Preparation method and application of cryolite-containing low-temperature electrolyte for aluminum electrolysis

Abstract

The invention discloses a preparation method and application of a cryogenic electrolyte of fluorine-bearing alumina for aluminum electrolysis, belonging to the field of aluminum electrolysis. Grinding and screening the hazardous waste of the aluminum electrolysis industry containing alumina salts to obtain a hazardous waste raw material containing alumina; then carrying out microwave hydrothermal-alkali leaching treatment on the hazardous waste raw material containing alumina to obtain a crude sodium aluminate solution; adding calcium oxide to the crude sodium aluminate solution and purifying it by ultrasonic to obtain a refined sodium aluminate solution; further acid-leaching the refined sodium aluminate solution to obtain aluminum hydroxide colloid; and calcining the aluminum hydroxide colloid by microwave assistance to obtain metallurgical-grade alumina; then modifying the metallurgical-grade alumina with carboxylic acid to obtain modified alumina; finally, adsorbing fluorine in industrial wastewater with the modified alumina to prepare fluorine-bearing alumina. Both rare earth metals and alumina are good adsorbents. Using the fluorine-bearing alumina as the solute of the cryogenic electrolyte can obtain a cryogenic electrolyte for aluminum electrolysis that takes into account both low electrolysis temperature and high solubility of alumina. The invention solves the environmental hazards of the hazardous waste containing alumina in the aluminum electrolysis industry and fluorine in industrial wastewater, and resourcefully utilizes the hazard sources.

Description

Technical Field

[0001] The present invention discloses a preparation method and application of cryogenic electrolyte of fluorine-carrying alumina for aluminum electrolysis, belonging to the field of aluminum electrolysis. Background Art

[0002] At present, the aluminum electrolysis industry is developing rapidly. China ranks first in the world in terms of the production capacity of electrolytic aluminum. China is the world's largest aluminum consumer, accounting for about 1 / 3 of the global total consumption. In 2022, the demand for primary aluminum in China reached 41.66 million tons, while the production of primary aluminum was 40.214 million tons. It is estimated that the annual output of electrolytic aluminum is about 41.2 million tons. Such a high output is bound to be accompanied by a large amount of waste containing alumina salts in the aluminum electrolysis industry. Since it is difficult to effectively treat the waste containing alumina salts in the aluminum electrolysis industry, currently 95% of the waste containing alumina salts can only be landfilled or stockpiled, and the historical stockpile has exceeded tens of millions of tons. If this waste is simply landfilled, it will cause: First, land salinization and water resource pollution will ultimately endanger human health; Second, it will cause waste of valuable metals (aluminum oxide) in the waste containing alumina salts.

[0003] At the same time, aluminum electrolysis is an industry with high energy consumption. With the expansion of the scale of the aluminum electrolysis industry, the total power consumption is also increasing year by year. Reducing energy consumption also needs to be solved urgently. In the aluminum electrolysis industry, using Na3AlF6 - AlF3 - Al2O3 melt as the electrolyte and carbon materials as the two electrodes, electrolysis is carried out under direct current at 950°C - 970°C, resulting in high energy consumption. For this reason, low-temperature aluminum electrolysis has become a research hotspot. However, in the low-temperature electrolyte system, when the electrolysis temperature drops, the solubility of alumina also decreases significantly.

[0004] Therefore, the present invention systematically solves the following two problems: First, the resource utilization of waste containing alumina salts in the aluminum electrolysis industry; and the treatment of waste containing fluorine wastewater and fluorine-containing dust; Second, it reduces the primary crystallization temperature in the low-temperature electrolyte system and reduces the electrolysis temperature in the aluminum electrolysis process.

[0005] CN211936015U discloses a dust removal system for a fluorine-carrying alumina bin in an electrolytic flue gas purification system. This prior art provides a dust removal system, which connects a valve to the top of the fluorine-carrying alumina bin through a top outlet pipe and the other end to an exhaust pipe, and uses a high-efficiency filter of the purification system as the main equipment of the dust removal system for the fluorine-carrying alumina bin. The technical problem to be solved by this prior art is: to improve the abrasion resistance of the flue and ultimately improve the service life of the dust removal system. Therefore, this prior art only discloses the device in which fluorine-carrying alumina is generated by the reaction of fresh alumina in the flue gas system, and does not disclose any method for preparing alumina into fluorine-carrying alumina, let alone disclose a method for preparing fluorine-carrying alumina using waste containing alumina salts in the aluminum electrolysis industry as raw materials.

