FR3026665A1 - INDUSTRIAL PROCESS FOR THE TREATMENT AND VALORISATION OF A PRODUCT CONTAINING ASBESTOS - Google Patents

Abstract

A method of treating an asbestos-containing product comprising as steps a) providing a divided solid product containing asbestos, b) preparing a first reaction medium comprising the divided solid product containing asbestos and an aqueous solution of a first mineral acid, c) leaching treatment of the solid product divided with the aid of the aqueous solution of the first mineral acid, d) solid separation / liquid leachate, and firstly e) pH treatment. acid leachate liquid obtained in step d) by addition of an alkaline agent and an oxidizing agent, f) solid / liquid separation, g) basic pH treatment of the liquid obtained in step f) by addition of an alkaline agent, h) solid / liquid separation to obtain in the solid phase a mixture containing nickel and cobalt derivatives and in the liquid phase a magnesium salt and secondly i) preparation of a second reaction medium by mixing the solid obtained with step d) with an aqueous solution of an alkaline agent, j) alkaline treatment of the solid obtained in step d) using the aqueous solution of the alkaline agent, k) solid / liquid separation, I) addition the liquid obtained in step k) of an aqueous solution of an ionic compound to obtain an ionic aqueous solution, m) adding to the ionic aqueous solution obtained in step I) a dilution liquid to obtain a dilute aqueous solution, n) adding an aqueous solution of a second mineral acid in the dilute aqueous solution obtained in step m) to obtain a precipitate containing silica.

Description

The present invention relates to an industrial process for the treatment and recovery of an asbestos-containing product and its applications. Asbestos is the generic term for the hydrous silicate crystal family of fibrous structure. Due to the physical properties of asbestos, many polymeric or inorganic composite materials use asbestos as an additive to achieve particular desired properties. Of all asbestos products worldwide, about 95% still use asbestos Fibrous structures in asbestos can easily be inhaled into the human airways and fixed in the lungs. Iron impurities are present in asbestos because of the replacement of silicon and magnesium in asbestos crystals. Therefore, iron doping affects the stability of asbestos crystals, thereby affecting its toxicity and carcinogenicity. Because of these dangerous effects, asbestos is considered a direct cause of mesothelioma and pleural diseases. During the first 30 years of the 20th century, mesothelioma research of workers in the asbestos industry was gradually systematized. Regulations concerning the limitation of work in an asbestos environment and exposure to asbestos in the environment were created in the early 1970s. But from 1971 to 2000 the number of patients with pleural lesions as a result exposure to asbestos has been doubled. After the 1990s, when Western countries ratified the ban on the use of asbestos, large amounts of asbestos continued to be exported as building materials to Southeast Asia. South America and Eastern Europe. Even in the United States and Europe, where the use of asbestos is strictly controlled, exposure to asbestos still occurs occasionally in older buildings. In the western region of China, particularly in the 35 mountains of Xinjiang, Qinghai and Gansu, the same problem is acute. For fifty years that asbestos has been exploited, the amount of residue that has accumulated is enormous. Asbestos particles are easily transported in suspension in the air. Asbestos residues in the areas in question are asbestos minerals of a unique structure, with fine, curly and soft fibers. The chemical structure of asbestos that is harmful to the environment and to humans is destroyed during leaching processes and the iron that catalyzes the formation of carcinogenic radicals is transformed into an atoxic iron precipitate. Because of asbestos contamination problems, asbestos waste recycling is particularly in line with the interests of the local economy and sustainable development, and local raw materials can be valued while improving the environment. W00017408 discloses a method of treating a serpentine ore with hydrochloric acid. The process is not practical for the treatment of asbestos because of the cost of the chemicals used. US4110400 uses gaseous sulfur dioxide to precipitate impurities such as nickel and cobalt in a solution of pH 1.5 to 5 after leaching. Sulfur dioxide accelerates the precipitation reaction to less than an hour, but this gas is complicated to handle. Thus, one always seeks simple and inexpensive and preferably fast methods for eliminating the harmful effects of asbestos while enhancing its constituents. Furthermore, the conventional known processes for the preparation of silica, for example by the precipitation reaction between silicate and acid solutions, are intended to obtain a silica which has a good dispersion and provides resistance to a polymer material. . Their participation in the composition of the material ensures good properties, in particular mechanical properties, rheology and other dynamic aspects.

After extensive research, the Applicant has developed a process using a leaching step that destroys the chemical structure of asbestos and eliminates the toxicity of asbestos residues. Most asbestos residues can be recovered.

