A method for preparing boehmite coproduction potassium salt from alunite

Abstract

The application provides a method for preparing boehmite and co-producing potassium salt from alunite, and relates to the technical field of alunite recovery. After alunite powder is subjected to acid leaching by oxalic acid, filter residue and filtrate are separated, the filter residue is cleaned by a complexing agent aqueous solution to obtain high-purity aluminum sulfate, and the aluminum sulfate is subjected to hydrothermal reaction with aluminum hydroxide seed slurry to obtain boehmite with high regularity of morphology; the filtrate is added with ethanol to induce crystallization of potassium ferrioxalate, and the remaining mother liquor after separation is used to induce crystallization of potassium sulfate to obtain potassium sulfate crystals. The method is simple, can co-produce boehmite and potassium salt, and realizes efficient recovery of resources.

Description

Technical Field

[0001] This invention belongs to the field of alunite recovery technology and relates to a method for preparing boehmite and producing potassium salt from alunite. Background Technology

[0002] Alunite is a complex sulfate containing hydroxide ions, with the chemical formula KAl3(SO4)2(OH)6. It is a natural mineral resource rich in aluminum, potassium, and sulfur, widely used in the preparation of alumina, potassium sulfate, and aluminum salt chemicals. However, traditional alunite processing techniques suffer from the following bottlenecks: 1) Low resource utilization, with difficulty in the synergistic extraction of aluminum, potassium, and sulfur; 2) Focus primarily on single-product production (such as alumina or potassium sulfate), lacking systematic design for high-value-added products, resulting in low product added value and resource waste; 3) High-salt wastewater generated by strong acid / alkali leaching processes is costly to treat, and sulfur is primarily extracted as SO42-. 2- Such discharges can easily lead to eutrophication of water bodies and serious environmental pollution.

[0003] Therefore, the existing processes for extracting alunite and preparing other chemicals still need to be improved. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for preparing boehmite and co-producing potassium salts from alunite.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing boehmite co-production of potassium salt from alunite, comprising the following steps: Alum stone powder and oxalic acid aqueous solution are mixed at a solid-liquid volume ratio of 1:4-6 and then leached and separated to obtain filter residue and filtrate. The filter residue is washed with a complexing agent aqueous solution, then water is added to form a slurry, aluminum hydroxide seed slurry is added, and alkali is added to adjust the pH to 8.5-10. Then, a hydrothermal reaction is carried out. The product is washed and dried to obtain the boehmite. Ethanol was added to the filtrate to induce the precipitation and crystallization of potassium trioxalatoferrate, and the potassium trioxalatoferrate crystals were separated. The remaining mother liquor was used to induce the precipitation and crystallization of potassium sulfate to obtain potassium sulfate crystals.

[0007] Preferably, the alunite powder is derived from alunite ore and contains a small amount of Fe. 3+ ; The average particle size of the alunite does not exceed 100 μm; The concentration of the oxalic acid aqueous solution is 5-20 wt%.

[0008] Preferably, the leaching is ultrasonic-assisted leaching, the leaching temperature is 50-90℃, and the leaching time is 1-5h.

[0009] Preferably, the complexing agent in the aqueous complexing agent solution is selected from one or more of EDTA and its derivatives, o-phenanthroline, and bipyridine; The concentration of the complexing agent aqueous solution is 0.01-0.2 mol / L.

[0010] Preferably, the aluminum hydroxide seed slurry is obtained by ball milling aluminum hydroxide particles and a dispersant mixed at a weight ratio of 1:0.01-0.03.

[0011] More preferably, the dispersant is selected from one or more of polyethyleneimine, polyallylamine hydrochloride, polydiallyl ammonium chloride, polyethylene polyamine, diethylenetriamine condensate, polyquaternary ammonium salt, amino-modified polyacrylamide, and polyvinylpyrrolidone.

[0012] Preferably, the average particle size of the seeds in the aluminum hydroxide seed slurry does not exceed 10 μm; The average particle size of the aluminum hydroxide particles is 20-50 μm; The weight ratio of the slurry after adding water to the filter residue to the aluminum hydroxide seed slurry is 1:0.05-0.25.

