Method for processing alumina-containing raw material

Abstract

The invention relates to the field of non-ferrous metallurgy, and more particularly to technology for the production of alumina from alumina-containing raw material. The present method includes crushing, grinding and pressure leaching a raw material containing alumina to produce aluminate liquor and red mud. The aluminate liquor is separated from the red mud and sent for decomposition to produce a mother liquor and a precipitate. The precipitate is separated from the mother liquor, classified and split into product aluminium hydroxide, which is washed and then sent for calcination to produce alumina, and aluminium hydroxide seed recycle, which is recycled to the decomposition stage. The invention makes it possible to increase the percent decomposition of aluminate liquor in the decomposition process.

Description

[0001] IPC COIF 7 / 14, 7 / 38

[0002] METHOD FOR PROCESSING ALUMINA-BEARING RAW MATERIALS

[0003] Field of technology to which the invention relates

[0004] The invention relates to the field of non-ferrous metallurgy, in particular to the technology of producing alumina from alumina-containing raw materials.

[0005] State of the art

[0006] Bauxite is the primary raw material for aluminum production. The Bayer process is a widely used method for extracting alumina from bauxite. The first step is wet milling. After wet milling, the pulp is fed to the leaching process, passing through a classifier. The Bayer process uses autoclaves combined into batteries for leaching.

[0007] A method for producing aluminum hydroxide according to USSR A.S. No. 1644452 (OAO All-Russian Aluminum-Magnesium Institute, IPC C01F7 / 14, September 27, 1998) is known in the art. The invention relates to a process for producing alumina from bauxite using the Bayer process. Seed aluminum hydroxide is added to an aluminate solution, the resulting suspension is fed to a battery of decomposers, the suspension is maintained under stirring, followed by its removal and separation into seed and product aluminum hydroxide, and the seed aluminum hydroxide is fed as a suspension into the aluminate solution. The product aluminum hydroxide is filtered, diluted with industrial water, and classified. Fine aluminum hydroxide is used as seed, and coarse filtered aluminum hydroxide is washed and removed from the process. This improves product quality by increasing its particle size and reducing impurity content. A disadvantage of this alternative is the low decomposition rate of the aluminate solution.PECHINEY ALUMINIUM IPC (France) received patent FR2709302, March 3, 1995, for a method for producing alumina with controlled alkali content and particle size. A key feature of this method is the high solids content of the aluminate solution (over 700 g / L). The seed for decomposition is aluminum hydroxide, as is common in traditional aluminate solution decomposition processes. A drawback of this method, like the previous one, is the insufficient percentage of aluminate solution decomposition.

[0008] A method for decomposing aluminate solutions is also known, according to Russian Patent No. 2231497 (OAO All-Russian Aluminum-Magnesium Institute, IPC C01F7 / 14, June 27, 2004). The method involves mixing the aluminate solution at a temperature of 45-70°C in the presence of aluminum hydroxide seed and a modifying additive, and separating the mother liquor from the aluminum hydroxide. Lithium carbonate is used as a modifying additive, introduced in an amount of 0.10 to 0.30 wt.% of the resulting aluminum hydroxide precipitate. A disadvantage of this method is the increased cost of alumina production due to the need to use a lithium compound as a modifying additive.

[0009] A method for processing alumina-containing raw materials is widely known (Lainer A.I., Alumina Production. Moscow: Metallurgy Publishing House, 1961. 620 p., p. 571), which was chosen as a prototype for the proposed invention.

[0010] A known method for processing alumina-containing raw materials includes autoclave leaching of raw materials containing alumina to produce an aluminate solution and red mud, separating the aluminate solution from the red mud and sending it to a decomposition stage to produce a mother liquor and a precipitate containing aluminum hydroxide, separating the precipitate from the mother liquor, with further classification of the precipitate by dividing the precipitate into production aluminum hydroxide, which after washing is sent for calcination to produce alumina, and into recycled aluminum hydroxide seed, which is again sent back into circulation for the decomposition operation.

[0011] According to the prototype, the crystallization stage is accomplished by decomposition (spinning) in the presence of a seed. The decomposition (spinning) operation is accomplished by continuous stirring at a temperature of 62-40°C (see the cited source by A.I. Layner, p. 267) of the aluminate solution seeded with freshly precipitated aluminum hydroxide for 60-100 hours (see the cited source by A.I. Layner, p. 255). It is also indicated that the percentage of decomposition of the aluminate solution during decomposition is 50-52%, but under production conditions it may be lower than these values, which reduces the overall process performance.