[0006] CN112520811A discloses a manganese-loaded activated alumina defluorination adsorbent and its preparation method. Using ordinary activated alumina particles as the carrier, the ordinary activated alumina particles are activated with a nano-aluminum solution; hydrogen peroxide and ammonia water are added to the manganese sulfate solution, and the activated activated alumina particles are put in, stirred, washed, and dried to obtain manganese-loaded activated alumina particles. The biggest differences between this invention and the present invention are: (1) The raw material carriers are different. This invention uses ordinary activated alumina particles as the raw material carrier, while the present invention uses aluminum electrolysis industrial hazardous waste containing alumina salts as the raw material carrier. Therefore, this invention cannot solve the technical problem of converting hazardous waste into fluorine-loaded alumina in the present invention; (2) The methods for activating alumina are different. This invention uses a nano-aluminum solution to activate ordinary activated alumina particles; while the aluminum electrolysis industrial hazardous waste containing alumina salts in the present invention is treated to obtain aluminum hydroxide colloid, and active metallurgical-grade alumina is obtained by microwave-assisted medium and low-temperature calcination of the aluminum hydroxide colloid; (3) The methods for modifying alumina are different. This invention adds hydrogen peroxide and ammonia water to the manganese sulfate solution, puts in the activated activated alumina particles, and obtains manganese-loaded activated alumina particles, that is, modification is carried out by loading manganese on the activated alumina particles, and the modification principle is to increase the porosity and specific surface area of the activated alumina; while the present invention uses carboxylic acid to modify the metallurgical-grade alumina to obtain activated alumina with more hydroxyl groups on the surface, and the modification principle is to increase the hydroxyl groups (-OH) on the surface of the alumina; (4) The ways of adsorbing fluorine are different. This invention's manganese-loaded activated alumina particles adsorb fluorine through having more adsorption sites; while in the present invention, the activated alumina modified by carboxylic acid increases the hydroxyl groups (-OH) on the surface of the alumina, thereby increasing the adsorption sites of fluoride ions. The principle of adsorbing fluorine is mainly to adsorb fluoride on the surface of the activated alumina through chemical adsorption and electrostatic attraction. Among them, the chemical adsorption is ion exchange and the formation of complexes, and ion exchange is achieved by F - substituting -OH; therefore, this invention is significantly different from the present invention.

[0007] CN115849419A discloses a production method of fluorine-bearing alumina and the application of the produced fluorine-bearing alumina. In this method, bauxite, iron ore and anthracite are mixed and ground into powder, made into balls with fluosilicic acid, and after high-temperature smelting, ferrosilicon is separated to obtain fluorine-modified alumina; the fluorine-modified alumina is mixed with ordinary alumina to prepare an alumina mixture, which is put into an electrolytic cell to dissolve the cryolite melt for electrolysis. The differences between this invention and the present invention are as follows: (1) Different raw materials. The raw materials of this invention are bauxite, iron ore, anthracite and fluosilicic acid, while the present invention uses hazardous waste containing alumina salts in the aluminum electrolysis industry as raw materials; (2) Different treatment methods. Different raw materials correspond to different treatment methods. This invention uses the method of making balls and high-temperature smelting to obtain fluorine-modified alumina; while the present invention goes through microwave hydrothermal-alkali leaching → ultrasonic purification → acid leaching → microwave medium and low temperature assisted calcination (to prepare alumina with higher activity) → carboxylic acid modification of activated alumina (to enhance the specific surface area and surface activity of activated alumina) → adsorbing fluorides in wastewater or soot to prepare fluorine-bearing alumina; (3) Different methods for alumina modification. This invention obtains fluorine-bearing alumina by fluorine-modifying alumina, while the present invention uses carboxylic acid to modify activated alumina to adsorb fluorides in industrial wastewater to prepare fluorine-bearing alumina. It can be seen that the ways to obtain fluorine-bearing alumina are different.

[0008] The current technology does not mention the effective recycling of aluminum industrial waste and the reduction of energy consumption in the aluminum industry. Therefore, it does not fundamentally solve the problems of environmental damage and waste of valuable metals caused by hazardous waste containing alumina salts in the aluminum electrolysis industry. Summary of the Invention

[0009] In view of the problems and deficiencies existing in the above-mentioned prior art, the present invention provides a preparation method and application of a low-temperature electrolyte of fluorine-bearing alumina for aluminum electrolysis. The present invention uses hazardous waste containing alumina salts in the aluminum electrolysis industry as raw materials, efficiently utilizes the valuable elements therein, and goes through microwave hydrothermal-alkali leaching → ultrasonic purification → acid leaching → microwave medium and low temperature assisted calcination (to prepare alumina with higher activity) → carboxylic acid modification of activated alumina (to enhance the specific surface area and surface activity of activated alumina) → adsorbing fluorides in wastewater or soot to prepare fluorine-bearing alumina. The present invention is realized through the following technical solutions.