[0013] Preferably, the alkali is ammonia. The hydrothermal reaction is carried out at 180-220℃ for 6-12 hours.

[0014] Preferably, the volume ratio of the filtrate to the ethanol is 1:1-3.

[0015] Preferably, when the remaining mother liquor induces potassium sulfate to crystallize, the mother liquor is evaporated and concentrated, and the ethanol is recovered before inducing potassium sulfate to crystallize.

[0016] The beneficial effects of this invention are as follows: This invention proposes a green and low-cost comprehensive utilization technology for alunite, which realizes the efficient extraction and high-value co-production of aluminum and potassium elements. By optimizing the acid leaching process to selectively remove impurities and introducing hydrothermal crystallization technology, the aluminum element in alunite is efficiently converted into boehmite (recovery rate ≥75%) and the morphology of boehmite is controllable. At the same time, potassium trioxalatoferrate and potassium sulfate are co-produced, which has the advantages of low raw material cost and green and efficient process. Attached Figure Description

[0017] Figure 1 This is a SEM image of boehmite obtained in Example 1.

[0018] Figure 2 This is a SEM image of boehmite obtained in Example 1.

[0019] Figure 3 This is a photograph of potassium trioxalatoferrate obtained in Example 1. Detailed Implementation

[0020] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0021] This invention proposes a method for preparing boehmite and co-producing potassium salts from alunite, the steps of which include: Alum stone powder and oxalic acid aqueous solution are mixed at a solid-liquid volume ratio of 1:4-6 and then leached and separated to obtain filter residue and filtrate. After washing the filter residue with a complexing agent aqueous solution, water is added to form a slurry, aluminum hydroxide seed slurry is added, and alkali is added to adjust the pH to 8.5-10. Then, a hydrothermal reaction is carried out. The product is washed and dried to obtain boehmite. Ethanol was added to the filtrate to induce the precipitation and crystallization of potassium trioxalatoferrate. The potassium trioxalatoferrate crystals were then separated. The remaining mother liquor was used to induce the precipitation and crystallization of potassium sulfate to obtain potassium sulfate crystals.

[0022] Oxalic acid, as a weak organic acid, is insufficient to disrupt the stable, complex sulfate lattice structure of alunite. Under normal conditions, oxalic acid is difficult to dissolve the bulk alunite. However, oxalic acid is also an excellent complexing agent, exhibiting superb dissolving and complexing ability for metallic impurities (such as iron, calcium, potassium, and sodium) in alunite, converting them into salts that dissolve in the filtrate. Therefore, this invention uses an aqueous oxalic acid solution to leach alunite powder, separating the aluminum sulfate component (filter residue) from its other components (mainly potassium trioxalatoferrate, potassium sulfate, oxalic acid, and small amounts of other oxalates dissolved in the filtrate). The main component of the filter residue is aluminum sulfate, along with trace amounts of other impurity metal ions (such as magnesium, calcium, and iron ions). Utilizing the characteristics of the complexing agent—stable but slow complexation with aluminum ions, and stable but fast complexation with other impurity metal ions—the other impurity metal ions are removed from the filter residue by washing with an aqueous solution of the complexing agent, based on the difference in complexation rates, thus obtaining high-purity aluminum sulfate. The aluminum sulfate then undergoes a hydrothermal reaction under alkaline conditions with aluminum hydroxide as a seed crystal to obtain high-purity boehmite. Based on the alunite content in the alunite powder, the boehmite recovery rate is over 75%.

[0023] Potassium tris(oxalato)ferrate is highly soluble in water but insoluble in ethanol (e.g., anhydrous ethanol). Adding ethanol reduces the solubility of potassium tris(oxalato)ferrate and causes it to crystallize out, yielding potassium tris(oxalato)ferrate crystals. Based on the iron content in the alunite powder, the recovery rate of potassium tris(oxalato)ferrate crystals is no less than 60%. The mother liquor also contains potassium sulfate, which can be separated by induced crystallization to obtain potassium sulfate crystals. Based on the potassium content in the alunite powder, the recovery rate of potassium sulfate is approximately 10% (or less), with the majority of potassium ions present in the potassium tris(oxalato)ferrate crystals.

