MXPA98004747A - Procedure to recover alumina and sil - Google Patents

Abstract

The present invention relates to: A process for the simultaneous recovery of substantially pure alumina and silica from aluminosilicate. The process comprises the following steps: (1) heating the aluminosilicate with hydrated CaCl 2 to obtain calcium-aluminum-silicate and calcium-aluminate products, wherein the CaCl 2 is substantially free of MgCl 2, leaching the products with HC 1 to form a solution comprising A1C13 and CaCl2, and insoluble silica, (iii) separating the insoluble silica from the solution, and (iv) crystallizing A1C13 from the solution and recovering the alumina from the crystallized A1C13. The process may further comprise the following steps: (v) substantial removal of the MgC12 from the CaC12 solution from step (iv), and (vi) recycling the CaC12 solution to be used in the step (

Description

PROCEDURE TO RECOVER ALUMINA AND SILICA DESCRIPTION OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a process for the recovery of substantially pure alumina and silica from raw materials containing aluminosilicates, and particularly from waste products resulting from the combustion of coal.

BACKGROUND OF THE INVENTION Coal combustion remains one of the main sources of energy in many parts of the world. The solid waste that remains after combustion is the so-called coal ash, which comprises fly ash, the fine particles collected from the combustion without gas by electrostatic precipitators, and the ashes remaining in the bottom of the combustion vessels. The volume of coal ash resulting from the combustion of coal around the world is constantly increasing, resulting in the problem of eliminating waste without harming the environment is increasing. In addition, the REF: 27709 availability of waste products without cost and its proximity to energy sources and transportation make them attractive as raw materials for the extraction of various chemical products. The chemical composition of coal ash varies as a function of the source and type of coal. However, A1203 and Si02 are almost always the main components of the ash, usually in the form of aluminosilicates and quartz. Therefore it could be advantageous to use coal ash as a source of alumina and silica: The main source of pure alumina today is bauxite, with alumina being generally extracted by the Bayer process. Since bauxite is found in large quantities and alumina can be extracted relatively easily and cheaply, any alternative methods for extracting alumina must be economically competitive with the Bayer process. In the calculation of the costs of the procedure, the savings in elimination and maintenance of the elimination site should be taken into account, as well as environmental considerations. Numerous methods have been reported for recovering carbon alumina (Seeley, F G., Canon, R.M. and McDowell, J., "Chemical Development of New Processes for the Recovery of Resource Materials from Coal Ash", Oak Ridge National Laboratory, Contract W-7405-eng-26; Felker, K., et al. , "Aluminum from Fly Ash"; Chemtech 12 (2): 123-8 (1982)). These include direct acid leaching methods, calcination sintering and lime sintering methods, a lime-sintering process and the Calsinterization procedure. Direct acid leaching (either single-stage or multi-stage) with HCl, HN03, or H2S04 usually results in very low recovery rates of Al (less than 50%). Calcining and lime / sinus sintering procedures involve the sintering of coal waste at 1200-1300 ° C with powdered limestone (CaC03) or limestone and soda ash (Na2C03) to form calcium or sodium aluminates. The aluminates are then dissolved by leaching with Na 2 CO 3. In the lime-sintering process, a mixture of NaCl-Na2CO3 is sintered with fly ash, cooled in a water leach and then leached in dilute HN03 or H2SO--? Solution. . The Calsinterization process (developed in the Oak Ridge National Laboratory, Tennessee, USA) involves the combustion of a system of -sinterization of CaS04-CaC03-fly ash and an acid leaching with H2S04.

