Method for producing high-purity alumina in bayer process circulation mother liquor

Abstract

The application discloses a method for producing high-purity alumina by recycling mother liquor of a Bayer process, comprising the following steps: A, sending the recycling mother liquor of the Bayer process into an extraction tank, adding N235 extractant with a concentration of 10-15% as an organic phase for extraction, and taking the water phase after extraction as sodium aluminate liquor after vanadium extraction; B, adding yellow blood salt and calcium aluminate desilication agent to the sodium aluminate liquor after vanadium extraction for reaction n, and then performing ceramic membrane precision filtration to obtain purified liquor; C, sending the purified liquor into a carbonation decomposition tank, continuously feeding in CO2 gas with a purity of greater than or equal to 95% under reaction conditions, and then separating and precipitating to obtain Al(OH)3 crystals; D, washing the Al(OH)3 crystals with deionized water, and then drying; E, calcining the dried Al(OH)3 at 1200-1400 DEG C for 3-5 h to obtain 4N-5N high-purity alumina. The application can realize efficient recovery of vanadium resources and synchronous preparation of high-purity alumina, and improve the economic efficiency and environmental protection of the process.

Description

Technical Field

[0001] This invention relates to the field of alumina production and resource recycling technology, specifically to a method for the co-production of high-purity alumina using Bayer process circulating mother liquor. Background Technology

[0002] The Bayer process is the mainstream technology for alumina production, but in traditional processes, the Bayer process circulating mother liquor (caustic alkali concentration of about 250 g / L and alumina concentration of about 130 g / L) has two major pain points: 1. The continuous accumulation of impurities such as iron, zinc, and silicon in the circulating mother liquor, as well as the associated vanadium element, makes it difficult to improve the purity of ordinary alumina products to 4N grade or above, and vanadium resources are wasted (vanadium is discarded as an impurity in traditional processes, without realizing resource utilization); among them, silicon impurities mainly exist in the form of sodium silicate, which reacts with sodium aluminate solution to form aluminosilicate precipitates, which not only affect the crystallization quality of high-purity alumina, but also reduce the purity of the product, and is one of the key impurities restricting the preparation of 4N-5N grade high-purity alumina; 2. The production of high-purity alumina relies on low-impurity raw materials, and the deep impurity removal process is complex and costly. At the same time, the accumulation of vanadium in the circulating mother liquor will affect the crystallization quality of alumina, leading to fluctuations in product performance. 3. Existing vanadium extraction technologies are mostly designed for independent vanadium mines or vanadium-containing wastewater, and have not been integrated with the Bayer process for high-purity alumina production. These technologies suffer from problems such as vanadium extraction agents disrupting the stability of sodium aluminate solutions, high Al2O3 loss rates, and poor process integration, and cannot be directly applied to the Bayer process's circulating mother liquor treatment and high-purity alumina production systems.

[0003] Therefore, developing a process adapted to the Bayer process circulating mother liquor, with a caustic alkali concentration of 240-260 g / L and an alumina concentration of 120-140 g / L, to achieve an integrated process of "vanadium extraction-impurity removal-high-purity alumina preparation" has become a key requirement for solving resource waste, reducing production costs, and increasing product added value. Summary of the Invention

[0004] The purpose of this invention is to provide a method for the co-production of high-purity alumina from Bayer process recycled mother liquor. This method uses Bayer process recycled mother liquor as raw material to achieve efficient recovery of vanadium resources and simultaneous preparation of high-purity alumina, thereby solving the problems of impurity accumulation in recycled mother liquor and waste of vanadium resources from the source, reducing the impurity removal cost of high-purity alumina production, and improving the economic efficiency and environmental friendliness of the process.

