Comprehensive utilization method of low-grade lepidolite

Abstract

The invention discloses a comprehensive utilization method of low-grade lepidolite, which relates to the technical field of lithium salt production, and comprises the following steps: leaching and purifying: mixing lepidolite with a sodium hydroxide solution and slaked lime, then preparing slurry, feeding the slurry into a high-pressure dissolver, carrying out autoclave dissolution, reacting at 240-290 DEG C to obtain mixed alkaline slurry containing lithium, potassium, rubidium and cesium, and recycling the mixed alkaline slurry; after solid-liquid separation, filtrate is subjected to aluminum, silicon and fluorine removal, impurity removal and other procedures, and purified liquid is obtained; precipitating lithium phosphate: adding a sodium phosphate solution into the purified liquid to precipitate lithium ions so as to realize primary separation of lithium and sodium to obtain a sodium dilithium phosphate precipitate, causticizing the sodium dilithium phosphate precipitate through a causticizing agent to obtain a lithium hydroxide solution, and adding a sodium carbonate solution through evaporation and concentration; after-treatment and reuse of the purified mother liquor; high-temperature roasting is effectively avoided, energy consumption is reduced, the quality of the obtained lithium salt product is also improved, and separation and extraction of elements of potassium, rubidium and cesium are realized.

Description

Technical Field

[0001] The invention relates to the technical field of lithium salt production, and in particular to a method for comprehensive utilization of low-grade lepidolite. Background Art

[0002] Lepidolite contains a variety of valuable elements. Currently, the main method for utilizing lepidolite is sulfate roasting, which produces a large amount of waste residue. When this method is used to treat low-grade mica ore, the unit product consumption increases, resulting in increased roasting energy consumption and poor economic efficiency. In view of the above problems, the present invention provides a new solution, which uses a high-temperature alkali leaching method to treat low-grade lepidolite ore to obtain a lithium-containing alkali solution, and then extracts and separates alkali metal elements, thereby avoiding high-temperature roasting and reducing energy consumption. The quality of the obtained lithium salt product is also improved, and the separation and extraction of potassium, rubidium and cesium elements are also achieved. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention provides a method for comprehensive utilization of low-grade lepidolite, which solves the technical problems raised in the above-mentioned background technology.

[0004] To achieve the above objectives, the present invention is implemented through the following technical solutions: S1, leaching purification: the lepidolite is mixed with sodium hydroxide solution and slaked lime to prepare slurry, and then sent to a high-pressure dissolver for pressure cooking and dissolution, and a mixed alkaline slurry containing lithium, potassium, rubidium and cesium is obtained by reaction at 240-290°C. After solid-liquid separation, the filtrate is subjected to the steps of removing aluminum, silicon, fluorine and impurities to obtain a purified liquid; S2, lithium phosphate precipitation: adding sodium phosphate solution to the purified liquid to precipitate lithium ions to achieve preliminary separation of lithium and sodium, obtaining sodium dilithium phosphate precipitate, subjecting the precipitate to causticizing with a causticizing agent to obtain a lithium hydroxide solution, adding sodium carbonate solution to precipitate lithium after evaporation and concentration, and then washing the lithium carbonate precipitate twice and performing solid-liquid separation again, and the precipitate obtained is pulped, carbonized and pyrolyzed to obtain battery-grade lithium carbonate; S3. Post-treatment and reuse of the purified mother liquor: Sodium phosphate is added to the purified liquid and sodium lithium phosphate precipitate is filtered out to obtain a purified mother liquor. The filtrate obtained after solid-liquid separation of the purified mother liquor is subjected to processes such as phosphorus removal, calcium removal, evaporation concentration and freezing sodium precipitation. The obtained sodium hydroxide ice crystals are remelted and reused as slurry ingredients before high-temperature leaching. The remaining alkaline mother liquor is subjected to a multi-stage carbonation process and solid-liquid separation to obtain products such as sodium carbonate, sodium bicarbonate, potassium bicarbonate and rubidium-cesium mother liquor.

[0005] Preferably, the high-temperature leaching step in S1 is carried out in a strong alkaline system with the presence of lime. After the mica is dissolved, calcium aluminosilicate and other precipitates are generated. In addition to the alkali metal elements, part of the aluminum and silicon elements are also leached into the filtrate. The filter residue separated from the leachate is washed and the iron concentrate is separated by magnetic separation.

