Preparation method and application of fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis

Abstract

The invention discloses a preparation method and application of a fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis, and belongs to the field of aluminum electrolysis. The method comprises the following steps: grinding and screening alumina salt-containing aluminum electrolysis industrial hazardous waste to obtain an alumina-containing hazardous waste raw material; then carrying out microwave hydrothermal-alkaline leaching treatment on the hazardous waste raw material containing alumina to obtain a sodium aluminate crude solution; adding calcium oxide into the sodium aluminate crude liquid, and performing ultrasonic purification to obtain sodium aluminate fine liquid; further performing acid leaching on the sodium aluminate fine liquid to obtain aluminum hydroxide colloid; carrying out microwave-assisted calcination on the aluminum hydroxide colloid to obtain metallurgical-grade aluminum oxide; modifying metallurgical-grade aluminum oxide with carboxylic acid to obtain modified aluminum oxide; finally, fluorine in industrial wastewater is adsorbed by the modified aluminum oxide, and fluorine-loaded aluminum oxide is prepared. The rare earth metal and the aluminum oxide are good adsorbents. The fluorine-loaded aluminum oxide is used as a solute of the low-temperature electrolyte, so that the low-temperature electrolyte for aluminum electrolysis, which is low in electrolysis temperature and high in aluminum oxide solubility, can be obtained. According to the method, the harm of fluorine in the aluminum electrolysis industrial aluminum oxide-containing hazardous waste and industrial wastewater to the environment is solved, and the hazardous source is recycled.

Description

Technical Field

[0001] The invention discloses a preparation method of a fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis and application thereof, belonging to the field of aluminum electrolysis. Background Art

[0002] The aluminum electrolysis industry is developing rapidly. my country's electrolytic aluminum production capacity ranks first in the world. China is the world's largest aluminum consumer, accounting for about 1 / 3 of the world's total consumption. In 2022, my country's demand for primary aluminum will reach 41.66 million tons, while the primary aluminum output will be 40.214 million tons. Based on this, it is estimated that the annual electrolytic aluminum output will be about 41.2 million tons. Such a high output will inevitably be accompanied by a large amount of hazardous waste containing aluminum oxide salts from the aluminum electrolysis industry. Since hazardous waste containing aluminum oxide salts from the aluminum electrolysis industry is difficult to be effectively treated, currently 95% of hazardous waste containing aluminum oxide salts can only be landfilled or stored, and the historical stockpile volume has exceeded 10 million tons. If the waste is simply landfilled, it will cause: first, land salinization and water resource pollution will eventually endanger human health; second, it will cause the waste of valuable metals (alumina) in hazardous waste containing aluminum oxide salts.

[0003] At the same time, electrolytic aluminum is a high-energy consumption industry. With the expansion of the scale of the electrolytic aluminum industry, the total power consumption is also increasing year by year, and reducing energy consumption is also an urgent problem. In the aluminum electrolysis industry, Na3AlF6-AlF3-Al2O3 melt is used as the electrolyte, carbon materials are used as the two poles, and electrolysis is carried out under 950℃-970℃ direct current, resulting in high energy consumption. For this reason, low-temperature aluminum electrolysis has become a hot topic in research. 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 hazardous waste containing alumina salts in the aluminum electrolysis industry; and the treatment of waste containing fluorine-containing wastewater and fluorine-containing smoke; second, it lowers the primary crystallization temperature in the low-temperature electrolyte system and lowers the electrolysis temperature of the aluminum electrolysis process.

[0005] CN211936015U discloses a dust removal system for a fluorine-carrying alumina bin in an electrolytic flue gas purification system. The prior art provides a dust removal system, in which a valve is connected to the top of the fluorine-carrying alumina bin through a bin top outlet pipe, and the other end is connected to an exhaust pipe, and a purification system high-efficiency filter is used as the subject equipment of the fluorine-carrying alumina bin dust removal system. The technical problem to be solved by the prior art is to improve the wear resistance of the flue and ultimately improve the service life of the dust removal system. Therefore, the prior art only discloses a device for generating fluorine-carrying alumina by reacting fresh alumina in a flue gas system, and does not disclose any method for preparing fluorine-carrying alumina from alumina, let alone a method for preparing fluorine-carrying alumina using hazardous waste from aluminum electrolysis industry containing alumina salt as raw materials.