This is why the present application relates to a method for treating an asbestos-containing product, characterized in that it comprises the following steps, in the following order: a) supply of a divided solid product containing asbestos, b) preparation of a first reaction medium comprising the divided solid product containing asbestos and an aqueous solution of a first mineral acid, c) leaching treatment of the solid product divided by means of the aqueous solution of the first mineral acid, d) solid separation / liquid leachate, and firstly e) treatment at acidic pH of the liquid leachate obtained in step d) by addition of an alkaline agent and an oxidizing agent, f) solid / liquid separation, g) basic pH treatment of the liquid obtained in step f) by addition of an alkaline agent, h) solid / liquid separation to obtain in the solid phase a mixture containing nickel hydroxides and cobalt or nickel and cobalt sulphides optionally, nickel or cobalt or these two metals are treated optionally and in the liquid phase a magnesium salt which is optionally subjected to a magnesium oxide conversion treatment and on the other hand i) preparing a second reaction medium by mixing the solid obtained in step d) with an aqueous solution of an alkaline agent; j) alkaline treatment of the solid obtained in step d) using the aqueous solution of the alkaline agent, k) solid / liquid separation, I) addition to the liquid obtained in step k) of an aqueous solution of an ionic compound to obtain an ionic aqueous solution, m) addition to the ionic aqueous solution obtained in stage I) of a dilution liquid to obtain a dilute aqueous solution, n) addition of an aqueous solution of a second mineral acid in the dilute aqueous solution obtained in stage m) to obtain a precipitate containing silica, and isolation of the precipitate if desired. Thus, the present process not only decontaminates asbestos, but also to obtain especially nickel, cobalt, magnesium or magnesium oxide, and silica. The divided solid product containing asbestos may be, for example, drilling muds, coatings, flame retardants, gypsum board or caulking, preferably flame retardant materials or plaster boards. After the exploitation of asbestos, the raw materials still contain asbestos residues. The divided solid product containing asbestos is particularly composed of such asbestos mining residues. In particular, these are residues of industrial exploitation of asbestos from western China. The solid product containing asbestos can be divided by grinding to increase its surface area and promote leaching. The size of the divided particles is, for example, less than 149 μm, preferably less than 125 μm, especially less than 120 μm, particularly approximately 74 μm, size evaluated by dry sieving. For this purpose, an ore crusher is advantageously used. In particular, it is possible to carry out a first grinding, for example at 150 μm, then at a second grinding, for example at 74 nm. When the solid product containing asbestos contains magnetite, a magnetic field is advantageously used to select the product to be treated. After submitting a magnetic field, the solid product containing asbestos that will be subjected to the process of the invention advantageously contains less than 6%, preferably less than 5%, especially less than 3% iron. The first mineral acid used in aqueous solution for the leaching treatment of the divided solid product may be, for example, sulfuric acid, nitric acid or hydrochloric acid, and preferably sulfuric acid. The second mineral acid used in aqueous solution for the precipitation of silica may be for example sulfuric acid, nitric acid or hydrochloric acid, preferably sulfuric acid or hydrochloric acid, and particularly acid sulfuric. In the first reaction medium obtained in step b), the mineral acid may represent, for example, from 1 × 10 2 to 1.260 g / ml, preferably from 1.139 to 1.235 g / ml, especially from 1.155 to 1.219 g / ml. mL, most preferably about 1.178 g / mL. In the first reaction medium obtained in step b), the ratio between the mass of solid product divided and the volume of the aqueous solution of the first mineral acid is from 0.1 kg / l to 1 kg / l, preferably from 0.2 kg / L to 0.7 kg / L, especially 0.23 kg / L to 0.5 kg / L, most preferably 0.25 kg / L to 0.4 kg / L. Under preferential conditions of implementation of the invention, during the lixiviation treatment of the solid product divided with an aqueous solution of a mineral acid, the liquid / solid ratio is, for example, 2.5 at 3.5 L / kg, preferably 2.7 to 3.3 L / kg, especially 2.8 to 3.2 L / kg, most preferably 2.9 to 3.1 L / kg. When the acid used is sulfuric acid, the acid represents, by weight / volume, advantageously from 15 to 35%, preferably from 20 to 32%, in particular from 22 to 30%, more particularly approximately 25% of the reaction medium of step b). Under very preferred conditions of practice of the invention, the first mineral acid used is sulfuric acid and the ratio between the mass of solid product divided and the volume of the aqueous solution of the first mineral acid in the first reaction medium obtained in step b) is 0.15 kg / l to 0.35 kg / l, preferably 0.2 kg / l to 0.32 kg / l, in particular 0.22 kg / l. at 0.3 kg / L, especially about 0.25 kg / L. The leaching treatment of the solid product which has been partitioned with an aqueous solution of a mineral acid is advantageously carried out at a temperature of 70 to 110.degree. C., preferably from 79 to 103.degree. C., especially from 84 to 99.degree. ° C, especially 89 to 95 ° C. The duration of the lixiviation treatment of the solid product divided with an aqueous solution of a mineral acid may for example be from 30 to 480 minutes, preferably from 40 to 240 minutes, in particular from 50 to 180 minutes. especially 60 to 150 minutes.