[0005] To solve the above technical problems, the present invention adopts the following technical solution: The method for co-producing high-purity alumina from Bayer process recycled mother liquor includes the following steps: A. The Bayer process circulating mother liquor is fed into the extraction tank, and N235 extractant with a concentration of 10-15% is added as the organic phase. The volume ratio of the organic phase to the aqueous phase is controlled at 1:3-1:5, the extraction temperature is 40-60℃, the stirring speed is 22-28 r / min, and the extraction time is 15-25 min. The organic phase and the aqueous phase are then separated. The aqueous phase is the sodium aluminate concentrate after vanadium extraction. After this step, the vanadium content in the sodium aluminate concentrate is ≤5ppm. B. Add 0.01-0.03% of ferrous sulfate (by mass of sodium aluminate) and 0.05-0.1% of calcium aluminate desiliconizing agent (by mass of sodium aluminate) to the sodium aluminate semen after vanadium extraction. Control the caustic ratio of the solution to 1.5-1.8 and the temperature to 60-70℃. React for 15-20 minutes. Then, filter through a ceramic membrane to remove fine particles, ferrous ferrocyanide precipitate, and calcium silicate precipitate impurities to obtain purified semen. C. The purified semen is sent into a carbonation decomposition tank, the temperature is controlled at 50-60℃, and continuous stirring is maintained. CO2 gas with a purity of ≥95% is continuously introduced under normal pressure or positive pressure of 0.1-0.2MPa until the pH of the semen drops to 8-10. Then the CO2 gas is stopped, and a mixed liquid system containing Al(OH)3 crystal precipitate is obtained. The system is filtered, the precipitate is separated, and Al(OH)3 crystals are obtained. D. Wash the Al(OH)3 crystals with deionizers 2-3 times to remove residual Na⁺ and Cl⁻, and then dry them at 100-150℃ for 2-3 hours. E. The dried Al(OH)3 is fed into a calcining furnace and calcined at 1200-1400℃ for 3-5 hours to obtain 4N-5N grade high-purity alumina.

[0006] In step A, the solvent for the N235 extractant is sulfonated kerosene.

[0007] The organic phase separated in step A is fed into a back-extraction tank. A 5-8 mol / L hydrochloric acid solution is added to the back-extraction tank as a back-extraction agent. Back-extraction is carried out under continuous stirring at a temperature of 50-60℃ for 20-30 minutes. The back-extraction aqueous phase and the back-extraction organic phase are separated. The back-extraction aqueous phase is a vanadium-enriched solution, and a vanadium-enriched solution with a vanadium content ≥5 g / L is obtained.

[0008] The stirring speed in the carbonation decomposition tank and the back-extraction tank is 22-28 r / min.

[0009] Vanadium product preparation: Add 1-2 mol / L ammonium chloride solution to vanadium enrichment solution, adjust pH to 2-3, vanadium chloride precipitate is generated, filter, take the precipitate and calcine at 500-600℃ for 2-3 hours to obtain V2O5 product with purity ≥99.0%.

[0010] In step B, the pore size of the ceramic membrane is 0.08-0.12 μm.

[0011] The ceramic membrane has a filtration pressure of 0.3-0.5 MPa and a filtration temperature of 60-70℃.

[0012] In step C, the rate at which CO2 gas is introduced is 1.0-1.4 L / L·h.

[0013] The caustic alkali concentration in the Bayer process circulating mother liquor is 240-260 g / L, and the alumina concentration is 120-140 g / L.

[0014] The reaction mechanism of this invention is as follows: 1. Vanadium separation stage: Under alkaline conditions (pH=13~14), the N235 extractant selectively binds to VO4³⁻ in the Bayer process circulating mother liquor, without reacting with AlO2⁻, thus achieving efficient separation of vanadium and aluminum; during the back-extraction process, hydrochloric acid destroys the binding between the extractant and VO4³⁻, releasing vanadium ions to form an enriched solution; 2. Concentration Suitability and Extraction Feasibility: In the Bayer process, the circulating mother liquor undergoes a subsequent carbonation decomposition step, involving the introduction of CO2 and controlled temperature and stirring, to efficiently precipitate Al(OH)3, which is then calcined to convert into high-purity alumina. Examples 1 and 2 clearly demonstrate that high-purity alumina with a purity ≥99.991% was successfully extracted from mother liquors with alumina concentrations of 128 g / L and 132 g / L, respectively, with an Al2O3 loss rate of only 0.7%-0.8% and a vanadium extraction rate ≥95%, fully proving that the reaction can proceed sufficiently. The preferred rotation speed of 22-28 r / min not only meets the requirements for energy saving and liquid stabilization but also, through auxiliary parameter optimization, completely solves the problem of incomplete reaction that may be caused by low rotation speed, perfectly matching the process objectives of this invention. Furthermore, CO2 carbonation decomposition replaces seed crystals, eliminating the need to purchase high-purity Al(OH)3 seed crystals, further reducing raw material costs and enhancing the environmental value of the process.

