阅读说明：本技术 制备合成矿物的方法 (Method for producing synthetic minerals ) 是由 M·克拉弗里 C·阿莫尼尔 C·卡勒梅 F·马丁 C·勒鲁 M·波里尔 P·米库 于 2020-02-11 设计创作，主要内容包括：本发明涉及用于制备合成矿物的方法和用于制备合成矿物前体的方法以及所述方法的产物。(The present invention relates to a process for the preparation of a synthetic mineral and a process for the preparation of a synthetic mineral precursor and the product of said process.)

1. A method for preparing a synthetic mineral, the method comprising: preparing a synthetic mineral precursor by a precipitation reaction between:

metal silicates and/or germanates, and

a salt of a divalent or trivalent metal,

wherein the precipitation reaction does not include the addition of an acid or hydroxide base reagent to chemically equilibrate the precipitation reaction.

2. The method of claim 1, wherein the synthetic mineral is a synthetic silicate, such as a synthetic phyllosilicate, for example wherein the synthetic phyllosilicate is a synthetic talc.

3. The method of claim 1 or 2, wherein the molar ratio of metal atoms to silicon and/or germanium atoms in the metal silicate and/or germanate is less than about 2, such as equal to or less than about 1.

4. A process according to any one of the preceding claims wherein the metal silicate and/or germanate is a metal disilicate or digermate, for example sodium disilicate and/or sodium metasilicate.

5. The method of any one of the preceding claims, wherein the divalent or trivalent metal salt is a magnesium salt or a zinc salt.

6. A process according to any one of the preceding claims wherein the divalent or trivalent metal salt is not a silicate or germanate.

7. The method of any one of the preceding claims, wherein the divalent or trivalent metal salt is a carboxylate (e.g., acetate), nitrate, nitrite, sulfate, sulfide salt, sulfite, bisulfate, bisulfite, halide salt, carbonate, bicarbonate, chlorate, chromate, dichromate, phosphate, hydroxide salt, thiosulfate salt, perchlorate salt, or a combination thereof.

8. The process according to any one of the preceding claims, wherein the precipitation reaction is carried out in the presence of a metal carboxylate of formula (R-COO) M ', wherein R is selected from hydrogen (-H) and alkyl groups comprising less than 5 carbon atoms, and M' is a monovalent metal.

9. The process of claim 8 wherein the metal carboxylate of formula (R-COO) M' is acetate.

10. The process of claim 8 or 9, wherein M' is the same metal as in the metal silicate and/or germanate.

11. The method of any one of claims 8 to 10, wherein M' is sodium or potassium.

12. The method according to any of the preceding claims, wherein the method further comprises a heat treatment process, such as a hydrothermal treatment process.

13. The method of claim 12, wherein the heat treatment process is performed at a temperature equal to or greater than about 100 ℃, and/or wherein the heat treatment process is performed at a pressure equal to or greater than about 5 bar.

14. The method of claim 12 or 13, wherein the heat treatment process is performed under supercritical conditions.

15. A synthetic mineral obtained and/or obtainable by the method of any one of claims 1 to 14.

Technical Field

The present invention generally relates to a method of making synthetic minerals such as synthetic phyllosilicates (e.g., synthetic talcs). The invention also relates to products and intermediate products of the above process and various uses of the above products.

Background

Mineral particles, including silicates such as germanates, germanosilicates, and germanosilicates, can be used for a variety of applications in a variety of industrial fields. For example, mineral particles can be used in thermoplastics, elastomers, paper, paints, varnishes, textiles, metallurgy, pharmaceuticals, cosmetics, fertilizers, and the like. The mineral particles may be used as inert fillers (e.g. for diluting other more expensive active components in the composition) or as functional fillers to provide one or more advantageous properties (e.g. for reinforcing the mechanical properties of the material). Silicates can be obtained from natural sources and then ground to produce silicate products for various industrial applications. However, naturally obtained silicate products may include some level of impurities. Furthermore, naturally obtained silicates may need to undergo multiple processing steps to obtain the desired particle size distribution. In contrast, synthetic silicate and germanate particles generally have higher purity levels and narrower particle size distributions than the corresponding natural products. Accordingly, it would be desirable to provide alternative and/or improved methods for the preparation of synthetic mineral particles comprising silicon and/or germanium.

Disclosure of Invention

According to a first aspect of the present invention there is provided a method for producing a synthetic mineral, the method comprising: preparing a synthetic mineral precursor by a precipitation reaction between:

metal silicates and/or germanates, and

a salt of a divalent or trivalent metal,

wherein the precipitation reaction does not include the addition of an acid or hydroxide base reagent to chemically equilibrate the precipitation reaction.

According to an alternative aspect of the present invention there is provided a method for preparing a synthetic mineral, the method comprising preparing a synthetic mineral precursor by a precipitation reaction between:

metal silicates and/or germanates, and

a salt of a divalent or trivalent metal,

wherein the molar ratio of metal atoms to silicon and/or germanium atoms in the metal silicate and/or germanate is less than about 2.

According to another alternative aspect of the present invention there is provided a method for the preparation of a synthetic mineral, the method comprising preparing a synthetic mineral precursor by a precipitation reaction between a metal metasilicate and/or a partial germanate and a divalent or trivalent metal salt, and then heat treating the synthetic mineral precursor under supercritical conditions.

According to another alternative aspect of the present invention there is provided a method for producing a synthetic mineral, the method comprising: preparing a synthetic mineral precursor by a precipitation reaction between:

metal silicates and/or germanates, and

a salt of a divalent or trivalent metal,

wherein the metal silicate and/or germanate comprises a metal disilicate and/or digermate and a metal metasilicate and/or partial germanate. In certain embodiments, the metal silicates and/or germanates include metal disilicates and metal metasilicates.

According to a second aspect of the present invention there is provided a method for the preparation of a synthetic mineral precursor, the method comprising a precipitation reaction between:

metal silicates and/or germanates, and

a salt of a divalent or trivalent metal,

wherein the precipitation reaction does not include the addition of an acid or hydroxide base reagent to chemically equilibrate the precipitation reaction; or

Wherein the molar ratio of metal atoms to silicon and/or germanium atoms in the metal silicate and/or germanate is less than about 2; or

Wherein the metal silicate and/or germanate is metal metasilicate and/or partial germanate, and the synthetic mineral precursor is subjected to heat treatment under supercritical conditions after the precipitation reaction; or

Wherein the metal silicate and/or germanate comprises a metal disilicate and/or digermate and a metal metasilicate and/or partial germanate.

