Method for extracting aluminum hydroxide from activated aluminum oxide-containing material

Abstract

The invention discloses a method for extracting aluminum hydroxide from a material containing activated aluminum oxide. The method comprises the following steps: S1, replacing aluminum oxide in the activated aluminum oxide material; S1.1, leaching aluminum in the activated aluminum oxide material by ammonium oxalate: mixing the activated aluminum oxide material with ammonium oxalate, heating and reacting in a water reaction system to generate ammonia gas, leaching aluminum in the activated aluminum oxide material to obtain a reacted material, and filtering the reacted material to obtain leaching residues and a leaching solution containing (NH4) 3Al (C2O4) 3; the activated aluminum oxide material is bauxite, light-burned bauxite, a material containing a metakaolin phase or aluminum ash; s2, ammonia is added into the leachate for a reaction, and reaction product slurry containing aluminum hydroxide solid precipitates is generated; and S3, filtering and separating the reaction product slurry obtained in the step S2 to obtain an aluminum hydroxide solid precipitate and an ammonium oxalate solution.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology, specifically to a method for extracting aluminum hydroxide from materials containing active alumina. Background Technology

[0002] Aluminum hydroxide is an important aluminum compound, mainly used in the thermal decomposition to prepare alumina as a raw material for electrolytic aluminum. Aluminum hydroxide can also be used as a flame retardant or in the production of aluminum salts.

[0003] Bauxite is the main raw material for the industrial production of aluminum hydroxide. It is a general term for ores composed primarily of gibbsite, boehmite, or diaspore. Currently, aluminum hydroxide production mainly uses the Bayer process to process bauxite. Bauxite is placed in a sodium hydroxide solution, heated, and pressurized to dissolve it, generating a NaAl(OH)4 solution. The leachate is then diluted and cooled, seed crystals are introduced to precipitate aluminum hydroxide, and the sodium hydroxide solution is regenerated. The regenerated sodium hydroxide solution is then evaporated, concentrated, and reused. The Bayer process for producing aluminum hydroxide has the advantages of low energy consumption and low cost, but it has stringent requirements for raw materials. Generally, it processes gibbsite-type bauxite that is easily soluble in sodium hydroxide, requiring an Al / Si ratio > 7 and a sulfur content < 0.2%. For diaspore-type bauxite (mainly composed of AlO(OH)) or bauxite containing kaolinite, which is difficult to dissolve in sodium hydroxide, directly using the Bayer process for aluminum smelting involves harsh reaction conditions, resulting in significant sodium hydroxide loss and poor economic efficiency.

[0004] To utilize kaolin-type bauxite with high silicon content, the ore powder needs to be calcined at high temperatures with limestone to activate it and transform it into active alumina that is easily soluble in sodium hydroxide. Aluminum hydroxide is then extracted using the Bayer process, a method known as the sintering method or the Bayer-sintering combined method. This method is energy-intensive and generates a significant amount of silica-calcium slag solid waste. Lightly calcined bauxite refers to bauxite that has been calcined and dehydrated at 600-900℃ to transform into an active alumina phase. Lightly calcined alumina is easily soluble in acids or alkalis.

[0005] Metakaolin is a product of calcining and dehydrating kaolin at 600-900℃, and its main components are alumina and silicon dioxide. Metakaolin is reactive, and its alumina component is readily soluble in strong acids such as hydrochloric acid and sulfuric acid. The fly ash produced from coal-based kaolin combustion in circulating fluidized bed (CFB) power generation is mainly composed of metakaolin and is also a potential resource for alumina extraction.

[0006] Aluminum ash is a byproduct of aluminum smelting and processing. It contains components such as aluminum oxide. The aluminum oxide in aluminum ash is soluble in acids and alkalis. It has a high silica content, which leads to large alkali losses and poor efficiency when using the Bayer process to process and recover aluminum oxide. It is often disposed of in landfills after being rendered harmless, resulting in a waste of resources.

[0007] Because the Bayer process has stringent requirements on the silicon content of raw materials, it is difficult to extract aluminum hydroxide from high-silicon aluminum resources containing phases such as kaolin and metakaolin for high-value development and application.

[0008] In addition, there is also the hydrochloric acid method for extracting alumina from high-silicon aluminum raw materials. This method involves leaching aluminum, iron and other components with hydrochloric acid, removing iron impurities, and then spraying the aluminum chloride leachate to obtain alumina. This method is energy-intensive, highly corrosive to equipment, and has unsatisfactory economic benefits. Summary of the Invention

[0009] This invention addresses the problem of poor adaptability of the current Bayer process for extracting aluminum hydroxide to high-silicon aluminum raw materials, and proposes a new method for extracting aluminum hydroxide from materials containing active alumina.

[0010] To achieve its objective, the present invention employs the following technical solution:

[0011] The present invention provides a method for extracting aluminum hydroxide from materials containing active alumina, comprising the following steps:

[0012] S1, Alumina in the replaced activated alumina material

[0013] S1.1, Aluminum in activated alumina material leached by ammonium oxalate

[0014] The activated alumina material is mixed with ammonium oxalate and heated in an aqueous reaction system to generate ammonia gas, which leaches aluminum from the activated alumina material, resulting in a post-reaction material. The post-reaction material is then filtered to obtain leaching residue and a leachate containing (NH4)3Al(C2O4)3. The activated alumina material is bauxite, lightly calcined bauxite, material containing metakaolinite phase, or aluminum ash.

[0015] S2. The leachate is reacted with ammonia to produce a reaction product slurry containing aluminum hydroxide solid precipitate; preferably, the ammonia comes from ammonia gas or ammonia water.

[0016] S3. Take the reaction product slurry obtained in step S2, filter and separate it to obtain aluminum hydroxide solid precipitate and ammonium oxalate solution.

[0017] Preferably, in step S1.1, ammonium oxalate and activated alumina are mixed and reacted according to a mass ratio of ammonium oxalate to activated alumina of 3 to 8:1.

[0018] The ammonium oxalate is further preferably (NH4)2C2O4·H2O, and the mass ratio of (NH4)2C2O4·H2O to the activated alumina material is 4 to 8:1.

[0019] Preferably, in step S1.1, the water reaction system is provided by introducing water vapor into the reaction vessel, or by adding water to the reaction raw materials and heating it to the reaction temperature; the reaction temperature in step S1.1 is 100-180°C, and the reaction time is 60-300 min.

[0020] Preferably, in step S1.1, the leaching residue is repeatedly leached: the obtained leaching residue is leached twice in an aqueous reaction system, and the reaction conditions for the second leaching are the same as those for the first leaching. The second leaching solution obtained after the second leaching is combined with the first leaching solution to obtain a mixed leaching solution, which is used in step S2.

[0021] Preferably, step S1 further includes step S1.2: the leachate obtained in step S1.1 is first subjected to iron removal before step S2: sulfide is added to the leachate until no new black ferrous sulfide precipitate is formed, and solid-liquid separation is performed to obtain an iron-removed solution and a ferrous sulfide filter cake. The iron-removed solution is used for the ammonia addition reaction in step S2. Preferably, the sulfide is ammonium sulfide or ammonium hydrogen sulfide.