In still other preferred conditions of implementation of the invention, the leaching treatment of the divided solid product is carried out in two or more successive reactors. It should be noted that the leachate generally contains sodium sulphate Na2SO4. Sodium sulphate can be used as an ionized compound as will be discussed hereinafter. In a first reactor, a new divided solid product, i.e., not yet leached, is installed, and in a 2nd reactor split solid product which has been previously leached is installed. This latter is then mixed with an acidic solvent, preferably of the same kind as that used for the first leaching. After solid / liquid separation, the liquid can be reintroduced into the first reactor to serve for the leaching of nine divided solid product. When this is done, the lixiviation treatment time of the nine divided solid product with an aqueous solution of a mineral acid may be, for example, 30 minutes to 4 hours, preferably 40 to 40 minutes. 120 minutes, in particular from 50 to 100 minutes, more particularly from 60 to 90 minutes in the first reactor, while the lixiviation treatment time in the second reactor can for example be from 20 minutes to 480 minutes, preferably from 20 minutes to 20 minutes to 120 minutes, especially 20 to 90 minutes, especially 20 to 60 minutes. At the end of the first leaching, the acid for example sulfuric acid may represent by weight / volume preferably about 20 g / l. And at the end of the second leaching, the sulfuric acid may be in weight / volume, preferably 3 to 10 g / L, most preferably about 5 g / L. For good leaching, the tank is advantageously provided with a stirrer, in particular a radial and axial stirrer. The solid / liquid separation step d) following the step of treating the solid product divided with an aqueous solution of an acid can be carried out for example by means of a vacuum filter, a centrifuge, a rotary drier or a pressure filter, preferably a rotary drier or a pressure filter, and particularly a pressure filter. The filter used is advantageously a vacuum drum rotary filter.

This separation step makes it possible to obtain on the one hand a solid containing, in particular, compounds based on iron and silicon and, on the other hand, a liquid. In a first branch of the process of the invention, the treatment of this solution is a treatment with an acidic pH in which an alkaline agent and an oxidizing agent are added to this solution. Note that in the present application, conventionally the indefinite article "a" must be considered as a generic plural (meaning "at least one" or "one or more"), except when the context shows the opposite (1 or "one"). Thus, for example, when it is stated above that an alkaline agent is added, it is the addition of one or more alkaline agents, and the same for the oxidizing agent. The alkaline agent used herein is preferably an alkali or alkaline earth metal oxide or hydroxide, such as an alkali metal oxide or hydroxide, such as, for example, magnesium hydroxide, sodium hydroxide, sodium hydroxide and the like. calcium oxide, sodium oxide or ammonia gas, preferably magnesium hydroxide or ammonia gas, and particularly magnesium hydroxide, or a mixture thereof. The latter may advantageously come, as will be seen hereinafter, from a subsequent step of the process of the present invention. The oxidant used may be, for example, chlorine, hydrogen peroxide, or gaseous oxygen, preferably hydrogen peroxide or oxygen gas, and particularly hydrogen peroxide, or a mixture of these as a mixture of hydrogen peroxide and gaseous oxygen. Part of the oxidant used may be the acid used in the previous step, when it is an oxidizing acid such as sulfuric acid. This treatment step e) at acidic pH in which an alkaline agent and an oxidizing agent can be used can be carried out for example at a pH of 1.5 to 4, preferably from 2 to 4, in particular from 2.5 to 3, 5, most preferably from 2.5 to about 30. The solid / liquid separation f) according to this step e) can be carried out under similar operating conditions in the previous solid / liquid separation step. It makes it possible to separate, on the one hand, compounds containing iron, in the solid phase, and on the other hand a liquid in the form of a solution that can be used as it is for the next step. Stage g) which consists of a treatment at basic pH comprises the addition of an alkaline agent until a basic pH, greater than or equal to 7.5 is obtained. The pH is for example 7 to 9.5, preferably from 7.5 to 9, especially from 7.5 to 8.5, most preferably from about 8. Under preferential conditions for carrying out step g), a metal flocculating agent, preferably a sulphurized compound, is added to the alkaline agent. Precipitation of metals is improved. The optional sulfur compound may for example be an alkali metal sulfide such as sodium sulfide or potassium sulfide, and particularly sodium sulfide. Note that if the sodium sulphide is chosen to aid the precipitation of nickel, the basic pH treatment step g) is advantageously carried out at a pH of 5 to 6 established for example with the aid of magnesium. If the sodium sulphide is chosen to aid the precipitation of nickel, the ratio of sodium sulphide and the solid product containing asbestos may represent in% for example from 0.4% to 0.8%, preferably from 0.5% to 0.7% especially 0.6%. If the sodium sulphide is selected to assist precipitation of the nickel, the precipitation is suitably carried out at 40 to 60 ° C, preferably 45 to 55 ° C, most preferably at about 50 ° C. For this purpose, the same alkaline agents can be used as before, and as before, magnesium oxide, or a mixture thereof with one or more other alkaline agents, is especially used, magnesium oxide being unable to come, as will be seen hereinafter, from a subsequent step of the process of the present invention. The solid / liquid separation h) following this step g) can be carried out under similar operating conditions in the previous solid / liquid separation step. It makes it possible to separate, on the one hand, compounds containing nickel or cobalt in the solid phase, in the hydroxide form of these metals, and, on the other hand, a liquid in the form of a solution which can be used as such for the next step.