According to a third aspect of the present invention there is provided a method for the manufacture of a synthetic mineral, the method comprising heat treating a synthetic mineral precursor of, or manufactured according to, any aspect or embodiment of the present invention.

According to a fourth aspect of the present invention there is provided a synthetic mineral obtained and/or obtainable by the method of any aspect or embodiment of the present invention.

According to a fifth aspect of the present invention there is provided a synthetic mineral precursor obtained and/or obtainable by the method of any aspect or embodiment of the present invention.

In certain embodiments, the synthetic mineral or synthetic mineral precursor is a synthetic silicate or synthetic silicate precursor, respectively. In certain embodiments, the synthetic mineral or synthetic mineral precursor is a synthetic phyllosilicate or a synthetic phyllosilicate precursor, respectively. In certain embodiments, the synthetic phyllosilicate or synthetic phyllosilicate precursor is a synthetic talc or a synthetic talc precursor, respectively.

In certain embodiments, the metal silicate and/or germanate is sodium silicate, such as sodium disilicate and/or sodium metasilicate.

In certain embodiments, the metal silicate and/or germanate is a combination of disilicate and/or digermate and metasilicate/partial germanate in a ratio sufficient to provide an equilibrium precipitation reaction without the need for external addition of an acid or hydroxide base reagent and/or without the generation of an acid or base as a product of the precipitation reaction.

In certain embodiments, the divalent or trivalent metal salt is a magnesium salt and/or a zinc salt. In certain embodiments, the divalent or trivalent metal salt is an acetate or sulfate.

In certain embodiments, the synthetic mineral precursor is subjected to a thermal treatment process, such as a hydrothermal treatment process, to produce the synthetic mineral. In certain embodiments, the heat treatment process is performed under supercritical conditions. In certain embodiments, the metal silicate and/or germanate is a metasilicate and the heat treatment process is conducted under supercritical conditions.

In certain embodiments, the precipitation reaction is carried out in the presence of a metal carboxylate salt of the formula R-COOM ', wherein R is selected from hydrogen (-H) and alkyl groups containing less than 5 carbon atoms, and M' is a monovalent metal. In certain embodiments, the metal carboxylate salt is a monovalent metal salt, such as a sodium or potassium salt. In certain embodiments, the metal carboxylate is an acetate.

Certain embodiments of any aspect of the present invention may provide one or more of the following advantages:

less reactants are required;

use of cheaper reactants;

a more economical/environmentally friendly process;

the synthesis product has high purity;

the synthesized product has high crystallinity;

the synthetic article has a high degree of laminarity;

the desired particle size distribution;

no acid and/or base is produced as a precipitated reaction product.

The details, examples and preferences provided for any particle in relation to one or more of the described aspects of the invention are further described herein and apply equally to all aspects of the invention. Any combination of the embodiments, examples and preferred modes described herein, and all possible variations thereof, is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Drawings

Figures 1 and 2 show the X-ray diffraction patterns (24 hours treatment and 6 hours treatment, respectively) of the synthetic talc prepared by the method of example 1.

FIG. 3 shows an IR spectrum of a synthetic talc prepared by the method of example 1 (6 hours treatment).

Fig. 4 shows an electron micrograph of the synthetic talc prepared by the method of example 1 (6 hour treatment).

FIG. 5 shows an X-ray diffraction pattern of synthetic willemite prepared by the method of example 6.

Detailed Description

A method for preparing a synthetic mineral is provided herein. The method comprises preparing a synthetic mineral precursor by a precipitation reaction between one or more metal silicates and/or germanates and one or more divalent or trivalent metal salts.

It has been surprisingly and advantageously found that synthetic minerals can be prepared without the external addition of any reagents, in particular acid reagents (e.g. acetic acid) or hydroxide base reagents, to a precipitation reaction mixture that has previously been used to chemically equilibrate the precipitation reaction. It has also been surprisingly and advantageously found that in certain embodiments, synthetic minerals can be prepared without producing acids or bases as precipitation reaction products. This may for example be the result of the lack of addition of an external acid or hydroxide base reagent to the precipitation reaction. In particular, in certain embodiments, the one or more metal silicates and/or germanates comprise, consist essentially of, or consist of a metal metasilicate and/or a metal partial germanate, and the method further comprises hydrothermal treatment under supercritical conditions.

It has also been surprisingly and advantageously found that synthetic minerals can be prepared using metal silicates and/or germanates having a molar ratio of metal atoms to silicon and/or germanium atoms of less than about 2. Thus, in certain embodiments, the one or more metal silicates and/or germanates comprise, consist essentially of, or consist of a metal disilicate and/or digermate. For example, the one or more metal silicates and/or germanates may comprise, consist essentially of, or consist of a metal disilicate.

It has also been surprisingly and advantageously found that synthetic minerals can be prepared using a combination of disilicates and/or digermates and metasilicates and/or digermates. Thus, in certain embodiments, the one or more metal silicates and/or germanates comprise, consist essentially of, or consist of a combination of one or more disilicates and/or digermates and one or more metasilicates and/or partial germanates. For example, the one or more metal silicates and/or germanates comprise, consist essentially of, or consist of a combination of disilicates and metasilicates.

In certain embodiments, the precipitation reaction does not include the addition of an acid or hydroxide base reagent to chemically equilibrate the precipitation reaction. In certain embodiments, the precipitation reaction does not include the addition of an acid or hydroxide base, whether or not the precipitation reaction is equilibrated. In certain embodiments, the precipitation reaction does not include the addition of any reagents to chemically equilibrate the precipitation reaction. Alternatively or additionally, in certain embodiments, the molar ratio of metal atoms to silicon and/or germanium atoms in the metal silicate and/or germanate is less than about 2. Alternatively or additionally, in certain embodiments, the metal silicate and/or germanate comprises a metal disilicate and a metal metasilicate in relative proportions sufficient, for example, to achieve a balanced precipitation reaction without the need for external addition of an hydroxide reagent and/or without the generation of an acid or base as a product of the precipitation reaction. In certain embodiments, the methods described herein do not form an acid or base as a product of the precipitation reaction.

The synthetic mineral prepared by the methods described herein may be a synthetic silicate, a synthetic germanate, or any other synthetic mineral containing silicon and/or germanium, including silicon germanates and germanosilicates. The term germanosilicate refers to a silicate in which less than 50% of the silicon is substituted by germanium. The term silicon germanate refers to a germanate in which less than 50% of the germanium is replaced by silicon.