Recently, another method has been described for the recovery of aluminosilicates alum in GB 2,205,558. In this method, the aluminosilicate is reacted with dehydrated calcium and / or magnesium chloride, with or without a minor portion of sodium chloride. An insoluble waste is obtained in leached water which is treated, preferably with the application of heat, with a mineral acid such as HCl, which forms a water soluble aluminum salt. The salt is then diluted with water to produce an aqueous solution of the aluminum salt and an insoluble residue comprising hydrated silica. The aluminum is then recovered from the saline solution. None of the above procedures is related to the simultaneous extraction of silica from coal ash. The U.S. No. 1,868,499 to Guertler discloses a process for the recovery of alumina from siliceous materials such as clay, leucite and siliceous bauxite. The procedure comprises the steps of heating the siliceous material with CaCl2 at 650-900 ° C, treating the hot mixture with HCl to dissolve and separating the CaCl2 for its reuse and conversion of aluminum to A1C13, separating the precipitate from non-gelatinous silicic acid, and purify the A1C13 solution and decompose it to form alumina. There is no indication of the purity of the metal oxides extracted, nor is there any indication that recycled CaCl2 undergoes any treatment.

BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to provide a process for the simultaneous recovery of alumina and silica from various aluminosilicate-containing materials, and in particular coal ash. A further object of the present invention is to provide a high performance process, which results in the recovery of substantially pure alumina and silica. A further object of the invention is to provide an extraction process, which is economically competitive with the known processes for the extraction of alumina. According to the present invention, there is provided a process for the simultaneous recovery of substantially pure alumina and silica from aluminosilicate, comprising the following steps: (i) heating the aluminosilicate with hydrated CaCl 2 to obtain calcium-alumina-silicate products and calcium-aluminate, wherein the CaCl 2 salt is substantially free of MgCl 2; (ii) leaching the products with HCl to form a solution comprising A1C13 and CaCl2 and insoluble silica; (iii) separating the insoluble silica from the solution; and (iv) crystallize the A1C13 from the solution and recover the alumina from the crystallized A1C13. The term "substantially pure" as used in the present specification with respect to the alumina and silica products is preferably related to a purity of > 97%, and more preferably with a purity of > 99% In one modality Preferred of the present invention, the process comprises the following additional steps: (v) substantially removing MgCl2 from the CaCl2 solution of step (iv); and (vi) recycling the CaCl 2 solution for use in step (i). The reuse of CaCl2 contributes to the efficiency of the process. According to another preferred embodiment of the present invention, Fe is extracted from the A1C13 solution of step (ii) either by ion exchange or solvent extraction before or after the crystallization of AICI3 from step (iv).

The novel process of the present invention differs from the processes described above, such as those described in GB 2,205,558 and US 1,868,499, in which MgCl 2 is removed from the CaCl 2 salt before the heating step. Heating the aluminosilicate-containing material in the presence of MgCl2 and A1C13 results in the formation of spinel MgO'Al203 (71.8% of A1203).

The spinel is insoluble in HCl therefore it precipitates with the silica along with the alumina contained in it, reducing the yield of the alumina and the contamination of the silica. The CaCl2 / which is recovered from the recycling process must also be purified from MgCl2, since many sources of aluminosilicates contain small amounts of Mg impurities, which are dissolved in HCl during the leaching stage. Preferably, MgCl2 is removed by precipitation with Ca (0H) 2. Thus, the use of CaCl 2, which is substantially free of Mg in the heating step, contributes significantly to the yield and purity of the products. This affects the efficiency and profitability of the procedure, making it economically competitive with respect to the Bayer procedure.