[0015] 3. Deep Impurity Removal: Yellow blood salt reacts with residual Fe³⁺ in the circulating mother liquor to form ferrocyanide precipitate; the simultaneously added calcium aluminate desiliconizing agent reacts with silicon impurities in the semen (mainly in the form of sodium silicate) to form water-insoluble calcium silicate precipitate, achieving efficient removal of silicon impurities; ceramic membrane filtration can simultaneously remove fine particles, ferrocyanide precipitate, and calcium silicate precipitate, ensuring the purity of the purified semen (silicon content ≤3ppm), suitable for subsequent high-purity alumina preparation, and avoiding the reaction of silicon impurities with AlO⁻ to form aluminosilicates, which would affect crystallization quality and product purity; 4. Carbonation Decomposition and Calcination: CO2 is introduced into the purified liquid for carbonation decomposition. Under alkaline conditions, CO2 reacts with AlO2⁻ in the sodium aluminate solution. The pH of the solution is adjusted to 8-10, causing AlO2⁻ to be converted into Al(OH)3 crystals and fully released. Controlling the CO2 introduction rate, reaction temperature, and stirring speed ensures uniform crystal particle size (D50 = 0.5-5μm) and avoids crystal agglomeration. Subsequently, calcination converts Al(OH)3 into high-purity α-Al2O3 or γ-Al2O3, ultimately yielding 4N-5N grade high-purity alumina. This decomposition method does not require seed crystals, making the process simpler and enabling the utilization of CO2 resources, which meets environmental protection requirements. At the same time, low-speed stirring minimizes energy consumption and ensures liquid stability.

[0016] The beneficial effects of this invention are as follows: The method of this invention can recover vanadium resources from Bayer process mother liquor (extraction rate ≥95%), deeply remove impurities such as silicon, iron, and zinc (silicon content ≤3ppm, total impurity content ≤10ppm (4N grade) or ≤1ppm (5N grade)), and produce high-purity alumina. After vanadium extraction, the vanadium content in the mother liquor is ≤5ppm, and the purity of the V2O5 product is ≥99.0%. It is a production method with high comprehensive benefits.

[0017] The method of this invention effectively solves the problems of impurity accumulation and low utilization rate of the circulating mother liquor in traditional processes, eliminating the need for additional low-impurity raw materials and reducing raw material costs by more than 30%. The vanadium-extracted product, sold as a by-product, increases output value and revenue, fully covering the additional costs of vanadium extraction and deep impurity removal. Simultaneously, the use of CO2 carbonation decomposition to replace high-purity Al(OH)3 seed crystals eliminates the need for additional seed crystal purchases, further reducing raw material costs. Furthermore, the high price of high-purity alumina products results in significant economic benefits. Overall, the net cost per ton of high-purity alumina is reduced by more than 40% compared to traditional processes.

[0018] The method of this invention is seamlessly integrated with the existing Bayer process. Based on the modification of existing Bayer process equipment, only extraction, back-extraction, and ceramic membrane filtration equipment need to be added. No new raw material pretreatment equipment is required. The investment payback period is 33-6 months. The modification difficulty is low and the industrialization feasibility is strong.

[0019] The method of this invention has excellent environmental performance, reusing the circulating mother liquor and reducing water consumption by 10%; impurities such as vanadium, iron, zinc, and silicon are effectively treated or recycled without secondary pollution; and CO2 carbonation decomposition is used to replace seed crystals, realizing the recycling of CO2 resources, reducing carbon emissions, and further aligning with the requirements of the comprehensive resource utilization policy.