Compounds containing nickel or cobalt may optionally be treated to extract nickel and cobalt. These treatments may consist of a precipitation produced by the addition of an alkaline agent, preferably an alkali or alkaline earth metal oxide, most preferably magnesium oxide. For its part, the solution liquid contains magnesium salts which can be converted into magnesium oxide by any appropriate treatment, this magnesium oxide can be used in the process described above as an alkaline agent. Suitable treatment may include treating the solution containing magnesium salts with a desiccant such as concentrated sulfuric acid, which provides magnesium sulfate which can be incinerated to give oxide. solid magnesium. Advantageously, the process of the invention comprises this step 15 for obtaining solid magnesium oxide and more particularly for using this solid magnesium oxide as an alkaline agent used in step e), in step g) or in these 2 steps. In the second branch of the process of the invention, in the second reaction medium obtained in step i), the ratio between the mass of solid obtained in step d) and the volume of the aqueous solution of the agent. alkali is 0.1 kg / L to 1 kg / L, preferably 0.4 kg / L to 0.6 kg / L, preferably 0.44 kg / L to 0.55 kg / L, especially 0 , 47 kg / L to 0.52 kg / L, most preferably about 0.5 kg / L. Under entirely preferred conditions of the invention, the alkaline agent used is sodium hydroxide and the ratio between the mass of solid obtained in step d) and the volume of the aqueous solution. of the alkaline agent in the second reaction medium obtained in stage e) is 0.4 kg / L to 0.6 kg / L, preferably 0.44 kg / L to 0.55 kg / L, in particular 0.47 kg / L to 0.52 kg / L, especially about 0.5 kg / L. The alkaline treatment of the solid obtained in step d) with the aid of the aqueous solution of the alkaline agent is advantageously carried out at a temperature of 60 ° C. to 100 ° C., preferably of 70 ° C. to 90 ° C. especially from 75 ° C to 85 ° C, most preferably about 80 ° C. The alkaline treatment time of the solid obtained in step d) with the aid of the aqueous solution of the alkaline agent can be, for example, 180 to 480 minutes, preferably 240 to 420 minutes, in particular 300 minutes. minutes to 360 minutes, especially about 320 minutes. The solid / liquid separation (k) following this alkaline agent treatment step j) can be carried out under similar operating conditions in the previous solid / liquid separation step d). This separation step makes it possible to obtain on the one hand a solid and on the other hand a liquid that can be used, such as for the next step. This liquid contains in particular silicon compounds such as silicates. To this liquid is added an ionic compound in aqueous solution which is an electronically neutral compound composed of ions. In a preferred embodiment of the invention, the ionic compound comprises ions identical to those of the compounds present in the liquid obtained in the solid / liquid separation step k). It is preferably selected from the group consisting of Na2SO4, NaCl, K2SO4, more preferably Na2SO4 or NaCl, and most preferably Na2SO4. For example, when the first mineral acid is sulfuric acid and the alkaline agent is sodium hydroxide, sodium sulfate will advantageously be chosen because it comprises both the anion and the cation of these compounds. The sodium sulphate may advantageously come from the liquid leachate of step d) above. A recycling is thus realized. The aqueous solution of the ionic compound is preferably saturated. Under very preferred conditions of implementation of the invention, the first mineral acid is sulfuric acid, the alkaline agent is sodium hydroxide and the ionic compound used is Na 2 SO 4. The ratio between the mass of solid obtained in step d) and the volume of the saturated aqueous solution of the ionic compound added in step I) is then advantageously from 1 kg / l to 5 kg / l, preferably from 1.5 kg / L to 4.5 kg / L especially 1.7 kg / L to 4.3 kg / L, especially 1.9 kg / L to 4.1 kg / L. The dilution liquid used in the next step is preferably an aqueous liquid, for example an aqueous solution of sodium sulfate, and preferably water. In still other preferred conditions of implementation of the invention, the ratio between the mass of solid obtained in step d) and the volume of dilution liquid added in step m) is 0.005 kg / L. at 0.4 kg / l, preferably from 0.075 kg / l to 0.3 kg / l, especially from 0.09 kg / l to 0.25 kg / l, more particularly from 0.01 kg / l to 0, 2kg / L. The pH of the dilute aqueous solution obtained in step m) is basic, greater than or equal to 7, preferably 10 to 13.75, especially 11 to 13.5, especially 11.5 to 13.5. 