[0022] More preferably, step S1 further includes step S1.3: the iron-removed solution obtained in step S1.2 is first desulfurized and then used for the ammonia addition reaction in step S2: hydrogen peroxide is added to the iron-removed solution or air is blown in to oxidize the residual sulfides into sulfur, the sulfur is separated by filtration, and a purified solution with iron and sulfur removed is obtained. The purified solution is used for the ammonia addition reaction in step S2.

[0023] Preferably, the aluminum hydroxide solid precipitate obtained in step S3 is placed in ammonium oxalate eluent, and the ammonium oxalate crystals mixed in the aluminum hydroxide solid precipitate are dissolved and eluted by recrystallization, thereby improving the purity of aluminum hydroxide and recovering ammonium oxalate.

[0024] The ammonium oxalate eluent can be ammonia water, the leachate obtained in step S1.1, or the purified solution obtained in step S1.3.

[0025] In the first case, when the ammonium oxalate eluent is ammonia: the ammonium oxalate eluent is ammonia (preferably 5-25 wt% ammonia). After the aluminum hydroxide solid precipitate obtained by filtering the reaction product slurry obtained in step S2 is dissolved by heating in ammonia to elute the ammonium oxalate, the solution after recrystallizing the filtrate obtained by filtration to precipitate some ammonium oxalate crystals is used as the eluent for the next solid precipitate. The solid precipitate is repeatedly soaked and eluted with ammonium oxalate. The precipitate is washed with water, dried, and purified aluminum hydroxide solid is obtained. The ammonium oxalate crystals are recovered by recrystallizing the filtrate.

[0026] Preferably, step S3 is performed as follows:

[0027] The reaction product slurry obtained in step S2 is filtered and separated to obtain a solid precipitate and an ammonium oxalate solution. The solid precipitate is added to ammonia water (preferably at a ratio of 1-4 L of 5-25 wt% ammonia water per 100 g of activated alumina material), and heated to 75-95°C to dissolve the mixed ammonium oxalate solids. The mixture is then filtered to obtain a primary precipitate and a primary filtrate. The primary filtrate is cooled to 20-40°C to allow the ammonium oxalate to crystallize. The ammonium oxalate crystals and a secondary filtrate are collected by filtration. The primary precipitate is then added to remove impurities... In the secondary filtrate of ammonium oxalate crystals, heating is performed to dissolve the ammonium oxalate in the primary precipitate into the secondary filtrate. The secondary precipitate and tertiary filtrate are obtained by filtration. After cooling, ammonium oxalate crystals precipitate from the tertiary filtrate. The ammonium oxalate crystals are collected by filtration. The tertiary filtrate is used to impregnate the secondary precipitate to dissolve and elute the ammonium oxalate. This process of elution and crystallization is repeated multiple times until all the ammonium oxalate in the solid precipitate is separated. The final precipitate is the aluminum hydroxide filter cake with the ammonium oxalate crystals removed. The precipitate is washed with water and dried to obtain purified aluminum hydroxide solid.

[0028] In the second scenario, when the ammonium oxalate eluent is a leachate or a purified solution, follow these steps:

[0029] Take a portion of the leachate obtained in step S1.1 or the purified solution obtained in step S1.3 above as the ammonium oxalate eluent in step S3.1; at this time, steps S2 and S3 are performed as follows:

[0030] S2, The leachate or purified solution reacts with ammonia to produce aluminum hydroxide.

[0031] Take the leachate obtained in step S1.1 or the purified solution obtained in step S1.3, add ammonia to it until no new precipitate is formed, and react fully to obtain the reaction product slurry;

[0032] S3.1 Recrystallization and Filtration Separation of Aluminum Hydroxide and Ammonium Oxalate: The reaction product slurry obtained in step S2 is filtered and separated to obtain a solid precipitate of aluminum hydroxide and an ammonium oxalate solution; the solid precipitate of aluminum hydroxide is dissolved and eluted in ammonium oxalate eluent by heating to 75-95℃; the solution after recrystallization of the filtrate obtained from the filtration separation to precipitate some ammonium oxalate crystals is used as the eluent for the next solid precipitate precipitate; the solid precipitate is impregnated and eluted with ammonium oxalate multiple times, the precipitate is washed with water and dried to obtain purified solid aluminum hydroxide; the ammonium oxalate crystals are recovered by recrystallization of the filtrate; the ammonium oxalate eluent is the remaining volume of leachate or purified solution not used in step S2.

[0033] Preferably, in this case, the following steps are also included:

[0034] S3.2. After recrystallization in step S3.1, ammonia is added to the final filtrate until no new precipitate is formed, and the reaction is fully carried out to obtain the reaction product slurry.

[0035] S3.3 The reaction product slurry obtained in step S3.2 is recrystallized and filtered to separate aluminum hydroxide and ammonium oxalate according to the method in step S3.1. The difference is that the eluent for ammonium oxalate in step S3.3 is ammonia.

[0036] Further preferably, in step S3.1, recrystallization and filtration separation of aluminum hydroxide and ammonium oxalate: the reaction product slurry obtained in step S2 is filtered and separated to obtain aluminum hydroxide solid precipitate and ammonium oxalate solution; the obtained solid precipitate is a mixture of aluminum hydroxide and ammonium oxalate crystals. The solid precipitate is added to ammonium oxalate eluent and heated to 75-95°C to dissolve the ammonium oxalate. The mixture is filtered, and the primary precipitate and primary filtrate are collected. The primary filtrate is cooled to 20-40°C to precipitate some of the ammonium oxalate crystals. The ammonium oxalate crystals are separated by filtration to obtain a secondary filtrate. The primary precipitate is added to the secondary filtrate and heated to dissolve the ammonium oxalate. The mixture is filtered, and the secondary precipitate and tertiary filtrate are collected. The tertiary filtrate is cooled to precipitate some of the ammonium oxalate crystals. Crystals are precipitated, and ammonium oxalate crystals are separated by filtration, yielding a fourth filtrate. The second precipitate is added to the fourth filtrate and heated to dissolve the ammonium oxalate. The precipitate is then filtered, and the third and fifth filtrates are collected. The fifth filtrate is cooled to allow some of the ammonium oxalate crystals to precipitate. The ammonium oxalate crystals are then separated by filtration, yielding a sixth filtrate. The sixth filtrate is used again to dissolve the ammonium oxalate in the third precipitate. This process of elution and crystallization is repeated multiple times until all the ammonium oxalate in the solid precipitate is separated. The final precipitate is the aluminum hydroxide filter cake with the ammonium oxalate crystals removed. The precipitate is washed with water and dried to obtain purified aluminum hydroxide solid. The final filtrate obtained by recrystallization is used in step S3.2 to replace the aluminum with ammonia to generate aluminum hydroxide.

[0037] This invention proposes a novel aluminum extraction method that employs a new reaction route and innovatively uses ammonium oxalate as a raw material to extract alumina from activated alumina materials, offering significant advantages:

[0038] 1) Compared to the traditional Bayer process, it is more suitable for alumina materials with high silicon content and has strong adaptability to raw materials.