[0006] CN112520811A discloses a manganese-loaded activated alumina defluorination adsorbent and a preparation method thereof. Ordinary activated alumina particles are used as carriers and activated by using a nano-aluminum solution. Hydrogen peroxide and ammonia water are added to a manganese sulfate solution, and activated activated alumina particles are placed therein. The mixture is stirred, washed and dried to obtain manganese-loaded activated alumina particles. The biggest differences between the prior art and the present invention are as follows: (1) The raw material carriers are different. The prior art uses ordinary activated alumina particles as the raw material carrier, while the present invention uses aluminum electrolysis industrial hazardous waste containing aluminum oxide salt as the raw material carrier. Therefore, the prior art cannot solve the technical problem of the present invention of converting hazardous waste into fluorine-loaded alumina; (2) The methods for activating alumina are different. The prior art uses nano-aluminum solution to activate ordinary activated alumina particles; while the present invention uses aluminum electrolysis industrial hazardous waste containing aluminum oxide salt to obtain aluminum hydroxide colloid after treatment, and then obtains active metallurgical grade alumina by microwave-assisted medium and low temperature calcination of aluminum hydroxide colloid; (3) The methods for modifying alumina are different. The prior art adds hydrogen peroxide and ammonia water to a manganese sulfate solution, and puts in activated activated alumina particles to obtain manganese-loaded alumina. Activated alumina particles, that is, modified by loading manganese on the activated alumina particles, 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 metallurgical grade alumina to obtain activated alumina with a large number of hydroxyl groups on the surface, the modification principle is to increase the hydroxyl groups (-OH) on the surface of the alumina; (4) The adsorption mode of fluorine is different. The manganese-loaded activated alumina particles of the present invention adsorb fluorine by having more adsorption sites; while the present invention uses carboxylic acid to modify the activated alumina so that the hydroxyl groups on the surface of the alumina increase (-OH) and thus increase the adsorption sites of fluoride ions. The principle of fluorine adsorption is mainly to adsorb fluoride on the surface of the activated alumina through chemical adsorption and electrostatic attraction, wherein the chemical adsorption is ion exchange and formation of complexes, through F - Substituting -OH enables ion exchange; therefore, this invention is clearly different from the present invention.

[0007] CN115849419A discloses a method for producing fluorine-loaded alumina and the application of the produced fluorine-loaded alumina. The method comprises grinding bauxite, iron ore and anthracite together, making balls with fluorosilicic acid, and smelting at high temperature to separate ferrosilicon to obtain fluorine-modified alumina; mixing the fluorine-modified alumina with ordinary alumina to prepare an alumina mixture, and putting the mixture into an electrolytic cell to dissolve cryolite melt for electrolysis. The differences between the prior invention and the present invention are as follows: (1) The raw materials are different. The raw materials of the prior invention are bauxite, iron ore, anthracite and fluorosilicic acid, while the raw materials of the present invention are hazardous waste from aluminum electrolysis containing alumina salts; (2) The treatment methods are different. The treatment methods are different depending on the raw materials. The prior invention adopts a high-temperature smelting method for ball making to obtain fluorine-modified alumina; while the present invention uses microwave hydrothermal-alkali leaching → ultrasonic purification → acid leaching → microwave medium and low temperature assisted calcination (to prepare alumina with higher activity) → carboxylic acid modified activated alumina (to enhance the specific surface area and surface activity of activated alumina) → adsorption of fluoride in wastewater or smoke to prepare fluoride-loaded alumina; (3) The alumina modification methods are different. The prior invention obtains fluorine-loaded alumina by fluorine-modified alumina, while the present invention uses carboxylic acid modified activated alumina to adsorb fluoride in industrial wastewater to prepare fluorine-loaded alumina. It can be seen that the methods of obtaining fluorine-loaded alumina are different.

[0008] Current technology does not mention the effective treatment and recycling of aluminum industry waste and the reduction of energy consumption in the aluminum industry. Therefore, it does not fundamentally solve the problem 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 shortcomings of the above-mentioned prior art, the present invention provides a method for preparing a fluorine-loaded alumina low-temperature electrolyte for aluminum electrolysis and its application. The present invention uses hazardous waste containing alumina salts in the aluminum electrolysis industry as raw materials, and efficiently utilizes the valuable elements therein, through microwave hydrothermal-alkali leaching → ultrasonic purification → acid leaching → microwave medium and low temperature assisted calcination (preparation of alumina with higher activity) → carboxylic acid modified activated alumina (enhancing the specific surface area and surface activity of activated alumina) → adsorption of fluoride in wastewater or smoke to prepare fluorine-loaded alumina. The present invention is achieved through the following technical solutions.