[0020] After the extraction of high-purity alumina, the alumina content in the circulating mother liquor is significantly reduced from the initial 130 g / L to a suitable circulating concentration, while the caustic alkali concentration remains basically unchanged. This can effectively reduce the alumina load in the subsequent bauxite leaching process, accelerate the mother liquor circulation speed, improve the circulation efficiency of the entire alumina production system, and further reduce system energy consumption and operating costs. Detailed Implementation

[0021] To facilitate a better understanding of the present invention, the following examples are provided. These examples fall within the scope of protection of the present invention, but do not limit the scope of protection of the present invention. Example 1

[0022] The method for co-producing high-purity alumina using Bayer process circulating mother liquor in this embodiment comprises the following steps: A. The Bayer process circulating mother liquor is fed into the extraction tank, and 10% N235 extractant is added as the organic phase. The volume ratio of the organic phase to the aqueous phase is controlled at 1:3, the extraction temperature is 40℃, the stirring speed is 22r / min, the extraction is carried out for 15min, and the organic phase and aqueous phase are separated. The aqueous phase is the sodium aluminate concentrate after vanadium extraction. The solvent for N235 extractant is sulfonated kerosene; the concentration of caustic alkali in the Bayer process circulating mother liquor is 240 g / L and the concentration of alumina is 120 g / L.

[0023] B. Add 0.01% of the sodium aluminate semen mass of yellow prussiate salt and 0.05% of the sodium aluminate semen mass of calcium aluminate desiliconizing agent to the sodium aluminate semen after vanadium extraction. Control the solution caustic ratio to 1.5 and the temperature to 60℃. React for 15 minutes. Then, filter through a ceramic membrane to remove fine particles, ferrous ferrocyanide precipitate and calcium silicate precipitate impurities to obtain purified semen. The ceramic membrane has a pore size of 0.08 μm, a filtration pressure of 0.3 MPa, and a filtration temperature of 60 °C.

[0024] C. The purified semen was sent into a carbonation decomposition tank, the temperature was controlled at 50℃, and the stirring was maintained at 22r / min. Under a positive pressure of 0.1MPa, CO2 gas with a purity of 95% was continuously introduced at a rate of 1.0L / L·h until the pH of the semen dropped to 8. Then the CO2 gas was stopped, and a mixed liquid system containing Al(OH)3 crystal precipitate was obtained. The precipitate was filtered and separated to obtain Al(OH)3 crystals. D. Wash the Al(OH)3 crystals twice with deionizers to remove residual Na⁺ and Cl⁻, and then dry them at 100℃ for 3 hours. E. The dried Al(OH)3 is fed into a calcining furnace and calcined at 1200℃ for 3 hours to obtain 4N grade high-purity alumina. F. The organic phase separated in step A is sent to the back-extraction tank. A 5 mol / L hydrochloric acid solution is added to the back-extraction tank as a back-extraction agent. The back-extraction is carried out by stirring continuously at a speed of 22 r / min. The back-extraction temperature is 50℃ and the back-extraction time is 20 min. The back-extraction aqueous phase and the back-extraction organic phase are separated. The back-extraction aqueous phase is a vanadium enriched solution, and a vanadium enriched solution with a vanadium content ≥ 5 g / L is obtained. G. Vanadium product preparation steps: Add 1 mol / L ammonium chloride solution to the vanadium enrichment solution, adjust the pH to 2, generate vanadium chloride precipitate, filter, take the precipitate and calcine at 500℃ for 2h to obtain V2O5 product. Example 2

[0025] The method for co-producing high-purity alumina using Bayer process circulating mother liquor in this embodiment comprises the following steps: A. The Bayer process circulating mother liquor is fed into the extraction tank, and N235 extractant with a concentration of 15% is added as the organic phase. The volume ratio of the organic phase to the aqueous phase is controlled at 1:5, the extraction temperature is 60℃, the stirring speed is 28r / min, the extraction time is 25min, and the organic phase and aqueous phase are separated. The aqueous phase is the sodium aluminate concentrate after vanadium extraction. The solvent for N235 extractant is sulfonated kerosene; the concentration of caustic alkali in the Bayer process circulating mother liquor is 260 g / L and the concentration of alumina is 140 g / L.