[0039] 2) The method of the present invention can be carried out at a relatively low reaction temperature (the traditional method uses hydrochloric acid leaching-calcination (temperature around 700℃) and soda lime calcination (around 1200℃)-leaching processes, etc.), and can be directly heated by steam, which is energy-saving. The main extraction reagent, ammonium oxalate, can be recycled, which is low in cost and has little corrosiveness to equipment, making it suitable for large-scale production.

[0040] 3) This method can separate iron and aluminum to obtain aluminum hydroxide with high purity. Attached Figure Description

[0041] Figure 1 This is a process flow diagram of the method of the present invention.

[0042] Figure 2 This is a process flow diagram of recrystallization separation of aluminum hydroxide and ammonium oxalate in Examples 1-4.

[0043] Figure 3 These are the XRD patterns of the raw materials and products from Examples 1-4.

[0044] Figure 4 This is the thermogravimetric spectrum of the aluminum hydroxide product from Example 3. Detailed Implementation

[0045] The present invention will be further described below with reference to embodiments, but these embodiments are not intended to limit the scope of the invention.

[0046] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0047] The method for extracting aluminum hydroxide according to the present invention involves replacing the alumina in the activated alumina material with ammonium oxalate to generate (NH4)3Al(C2O4)3 and ammonia gas. Further, (NH4)3Al(C2O4)3 reacts with ammonia (ammonia water or ammonia gas) to generate an Al(OH)3 filter cake. The Al(OH)3 is then separated and purified to obtain the aluminum hydroxide product. The specific operating steps and principles are as follows (see process flow diagram). Figure 1 ):

[0048] S1, Alumina in the replaced activated alumina material

[0049] S1.1, Aluminum in activated alumina material leached by ammonium oxalate

[0050] The reaction raw materials, ammonium oxalate and activated alumina, are mixed at a mass ratio of ammonium oxalate to activated alumina of 4–8:1. The mixture is then leached in a reaction system containing steam or an aqueous solution at 100–180°C for 60–300 minutes, leaching alumina and releasing ammonia gas to obtain the reacted material. The alumina component in the activated alumina material is readily soluble in the ammonium oxalate solution. The reaction system can be provided in two ways: one is by introducing high-temperature steam into the reactor, which liquefies to form an aqueous reaction system; the other is by adding water to the reaction raw materials and heating it to 100–180°C, using the high-temperature aqueous solution as the reaction system.

[0051] Among them, the active alumina material is bauxite, lightly calcined bauxite, or alumina ash or metakaolinite phase material.

[0052] Bauxite: Boehmite trihydrate (mainly composed of Al(OH)3) and diaspore monohydrate (mainly composed of AlOOH) can react directly with ammonium oxalate. The chemical reactions that occur are as follows:

[0053] Al(OH)3+3(NH4)2C2O4=(NH4)3Al(C2O4)3+3NH3↑+3H2O (1)

[0054] AlOOH+3(NH4)2C2O4=(NH4)3Al(C2O4)3+3NH3↑+2H2O (2)

[0055] Reactions (1) and (2) are reversible reactions. The reaction proceeds in the forward direction as ammonia continues to volatilize and overflow in an open environment.

[0056] The reaction formula between the alumina component and ammonium oxalate in lightly calcined bauxite, bauxite ash, or metakaolin is as follows:

[0057] Al2O3+6(NH4)2C2O4=2(NH4)3Al(C2O4)3+6NH3↑+3H2O (3)

[0058] Aluminum hydroxide or aluminum oxide can be dissolved through reactions (1), (2), and (3), and then separated by filtration.

[0059] The resulting reaction material (dry salt or slurry) is separated into solid and liquid components (at this time, some ammonium oxalate precipitates and mixes in the leaching residue), resulting in primary leaching residue (mainly composed of silicon dioxide, ammonium oxalate crystals and incompletely converted active alumina) and primary leaching solution (mainly composed of (NH4)2C2O4 and (NH4)3Al(C2O4)3).

[0060] Secondary leaching (preferred step):

[0061] The primary leaching residue obtained earlier is placed in an aqueous reaction system for secondary leaching to release ammonia gas, separating the secondary leaching solution and secondary leaching residue. By reacting the ammonium oxalate in the primary leaching residue with the residual activated alumina through secondary leaching, the conversion rate of ammonium oxalate and activated alumina can be improved. The secondary leaching solution and the primary leaching solution are combined and used in step S2.1 for reaction with ammonia water or ammonia gas.

[0062] Preferably, the leachate can be de-ironized before being used in step S2.1.

[0063] S1.2, Iron removal from leachate (preferred step):Bauxite raw materials often contain iron oxide. In step S1, iron oxide reacts with ammonium oxalate solution to form impurities (as shown in reaction formula (4)). At this time, the leachate contains: (NH4)2C2O4, (NH4)3Al(C2O4)3, and (NH4)3Fe(C2O4)3. When ammonia is added in step S2.1, the iron impurities in the solution will generate ferric hydroxide impurities that will be mixed into the aluminum hydroxide product. Since the downstream industry of aluminum hydroxide generally requires low iron impurity content, sulfides are added to the leachate to generate ferrous sulfide precipitate. Ferrous sulfide is removed by filtration to obtain a (NH4)3Al(C2O4)3 solution without iron impurities, thus avoiding the mixing of ferric hydroxide into the aluminum hydroxide product.

[0064] Fe2O3+6(NH4)2C2O4=2(NH4)3Fe(C2O4)3+6NH3↑+3H2O (4)

[0065] The method for removing iron impurities is as follows: add sulfide (ammonium sulfide or ammonium hydrogen sulfide solution) to the leachate until no new black ferrous sulfide precipitate is formed. The solid and liquid are separated to obtain the iron-removed solution and ferrous sulfide filter cake. The chemical reaction that occurs is shown in reaction formula (5) or (6).

[0066] 2(NH4)3Fe(C2O4)3+3(NH4)2S=2FeS↓+S↓+6(NH4)2C2O4 (5)

[0067] 2(NH4)3Fe(C2O4)3+3NH4HS=2FeS↓+S↓+3(NH4)2C2O4+3NH4HC2O4 (6)

[0068] S1.3, Desulfurization of the solution after iron removal (preferred step):

[0069] To precipitate and remove iron impurities as much as possible, ammonium sulfide or ammonium hydrogen sulfide is usually added in excess. After filtration to remove ferrous sulfide, excess sulfides in the solution need to be removed. Hydrogen peroxide or air is added to the iron-removed solution obtained in step S1.2 to oxidize the remaining sulfides into sulfur. The sulfur and the purified solution (i.e. the solution obtained after removing iron and sulfur impurities) are separated by filtration. The purified solution is used to react with ammonia in step S2.1.

[0070] S2, Ammonia is introduced to produce aluminum hydroxide.