[0010] A preparation method of a low-temperature electrolyte of fluorine-bearing alumina for aluminum electrolysis, the steps of which include,

[0011] S1: Grinding and screening hazardous waste containing alumina salts in the aluminum electrolysis industry to obtain a raw material of hazardous waste containing alumina;

[0012] S2: Using a rare earth metal catalyst to adsorb heavy metals in the raw material of hazardous waste containing alumina, and subjecting the raw material of hazardous waste containing alumina to microwave hydrothermal-alkali leaching to obtain a crude sodium aluminate solution;

[0013] S3: Add calcium oxide to the crude sodium aluminate solution and purify it by ultrasonic treatment to obtain the refined sodium aluminate solution;

[0014] S4: Acid-leach the refined sodium aluminate solution to obtain aluminum hydroxide colloid;

[0015] S5: Calcinate the aluminum hydroxide colloid by microwave-assisted medium and low temperature to obtain metallurgical grade alumina;

[0016] S6: Modify the metallurgical grade alumina with carboxylic acid to obtain modified activated alumina;

[0017] S7: Prepare fluoride-bearing alumina cryolite with the modified activated alumina.

[0018] In the above S1, the main component of the hazardous waste from the aluminum electrolysis industry containing aluminum oxide salt is aluminum oxide. After grinding and screening to 100 mesh, the hazardous waste raw material containing aluminum oxide is obtained.

[0019] The microwave hydrothermal-alkali leaching in the above S2 is as follows:

[0020] S2.1: Prepare an alkali solution with a concentration of 180 g / L - 250 g / L.

[0021] S2.2: Mix the hazardous waste raw material containing aluminum oxide ground and screened in S1 with the alkali solution prepared in S2.1 to obtain a mixed slurry with a solid-liquid ratio of 0.04 - 0.4:1 g / mL;

[0022] S2.3: Carry out alkali leaching on the mixed slurry prepared in S2.2 under microwave hydrothermal conditions, with a microwave power of 380 W - 600 W, a pressure of 100 Pa - 800 Pa, a heating rate of 8 - 12 °C / min, a temperature of 160 °C - 250 °C, and a heat preservation time of 2 - 6 h;

[0023] S2.4: Centrifuge the solution after microwave heating in S2.3 at 4500 r / min - 6500 r / min for 10 min, take the supernatant to obtain the crude sodium aluminate solution.

[0024] The calcium oxide-ultrasonic purification is as follows:

[0025] Add CaO to the crude sodium aluminate solution taken in S2.4 under ultrasonic conditions for water bath heating and purification treatment, with ultrasonic frequencies of 20 kHz - 20.4 kHz, a power of 200 W - 1000 W, a time of 1.5 - 2.5 h, a temperature of 80 °C, a magnetic stirring rate of 400 r / min, and a CaO addition amount of 5 g / L - 15 g / L, and then carry out suction filtration to obtain the refined sodium aluminate solution.

[0026] The above acid leaching is as follows: Add hydrochloric acid solution to the refined sodium aluminate solution in S3 until white flocculates are formed, and then carry out suction filtration to take the filter residue to obtain aluminum hydroxide colloid.

[0027] The microwave-assisted medium and low temperature calcination is as follows: The aluminum hydroxide colloid obtained in S4 is placed in a microwave field for microwave calcination with a power of 1200 W - 1500 W, a temperature of 700 °C - 800 °C, and held for 2 h to obtain metallurgical-grade alumina with relatively high activity.

[0028] The carboxylic acid modification in S6 is as follows:

[0029] S6.1. Prepare a carboxylic acid modifier. The carboxylic acid includes one or a mixture of malic acid, oxalic acid, and citric acid in any proportion, and the mass fraction of the carboxylic acid modifier is 5 wt.% - 10 wt.%.

[0030] S6.2. Place the metallurgical-grade activated alumina prepared in S5 in the carboxylic acid modifier solution, magnetically stir at 500 r / min at room temperature for 12 h, filter off the supernatant, and dry in a vacuum drying oven for 12 h to obtain modified activated alumina.

[0031] The preparation of the cryolite-containing alumina low-temperature electrolyte in S7 is as follows: The modified activated alumina obtained in S6 adsorbs fluorides in wastewater or soot to prepare the cryolite-containing alumina low-temperature electrolyte.

[0032] A preparation method of a cryolite-containing alumina low-temperature electrolyte for aluminum electrolysis prepares the cryolite-containing alumina low-temperature electrolyte, which can be applied in the process of preparing aluminum by the fused salt electrolysis method.