25. The addition of the aqueous solution of the second mineral acid in the dilute aqueous solution obtained in step m) makes it possible to lower the pH of said dilute aqueous solution and to precipitate the silicon compounds in the form of SiO 2 silica. The precipitation step n) is carried out by addition of an aqueous solution of the second mineral acid in the dilute aqueous solution obtained in step m) to obtain a pH value of less than or equal to 9, preferably of less than 8, especially less than 7, most preferably 5 to 6, singularly a pH of less than or equal to 5.5. The precipitation step n) is preferably carried out at a temperature of 80 ° C to 100 ° C, preferably 80 ° C to 98 ° C, especially 85 ° C to 97 ° C, most preferably 88 ° C to 80 ° C. 95 ° C. The duration of step n) may be, for example, 20 to 80 minutes, preferably 25 to 70 minutes, especially 30 minutes to 60 minutes, most preferably about 45 minutes. Under preferred conditions of implementation of the invention, step n) is carried out by successive additions of aqueous solutions of the second mineral acid, these additions being preferably less and less concentrated in acid. Under particular conditions of implementation of this last embodiment of the invention, the first aqueous solution of the second mineral acid comprises from 30 to 65% by weight, preferably from 35 to 60% by weight, in particular from 40 to 55% by weight. % by mass of mineral acid, and the second aqueous solution of the second mineral acid comprises from 5 to 20% by weight, preferably from 8 to 17% by weight, especially from 10 to 15% by weight of mineral acid. Under entirely preferred conditions of implementation of the invention, a first aqueous solution comprising from 40 to 55% by weight of sulfuric acid is added to the aqueous solution diluted in stage m) in order to lower the pH of said aqueous solution diluted to a value of about 6, then a second aqueous solution comprising from 10 to 15% by weight of sulfuric acid is added in order to lower the pH of said dilute aqueous solution to a value of 5 to 6. L The use of aqueous solutions which are less and less concentrated in mineral acid makes it possible firstly to save energy by means of the heat emitted by the acid / water reaction, and secondly to control the morphology. precipitate. Advantageously, the precipitate obtained in step n) is isolated, preferably by solid / liquid separation. The solid / liquid separation according to this step n) can be carried out under operating conditions similar to the previous solid / liquid separation step d). This separation step makes it possible to obtain, on the one hand, a liquid and, on the other hand, silica in the form of amorphous particles, that is to say particles having no crystalline periodicity of the Si and O atoms. constituting them. It is preferable to add a small amount of stabilizer such as NaCl, finally the stabilization time of the acidic silica sol can be maintained for 36 hours. The process of the invention may be carried out continuously, or preferably batchwise. Under entirely preferred conditions for carrying out the first branch of the invention, use is made of a divided solid product containing asbestos having a particle size of 200 to 400 mesh, in an aqueous solution ratio of sulfuric acid / solid product divided by about 3 L per kilogram, with a sulfuric acid concentration of 25%, the leaching being carried out at a temperature of 80 to 100 ° C, the oxidizing agent comprising hydrogen peroxide and gaseous oxygen. In such a process, preferably the leaching is carried out in 2 separate reactors and advantageously under the conditions previously described for this step. Even more preferentially, the alkaline agent used in steps e) and g) comprises magnesium oxide obtained at the end of the process.

