Method for preparing aluminum sulfate

Abstract

The invention relates to the technical field of aluminum sulfate, in particular to a method for preparing aluminum sulfate. According to the method, the process of leaching the aluminum element from the aluminum ash and removing impurities in the prior art is optimized, the leaching rate of the aluminum element in the aluminum ash is greatly increased by two steps of alkaline leaching and ultrasonic-assisted alkaline leaching in the alkaline leaching process, the reaction conditions are mild, high temperature and high pressure are not needed, the nitrogen removal efficiency is high, meanwhile, the aluminum loss in the aluminum leaching process is reduced, and the method is suitable for industrial production. The organic complexing impurities are precipitated, and the precipitate generated by the complexing impurities is adsorbed by using the hydrogel as a carrier, so that the difficulty of impurity removal, precipitation and filtration is reduced, and the prepared aluminum sulfate is high in purity.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum ash recycling, and specifically relates to a method for preparing aluminum sulfate. Background Art

[0002] At present, the preparation process of aluminum sulfate is mainly to use sulfuric acid to decompose bauxite to prepare aluminum sulfate. Although this method is mature and low-cost, bauxite is a non-renewable resource. With the increasing annual aluminum demand in my country, the mining volume of bauxite has increased year by year, resulting in the gradual depletion of bauxite resources in many regions. Therefore, it is necessary to explore other ways to prepare aluminum sulfate to slow down the consumption of bauxite. Aluminum ash is a solid waste residue produced during the smelting, cutting and recycling of aluminum materials in the aluminum-related industrial production process. It is mainly composed of aluminum, soluble salts and oxides, and contains a variety of valuable heavy metals, nitrides and fluorides and other harmful substances. Most of the aluminum in aluminum ash is wrapped by aluminum oxide and aluminum nitride. At present, the main treatment method for aluminum ash resource recovery in China is to recover the metallic aluminum in aluminum ash, but the research on the secondary aluminum ash related resource recovery after the recovery of metallic aluminum is still in the experimental stage.

[0003] The Chinese invention patent with publication number CN112142085A discloses a method for producing polyaluminium sulfate using aluminium ash, wherein the aluminium ash is ground, and water 3-5 times the weight of the aluminium ash is added and stirred to obtain an aluminium ash suspension, and calcium chloride and calcium acetate are added to the suspension for denitrification and defluorination, and then solid-liquid separation is performed, and the separated solid is harmless aluminium ash; 1.0-1.5 tons of harmless aluminium ash, 1.5-2.0 tons of concentrated sulfuric acid and 5-10 tons of water are added to a reactor, reacted for 2-4 hours, and then 5-10 kg of a stabilizer, 10-15 kg of polyethylene glycol and 3-5 kg ​​of hexadecyltrimethylammonium bromide are added, stirred for 0.5-1.5 hours, and aluminium sulfate liquid is obtained; and then filtered, dried and packaged to obtain polyaluminium sulfate. However, the prior art has the technical problems that the energy consumption loss in the aluminium ash preparation process is large, the equipment is easily worn out, and the purity of the obtained aluminium sulfate is low. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing aluminum sulfate, which is used to solve the technical problems in the prior art that the aluminum ash preparation process has large energy loss and easy equipment wear, and the purity of the prepared aluminum sulfate is low.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing aluminum sulfate comprises the following steps: S1. Pretreatment: grinding the aluminum ash in a grinder, passing through a 200-300 mesh sieve, adding the ground aluminum ash into deionized water to wash and remove soluble salt substances, filtering and separating the chlorine-containing and fluorine-containing solution and the solid, and collecting the solid to obtain low-chlorine and low-fluorine aluminum ash; S2, alkali leaching: alkali leaching is divided into two steps. In the first alkali leaching, low-chlorine and low-fluorine aluminum ash is added to a dilute alkali solution, and the reaction is carried out under stirring to remove nitrogen. The generated ammonia gas is absorbed by carbonic acid to obtain ammonium bicarbonate. After the reaction is completed, the solution and solid are separated by filtration, and the solid is collected to obtain denitrified aluminum ash. In the second alkali leaching, the denitrified aluminum ash is added to a concentrated alkali solution, and ultrasonic-assisted leaching is performed. After the reaction is completed, the salt residue is filtered to obtain a sodium aluminate solution; S3, purification: adding the sodium aluminate solution to the ammonium bicarbonate obtained in S2, adjusting the pH to 8-9 to precipitate aluminum hydroxide, and collecting the precipitate to obtain a crude aluminum hydroxide product; S4, acid leaching: adding the crude aluminum hydroxide to sulfuric acid, adjusting the pH to 4-4.5 to obtain a crude aluminum sulfate solution, adding an impurity complexing agent to complex the impurities and precipitate them, filtering the impurities, and obtaining an aluminum sulfate solution; S5. Crystallization: Concentrate the aluminum sulfate solution at 50-80°C to a concentration of 30-60wt%, cool it down to crystallize, collect the crystals, grind them, wash them with an organic solvent, and dry them to obtain aluminum sulfate.

