A method for preparing large-particle-size aluminum fluoride products from aluminum electrolyte leaching solution

Abstract

The present invention provides a method for preparing large-sized aluminum fluoride products from aluminum electrolyte leaching solution, belonging to the technical field of aluminum electrolyte resource recovery. S1: Take the aluminum electrolyte leaching solution, and the molar ratio of F element to Al element in the aluminum electrolyte leaching solution is 1-2.5:1; S2: Heat the aluminum electrolyte leaching solution and add an alkali solution. When hydroxyaluminum fluoride precipitates in the aluminum electrolyte leaching solution, add crystal seeds and an organic surfactant, and continue to add the alkali solution to adjust the pH value to 2-7; stir and age, and then filter to obtain a filter cake and a filtrate; S3: Dry the filter cake, add ammonium bifluoride, mix well and then calcine to obtain aluminum fluoride products. The present invention provides a method for preparing large-sized aluminum fluoride products from aluminum electrolyte leaching solution, which solves the technical problems of too fine particle size and low purity of aluminum fluoride products in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum electrolyte resource recovery, and specifically relates to a method for preparing large-particle-size aluminum fluoride products from aluminum electrolyte leaching solution. Background Art

[0002] In recent years, the electrolytic aluminum industry in China has developed rapidly, and the production capacity and output of electrolytic aluminum have ranked first in the world for many consecutive years. The industrial electrolytic aluminum production uses the traditional Hall-Heroult electrolytic aluminum smelting method. Alumina is used as the raw material and added to the cryolite (xNaF·AlF3)-based molten salt electrolyte for dissolution. The generated aluminum ions diffuse to the cathode to gain electrons and are reduced to metallic aluminum. A certain amount of sodium oxide is contained in the added alumina raw material. After this component enters the electrolytic cell, it will react with the AlF3 component of the electrolyte: 3Na2O + 2AlF3 = 6NaF + Al2O3, consuming AlF3 and generating NaF, resulting in an increase in the electrolyte molecular ratio (the molar ratio of NaF to AlF3) and a decrease in the initial crystallization temperature of the electrolyte. During the production process, in order to maintain a stable molecular ratio and the thermal balance of the electrolytic cell, it is necessary to regularly supplement AlF3 into the cell, which will increase the total amount of electrolyte in the cell. Therefore, it is necessary to regularly remove it to ensure the stability of the electrolyte level and total amount. It is estimated that 22 - 32 kg of excess electrolyte will be generated for every 1 ton of aluminum produced, and the excess electrolyte generated by the electrolytic aluminum industry in China each year is about 800,000 - 1,200,000 tons.

[0003] Currently, domestic electrolytic aluminum enterprises lack suitable means for resource utilization of aluminum electrolyte solid waste. The aluminum electrolyte contains a high content of fluorine element, which is a potential fluorine resource. If not utilized, it will cause resource waste and environmental pollution. Therefore, how to achieve the efficient resource utilization of waste aluminum electrolyte is a major common problem that urgently needs to be solved in the aluminum electrolysis industry in China.

[0004] In the prior art, the invention patent CN202010594435.9 discloses a preparation method of aluminum fluoride for an electrolytic aluminum cell. Adding alkali to the aluminum electrolyte leaching solution produces hydroxyaluminum fluoride (Al(OH)1 .38 F 1.62·0.5H2O) precipitate, and then calcined to prepare aluminum fluoride that can be used in the production of electrolytic aluminum. However, this technology has limitations: 1) The particle size of the aluminum fluoride product is too fine: The precipitation reaction rate of hydroxyaluminum fluoride induced by directly adding alkali is fast, the crystal nucleation rate of hydroxyaluminum fluoride is high, and the number density of crystal nuclei is large, resulting in extremely fine precipitation particles. Usually, a jelly-like substance is obtained, and solid-liquid separation is difficult; and it directly leads to a small particle size and poor fluidity of the final aluminum fluoride product, which cannot match the current feeding system of the aluminum electrolysis cell; 2) The purity of the aluminum fluoride is not high: The molar ratio of F:Al elements in hydroxyaluminum fluoride is usually ≤2. From the perspective of material balance analysis, directly calcining hydroxyaluminum fluoride cannot obtain pure-phase AlF3, and there must be excess Al elements that cannot combine with F, and finally are converted into alumina through hydrolysis reaction (2AlF3 + 3H2O = Al2O3 + 6HF), resulting in a high impurity content in the aluminum fluoride product. In short, the aluminum fluoride products obtained by the existing technology have too fine particle size and low purity. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing large-particle-size aluminum fluoride products from aluminum electrolyte leachate, which solves the technical problems of too fine particle size and low purity of aluminum fluoride products in the existing technology.

