Method for treating electrolytic aluminum lithium-containing waste electrolyte by alkaline process

Abstract

The invention provides a method for treating an electrolytic aluminum lithium-containing waste electrolyte by an alkaline process, which comprises the following steps: crushing and grinding the electrolyte, fully mixing with a first alkaline solution, and leaching; after leaching is completed, solid-liquid separation is conducted, and first filtrate and a first filter cake are obtained; mixing and washing the first filter cake with hot water, and then carrying out solid-liquid separation to obtain a second filter cake; mixing the second filter cake with a second alkali solution, and leaching; after leaching is completed, solid-liquid separation is conducted, and second filtrate and a third filter cake are obtained; adsorbing the second filtrate and then carrying out solid-liquid separation to obtain a fourth filter cake; mixing and washing the third filter cake with hot water, then carrying out solid-liquid separation to obtain a fifth filter cake, and discharging the fifth filter cake; performing desorption, concentration and lithium precipitation on the fourth filter cake to synthesize lithium carbonate; and carbonizing the first filtrate, controlling the pH value of the solution, and synthesizing cryolite. By means of the method, efficient and low-cost extraction of lithium and harmless treatment of fluorine can be achieved, and further the alkali solution can be recycled.

Description

Technical Field

[0001] The present invention relates to the field of resource treatment of metallurgical solid waste, and in particular to a method for treating lithium-containing waste electrolyte from aluminum electrolysis by an alkali method and extracting lithium and fluorine therefrom. Background Art

[0002] In some parts of China, the lithium content in bauxite is high, which leads to the enrichment of lithium in the final product during the production of alumina by the Bayer process. Aluminum electrolytic enterprises that have long used alumina with high lithium content as raw materials will face the problem of lithium content in the electrolyte exceeding the appropriate range, which will deteriorate the working conditions of the electrolytic cell and force enterprises to regularly treat electrolytes with excessive lithium content to maintain the lithium balance of the electrolytic cell. In addition, by-products such as overhaul slag, carbon slag and residual anodes will also carry a large amount of waste electrolyte. Given that the new capacity of aluminum electrolysis is strictly controlled, these waste electrolytes cannot be quickly processed through the new capacity. Except for a small part used to start the overhaul cell, most of them can only be piled up. These piled waste electrolytes not only take up space, but their soluble fluorine may also penetrate into the soil with rainwater, causing environmental pollution problems. Therefore, realizing the resource utilization of waste aluminum electrolytes has become a key issue that the aluminum industry needs to solve urgently.

[0003] The aluminum electrolyte is mainly composed of low molecular weight cryolite, and also contains a small amount of potassium fluoride (KF), lithium fluoride (LiF), calcium fluoride (CaF 2 ), aluminum oxide (Al 2 O 3 ), magnesium fluoride (MgF 2 ) and impurities such as carbon, silica, and iron. With the rapid development of the new energy industry chain, the supply of lithium resources has become a hot topic. Therefore, in order to rationally utilize resources and reduce the potential impact of waste electrolytes on the environment, a practical technical solution is provided for factories using lithium-rich alumina across the country to achieve harmless and comprehensive utilization of resources, and to seek a method for extracting lithium from lithium-containing electrolytes and recovering fluorine in the leachate by synthesizing cryolite to achieve harmless treatment of fluorine-containing leachates. Summary of the invention

[0004] 1. Technical issues to be resolved In order to solve the above technical problems, the present invention provides a method for treating lithium-containing waste electrolyte of electrolytic aluminum by alkali method. The method leaches the waste electrolyte through alkali of different concentrations to extract lithium and fluorine in the leachate, thereby realizing efficient and low-cost extraction of lithium and harmless treatment of fluorine.