BRIEF DESCRIPTION OF THE DRAWING The present invention will be better understood from the following detailed description of the preferred embodiments, taken in conjunction with Figure 1, which is a flowchart of the method of the invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Now the procedure will be described in a general way. Raw materials that can be used in the process of the invention include rejected carbon, fly ash, collars, kaolin, slate, clays and other materials containing aluminosilicate. The hydrated CaCl2 may be in the form of salt or brine. In the first step of the process of the invention, the hydrated CaCl 2 is reacted with a material containing aluminosilicates and at a temperature between 900-1300 ° C, and preferably at a temperature of 1000-1100 ° C. This temperature is lower than the temperatures of the previously described procedures (1300-1400 ° C), but higher than the temperature used in the process described in the Guetler patent, supra. He CaCl2 is added to the aluminosilicate-containing material at a weight ratio of 0.5: 1 - 3: 1 depending on the composition of the material phase and its relative aluminum content, as well as the concentrations of mulite and silica. More preferably, the weight ratio is in the range of 0.5: 1 - 2: 1. Preferably, the mixture of aluminosilicate and CaCl 2 salt is dried at 200-250 ° C to obtain a solid mixture before heating (sintering). The aluminosilicate reacts with CaCl2, for example according to the following reaction: A16S¡; 013 + (Al: O3-SiO, "CaO) + SiO: + xCaCl2 + yH2O -> 2CaO-Al203-Si02 + Al2O3-2Si? ': CaO + 12CaO-7Al2O3 + 2yHCl where x and y = 2-4. Released HCl can be absorbed in a gas trap and used in the last steps. In the second step, the aluminum and calcium salts are leached from calcium-aluminum-silicate by HCl at a concentration of 2-8N. According to the previous example, the reaction is as follows: Ca ^ A SiO, + CaAl, Si203 + CaI2Al? 4033 + 84HC1 I8AICI3 x 15CaCl2 + 42H20 + 3Si02 The resulting solution may contain a number of salts in addition to A1C13 and CaCl2 such as FeCl3, MgCl2 and heavy metals. The Si02 residue can be separated from the saline by known methods such as filtration and decantation. Si02 will usually have a purity greater than 97% and a yield > 90% In the final step of the procedure, A1C13 is separated from the solution by concentration and crystallization in a strongly acidic environment (HCl). Due to differences in solubility in the presence of a high concentration of chloride ion, A1C13 crystallizes earlier than other salts in the solution. The crystals of AICI3 are filtered and the alumina is recovered by hydrolytic decomposition according to the following reaction: heat 2AIC13 + 3H, 0 > AI3O3 + 6HC1 The HCl can be recovered for reuse. The A1203 will usually be recovered to a purity of > 99% and a performance > 95% The Fe can also be recovered from the solution either by ion exchange or liquid extraction before or after the crystallization of A1C13.

The remaining solution contains a high concentration of CaCl2, which can be recovered for reuse in the first step of the procedure after the removal of MgCl2, for example by precipitation with Ca (OH) 2. Precipitation with Ca (0H) 2 also removes other metal chlorides present in the solution. Figure 1 illustrates the complete procedure of the invention, which includes recycling the different components. The following examples illustrate the different aspects of the invention.

Example 1 50 parts by weight of fly ash were mixed with 50 parts by weight of calcium chloride dihydrate. The mixture was heated for 1 hour at 1100 ° C and then kept at 1100 ° C for an additional 1 hour during which HCl vapors were released. The solid product was leached perfectly with hot 6N HCl solution. 20 parts by weight of the product were leached for 2 hours with 100 ml of 6N HCl at 103 ° C. The analysis of the residue on dry basis was: % by weight Si02 98 CaO 0.5 A1203 0.6 Fe203 0.1 Ti02 0.6 lcalis 0.2 The examination of the acid solution obtained by leaching showed that it contained more than 95% of the total alumina content in the fly ash used, and other metal chlorides in smaller amounts. The A1C13 * 6H20 was crystallized from the leaching solution increasing the concentration of hydrochloric acid to 30%. The crystals were filtered, washed with HCl and dissolved before being decomposed hydrolytically by heating to 400-600 ° C to produce pure alumina.

Example 2 930 parts by weight of CaCl2 * 2H20 were dissolved in 485 parts by weight of water. 790 parts by weight of fly ash were added to the solution. The mixture was dried for 3 hours at 230 ° C. The dried product was then heated at 1100 ° C for 1 hour and maintained at 1100 ° C for an additional 1 hour during which HCl vapors were released.

The product was leached perfectly with hot 6N HCl solution. 20 parts by weight of the product were leached for 2 hours with 100 ml of 6N HCl at 103 ° C. The silica content in the residue was 98.6% of the dry material. The yield was 95%. The examination of the acid solution obtained by leaching showed that it contained 98% of the total alumina content in the fly ash used. The A1C13 * 6H20 was crystallized from the leaching solution increasing the HCl concentration to 30%. The crystals were filtered and dissolved before hydrolytic decomposition by heating at 400-600 ° C to produce pure alumina.