[0006] Preferably, the water washing related parameters in S1 are set as follows: the water washing temperature is 50-60° C., the water washing time is 6-12 hours, and the solid-liquid volume ratio of aluminum ash to deionized water is 1:6-9.

[0007] Preferably, the chlorine-containing and fluorine-containing solution collected by filtration in S1 absorbs fluorine element through calcium chloride to produce calcium fluoride byproduct and defluorinated liquid phase, and the defluorinated liquid phase is mixed with the liquid collected by filtration once through alkaline leaching in S2, and then concentrated and crystallized after neutralization with acid to obtain electrolyte salt.

[0008] Preferably, the dilute alkali solution in the first alkali leaching process in S2 is 2-4 g / L sodium hydroxide solution, the solid-liquid volume ratio of the low-chlorine and low-fluorine aluminum ash to the dilute alkali solution is 1:6-9, the alkali leaching temperature is 75-85°C, and the alkali leaching time is 3-4 h.

[0009] Preferably, the concentrated alkali solution in the secondary alkali leaching process in S2 is 200-250 g / L sodium hydroxide solution, the solid-liquid volume ratio of aluminum ash to concentrated alkali solution is 1:7-10, the alkali leaching temperature is 50-60°C, the alkali leaching time is 4-6 h, and the ultrasonic power is 100 w.

[0010] Preferably, the concentration of sulfuric acid in S4 is 5-12.5wt%.

[0011] Preferably, the amount of the impurity complexing agent added in S4 is 5-8% of the crude aluminum sulfate solution.

[0012] Preferably, the aluminum sulfate solution in S5 is cooled to room temperature for crystallization.

[0013] Preferably, the organic solvent in S5 is one or more combinations of anhydrous ethanol, anhydrous methanol, anhydrous n-propanol and anhydrous isopropanol.

[0014] Preferably, the method for preparing the impurity complexing agent in S4 comprises the following steps: S11, adding deionized water and polyacrylic acid into a blender, stirring for 10 to 30 minutes, then adding sodium dimethyldithiocarbamate, diammonium dihydrogen phosphate and phytic acid, stirring for 10 to 30 minutes to obtain a mixture; S12, adding a cross-linking agent to the mixture, heating in a water bath at 60-65°C for 0.5-1h, adding an initiator and continuing to heat in a water bath at 60-65°C until gelation, to obtain an impurity complexing agent.

[0015] Preferably, in the preparation method of the impurity complexing agent, the mass ratio of sodium dimethyldithiocarbamate, diammonium dihydrogen phosphate, phytic acid, deionized water, polyacrylic acid, crosslinking agent and initiator is 20~30:10~15:5~8:100:20~50:0.5~1.5:0.3~0.5.

[0016] Preferably, the cross-linking agent in S12 is one or more combinations of N,N'-methylenebisacrylamide, diethylene glycol dimethacrylate and ethylene glycol diacrylate.

[0017] Preferably, the initiator in S12 is one or more combinations of ammonium persulfate, potassium persulfate and ammonium persulfate-sodium bisulfite initiator.

[0018] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. The present invention improves the resource utilization of aluminum ash by optimizing the process of leaching aluminum element and removing impurities from aluminum ash in the prior art, and further processes the waste liquid and waste gas in the recovery process to generate calcium fluoride by-products and electrolyte salt by-products used in the aluminum refining process, and the obtained aluminum sulfate solid has high purity, low energy consumption in the preparation process, and improved economic benefits.

[0019] 2. The present invention adopts two-stage alkali leaching and ultrasound-assisted aluminum leaching. The alkali leaching reaction conditions are relatively mild and do not require high temperature and high pressure. While achieving high denitrification efficiency, it reduces aluminum loss during the aluminum leaching process and saves recovery costs.