The processes that are the subject of the present invention possess very interesting qualities. In particular, they make it possible to treat asbestos or asbestos waste or residues, while allowing the manufacture of magnesium as well as other metals such as cobalt, nickel, iron and their alloys. They also allow the manufacture of silica. The amorphous SiO 2 particles obtained have a porosity of at least 50% generated by pores whose diameter is less than or equal to 40 nm. The porosity of the amorphous SiO 2 particles is measured by Micromeritics Autopore porosity analyzer. These qualities are illustrated below in the experimental part.

They justify the use of the process of the invention in the treatment of asbestos waste or asbestos waste or asbestos waste. They also justify the use of amorphous SiO 2 particles obtained by the process of the invention, especially as a raw material for the production of monocrystalline silicon solar panels.

The process of the invention can be carried out on an industrial scale, that is to say on a scale allowing the treatment of at least 500 kg of asbestos residues per day, preferably at least 900 kg a day. This is why the present application also relates to the use of the processes described above, in particular - for the decontamination of asbestos residues or residues of asbestos mining materials, or - for the recovery of asbestos, to prepare magnesium and other metals such as those mentioned above. - for the manufacture of the catalyst support, - for the manufacture of food additives, - for the manufacture of reinforcing agents in macromolecular compounds including rubber and plastic, - for the manufacture of amorphous silicon solar panels, particularly the latter use.

The preferred conditions of implementation of the methods described above also apply to the other objects of the invention referred to above, in particular to their uses. They tend to obtain the best extraction yields possible.

The following examples illustrate the present application. Examples Common Steps Large blocks of asbestos residues containing magnetite were milled to a particle size of 74 and then 37 micrometers (respectively 200 and 400 mesh - measured by square mesh sieve). After grinding, the proportion of iron in the powder obtained is 3%. Step 1 In a first reactor, 65 g of the powder obtained was mixed with an aqueous solution of sulfuric acid at high temperature in a ratio (R) volume of sulfuric acid solution / weight of powders, at a temperature (0.degree. ) for a time (T). A solution containing a weight percent P1 of sulfuric acid was used. A solid phase Si of a liquid phase L1 was then filtered off using a Buchner funnel. The Si solid phase contained silicon. Stage 2 The liquid phase L1 is then transferred to a second reactor of the crystallizer type with a baffle circulation tube and carried with stirring. Sodium hydroxide, oxygen gas introduced at the base of the stirrer is added to adjust and maintain the pH to the pHi value. A precipitate is obtained. A solid phase S 2 is separated by filtration, using a Buchner funnel, from a liquid phase L 2. The solid phase S2 contains iron in the form of ferric oxide. Stage 3 The liquid phase L2 is then transferred to a 3rd reactor of the crystallizer type and stirred. Sodium hydroxide is added until a pH value of pH 9 is obtained. This gives a solid S3 precipitate containing hydroxides of nickel and cobalt and a solution L3 rich in salified magnesium, which is separated. by filtration using a Buchner funnel. Step 4 The liquid phase L2 is then treated with concentrated sulfuric acid to obtain a hydrated magnesium sulfate precipitate, which is calcined in the presence of sulfur to obtain magnesium oxide. Extraction rates of magnesium, iron, nickel and cobalt were determined. The extraction rates were expressed as a percentage based on the total amount of the corresponding element present in the starting material of the asbestos-containing process. Examples 1 to 6. Example H2SO4 Ratio Liq / Sol Time T Temperature 0% by weight L / Kg Min. ° C 1 10 7,625 120 81 2 18 3,908 120 75 3 26 2,596 120 92 4 26 2,567 120 84 28 2,564 120 71 6 40 1,526 120 73 The extraction results (`) / 0) obtained are as follows Example Magnesium Iron Nickel Cobalt 1 84% 42% 75% 28% 2 80% 38% 71% 32% 3 87% 56% 82% 45% 4 81% 51% 76% 35% 5 75% 44% 71% 34% 6 41% 78 % 24% 17% The results obtained show that above 30% by weight of sulfuric acid, the extraction rates of magnesium, nickel and cobalt drop significantly. With lower proportions of sulfuric acid, excellent results are obtained for these 3 metals, in particular for values of the order of 26-28% of sulfuric acid. Examples 7 to 16. Example H2SO4 Ratio Liq / Sol Time T Temperature 0% by weight L / Kg Min. ° C 7 26 2.567 60 92 8 26 2.567 90 93 9 26 2.567 120 92 26 2.596 60 103 11 26 2.596 90 104 12 26 2.596 120 103 13 28 2.564 60 73 14 28 2.564 90 72 28 2.564 120 71 16 28 2.564 150 71 The extraction results (`) / 0) obtained are as follows Example Magnesium Iron Nickel Cobalt 7 93% 57% 88% 41% 8 89% 55% 83% 37% 9 87% 56% 82% 45% 10 90% 53% 84% 42% 11 86% 58% 77% 38% 12 84% 59% 75% 39% 13 71% 38% 65% 30% 14 74% 41% 68% 32% 15 75% 44% 71% 34% 16 70% 49% 65% 29% The results obtained show that the extraction rates of magnesium, nickel and cobalt are excellent at high temperature, particularly for a leaching time of about one hour.