[0012] Disclosure of the essence of the invention

[0013] The technical objective of the invention is to increase the percentage of decomposition of the aluminate solution during the decomposition process.

[0014] The technical result consists in increasing the percentage of decomposition of the total flow of aluminate solution in the decomposition process, and the productivity of evaporation batteries also increases, since the initial alkali-aluminate solution becomes more concentrated in Na2Ototal, and the removal of alumina from 1 m3 increases. 3 solution and the productivity of the technological process as a whole.

[0015] In order to solve the stated problem and achieve the technical result, a method for processing alumina-containing raw materials is proposed, including autoclave leaching of raw materials containing alumina, with the production of an aluminate solution and red mud, separation of the aluminate solution from the red mud and sending it to the decomposition stage, with the production of a mother liquor and a precipitate containing aluminum hydroxide, separation of the precipitate from the mother liquor, with further classification of the precipitate by dividing the precipitate into production aluminum hydroxide, which after washing is sent for calcination to obtain alumina, and into recycled seed aluminum hydroxide, which is again sent into circulation for the decomposition operation.

[0016] Unlike the prototype, part of the aluminate solution obtained after autoclave leaching is sent to the preparation of an active seed, and the remaining part of the aluminate solution is mixed with the recycled seed and the obtained active seed and sent to the decomposition stage, in particular, the aluminate solution is divided into two parts before decomposition, sodium bicarbonate is added to the first part to obtain a solid precipitate of aluminum hydroxide as an active seed, the second part of the aluminate solution is sent to the decomposition stage in the presence of the recycled seed with preliminary mixing of the recycled seed with the obtained active seed.

[0017] Experiments have shown that dividing the aluminate solution into two parts allows one portion to be isolated to produce active seed. This can be accomplished by adding sodium bicarbonate. The second portion of the aluminate solution, after mixing with the recycled seed and the active seed, is sent to the decomposition process. The active seed obtained in this processing method has a developed specific surface area, significantly larger than that of the recycled seed. Active seed implies a high specific surface area. As the authors' experiments have shown, this allows for a more complete decomposition of the aluminate solution, i.e., a higher percentage.

[0018] Brief description of the drawings

[0019] Fig. 1 shows the process flow diagram of the proposed method. Implementation of the invention

[0020] The process flow diagram of the proposed method, shown in Fig. 1, includes the following stages: bauxite crushing, grinding with the addition of recycled liquor, autoclave leaching of alumina-containing raw materials to produce an aluminate solution and red mud, separation of the aluminate solution from the red mud, and sending it to a decomposition stage, where the solution flow is divided into two parts. The first part of the aluminate solution is sent to produce an active seed by adding sodium bicarbonate. The second part of the aluminate solution, after mixing with the recycled liquor and the active seed, is sent to decomposition to produce a mother liquor and a precipitate containing aluminum hydroxide.Next comes the stage of separating the precipitate from the mother liquor, with further classification of the precipitate by dividing the precipitate into production aluminum hydroxide, which after washing is sent for calcination to obtain alumina, and into recycled aluminum hydroxide seed, which is again sent back into circulation for the decomposition operation.

[0021] In Experiment 1, to enable comparison of results, the process was conducted under prototype conditions. Under laboratory conditions, the process involved autoclave leaching of alumina-containing raw materials to produce an aluminate solution and red mud. The aluminate solution was separated from the red mud and sent to the decomposition stage, producing a mother liquor and a precipitate containing aluminum hydroxide. The precipitate was separated from the mother liquor, followed by classification of the precipitate by separating it into product aluminum hydroxide, which after washing was sent for calcination to produce alumina, and into recycled aluminum hydroxide seed, which was recycled back to the decomposition stage. The resulting aluminate solution had the following chemical composition: Na2O K =l 33.3g / dm 3 ; AI2O3 = 132.4 g / dm3 3 (caustic modulus of the initial solution a к = 1.66).

[0022] The decomposition (spinning) operation was carried out by continuous stirring of the aluminate solution pulp with a recycled aluminum hydroxide seed at a temperature (according to the prototype) of 62-40°C for 60 hours. As a result of this operation, aluminum hydroxide is released from the aluminate solution.

