are consistent with those of the reference spectrum of Zn ₂ TiO ₄ , known to those skilled in the art ( according to JCPDS 04-015-4152), both for their angular positions and for their relative intensities.

So :

we note the presence of the three main peaks (crystallographic planes [220], [31 1] and [440], respectively at 29.8137 35.1 13 ° and 61.927 °,

- all other significant peaks are present at the predicted angles, such as 42.7127 56.4057 88.629 °; with substantially the expected intensities.

The XRD spectrum also shows that the sample analyzed has excellent purity. Indeed, no contamination is listed:

- the main peaks of ZnO (according to JCPDS 04-003-2106), which are at 31, 7667 34.4197 36.2517 56.591 ⁰ are very low;

- the main peaks of Ti0 ₂ (according to JCPDS 00-021 -1272), which are at 25.2817

48.050 ° / 53.891 ⁰ do not appear there.

In conclusion, the process of the invention makes it possible to easily obtain pure titanium zincate Zn ₂ TiO ₄ crystals, and this, by using a dioxide as the mineral source of the metallic element.

E. Characterization of iron zincate crystals ZnFe · Q4 obtained using a hydroxide oxide as a mineral source of the metallic element

The iron zincate crystals were synthesized according to the general procedure mentioned above, with initial suspensions containing 300 g of reagents (ZnO + FeOOH) per liter of solvent (water). It should be noted that we initially used a molar ratio (Fe): (Zn) equal to 1, in order to obtain a final powder containing iron zincate ZnFe ₂ O ₄ as well as an excess of ZnO with a molar ratio of 1 . Only one passage in the mill at a rate of 30L / ha was performed. The calcination was carried out at 1200 ° C for 1 h.

Referring to FIG. 7, it can be seen that the lines of the DRX spectrum obtained for the iron zincate ZnFe ₂ 0 ₄ are consistent with those of the reference spectrum of ZnFe ₂ 0 ₄ , known to those skilled in the art ( according to JCPDS 04-006-8036), both for their angular positions and for their relative intensities.

So :

we note the presence of the three main peaks (crystallographic planes [222], [400] and [440]), respectively at 36.7727 42.718 ° and 62.005 °,

- all other significant peaks are present at the predicted angles, such as

56.475 ° / 88.765 52.983 °; with substantially the expected intensities. Also, as an over-stoichiometry of ZnO has been introduced, we find:

- the main peaks (according to JCPDS 04-003-2106), which are at 31, 7667 34.4197 36.2517 56.591 °;

- all other significant peaks are present at the predicted angles, such as 47.535 ° / 62.8527 67.942 °; with substantially the expected intensities.

In conclusion, the process of the invention makes it easy to obtain a powder containing ZnFe ₂ O ₄ iron zincate crystals and ZnO crystals, using a hydroxide oxide as the mineral source of the metal element. It will be pointed out that the use of the appropriate stoichiometry initially makes it possible to obtain pure ZnFe ₂ 0 ₄ iron zincate crystals under the same conditions.

F ° Particular case of obtaining a stable intermediate hydrated zincate: characterization of crystals of strontium zincate SrZnfOHk-HpO

The SrZn (OH) ₄ -H ₂ 0 hydrated zincate strontium crystals were synthesized based on steps (1) to (4) of the general procedure mentioned above. Thus, the calcination step (5) has not been carried out.

The synthesis was carried out with an initial suspension containing 100 g of reagents (ZnO + Sr (OH) ₂ ) per liter of solvent (water). A single passage in the mill at a rate of 30L / ha was performed.

The electron-scanning microscopy images, one of which is presented in FIG. 8, show the crystals of hydrated strontium zincate synthesized. We observe that the conversion is close to 100%.

Referring to FIG. 9, it can be seen that the lines of the DRX spectrum obtained for the hydrated strontium zincate are in agreement with those of the reference spectrum of SrZn (OH) ₄ -H ₂ O, known to the human of the profession (according to JCPDS 04-012-2174), both for their angular positions and for their relative intensities. So : we note the presence of the three main peaks (crystallographic planes [100], [021] and [-123]), respectively at 16.4037 34.696 ° and 46.890 °,

- all other significant peaks are present at the predicted angles, such as 24.5927 31.1997 32.430 °; with substantially the expected intensities. The XRD spectrum also shows that the sample analyzed has excellent purity. Indeed, no contamination is listed:

- the main peaks of ZnO (according to JCPDS 04-003-2106), which are at 31, 7667 34.4197 36.2517 56.591 are very low;

- the main peaks of Sr (OH) ₂ (according to JCPDS 00-027-0847), which are 28.4947 30.7757 43.232 ° do not appear there.