[0006] To achieve the above object, the present invention provides a method for preparing large-particle-size aluminum fluoride products from aluminum electrolyte leachate, including the following steps:

[0007] S1. Take the aluminum electrolyte leachate, and the molar ratio of F element to Al element in the aluminum electrolyte leachate is 1~2.5:1;

[0008] S2. Heat the aluminum electrolyte leachate, add alkali solution, when hydroxyaluminum fluoride precipitates in the aluminum electrolyte leachate, add crystal seeds and an organic surfactant, continue to add alkali solution to adjust the pH value to 2~7; stir and age, and then filter to obtain a filter cake;

[0009] S3. Dry the filter cake, add ammonium bifluoride, mix well and then calcine to obtain the aluminum fluoride product.

[0010] Optionally, the crystal seeds are anhydrous AlF3 or 3H2O·AlF3.

[0011] Optionally, the seed ratio of the crystal seeds is 0.5~2.5.

[0012] Optionally, the addition amount of the organic surfactant is 0.1%~2% of the mass of the aluminum electrolyte leachate.

[0013] Optionally, the organic surfactant is one or more of stearic acid, liquid paraffin, polyglycerol, dextran, polyacrylic acid and mineral oil.

[0014] Optionally, the heating temperature of the aluminum electrolyte leaching solution is 20~100°C.

[0015] Optionally, the addition amount of ammonium bifluoride is 10~100% of the mass of the filter cake.

[0016] Optionally, the aging time is 0~10h.

[0017] Optionally, the calcination temperature is 300~650°C.

[0018] Optionally, the calcination time is 1~5h.

[0019] The above technical solutions of the present invention have at least the following beneficial effects:

[0020] 1. A method for preparing large-particle-size aluminum fluoride products from aluminum electrolyte leaching solution provided by the present invention can effectively increase the particle size of the precipitate by adding seeds and organic surfactants during the precipitation process of hydroxyaluminum fluoride. The precipitation process of hydroxyaluminum fluoride includes crystal nucleation, crystal nucleus growth, and particle agglomeration processes. As Figure 1 shown, in the technical solution of the present invention, adding seeds externally can provide heterogeneous nucleation sites for the precipitation of particles, and the number of nucleations can be controlled by adjusting the seed parameters to promote crystal growth; at the same time, adding an organic surfactant can induce the surface of the hydroxyaluminum fluoride precipitation particles to be hydrophobic, strengthen the effective collision times between fine particles, and promote the combination, adhesion, and aggregation of the precipitation fine particles to form coarse particles.

[0021] 2. A method for preparing large-particle-size aluminum fluoride products from aluminum electrolyte leaching solution provided by the present invention can obtain high-purity aluminum fluoride products by adding a fluorinating agent during the calcination process of hydroxyaluminum fluoride. The hydroxyaluminum fluoride precipitation product contains crystal water and adsorbed water, and the dehydration process requires calcination at a high temperature. At this temperature, due to the presence of water vapor in the gas phase, the hydrolysis reaction of aluminum fluoride is likely to occur. In the technical solution of the present invention, by adding ammonium bifluoride as a fluorinating agent, HF gas is generated during the calcination process when ammonium bifluoride decomposes, shifting the aforementioned hydrolysis reaction to the left to inhibit hydrolysis. At the same time, the generated HF acts as a fluorine source to react with hydroxyaluminum fluoride and the products of the calcination process to form AlF3, thereby greatly increasing the aluminum fluoride content in the product. As shown in the Figure 2 attached XRD results, the phase detection results of the product show that the calcined product is a pure AlF3 phase.