[0024] In some embodiments, the alunite powder is derived from alunite ore and contains a small amount of Fe. 3+ ; The average particle size of alunite does not exceed 100 μm; The concentration of oxalic acid aqueous solution is 5-20 wt%.

[0025] In this invention, the alunite powder is derived from alunite ore (or alunite tailings after flotation, which basically does not contain silicon dioxide) and contains a certain amount of Fe. 3+ For alunite tailings, Fe 3+ The content (calculated as iron oxide) can reach about 4-5 wt%.

[0026] The lower the average particle size of alunite, the more complete the leaching with oxalic acid aqueous solution, and the higher the leaching efficiency. Specifically, the concentration of the oxalic acid aqueous solution can be 5wt%, 10wt%, 15wt%, 20wt%, etc.

[0027] In some embodiments, leaching is ultrasonic-assisted leaching, the leaching temperature is 50-90°C, and the leaching time is 1-5 hours.

[0028] Ultrasonic-assisted leaching can improve leaching efficiency. There are no particular limitations on the frequency of the ultrasound, for example, it can be 20-70kHz. The leaching temperature can be 50℃, 60℃, 70℃, 80℃, 90℃, etc., and the leaching time can be 1h, 2h, 3h, 4h, 5h, etc.

[0029] In some embodiments, the complexing agent in the aqueous complexing agent solution is selected from one or more of EDTA and its derivatives, o-phenanthroline, and bipyridine; The concentration of the complexing agent aqueous solution is 0.01-0.2 mol / L.

[0030] The complexing agent mentioned above has a slow complexing rate with aluminum ions but a fast complexing rate with other metal ions, thereby removing other metal ions through the washing method of the complexing agent.

[0031] For example, the concentration of the complexing agent aqueous solution can be 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.13 mol / L, 0.15 mol / L, 0.17 mol / L, 0.2 mol / L, etc.

[0032] In some embodiments, the aluminum hydroxide seed slurry is obtained by ball milling aluminum hydroxide particles and a dispersant mixed at a weight ratio of 1:0.01-0.03.

[0033] Dispersants not only facilitate the grinding of aluminum hydroxide particles and their transformation into low-size aluminum hydroxide seed crystals, but also serve as dispersants and regulate the morphology of boehmite during subsequent hydrothermal reactions, resulting in more regularly structured boehmite. For example, the weight ratio of aluminum hydroxide particles to dispersant can be 1:0.01, 1:0.015, 1:0.02, 1:0.025, 1:0.03, etc.

[0034] There are no particular limitations on the ball milling time; it can be set as needed, such as 2-6 hours. There are also no particular limitations on the milling media; for example, zirconium oxide media can be used, the ball-to-material ratio can be 3-5:1, and the milling speed can be 200-500 rpm.

[0035] In some embodiments, the dispersant is selected from one or more of polyethyleneimine, polyallylamine hydrochloride, polydiallyl ammonium chloride, polyethylene polyamine, diethylenetriamine condensate, polyquaternary ammonium salt, amino-modified polyacrylamide, and polyvinylpyrrolidone.

[0036] In some embodiments, the average particle size of the seeds in the aluminum hydroxide seed slurry does not exceed 10 μm; The average particle size of aluminum hydroxide particles is 20-50 μm; The weight ratio of the slurry after adding water to the filter residue to the aluminum hydroxide seed slurry is 1:0.05-0.25.

[0037] For example, the weight ratio of the filter residue slurry after water conditioning to the aluminum hydroxide seed slurry can be 1:0.05, 1:0.1, 1:0.15, 1:0.2, 1:0.25, etc. The concentration of the filter residue slurry after water conditioning can be 10-50 wt%.

[0038] Furthermore, the average particle size of the seeds in the aluminum hydroxide seed slurry does not exceed 5 μm, or even further, the average particle size of the seeds does not exceed 1 μm.

[0039] In some embodiments, the alkali is ammonia water; The hydrothermal reaction is carried out at 180-220℃ for 6-12 hours.

[0040] In some embodiments, the volume ratio of filtrate to ethanol is 1:1-3. For example, the volume ratio of filtrate to ethanol can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, etc.