[0010] A method for preparing a fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis, the steps comprising:

[0011] S1: Grinding and screening the hazardous waste from aluminum electrolysis industry containing aluminum oxide salt to obtain hazardous waste raw materials containing aluminum oxide;

[0012] S2: using rare earth metal catalysts to adsorb heavy metals in hazardous waste materials containing aluminum oxide, subjecting the hazardous waste materials containing aluminum oxide to microwave hydrothermal-alkali leaching to obtain a crude sodium aluminate solution;

[0013] S3: adding calcium oxide to the sodium aluminate crude liquid and purifying it by ultrasonication to obtain sodium aluminate fine liquid;

[0014] S4: acid leaching the sodium aluminate semen to obtain aluminum hydroxide colloid;

[0015] S5: calcining aluminum hydroxide colloid with microwave assistance at medium and low temperature to obtain metallurgical grade alumina;

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

[0017] S7: Prepare fluorine-loaded alumina low-temperature electrolyte by modifying activated alumina.

[0018] The aluminum oxide salt in S1 is mainly aluminum oxide, and the aluminum electrolysis industrial hazardous waste is ground and sieved to 100 mesh to obtain the aluminum oxide-containing hazardous waste raw material.

[0019] The microwave hydrothermal-alkali leaching in S2 is:

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

[0021] 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;

[0022] 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;

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

[0024] Calcium oxide-ultrasonic purification is:

[0025] The crude sodium aluminate liquid obtained from S2.4 is treated with water bath heating and purification by adding CaO under ultrasonic conditions, with the ultrasonic frequency 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, the amount of CaO added of 5g / L-15g / L, and then filtered to obtain sodium aluminate semen.

[0026] 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.

[0027] The microwave-assisted medium-low temperature calcination is as follows: the aluminum hydroxide colloid obtained by 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.

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

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

[0030] 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.

[0031] 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.

[0032] A method for preparing a fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis is disclosed, wherein the fluorine-loaded aluminum oxide low-temperature electrolyte is prepared and can be applied in the process of preparing aluminum by molten salt electrolysis.

[0033] The working principle of the present invention is: using the hazardous waste containing alumina salts in the aluminum electrolysis industry, mainly using the large amount of alumina contained in it, through microwave hydrothermal-alkali leaching, ultrasonic purification, acid leaching can effectively remove impurities such as silicon, vanadium, and iron in the raw materials. Specifically, when using microwave hydrothermal-alkali leaching, alumina can be fully reacted with alkali solution to generate sodium aluminate solution, silicon dioxide can react with alkali solution to generate sodium silicate, and impurities such as iron and magnesium in the raw materials can generate precipitation substances such as iron hydroxide and magnesium hydroxide, and a part of silicon dioxide can react with aluminum hydroxide to generate sodium silicon slag; when using microwave hydrothermal conditions, there are the following beneficial effects: first, the reaction can be fully carried out; second, during the alkali leaching process, some reactants will generate oxides as the reaction occurs, and the oxides will cover the surface of the reactants, thereby hindering the mass transfer process of oxygen, resulting in the reactants wrapped inside failing to react completely. However, the use of microwave heating can effectively solve this technical problem, and this process can obtain a crude sodium aluminate solution. Adding calcium oxide during ultrasonic purification can effectively precipitate silicon and vanadium. Purification in an ultrasonic environment will produce mechanical effects and cavitation effects, forming high temperature and high pressure locally. The strong jet generated is conducive to breaking particles and enhancing the surface area of ​​particles. Under the impact of micro-jet, the boundary layer of the solid-liquid interface is weakened or destroyed. The broken particles and liquid form a new boundary layer so that the reaction continues. This process obtains sodium aluminate semen; recently, acid leaching is carried out. Acid is added to the sodium aluminate solution and the pH is adjusted to obtain aluminum hydroxide colloid. Aluminum hydroxide is then subjected to microwave-assisted low-temperature calcination. Low-temperature calcination can make aluminum hydroxide generate metallurgical grade alumina with high activity. Then, the activated alumina is modified with carboxylic acid to increase the specific surface area and surface roughness of the activated alumina, thereby obtaining more adsorption sites and increasing the number of hydroxyl groups on the surface, thereby increasing the ion exchange sites of fluorine and effectively improving the fluorine carrying performance of the activated alumina.