[0071] The leachate or purified solution obtained in step S1 (which can be the entire volume or a portion of the volume obtained in step S1) is passed through ammonia gas or ammonia water (5-25 wt%) is added to react until no new aluminum hydroxide precipitate is formed. The resulting reaction product slurry is a slurry containing solids and ammonium oxalate solution. Due to the solubility of ammonium oxalate, some ammonium oxalate cannot dissolve; therefore, the solids in the reaction product slurry are a mixture of aluminum hydroxide and ammonium oxalate crystals. The reaction product slurry is separated by filtration in step S2.2. The main chemical reactions in this step are as follows:

[0072] 2(NH4)3Al(C2O4)3+6NH3·H2O=2Al(OH)3↓+6(NH4)2C2O4 (7)

[0073] S3. Separation, purification of aluminum hydroxide, and recovery of ammonium oxalate.

[0074] Separation and purification of aluminum hydroxide and recovery of ammonium oxalate: The reaction product slurry obtained in step S2 is filtered and separated to obtain a solid precipitate and an ammonium oxalate solution. The obtained solid precipitate is a mixture of aluminum hydroxide and ammonium oxalate crystals. The solid precipitate is impregnated with an ammonium oxalate eluent to dissolve the ammonium oxalate. Recrystallization is then performed to dissolve as many ammonium oxalate crystals as possible into the liquid through multiple dissolutions, ultimately obtaining high-purity aluminum hydroxide solid, while the ammonium oxalate is also dissolved in the liquid and recovered. The ammonium oxalate eluent solution is different depending on the product of step S1 used in step S2.

[0075] Case 1: When the leachate or purified solution obtained in step S1 is used entirely for ammonia reaction to generate aluminum hydroxide precipitate in step S2, the ammonium oxalate eluent is ammonia water. See Examples 1 and 2.

[0076] The second scenario: When all or part of the leachate or purified solution obtained in step S1 is used in step S2 for ammonia reaction to generate aluminum hydroxide precipitate, the ammonium oxalate eluent in step S3 is the leachate or purified solution. The leachate or purified solution obtained in step S1 can be used in part in step S2, with the remainder used as the ammonium oxalate eluent in step S3; alternatively, it can be used entirely in step S2, and then the leachate or purified solution prepared according to the method in step S1 can be used as the ammonium oxalate eluent in step S3. In other words, the leachate or purified solution prepared according to the method in step S1 can be used as a backup ammonium oxalate eluent, to be used when needed. See Examples 3 and 4.

[0077] During this experimental study, the inventors discovered that adding ammonium oxalate solution to a household pressure cooker could pressure leach alumina and release ammonia gas. Adding ammonia water to the leachate could precipitate aluminum hydroxide. Further quantitative experiments were conducted using rented company equipment. The main equipment included a steam generator, a reaction vessel, an adjustable constant pressure valve, and auxiliary equipment such as pipelines. High-temperature steam generated by the steam generator was directly introduced into the reaction vessel containing pre-added ammonium oxalate and activated alumina for heating, or water was added to the reaction vessel containing ammonium oxalate and activated alumina and electrically heated. Stirring was maintained, and the constant pressure valve connected to the exhaust port of the reaction vessel was adjusted to keep the temperature of the reaction vessel in a constant temperature-ammonia-removal environment of 100–180°C.

[0078] Examples 1-4 were performed according to the above method. The bauxite, light-burned bauxite, metakaolin, and aluminum ash in the examples were commercially available. XRD analysis was performed on the samples to identify the phases, and the results are as follows: Figure 3 As shown.

[0079] The bauxite used in Example 1 was primarily in the diaspore monohydrate crystal form, consistent with standard card PDF-01-079-1781, with a molecular weight loss percentage of 35.2%. XRF analysis showed that the main components were Al2O3 (49.55%) and silica (10.46%).

[0080] The lightly calcined bauxite mineral phase used in Example 2 is consistent with alumina PDF-01-081-2267, with the main component Al2O3 accounting for 75.1%.

[0081] The raw material phase used in Example 3 was metakaolin. XRD analysis of the dry salt product from the reaction of ammonium oxalate and metakaolin in Example 3 showed that the raw material phase matched the standard cards for silica (PDF-01-089-1961) and alumina (PDF-01-076-0144), with Al2O3 accounting for 43.02% and SiO2 content for 48.15%. The dry salt product was composed of ammonium trioxalate complexed aluminate trihydrate (with (NH4)3Al(C2O4)3·3H2O) (standard card PDF-00-049-118). The results show that reactions (1), (2), and (3) are real. In addition, the dry salt product has excess ammonium oxalate (which matches the standard card (NH4)2C2O4·H2O-PDF-01-087-0657). XRD analysis of the aluminum hydroxide product shows that the crystal form of the aluminum hydroxide product (Al(OH)3) matches the standard card PDF-01-074-1775, indicating that reaction (7) is real. There is no residual ammonium oxalate peak, and the precipitated aluminum hydroxide and the precipitated ammonium oxalate crystals can be separated.

[0082] The aluminum ash used in Example 4 mainly consists of metallic aluminum and aluminum oxide, with an aluminum oxide content of 67.3%, and also contains some magnesium aluminum spinel phase.

[0083] Example 1: Extraction of aluminum hydroxide from bauxite

[0084] To extract aluminum hydroxide from bauxite, follow these steps:

[0085] S1, Alumina in replaced bauxite

[0086] S1.1, Ammonium oxalate leaching of aluminum from bauxite

[0087] 1. One-time leaching

[0088] Take 100g of bauxite powder and mix ammonium oxalate monohydrate (NH4)2C2O4·H2O with bauxite powder at a mass ratio of 5:1. Use high-temperature steam as the reaction system: mix bauxite and ammonium oxalate in a reactor, and continuously introduce high-temperature steam into the reactor through the air inlet at the bottom to raise the internal temperature to 180℃ for ammonia stripping. Continue introducing steam for 60 minutes. The ammonia gas generated by the reaction is discharged from the exhaust port at the top of the reactor, yielding the reacted material. The reacted material is then filtered and subjected to solid-liquid separation to obtain primary leaching residue and primary leaching solution. The primary leaching residue mainly consists of unreacted bauxite and (NH4)2C2O4 (since the leaching of bauxite by ammonium oxalate is a reversible reaction, some raw materials are not completely reacted). The primary leaching solution mainly contains (NH4)3Al(C2O4)3, (NH4)2C2O4, and (NH4)3Fe(C2O4)3.

[0089] 2. Secondary leaching

[0090] Repeated leaching was used to improve the alumina replacement rate and increase the yield: the primary leaching residue was retained in the reactor, and high-temperature steam was continuously introduced into the reactor through the air inlet at the bottom of the reactor to raise the solution temperature to 180°C for ammonia stripping. The steam was continuously introduced for 60 minutes, and a secondary leaching was performed to obtain a secondary leaching solution and a secondary leaching residue. The secondary leaching residue mainly consisted of unreacted silicon impurities, and the main components of the secondary leaching solution were the same as those of the primary leaching solution. The leaching solutions obtained from the two leaching processes were mixed for use in the next step of the experiment.

[0091] S1.2, Iron removal from leachate

[0092] Add ammonium sulfide solution to the leachate until no new black ferrous sulfide precipitate is formed. Use 48g of 20% ammonium sulfide solution. Separate the solid and liquid to obtain the iron-removed solution and ferrous sulfide filter cake. Since (NH4)3Fe(C2O4)3 is decomposed and removed, the green leachate is transformed into a colorless iron-removed solution.