[0005] (II) Technical solution Specifically, the present invention provides a method for treating lithium-containing waste electrolyte of aluminum electrolysis by alkaline method, which comprises: (1) crushing and grinding the electrolyte to obtain a crushed and ground electrolyte; (2) fully mixing the crushed and ground electrolyte obtained in step (1) with a first alkaline solution for leaching; (3) After the leaching in step (2) is completed, the leached slurry is subjected to solid-liquid separation to obtain a first filtrate and a first filter cake; (4) mixing the first filter cake obtained in step (3) with hot water, performing slurry washing, and performing solid-liquid separation after washing to obtain a second filter cake and a first washing liquid; (5) mixing the second filter cake obtained in step (4) with a second alkaline solution for leaching; (6) After the leaching in step (5) is completed, the leached material is subjected to solid-liquid separation to obtain a second filtrate and a third filter cake; (7) adsorbing the second filtrate obtained in step (6) by a lithium adsorbent, and performing solid-liquid separation after adsorption to obtain a third filtrate and a fourth filter cake; (8) mixing the third filter cake obtained in step (6) with hot water and performing slurry washing, performing solid-liquid separation after washing to obtain a second washing liquid and a fifth filter cake, and discharging the fifth filter cake; (9) desorbing, concentrating, and precipitating lithium from the fourth filter cake obtained in step (7) to synthesize lithium carbonate; (10) mixing the first washing liquid obtained in step (4) and the second washing liquid obtained in step (8) with the first filtrate obtained in step (3) and mixing with CO 2 Carry out carbonization reaction, control solution pH, and synthesize cryolite.

[0006] According to the alkaline method for treating lithium-containing waste electrolyte of aluminum electrolysis of the present invention, efficient and low-cost extraction of lithium and harmless treatment of fluorine can be achieved.

[0007] In some embodiments, the alkaline method for treating lithium-containing waste electrolyte from aluminum electrolysis further comprises: (11) concentrating the third filtrate obtained in step (7) and returning it to step (5) to continue circulating as the second alkaline solution.

[0008] Thus, after lithium is extracted, the remaining alkaline solution can be recovered and used again as a leaching solution.

[0009] In some embodiments, in step (1), the particle size d50 of the crushed and ground electrolyte is ≤ 20 μm.

[0010] In some embodiments, in step (2), the first alkaline solution is a sodium hydroxide solution having a mass concentration of 3% to 10%; a solid-liquid mass ratio of 1:7 to 1:15; and leaching is performed by steam heating at 80 to 100° C. under normal pressure.

[0011] In some embodiments, in step (5), the second alkaline solution is a sodium hydroxide solution having a mass concentration of 25% to 45%; a solid-liquid mass ratio of 1:7 to 1:15; and leaching is performed under high temperature and high pressure conditions of 200 to 250° C. by heating with high-pressure steam.

[0012] Thus, the lithium in the electrolyte can be leached using a high-concentration alkaline solution. While leaching lithium, the high-concentration alkaline solution inhibits the dissolution of sodium fluoride, so that the fluorine content in the leachate is at a lower level, thus avoiding the problem of defluorination in the subsequent production of lithium carbonate from the lithium leachate.

[0013] In addition, the electrolyte can be leached in two stages using the alkaline solutions of different concentrations to efficiently and harmlessly recycle lithium and fluorine in the electrolyte. The two-stage leaching can achieve a leaching rate of lithium and fluorine of more than 95%, thereby reducing their residues in the final waste residue.

[0014] In step (2) and step (5), the main chemical reactions of alkali solution leaching are: Na 3 AlF 6 +4NaOH=6NaF+NaAlO 2 +2H 2 O In some embodiments, in step (7), the lithium adsorbent is a titanium-based lithium ion sieve.

[0015] In step (8), the fifth filter cake is insoluble fluoride and impurities.

[0016] In some embodiments, in step (10), the pH of the solution is controlled at 9-10.