[0022] 3. A method for preparing large-particle-size aluminum fluoride products from aluminum electrolyte leaching solution provided by the present invention can promote the melting and growth of hydroxyaluminum fluoride crystals and prepare large-particle-size aluminum fluoride products by combining the addition of seeds, organic surfactants, and calcination fluorinating agents. As Figure 3As shown, the final aluminum fluoride product obtained in the technical solution of the present invention has large particle size, smooth surface, spherical structure, and good fluidity. Since the technical solution of the present invention adds crystal seeds and organic surfactants during the precipitation process of hydroxyaluminum fluoride, small-sized precipitation particles agglomerate to form coarse particles. At this time, the binding force between particles is relatively weak. Ammonium bifluoride fluorinating agent is added during the calcination stage. At high temperature, fluoride ions in the fluorinating agent can be embedded in the crystal, thereby forming defects inside the crystal or providing an additional diffusion source, which helps the growth and morphology control of the crystal; the fluorinating agent can reduce the energy of the crystal surface, thereby reducing the surface tension of the crystal, making it easier for the crystal to grow; the fluorinating agent can also react with some components in the crystal raw material to form a compound with a lower melting point, reducing the overall melting temperature of hydroxyaluminum fluoride, so that the crystal starts to melt at a lower temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a scanning electron microscope (SEM) image of the precipitation of hydroxyaluminum fluoride in Example 1 of the present invention;

[0024] Figure 2 It is an X-ray diffraction (XRD) pattern of hydroxyaluminum fluoride before and after calcination in Example 1 of the present invention;

[0025] Figure 3 It is a SEM scanning electron microscope (SEM) image of the aluminum fluoride product obtained in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] For the purpose of making the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will combine the accompanying drawings of the embodiments of the present invention Figures 1-3 to clearly and completely describe the technical solutions of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0027] In the present invention, the aluminum electrolyte leaching solution is an aluminum electrolyte leaching solution leached by an inorganic acid and / or an aluminum salt leaching agent at normal temperature or high temperature, and the aluminum electrolyte leaching solution contains fluoroaluminum complex ions. The seed ratio in the present invention refers to the ratio of the mass of the added crystal seeds to the mass of aluminum fluoride converted from the aluminum content in the solution. The alkali solution used in the present invention is a common alkali solution, such as alkali solutions like NaOH solution, KOH solution, and NH3·H2O solution.

[0028] Example 1

[0029] S1 Use a graduated cylinder to measure 1000 mL of aluminum electrolyte leaching solution and place it in a beaker. The molar ratio of F to Al elements in the aluminum electrolyte leaching solution is 2:1;

[0030] S2 Stir and heat the aluminum electrolyte leaching solution to 80 °C, add a NaOH solution with a concentration of 2 mol / L, and use a pH meter to measure the change in the pH value of the solution. When hydroxyaluminum fluoride precipitate appears in the aluminum electrolyte leaching solution, add crystal seeds and an organic surfactant. Add anhydrous AlF3 crystal seeds at a seed ratio of 1, and add 2.5 g of stearic acid (dissolved in ethanol solvent) and 2.5 mL of liquid paraffin. Continue to add the alkali solution until the pH value reaches 3 and then stop. Stir and age for 10 h, filter the solution to obtain a filter cake;

[0031] S3 Dry the filter cake to obtain 20.7 g of hydroxyaluminum fluoride precipitate; mix the hydroxyaluminum fluoride with an equal mass of ammonium bifluoride evenly, and slowly heat it to 650 °C in a muffle furnace for calcination to obtain 13.9 g of aluminum fluoride, and the average particle size of the product > 45 μm.