[0026] B. Add 0.03% of the sodium aluminate semen mass of yellow prussiate salt and 0.1% of the sodium aluminate semen mass of calcium aluminate desiliconizing agent to the sodium aluminate semen after vanadium extraction. Control the solution caustic ratio to 1.8 and the temperature to 70℃. React for 20 minutes. Then, filter through a ceramic membrane to remove fine particles, ferrous ferrocyanide precipitate and calcium silicate precipitate impurities to obtain purified semen. The ceramic membrane has a pore size of 0.12 μm, a filtration pressure of 0.5 MPa, and a filtration temperature of 70 °C.

[0027] C. The purified semen was sent into a carbonation decomposition tank, the temperature was controlled at 60℃, and the stirring speed was maintained at 28r / min. Under a positive pressure of 0.2MPa, CO2 gas with a purity of 95% was continuously introduced at a rate of 1.4L / L·h until the pH of the semen dropped to 10. Then the CO2 gas was stopped, and a mixed liquid system containing Al(OH)3 crystal precipitate was obtained. The precipitate was filtered and separated to obtain Al(OH)3 crystals. D. Wash the Al(OH)3 crystals twice with deionizers to remove residual Na⁺ and Cl⁻, and then dry them at 150℃ for 3 hours. E. The dried Al(OH)3 is fed into a calcining furnace and calcined at 1400℃ for 5 hours to obtain 4N grade high-purity alumina. F. The organic phase separated in step A is sent to the back-extraction tank. An 8 mol / L hydrochloric acid solution is added to the back-extraction tank as a back-extraction agent. The back-extraction is carried out by stirring continuously at a speed of 28 r / min. The back-extraction temperature is 60℃ and the back-extraction time is 30 min. The back-extraction aqueous phase and the back-extraction organic phase are separated. The back-extraction aqueous phase is a vanadium enriched solution, and a vanadium enriched solution with a vanadium content ≥5 g / L is obtained. G. Vanadium product preparation steps: Add 2 mol / L ammonium chloride solution to the vanadium enrichment solution, adjust the pH to 3, generate vanadium chloride precipitate, filter, take the precipitate and calcine at 600℃ for 3h to obtain V2O5 product. Example 3

[0028] The method for co-producing high-purity alumina using Bayer process circulating mother liquor in this embodiment comprises the following steps: A. The Bayer process circulating mother liquor is fed into the extraction tank, and N235 extractant with a concentration of 13% is added as the organic phase. The volume ratio of the organic phase to the aqueous phase is controlled at 1:4, the extraction temperature is 50℃, the stirring speed is 25r / min, the extraction is carried out for 20min, and the organic phase and aqueous phase are separated. The aqueous phase is the sodium aluminate concentrate after vanadium extraction. The solvent for N235 extractant is sulfonated kerosene; the concentration of caustic alkali in the Bayer process circulating mother liquor is 250 g / L and the concentration of alumina is 130 g / L.

[0029] B. Add 0.02% of the sodium aluminate semen mass of yellow prussiate salt and 0.08% of the sodium aluminate semen mass of calcium aluminate desiliconizing agent to the sodium aluminate semen after vanadium extraction. Control the solution caustic ratio at 1.7 and the temperature at 65℃, react for 18 minutes, and then filter through a ceramic membrane to remove fine particles, ferrous ferrocyanide precipitate and calcium silicate precipitate impurities to obtain purified semen. The ceramic membrane has a pore size of 0.1 μm, a filtration pressure of 0.4 MPa, and a filtration temperature of 65 °C.

[0030] C. The purified semen is sent into a carbonation decomposition tank, the temperature is controlled at 55℃, and the stirring speed is maintained at 25r / min. Under normal pressure, CO2 gas with a purity of 95% is continuously introduced at a rate of 1.2L / L·h until the pH of the semen drops to 9. Then the CO2 gas is stopped, and a mixed liquid system containing Al(OH)3 crystal precipitate is obtained. The system is filtered, the precipitate is separated, and Al(OH)3 crystals are obtained. D. Wash the Al(OH)3 crystals three times with deionized water to remove residual Na⁺ and Cl⁻, and then dry them at 130℃ for 2.5h; E. The dried Al(OH)3 is fed into a calcining furnace and calcined at 1300℃ for 4 hours to obtain 4N grade high-purity alumina. F. The organic phase separated in step A is sent to the back-extraction tank. 5-8 mol / L hydrochloric acid solution is added to the back-extraction tank as a back-extraction agent. Back-extraction is carried out by stirring continuously at a speed of 25 r / min. The back-extraction temperature is 55℃ and the back-extraction time is 25 min. The back-extraction aqueous phase and the back-extraction organic phase are separated. The back-extraction aqueous phase is a vanadium enriched solution, and a vanadium enriched solution with a vanadium content ≥5 g / L is obtained. G. Vanadium product preparation steps: Add 1-2 mol / L ammonium chloride solution to the vanadium enrichment solution, adjust the pH to 2.4, generate vanadium chloride precipitate, filter, take the precipitate and calcine at 550℃ for 2.5h to obtain V2O5 product. Example 4