EXAMPLE 17 Step 1 In a reactor equipped with a mechanical stirrer, 64.51 g of the powder obtained in the above step was mixed with 200 ml of an aqueous solution of sulfuric acid (25.5% by weight). weight). The resulting reaction mixture was stirred for 60 minutes at 80 ° C. A precipitate is formed. Then filtered, using a ZPG vacuum filter disc from Shanghai Joyal Machinery Co., Ltd., 54.37 g of a solid phase S1a. Step 2 The solid phase S1a is then transferred to a second reactor and mixed with 110 mL of aqueous sodium hydroxide solution (977 g / L). The reaction mixture thus obtained was stirred for 90 minutes at 90 ° C. A solid phase S2a of a liquid phase L2a was then filtered off using a Shanghai Joyal Machinery Co., Ltd ZPG vacuum filter disc which was used as it was for the next step. Step 3 98 mL of L2a liquid phase was then transferred to a 3rd reactor and mixed with 27.2 mL of saturated aqueous Na2SO4 solution (300 g / L). This mixture was then diluted by adding water until an aqueous solution with a volume of 680 ml and a pH of 13.22 was obtained. 21.0 ml of an aqueous solution of sulfuric acid (44% by weight) in the preceding aqueous solution were then added and thus the pH of the aqueous solution was reduced to 9.63.

Addition of 3.2 mL of a second less concentrated aqueous sulfuric acid solution (25% by weight) lowered the pH of the previous aqueous solution to 5.91. Finally, the addition of 0.7 ml of a third aqueous solution of sulfuric acid even less concentrated (13.5% by weight) made it possible to lower the pH of the previous aqueous solution to 5. After 45 minutes, the resulting precipitate, consisting essentially of amorphous SiO 2 particles, is separated by filtration using a ZPG vacuum filter disc from Shanghai Joyal Machinery Co., Ltd. The mass of amorphous SiO 2 particles obtained is 12.1 g. The yield is 59.8% relative to the total silicon of the starting powder. Example 18 Step 1 In a reactor, 129.7 g of the powder obtained in the common step was mixed with 349 ml of an aqueous solution of sulfuric acid (25% by weight). The resulting reaction mixture was stirred for 120 minutes at 90 ° C. The filtration was then filtered off using a Shanghai Joyal Machinery Co., Ltd. ZPG vacuum filter disc (110.3 g) of a solid phase S1b. Step 2 48.6 g of the solid phase S1b was then transferred to a second reactor and mixed with 100 mL of aqueous sodium hydroxide solution (200 g / L). The reaction mixture thus obtained was stirred for 90 minutes at 90 ° C. Then filtered off, using a ZPG Vacuum Filter Disk from Shanghai Joyal Machinery Co., Ltd., 24 mL of a L2b liquid phase. Step 3 The liquid phase L2b was then transferred to a 3rd reactor and mixed with 12.5 mL of a saturated aqueous solution of Na2SO4 (300 g / L).