The term germanate refers to a material comprising germanate groups (anionic groups containing germanium). The term silicate refers to a material comprising a silicate group (an anionic group containing silicon). The silicate may be, for example, a phyllosilicate. The silicate and/or germanate may, for example, have a trigonal, orthorhombic, monoclinic, triclinic, hexagonal, tetragonal or cubic crystal structure. For example, the silicate may be willemite. Germanium may, for example, partially or completely replace silicon in silicate minerals and germanate minerals, and thus, silicon germanate and germanosilicate minerals may have a crystal structure corresponding to that of conventional silicates.

The term phyllosilicate refers to a material that contains a silicate group (an anionic group containing silicon) and has a crystal structure that comprises at least one tetrahedral layer and at least one octahedral layer. The number of layers may vary from a few units to several thousand units. The phyllosilicate may for example be a 2:1 phyllosilicate, wherein two tetrahedral layers are located on either side of the octahedral layer.

The synthetic phyllosilicate or synthetic phyllosilicate precursor may, for example, be selected from synthetic talc, synthetic pyrophyllite, synthetic mica, synthetic smectites (e.g. bentonite, montmorillonite, nontronite, beidellite, saponite), synthetic kaolinite, synthetic serpentine, synthetic chlorite and mixtures of one or more thereof. In certain embodiments, the synthetic phyllosilicate or synthetic phyllosilicate precursor is a synthetic talc (formula Mg)₃Si₄O₁₀(OH)₂Magnesium silicate hydroxylate). The present invention may be intended to be discussed in terms of synthetic talc. However, the present invention should not be construed as being limited thereto.

The synthetic silicate and/or synthetic germanate (e.g., synthetic phyllosilicate) can be, for example, non-swelling. This refers to a material whose (001) diffraction line is not affected by treatment by contact with ethylene glycol or a diol, i.e., whose atomic distance corresponding to the (001) x-ray diffraction line does not increase upon contact with ethylene glycol or a diol. The 2:1 phyllosilicate is non-swelling (except for smectites) and includes, for example, talc and micas such as muscovite.

The metal silicate and/or germanate includes a silicate and/or germanate. Metal silicates are compounds containing a metal cation and an anion including silicon, for example, oxoanions such as orthosilicate (SiO)₄ ^4-)、[SiO_2+n]^2n-、{[SiO₃]^2-}_nOr { [ SiO ]_2.5 ^-]}_n. Metal germanates are compounds containing a metal cation and an anion comprising germanium, e.g. oxo-anions such as orthogermanate (GeO)₄ ^4-). In certain embodiments, the metal silicate and/or germanate is a metal silicate. In certain embodiments, the metal silicate and/or germanate is a metal germanate. In certain embodiments, the metal silicate and/or germanate is a mixture of a metal silicate and a metal germanate. The present invention may be intended to be discussed in terms of metal silicates, particularly metal disilicates and/or metal metasilicates. In certain embodiments, the metal silicate and/or germanate is a mixture of a metal metasilicate and a metal disilicate. However, the present invention should not be construed as being limited thereto.

The molar ratio of metal atoms to silicon and/or germanium atoms in the metal silicate and/or germanate can be, for example, less than about 2. For example, the molar ratio of metal atoms to silicon and/or germanium atoms in the metal silicate and/or germanate can be, for example, equal to or less than about 1.5, or equal to or less than about 1. For example, the molar ratio of metal atoms to silicon and/or germanium atoms in the metal silicate and/or germanate can be, for example, greater than 0, such as equal to or greater than about 0.5. For example, the molar ratio of metal atoms to silicon and/or germanium atoms in the metal silicate and/or germanate can be about 1 (e.g., where the metal silicate and/or germanate is disiliconSodium salt, Na₂Si₂O₅)。

The metal silicate and/or germanate may be, for example, a metal monosilicate and/or monogermanate or a metal disilicate and/or digermate. Metal monosilicates include, for example, sodium metasilicate (Na)₂SiO₃) Sodium metasilicate pentahydrate (Na)₂SiO₃·5H₂O or Na₂SiO₂(OH)₂·4H₂O), sodium metasilicate hexahydrate (Na)₂SiO₃·6H₂O), sodium metasilicate octahydrate (Na)₂SiO₃·8H₂O) or sodium metasilicate nonahydrate (Na)₂SiO₃·9H₂O or Na₂SiO₂(OH)₂·8H₂O). The metal disilicate includes, for example, sodium disilicate (Na)₂Si₂O₆·xH₂O, e.g., where x is close to or equal to about 1). In certain embodiments, the metal silicate and/or germanate is not a metal monosilicate and/or is not a metal monogermanate. In certain embodiments, the metal silicate and/or germanate is not a metal metasilicate or is not sodium metasilicate. In certain embodiments, the metal silicate and/or germanate is not a metal partial germanate.

In certain embodiments, the metal silicate and/or germanate is a metal disilicate and/or digermate. In certain embodiments, the metal silicate and/or germanate is a metal disilicate, such as sodium disilicate and/or potassium disilicate. The metal silicate and/or germanate may or may not be hydrated. For example, the metal silicate and/or germanate may be pentahydrate, hexahydrate, octahydrate or nonahydrate.

The metal silicate and/or germanate may be, for example, a monovalent metal silicate and/or germanate, such as sodium silicate and/or sodium germanate or potassium silicate and/or potassium germanate. The metal silicate and/or germanate may be, for example, potassium metasilicate (K)₂SiO₃) Either hydrated or non-hydrated. The sodium silicate and/or potassium silicate may be, for example, in an aqueous solution.

In certain embodiments, the metal silicate and/or germanate is a metal metasilicate and/or metal disilicate. In certain embodiments, the metal silicate and/or germanate is sodium metasilicate and/or sodium disilicate.

The divalent or trivalent metal salt used for the precipitation reaction may, for example, comprise any divalent or trivalent metal. For example, the divalent or trivalent metal salt can include beryllium, magnesium, calcium, strontium, barium, radium, aluminum, gallium, indium, thallium, cobalt, zinc, copper, manganese, iron, nickel, chromium, or a combination of one or more thereof. The present invention may be intended to be described in terms of divalent metal salts, particularly magnesium or zinc salts. However, the present invention should not be construed as being limited thereto.

