Method for treating electrolytic aluminum lithium-containing overhaul slag through alkaline process

Abstract

The invention provides a method for treating electrolytic aluminum lithium-containing overhaul slag by an alkaline process, which comprises the following steps of: crushing and grinding the lithium-containing overhaul slag to obtain the crushed and ground lithium-containing overhaul slag; mixing the obtained crushed and ground lithium-containing overhaul slag with lime, fully mixing a solid obtained by mixing with an alkali solution, and leaching; after leaching is completed, slurry obtained after leaching is subjected to solid-liquid separation and washing, and filtrate, washing liquid and a filter cake are obtained; and carrying out concentration and lithium precipitation on the obtained filtrate and washing liquor to obtain lithium carbonate and filtrate. By means of the method, high-efficiency and low-cost extraction of lithium can be achieved, harmless treatment of fluorine is achieved, and further the alkali solution can be recycled.

Description

Technical Field

[0001] The invention relates to the field of resource treatment of metallurgical solid waste, and in particular to a method for extracting lithium from lithium-containing overhaul slag of electrolytic aluminum. 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. If alumina with high lithium content is used as raw material for a long time, the lithium content in the electrolyte of the electrolytic aluminum plant will exceed the appropriate range, which will lead to the deterioration of the working condition of the electrolytic cell. In order to maintain the lithium balance in the electrolytic cell, these electrolytes with excessive lithium content need to be treated regularly. The overhaul slag generated in the electrolytic aluminum production process is mainly waste slag generated by repairing or replacing the cathode lining of the electrolytic cell. Its main components include about 65% carbon and about 30% fluoride, mainly in the form of cryolite, sodium fluoride and calcium fluoride. In addition, overhaul slag, carbon slag and residual anode also contain a large amount of waste electrolyte. If these lithium-containing overhaul slags are improperly handled or directly discharged, they will cause irreversible pollution and damage to the soil, environment, air and organisms. Therefore, realizing the resource utilization of lithium-containing overhaul slag from waste electrolytic aluminum has become a key issue that needs to be urgently solved in the aluminum industry.

[0003] With the rapid development of the new energy industry chain, the supply of lithium resources has received increasing attention. In order to make rational use of these resources and reduce the potential impact of waste electrolytes on the environment, a method is sought to extract lithium from lithium-containing overhaul slag and achieve harmless treatment of fluorine-containing leachate. This method will provide a practical technical solution for factories using lithium-rich alumina across the country to achieve harmless and comprehensive utilization of resources. 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 alkaline treatment of electrolytic aluminum lithium-containing overhaul slag, which uses a low-concentration alkaline solution to efficiently leach lithium from the lithium-containing overhaul slag. Different from the existing acid leaching, the method can achieve 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 overhaul slag from electrolytic aluminum using an alkaline method, which comprises: (1) crushing and grinding the lithium-containing overhaul slag to obtain crushed and ground lithium-containing overhaul slag; (2) mixing the crushed and ground lithium-containing overhaul slag obtained in step (1) with lime, and fully mixing the solid obtained by the mixture with an alkaline solution for leaching; (3) After the leaching is completed, the leached slurry is subjected to solid-liquid separation and washing to obtain a filtrate, a washing liquid and a filter cake; (4) Concentrating and precipitating lithium from the filtrate and washing liquid obtained in step (3) to obtain lithium carbonate and a filtrate.

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

[0007] In some embodiments, the alkaline method for treating lithium-containing overhaul slag from electrolytic aluminum further comprises: (5) returning the filtrate obtained in step (4) to step (2) for recycling as the 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 lithium-containing overhaul slag is ≤100 μm.

[0010] In some embodiments, in step (2), the crushed and ground lithium-containing overhaul slag is mixed with lime in a ratio of 1:2 to 1:3.

[0011] Thus, the fluorine in the lithium-containing overhaul slag can be converted into insoluble fluoride, reducing the harmful effects of leached waste slag on the environment.

[0012] In some embodiments, in step (2), the alkaline solution is a sodium hydroxide solution with a mass concentration of 8% to 12%.

[0013] As a result, lithium in lithium-containing overhaul slag can be efficiently leached, achieving a leaching rate of more than 90%.

[0014] In some embodiments, in step (2), the solid-liquid mass ratio is 1:7 to 1:12.

[0015] In some embodiments, in step (2), steam is heated to a temperature of 60°C to 80°C, and leaching is performed at this temperature for 3 to 5 hours.

[0016] In step (2), the main chemical reaction of leaching with alkaline solution is: Na 3 AlF 6 +4NaOH=6NaF+NaAlO 2 +2H 2 O 2NaF+CaO+H 2 O=CaF 2 +2NaOH In the step (3), the filter cake is fluoride and impurities.