In conclusion, the process of the invention makes it possible easily to obtain crystals of pure SrZn (OH) ₄ -H ₂ 0 hydrated strontium zincate, without including step (5) of the general procedure. G ° Conclusion

Thus, it has been demonstrated, after control by XRD analysis, that different zincates have been synthesized (all the XRD spectra carried out by the Applicant show an integral transformation of the starting compounds). It has been demonstrated that several mineral sources of the metallic element can be used in the method of the invention. On the other hand, it has been shown that zincates, of the empirical formula Zn _x A _1-x O, have been synthesized by the present invention for discrete values of x, but also for values of x varying over a range. given.

In addition, the laboratory mill makes it possible, for example, to produce 54 kg / h of crystals of the various zincates. This figure could be multiplied by 10 with the addition of an accelerator accessory. Also, there are industrial versions of the mill using for example up to 100 kg of beads. With this type of mill, it would therefore be possible to manufacture several tons per hour of different zincates.

Claims

1. A method of manufacturing zincate crystals of one or more element (s) other than zinc (Zn), denoted by "A" independently selected from a metal, a metalloid or a lanthanide, with the exception zincate crystals comprising as element A only calcium (Ca), said process comprising at least the following steps:

(4) optionally, drying or concentrating the final suspension obtained at the end of step (3), so as to obtain a powder or a concentrate comprising, respectively, said starting reagents in the form of activated or said zincate crystals, generally in hydrated form, of said element (s) A;

(5) if applicable, calcination:

of said final suspension obtained at the end of step (3) when it comprises said starting reagents in activated form, or

the powder or concentrate obtained at the end of step (4) when it comprises said starting reagents in activated form,

so as to obtain crystals, generally not hydrated, zincate said element (s) A.

2, Process according to claim 1, comprising a calcination step: of said final suspension obtained at the end of step (3) when it comprises said zincate crystals of said element (s) in hydrated form or,

so as to obtain unhydrated crystals of zincate of said element (s) A.

The process according to claim 1 or claim 2, wherein the calcining step (5) is carried out at a temperature of between 400 ° C and 1500 ° C, preferably between 700 ° C and 1250 ° C for duration preferably ranging from 15 minutes to 3 hours, in particular from 30 minutes to 1 hour 30 minutes.

4. Process according to any of the preceding claims, wherein the source of the zinc element and the source of said element (s) A are mixed in the starting slurry in stoichiometric proportion.

5. The process as claimed in any one of the preceding claims, wherein the source of the zinc element is chosen from one or more of the following compounds: zinc oxide (ZnO), zinc peroxide (ZnO ₂ ), zinc hydroxide (Zn (OH) ₂ ) and zinc carbonate (ZnCO ₃ ) or a precursor thereof; preferably, the source compound of the zinc element is chosen from: zinc oxide (ZnO), zinc hydroxide (Zn (OH) ₂ ), zinc carbonate (ZnCO ₃ ) or a precursor thereof .

6. Process according to any one of the preceding claims, in which the source of said element (s) A is in the form of: an oxide, a dioxide, a peroxide, a hydroxide, a a di- or trihydroxide, a hydroxide oxide, a carbonate, a precursor thereof or a mixture thereof.

7, Process according to any one of the preceding claims, wherein said element (s) A are chosen from:

the following transition metals: titanium (Ti), chromium (Cr), manganese

(Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), niobium (Nb), molybdenum (Mo), cadmium (Cd ), hafnium (Hf), tantalum (Ta);

the following metalloids: silicon (Si), boron (B);

the following lanthanides: lanthanum (La); and

one of their combinations.