[0033] The working principle of the present invention is as follows: The hazardous waste containing alumina salts in the aluminum electrolysis industry mainly utilizes the large amount of alumina contained therein. Through microwave hydrothermal-alkali leaching, ultrasonic purification, and acid leaching, impurities such as silicon, vanadium, and iron in the raw materials can be effectively removed. Specifically, in the use of microwave hydrothermal-alkali leaching, alumina can fully react with the alkali solution to form sodium aluminate solution, silicon dioxide reacts with the alkali solution to form sodium silicate, and impurities such as iron and magnesium in the raw materials form precipitation substances such as iron hydroxide and magnesium hydroxide. A part of the silicon dioxide reacts with aluminum hydroxide to form sodium silicon slag; when under microwave hydrothermal conditions, there are the following beneficial effects. First, it can make the reaction proceed fully; second, during the alkali leaching process, some reactants will form oxides as the reaction occurs, and the oxides will cover the surface of the reactants, thus hindering the mass transfer process of oxygen, resulting in the incomplete reaction of the reactants wrapped inside. However, using microwave heating can effectively solve this technical problem, and sodium aluminate crude liquid can be obtained in this process. Adding calcium oxide during ultrasonic purification can effectively precipitate silicon and vanadium. In the ultrasonic environment, mechanical effects and cavitation effects will be generated, forming high temperature and high pressure locally. The generated strong jet is conducive to breaking particles and enhancing the surface area of the particles. Under the impact of the micro-jet, the boundary layer at the solid-liquid interface becomes weak or is broken, and the broken particles form a new boundary layer with the liquid, so that the reaction continues to occur. Sodium aluminate refined liquid is obtained in this process; recently, acid leaching is carried out. Adding acid to the sodium aluminate solution and adjusting the pH can obtain aluminum hydroxide colloid. Then, the aluminum hydroxide is subjected to microwave-assisted low-temperature calcination. Low-temperature calcination can make the aluminum hydroxide generate metallurgical-grade alumina with higher activity. Then, using carboxylic acid to modify the activated alumina can increase the specific surface area and surface roughness of the activated alumina, thereby obtaining more adsorption sites and increasing the number of surface hydroxyl groups, thus increasing the ion exchange sites for fluorine and effectively improving the fluorine-carrying performance of the activated alumina.

[0034] The beneficial effects of the present invention are as follows:

[0035] (1) By utilizing the beneficial reaction of microwave hydrothermal, the present invention can effectively solve the problem that the covering material hinders the mass transfer process of oxygen, enabling the alumina-containing salt to fully react with the alkali solution. Alumina reacts with the alkali solution to form sodium aluminate solution, and silicon dioxide reacts with the alkali solution to form a part of sodium silicon slag, which can remove a part of silicon. Impurities such as iron and magnesium react with the alkali solution to form corresponding precipitation substances.

[0036] (2) By adding calcium oxide during ultrasonic purification, the present invention effectively removes silicon and precipitates vanadium. Calcium oxide can fully react with sodium silicate solution to form calcium silicate precipitation under normal temperature and pressure. Placing this reaction under ultrasonic conditions in an environment of 80 °C can effectively precipitate silicon. Because it is difficult to completely precipitate during the reaction of calcium oxide and sodium silicate, the precipitate can effectively fall off in the ultrasonic environment.

[0037] (3) The present invention can effectively prepare metallurgical-grade alumina with relatively high activity through microwave hydrothermal alkali leaching, ultrasonic purification, acid leaching, and microwave-assisted medium and low-temperature calcination. This alumina has the characteristic of relatively high activity. And the fluorine-carrying performance of metallurgical-grade alumina is effectively improved through carboxylic acid modification. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is the XRD pattern of the microwave hydrothermal alkali leaching Figure 1 (a) and ultrasonic purification Figure 1 (b) in Example 1 of the present invention;

[0039] Figure 2 is the physical object of the flocculent aluminum hydroxide generated in Example 1 Figure 2 (a) and the XRD pattern Figure 2 (b);

[0040] Figure 3 is the XRD pattern of the metallurgical-grade alumina in Example 1 Figure 3 (a) and the physical object diagram of the fluorine-carrying alumina prepared in Example 1 Figure 3 (b);

[0041] Figure 4 is the infrared spectrum of the modified activated alumina in Example 1 and the fluoride in the adsorbed wastewater Figure 4 (a) and the fine spectrum of XPS-F 1S Figure 4 (b);

[0042] Figure 5 is the cooling curve pattern of the low-temperature electrolyte of the fluorine-carrying alumina for aluminum electrolysis obtained in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention. It should be noted that, without conflict, the embodiments and features in the embodiments of this application can be combined with each other arbitrarily.