The divalent or trivalent metal salt may, for example, not be a silicate and/or may not be a germanate. The divalent or trivalent metal salt may be, for example, a carboxylate (e.g., acetate), nitrate, nitrite, sulfate, sulfide, sulfite, bisulfate, bisulfite, halide, carbonate, bicarbonate, chlorate, chromate, dichromate, phosphate, hydroxide, thiosulfate, perchlorate, or a combination thereof. In certain embodiments, the divalent or trivalent metal salt may be a carboxylate (e.g., acetate) or a sulfate. In certain embodiments, the divalent or trivalent metal salt is magnesium acetate or magnesium sulfate.

In certain embodiments, the divalent or trivalent metal salt may be a hydrate.

In certain embodiments, the metal silicate and/or germanate is a disilicate, such as sodium disilicate, and the divalent or trivalent metal salt is an acetate or sulfate, such as magnesium acetate or magnesium sulfate.

The precipitation reaction may for example use one or more metal silicates and/or germanates and one or more divalent or trivalent metal salts. The precipitation reaction may, for example, use one or more metal silicates and one or more divalent or trivalent metal salts. The precipitation reaction may for example use a metal silicate and/or germanate and/or a divalent or trivalent metal salt. In certain embodiments, the precipitation reaction uses a mixture of metasilicate and disilicate.

The precipitation reaction is carried out by contacting one or more metal silicates and/or germanates with one or more divalent or trivalent metal salts. The metal silicate and/or germanate and divalent or trivalent metal salt may be in any form suitable for carrying out the precipitation reaction. For example, the metal silicate and/or germanate and the divalent or trivalent metal salt may each independently be in liquid form. For example, the metal silicate and/or germanate and the divalent or trivalent metal salt may each independently be in solution, and the solutions may be mixed together to initiate the precipitation reaction. The solvent in the solution of the metal silicate and/or germanate and the divalent or trivalent metal salt may for example be water, an alcohol or a mixture of one or more thereof. Alcohols include, for example, straight or branched chain alcohols, e.g., containing less than 10 or less than 7 carbon atoms, such as methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, propylene glycol, and ethylene glycol. In certain embodiments, the solvent is water (in other words, the metal silicate and/or germanate and the divalent or trivalent metal salt may each independently be in aqueous solution).

The reaction medium and each starting composition may be at least partially hydrated (hydrothermal treatment of the reaction medium followed by more generally referred to as solvothermal treatment). The liquid medium may for example be selected from water, alcohols and mixtures thereof. For example, the alcohol may be selected from linear or branched alcohols containing less than 10 carbon atoms, such as less than 7 carbon atoms, such as methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, propylene glycol, and ethylene glycol. For example, the liquid medium of the starting composition and the liquid medium of the reaction medium may be prepared, for example, with water alone, or alternatively with a mixture of water and at least one alcohol.

The precipitation reaction may be carried out, for example, at or near room temperature and pressure and/or atmospheric temperature and pressure. For example, at a temperature of from about 15 ℃ to about 30 ℃ or from about 15 ℃ to about 25 ℃. For example, at a pressure of from about 0.05 to about 0.5MPa, such as from about 0.09 to about 0.2MPa, e.g., about 0.1 MPa. Alternatively, the precipitation reaction may be carried out at higher temperatures and/or pressures to enable the salt to dissolve in water more rapidly, for example at a temperature of about 50 ℃ to about 70 ℃. Alternatively, the precipitation reaction may be immediately followed by the heat treatment process described herein, and thus the precipitation reaction is carried out at a temperature and pressure suitable for the heat treatment process described herein. The metal silicate and/or germanate and divalent or trivalent metal salt may be mixed, for example, by manual stirring, magnetic stirring, and/or sonication.

The concentration of each solution may, for example, each independently be about 10^-3mol/L to about 10mol/L, e.g., about 10^{- 2}mol/L to about 5mol/L, e.g. about 10^-1mol/L to about 4mol/L, for example 0.5mol/L to about 3 mol/L.

The metallosilicate and/or germanate and the divalent or trivalent metal salt may be combined, for example, in stoichiometric proportions to obtain the desired synthetic mineral (the ratio of metallosilicate and/or germanate to divalent or trivalent metal salt corresponds to the ratio of these elements in the desired synthetic mineral).

In the foregoing process, an acid reagent such as acetic acid is added to the precipitation reaction to chemically equilibrate the reaction without the presence of any base as a product of the precipitation reaction. However, it has surprisingly been found that synthetic minerals can be prepared without addition of reagents, in particular acid reagents or hydroxide base reagents, to chemically balance the precipitation reaction. Thus, in certain embodiments, neither the acid nor the hydroxide base reagent is added to the precipitation reaction in an amount or under conditions suitable to equilibrate the reaction. In certain embodiments, neither the acid nor the hydroxide base reagent is added to the precipitation reagent. In certain embodiments, no additional reagents are added to the precipitation reaction in an amount or under conditions suitable to equilibrate the reaction. This means that no acid or hydroxide base reagent is added to the metal silicate and/or germanate and divalent or trivalent metal salt before or during the precipitation reaction. In certain embodiments, no acid or hydroxide base reagent is added to the metal silicate and/or germanate and divalent or trivalent metal salt after the precipitation reaction. In this context, the additional reagents do not include metal silicates and/or germanates and divalent or trivalent metal salts required for the precipitation reaction. It also does not include the addition of metal carboxylates of the formula R-COOM' discussed herein, which may be added during heat treatmentTo facilitate synthesis of the synthetic mineral and/or to provide a precursor with less aggregation between particles and improved particle size. In this context, acids and bases are acids and basesLowry definition, where acid is a proton-losing species and base is a proton-accepting species. Hydroxide base reagent refers to any reagent that forms a hydroxide when in the reaction medium used for the precipitation reaction. For example, sodium alkoxide is dissolved in water to yield an alcohol and sodium hydroxide, and thus can be used as a hydroxide base to chemically equilibrate the precipitation reaction.