[0032] Example 2

[0033] S1 Use a graduated cylinder to measure 1200 mL of aluminum electrolyte leaching solution and place it in a beaker. The molar ratio of F to Al elements in the aluminum electrolyte leaching solution is 1.5:1;

[0034] S2 Stir and heat the aluminum electrolyte leaching solution to 70 °C, add a KOH solution with a concentration of 1 mol / L, and use a pH meter to measure the change in the pH value of the solution. When hydroxyaluminum fluoride precipitate appears in the aluminum electrolyte leaching solution, add crystal seeds and an organic surfactant. Add anhydrous AlF3 crystal seeds at a seed ratio of 1.5, and add 20 ml of polyglycerol. Continue to add the alkali solution until the pH value reaches 7 and then stop. Stir and age for 5 h, filter the solution to obtain a filter cake;

[0035] S3 Dry the filter cake to obtain 35.5 g of hydroxyaluminum fluoride precipitate; mix the hydroxyaluminum fluoride with 20 g of ammonium bifluoride evenly, and slowly heat it to 550 °C in a muffle furnace for calcination to obtain 26.8 g of aluminum fluoride, and the average particle size of the product > 65 μm.

[0036] Example 3

[0037] S1 Use a graduated cylinder to measure 500 mL of aluminum electrolyte leaching solution and place it in a beaker. The molar ratio of F to Al elements in the aluminum electrolyte leaching solution is 2.5:1;

[0038] S2 Stir and heat the aluminum electrolyte leaching solution to 100 °C, add a solution of NH₃·H₂O with a concentration of 1 mol / L, test the change in the pH value of the solution with a pH meter. When hydroxyl aluminum fluoride precipitate appears in the aluminum electrolyte leaching solution, add crystal seeds and an organic surfactant, add hydrated AlF₃ crystal seeds according to a seed ratio of 2, and add 10 g of dextran and 2 g of polyacrylic acid. Continue to add the alkali solution until the pH value reaches 4 and then stop. Stir and age for 5 h, filter the solution to obtain a filter cake;

[0039] S3 Dry the filter cake to obtain 11.2 g of hydroxyl aluminum fluoride precipitate; mix 5 g of ammonium bifluoride with the hydroxyl aluminum fluoride evenly, and slowly heat it to 300 °C in a muffle furnace for calcination to obtain 7.8 g of aluminum fluoride, and the average particle size of the product > 45 μm.

[0040] Example 4

[0041] S1 Use a measuring cylinder to measure 1000 mL of the aluminum electrolyte leaching solution and place it in a beaker. The molar ratio of F to Al elements in the aluminum electrolyte leaching solution is 1:1;

[0042] S2 Stir and heat the aluminum electrolyte leaching solution to 20 °C, add a NaOH solution with a concentration of 2 mol / L, test the change in the pH value of the solution with a pH meter. When hydroxyl aluminum fluoride precipitate appears in the aluminum electrolyte leaching solution, add crystal seeds and an organic surfactant, add anhydrous AlF₃ crystal seeds according to a seed ratio of 0.5, and add 5 ml of mineral oil. Continue to add the alkali solution until the pH value reaches 2 and then stop. Filter the solution to obtain a filter cake;

[0043] S3 Dry the filter cake to obtain 15.8 g of hydroxyl aluminum fluoride precipitate; mix 1.58 g of ammonium bifluoride with the hydroxyl aluminum fluoride evenly, and slowly heat it to 300 °C in a muffle furnace for calcination to obtain 6.9 g of aluminum fluoride, and the average particle size of the product > 45 μm.