[0020] 3. The present invention compounds the content of sodium dimethyldithiocarbamate, ammonium dihydrogen phosphate and phytic acid components, and wraps the impurity complexing agent made of polyacrylic acid cross-linked hydrogel to achieve the purpose of impurity removal by organic complexing other impurities, and uses the polyacrylic acid hydrogel as a carrier to adsorb the precipitate generated by the complexed impurities, thereby reducing the difficulty of impurity removal precipitation filtering and improving the purity of the prepared aluminum sulfate solid. The impurity complexing agent used is easy to obtain and the production cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 It is a process flow chart of the method for preparing aluminum sulfate of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] The aluminum ash used in the present invention has a gray powdery solid appearance, and the contents of the various components of the aluminum ash are shown in Table 1: Table 1 Example 1, see Figure 1 As shown, a method for preparing aluminum sulfate in this embodiment comprises the following steps: S1. Pretreatment: add 1 t of aluminum ash into a grinder and grind it, pass it through a 200-mesh sieve, add the ground aluminum ash into deionized water with a volume of 9 times that of the aluminum ash, set the water washing temperature to 50°C and the water washing time to 10 hours, wash away soluble salt substances, filter and separate the chlorine-containing and fluorine-containing solution and solid, and collect the solid to obtain low-chlorine and low-fluorine aluminum ash; S2, alkali leaching: alkali leaching in two steps, in the first alkali leaching, low chlorine and low fluorine aluminum ash is added to 3g / L sodium hydroxide solution with 8 times the volume of low chlorine and low fluorine aluminum ash, the alkali leaching temperature is 80°C, and the alkali leaching is carried out for 4 hours under stirring. The generated ammonia gas is absorbed by carbonic acid to obtain ammonium bicarbonate. After the reaction is completed, the solution and solid are separated by filtration, and the solid is collected to obtain denitrified aluminum ash. In the second alkali leaching, the denitrified aluminum ash is added to 200g / L sodium hydroxide solution with 8 times the volume of denitrified aluminum ash, the alkali leaching temperature is 50°C, the alkali leaching time is 5h, and the ultrasonic power of ultrasonic assisted leaching is 100w. After the reaction is completed, the salt residue is filtered to obtain sodium aluminate solution; S3, purification: adding the sodium aluminate solution to the ammonium bicarbonate obtained in S2, adjusting the pH to 9 to precipitate aluminum hydroxide, and collecting the precipitate to obtain a crude aluminum hydroxide product; S4, acid leaching: adding the crude aluminum hydroxide to 5wt% sulfuric acid, adjusting the pH to 4.5 to obtain a crude aluminum sulfate solution, adding an impurity complexing agent at 5% of the mass of the crude aluminum sulfate solution to complex impurities and precipitate, filtering the impurities, and obtaining an aluminum sulfate solution; S5. Crystallization: Concentrate the aluminum sulfate solution at 70°C to a concentration of 50 wt%, then reduce the temperature to room temperature to allow the aluminum sulfate to crystallize, collect the crystals, grind them, wash them with anhydrous ethanol, and dry them to obtain aluminum sulfate.

[0025] The preparation method of the impurity complexing agent S4 comprises the following steps: S11, adding 1 kg of deionized water and 500 g of polyacrylic acid into a blender, stirring for 30 min, then adding 300 g of sodium dimethyldithiocarbamate, 150 g of diammonium dihydrogen phosphate and 50 g of phytic acid, stirring for 30 min, to obtain a mixture; S12. Add 10 g of N, N'-methylenebisacrylamide to the mixture, heat it in a water bath at 60°C for 1 h, add 5 g of ammonium persulfate, and continue heating in a water bath at 60°C until gelation occurs to obtain an impurity complexing agent.