[0017] As a preferred embodiment, the present invention provides a method for treating lithium-containing overhaul slag from electrolytic aluminum using an alkaline method, which comprises: (1) crushing and grinding the lithium-containing overhaul slag collected from the electrolytic aluminum plant to a particle size of d50≤100μm; (2) mixing the obtained overhaul slag with a particle size of d50≤100 μm with lime in a ratio of 1:2 to 1:3, and fully mixing the mixed solid with a sodium hydroxide solution with a mass concentration of 8% to 12% in a solid-liquid mass ratio of 1:7 to 1:12 to form a slurry; (3) heating the slurry by steam to a temperature of 60°C to 80°C and leaching at this temperature for 3 to 5 hours; (4) After the leaching is completed, the leached slurry is passed through a filter press for solid-liquid separation and washed with 3 times the amount of water; (5) After solid-liquid separation, the filter cake obtained contains insoluble impurities such as fluoride and carbon, which can be discharged harmlessly; (6) After solid-liquid separation, the filtrate and washing liquid are concentrated by evaporation to obtain a concentrated solution with a lithium content of 20 g / L. Finally, sodium carbonate is added to the concentrated solution to precipitate lithium to synthesize a lithium carbonate product, and the filtrate is returned to the pulping for recycling.

[0018] (III) Beneficial effects 1. The present invention is the first to utilize a low-concentration alkaline solution to efficiently leach lithium from lithium-containing overhaul slag, and can achieve a leaching rate of more than 90%.

[0019] 2. The present invention uses lime as an additive for the first time to leach lithium-containing overhaul slag, which can convert fluorine in the lithium-containing overhaul slag into insoluble fluoride, thereby reducing the harmful effects of leached waste slag on the environment.

[0020] 3. The present invention is different from the acid leaching method in that the leachate can be recycled. When treating lithium-containing overhaul slag, the use of a low-concentration alkaline solution for leaching can not only avoid the consumption of additional alkali, but also after the lithium is extracted, the remaining alkaline solution can still be recovered and used as a 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 1A process flow chart for alkaline treatment of lithium-containing overhaul slag from electrolytic aluminum 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 the lithium-containing overhaul slag of electrolytic aluminum by alkaline method. The process flow is shown in Figure 1 , the specific steps are as follows: 1. Crushing and grinding the lithium-containing overhaul slag collected from the electrolytic aluminum plant to make its particle size reach d50≤100μm; 2. The overhaul slag with a particle size of d50≤100 μm is mixed with lime in a ratio of 1:2, and the mixed solid is fully mixed with a sodium hydroxide solution with a mass concentration of 10% in a solid-liquid mass ratio of 1:10 to form a slurry; 3. Heat the slurry with steam to a temperature of 75°C and leach at this temperature for 4 hours; 4. After leaching is completed, the leached slurry is passed through a filter press for solid-liquid separation and washed with 3 times the amount of water; 5. After solid-liquid separation, the filter cake is insoluble impurities such as fluoride and carbon, which can be discharged harmlessly; 6. After solid-liquid separation, the filtrate and washing liquid are concentrated by evaporation to obtain a concentrated solution with a lithium content of 20 g / L. Finally, sodium carbonate is added to the concentrated solution to precipitate lithium to synthesize a lithium carbonate product, and the filtrate is returned to the pulping for recycling.

[0026] The lithium-containing overhaul slag before leaching and the leached slag after leaching were measured by X-ray fluorescence spectrometry (XRF). The results are as follows: [Table 1] (Unit: %) In addition, the lithium-containing overhaul slag before leaching and the leached slag after leaching were digested by microwave and then detected by atomic absorption spectrophotometer. The results are as follows: [Table 2] (Unit: %) According to the results in Table 2, the lithium leaching rate reached 92.15%.

[0027] Example 2 The electrolytic aluminum lithium-containing overhaul slag was treated in the same manner as in Example 1, except that the mass concentration of the sodium hydroxide solution was adjusted to 8%.

[0028] XRF measurements were performed on the lithium-containing overhaul slag before leaching and the leached slag after leaching in the same manner as in Example 1, and the results are as follows: [Table 3] (Unit: %) In addition, lithium was detected in the lithium-containing overhaul slag before leaching and the leached slag after leaching in the same manner as in Example 1. The results are as follows: [Table 4] (Unit: %) According to the results in Table 4, the lithium leaching rate reached 90.36%.

[0029] Example 3 The electrolytic aluminum lithium-containing overhaul slag was treated in the same manner as in Example 1, except that the mass concentration of the sodium hydroxide solution was adjusted to 12%.