[0044] Example 1

[0045] The preparation method of the low-temperature electrolyte of the fluorine-carrying alumina for aluminum electrolysis includes the following steps:

[0046] S1: Grinding and screening the aluminum electrolysis industrial hazardous waste containing alumina salts (secondary aluminum ash is mainly alumina, 40 wt.%) to 100 meshes to obtain a hazardous waste raw material containing alumina;

[0047] S2: Hydrothermally treat the alumina-containing hazardous waste raw material with microwave and then perform alkali leaching to obtain crude sodium aluminate solution;

[0048] Among them, the hydrothermal treatment with microwave and alkali leaching in S2 is as follows:

[0049] S2.1: Prepare an alkali solution with a concentration of 250 g / L.

[0050] S2.2: Mix the alumina-containing hazardous waste raw material ground and screened in S1 with the alkali solution prepared in S2.1 to obtain a mixed slurry, and the solid-liquid ratio is 0.08:1 g / mL;

[0051] S2.3: Perform alkali leaching on the mixed slurry prepared in S2.2 under hydrothermal conditions with microwave. The microwave power is 600 W, the pressure is 800 Pa, the heating rate is 12 °C / min, the temperature is 250 °C, and the heat preservation time is 6 h;

[0052] S2.4: Centrifuge the solution after microwave heating in S2.3 at 6500 r / min for 10 min, take the supernatant to obtain crude sodium aluminate solution;

[0053] S3: Add calcium oxide to the crude sodium aluminate solution for ultrasonic purification to obtain refined sodium aluminate solution; among them, add CaO to the crude sodium aluminate solution taken in S2.4 under ultrasonic conditions for water bath heating and purification treatment. The ultrasonic frequency is 20.2 KHZ, the power is 800 W, the time is 2.5 h, the temperature is 80 °C, the magnetic stirring rate is 400 r / min, the addition amount of CaO is 10 g / L, and then perform suction filtration to obtain refined sodium aluminate solution;

[0054] S4: Acid-leach the refined sodium aluminate solution to obtain aluminum hydroxide colloid; add a hydrochloric acid solution with a concentration of 150 g / L to the refined sodium aluminate solution until white flocculates are formed at pH = 5.5, and then perform suction filtration to obtain refined sodium aluminate solution;

[0055] S5: Calcinate the aluminum hydroxide colloid with microwave-assisted medium and low temperature to obtain metallurgical-grade alumina; among them, the microwave-assisted medium and low temperature calcination is as follows: Place the aluminum hydroxide colloid obtained in S4 in a microwave field for microwave calcination. The power is 1200 W, the temperature is 800 °C, and the heat preservation is 2 h to obtain metallurgical-grade alumina with higher activity;

[0056] S6: Modify the metallurgical-grade alumina with carboxylic acid. The carboxylic acid is malic acid, and the mass fraction of the carboxylic acid modifier is 5 wt.%. Perform modification at room temperature according to the solid-liquid ratio of 0.01:1 g / mL to obtain modified activated alumina;

[0057] S6.1: Prepare a carboxylic acid modifier. The carboxylic acid is malic acid, and the mass fraction of the carboxylic acid modifier is 5 wt.%.

[0058] S6.2. Place the metallurgical-grade activated alumina prepared in S5 into a carboxylic acid modifier solution, stir magnetically at 500 r / min at room temperature for 12 h, filter off the supernatant, and dry in a vacuum drying oven for 12 h to obtain modified activated alumina;

[0059] S7: Prepare a fluoride-bearing alumina cryolite electrolyte from the modified activated alumina. Use 2 g of the modified activated alumina obtained in S6 as an adsorbent to adsorb fluoride in wastewater (fluoride concentration is 200 mg / L) at room temperature for 2 h to prepare a fluoride-bearing alumina cryolite electrolyte.

[0060] The fluoride-bearing alumina cryolite electrolyte prepared by this preparation method of the fluoride-bearing alumina cryolite electrolyte for aluminum electrolysis can be applied in the process of preparing aluminum by the fused salt electrolysis method.