[0031] The method for co-producing high-purity alumina using Bayer process circulating mother liquor in this embodiment comprises the following steps: A. The Bayer process circulating mother liquor was fed into the extraction tank, and 12% N235 extractant was added as the organic phase. The volume ratio of the organic phase to the aqueous phase was controlled at 1:4. The extraction temperature was 50℃, the stirring speed was 25 r / min, and the extraction was carried out for 20 min. The organic phase and the aqueous phase were separated. The aqueous phase was the sodium aluminate concentrate after vanadium extraction. The vanadium content in the sodium aluminate concentrate after vanadium extraction was 3.8 ppm. The solvent for N235 extractant is sulfonated kerosene; the concentration of caustic alkali in the Bayer process circulating mother liquor is 248 g / L and the concentration of alumina is 128 g / L.

[0032] B. Add 0.02% of the sodium aluminate semen mass of yellow prussiate salt and 0.08% of the sodium aluminate semen mass of calcium aluminate desiliconizing agent (purity 98%, D50=8μm) to the sodium aluminate semen after vanadium extraction. Control the solution caustic ratio to 1.6 and the temperature to 65℃, react for 18 minutes, and then filter through a ceramic membrane to remove fine particles, ferrous ferrocyanide precipitate and calcium silicate precipitate impurities to obtain purified semen. The ceramic membrane has a pore size of 0.12 μm, a filtration pressure of 0.5 MPa, and a filtration temperature of 65 °C.

[0033] C. The purified semen was sent into a carbonation decomposition tank, the temperature was controlled at 55℃, and the stirring speed was maintained at 26r / min. Under a positive pressure of 0.1MPa, CO2 gas with a purity of 95% was continuously introduced at a rate of 1.2L / L·h until the pH of the semen dropped to 9. Then the CO2 gas was stopped, and a mixed liquid system containing Al(OH)3 crystal precipitate was obtained. The precipitate was filtered and separated to obtain Al(OH)3 crystals. D. Wash the Al(OH)3 crystals twice with deionizers to remove residual Na⁺ and Cl⁻, and then dry them at 120℃ for 4 hours. E. The dried Al(OH)3 was fed into a calcining furnace and calcined at 1300℃ for 5 hours to obtain 4N grade high-purity alumina (D50=2.8μm, purity 99.992%). F. The organic phase separated in step A is sent to the back-extraction tank. A 6 mol / L hydrochloric acid solution is added to the back-extraction tank as a back-extraction agent. The back-extraction is carried out by stirring continuously at a speed of 28 r / min. The back-extraction temperature is 55℃ and the back-extraction time is 25 min. The back-extraction aqueous phase and the back-extraction organic phase are separated. The back-extraction aqueous phase is a vanadium enriched solution, and a vanadium enriched solution with a vanadium content ≥5 g / L is obtained. G. Vanadium product preparation steps: Add 1.5 mol / L ammonium chloride solution to the vanadium enrichment solution, adjust the pH to 2.5, generate vanadium chloride precipitate, filter, take the precipitate and calcine at 550℃ for 2.5 h to obtain V2O5 product (purity 99.3%).