[0044] Example 5

[0045] S1 Use a measuring cylinder to measure 1000 mL of the aluminum electrolyte leaching solution and place it in a beaker. The molar ratio of F to Al elements in the aluminum electrolyte leaching solution is 2.5:1;

[0046] S2 Stir and heat the aluminum electrolyte leaching solution to 100 °C, add a NaOH solution with a concentration of 2 mol / L, test the change in the pH value of the solution with a pH meter. When hydroxyl aluminum fluoride precipitate appears in the aluminum electrolyte leaching solution, add crystal seeds and an organic surfactant, add anhydrous AlF₃ crystal seeds according to a seed ratio of 2.5, and add 2.5 g of stearic acid (dissolved in ethanol solvent) and 2.5 mL of mineral oil. Continue to add the alkali solution until the pH value reaches 7 and then stop. Filter the solution to obtain a filter cake;

[0047] S3 Dry the filter cake to obtain 20.1 g of hydroxyaluminum fluoride precipitate; mix 2.01 g of ammonium bifluoride with the hydroxyaluminum fluoride evenly, and slowly heat it to 650 °C in a muffle furnace for calcination to obtain 12.4 g of aluminum fluoride, with the average particle size of the product > 75 μm.

[0048] Example 6

[0049] S1 Use a measuring cylinder to measure 1200 mL of aluminum electrolyte leaching solution and place it in a beaker. The molar ratio of F to Al elements in the aluminum electrolyte leaching solution is 1.5:1;

[0050] S2 Stir and heat the aluminum electrolyte leaching solution to 70 °C, add a 1 mol / L NaOH solution, and use a pH meter to measure the change in the pH value of the solution. When hydroxyaluminum fluoride precipitate precipitates in the aluminum electrolyte leaching solution, add seed crystals and an organic surfactant, add anhydrous AlF3 seed crystals according to a seeding ratio of 1, and add 20 ml of liquid paraffin. Continue to add the alkali solution until the pH value reaches 7 and then stop. Stir and age for 5 h, filter the solution to obtain a filter cake;

[0051] S3 Dry the filter cake to obtain 34.8 g of hydroxyaluminum fluoride precipitate; mix 20 g of ammonium bifluoride with the hydroxyaluminum fluoride evenly, and slowly heat it to 450 °C in a muffle furnace for calcination to obtain 24.3 g of aluminum fluoride, with the average particle size of the product > 50 μm.

[0052] Comparative Example 1

[0053] S1 Use a measuring cylinder to measure 1200 mL of aluminum electrolyte leaching solution and place it in a beaker. The molar ratio of F to Al elements in the aluminum electrolyte leaching solution is 1.5:1;

[0054] S2 Directly add a 1 mol / L KOH solution to the aluminum electrolyte leaching solution, use a pH meter to measure the change in the pH value of the solution, continue to add the alkali solution until the pH value reaches 7 and then stop. Stir and age for 5 h, filter the solution to obtain a filter cake;

[0055] S3 Dry the filter cake to obtain 26.5 g of hydroxyaluminum fluoride precipitate; mix 13 g of ammonium bifluoride with the hydroxyaluminum fluoride evenly, and slowly heat it to 550 °C in a muffle furnace for calcination to obtain 19.8 g of aluminum fluoride, with the average particle size of the product < 5 μm.

[0056] Comparative Example 2

[0057] S1 Use a measuring cylinder to measure 1200 mL of aluminum electrolyte leaching solution and place it in a beaker. The molar ratio of F to Al elements in the aluminum electrolyte leaching solution is 1.5:1;

[0058] S2 Stir and heat the aluminum electrolyte leaching solution to 70 °C, add a KOH solution with a concentration of 1 mol / L, test the change in the pH value of the solution with a pH meter. When hydroxyaluminum fluoride precipitate appears in the aluminum electrolyte leaching solution, add an organic surfactant, add 20 ml of polyglycerol, continue to add the alkali solution until the pH value reaches 7 and then stop, stir and age for 5 h, filter the solution to obtain a filter cake;

[0059] S3 Dry the filter cake to obtain 34.3 g of hydroxyaluminum fluoride precipitate; mix 20 g of ammonium bifluoride with the hydroxyaluminum fluoride evenly and slowly heat it to 550 °C in a muffle furnace for calcination to obtain 21.7 g of aluminum fluoride, and the average particle size of the product is <5 μm.