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

[0035] (1) The present invention can effectively solve the problem of the covering material hindering the mass transfer of oxygen by utilizing microwave hydrothermal reaction to fully proceed. The alumina-containing salt is fully reacted with the alkali solution, the alumina reacts with the alkali solution to generate a sodium aluminate solution, the silicon dioxide reacts with the alkali solution to generate a part of sodium silicon slag, and a part of silicon is removed, and the impurities such as iron and magnesium react with the alkali solution to generate corresponding precipitation substances.

[0036] (2) The present invention effectively removes silicon and precipitates vanadium by adding calcium oxide through ultrasonic purification. Calcium oxide can fully react with sodium silicate solution at room temperature and pressure to generate calcium silicate precipitate. The reaction is placed under ultrasonic conditions and in an environment of 80°C to effectively precipitate silicon. Since it is difficult to completely precipitate calcium oxide during the reaction of calcium oxide and sodium silicate, the precipitate can be effectively removed in an ultrasonic environment.

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

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

[0039] Figure 2 The aluminum hydroxide substance ( Figure 2 a) and XRD patterns ( Figure 2 b);

[0040] Figure 3 is the XRD pattern of metallurgical grade alumina in Example 1 ( Figure 3 a) and the actual picture of fluorine-loaded aluminum oxide prepared in Example 1 ( Figure 3 b);

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

[0042] Figure 5 This is the step cooling curve of the fluorine-loaded alumina low-temperature electrolyte for aluminum electrolysis obtained in Example 1. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. It should be noted that the embodiments in this application and the features in the embodiments can be combined with each other arbitrarily without conflict.

[0044] Example 1

[0045] The method for preparing the fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis comprises the following steps:

[0046] S1: grinding and sieving 100 mesh aluminum electrolysis industrial hazardous waste containing aluminum oxide salt (secondary aluminum ash is mainly aluminum oxide, 40wt.%) to obtain alumina-containing hazardous waste raw materials;

[0047] S2: Microwave hydrothermal-alkali leaching of hazardous waste materials containing aluminum oxide to obtain a crude sodium aluminate solution;

[0048] The microwave hydrothermal-alkali leaching in S2 is:

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

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

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

[0052] S2.4, centrifuge the solution heated by microwave in S2.3 at 6500 r / min for 10 min, take the supernatant to obtain crude sodium aluminate solution;

[0053] S3: adding calcium oxide to the sodium aluminate crude liquid for ultrasonic purification to obtain sodium aluminate semen; wherein the sodium aluminate crude liquid obtained in S2.4 is subjected to water bath heating purification treatment by adding CaO under ultrasonic conditions, with an ultrasonic temperature of 20.2KHZ, a power of 800W, a time of 2.5h, a temperature of 80°C, a magnetic stirring rate of 400r / min, and an amount of CaO added of 10g / L, followed by suction filtration to obtain sodium aluminate semen;

[0054] S4: acid leaching the sodium aluminate semen to obtain aluminum hydroxide colloid; adding a hydrochloric acid solution with a concentration of 150 g / L to the sodium aluminate semen until the pH is 5.5 and white floccules are generated, and then filtering to obtain the sodium aluminate semen;

[0055] S5: calcining the aluminum hydroxide colloid with microwave assistance at medium and low temperature to obtain metallurgical grade aluminum oxide; wherein the microwave assisted medium and low temperature calcination comprises placing the aluminum hydroxide colloid obtained in S4 in a microwave field for microwave calcination at a power of 1200 W and a temperature of 800° C. for 2 hours to obtain metallurgical grade aluminum oxide with high activity;

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

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

[0058] S6.2, placing the metallurgical grade activated alumina prepared in S5 in a carboxylic acid modifier solution, stirring magnetically at 500 r / min for 12 h at room temperature, filtering out the supernatant, and drying in a vacuum drying oven for 12 h to obtain the modified activated alumina;

[0059] S7: The modified activated alumina is used to prepare a fluorine-loaded alumina low-temperature electrolyte. The modified activated alumina obtained in S6 is used to adsorb fluoride in the wastewater (fluoride concentration is 200 mg / L). The amount of adsorbent is 2 g. The adsorption is carried out at room temperature for 2 hours to prepare a fluorine-loaded alumina low-temperature electrolyte.

[0060] The method for preparing a fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis prepares a fluorine-loaded aluminum oxide low-temperature electrolyte, which can be used in the process of preparing aluminum by molten salt electrolysis.