Example 3 The composition of the acid filtrate of the crystallization step of A1C13 * 6H20 of Example 2 was: % by weight A1C13 1.54 FeCl3 1.38 CaCl2 14.4 MgCl2 0.7 TÍC14 - 0.41 Solubles 1.02 Sulfates 4.71 H20 41.8 HCl (liquid) 34.1 total 100 Fe ions were extracted from the previous solution. Then 654, parts by weight of the solution were treated with 7.35 parts by weight of CaCO3 and subsequently with 20.5 parts by weight of Ca (OH) 2 to precipitate the Mg (OH) 2 and the insoluble metal hydroxides and gypsum. The composition of the purified solution is: % by weight A1C13 1.6 CaCl2 35 alkali: i-s 1.5 other chlorides 0.7 H20 61.2 total 100 420 parts by weight of the purified solution were mixed with 200 parts by weight of fly ash. The mixture was heated to dryness at 220 ° C. The dried product was heated at 1100 ° C for 1 hour and then kept at 1100 ° C for an additional 30 minutes during which vapors of HCl, NaCl, FeCl3, etc. were released.

The product was leached thoroughly with a hot 6N HCl solution. 20 parts by weight of the product were leached for 2 hours with 200 ml of 3N HCl at 103 ° C. The silica content in the residue was 98.8% of the dried material. The yield was 95.5%. The examination of the acid solution obtained by leaching showed that it contained 97% of the total alumina content in the fly ash used. The A1C13 * 6H20 was crystallized from the leaching solution increasing the concentration of hydrochloric acid to 30%. The crystals were filtered and dissolved before hydrolytic decomposition by heating to 400-600 ° C to produce pure alumina. Although the present invention has been described in terms of several preferred embodiments, it is expected that several modifications and improvements will occur to those skilled in the art after consideration of this description. The scope of the invention should not be limited to the illustrative embodiments set forth herein, but is determined in accordance with the appended claims.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (13)

1. A process for the simultaneous recovery of substantially pure alumina and silica from an aluminosilicate, characterized in that it comprises the following steps: (i) heating the aluminosilicate with hydrated CaCl 2 to obtain products of calcium-alumina-silicate and calcium-aluminate, wherein CaCl 2 is substantially free from MgCl 2; (ii) leaching the products with HCl to form a solution comprising A1C13 and CaCl2 and insoluble silica; (iii) separating the insoluble silica from such a solution; (iv) crystallize the A1C13 from the solution and recover the alumina from the crystallized A1C13; (v) substantially removing MgCl2 from the CaCl2 solution of step (iv); and (vi) recycling the CaCl2 solution for use in step (i).

2. The process according to claim 1, characterized in that the aluminosilicate is contained in a material selected from the group comprising rejected carbon, fly ash, kaolin, slate, and clays.

3. The process according to claim 1, characterized in that the CaCl2 is added to the aluminosilicate in a weight ratio of 0.5: 1 - 3: 1.

4. The process according to claim 1, characterized in that the insoluble silica is separated from the solution in step (iii) by filtration.

5. The process according to claim 1, characterized in that the insoluble silica is separated from the solution in step (iii) by decantation.

6. The process according to claim 1, characterized in that the alumina is recovered from the A1C13 crystallized in step (iv) by hydrolytic decomposition.

7. The process according to claim 1, characterized in that the Mg is removed from the salt by precipitation with Ca (0H) 2.

8. The process according to claim 1, characterized in that the CaCl 2 salt used in step (i) is in the form of a brine.

9. The process according to claim 1, characterized in that the mixture of aluminosilicate and CaCl 2 salt of step (i) is dried at 200-250 ° C before heating.

10. The method according to claim 1, characterized in that the heating is carried out at a temperature of 900-1300 ° C.

11. The method according to claim 10, characterized in that the heating is carried out at a temperature of 1100-1220 ° C.

12. The process according to claim 1, characterized in that Fe is extracted from the A1C13 solution of step (ii) either by ion exchange or liquid extraction before the crystallization of A1C13 from step (iv).

13. The process according to claim 1, characterized in that Fe is extracted from the A1C13 solution of step (ii) either by ion exchange or liquid extraction after crystallization of A1C13 from step (iv).