[0017] As a preferred embodiment, the present invention provides a method for treating lithium-containing waste electrolyte of aluminum electrolysis by alkaline method, which comprises: (1) crushing and coarse grinding the electrolyte collected from the aluminum electrolytic plant and then fine grinding it to a particle size of d50≤20μm; (2) the electrolyte with a particle size of d50≤20 μm and a sodium hydroxide solution with a mass concentration of 3% to 10% are fully mixed in a solid-liquid mass ratio of 1:7 to 1:15 to form a slurry, and leaching is performed under normal pressure at 80 to 100° C. by steam heating; (3) After the leaching is completed, the leached slurry is passed through a filter press for solid-liquid separation to obtain a first filtrate and a first filter cake. The first filtrate is added to a filtrate tank A, and CO is introduced into the filtrate tank A. 2 Carry out carbonization reaction, and obtain cryolite product by controlling the pH of the solution at 9-10; (4) adding the first filter cake into filter cake tank A, mixing with 20 times hot water for slurry washing, and performing solid-liquid separation through a filter press after washing to obtain a first washing liquid and a second filter cake, and adding the first washing liquid into the filtrate tank A to mix with the first filtrate; (5) mixing the second filter cake with a sodium hydroxide solution having a mass concentration of 25% to 45% at a solid-liquid mass ratio of 1:7 to 1:15 to form a slurry, pumping the mixture into a high-pressure reaction pipeline through a diaphragm pump, heating the mixture with high-pressure steam, and leaching the mixture under high-temperature and high-pressure conditions of 200 to 250° C.; (6) After the leaching is completed, the leached material is subjected to solid-liquid separation to obtain a second filtrate and a third filter cake, the second filtrate is added to the filtrate tank B, adsorbed by a titanium-based lithium ion sieve, and subjected to solid-liquid separation after adsorption to obtain a third filtrate and a fourth filter cake, the third filtrate is concentrated to a certain extent, and returned to continue to serve as the second alkaline solution for circulation, the fourth filter cake is desorbed, the desorbed liquid is concentrated, and lithium is precipitated to synthesize a lithium carbonate product; (7) The third filter cake is added to the filter cake tank B and mixed with 20 times hot water for slurry washing. After washing, solid-liquid separation is performed by a filter press to obtain a second washing liquid and a fifth filter cake. The second washing liquid is added to the filtrate tank A and mixed with the first filtrate and the first washing liquid. The fifth filter cake contains a small amount of insoluble impurities such as fluoride and carbon.

[0018] (III) Beneficial effects 1. The present invention utilizes a high-concentration alkaline solution for the first time to leach lithium from the electrolyte. The high-concentration alkaline solution inhibits the dissolution of sodium fluoride while leaching lithium, so that the fluorine content in the leachate is at a lower level, thus avoiding the difficulty of defluorination in the subsequent production of lithium carbonate from the lithium leachate.

[0019] 2. The present invention is the first to use alkaline solutions of different concentrations to perform two-stage leaching of the electrolyte, so as to efficiently and harmlessly recycle the lithium and fluorine in the electrolyte. The two-stage leaching can achieve a leaching rate of lithium and fluorine of more than 95%, thereby reducing their residues in the final waste residue.

[0020] 3. The present invention is different from the acid leaching method in that the alkaline leachate can be recycled. The high-concentration alkaline solution is used to leach lithium from the electrolyte, consuming only a small amount of alkali. After the lithium in the leachate is extracted, the remaining alkaline solution can still be recovered and used as the leachate again. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. It is obvious that the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 A process flow chart for treating lithium-containing waste electrolyte from aluminum electrolysis using an alkaline method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] If no specific technology or conditions are specified in the embodiments of the present invention, the technology or conditions described in the literature in this field or the product instructions are used. If the manufacturer of the devices, instruments, reagents, etc. is not specified, they are all conventional products that can be purchased through regular channels. The raw materials used in the present invention can be easily purchased in the domestic product market.