[0093] S1.3, Remove excess ammonium sulfide

[0094] Hydrogen peroxide is added to the solution after iron removal to oxidize the residual ammonium sulfide into sulfur. The sulfur and the purified solution (i.e., the solution obtained after iron and sulfur removal from the leachate) are separated by filtration.

[0095] S2, The purified solution reacts with ammonia to produce aluminum hydroxide.

[0096] Add ammonia to the purified solution obtained in step S1.3 until no new aluminum hydroxide precipitate is formed. Allow the reaction to proceed fully to obtain a reaction product slurry. The reaction product slurry contains solids and ammonium oxalate solution. Due to the solubility of ammonium oxalate, some ammonium oxalate cannot be dissolved. Therefore, the solids in the reaction product slurry are a mixture of aluminum hydroxide and ammonium oxalate crystals.

[0097] S3. Separation, purification of aluminum hydroxide, and recovery of ammonium oxalate.

[0098] S3.1 Recrystallization and filtration separation of aluminum hydroxide and ammonium oxalate (e.g.) Figure 2 As shown):

[0099] The reaction product slurry was filtered and separated, and the resulting solid precipitate was a mixture of aluminum hydroxide and ammonium oxalate crystals. The solid precipitate was added to ammonium oxalate eluent (2 L of 10 wt% ammonia water in this example), and heated to 75°C to dissolve the ammonium oxalate. The mixture was filtered, and the primary precipitate and primary filtrate were collected. The primary filtrate was cooled to 20°C to allow some of the ammonium oxalate to crystallize. The ammonium oxalate crystals were separated by filtration, and a secondary filtrate was obtained. The primary precipitate (due to the solubility of ammonium oxalate, it could not be completely dissolved at once, and the primary precipitate still contained ammonium oxalate) was added to the secondary filtrate and heated to 75°C to dissolve the ammonium oxalate. The mixture was filtered, and the secondary precipitate and tertiary filtrate were collected. The tertiary filtrate was cooled to 20°C to allow some of the ammonium oxalate to crystallize. The ammonium oxalate crystals were separated by filtration, and a quaternary filtrate was obtained. The secondary precipitate is added to the fourth filtrate and heated to 75°C to dissolve the ammonium oxalate. The mixture is then filtered, and the third and fifth filtrates are collected. The fifth filtrate is cooled to 20°C to allow some of the ammonium oxalate to crystallize. The ammonium oxalate crystals are separated by filtration, and the sixth filtrate is obtained. This sixth filtrate is then used again to dissolve the ammonium oxalate in the next solid precipitate (i.e., the third precipitate). This process of elution and crystallization is repeated multiple times until all the ammonium oxalate in the solid precipitate is separated. The final precipitate is the aluminum hydroxide filter cake with the ammonium oxalate crystals removed. The remaining ammonium oxalate entrained by the eluent is then removed by washing with deionized water, and the aluminum hydroxide filter cake is dried.

[0100] In this step, the aluminum hydroxide solid precipitate mixed with ammonium oxalate crystals is first heated in ammonia water to dissolve the ammonium oxalate crystals in the liquid. Then, the aluminum hydroxide solid precipitate and filtrate are separated by filtration. Each time, the filtrate is first cooled to allow some of the ammonium oxalate to precipitate as crystals. The ammonium oxalate crystals and the remaining filtrate are then recovered by filtration, further reducing the ammonium oxalate content in the filtrate. This filtrate is then used to redissolve the aluminum hydroxide filter cake, further dissolving and eluting the ammonium oxalate mixed in the aluminum hydroxide filter cake to improve the purity of the aluminum hydroxide product and recover the ammonium oxalate.

[0101] Example 2: Extraction of aluminum hydroxide from lightly calcined bauxite

[0102] The starting material was lightly calcined bauxite. Aluminum hydroxide was extracted using the method described in Example 1, except that water was added as part of the reaction system in step S1, and ammonia gas was introduced in step S2. The remaining steps were the same.

[0103] S1.1, Ammonium oxalate leaching of aluminum from light-burned bauxite

[0104] 1. Primary Leaching: Take 100g of light-burned bauxite powder, mix ammonium oxalate monohydrate (NH4)2C2O4·H2O with the light-burned bauxite powder at a mass ratio of 8:1, and add 2L of water as the reaction system. Mix the light-burned bauxite and ammonium oxalate in a reactor, and heat the solution to 100℃ by electric heating to remove ammonia. Continue heating for 300min. The ammonia gas generated by the reaction is discharged from the exhaust port at the top of the reactor, and the reacted material is obtained. The reacted material is filtered and separated into solid and liquid components to obtain primary leaching residue and primary leaching solution. The main components of the primary leaching residue are unreacted (NH4)2C2O4 and light-burned bauxite (since the leaching of light-burned bauxite by ammonium oxalate is a reversible reaction, some raw materials are not completely reacted). The primary leaching solution mainly contains (NH4)3Al(C2O4)3, (NH4)2C2O4, and (NH4)3Fe(C2O4)3.

[0105] 2. Secondary leaching: The residue from the primary leaching is retained in the reactor. 2L of water is added to the reactor, and the internal temperature of the reactor is raised to 100℃ by electric heating for secondary ammonia leaching. Heating is continued for 300 minutes. The secondary leaching yields a secondary leachate and a secondary leaching residue. The secondary leaching residue mainly consists of unreacted silicon impurities. The main components of the secondary leachate are the same as those of the primary leachate. The leachates obtained from the two leaching processes are mixed for use in the next step of the experiment.

[0106] S1.2, Iron removal from leachate

[0107] Ammonium hydrogen sulfide solution was added to the leachate until no new black ferrous sulfide precipitate was formed. A total of 27g of 20% ammonium hydrogen sulfide solution was consumed. Solid-liquid separation yielded the iron-removed solution and the ferrous sulfide filter cake. Due to the decomposition and removal of (NH4)3Fe(C2O4)3, the green leachate was transformed into a colorless iron-removed solution.

[0108] S1.3, removing excess ammonium hydrogen sulfide

[0109] Air is introduced into the iron-removed solution to oxidize the residual ammonium hydrogen sulfide into sulfur. The sulfur and the purified solution after iron and sulfur removal are then separated by filtration.

[0110] S2. Reaction of purified solution with ammonia: Ammonia gas is introduced into the purified solution obtained in step S1.3 until no new aluminum hydroxide precipitate is formed, and the reaction is fully carried out to obtain the reaction product slurry.

[0111] S3. Separation, purification of aluminum hydroxide and recovery of ammonium oxalate: The operation steps and principles are the same as in Example 1, but the raw material ratio and experimental conditions are different from those in Example 1, as shown in Table 1.