[0061] The fluorine-loaded alumina prepared by the present invention mainly generates garnet and sodium aluminum silicate after microwave hydrothermal-alkali leaching, and most of the alumina reacts with the alkali solution to generate sodium aluminate solution (such as Figure 1 As shown in a), after adding calcium oxide for purification, the silicon removal effect can be achieved efficiently, and a large amount of silicon-containing precipitate (such as Figure 1 b). Adding hydrochloric acid to sodium aluminate semen yields aluminum hydroxide flocculent (such as Figure 2 a) and the XRD pattern of aluminum hydroxide (such as Figure 2 b), aluminum hydroxide is calcined at low temperature with microwave assistance to obtain metallurgical grade alumina (such as Figure 3 a) and the actual picture of fluorine-loaded aluminum oxide ( Figure 3 b). After metallurgical grade alumina is modified with carboxylic acid, the number of -OH on its surface increases. After adsorbing fluoride, it can be seen that fluorine mainly replaces the -OH on the metallurgical grade alumina, so the -OH peak is weakened (such as Figure 4 ). Preparing fluorine-loaded aluminum oxide into a low-temperature electrolyte system can effectively reduce the initial crystallization temperature, which is 913°C (such as Figure 5 ), compared with the conventional crystallization temperature of 953°C, the fluorine-loaded aluminum oxide low-temperature electrolyte prepared in this embodiment can effectively reduce the crystallization temperature and lower the electrolysis temperature of the aluminum electrolysis process.

[0062] Comparative Example 1

[0063] In the processing steps S1 to S5 and S7 of this comparative example 1, the same processing steps and control parameters as those of Example 1 are used, and the only difference from Example 1 is 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 fluorine-loaded alumina low-temperature electrolyte prepared in this comparative example 1 is 953° C., which cannot effectively reduce the primary crystallization temperature.

[0064] Example 2

[0065] The method for preparing the fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis comprises the following steps:

[0066] S1: grinding and sieving 100 mesh aluminum electrolysis industrial hazardous waste containing aluminum oxide salt (secondary aluminum ash is mainly aluminum oxide, 30wt.%) to obtain alumina-containing hazardous waste raw materials;

[0067] S2: Microwave hydrothermal-alkali leaching of hazardous waste materials containing aluminum oxide to obtain a crude sodium aluminate solution;

[0068] The microwave hydrothermal-alkali leaching in S2 is:

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

[0070] S2.2, mixing the aluminum oxide-containing hazardous waste raw material ground and sieved 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, alkali leaching the mixed slurry prepared in S2.2 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 heated by microwave in S2.3 at 6500 r / min for 10 min, take the supernatant to obtain crude sodium aluminate solution;

[0073] S3: adding calcium oxide to the sodium aluminate crude liquid for ultrasonic purification to obtain sodium aluminate semen; wherein the sodium aluminate crude liquid obtained in S2.4 is subjected to water bath heating purification treatment by adding CaO under ultrasonic conditions, with an ultrasonic temperature of 20.2KHZ, a power of 200W, a time of 1.5h, a temperature of 80°C, a magnetic stirring rate of 400r / min, and an amount of CaO added of 5g / L, followed by suction filtration to obtain sodium aluminate semen;

[0074] S4: acid leaching the sodium aluminate semen to obtain aluminum hydroxide colloid; adding a hydrochloric acid solution with a concentration of 140 g / L to the sodium aluminate semen until the pH is 5.5 and white floccules are generated, and then filtering to obtain the sodium aluminate semen;

[0075] S5: calcining the aluminum hydroxide colloid with microwave assistance at medium and low temperature to obtain metallurgical grade aluminum oxide; wherein the microwave assisted medium and low temperature calcination comprises placing the aluminum hydroxide colloid obtained in S4 in a microwave field for microwave calcination at a power of 1500 W and a temperature of 700° C. for 2 hours to obtain metallurgical grade aluminum oxide with high activity;

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

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

[0078] S6.2, placing the metallurgical grade activated alumina prepared in S5 in a carboxylic acid modifier solution, stirring magnetically at 500 r / min for 12 h at room temperature, filtering out the supernatant, and drying in a vacuum drying oven for 12 h to obtain the modified activated alumina;

[0079] S7: The modified activated alumina is used to prepare a fluorine-loaded alumina low-temperature electrolyte. The modified activated alumina obtained in S6 is used to adsorb fluoride in the wastewater (fluoride concentration is 200 g / mL). The amount of adsorbent is 2.5 g. The adsorption is carried out at room temperature for 2 hours to prepare a fluorine-loaded alumina low-temperature electrolyte.

[0080] The method for preparing a fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis prepares a fluorine-loaded aluminum oxide low-temperature electrolyte, which can be used in the process of preparing aluminum by molten salt electrolysis.