[0026] Example 2, see Figure 1 As shown, a method for preparing aluminum sulfate in this embodiment comprises the following steps: S1. Pretreatment: add 1 t of aluminum ash into a grinder and grind it, pass it through a 200-mesh sieve, add the ground aluminum ash into deionized water with a volume of 9 times that of the aluminum ash, set the water washing temperature to 60°C, and the water washing time to 12 hours to wash away soluble salt substances, filter and separate the chlorine-containing and fluorine-containing solution and solids, and collect the solids to obtain low-chlorine and low-fluorine aluminum ash; S2, alkali leaching: alkali leaching in two steps, in the first alkali leaching, low chlorine and low fluorine aluminum ash is added to 4g / L sodium hydroxide solution with a volume of 6 times that of low chlorine and low fluorine aluminum ash, the alkali leaching temperature is 75°C, and the alkali leaching is carried out for 4 hours under stirring. The generated ammonia gas is absorbed by carbonic acid to obtain ammonium bicarbonate. After the reaction is completed, the solution and solid are separated by filtration, and the solid is collected to obtain denitrogenated aluminum ash. In the second alkali leaching, the denitrogenated aluminum ash is added to 250g / L sodium hydroxide solution with a volume of 7 times that of low denitrogenated aluminum ash, the alkali leaching temperature is 55°C, the alkali leaching time is 5h, and the ultrasonic power of ultrasonic assisted leaching is 100w. After the reaction is completed, the salt residue is filtered to obtain sodium aluminate solution; S3, purification: adding the sodium aluminate solution to the ammonium bicarbonate obtained in S2, adjusting the pH to 8.8 to precipitate aluminum hydroxide, and collecting the precipitate to obtain a crude aluminum hydroxide product; S4, acid leaching: adding the crude aluminum hydroxide to 12.5wt% sulfuric acid, adjusting the pH to 4.5 to obtain a crude aluminum sulfate solution, adding an impurity complexing agent in an amount of 8% by mass of the crude aluminum sulfate solution to complex impurities and precipitate them, filtering the impurities, and obtaining an aluminum sulfate solution; S5. Crystallization: Concentrate the aluminum sulfate solution at 80°C to a concentration of 30 wt%, cool it down for crystallization, collect the crystals, grind them, wash them with anhydrous ethanol, and dry them to obtain aluminum sulfate.

[0027] The preparation method of the impurity complexing agent S4 comprises the following steps: S11, adding 1 kg of deionized water and 500 g of polyacrylic acid into a blender, stirring for 30 min, then adding 300 g of sodium dimethyldithiocarbamate, 150 g of diammonium dihydrogen phosphate and 50 g of phytic acid, stirring for 30 min, to obtain a mixture; S12. Add 10 g of ethylene glycol diacrylate to the mixture, heat it in a water bath at 60° C. for 1 h, add 5 g of ammonium persulfate, and continue heating in a water bath at 60° C. until gelation occurs to obtain an impurity complexing agent.

[0028] Example 3, see Figure 1 As shown, a method for preparing aluminum sulfate in this embodiment comprises the following steps: S1. Pretreatment: add 1 t of aluminum ash into a grinder and grind it, pass it through a 250-mesh sieve, add the ground aluminum ash into deionized water 6 times the volume of the aluminum ash, set the water washing temperature to 50°C, and the water washing time to 12 hours to wash away soluble salt substances, filter and separate the chlorine-containing and fluorine-containing solution and the solid, and collect the solid to obtain low-chlorine and low-fluorine aluminum ash; S2, alkali leaching: alkali leaching in two steps, in the first alkali leaching, low chlorine and low fluorine aluminum ash is added to 4g / L sodium hydroxide solution with 6 times the volume of low chlorine and low fluorine aluminum ash, the alkali leaching temperature is 85°C, and the alkali leaching is carried out for 3 hours under stirring. The generated ammonia gas is absorbed by carbonic acid to obtain ammonium bicarbonate. After the reaction is completed, the solution and solid are separated by filtration, and the solid is collected to obtain denitrified aluminum ash. In the second alkali leaching, the denitrified aluminum ash is added to 250g / L sodium hydroxide solution with 7 times the volume of low denitrified aluminum ash. The alkali leaching temperature is 55°C, the alkali leaching time is 5h, and the ultrasonic power of ultrasonic assisted leaching is 100w. After the reaction is completed, the salt residue is filtered to obtain sodium aluminate solution; S3, purification: adding the sodium aluminate solution to the ammonium bicarbonate obtained in S2, adjusting the pH to 8.8 to precipitate aluminum hydroxide, and collecting the precipitate to obtain a crude aluminum hydroxide product; S4, acid leaching: adding the crude aluminum hydroxide to 10wt% sulfuric acid, adjusting the pH to 4.5 to obtain a crude aluminum sulfate solution, adding an impurity complexing agent in an amount of 8% by mass of the crude aluminum sulfate solution to complex impurities and precipitate them, filtering the impurities, and obtaining an aluminum sulfate solution; S5. Crystallization: Concentrate the aluminum sulfate solution at 80°C to a concentration of 30 wt%, cool it down for crystallization, collect the crystals, grind them, wash them with anhydrous ethanol, and dry them to obtain aluminum sulfate.