[0023] According to the formula (see formula (X-5) in the indicated source by A.I. Lainer, p. 268), the percentage of decomposition of the aluminate solution was calculated, which in this experiment turned out to be equal to 50-52%: t|Al2O3 = (a м -A а )*100% / a м , where t|Al2oz is the percentage of decomposition of the aluminate solution, and м - caustic modulus of the mother liquor, and м - caustic modulus of the original aluminate solution.

[0024] Experiments (examples) 2-14 in Table 1 are provided to illustrate the proposed method. Bauxite was crushed using a laboratory jaw crusher, then ground in recycled liquor in a rod mill. Autoclave leaching of the bauxite was performed, followed by thickening and washing, separating the aluminate solution from the red mud. The aluminate solution was then mixed with active and recycled seed materials, and then decomposed to produce a mother liquor and a precipitate containing aluminum hydroxide. The mother liquor was then classified to produce aluminum hydroxide as aluminum hydroxide precipitate and recycled seed material. The aluminum hydroxide was then calcined to produce alumina. The mother liquor was then evaporated. After evaporation, the recycled solution was sent to the bauxite grinding stage. After classification, the recycled seed was sent to the mixing stage.

[0025] In experiments 2-14, the amount of sodium bicarbonate added was varied within the range of 1 to 10% to obtain the active seed, which was then mixed with the recycled seed. The aluminate solution obtained after autoclave leaching of bauxite, containing 133.3 g / dm 3 NaiO K , 132.4 g / dm 3 AЬОз (caustic modulus of the initial solution a к= 1.66) was divided into two parts. The first part of the aluminate solution in the amount of 0.3% of the total flow was sent to the preparation of an active seed by adding sodium bicarbonate salt to the aluminate solution in an amount of 1 - 10% of the ACO3 content in the original aluminate solution, and kept for 8 hours in a crystallizer at a temperature of 40-45 °C without stirring. This technique allows for an increase in the percentage of decomposition of the aluminate solution due to the production of an active seed of aluminum hydroxide with a developed specific surface area. The second part of the aluminate solution in the amount of 99.7 wt. % of the total amount was sent for decomposition with the addition of a mixture of recycled and active seeds.

[0026] The results of the experiments are presented in Table 1.

[0027] Table 1. Comparison of process indicators for the prototype and the proposed technical solution in the preparation of the active primer.

[0028] In the table, row 1 shows the conditions for implementing the process according to the prototype; the decomposition percentage reaches 50-52%. When adding the active seed according to the proposed variant (experiments 2-12) at a temperature of 62-50°C and varying the amount of sodium bicarbonate added during the preparation of the active seed within the range of 1-4.0% of the AI2O3 content in the solution (experiments 2-6), no signs of solution decomposition were detected, which is associated with the small number of crystallization centers and the low diffusion capacity of the medium.

[0029] At a temperature of 62-50°C and varying the amount of sodium bicarbonate added during the preparation of the active seed within the range of 5-9% of the AI2O3 content in the aluminate solution (experiments 7-11), the percentage of solution decomposition was achieved in the range of 52.2-55.5%. However, with an increase in the addition of sodium bicarbonate salt in an amount of 10% (experiment 12), no increase in the percentage of aluminate solution decomposition was observed. Furthermore, a further increase in the addition of sodium bicarbonate salt is undesirable, as it leads to the accumulation of carbonate ions in the solution, leading to the decausticization of the active alkali, which may subsequently negatively affect the technological parameters of the autoclave leaching process of the original bauxite raw material.

[0030] In the description of experiments 2-14 it is shown that the temperature for obtaining the active seed is preferably 40-45 °C to ensure the required effect.

[0031] In example (experiment) 9, the obtained active seed pulp, without separating the mother liquor from it, was sent to the operation of mixing the second part of the aluminate solution with the recycled seed and to the decomposition operation with a holding time of 60 hours, the resulting aluminum hydroxide precipitate was separated from the liquid phase (mother liquor), which was analyzed for its Na2O content. к and AI2O3, the caustic modulus of the resulting mother liquor was calculated, and the percentage of decomposition of the aluminate solution was calculated using the well-known formula (X-5) (see the cited source by A.I. Lainer, p. 268). The amount of added NaHCO3 was fixed at 7 wt.% of the Al2O3 content in the aluminate solution. The amount of aluminate solution used to prepare the active seed was varied in the range of 0.1-0.6 wt.% of the total volume of the aluminate solution fed to decomposition.