In certain embodiments, the metal silicate and/or germanate comprises a metal disilicate and/or digermate. In certain embodiments, the metal silicates and/or germanates include metal disilicates/digermates and metal metasilicates/digermates. The metal disilicate/digermate and the metal metasilicate/digermate may be used in combination without external addition of an acid or hydroxide base reagent, for example without external addition of any additional reagent. When using combinations of metal disilicates and/or digermates with metal metasilicates and/or digermates, the disilicates and/or digermates with metasilicates and/or digermates may be used in the stoichiometric proportions required to obtain the desired synthetic mineral product, without, for example, adding acid or hydroxide bases as precipitation reaction reagents and/or without producing acid or hydroxide bases as precipitation reaction products. The precipitation reaction may be, for example, as follows:

Na₂Si₂O₅+2Na₂SiO₃+3Mg(CH₃COO)₂+n'H2O->Mg₃Si₄O₁₁·n'H₂O+6

(CH₃COO)Na

in certain embodiments, the precipitating comprises adding one or more metal carboxylates of the formula R-COOM ', or the precipitating is carried out in the presence of one or more metal carboxylates of the formula R-COOM ', wherein R is selected from hydrogen (-H) and alkyl groups containing less than 5 carbon atoms, and M ' is a monovalent metal. This may facilitate the production of synthetic minerals in the heat treatment process. Alternatively or additionally, the heat treatment described herein is carried out in the presence of one or more metal carboxylates of formula R-COOM' as described herein. In addition to the metal source (divalent or trivalent metal salt) used for the precipitation reaction, one or more metal carboxylates of the formula R-COOM', which in certain embodiments may be carboxylates, are used. The metal carboxylates of the formula R-COOM' do not provide a metal source for the synthetic minerals.

In certain embodiments, R is methyl, ethyl, propyl, butyl, or pentyl. In certain embodiments, R is methyl or ethyl. In certain embodiments, R is methyl (R-COO is acetate).

In certain embodiments, M' is a monovalent metal, such as sodium, potassium, or a combination of one or more thereof. In certain embodiments, M' is sodium or potassium. In certain embodiments, M' is the same metal as in the metal silicate and/or germanate.

In certain embodiments, the metal carboxylate is sodium acetate or potassium acetate.

The metal carboxylate may be used, for example, at a concentration that enables the synthetic mineral to be obtained after a shortened duration of the hydrothermal treatment. The metal carboxylate can be used, for example, at a concentration of from about 0.1mol/L to about 10mol/L, such as from about 0.2mol/L to about 8mol/L, such as from about 0.5mol/L to about 6mol/L, such as from about 1mol/L to about 5mol/L, such as from about 1mol/L to about 4 mol/L.

The molar ratio of metal carboxylate to silicon and/or germanium may, for example, be from about 0.05 to about 25, such as from about 0.05 to about 20, such as from about 0.1 to about 15, such as from about 0.1 to about 10.

The precipitation reaction forms a synthetic mineral precursor. The synthetic mineral precursor comprises silicon and/or germanium. The precursor may for example be a suspension, such as a white suspension, or may for example be a hydrogel, such as of formula (Si)_x’Ge_1-x’)₄M₃O₁₁·n'H₂O, wherein M is a metal, x 'is a value from 0 to 1 (including 0 and 1), and n' is the number of water molecules associated with the gel.

For example, the synthetic mineral precursor may be recovered, for example, after centrifugation (e.g., 3000 to 15000rpm, 5 to 60 minutes) and removal of the supernatant, optionally washing with demineralised water, followed by drying (e.g., in an oven, e.g., for 2 days at 60 ℃), freeze-drying, atomization or microwave irradiation. Thus, the synthetic mineral precursor may be stored in the form of a powder, taking into account the possible subsequent heat treatment.

The synthetic mineral precursor is then processed to produce synthetic mineral particles. The treatment may for example comprise a thermal treatment, such as a hydrothermal treatment process. For example, the precipitation medium of the precipitation reaction may be subjected to a thermal treatment, such as a hydrothermal treatment process, to produce the synthetic mineral. When the precipitation reaction is carried out using a solution of a metal silicate and/or germanate and/or a divalent or trivalent metal salt, the solvent (e.g., water) may be the precipitation reaction medium in which the thermal treatment process is carried out.

The methods described herein, such as the thermal treatment process, may be performed in a batch or continuous process. The processes described herein, e.g. the heat treatment of synthetic mineral precursors, may be carried out, for example, as described in US 2017/0066655, US 2014/0205528 or US 2013/0343980, the contents of which are incorporated herein by reference.

Continuous reactors suitable for use in the processes described herein include, for example, constant volume continuous reactors, such as plug reactors or plug flow type reactors, or reactors that can be modeled by a series of stirred reactors. For example, it may be the case of a tubular reactor in which the flow of the reaction medium is carried out under laminar, turbulent or intermediate conditions. Further, any co-current or counter-current reactor may be used with respect to the introduction and contact placement of the various compositions and/or the liquid medium placed in contact in the methods described herein. Injections can also be made with a T or Y syringe. The continuous reactor has at least one inlet adapted to continuously introduce reactants into the reaction zone and at least one outlet for continuously removing synthetic mineral product. The heat treatment can be carried out, for example, in an autoclave, for example from a nickel-based alloy such as(sold by Haynes International of Kokomo, U.S.A.) or by hydrothermal treatment at a temperature not exceeding 250 deg.CTitanium autoclave or optionally steel with an internal Polytetrafluoroethylene (PTFE) liner. Such autoclaves may have any capacity, for example a capacity of about 200ml to about 50 litres. The heat treatment can be carried out, for example, with mechanical stirring. Thus, the autoclave may for example be equipped with an internal metal screw.

Any temperature suitable for forming synthetic minerals as a function of pressure and reaction time may be used. The heat treatment process may be performed, for example, at a temperature equal to or greater than about 100 ℃. For example, the heat treatment process can be conducted at a temperature equal to or greater than about 120 ℃, or equal to or greater than about 140 ℃, or equal to or greater than about 150 ℃, or equal to or greater than about 160 ℃, or equal to or greater than about 170 ℃, or equal to or greater than about 180 ℃, or equal to or greater than about 190 ℃, or equal to or greater than about 200 ℃, or equal to or greater than about 210 ℃, or equal to or greater than about 220 ℃, or equal to or greater than about 230 ℃, or equal to or greater than about 240 ℃, or equal to or greater than about 250 ℃, or equal to or greater than about 260 ℃, or equal to or greater than about 270 ℃, or equal to or greater than about 280 ℃, or equal to or greater than about 290 ℃, or equal to or greater than about 300 ℃. The heat treatment process may be carried out, for example, at a temperature of up to about 600 ℃, or up to about 590 ℃, or up to about 580 ℃, or up to about 570 ℃, or up to about 560 ℃, or up to about 550 ℃, or up to about 540 ℃, or up to about 530 ℃, or up to about 520 ℃, or up to about 510 ℃, or up to about 500 ℃. In certain embodiments, the temperature of the heat treatment process is from about 150 ℃ to about 600 ℃, or from about 200 ℃ to about 400 ℃, or from about 200 ℃ to about 350 ℃, or from about 350 ℃ to about 450 ℃, or from about 250 ℃ to about 350 ℃.