[0112] Example 3: Extraction of aluminum hydroxide from metakaolin powder

[0113] To extract aluminum hydroxide from metakaolin, follow these steps:

[0114] S1, replacing aluminum oxide in metakaolin

[0115] S1.1, Ammonium oxalate leaching of aluminum from metakaolin

[0116] 1. One-time leaching

[0117] Take 100g of metakaolin ore powder, mix ammonium oxalate monohydrate (NH4)2C2O4·H2O with metakaolin at a mass ratio of 4:1, and use high-temperature steam as the reaction system for the reaction: mix metakaolin and ammonium oxalate in a reaction vessel, and continuously introduce high-temperature steam into the reaction vessel through the air inlet at the bottom of the reaction vessel to raise the solution temperature to 180℃ for ammonia stripping. Continue to introduce steam for 120 minutes, and the ammonia gas generated by the reaction is discharged from the exhaust port at the top of the reaction vessel to obtain the reaction material. Filter the reaction material and separate the solid and liquid to obtain primary leaching residue and primary leaching solution. The primary leaching residue mainly consists of unreacted (NH4)2C2O4 and metakaolin (since the leaching of metakaolin with ammonium oxalate is a reversible reaction, some raw materials are not completely reacted). The primary leaching solution mainly contains (NH4)3Al(C2O4)3, (NH4)2C2O4, and (NH4)3Fe(C2O4)3.

[0118] 2. Secondary leaching

[0119] Repeated leaching was used to improve the alumina replacement rate and increase the yield: the primary leaching residue was retained in the reactor, and high-temperature steam was continuously introduced into the reactor through the air inlet at the bottom of the reactor to raise the solution temperature to 180°C for ammonia stripping. The steam was continuously introduced for 120 minutes, and a secondary leaching was performed to obtain a secondary leaching solution and a secondary leaching residue. The secondary leaching residue mainly consisted of unreacted silicon impurities, and the main components of the secondary leaching solution were the same as those of the primary leaching solution. The leaching solutions obtained from the two leaching processes were mixed for use in the next step of the experiment.

[0120] S1.2, Iron removal from leachate

[0121] Ammonium hydrogen sulfide solution was added to the leachate until no new black ferrous sulfide precipitate was formed. A total of 16g ​​of 20% ammonium hydrogen sulfide solution was consumed. Solid-liquid separation yielded the iron-removed solution and the ferrous sulfide filter cake. Due to the decomposition and removal of (NH4)3Fe(C2O4)3, the green leachate was transformed into a colorless iron-removed solution.

[0122] S1.3, removing excess ammonium hydrogen sulfide

[0123] Hydrogen peroxide is added to the iron-removed solution to oxidize the residual ammonium hydrogen sulfide into sulfur. The sulfur and the purified solution after iron and sulfur removal are then separated by filtration.

[0124] S2, After purification, the solution reacts with ammonia to produce aluminum hydroxide.

[0125] Take the purified solution obtained in step S1.3, take 50% of the volume of the purified solution, add ammonia water until no new precipitate is formed, and react fully to obtain the reaction product slurry.

[0126] S3. Separation, purification of aluminum hydroxide, and recovery of ammonium oxalate.

[0127] S3.1 Recrystallization and Filtration Separation of Aluminum Hydroxide and Ammonium Oxalate: The reaction product slurry is filtered to separate the solid precipitate, which is a mixture of aluminum hydroxide and ammonium oxalate crystals. The mixture is added to ammonium oxalate eluent (i.e., the remaining 50% volume of the purified solution), heated to 80°C to dissolve the ammonium oxalate, filtered, and the primary precipitate and primary filtrate are collected. The primary filtrate is cooled to 30°C to allow some of the ammonium oxalate to precipitate as crystals. The ammonium oxalate crystals are separated by filtration to obtain a secondary filtrate. The primary precipitate (which still contains ammonium oxalate due to its solubility) is added to the secondary filtrate and heated to 80°C to dissolve the ammonium oxalate. The secondary precipitate and tertiary filtrate are collected by filtration. The tertiary filtrate is cooled to 30°C to allow some of the ammonium oxalate to precipitate as crystals. The ammonium oxalate crystals are separated by filtration to obtain a quaternary filtrate. The secondary precipitate is added to the fourth filtrate and heated to 80°C to dissolve the ammonium oxalate. The mixture is then filtered, and the third and fifth filtrates are collected. The fifth filtrate is cooled to 30°C to allow some of the ammonium oxalate to crystallize. The ammonium oxalate crystals are separated by filtration, yielding a sixth filtrate. This sixth filtrate is then used again to dissolve the ammonium oxalate in the next solid precipitate (i.e., the third precipitate). This process of elution and crystallization is repeated multiple times until all the ammonium oxalate in the solid precipitate is separated. The final precipitate is the aluminum hydroxide filter cake with the ammonium oxalate crystals removed. The filter cake is then washed with deionized water to remove any remaining ammonium oxalate entrained by the eluent, and then dried. The final filtrate obtained from recrystallization is used in step S3.2 to replace the aluminum with ammonia to generate aluminum hydroxide.

[0128] In this step, the aluminum hydroxide solid precipitate mixed with ammonium oxalate crystals is first placed in an ammonium oxalate eluent (i.e., the remaining 50% volume of the purified solution) and heated to dissolve the ammonium oxalate crystals in the liquid. Then, the aluminum hydroxide solid precipitate and filtrate are separated by filtration. Each time, the filtrate is first cooled to allow some of the ammonium oxalate to precipitate as crystals. The ammonium oxalate crystals and the remaining filtrate are then recovered by filtration, further reducing the ammonium oxalate content in the filtrate. This filtrate is then used to redissolve the aluminum hydroxide filter cake, further dissolving and eluting the ammonium oxalate mixed in the aluminum hydroxide filter cake to improve the purity of the aluminum hydroxide product and recover the ammonium oxalate.

[0129] S3.2 After recrystallization in step S3.1, the (NH4)3Al(C2O4)3 in the final filtrate is converted into aluminum hydroxide by ammonia addition. The principle is the same as in step S2: ammonia is added to the final filtrate until no new precipitate is formed, and the reaction is fully completed to obtain the reaction product slurry.