[0034] Test results: In high-purity alumina, Fe≤0.0005%, Si≤0.0003%, V≤0.0004%, Zn≤0.0008%; vanadium extraction rate 96.5%; Al2O3 loss rate 0.8%. Example 5

[0035] The method for co-producing high-purity alumina using Bayer process circulating mother liquor in this embodiment comprises the following steps: A. The Bayer process circulating mother liquor was fed into the extraction tank, and 10% N235 extractant was added as the organic phase. The volume ratio of the organic phase to the aqueous phase was controlled at 1:3. The extraction temperature was 45℃, the stirring speed was 24 r / min, and the extraction was carried out for 18 min. The organic phase and the aqueous phase were separated. The aqueous phase was the sodium aluminate concentrate after vanadium extraction. The vanadium content in the sodium aluminate concentrate after vanadium extraction was 4.2 ppm. The solvent for N235 extractant is sulfonated kerosene; the concentration of caustic alkali in the Bayer process circulating mother liquor is 252 g / L and the concentration of alumina is 132 g / L.

[0036] B. Add 0.015% of the sodium aluminate semen by mass of vanadium extraction to the sodium aluminate semen, and 0.06% of the sodium aluminate semen by mass of calcium aluminate desiliconizing agent (purity 98%, D50=6μm). Control the solution caustic ratio at 1.7 and the temperature at 60℃, react for 15 minutes, and then filter through a ceramic membrane to remove fine particles, ferrous ferrocyanide precipitate and calcium silicate precipitate impurities to obtain purified semen. The ceramic membrane has a pore size of 0.1 μm, a filtration pressure of 0.3 MPa, and a filtration temperature of 60 °C.

[0037] C. The purified semen is sent into a carbonation decomposition tank, the temperature is controlled at 50℃, and the stirring speed is maintained at 25r / min. Under a positive pressure of 0.15MPa, CO2 gas with a purity of 95% is continuously introduced at a rate of 1.1L / L·h until the pH of the semen drops to 8.5. Then the CO2 gas is stopped, and a mixed liquid system containing Al(OH)3 crystal precipitate is obtained. The precipitate is filtered and separated to obtain Al(OH)3 crystals. D. Wash the Al(OH)3 crystals twice with deionized water to remove residual Na⁺ and Cl⁻, and then dry them at 110℃ for 2 hours. E. The dried Al(OH)3 is fed into a calcining furnace and calcined at 1250℃ for 3.5h to obtain 4N grade high-purity alumina (D50=3.2μm, purity 99.991%). F. The organic phase separated in step A is sent to the back-extraction tank. A 5 mol / L hydrochloric acid solution is added to the back-extraction tank as a back-extraction agent. The back-extraction is carried out by stirring continuously at a speed of 24 r / min. The back-extraction temperature is 50℃ and the back-extraction time is 222 min. The back-extraction aqueous phase and the back-extraction organic phase are separated. The back-extraction aqueous phase is a vanadium enriched solution, and a vanadium enriched solution with a vanadium content ≥5 g / L is obtained. G. Vanadium product preparation steps: Add 1 mol / L ammonium chloride solution to the vanadium enrichment solution, adjust the pH to 2.2, generate vanadium chloride precipitate, filter, take the precipitate and calcine at 520℃ for 2h to obtain V2O5 product (purity 99.1%).

[0038] Test results: The total impurity content of high-purity alumina is ≤8ppm, of which Si≤0.0002% and Fe≤0.0004%; vanadium extraction rate is 95.3%; Al2O3 loss rate is 0.7%.

[0039] Comparative example (traditional process):

[0040] The process employs a combination of "traditional Bayer process circulating mother liquor treatment + separate vanadium extraction + high-purity alumina purification". Using Bayer process circulating mother liquor with a caustic alkali concentration of 250 g / L and an alumina concentration of 130 g / L as raw material, vanadium is first extracted by ion exchange, and then alumina is purified by multi-stage recrystallization. However, there is no synergistic connection between the impurity removal and vanadium extraction processes.

[0041] Test results: High-purity alumina purity 99.99%, vanadium extraction rate 88%; Al2O3 loss rate 3.5%; processing cost 32,000 yuan / ton of high-purity alumina, vanadium recovery revenue only 8 million yuan / year (based on 100,000-ton capacity); investment payback period 18 months.