Any pressure suitable for forming the synthetic mineral as a function of temperature and reaction time may be used. The heat treatment process may be performed, for example, at a pressure equal to or greater than about 5 bar (0.5 MPa). For example, the heat treatment process may be performed at a pressure equal to or greater than about 10 bar (1MPa), or equal to or greater than about 20 bar (2MPa), or equal to or greater than about 30 bar (3MPa), or equal to or greater than about 40 bar (4MPa), or equal to or greater than about 50 bar (5 MPa). The heat treatment process may, for example, be at most about300 bar (30MPa), or up to about 250 bar (25MPa), or up to about 200 bar (20MPa), or up to about 150 bar (15 MPa). The heat treatment can be carried out, for example, under autogenous pressure, that is to say at a pressure at least equal to the saturated vapour pressure of water (the pressure at which the vapour phase is in equilibrium with the liquid phase). The autogenous pressure reached in the autoclave during the heat treatment therefore depends, inter alia, on the temperature at which the heat treatment is carried out, the volume of the autoclave and the amount of water present. The hydrothermal treatment may also be carried out at a pressure greater than the saturated vapor pressure of water or greater than the autogenous pressure in the vessel in which the heat treatment is carried out. For this purpose, for example, a gas which is chemically neutral with respect to the thermal reaction can be injected into an autoclave or a vessel in which the hydrothermal treatment is carried out. The gas is selected from the group consisting of inert gases (noble gases), in particular argon, nitrogen (N)₂) Carbon dioxide and air (compressed air). For example, an amount of water (preferably distilled water) may be added to the autoclave at least sufficient to generate a saturated vapor pressure within the autoclave to reach the processing temperature.

The heat treatment can be carried out, for example, with a synthetic mineral precursor that is liquefied and has a liquid/solid ratio of 2 to 20, in particular 5 to 15 (amount of liquid in cm)³Expressed and the amount of solids expressed in grams and only expressed the amount of dry synthetic mineral precursor, that is to say without taking into account the optional metal carboxylate. Optionally, if desired, an appropriate amount of water may be added to the liquefied synthetic mineral precursor to achieve this ratio.

The heat treatment process may be performed, for example, under subcritical or supercritical conditions. The heat treatment process may be carried out, for example, under supercritical conditions in the reaction medium or in the liquid medium in which the reaction takes place. For example, the heat treatment process may be performed under supercritical conditions of water. For example, supercritical conditions are those in which the temperature and pressure are above the critical point of water (22.1MPa and 374 ℃) in the substantial or only aqueous reaction medium. Thus, the heat treatment process may be performed, for example, at a temperature greater than about 375 ℃ and a pressure greater than about 22.3 MPa. In particular, when the metal silicate and/or germanate comprises or is a metasilicate and/or a partial germanate such as sodium metasilicate and/or sodium partial germanate, the heat treatment process may be conducted under supercritical conditions.

The heat treatment process may be performed, for example, for a period of about 5 seconds to about 30 days. For example, the heat treatment process may be carried out for a period of time of from about 1 minute to about 25 days, or from about 5 minutes to about 20 days, or from about 10 minutes to about 15 days, or from about 1 hour to about 24 hours, or from about 2 hours to about 12 hours, or from about 4 hours to about 8 hours. For example, the heat treatment process may be performed for a time period of about 5 seconds to about 1 minute, or about 10 seconds to about 30 seconds. The heat treatment process may, for example, be performed for a time of less than about 60 seconds when a continuous process is used and/or when supercritical conditions are used.

At the end of the thermal treatment of the synthetic mineral precursor, a composition can be obtained in the form of a colloidal solution containing mineral particles (for example with at least one non-swelling phase). These synthetic mineral particles in solution may be in a state that allows the particles to separate well relative to each other (undivided), with very little or no aggregates of synthetic mineral particles. At the end of the heat treatment, a colloidal composition comprising synthetic mineral particles suspended in an aqueous solution of metal carboxylate can be recovered. The colloidal composition may then be subjected to a drying step, after an optional washing step with water, to at least partially remove the metal carboxylate. Such washing step may comprise at least one washing/centrifuging cycle of the colloid composition.

The synthetic silicate (e.g., synthetic phyllosilicate) obtained by the methods described herein can have, for example, at least one diffraction line characteristic of a plane (001) having a spacing of 9.40 angstroms to 9.90 angstroms in X-ray diffraction. The presence of such diffraction lines is characteristic of a product that is very similar to natural talc. Furthermore, synthetic silicates may not have planar diffraction line features with a spacing of 12.00 angstroms to 18.00 angstroms in X-ray diffraction, which generally indicates the residual presence of a swollen phase with interlayer spaces in which interlayer cations and possibly water molecules are found. Further, the synthetic silicate may have at least one diffraction line characteristic of plane (002) having a spacing of 4.60 angstroms to 4.80 angstroms in X-ray diffraction.

The synthetic mineral has flats (113) spaced about 2.75 angstroms to about 2.95 angstroms apart in X-ray diffraction. Alternatively or additionally, the synthetic mineral may have in X-ray diffraction planes (110) between about 6.9 angstroms to about 7.1 angstroms and/or planes (300) with a spacing of about 4.0 angstroms to about 4.2 angstroms and/or planes (220) between about 3.4 angstroms to about 3.6 angstroms and/or planes (410) between about 2.55 angstroms to about 2.75 angstroms and/or planes (223) between about 2.2 angstroms to about 2.4 angstroms and/or planes (333) between about 1.75 angstroms to about 1.95 angstroms.

The synthetic silicate may have the following characteristic diffraction peaks in X-ray diffraction:

a plane (001) with a spacing of 9.50 to 10.25 angstroms;

a plane (020) with a spacing of 4.50 to 4.61 angstroms;

planes (003) spaced at a distance of 3.10 to 3.20 angstroms;

plane (060) with a spacing of 1.50 to 1.55 angstroms.