[0041] In some embodiments, when the remaining mother liquor induces potassium sulfate to crystallize, the mother liquor is evaporated and concentrated, and ethanol is recovered before inducing potassium sulfate to crystallize.

[0042] When the mother liquor is evaporated and concentrated, ethanol can be recovered and the concentration of potassium sulfate can be increased to achieve supersaturation and crystallization can be induced.

[0043] Therefore, the method for preparing boehmite and producing potassium salt from alum stone of the present invention has the following characteristics: (1) The raw material cost for preparing boehmite is reduced by more than 40%, and the waste liquid can recover potassium salt by-products - potassium sulfate and potassium trioxalate ferrate, realizing the high-value utilization of resources. The recovery rate of boehmite reaches more than 75%, the recovery rate of potassium trioxalate ferrate crystals is not less than 60%, and some potassium sulfate is also recovered; (2) The synergistic system of oxalic acid leaching-EDTA washing is adopted, and the impurity removal rate of aluminum sulfate is increased to not less than 98% (the impurity removal rate of single acid leaching is only about 85%); (3) Boehmite is prepared by the coupled process of acid leaching-hydrothermal reaction, avoiding the high energy consumption problem of traditional high-temperature calcination. The reaction conditions are mild and suitable for industrial continuous production; (4) For alum stone containing iron ions, Fe can be recovered together, which not only improves the resource recovery efficiency, but also avoids the iron removal process and improves production efficiency.

[0044] When the iron content in alunite powder is low (e.g., below 0.5%), less potassium tris(oxalato)ferrate is formed. In the filtrate obtained after leaching, potassium sulfate crystals can be first concentrated and separated, and then a larger volume of anhydrous ethanol can be added to separate potassium tris(oxalato)ferrate. Under this technical approach, the potassium sulfate recovery rate is relatively high, reaching 30-50%, and the potassium tris(oxalato)ferrate (calculated as Fe) recovery rate can reach approximately 70%.

[0045] The technical solution of the present invention will be further described and illustrated below with reference to various embodiments. Unless otherwise specified, the parts mentioned in the following embodiments are parts by weight.

[0046] Example 1 Alunite (alumite tailings, silica removed by flotation) was crushed and ground to an average particle size of 42 μm to obtain alunite powder with an iron oxide content of 4.2 wt%.

[0047] Alum stone powder and an 8 wt% oxalic acid aqueous solution were mixed at a volume ratio of 1:5, and ultrasonic-assisted leaching was performed at 80°C for 2 hours (ultrasonic frequency 40 kHz). Fe 3+ K + Allow soluble ions to fully dissolve in the solution. After leaching, filter to separate the residue and filtrate.

[0048] The main component of the filter residue is aluminum sulfate, and it also contains sulfates of other impurity metal ions. The filter residue is washed twice with a 0.1 mol / L EDTA aqueous solution at a solid-liquid volume ratio of 1:3 for 30 minutes to remove adsorbed or residual magnesium, calcium, iron and other impurity metal ions, resulting in pretreated filter residue, which is aluminum sulfate.

[0049] Ultrafine aluminum hydroxide (average particle size 30 μm) and polyethyleneimine dispersant were mixed at a weight ratio of 1:0.02 and added to a zirconia ball mill jar (ball-to-material ratio 5:1). The mixture was ball-milled at 300 rpm for 4 hours to obtain a highly dispersible seed slurry.

[0050] The pretreated filter residue was mixed with deionized water to obtain a slurry with a concentration of 50 wt%. This slurry was then mixed with a highly dispersible seed slurry at a weight ratio of 1:0.1 and added to a high-pressure reactor. The pH of the system was adjusted to 9.5 with ammonia, and then a hydrothermal reaction was carried out at 180°C for 12 hours. After the reaction, the solid product was separated by centrifugation, washed three times each with anhydrous ethanol and deionized water, and then vacuum dried at 60°C for 6 hours to obtain boehmite powder.

[0051] The SEM image of the boehmite powder obtained in this embodiment is attached. Figure 1 and attached Figure 2 As shown, it exhibits a highly regular morphology. Based on the aluminum content in the alunite powder, the boehmite recovery rate in this embodiment is 78%.