[0060] Comparative Example 3

[0061] S1 Use a measuring cylinder to measure 1200 mL of aluminum electrolyte leaching solution and place it in a beaker. The molar ratio of F to Al elements in the aluminum electrolyte leaching solution is 1.5:1;

[0062] S2 Stir and heat the aluminum electrolyte leaching solution to 70 °C, add a KOH solution with a concentration of 1 mol / L, test the change in the pH value of the solution with a pH meter, continue to add the alkali solution until the pH value reaches 7 and then stop, stir and age for 5 h, filter the solution to obtain a filter cake;

[0063] S3 Dry the filter cake to obtain 26.5 g of hydroxyaluminum fluoride precipitate; slowly heat it to 550 °C in a muffle furnace for calcination to obtain a mixture of 16.9 g of aluminum fluoride and alumina, and the average particle size of the product is <2 μm.

[0064] Comparative Example 4

[0065] S1 Use a measuring cylinder to measure 1200 mL of aluminum electrolyte leaching solution and place it in a beaker. The molar ratio of F to Al elements in the aluminum electrolyte leaching solution is 1.5:1;

[0066] S2 Stir and heat the aluminum electrolyte leaching solution to 70 °C, add a KOH solution with a concentration of 1 mol / L, test the change in the pH value of the solution with a pH meter. When hydroxyaluminum fluoride precipitate appears in the aluminum electrolyte leaching solution, add seed crystals, add anhydrous AlF3 seed crystals at a seed ratio of 1.5, continue to add the alkali solution until the pH value reaches 7 and then stop, stir and age for 5 h, filter the solution to obtain a filter cake;

[0067] S3 Dry the filter cake to obtain 32.7 g of hydroxyaluminum fluoride precipitate; mix 20 g of ammonium bifluoride with the hydroxyaluminum fluoride evenly and slowly heat it to 550 °C in a muffle furnace for calcination to obtain 24.6 g of aluminum fluoride, and the average particle size of the product is <5 μm.

[0068] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing large-particle-size aluminum fluoride products from aluminum electrolyte leaching solution, characterized in that, Comprising the following steps: S1. Take the aluminum electrolyte leaching solution, wherein the molar ratio of F element to Al element in the aluminum electrolyte leaching solution is 1-2.5:1; S2. Heat the aluminum electrolyte leaching solution, the heating temperature of the aluminum electrolyte leaching solution is 20-100 °C, add alkali solution, when hydroxyaluminum fluoride precipitate precipitates in the aluminum electrolyte leaching solution, add crystal seeds and an organic surfactant, continue to add alkali solution to adjust the pH value to 2-7; stir and age, the aging time is 0-10 h, and then filter to obtain a filter cake; the addition amount of the organic surfactant is 0.1%-2% of the mass of the aluminum electrolyte leaching solution, and the organic surfactant is one or more of stearic acid, liquid paraffin, polyglycerol, dextran, polyacrylic acid and mineral oil; S3. Dry the filter cake, add ammonium bifluoride, mix well and then calcine to obtain aluminum fluoride products.

2. The method for preparing large-particle-size aluminum fluoride products from aluminum electrolyte leaching solution according to claim 1, characterized in that, The crystal seeds are anhydrous AlF3 or 3H2O·AlF3.

3. The method for preparing large-particle-size aluminum fluoride products from aluminum electrolyte leaching solution according to claim 1 or 2, characterized in that, The seed ratio of the crystal seeds is 0.5-2.

5.

4. The method for preparing large-particle-size aluminum fluoride products from aluminum electrolyte leaching solution according to claim 1, characterized in that, The addition amount of ammonium bifluoride is 10%-100% of the mass of the filter cake.

5. The method for preparing large-particle-size aluminum fluoride product from aluminum electrolyte leaching solution according to claim 1, characterized in that, The calcination temperature is 300-650 °C.

6. The method for preparing large particle size aluminum fluoride product from aluminum electrolyte leaching solution according to claim 5, characterized in that, The calcination time is 1-5 h.

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