[0130] S3.3 Recrystallization and Filtration Separation of Aluminum Hydroxide and Ammonium Oxalate: The reaction product slurry obtained in step S3.2 is filtered and separated. The resulting solid precipitate is a mixture of aluminum hydroxide and ammonium oxalate crystals. The mixture is added to ammonium oxalate eluent (1 L of 10 wt% ammonia water is used in this step), heated to 80°C to dissolve the ammonium oxalate. The mixture is filtered, and the primary precipitate and primary filtrate are collected. The primary filtrate is cooled to 30°C to allow some of the ammonium oxalate to precipitate as crystals. The ammonium oxalate crystals are separated by filtration, and a secondary filtrate is obtained. The primary precipitate (which still contains ammonium oxalate due to its solubility) is added to the secondary filtrate and heated to 80°C to dissolve the ammonium oxalate. The mixture is filtered, and the secondary precipitate and tertiary filtrate are collected. The tertiary filtrate is cooled to 30°C to allow some of the ammonium oxalate to precipitate as crystals. The ammonium oxalate crystals are separated by filtration, and a quaternary filtrate is obtained. The secondary precipitate is added to the fourth filtrate and heated to 80°C to dissolve the ammonium oxalate. The mixture is then filtered, and the third and fifth filtrates are collected. The fifth filtrate is cooled to 30°C to allow some of the ammonium oxalate to crystallize. The ammonium oxalate crystals are separated by filtration, and the sixth filtrate is obtained. This sixth filtrate is then used again to dissolve the ammonium oxalate in the next solid precipitate (i.e., the third precipitate). This process is repeated multiple times until all the ammonium oxalate in the solid precipitate is separated. The final precipitate is the aluminum hydroxide filter cake with the ammonium oxalate crystals removed. The aluminum hydroxide filter cake is then washed with deionized water to remove any residual eluent-carried ammonium oxalate and dried. In this step, the aluminum hydroxide solid precipitate mixed with ammonium oxalate crystals is first heated in ammonia water to dissolve the ammonium oxalate crystals in the liquid. Then, the aluminum hydroxide solid precipitate and filtrate are separated by filtration. Each time, the filtrate is first cooled to allow some of the ammonium oxalate to precipitate as crystals. The ammonium oxalate crystals and the remaining filtrate are then recovered by filtration, further reducing the ammonium oxalate content in the filtrate. This filtrate is then used to redissolve the aluminum hydroxide filter cake, further dissolving and eluting the ammonium oxalate mixed in the aluminum hydroxide filter cake to improve the purity of the aluminum hydroxide product and recover the ammonium oxalate.

[0131] Example 4: Extraction of aluminum hydroxide from aluminum ash

[0132] To extract aluminum hydroxide from aluminum ash, follow these steps:

[0133] S1, Alumina in replaced aluminum ash

[0134] S1.1, Ammonium oxalate leaching of aluminum ash

[0135] 1. One-time leaching

[0136] Take 100g of aluminum ash and mix ammonium oxalate monohydrate (NH4)2C2O4·H2O with aluminum ash at a mass ratio of 6:1. Use high-temperature steam as the reaction system: mix aluminum ash and ammonium oxalate in a reactor, and continuously introduce high-temperature steam into the reactor through the inlet at the bottom to raise the solution temperature to 180℃ for ammonia stripping. Continue introducing steam for 120 minutes. The ammonia gas generated in the reaction is discharged from the exhaust port at the top of the reactor, yielding the reacted material. Filter and separate the reacted material into solid and liquid components, obtaining primary leaching residue and primary leaching solution. The primary leaching residue mainly consists of unreacted (NH4)2C2O4 and aluminum ash (since the leaching of aluminum ash by ammonium oxalate is a reversible reaction, some raw materials are not completely reacted). The primary leaching solution mainly contains (NH4)3Al(C2O4)3, (NH4)2C2O4, and (NH4)3Fe(C2O4)3.

[0137] 2. Secondary leaching

[0138] The primary leaching residue is retained in the reactor. High-temperature steam is continuously introduced into the reactor through the air inlet at the bottom of the reactor to raise the solution temperature to 180°C for ammonia stripping. The steam is continuously introduced for 120 minutes to obtain a secondary leaching solution and a secondary leaching residue. The secondary leaching residue mainly consists of unreacted silicon impurities. The main components of the secondary leaching solution are the same as those of the primary leaching solution. The leaching solutions obtained from the two leaching processes are mixed for use in the next step of the experiment.

[0139] S2, The leachate reacts with ammonia to produce aluminum hydroxide.

[0140] Take 50% of the mixed leachate obtained in step S1 and add ammonia water until no new precipitate is formed. Allow the mixture to react fully to obtain the reaction product slurry.

[0141] S3. Separation, purification of aluminum hydroxide, and recovery of ammonium oxalate.

[0142] The steps S3.1 to S3.3 of Example 3 are the same, except that the ammonium oxalate eluent used in S3.1 of Example 4 is the remaining 50% volume of leachate that was not used in step S2.

[0143] The raw material usage, aluminum recovery rate, and different experimental conditions for Examples 1-4 are shown in Table 1:

[0144] Table 1

[0145]

[0146]

[0147]

[0148] From the aluminum hydroxide mass obtained in steps S3.1 and S3.3 of Table 1, it can be seen that the aluminum hydroxide filter cake obtained by adding ammonia to 50% of the purified solution in Example 3, and recrystallizing it in the remaining 50% of the purified solution, has a mass that is basically the same as that obtained by recrystallizing in ammonia water. Similarly, the aluminum hydroxide filter cake obtained by adding ammonia to 50% of the leachate in Example 4, and recrystallizing it in the remaining 50% of the leachate, has a mass that is basically the same as that obtained by recrystallizing in ammonia water. This indicates that the leachate or purified solution and ammonia water can both be used as media for recrystallization separation and as solvents for ammonium oxalate. The purity of the extracted aluminum hydroxide was tested using XRF, and the results are shown in Table 1. The aluminum recovery rate in Table 1 refers to the proportion of the mass of aluminum in the extracted aluminum hydroxide to the total mass of aluminum in the starting raw material activated alumina. The aluminum recovery rates of Examples 1-4 all reached approximately 70% or higher, indicating a high aluminum recovery rate. Figure 4 The thermogravimetric curve of aluminum hydroxide in Example 3 shows that as the aluminum hydroxide product is heated from room temperature, the weight loss accelerates, reaching the maximum weight loss rate at 300°C. After that, the weight loss slows down, and the weight becomes basically constant at 700°C, with the remaining mass accounting for 65.16%, which is close to the theoretical mass accounting for 65.35%.

Claims

1. A method for extracting aluminum hydroxide from materials containing active alumina, characterized in that, Includes the following steps: S1, Alumina in the replaced activated alumina material S1.1, Aluminum in activated alumina material leached by ammonium oxalate The activated alumina material is mixed with ammonium oxalate and heated in an aqueous reaction system to generate ammonia gas, which leaches aluminum from the activated alumina material, resulting in a post-reaction material. The post-reaction material is then filtered to obtain leaching residue and a leachate containing (NH4)3Al(C2O4)3. The activated alumina material is bauxite, lightly calcined bauxite, material containing metakaolinite phase, or aluminum ash. S2. The leachate is reacted with ammonia to produce a reaction product slurry containing aluminum hydroxide solid precipitate; preferably, the ammonia comes from ammonia gas or ammonia water. S3. Take the reaction product slurry obtained in step S2, filter and separate it to obtain aluminum hydroxide solid precipitate and ammonium oxalate solution.

2. The method according to claim 1, characterized in that: In step S1.1, ammonium oxalate and activated alumina are mixed and reacted according to a mass ratio of ammonium oxalate to activated alumina of 3 to 8:

1. Preferably, the ammonium oxalate is (NH4)2C2O4·H2O, and the mass ratio of (NH4)2C2O4·H2O to the activated alumina material is 4 to 8:

1.

3. The method according to claim 1, characterized in that: In step S1.1, the water reaction system is provided by introducing water vapor into the reaction vessel, or by adding water to the reaction raw materials and heating it to the reaction temperature; the reaction temperature in step S1.1 is 100-180°C, and the reaction time is 60-300 min.