[0032] The experimental results are presented in Table 2, experiments (examples) 15-21. It should be noted that experiments 9 and 18 were performed under identical conditions; in the others, the proportion of the flow allocated to the preparation of the active seed was changed at a dosage of 7% of the ACO3 content in the solution.

[0033] Table 2. Comparison of process indicators for the prototype and the proposed technical solution when mixing the active seed with the main mass of the recycled seed.

[0034] As can be seen from the presented results, the use of active seed mixed with recycled seed allows for an increase in the percentage of aluminate solution decomposition by 3-5% compared to the prototype. With a further increase or decrease in the aluminate solution flow to more than 0.5% or less than 0.2% of the total flow fed to obtain the active seed, no positive effect is observed. Thus, the optimal range for the volume of aluminate solution sent for the preparation of the active seed was established, equal to 0.2-0.5 wt.% of the total flow with the addition of sodium bicarbonate in an amount of 5-9 wt.% of the AI2O3 content, g / dm3. 3 in solution.

[0035] As experiments carried out by the authors of the present invention have shown, adding sodium bicarbonate to the isolated portion of the aluminate solution and holding it at a certain temperature makes it possible to sharply intensify the process of separating aluminum hydroxide from the solution with the production of an active seed due to an increase in the rate of the polymerization reaction of aluminum ions with the release of aluminum hydroxide from the aluminate solution with a developed specific surface area into the solution.

[0036] Taking into account the given description, examples, and the technical result achieved, the scope of legal protection is claimed for a method for processing alumina-containing raw materials, including crushing, grinding, and autoclave leaching of raw materials containing alumina to obtain an aluminate solution and red mud, separating the aluminate solution from the red mud and sending it to the decomposition stage, to obtain a mother liquor and a precipitate containing aluminum hydroxide, separating the precipitate from the mother liquor, with further classification of the precipitate by dividing the precipitate into production aluminum hydroxide, which after washing is sent for calcination to obtain alumina, and into recycled aluminum hydroxide seed, which is again sent back into circulation to the decomposition stage, wherein part of the aluminate solution obtained after autoclave leaching is sent to the preparation of an active seed,and the remaining portion of the aluminate solution is mixed with the recycled seed and the resulting active seed and sent to the decomposition stage.

[0037] Preferably, the aluminate solution is divided into two parts before decomposition. Sodium bicarbonate is added to the first part to form a solid aluminum hydroxide precipitate as an active seed. The second part of the aluminate solution is sent to the decomposition stage in the presence of recycled seed, with the recycled seed premixed with the resulting active seed. To prepare the active seed, sodium bicarbonate is added to the aluminate solution in an amount of preferably 5-9 wt.% of the AI2O3 content in the solution. Preferably, 0.2-0.5 wt.% of the aluminate solution obtained after autoclave leaching is used to prepare the active seed. The active seed preparation temperature is preferably 40-45°C.

Claims

CLAUSES OF THE INVENTION E. A method for processing alumina-containing raw materials, including crushing, grinding and autoclave leaching of raw materials containing alumina, with the production of an aluminate solution and red mud, separating the aluminate solution from the red mud and sending it to the decomposition stage, with the production of a mother liquor and a precipitate containing aluminum hydroxide, separating the precipitate from the mother liquor, with further classification of the precipitate by dividing the precipitate into production aluminum hydroxide, which after washing is sent for calcination to obtain alumina, and into a recycled seed of aluminum hydroxide, which is again sent back into circulation to the decomposition stage, wherein part of the aluminate solution obtained after autoclave leaching is sent to the preparation of an active seed, and the remaining part of the aluminate solution is mixed with the recycled seed and the obtained active seed and sent to the stage decomposition.

2. The method according to item 1, in which the aluminate solution is divided into two parts before decomposition, sodium bicarbonate is added to the first part to obtain a solid precipitate of aluminum hydroxide as an active seed, and the second part of the aluminate solution is sent to the decomposition stage in the presence of a recycled seed with preliminary mixing of the recycled seed with the obtained active seed.

3. The method according to paragraph 1 or 2, characterized in that, to prepare the active seed, sodium bicarbonate is added to the aluminate solution in an amount of preferably 5-9 wt.% of the Al2O3 content in the solution.

4. The method according to item 1 or item 2, characterized in that 0.2-0.5 wt.% of the aluminate solution obtained after autoclave leaching is preferably used to prepare the active seed.

5. The method according to paragraph 1 or 2, wherein the temperature for producing the active seed is preferably 40-45 °C.

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