8. Method according to any one of the preceding claims, wherein the source of said element (s) A is chosen from:

LiOH, U2CO ₃ or a precursor thereof;

NaOH, Na ₂ CO ₃ , Na ₂ O or a precursor thereof;

Cs ₂ CO ₃ , Cs (OH) -yH ₂ O or one of their precursors,

MgO, Mg (OH) ₂ , MgCO ₃ , C ₄ Mg ₄ O ₂ -H ₂ MgO ₂ -xH ₂ O or a precursor thereof;

CaO, CaCO ₃ , Ca (OH) ₂ or a precursor thereof;

Sr (OH) ₂ , SrO, SrCO ₃ or SrO ₂ , or a precursor thereof;

BaO, BaO ₂ , BaCO 3, Ba (OH) ₂ or a precursor thereof;

TiO, ΤΊΟ ₂ , H ₂ TiO ₃ or one of their precursors;

Cr0 ₃ , Cr ₂ 0 ₃ , Cr ₂ (CO ₃ ) ₃ , Cr (OH) 3 or a precursor thereof;

- Mn (OH) ₃ , Mn (OH) ₂ , MnO, Mn ₂ 0 ₃ or a precursor thereof;

Fe ₂ O ₃ , FeO (OH), Fe (OH) ₃ , FeCO ₃ , Fe ₃ O ₄ or a precursor thereof CoO, Co ₃ O ₄ , Co ₂ O ₃ , CoCO ₃ , Co (OH) ₂ , or one of their precursors; NiO, Ni ₂ O ₃ , Ni (OH) ₂ , NiO (OH), NiCO ₃ or a precursor thereof;

Cu (OH) ₂ , CuCO ₃ , CuO, Cu ₂ O, or a precursor thereof;

Zr (OH) ₄ , Zr (OH) ₂ CO ₃ -ZrO ₂ , ZrO ₂ , or one of their precursors;

Nb ₂ O ₅ , Nb (OH) ₅ , NbO ₂ , or a precursor thereof;

Mo03, Mo02, or one of their precursors;

Cd (OH) ₂ , CdO, CdC0 ₃ or a precursor thereof;

Ta (OH) ₅ , Ta ₂ 0 ₅ or a precursor thereof;

- Al (OH) ₃ , AlO (OH), Al ₂ O ₃ or a precursor thereof;

Ga (OH) ₃ , Ga ₂ O ₃ or a precursor thereof;

ln (OH) ₃ , ln ₂ 0 ₃ or a precursor thereof;

Sn (OH) ₂ , SnO ₂ , SnO, or one of their precursors;

La ₂ 0 _3, La ₂ (C0 ₃₎ _3, La (OH) ₃ or a precursor thereof ■

Si0 ₂ , H ₂ SiO ₃ or one of their precursors

or one of their combinations.

9. A process according to any one of the preceding claims, wherein the liquid phase is water (H ₂ 0).

10. The process as claimed in any one of the preceding claims, in which the microbeads are spherical in shape and have a mean diameter ranging from 0.05 mm to 4 mm, preferably from 0.2 to 3 mm, in particular from 0, 3 to 2 mm and typically of the order of 0.5 to 1 mm.

1 1. Process according to any one of the preceding claims, in which the microbeads have a Vickers hardness measured according to EN ISO 6507-1 greater than or equal to 900 HV1, preferably ranging from 900 HV1 to 1600 HV1, typically ranging from 1000 to 1400 HV1.

12. Process according to any one of the preceding claims, in which the microbeads have a real density ranging from 2 to 15 g / cm ³ .

13. The method according to any one of the preceding claims, wherein the three-dimensional micro-bead mill comprises at least:

a stationary grinding chamber of generally cylindrical shape extending along a longitudinal axis XX, said chamber being at least partially filled with said microbeads and comprising: at a first end, at least one inlet serving to introduce said starting suspension , and at a second end, an outlet having a separating means adapted to evacuate only the crystal suspension formed in said chamber; and

an agitator, arranged in the stationary grinding chamber, in the form of an elongate rod along the longitudinal axis XX, said stirrer being able to set in motion the microbeads / starting suspension assembly.

14. A method according to any one of the preceding claims, wherein the microbeads represent, in volume, based on the total volume of the stationary chamber of 5% to 85%, preferably 55% to 70%.

15. The method of any of the preceding claims, wherein the mill operates continuously.