[0030] XRF measurements were performed on the lithium-containing overhaul slag before leaching and the leached slag after leaching in the same manner as in Example 1, and the results are as follows: [Table 5] (Unit: %) In addition, lithium was detected in the lithium-containing overhaul slag before leaching and the leached slag after leaching in the same manner as in Example 1. The results are as follows: [Table 6] (Unit: %) According to the results in Table 6, the lithium leaching rate reached 94.17%.

[0031] Comparative Example 1 The electrolytic aluminum lithium-containing overhaul slag was treated in the same manner as in Example 1, except that the mass concentration of the sodium hydroxide solution was adjusted to 5%.

[0032] XRF measurements were performed on the lithium-containing overhaul slag before leaching and the leached slag after leaching in the same manner as in Example 1, and the results are as follows: [Table 7] (Unit: %) In addition, lithium was detected in the lithium-containing overhaul slag before leaching and the leached slag after leaching in the same manner as in Example 1. The results are as follows: [Table 8] (Unit: %) According to the results in Table 8, the lithium leaching rate is 80.54%.

[0033] Comparative Example 2 The electrolytic aluminum lithium-containing overhaul slag was treated in the same manner as in Example 1, except that the mass concentration of the sodium hydroxide solution was adjusted to 15%.

[0034] XRF measurements were performed on the lithium-containing overhaul slag before leaching and the leached slag after leaching in the same manner as in Example 1, and the results are as follows: [Table 9] (Unit: %) In addition, lithium was detected in the lithium-containing overhaul slag before leaching and the leached slag after leaching in the same manner as in Example 1. The results are as follows: [Table 10] (Unit: %) According to the results in Table 10, the lithium leaching rate is 94.06%.

[0035] Comparative Example 3 The electrolytic aluminum lithium-containing overhaul slag was treated in the same manner as in Example 1, except that no lime was added.

[0036] XRF measurements were performed on the lithium-containing overhaul slag before leaching and the leached slag after leaching in the same manner as in Example 1, and the results are as follows: [Table 11] (Unit: %) In addition, lithium was detected in the lithium-containing overhaul slag before leaching and the leached slag after leaching in the same manner as in Example 1. The results are as follows: [Table 12] (Unit: %) According to the results in Table 12, the lithium leaching rate is 66.19%.

[0037] It can be seen from Examples 1 to 3 and Comparative Example 1 that, compared with the case where the mass concentration of the alkaline solution is lower than 8%, according to the treatment method of the present invention, the lithium leaching rate reaches more than 90% due to the use of a low-concentration alkaline solution (mass concentration of 8 to 12%) to leach lithium from lithium-containing overhaul slag, and efficient and low-cost extraction of lithium can be achieved. In addition, it can be seen from Example 3 and Comparative Example 2 that even if the mass concentration of the alkaline solution is increased to more than 12%, the leaching rate will not be significantly improved, but will cause waste of the alkaline solution. Further, it can be seen from Example 1 and Comparative Example 3 that, compared with the case where lime is not used, the treatment method of the present invention can achieve efficient and low-cost extraction of lithium.

[0038] 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 overhaul slag from electrolytic aluminum using an alkaline method, characterized in that: include: (1) crushing and grinding the lithium-containing overhaul slag to obtain crushed and ground lithium-containing overhaul slag; (2) mixing the crushed and ground lithium-containing overhaul slag obtained in step (1) with lime, and fully mixing the solid obtained by the mixture with an alkaline solution for leaching; (3) After the leaching is completed, the leached slurry is subjected to solid-liquid separation and washing to obtain a filtrate, a washing liquid and a filter cake; (4) Concentrating and precipitating lithium from the filtrate and washing liquid obtained in step (3) to obtain lithium carbonate and a filtrate.

2. The method according to claim 1, characterized in that: Further including: (5) The filtrate obtained in step (4) is returned to step (2) for recycling as the 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 lithium-containing overhaul slag is ≤100 μm.

4. The method according to claim 1 or 2, characterized in that: In step (2), the crushed and ground lithium-containing overhaul slag is mixed with lime in a ratio of 1:2 to 1:

3.

5. The method according to claim 1 or 2, characterized in that: In step (2), the alkaline solution is a sodium hydroxide solution with a mass concentration of 8% to 12%.

6. The method according to claim 1 or 2, characterized in that: In step (2), the solid-liquid mass ratio is 1:7 to 1:

12.

7. The method according to claim 1 or 2, characterized in that: In step (2), steam is heated to a temperature of 60°C to 80°C, and leaching is performed at this temperature for 3 to 5 hours.

8. The method according to claim 1 or 2, characterized in that: In step (3), the filter cake is fluoride and impurities.

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