[0029] The preparation method of the impurity complexing agent S4 comprises the following steps: S11, adding 1 kg of deionized water and 200 g of polyacrylic acid into a blender, stirring for 10 min, then adding 200 g of sodium dimethyldithiocarbamate, 100 g of diammonium dihydrogen phosphate and 80 g of phytic acid, stirring for 30 min, to obtain a mixture; S12. Add 10 g of ethylene glycol diacrylate to the mixture, heat it in a water bath at 60° C. for 1 h, add 5 g of ammonium persulfate-sodium bisulfite initiator, and continue heating in a water bath at 60° C. until gelation occurs to obtain an impurity complexing agent.

[0030] Example 4, see Figure 1 As shown, a method for preparing aluminum sulfate in this embodiment comprises the following steps: S1. Pretreatment: add 1 t of aluminum ash into a grinder and grind it, pass it through a 300-mesh sieve, add the ground aluminum ash into deionized water with a volume 7 times that of the aluminum ash, set the water washing temperature to 60°C, and the water washing time to 6 hours to wash away soluble salt substances, filter and separate the chlorine-containing and fluorine-containing solution and solid, and collect the solid to obtain low-chlorine and low-fluorine aluminum ash; S2, alkali leaching: alkali leaching in two steps, in the first alkali leaching, low chlorine and low fluorine aluminum ash is added to 4g / L sodium hydroxide solution with a volume of 6 times that of low chlorine and low fluorine aluminum ash, the alkali leaching temperature is 75°C, and the alkali leaching is carried out for 4 hours under stirring. The generated ammonia gas is absorbed by carbonic acid to obtain ammonium bicarbonate. After the reaction is completed, the solution and solid are separated by filtration, and the solid is collected to obtain denitrified aluminum ash. In the second alkali leaching, the denitrified aluminum ash is added to 230g / L sodium hydroxide solution with a volume of 7 times that of low denitrified aluminum ash, the alkali leaching temperature is 55°C, the alkali leaching time is 5h, and the ultrasonic power of ultrasonic assisted leaching is 100w. After the reaction is completed, the salt residue is filtered to obtain sodium aluminate solution; S3, purification: adding the sodium aluminate solution to the ammonium bicarbonate obtained in S2, adjusting the pH to 8.8 to precipitate aluminum hydroxide, and collecting the precipitate to obtain a crude aluminum hydroxide product; S4, acid leaching: adding the crude aluminum hydroxide to 5wt% sulfuric acid, adjusting the pH to 4.5 to obtain a crude aluminum sulfate solution, adding an impurity complexing agent in an amount of 8% by mass of the crude aluminum sulfate solution to complex impurities and precipitate them, filtering the impurities, and obtaining an aluminum sulfate solution; S5. Crystallization: Concentrate the aluminum sulfate solution at 80°C to a concentration of 30 wt%, cool it down for crystallization, collect the crystals, grind them, wash them with anhydrous n-propanol, and dry them to obtain aluminum sulfate.

[0031] The preparation method of the impurity complexing agent S4 comprises the following steps: S11, adding 1 kg of deionized water and 400 g of polyacrylic acid into a blender, stirring for 20 min, then adding 300 g of sodium dimethyldithiocarbamate, 150 g of diammonium dihydrogen phosphate and 50 g of phytic acid, stirring for 20 min, to obtain a mixture; S12. Add 5 g of diethylene glycol dimethacrylate to the mixture, heat it in a water bath at 60° C. for 1 h, add 5 g of ammonium persulfate, and continue heating in a water bath at 60° C. until gelation occurs to obtain an impurity complexing agent.