[0061] The fluoride-bearing alumina prepared in the present invention mainly forms garnet and sodium aluminosilicate after microwave hydrothermal-alkali leaching. Most of the alumina reacts with the alkali solution to form a sodium aluminate solution (as shown in Figure 1 a). After adding calcium oxide for purification, the effect of efficient silicon removal can be achieved, and a large amount of silicon-containing precipitate is formed (as shown in Figure 1 b). Adding hydrochloric acid to the sodium aluminate mother liquor gives flocculent aluminum hydroxide (as shown in Figure 2 a) and the XRD pattern of aluminum hydroxide (as shown in Figure 2 b). Aluminum hydroxide is calcined at low temperature with microwave assistance to obtain metallurgical-grade alumina (as shown in Figure 3 a) and the physical picture of fluoride-bearing alumina ( Figure 3 b). After the metallurgical-grade alumina is modified with carboxylic acid, the number of -OH on its surface increases. After adsorbing fluoride, it can be seen that fluoride mainly replaces -OH on the metallurgical-grade alumina, so the -OH peak weakens (as shown in Figure 4 ). Preparing the fluoride-bearing alumina into a cryolite electrolyte system can effectively reduce the primary crystallization temperature, and the primary crystallization temperature is 913 °C (as shown in Figure 5 ). Compared with the conventional primary crystallization temperature of 953 °C, the fluoride-bearing alumina cryolite electrolyte prepared in this example can effectively reduce the primary crystallization temperature and reduce the electrolysis temperature in the aluminum electrolysis process.

[0062] Comparative Example 1

[0063] In this Comparative Example 1, the treatment steps S1 to S5 and S7 are the same as those in Example 1, and the control parameters are the same. The difference from Example 1 is only that: the metallurgical-grade alumina in this Comparative Example 1 is modified with a conventional alkaline earth metal modifier. The primary crystallization temperature of the fluoride-bearing alumina cryolite electrolyte prepared in this Comparative Example 1 is 953 °C, and it cannot effectively reduce the primary crystallization temperature.

[0064] Example 2

[0065] The preparation method of the fluorine-bearing alumina low-temperature electrolyte for aluminum electrolysis includes the following steps:

[0066] S1: Grind and screen the hazardous waste from the aluminum electrolysis industry containing alumina salts (secondary aluminum ash is mainly alumina, 30 wt.%) to 100 meshes to obtain the hazardous waste raw material containing alumina.

[0067] S2: Subject the hazardous waste raw material containing alumina to microwave hydrothermal-alkali leaching to obtain crude sodium aluminate solution.

[0068] Among them, the microwave hydrothermal-alkali leaching in S2 is as follows:

[0069] S2.1: Prepare the alkali solution with a concentration of 180 g / L.

[0070] S2.2: Mix the hazardous waste raw material containing alumina ground and screened in S1 with the alkali solution prepared in S2.1 to obtain a mixed slurry, with a solid-liquid ratio of 0.4:1 g / mL.

[0071] S2.3: Subject the mixed slurry prepared in S2.2 to alkali leaching under microwave hydrothermal conditions, with a microwave power of 380 W, a pressure of 100 Pa, a heating rate of 8 °C / min, a temperature of 160 °C, and a holding time of 2 h.

[0072] S2.4: Centrifuge the solution after microwave heating in S2.3 at 6500 r / min for 10 min, take the supernatant to obtain the crude sodium aluminate solution.

[0073] S3: Add calcium oxide to the crude sodium aluminate solution for ultrasonic purification to obtain refined sodium aluminate solution; among them, add CaO to the crude sodium aluminate solution taken in S2.4 under ultrasonic conditions for water bath heating and purification treatment, with an ultrasonic frequency of 20.2 KHZ, a power of 200 W, a time of 1.5 h, a temperature of 80 °C, a magnetic stirring rate of 400 r / min, and an addition amount of CaO of 5 g / L, and then perform suction filtration to obtain the refined sodium aluminate solution.

[0074] S4: Acid-leach the refined sodium aluminate solution to obtain aluminum hydroxide colloid; add a hydrochloric acid solution with a concentration of 140 g / L to the refined sodium aluminate solution until white flocculates are formed at pH = 5.5, and then perform suction filtration to obtain the refined sodium aluminate solution.

[0075] S5: Subject the aluminum hydroxide colloid to microwave-assisted medium and low-temperature calcination to obtain metallurgical-grade alumina; among them, the microwave-assisted medium and low-temperature calcination is as follows: Place the aluminum hydroxide colloid obtained in S4 in a microwave field for microwave calcination, with a power of 1500 W, a temperature of 700 °C, and a holding time of 2 h to obtain metallurgical-grade alumina with higher activity.

[0076] S6: Modify metallurgical grade alumina with carboxylic acid. The carboxylic acid is citric acid, and the mass fraction of the carboxylic acid modifier is 10 wt.%. Carry out room-temperature modification according to a solid-liquid ratio of 0.01:1 g / mL to obtain modified activated alumina;

[0077] S6.1: Prepare the carboxylic acid modifier. The carboxylic acid is citric acid, and the mass fraction of the carboxylic acid modifier is 10 wt.%.