[0052] The filtrate described above is an oxalic acid leachate, mainly composed of potassium trioxalatoferrate, potassium sulfate, oxalic acid, and small amounts of other oxalates. Anhydrous ethanol was added to the filtrate (filtrate to anhydrous ethanol volume ratio of 1:1), and after stirring for 30 minutes, the mixture was allowed to stand for crystallization. The potassium trioxalatoferrate crystals and mother liquor were obtained by filtration. A photograph of the potassium trioxalatoferrate obtained in this example is attached. Figure 3 As shown.

[0053] The mother liquor was evaporated under reduced pressure at 80°C to one-third of its volume, while simultaneously recovering ethanol. After cooling to room temperature, a small amount of potassium sulfate microcrystals was added to induce potassium sulfate crystallization. The crystals were then filtered and dried under vacuum at 60°C to obtain the potassium sulfate product. The remaining liquid contained oxalic acid, which could be recycled back to the leaching step.

[0054] Based on the iron content in alunite powder, the recovery rate of potassium trioxalatoferrate crystals is 68%. Based on the potassium content in alunite powder, the recovery rate of potassium sulfate is 11%.

[0055] Example 2 The difference between this embodiment and Embodiment 1 is that in Embodiment 1, the concentration of the oxalic acid aqueous solution was adjusted from 8 wt% to 15 wt%. The remaining steps remain unchanged.

[0056] The boehmite powder obtained in this embodiment has a highly regular morphology. Based on the aluminum content in the alunite powder, the boehmite recovery rate in this embodiment is 83%.

[0057] Based on the iron content in alunite powder, the recovery rate of potassium trioxalatoferrate crystals was 74%. Based on the potassium content in alunite powder, the recovery rate of potassium sulfate was 12.5%.

[0058] Example 3 Alunite was crushed and ground to an average particle size of 45 μm to obtain alunite powder with an iron oxide content of 4.6 wt%.

[0059] Alum stone powder and a 10wt% oxalic acid aqueous solution were mixed at a volume ratio of 1:4, and ultrasonic-assisted leaching was performed at 70℃ for 3 hours (ultrasonic frequency 40kHz). Fe 3+ K + Allow soluble ions to fully dissolve in the solution. After leaching, filter to separate the residue and filtrate.

[0060] The main component of the filter residue is aluminum sulfate, and it also contains sulfates of other impurity metal ions. The filter residue is washed twice with a 0.05 mol / L disodium EDTA aqueous solution at a solid-liquid volume ratio of 1:4 for 30 minutes to remove adsorbed or residual magnesium, calcium, iron and other impurity metal ions, resulting in pretreated filter residue, which is aluminum sulfate.

[0061] Ultrafine aluminum hydroxide (average particle size 30 μm) and polyethyleneimine dispersant were mixed at a weight ratio of 1:0.01 and added to a zirconia ball mill jar (ball-to-material ratio 5:1). The mixture was ball-milled at 300 rpm for 4 hours to obtain a highly dispersible seed slurry.

[0062] The pretreated filter residue was mixed with deionized water to obtain a slurry with a concentration of 30 wt%. This slurry was then mixed with a highly dispersible seed slurry at a weight ratio of 1:0.15 and added to a high-pressure reactor. The pH of the system was adjusted to 9 with ammonia, and then a hydrothermal reaction was carried out at 210°C for 8 hours. After the reaction, the solid product was separated by centrifugation, washed three times each with anhydrous ethanol and deionized water, and then vacuum dried at 60°C for 6 hours to obtain boehmite powder.

[0063] The boehmite powder obtained in this embodiment has a highly regular morphology. Based on the aluminum content in the alunite powder, the boehmite recovery rate in this embodiment is 80%.

[0064] The above filtrate is an oxalic acid leachate, the main components of which are potassium trioxalatoferrate, potassium sulfate, oxalic acid, and a small amount of other oxalates. Anhydrous ethanol was added to the filtrate (the volume ratio of filtrate to anhydrous ethanol was 1:3), and the mixture was stirred for 30 minutes before being allowed to stand for crystallization. The resulting solution was filtered to obtain potassium trioxalatoferrate crystals and the mother liquor.