4. The method according to claim 1, characterized in that: In step S1.1, the leaching residue is repeatedly leached: the obtained leaching residue is leached twice in an aqueous reaction system. The reaction conditions for the second leaching are the same as those for the first leaching. The second leaching solution obtained after the second leaching is combined with the first leaching solution to obtain a mixed leaching solution, which is used in step S2.

5. The method according to claim 1 or 4, characterized in that: Step S1 further includes step S1.2: the leachate obtained in step S1.1 is first subjected to iron removal and then step S2: sulfide is added to the leachate until no new black ferrous sulfide precipitate is formed, and solid-liquid separation is performed to obtain an iron-removed solution and a ferrous sulfide filter cake. The iron-removed solution is used for the ammonia addition reaction in step S2. Preferably, the sulfide is ammonium sulfide or ammonium hydrogen sulfide.

6. The method according to claim 5, characterized in that: Step S1 also includes step S1.3: the iron-removed solution obtained in step S1.2 is first desulfurized and then used for the ammonia addition reaction in step S2: hydrogen peroxide is added to the iron-removed solution or air is blown in to oxidize the residual sulfides into sulfur, the sulfur is separated by filtration, and a purified solution with iron and sulfur removed is obtained. The purified solution is used for the ammonia addition reaction in step S2.

7. The method according to claim 1, characterized in that: The aluminum hydroxide solid precipitate obtained in step S3 is placed in ammonium oxalate eluent. The ammonium oxalate crystals mixed in the aluminum hydroxide solid precipitate are dissolved and eluted by recrystallization, thereby improving the purity of aluminum hydroxide and recovering ammonium oxalate.

8. The method according to claim 7, characterized in that: The ammonium oxalate eluent is ammonia water. The aluminum hydroxide solid precipitate obtained by filtering the reaction product slurry obtained in step S2 is dissolved in ammonia water by heating and eluting ammonium oxalate. The solution after recrystallizing the filtrate obtained by filtration to precipitate some ammonium oxalate crystals is used as the eluent for the next solid precipitate. The solid precipitate is soaked and eluted with ammonium oxalate multiple times. The precipitate is washed with water and dried to obtain purified aluminum hydroxide solid. The ammonium oxalate crystals are recovered by recrystallizing the filtrate. Preferably, step S3 is performed as follows: The reaction product slurry obtained in step S2 is filtered and separated to obtain a solid precipitate and an ammonium oxalate solution. The solid precipitate is added to ammonia water and heated to 75-95°C to dissolve the ammonium oxalate solid mixed in it. The mixture is filtered to obtain a primary precipitate and a primary filtrate. The primary filtrate is cooled to 20-40°C to allow the ammonium oxalate crystals to precipitate. The ammonium oxalate crystals and a secondary filtrate are collected by filtration. The primary precipitate is added to the secondary filtrate from which the ammonium oxalate crystals have been removed. The mixture is heated to dissolve the ammonium oxalate in the primary precipitate in the secondary filtrate. The mixture is filtered and separated to obtain a secondary precipitate and a tertiary filtrate. The tertiary filtrate is cooled to precipitate ammonium oxalate crystals. The ammonium oxalate crystals are collected by filtration. The tertiary filtrate is used to impregnate the secondary precipitate to dissolve and elute the ammonium oxalate. This process of elution and crystallization is repeated multiple times until all the ammonium oxalate in the solid precipitate is separated. The final precipitate is the aluminum hydroxide filter cake from which the ammonium oxalate crystals have been removed. The precipitate is washed with water and dried to obtain purified aluminum hydroxide solid.

9. The method according to claim 7, characterized in that: Take a portion of the leachate obtained in step S1.1 or the purified solution obtained in step S1.3 of claim 6 as the ammonium oxalate eluent in step S3.1; at this time, steps S2 and S3 are performed as follows: S2, The leachate or purified solution reacts with ammonia to produce aluminum hydroxide. Take the leachate obtained in step S1.1 or the purified solution obtained in step S1.3, add ammonia to it until no new precipitate is formed, and react fully to obtain the reaction product slurry; S3.1 Recrystallization and Filtration Separation of Aluminum Hydroxide and Ammonium Oxalate: The reaction product slurry obtained in step S2 is filtered and separated to obtain a solid precipitate of aluminum hydroxide and an ammonium oxalate solution; the solid precipitate of aluminum hydroxide is dissolved and eluted in ammonium oxalate eluent by heating to 75-95℃; the solution after recrystallization of the filtrate obtained from the filtration separation to precipitate some ammonium oxalate crystals is used as the eluent for the next solid precipitate precipitate; the solid precipitate is impregnated and eluted with ammonium oxalate multiple times, the precipitate is washed with water and dried to obtain purified solid aluminum hydroxide; the ammonium oxalate crystals are recovered by recrystallization of the filtrate; the ammonium oxalate eluent is the remaining volume of leachate or purified solution not used in step S2. Preferably, the method further includes the following steps: S3.

2. After recrystallization in step S3.1, ammonia is added to the final filtrate until no new precipitate is formed, and the reaction is fully carried out to obtain the reaction product slurry. S3.3 The reaction product slurry obtained in step S3.2 is recrystallized and filtered to separate aluminum hydroxide and ammonium oxalate according to the method in step S3.

1. The difference is that the eluent for ammonium oxalate in step S3.3 is ammonia.

10. The method according to claim 9, characterized in that: S3.1 Recrystallization and Filtration Separation of Aluminum Hydroxide and Ammonium Oxalate: The reaction product slurry obtained in step S2 is filtered and separated to obtain a solid precipitate of aluminum hydroxide and an ammonium oxalate solution. The obtained solid precipitate is a mixture of aluminum hydroxide and ammonium oxalate crystals. The solid precipitate is added to the ammonium oxalate eluent and heated to 75-95°C to dissolve the ammonium oxalate. The precipitate and filtrate are filtered and collected. The filtrate is cooled to 20-40°C to precipitate some of the ammonium oxalate crystals. The ammonium oxalate crystals are separated by filtration, and a secondary filtrate is obtained. The precipitate is added to the secondary filtrate and heated to dissolve the ammonium oxalate. The precipitate and filtrate are filtered and collected. The filtrate is cooled to precipitate some of the ammonium oxalate crystals. Ammonium oxalate crystals were separated by filtration, and four filtrates were obtained. The second precipitate was added to the fourth filtrate and heated to dissolve the ammonium oxalate. The precipitate was filtered, and the third and fifth filtrates were collected. The fifth filtrate was cooled to allow some of the ammonium oxalate crystals to precipitate. The ammonium oxalate crystals were separated by filtration, and a sixth filtrate was obtained. The sixth filtrate was used again to dissolve the ammonium oxalate in the third precipitate. This process of elution and crystallization was repeated until all the ammonium oxalate in the solid precipitate was separated. The final precipitate was the aluminum hydroxide filter cake with the ammonium oxalate crystals removed. The precipitate was washed with water and dried to obtain purified aluminum hydroxide solid. The final filtrate obtained by recrystallization was used in step S3.2 to replace the aluminum with ammonia to generate aluminum hydroxide.

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