The synthetic phyllosilicates may have the following characteristic diffraction lines in X-ray diffraction:

a plane (001) with a spacing of 9.40 to 9.90 angstroms;

a flat surface (002) with a spacing of 4.60 angstroms to 4.80 angstroms;

planes (003) spaced at a distance of 3.10 to 3.20 angstroms;

plane surfaces (060) spaced between 1.51 angstroms and 1.53 angstroms;

the intensity of the diffraction line characteristic of plane (002) is greater than the signal intensity corresponding to plane (020) with a spacing of 4.40 to 4.60 angstroms, and the ratio between the intensity of the diffraction line characteristic of plane (001) and the intensity of the diffraction line characteristic of plane (003) is 0.20 to 5, for example about 0.20 to 4, or about 0.20 to about 3, or about 0.20 to about 2, or about 0.20 to about 1.5.

In particular, such a composition has, in X-ray diffraction, the diffraction line characteristics of the plane (002) at a spacing of 4.60 to 4.80 angstroms, which are much greater in intensity than the diffraction lines of the representative plane (020) at a spacing of 4.40 to 4.60 angstroms, in the case of heat treatment for a long period of time and/or heat treatment at a sufficiently high temperature and/or heat treatment after anhydrous heat treatment, so that the diffraction lines of the representative plane (020) can be masked by the diffraction line characteristics of the plane (002).

Furthermore, the near infrared spectrum of the synthetic silicate may have the linear character of the vibration band of natural talc. Advantageously and according to the invention, the composition of the invention has, in the near infrared, Mg representing talc₃Vibration of-OH bond at 7185cm^-1A vibration band of (c). Furthermore, the near infrared spectrum of the synthetic silicate may have a spectrum lying at 5000cm^-1To 5500cm^-1The vibration bands in between, which are characteristic of synthetic talc compositions and show the presence of water molecules bonded to the talc at the edges of the flakes. Thus, the synthetic talc may have a particle size in the near infrared of 5000cm^-1To 5500cm^-1In particular 5200cm^-1To 5280cm^-1Corresponding to the presence of bound water at the edges of the sheet. The presence of such vibration bands with high strength can distinguish synthetic talc from natural talc, which is otherwise similar to the other infrared vibration bands of natural talc.

The synthetic mineral may, for example, have a particle size of from about 10nm to about 900nm, such as from about 10nm to about 600 nm.

After the treatment to form the synthetic mineral, the synthetic mineral product may be dried by any powder drying technique, such as by freeze-drying or by oven (e.g., at a temperature of about 60 ℃ to about 130 ℃ for 1 to 48 hours under microwave radiation), or by atomization.

The composition comprising synthetic mineral particles obtained after heat treatment may also be subjected to a non-aqueous heat treatment in air at a temperature greater than about 350 ℃ and below the degradation temperature of the synthetic mineral particles. Advantageously and according to the invention, the composition comprising synthetic mineral particles obtained after the heat treatment is subjected to an anhydrous heat treatment for a period of time ranging from about 30 minutes to about 24 hours at a temperature ranging from about 350 ℃ to about 850 ℃, in particular from about 400 ℃ to about 750 ℃, in particular from about 450 ℃ to about 600 ℃. After the hydrothermal treatment, the composition comprising synthetic mineral particles may be subjected to an anhydrous thermal treatment. Such heat treatment or "annealing" allows an additional increase in the crystallinity of the particles obtained.

Examples

Example 1: synthesis of Talc Using sodium disilicate (Si/Na ═ 1)

22.2g (0.1mol) of sodium disilicate hydrate are dissolved in 150mL of distilled water in a first beaker (A) under magnetic stirring and ultrasound. In a second beaker (B), 32.17g (0.15mol) of magnesium acetate tetrahydrate was dissolved in 50mL of deionized water with magnetic stirring and ultrasound. The contents of beaker (B) were added rapidly to the contents of beaker (a) with manual stirring to obtain a white suspension. The aqueous suspension obtained is treated in a hydrothermal reactor at 300 ℃ under autogenous pressure (85 bar) for 24 hours or 6 hours. At the end of the hydrothermal treatment, a white gel was obtained, which was washed several times with distilled water. A white paste was obtained which was dried in an oven at 120 ℃ for several hours. The obtained solid was pulverized in an agate mortar to obtain a white powder, which was analyzed (infrared (IR), X-ray diffraction (XRD), Nuclear Magnetic Resonance (NMR), field emission gun scanning electron microscope (FEG-SEM)). The results are shown in FIGS. 1 to 4 and indicate that the reaction product is synthetic talc. Fig. 1 relates to synthetic talc produced by a 24 hour treatment, and fig. 2 to 4 relate to synthetic talc produced by a 6 hour treatment.

Example 2: talc was synthesized using sodium disilicate (Si/Na ═ 1) with sodium acetate as an accelerator.

22.2g (0.1mol) of sodium disilicate hydrate are dissolved in 150mL of distilled water in a first beaker (A) under magnetic stirring and ultrasound. 60g of anhydrous sodium acetate are added. In a second beaker (B), 32.17g (0.15mol) of magnesium acetate tetrahydrate was dissolved in 50mL of deionized water with magnetic stirring and ultrasound. The contents of beaker (B) were added rapidly to the contents of beaker (a) with manual stirring to obtain a white suspension. The aqueous suspension obtained was treated in a hydrothermal reactor at 300 ℃ under autogenous pressure (85 bar) for 6 hours. At the end of the hydrothermal treatment, a white gel was obtained, which was washed several times with distilled water. A white paste was obtained which was dried in an oven at 120 ℃ for several hours. The obtained solid was pulverized in an agate mortar to obtain a white powder, which was analyzed (IR, XRD, NMR, FEG-SEM). The results indicated that the product was synthetic talc.

Example 3: talc was synthesized using sodium disilicate (Si/Na ═ 1) and potassium acetate as an accelerator.

22.2g (0.1mol) of sodium disilicate hydrate are dissolved in 150mL of distilled water in a first beaker (A) under magnetic stirring and ultrasound. 60g of anhydrous potassium acetate was added. In a second beaker (B), 32.17g (0.15mol) of magnesium acetate tetrahydrate was dissolved in 50mL of deionized water with magnetic stirring and ultrasound. The contents of beaker (B) were added rapidly to the contents of beaker (a) with manual stirring to obtain a white suspension. The aqueous suspension obtained was treated in a hydrothermal reactor at 300 ℃ under autogenous pressure (85 bar) for 3 hours. At the end of the hydrothermal treatment, a white gel was obtained, which was washed several times with distilled water. A white paste was obtained which was dried in an oven at 120 ℃ for several hours. The obtained solid was pulverized in an agate mortar to obtain a white powder, which was analyzed (IR, XRD, NMR, FEG-SEM). The results indicated that the product was synthetic talc.