This mixture was then diluted by adding water until an aqueous solution with a volume of 303.7 ml and a pH of 11.59 was obtained. 7.0 ml of an aqueous sulfuric acid solution (44% by weight) was then added to the above aqueous solution and thus the pH of said 2.56 aqueous solution was lowered. After 45 minutes, the resulting precipitate, consisting essentially of amorphous particulate SiO 2, is filtered off using a Shanghai Joyal Machinery Co., Ltd. ZPG vacuum filter disc. The mass of amorphous particles of SiO 2 obtained is 1.95 g.

The yield is 96.0% based on the total silicon of the starting powder.

Claims (12)

REVENDICATIONS1. A process for treating an asbestos-containing product characterized in that it comprises the following steps, in the following order: a) supply of a divided solid product containing asbestos, b) preparation of a first reaction medium comprising the divided solid product containing asbestos and an aqueous solution of a first mineral acid, c) leaching treatment of the solid product divided with the aid of the aqueous solution of the first mineral acid, d) separation solid / liquid leachate, and firstly e) acid pH treatment of the liquid leachate obtained in step d) by addition of an alkaline agent and an oxidizing agent, f) solid / liquid separation, g) basic pH treatment of the liquid obtained in step f) by addition of an alkaline agent, h) solid / liquid separation to obtain in the solid phase a mixture containing nickel and cobalt hydroxides or nickel sulphides and cobalt, which is optionally treated to extracting nickel or cobalt or these two metals and in the liquid phase a magnesium salt which is optionally subjected to a magnesium oxide conversion treatment and, secondly, i) preparing a second reaction medium by mixing the solid obtained in stage d) with an aqueous solution of an alkaline agent, j) alkaline treatment of the solid obtained in stage d) with the aid of the aqueous solution of the alkaline agent, k) solid / liquid separation, I) addition to the liquid obtained in step k) of an aqueous solution of an ionic compound to obtain an ionic aqueous solution, m) addition to the ionic aqueous solution obtained in step I ) a dilution liquid to obtain a dilute aqueous solution, n) adding an aqueous solution of a second mineral acid in the dilute aqueous solution obtained in step m) to obtain a precipitate containing silica, and isolation of the precipitate if desired. 2. A method according to claim 1, characterized in that the first mineral acid is sulfuric acid and represents weight / volume of 22 to 30% of the reaction medium of step b). 3. A process according to claim 1 or 2, characterized in that the treatment of the solid product divided with an aqueous solution of a mineral acid is carried out at a temperature of 70 to 110 ° C. 4. A process according to one of claims 1 to 3, characterized in that during the leaching treatment of the solid product divided with the aid of an aqueous solution of a mineral acid, the liquid / solid ratio is 2.5 to 3.5 L per Kg. 5. A process according to one of claims 1 to 4, characterized in that the lixiviation treatment of the divided solid product is carried out in two successive reactors and in that in a first reactor, the solid product is divided Nine, and in a 2nd reactor is installed divided solid product which has been previously leached, which is mixed with an acidic solvent. 25 6. A process according to one of claims 1 to 5, characterized in that the alkaline agent of step e) or step g) is the magnesium oxide of step h) optional. 7. A process according to one of claims 1 to 6, characterized in that in step g) of basic pH treatment of the liquid obtained in step f), a flocculating agent is also used. metals as a sulfur compound. 8. The process according to one of claims 1 to 7, characterized in that the alkaline agent of step i) is sodium hydroxide and the ratio between the solid mass obtained in step d) and the the volume of aqueous solution of the alkaline agent in the second reaction medium obtained in step i) is 0.1 kg / l to 1 kg / l. 9. The method according to one of claims 1 to 8, characterized in that the ionic compound comprises ions identical to those of the compounds present in the liquid obtained in step k) and is Na2SO4 sodium sulfate. 10. The process as claimed in one of claims 1 to 9, characterized in that the precipitation step n) is carried out by adding an aqueous solution of the second mineral acid to the dilute aqueous solution obtained in step m). at a pH less than or equal to 5.5. 11. Use of a process as defined in one of claims 1 to 10 comprising the steps a) to h), for the decontamination of asbestos residues or residues of asbestos mining materials or - for the recovery of asbestos, to prepare magnesium and other metals. 20 12. Use of a process as defined in one of claims 1 to 10 comprising steps a) to d) and i) to n), for the manufacture of the catalyst support, for the manufacture of additives foodstuffs, for the manufacture of reinforcing agents in macromolecular compounds including rubber and plastic, or for the manufacture of amorphous silicon solar panels