[0025] Example 1 This embodiment provides a method for treating lithium-containing waste electrolyte from aluminum electrolysis using an alkali process. Figure 1 , the specific steps are as follows: 1. The electrolyte collected from the electrolytic aluminum plant is crushed and coarsely ground and then finely ground to a particle size of d50≤20μm; 2. The electrolyte with a particle size of d50≤20 μm and a sodium hydroxide solution with a mass concentration of 5% are fully mixed at a solid-liquid mass ratio of 1:10 to form a slurry, and leached at 90° C. under normal pressure by steam heating; 3. After leaching is completed, the leached slurry is passed through a filter press for solid-liquid separation to obtain filtrate 1 and filter cake 1. Filtrate 1 enters filtrate tank A, and CO is introduced into filtrate tank A. 2 Carrying out a carbonization reaction, and obtaining a cryolite product by controlling the pH of the solution at 9.5; 4. Filter cake 1 enters filter cake tank A, is mixed with 20 times hot water for slurry washing, and after washing, solid-liquid separation is performed through a filter press to obtain washing liquid 1 and filter cake 2. Washing liquid 1 enters filtrate tank A and is mixed with filtrate 1; 5. The filter cake 2 is mixed with a sodium hydroxide solution with a mass concentration of 30% at a solid-liquid mass ratio of 1:10 to form a slurry, and pumped into a high-pressure reaction pipeline through a diaphragm pump, and heated by high-pressure steam to perform leaching at a high temperature and high pressure of 220°C; 6. After leaching is completed, the leached material is subjected to solid-liquid separation to obtain filtrate 2 and filter cake 3. Filtrate 2 enters filtrate tank B and is adsorbed by a titanium-based lithium ion sieve. After adsorption, solid-liquid separation is performed to obtain filtrate 3 and filter cake 4. Filtrate 3 is concentrated to a certain extent and returned to continue to circulate as alkaline solution. Filter cake 4 is desorbed, and the desorbed liquid is concentrated to precipitate lithium to synthesize lithium carbonate products; 7. Filter cake 3 enters filter cake tank B and is mixed with 20 times hot water for slurry washing. After washing, solid-liquid separation is performed by filter press to obtain washing liquid 2 and filter cake 5. Washing liquid 2 enters filtrate tank A and is mixed with filtrate 1 and washing liquid 1. Filter cake 5 contains a small amount of insoluble impurities such as fluoride and carbon.

[0026] The solid electrolyte before leaching, the solid electrolyte after the first low-alkali leaching, the solid electrolyte after the second high-alkali leaching, and the solid electrolyte after the second washing were measured by X-ray fluorescence spectrometry (XRF). The results are as follows: [Table 1] (Unit: %) In addition, the solid electrolyte before leaching, the solid electrolyte after the first low-alkali leaching, the solid electrolyte after the second high-alkali leaching, and the solid electrolyte after the second washing were subjected to microwave digestion and then lithium was detected using an atomic absorption spectrophotometer. The results are as follows: [Table 2] (Unit: %) According to the results in Table 2, the leaching rate of lithium reached 96.62% and the leaching rate of fluorine was 95.09%.

[0027] Comparative Example 1 The electrolyte was treated in the same manner as in Example 1, except that the sodium hydroxide solution having a mass concentration of 5% was replaced by a sodium hydroxide solution having a mass concentration of 30%.

[0028] XRF measurements were performed on the solid electrolyte before leaching, the solid electrolyte after the first stage of high alkali leaching, the solid electrolyte after the second stage of high alkali leaching, and the solid electrolyte after the second stage of washing in the same manner as in Example 1, and the results are as follows: [Table 3] (Unit: %) In addition, the solid electrolyte before leaching, the solid electrolyte after the first stage of high alkali leaching, the solid electrolyte after the second stage of high alkali leaching, and the solid electrolyte after the second stage of washing were tested for lithium in the same manner as in Example 1. The results are as follows: [Table 4] (Unit: %) According to the results in Table 4, the leaching rate of lithium reached 96.86% and the leaching rate of fluorine reached 94.88%.

[0029] Comparative Example 2 The electrolyte was treated in the same manner as in Example 1, except that the sodium hydroxide solution with a mass concentration of 30% was replaced by a sodium hydroxide solution with a mass concentration of 5%.