[0078] S6.2: Place the metallurgical grade activated alumina prepared in S5 into the carboxylic acid modifier solution, carry out magnetic stirring at 500 r / min for 12 h at room temperature, filter off the supernatant, and dry in a vacuum drying oven for 12 h to obtain modified activated alumina;

[0079] S7: Prepare fluoride-bearing alumina cryolite electrolyte from the modified activated alumina. Use the modified activated alumina obtained in S6 to adsorb fluoride in wastewater (the fluoride concentration is 200 g / mL), with an adsorbent dosage of 2.5 g, and carry out room-temperature adsorption for 2 h to prepare fluoride-bearing alumina cryolite electrolyte.

[0080] The fluoride-bearing alumina cryolite electrolyte prepared by the preparation method of the fluoride-bearing alumina cryolite electrolyte for aluminum electrolysis can be applied in the process of preparing aluminum by the molten salt electrolysis method.

[0081] Example 3

[0082] The preparation method of the fluoride-bearing alumina cryolite electrolyte for aluminum electrolysis includes the following steps:

[0083] S1: Grind and screen aluminum electrolysis industrial hazardous waste containing alumina salts (secondary aluminum ash is mainly alumina, 50 wt%) to 100 mesh to obtain alumina-containing hazardous waste raw materials;

[0084] S2: Subject the alumina-containing hazardous waste raw materials to microwave hydrothermal-alkali leaching to obtain crude sodium aluminate solution;

[0085] Among them, the microwave hydrothermal alkali leaching in S2 is as follows:

[0086] S2.1: Prepare the alkali solution with a concentration of 200 g / L.

[0087] S2.2: Mix the alumina-containing hazardous waste raw materials ground and screened in S1 with the alkali solution prepared in S2.1 to obtain a mixed slurry with a solid-liquid ratio of 0.06:1 g / mL;

[0088] S2.3: Subject the mixed slurry prepared in S2.2 to alkali leaching under microwave hydrothermal conditions, with a microwave power of 500 W, a pressure of 200 Pa, a heating rate of 12 °C / min, a temperature of 200 °C, and a holding time of 4 h;

[0089] S2.4. Centrifuge the solution after microwave heating in S2.3 at 5500 r / min for 10 min, take the supernatant to obtain crude sodium aluminate solution;

[0090] S3: Add calcium oxide to the crude sodium aluminate solution for ultrasonic purification to obtain refined sodium aluminate solution; specifically, add the crude sodium aluminate solution taken in S2.4 to CaO under ultrasonic conditions for water bath heating and purification treatment, with ultrasonic frequency of 20.4 KHZ, power of 600 W, time of 2 h, temperature of 80 °C, magnetic stirring rate of 400 r / min, and the addition amount of CaO being 7 g / L, and then perform suction filtration to obtain refined sodium aluminate solution;

[0091] S4: Acid-leach the refined sodium aluminate solution to obtain aluminum hydroxide colloid; add hydrochloric acid solution with a concentration of 120 g / L to the refined sodium aluminate solution until white flocculants are formed at pH = 5.5, and then perform suction filtration to obtain refined sodium aluminate solution;

[0092] S5: Microwave-assisted medium and low-temperature calcine the aluminum hydroxide colloid to obtain metallurgical-grade alumina; specifically, microwave-assisted medium and low-temperature calcination means placing the aluminum hydroxide colloid obtained in S4 in a microwave field for microwave calcination, with a power of 1200 W, a temperature of 800 °C, and holding for 2 h to obtain metallurgical-grade alumina with higher activity;

[0093] S6: Modify the metallurgical-grade alumina with carboxylic acid, the carboxylic acid is malic acid, and the mass fraction of the carboxylic acid modifier is 7 wt.%, and perform room-temperature modification according to the solid-liquid ratio of 0.01:1 g / mL to obtain modified activated alumina;

[0094] S6.1. Prepare the carboxylic acid modifier, the carboxylic acid is malic acid, and the mass fraction of the carboxylic acid modifier is 7 wt.%.

[0095] S6.2. Place the metallurgical-grade activated alumina prepared in S5 in the carboxylic acid modifier solution, perform magnetic stirring at 500 r / min at room temperature for 12 h, filter off the supernatant, and dry in a vacuum drying oven for 12 h to obtain modified activated alumina;

[0096] S7: Prepare low-temperature electrolyte of fluorine-loaded alumina from the modified activated alumina, adsorb fluoride in wastewater (fluoride concentration is 200 g / mL) with the modified activated alumina obtained in S6, the adsorbent dosage is 2.5 g, and perform room-temperature adsorption for 2 h to prepare low-temperature electrolyte of fluorine-loaded alumina.