[0032] Example 5, see Figure 1 As shown, a method for preparing aluminum sulfate in this embodiment comprises the following steps: S1. Pretreatment: add 1 t of aluminum ash into a grinder and grind it, pass it through a 200-mesh sieve, add the ground aluminum ash into deionized water with a volume of 9 times that of the aluminum ash, set the water washing temperature to 60°C, and the water washing time to 12 hours to wash away soluble salt substances, filter and separate the chlorine-containing and fluorine-containing solution and solid, and collect the solid to obtain low-chlorine and low-fluorine aluminum ash; S2, alkali leaching: alkali leaching in two steps, in the first alkali leaching, low chlorine and low fluorine aluminum ash is added to 4g / L sodium hydroxide solution with a volume of 6 times that of low chlorine and low fluorine aluminum ash, the alkali leaching temperature is 75°C, and the alkali leaching is carried out for 4 hours under stirring. The generated ammonia gas is absorbed by carbonic acid to obtain ammonium bicarbonate. After the reaction is completed, the solution and solid are separated by filtration, and the solid is collected to obtain denitrogenated aluminum ash. In the second alkali leaching, the denitrogenated aluminum ash is added to 250g / L sodium hydroxide solution with a volume of 7 times that of low denitrogenated aluminum ash, the alkali leaching temperature is 55°C, the alkali leaching time is 5h, and the ultrasonic power of ultrasonic assisted leaching is 100w. After the reaction is completed, the salt residue is filtered to obtain sodium aluminate solution; S3, purification: adding the sodium aluminate solution to the ammonium bicarbonate obtained in S2, adjusting the pH to 8.8 to precipitate aluminum hydroxide, and collecting the precipitate to obtain a crude aluminum hydroxide product; S4, acid leaching: adding the crude aluminum hydroxide to 5wt% sulfuric acid, adjusting the pH to 4.5 to obtain a crude aluminum sulfate solution, adding an impurity complexing agent at 6% of the mass of the crude aluminum sulfate solution to complex impurities and precipitate, filtering the impurities, and obtaining an aluminum sulfate solution; S5. Crystallization: Concentrate the aluminum sulfate solution at 80°C to a concentration of 30 wt%, cool it down for crystallization, collect the crystals, grind them, wash them with anhydrous isopropanol, and dry them to obtain aluminum sulfate.

[0033] The preparation method of the impurity complexing agent S4 comprises the following steps: S11, adding 1 kg of deionized water and 200 g of polyacrylic acid into a blender, stirring for 20 min, then adding 200 g of sodium dimethyldithiocarbamate, 150 g of diammonium dihydrogen phosphate and 80 g of phytic acid, stirring for 30 min, to obtain a mixture; S12. Add 5 g of N,N'-methylenebisacrylamide to the mixture, heat it in a water bath at 65°C for 1 h, add 3 g of ammonium persulfate, and continue heating in a water bath at 65°C until gelation occurs to obtain an impurity complexing agent.

[0034] Comparative Example 1: This comparative example differs from Example 1 in that the secondary alkaline leaching is performed without ultrasonic-assisted leaching.

[0035] Comparative Example 2: The difference between this comparative example and Example 1 is that the alkaline leaching process is changed to adding low-chlorine and low-fluorine aluminum ash into a 200 g / L sodium hydroxide solution with a volume that is 6 times that of the low-chlorine and low-fluorine aluminum ash, and leaching at 200°C for 3 hours.

[0036] Comparative Example 3: This comparative example differs from Example 1 in that ferrous sulfate and potassium permanganate are used as impurity removers instead of impurities.

[0037] Performance Testing The aluminum sulfate obtained in each embodiment and comparative example was tested for yield, iron content and purity by commercially available testing equipment, wherein the yield is the mass of aluminum in the aluminum sulfate product actually generated divided by the theoretical mass of aluminum in the aluminum ash, the iron content is the proportion of iron in the aluminum sulfate product, and the purity is the proportion of aluminum sulfate molecules in the aluminum sulfate product. The test results are shown in Table 2 below: Table 2 It can be seen from the data in Table 2 that the iron content of the aluminum sulfate prepared in Examples 1 to 5 is less than 0.005%, which meets the requirements of first-class iron-free aluminum sulfate; the yield of aluminum sulfate prepared in Examples 1 to 5 is between 85.3% and 89.3% and the purity is above 95%, indicating that the aluminum sulfate prepared by the present invention using aluminum ash by-product has high yield and high purity.