[0065] The mother liquor was evaporated under reduced pressure at 80°C to one-third of its volume, while simultaneously recovering ethanol. After cooling to room temperature, a small amount of potassium sulfate microcrystals was added to induce potassium sulfate crystallization. The crystals were then filtered and dried under vacuum at 60°C to obtain the potassium sulfate product. The remaining liquid contained oxalic acid, which could be recycled back to the leaching step.

[0066] Based on the iron content in alunite powder, the recovery rate of potassium trioxalatoferrate crystals is 72%. Based on the potassium content in alunite powder, the recovery rate of potassium sulfate is 8%.

[0067] As described above, the basic principles, main features, and advantages of the present invention have been shown and described. Those skilled in the art should understand that the present invention is not limited to the above embodiments, which are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent changes and modifications made in accordance with the scope of the patent and the description should still fall within the scope of the present invention. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing boehmite and co-producing potassium salts from alunite, characterized in that the steps include... include: Alum stone powder and oxalic acid aqueous solution are mixed at a solid-liquid volume ratio of 1:4-6 and then leached and separated to obtain filter residue and filtrate. The filter residue is washed with a complexing agent aqueous solution, then water is added to form a slurry, aluminum hydroxide seed slurry is added, and alkali is added to adjust the pH to 8.5-10. Then, a hydrothermal reaction is carried out. The product is washed and dried to obtain the boehmite. Ethanol was added to the filtrate to induce the precipitation and crystallization of potassium trioxalatoferrate, and the potassium trioxalatoferrate crystals were separated. The remaining mother liquor was used to induce the precipitation and crystallization of potassium sulfate to obtain potassium sulfate crystals.

2. The method for preparing boehmite and co-producing potassium salt from alunite according to claim 1, characterized in that, The alunite powder is derived from alunite ore and contains a small amount of Fe. 3+ ; The average particle size of the alunite does not exceed 100 μm; The concentration of the oxalic acid aqueous solution is 5-20 wt%.

3. The method for preparing boehmite and co-producing potassium salt from alunite according to claim 1, characterized in that, The leaching is ultrasonic-assisted leaching, with a leaching temperature of 50-90℃ and a leaching time of 1-5 hours.

4. The method for preparing boehmite and co-producing potassium salt from alunite according to claim 1, characterized in that, The complexing agent in the aqueous solution is selected from one or more of EDTA and its derivatives, o-phenanthroline and bipyridine; The concentration of the complexing agent aqueous solution is 0.01-0.2 mol / L.

5. The method for preparing boehmite and co-producing potassium salt from alunite according to claim 1, characterized in that, The aluminum hydroxide seed slurry is obtained by ball milling aluminum hydroxide particles and dispersant mixed at a weight ratio of 1:0.01-0.

03.

6. The method for preparing boehmite and co-producing potassium salt from alunite according to claim 5, characterized in that, The dispersant is selected from one or more of polyethyleneimine, polyallylamine hydrochloride, polydiallyl ammonium chloride, polyethylene polyamine, diethylenetriamine condensate, polyquaternary ammonium salt, amino-modified polyacrylamide, and polyvinylpyrrolidone.

7. The method for preparing boehmite and co-producing potassium salt from alunite according to claim 1, characterized in that, The average particle size of the seeds in the aluminum hydroxide seed slurry does not exceed 10 μm; The average particle size of the aluminum hydroxide particles is 20-50 μm; The weight ratio of the slurry after adding water to the filter residue to the aluminum hydroxide seed slurry is 1:0.05-0.

25.

8. The method for preparing boehmite and co-producing potassium salt from alunite according to claim 1, characterized in that, The alkali is ammonia water; The hydrothermal reaction is carried out at 180-220℃ for 6-12 hours.

9. The method for preparing boehmite and co-producing potassium salt from alunite according to claim 1, characterized in that, The volume ratio of the filtrate to the ethanol is 1:1-3.

10. The method for preparing boehmite and co-producing potassium salt from alunite according to claim 1, characterized in that, When the remaining mother liquor induces potassium sulfate to crystallize, the mother liquor is evaporated and concentrated, and the ethanol is recovered before inducing potassium sulfate to crystallize.

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