[0097] The low-temperature electrolyte of fluorine-loaded alumina for aluminum electrolysis prepared by this preparation method of low-temperature electrolyte of fluorine-loaded alumina can be applied in the process of preparing aluminum by molten salt electrolysis method.

[0098] The specific embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the scope of knowledge possessed by those of ordinary skill in the art.

Claims

1. A method for preparing a fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis, characterized in that The steps include, S1: Grinding and screening the hazardous waste from aluminum electrolysis industry containing aluminum oxide salt to obtain hazardous waste raw materials containing aluminum oxide; S2: Microwave hydrothermal-alkali leaching of hazardous waste materials containing aluminum oxide to obtain a crude sodium aluminate solution; S3: adding calcium oxide to the sodium aluminate crude liquid and purifying it by ultrasonication to obtain sodium aluminate fine liquid; S4: acid leaching the sodium aluminate semen to obtain aluminum hydroxide colloid; S5: calcining aluminum hydroxide colloid with microwave assistance at medium and low temperature to obtain metallurgical grade alumina; S6: modifying the metallurgical grade alumina with carboxylic acid to obtain modified activated alumina; S7: preparing fluorine-loaded alumina low-temperature electrolyte by modifying activated alumina; The microwave hydrothermal-alkali leaching in S2 is: S2.1, prepare alkali solution, the concentration of which is 180g / L-250g / L; S2.2, mixing the aluminum oxide-containing hazardous waste raw material ground and screened in S1 with the alkali solution prepared in S2.1 to obtain a mixed slurry with a solid-liquid ratio of 0.04-0.4:1 g / mL; S2.3, alkali leaching the mixed slurry prepared in S2.2 under microwave hydrothermal conditions, with a microwave power of 380W-600W, a pressure of 100Pa-800Pa, a heating rate of 8-12°C / min, a temperature of 160°C-250°C, and a holding time of 2-6h; S2.4, centrifuge the solution heated by microwave in S2.3 at 4500-6500 r / min for 10 min, take the supernatant to obtain crude sodium aluminate solution; Calcium oxide-ultrasonic purification is: The sodium aluminate crude liquid obtained in S2.4 is subjected to water bath heating purification treatment by adding CaO under ultrasonic conditions, with the ultrasonic temperature of 20KHZ-20.4KHZ, the power of 200W-1000W, the time of 1.5-2.5h, the temperature of 80°C, the magnetic stirring rate of 400r / min, and the amount of CaO added of 5g / L-15g / L, followed by suction filtration to obtain sodium aluminate semen; The aluminum hydroxide colloid obtained in S4 is placed in a microwave field for microwave calcination at a power of 1200W-1500W and a temperature of 700°C-800°C for 2 hours to obtain metallurgical grade alumina with high activity; The carboxylic acid in S6 is modified as follows: S6.

1. Prepare a carboxylic acid modifier, wherein the carboxylic acid comprises one or a mixture of malic acid and oxalic acid in any proportion, and the mass fraction of the carboxylic acid modifier is 5wt.%-10wt.%; S6.

2. Place the metallurgical grade activated alumina prepared in S5 in a carboxylic acid modifier solution and stir magnetically at 500 r / min for 12 h at room temperature. Filter out the supernatant and dry in a vacuum drying oven for 12 h to obtain the modified activated alumina.

2. The method for preparing the fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis according to claim 1, characterized in that: The aluminum oxide salt in S1 is mainly aluminum oxide, and the aluminum electrolysis industrial hazardous waste is ground and sieved to 100-300 mesh to obtain the aluminum oxide-containing hazardous waste raw material.

3. The method for preparing the fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis according to claim 1, characterized in that: The acid leaching is as follows: adding hydrochloric acid solution into the S3 sodium aluminate semen until white floccules are generated, and then filtering and taking the filter residue to obtain aluminum hydroxide colloid.

4. The method for preparing a fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis according to claim 1, characterized in that: The preparation of the fluorine-loaded alumina low-temperature electrolyte in S7 is as follows: the modified activated alumina obtained in S6 is used to adsorb fluoride in wastewater or smoke to prepare the fluorine-loaded alumina low-temperature electrolyte.

5. A method for preparing a fluorine-loaded alumina low-temperature electrolyte for aluminum electrolysis according to any one of claims 1 to 4, wherein the fluorine-loaded alumina low-temperature electrolyte is prepared and can be used in the process of preparing aluminum by molten salt electrolysis.

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