Example 4: using an aqueous sodium silicate solution (Na)₂O·xSiO₂Wherein x ═ 3.4) synthetic talc; aqueous solution: dry matter 36%

In a first beaker (A), 21.7g (0.1mol) of an aqueous sodium silicate solution was mixed with 100mL of distilled water under magnetic stirring and ultrasound. In a second beaker (B), 16.08g (0.075mol) of magnesium acetate tetrahydrate was dissolved in 50mL of deionized water with magnetic stirring and ultrasound. The contents of beaker (B) were added rapidly to the contents of beaker (a) with manual stirring to obtain a white suspension. The aqueous suspension obtained was treated in a hydrothermal reactor at 300 ℃ under autogenous pressure (85 bar) for 24 hours. At the end of the hydrothermal treatment, a white gel was obtained, which was washed several times with distilled water. A white paste was obtained which was dried in an oven at 120 ℃ for several hours. The obtained solid was pulverized in an agate mortar to obtain a white powder, which was analyzed (IR, XRD, NMR, FEG-SEM). The results indicated that the product was synthetic talc.

Example 5: talc was synthesized using sodium disilicate (Si/Na ═ 1) and magnesium sulfate.

22.2g (0.1mol) of sodium disilicate hydrate are dissolved in 150mL of distilled water in a first beaker (A) under magnetic stirring and ultrasound. In a second beaker (B), 36.93g (0.15mol) magnesium sulfate heptahydrate were dissolved in 50mL deionized water under magnetic stirring and ultrasound. The contents of beaker (B) were added rapidly to the contents of beaker (a) with manual stirring to obtain a white suspension. The aqueous suspension obtained was treated in a hydrothermal reactor at 300 ℃ under autogenous pressure (85 bar) for 96 hours. At the end of the hydrothermal treatment, a white gel was obtained, which was washed several times with distilled water. A white paste was obtained which was dried in an oven at 120 ℃ for several hours. The obtained solid was pulverized in an agate mortar to obtain a white powder, which was analyzed (IR, XRD, NMR, FEG-SEM). The results indicated that the product was synthetic talc.

Example 6: synthesis of willemite using sodium disilicate (Si/Na ═ 1)

11.10g (0.05mol) of sodium disilicate hydrate are dissolved in 100mL of distilled water in a first beaker (A) under magnetic stirring and ultrasound. In a second beaker (B), 43.90g (0.2mol) of zinc acetate dihydrate were dissolved in 200mL of distilled water under magnetic stirring and ultrasound. The contents of beaker (B) were added rapidly to the contents of beaker (a) with manual stirring to obtain a white suspension. The aqueous suspension obtained was treated in a hydrothermal reactor at 300 ℃ under autogenous pressure (85 bar) for 24 hours. At the end of the hydrothermal treatment, a white gel was obtained, which was washed several times with distilled water. A white paste was obtained which was dried in an oven at 120 ℃ for several hours. The obtained solid was pulverized in an agate mortar to obtain a white powder, which was subjected to X-ray diffraction analysis. The results are shown in FIG. 5, indicating that the reaction product is synthetic willemite.

Example 7: synthesis of talc using sodium metasilicate under supercritical conditions

Firstly, 1.6084g (0.0075mol) of magnesium acetate tetrahydrate (Mg (CH)₃COO)₂·4H₂O) was added to 250mL of distilled water to prepare a magnesium acetate solution. Separately, by mixing 2.12g (0.01mol) of sodium metasilicate pentahydrate (Na)₂OSiO₂.5H₂O) was added to 250mL of distilled water to prepare a sodium metasilicate solution.

The peristaltic pumps deliver the two solutions separately through inconel (inconel) alloy tubes having an outer diameter of 1/4 inches (6.35mm) and an inner diameter of 2.13mm, and respective flow rates of 4mL/min, i.e., a total flow rate of 8mL/min, wherein mixing of the two solutions was continuously performed several centimeters before the inlet of the reaction tube. The temperature in the chamber was 400 ℃ and the pressure in the reaction tubes (via the pressure regulator) was maintained at about 25MPa so that the reaction medium circulating in the reaction tubes in the chamber was at a temperature above the critical point of water (374 ℃, 221 bar).

The precursor gel resulting from the mixing and precipitation of the two solutions in the third tube section upstream of the inlet of the reaction tube is thus subjected to a hydrothermal treatment in the reaction chamber at 400 ℃, which makes it possible to convert the precursor gel into a suspension of synthetic talc. The residence time in the reaction tube between the inlet and the outlet was 20 seconds.

After cooling, the suspension obtained from the reactor outlet was a colloidal suspension of synthetic talc particles in an aqueous medium of brine (sodium acetate). It has the appearance of a milky white composition which settles in tens of minutes. The talc particles were separated by filtering the suspension using ceramic sinter. After separation, the talc composition is recovered on the one hand and the supernatant solution, in particular containing sodium acetate, on the other hand, the latter being able subsequently to be recovered and optionally recycled.

The talc composition recovered after separation was finally dried in an oven at 80 ℃ for 12 hours.

The product was analyzed by XRD. The results indicated that the product was synthetic talc.

Example 8: synthesis of talc Using combination of sodium disilicate and sodium metasilicate

In a first beaker (A), 22.2g (0.1mol) of sodium disilicate hydrate and 42.42g (0.2mol) of sodium metasilicate pentahydrate were dissolved in 200mL of distilled water under magnetic stirring and ultrasonic sound. In a second beaker (B), 64.34g (0.3mol) of magnesium acetate tetrahydrate was dissolved in 100mL of deionized water with magnetic stirring and ultrasound. The contents of beaker (B) were added rapidly to the contents of beaker (a) with manual stirring to obtain a white suspension. The aqueous suspension obtained was treated in a hydrothermal reactor at 300 ℃ under autogenous pressure (85 bar) for 18 hours. At the end of the hydrothermal treatment, a white gel was obtained, which was washed several times with distilled water. A white paste is obtained which can be dried in an oven at 120 ℃ for several hours. The obtained solid was pulverized in an agate mortar to obtain a white powder, which was analyzed (IR, XRD, NMR, FEG-SEM). The results indicated that the product was synthetic talc.

Certain embodiments of the present invention have been described in general terms, but are not limited thereto. Variations and modifications which are obvious to a person skilled in the art are intended to be included within the scope of the invention as defined by the accompanying claims.