[0038] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

[0039] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing aluminum sulfate, characterized in that: The steps include: S1. Pretreatment: grinding the aluminum ash in a grinder, passing through a 200-300 mesh sieve, adding the ground aluminum ash into deionized water to wash and remove soluble salt substances, filtering and separating the chlorine-containing and fluorine-containing solution and the solid, and collecting the solid to obtain low-chlorine and low-fluorine aluminum ash; S2, alkali leaching: alkali leaching is divided into two steps. In the first alkali leaching, low-chlorine and low-fluorine aluminum ash is added to a dilute alkali solution, and the reaction is carried out under stirring to remove nitrogen. The generated ammonia gas is absorbed by carbonic acid to obtain ammonium bicarbonate. After the reaction is completed, the solution and solid are separated by filtration, and the solid is collected to obtain denitrified aluminum ash. In the second alkali leaching, the denitrified aluminum ash is added to a concentrated alkali solution, and ultrasonic-assisted leaching is performed. After the reaction is completed, the salt residue is filtered to obtain a sodium aluminate solution; S3, purification: adding the sodium aluminate solution to the ammonium bicarbonate obtained in S2, adjusting the pH to 8-9 to precipitate aluminum hydroxide, and collecting the precipitate to obtain a crude aluminum hydroxide product; S4, acid leaching: adding the crude aluminum hydroxide to sulfuric acid, adjusting the pH to 4-4.5, adding an impurity complexing agent to complex the impurities and precipitate them, filtering the impurities, and obtaining an aluminum sulfate solution; S5. Crystallization: Concentrate the aluminum sulfate solution at 50-80°C to a concentration of 30-60wt%, cool it down to crystallize, collect the crystals, grind them, wash them with an organic solvent, and dry them to obtain aluminum sulfate.

2. A method for preparing aluminum sulfate according to claim 1, characterized in that: The chlorine-containing and fluorine-containing solution collected by filtration in S1 absorbs fluorine element through calcium chloride to produce calcium fluoride byproduct and defluorinated liquid phase, and the defluorinated liquid phase is mixed with the liquid collected by filtration in the first alkaline leaching in S2, and then concentrated and crystallized after neutralization with acid to obtain electrolyte salt.

3. A method for preparing aluminum sulfate according to claim 1, characterized in that: In the first alkali leaching process in S2, the dilute alkali solution is 2-4 g / L sodium hydroxide solution, the solid-liquid volume ratio of low-chlorine and low-fluorine aluminum ash to the dilute alkali solution is 1:6-9, the alkali leaching temperature is 75-85°C, and the alkali leaching time is 3-4 hours; in the second alkali leaching process, the concentrated alkali solution is 200-250 g / L sodium hydroxide solution, the solid-liquid volume ratio of aluminum ash to the concentrated alkali solution is 1:7-10, the alkali leaching temperature is 50-60°C, the alkali leaching time is 4-6 hours, and the ultrasonic power is 100w.

4. A method for preparing aluminum sulfate according to claim 1, characterized in that: The impurity complexing agent in S4 is added in an amount of 5-8% of the crude aluminum sulfate solution.

5. A method for preparing aluminum sulfate according to claim 1, characterized in that: The concentration of sulfuric acid in the S4 is 5-12.5wt%.

6. A method for preparing aluminum sulfate according to claim 1, characterized in that: The aluminum sulfate solution in S5 is cooled to room temperature for crystallization; the organic solvent is one or more combinations of anhydrous ethanol, anhydrous methanol, anhydrous n-propanol and anhydrous isopropanol.

7. A method for preparing aluminum sulfate according to claim 1, characterized in that: The method for preparing the impurity complexing agent in S4 comprises the following steps: S11, adding deionized water and polyacrylic acid into a blender, stirring for 10 to 30 minutes, then adding sodium dimethyldithiocarbamate, diammonium dihydrogen phosphate and phytic acid, stirring for 10 to 30 minutes to obtain a mixture; S12, adding a cross-linking agent to the mixture, heating in a water bath at 60-65°C for 0.5-1h, adding an initiator and continuing to heat in a water bath at 60-65°C until gelation, to obtain an impurity complexing agent.

8. A method for preparing aluminum sulfate according to claim 7, characterized in that: In the preparation method of the impurity complexing agent, the mass ratio of sodium dimethyldithiocarbamate, diammonium dihydrogen phosphate, phytic acid, deionized water, polyacrylic acid, cross-linking agent and initiator is 20~30:10~15:5~8:100:20~50:0.5~1.5:0.3~0.5; the cross-linking agent in S12 is one or more combinations of N,N'-methylenebisacrylamide, diethylene glycol dimethacrylate and ethylene glycol diacrylate; the initiator in S12 is one or more combinations of ammonium persulfate, potassium persulfate and ammonium persulfate-sodium bisulfite initiator.

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