[0030] XRF measurements were performed on the solid electrolyte before leaching, the solid electrolyte after the first low-alkali leaching, the solid electrolyte after the second low-alkali leaching, and the solid electrolyte after the second washing in the same manner as in Example 1, and the results are as follows: [Table 5] (Unit: %) In addition, the solid electrolyte before leaching, the solid electrolyte after the first low-alkali leaching, the solid electrolyte after the second low-alkali leaching, and the solid electrolyte after the second washing were tested for lithium in the same manner as in Example 1. The results are as follows: [Table 6] (Unit: %) According to the results in Table 6, the leaching rate of lithium reached 67.22% and the leaching rate of fluorine reached 88.07%.

[0031] It can be seen from Example 1 and Comparative Example 1 that even if a high concentration of alkaline solution is used in both leaching stages, the leaching rate will not be significantly improved, but will cause a waste of alkaline solution. In addition, it can be seen from Example 1 and Comparative Example 2 that compared with Comparative Example 2 in which a high concentration of alkaline solution is not used, the treatment method according to the present invention uses alkaline solutions of different concentrations to perform two-stage leaching on the electrolyte, so that lithium and fluorine in the electrolyte can be efficiently and harmlessly recycled, and the leaching rate of lithium and fluorine reaches more than 95% through two-stage leaching, reducing their residues in the final waste residue.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating lithium-containing waste electrolyte from aluminum electrolysis using an alkali method, characterized in that: include: (1) crushing and grinding the electrolyte to obtain a crushed and ground electrolyte; (2) fully mixing the crushed and ground electrolyte obtained in step (1) with a first alkaline solution for leaching; (3) After the leaching in step (2) is completed, the leached slurry is subjected to solid-liquid separation to obtain a first filtrate and a first filter cake; (4) mixing the first filter cake obtained in step (3) with hot water, performing slurry washing, and performing solid-liquid separation after washing to obtain a second filter cake and a first washing liquid; (5) mixing the second filter cake obtained in step (4) with a second alkaline solution for leaching; (6) After the leaching in step (5) is completed, the leached material is subjected to solid-liquid separation to obtain a second filtrate and a third filter cake; (7) adsorbing the second filtrate obtained in step (6) by a lithium adsorbent, and performing solid-liquid separation after adsorption to obtain a third filtrate and a fourth filter cake; (8) mixing the third filter cake obtained in step (6) with hot water and performing slurry washing, performing solid-liquid separation after washing to obtain a second washing liquid and a fifth filter cake, and discharging the fifth filter cake; (9) desorbing, concentrating, and precipitating lithium from the fourth filter cake obtained in step (7) to synthesize lithium carbonate; (10) The first washing liquid obtained in step (4) and the second washing liquid obtained in step (8) are mixed with the first filtrate obtained in step (3), and carbonized with CO2 to control the pH of the solution to synthesize cryolite.

2. The method according to claim 1, characterized in that Further including: (11) The third filtrate obtained in step (7) is concentrated and returned to step (5) to continue circulating as the second alkaline solution.

3. The method according to claim 1 or 2, characterized in that: In step (1), the particle size d50 of the crushed and ground electrolyte is ≤20 μm.

4. The method according to claim 1 or 2, characterized in that: In step (2), the first alkaline solution is a sodium hydroxide solution with a mass concentration of 3% to 10%; the solid-liquid mass ratio is 1:7 to 1:15; and leaching is performed by steam heating at 80 to 100° C. under normal pressure.

5. The method according to claim 1 or 2, characterized in that: In step (5), the second alkaline solution is a sodium hydroxide solution with a mass concentration of 25% to 45%; the solid-liquid mass ratio is 1:7 to 1:15; and the leaching is carried out under high temperature and high pressure conditions of 200 to 250° C. by heating with high-pressure steam.

6. The method according to claim 1 or 2, characterized in that: In step (7), the lithium adsorbent is a titanium-based lithium ion sieve.

7. The method according to claim 1 or 2, characterized in that: In step (8), the fifth filter cake is insoluble fluoride and impurities.

8. The method according to claim 1 or 2, characterized in that: In step (10), the pH of the solution is controlled at 9-10.

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