[0042] The comparison shows that the method of the present invention improves the vanadium extraction rate by more than 8.5%, reduces the Al2O3 loss rate by 79%, reduces the processing cost by 40%, and shortens the investment payback period by 75%, demonstrating significant comprehensive advantages.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for co-producing high-purity alumina from Bayer process recycled mother liquor, characterized in that, Includes the following steps: A. The Bayer process circulating mother liquor is fed into the extraction tank, and N235 extractant with a concentration of 10-15% is added as the organic phase. The volume ratio of the organic phase to the aqueous phase is controlled at 1:3-1:5, the extraction temperature is 40-60℃, the stirring speed is 22-28r / min, and the extraction is carried out for 15-25min. The organic phase and the aqueous phase are separated. The aqueous phase is the sodium aluminate concentrate after vanadium extraction. B. Add 0.01-0.03% of the sodium aluminate semen by mass of vanadium extraction to prussiate sulfadiazine and 0.05-0.1% of the calcium aluminate desiliconizing agent by mass of vanadium extraction to the sodium aluminate semen. Control the caustic ratio of the solution to 1.5-1.8 and the temperature to 60-70℃. React for 15-20 minutes, and then filter through a ceramic membrane to obtain purified semen. C. The purified semen is sent into a carbonation decomposition tank, the temperature is controlled at 50-60℃, and continuous stirring is maintained. CO2 gas with a purity of ≥95% is continuously introduced under normal pressure or positive pressure of 0.1-0.2MPa until the pH of the semen drops to 8-10. Then the CO2 gas is stopped, and a mixed liquid system containing Al(OH)3 crystal precipitate is obtained. The system is filtered, the precipitate is separated, and Al(OH)3 crystals are obtained. D. Wash the Al(OH)3 crystals with deionizer 2-3 times, and then dry them at 100-150℃ for 2-3 hours; E. The dried Al(OH)3 is fed into a calcining furnace and calcined at 1200-1400℃ for 3-5 hours to obtain 4N-5N grade high-purity alumina.

2. The method for co-producing high-purity alumina using Bayer process circulating mother liquor according to claim 1, characterized in that: In step A, the solvent for the N235 extractant is sulfonated kerosene.

3. The method for co-producing high-purity alumina using Bayer process circulating mother liquor according to claim 1, characterized in that: The organic phase separated in step A is fed into a back-extraction tank. A 5-8 mol / L hydrochloric acid solution is added to the back-extraction tank as a back-extraction agent. Back-extraction is carried out under continuous stirring at a temperature of 50-60℃ for 20-30 minutes. The back-extraction aqueous phase and the back-extraction organic phase are separated. The back-extraction aqueous phase is a vanadium-enriched solution, and a vanadium-enriched solution with a vanadium content ≥5 g / L is obtained.

4. The method for co-producing high-purity alumina using Bayer process circulating mother liquor according to claim 3, characterized in that: The stirring speed in the carbonation decomposition tank and the back-extraction tank is 22-28 r / min.

5. The method for co-producing high-purity alumina using Bayer process circulating mother liquor according to claim 3, characterized in that: It also includes the vanadium product preparation process, as follows: add 1-2 mol / L ammonium chloride solution to the vanadium enrichment solution, adjust the pH to 2-3, generate vanadium chloride precipitate, filter, take the precipitate and calcine at 500-600℃ for 2-3 h to obtain V2O5 product.

6. The method for co-producing high-purity alumina using Bayer process circulating mother liquor according to claim 1, characterized in that: In step B, the pore size of the ceramic membrane is 0.08-0.12 μm.

7. The method for co-producing high-purity alumina using Bayer process circulating mother liquor according to claim 1, characterized in that: The ceramic membrane has a filtration pressure of 0.3-0.5 MPa and a filtration temperature of 60-70℃.

8. The method for co-producing high-purity alumina using Bayer process circulating mother liquor according to claim 1, characterized in that: In step C, the rate at which CO2 gas is introduced is 1.0-1.4 L / L·h.

9. The method for co-producing high-purity alumina using Bayer process circulating mother liquor according to claim 1, characterized in that: The caustic alkali concentration in the Bayer process circulating mother liquor is 240-260 g / L, and the alumina concentration is 120-140 g / L.