[0081] Example 3

[0082] The method for preparing the fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis comprises the following steps:

[0083] S1: grinding and sieving 100 meshes of hazardous waste from aluminum electrolysis industry containing aluminum oxide salt (secondary aluminum ash is mainly aluminum oxide, 50wt%) to obtain hazardous waste raw materials containing aluminum oxide;

[0084] S2: Microwave hydrothermal-alkali leaching of hazardous waste materials containing aluminum oxide to obtain a crude sodium aluminate solution;

[0085] The microwave hydrothermal alkaline leaching in S2 is:

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

[0087] S2.2, mixing the aluminum oxide-containing hazardous waste raw material ground and sieved 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, alkali leaching the mixed slurry prepared in S2.2 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 heated by microwave in S2.3 at 5500 r / min for 10 min, take the supernatant to obtain crude sodium aluminate solution;

[0090] S3: adding calcium oxide to the sodium aluminate crude liquid for ultrasonic purification to obtain sodium aluminate semen; wherein the sodium aluminate crude liquid obtained in S2.4 is subjected to water bath heating purification treatment by adding CaO under ultrasonic conditions, with an ultrasonic temperature of 20.4KHZ, a power of 600W, a time of 2h, a temperature of 80°C, a magnetic stirring rate of 400r / min, and an amount of CaO added of 7g / L, followed by suction filtration to obtain sodium aluminate semen;

[0091] S4: acid leaching the sodium aluminate semen to obtain aluminum hydroxide colloid; adding a hydrochloric acid solution with a concentration of 120 g / L to the sodium aluminate semen until the pH is 5.5 and white floccules are generated, and then filtering to obtain the sodium aluminate semen;

[0092] S5: calcining the aluminum hydroxide colloid with microwave assistance at medium and low temperature to obtain metallurgical grade aluminum oxide; wherein the microwave assisted medium and low temperature calcination comprises placing the aluminum hydroxide colloid obtained in S4 in a microwave field for microwave calcination at a power of 1200 W and a temperature of 800° C. for 2 hours to obtain metallurgical grade aluminum oxide with high activity;

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

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

[0095] S6.2, placing the metallurgical grade activated alumina prepared in S5 in a carboxylic acid modifier solution, stirring magnetically at 500 r / min for 12 h at room temperature, filtering out the supernatant, and drying in a vacuum drying oven for 12 h to obtain the modified activated alumina;

[0096] S7: The modified activated alumina is used to prepare a fluorine-loaded alumina low-temperature electrolyte. The modified activated alumina obtained in S6 is used to adsorb fluoride in the wastewater (fluoride concentration is 200 g / mL). The amount of adsorbent is 2.5 g. The adsorption is carried out at room temperature for 2 hours to prepare a fluorine-loaded alumina low-temperature electrolyte.

[0097] The method for preparing a fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis prepares a fluorine-loaded aluminum oxide low-temperature electrolyte, which can be used in the process of preparing aluminum by molten salt electrolysis.

[0098] The specific implementation modes of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

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: Prepare fluorine-loaded alumina low-temperature electrolyte by modifying 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 microwave hydrothermal-alkali leaching in S2 is: S2.

1. Prepare alkali solution with a concentration of 180 g / L-250 g / 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 r / min-6500 r / min for 10 min, take the supernatant and obtain crude sodium aluminate solution.

4. The method for preparing the fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis according to claim 3, characterized in that: Calcium oxide-ultrasonic purification is: The crude sodium aluminate liquid obtained from S2.4 is treated with water bath heating and purification by adding CaO under ultrasonic conditions, with the ultrasonic frequency 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, the amount of CaO added of 5g / L-15g / L, and then filtered to obtain sodium aluminate semen.

5. The method for preparing the fluorine-loaded alumina low-temperature electrolyte for aluminum electrolysis according to claim 4, 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.

6. The method for preparing the fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis according to claim 5, characterized in that: The microwave-assisted medium-low temperature calcination is as follows: the aluminum hydroxide colloid obtained by 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.

7. The method for preparing the fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis according to claim 6, characterized in that: 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 any proportion of malic acid, oxalic acid, and citric acid, 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.

8. The method for preparing the fluorine-loaded aluminum oxide low-temperature electrolyte for aluminum electrolysis according to claim 7, 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.

9. A method for preparing a fluorine-loaded alumina low-temperature electrolyte for aluminum electrolysis according to any one of claims 1 to 8, 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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