[0006] Preferably, after solid-liquid separation in S1, purified slag is obtained, and the liquid obtained after secondary washing of the purified slag is mixed with sodium hydroxide solution and slaked lime and then recycled for slurry preparation.

[0007] Preferably, the phosphorus slag obtained after filtration in the causticizing step in S2 is acidified with sulfuric acid, filtered and separated to obtain regenerated phosphoric acid, which is reused in the lithium phosphate precipitation step. The reused phosphoric acid undergoes a neutralization reaction with the alkali in the purified liquid to generate sodium phosphate, which can also participate in the sodium lithium phosphate precipitation reaction.

[0008] Preferably, the phosphorus slag obtained after filtration in the causticizing step in S2 is acidified with sulfuric acid, subjected to solid-liquid separation, and washed twice to obtain calcium sulfate.

[0009] Preferably, lime milk and sodium carbonate solution are added to the purified mother liquor obtained in S3 to remove phosphorus and calcium, and then the mother liquor is evaporated and concentrated, and cooled to below 15°C, and enters a freezing and de-sodiumization process, sodium hydroxide is crystallized from the mother liquor, and after solid-liquid separation, the obtained sodium hydroxide hydrate is heated and remelted to obtain a sodium hydroxide solution, which is reused for slurrying ingredients before high-temperature leaching.

[0010] Preferably, after freezing and removing sodium to separate sodium hydroxide in S3, carbon dioxide is introduced into the filtrate, and after multi-stage carbonation and solid-liquid separation, part of the mother liquor obtained withdraws from the circulation and is used as rubidium and cesium mother liquor to go to the extraction process; the remaining mother liquor is evaporated and concentrated and then circulated back to the primary carbonation. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0012] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0013] The main components of lithium mica are shown in the following table: See also Figure 1 The present invention provides a technical solution: a method for comprehensive utilization of low-grade lepidolite, characterized in that it comprises the following steps in sequence: S1, leaching purification: the lepidolite is mixed with sodium hydroxide solution and slaked lime to prepare slurry, and then sent to a high-pressure dissolver for pressure cooking and dissolution, and a mixed alkaline slurry containing lithium, potassium, rubidium and cesium is obtained by reaction at 240-290°C. After solid-liquid separation, the filtrate is subjected to the steps of removing aluminum, silicon, fluorine and impurities to obtain a purified liquid; In S1, lepidolite is mixed with sodium hydroxide solution and slaked lime to prepare slurry, and then the slurry is sent to a high-pressure dissolver for pressure cooking and dissolution, and a mixed alkaline slurry containing lithium, potassium, rubidium and cesium is obtained by reaction at 240-290°C. After the reaction, the slurry is cooled to below 90°C and sent to a filter press to achieve solid-liquid separation. The separated calcium slag is discharged after washing, and an excess amount of impurity remover is added to the separated pressure leaching mother liquor, and the reaction is stirred at 25°C for 3 hours, followed by filtration and impurity removal to obtain a purified liquid.

[0014] S2, lithium phosphate precipitation: adding sodium phosphate solution to the purified liquid to precipitate lithium ions to achieve preliminary separation of lithium and sodium, obtaining sodium dilithium phosphate precipitate, subjecting it to causticizing agent to obtain lithium hydroxide solution, adding sodium carbonate solution to precipitate lithium after evaporation and concentration, and then washing the lithium carbonate precipitate twice and then performing solid-liquid separation again, and the precipitate obtained is pulped, carbonized and pyrolyzed to obtain battery-grade lithium carbonate; In S2, the molar ratio of phosphorus to lithium is controlled to be 1:2, so that lithium ions are precipitated to achieve preliminary separation of lithium and sodium, and sodium dilithium phosphate precipitate is obtained. The precipitate is causticized with a causticizing agent to obtain a lithium hydroxide solution. After evaporation and concentration, the lithium ion concentration is greater than 15 g / L. Sodium carbonate solution is added to precipitate lithium, and the molar ratio of lithium to carbonate is controlled to be 4:3. After reacting at 95°C for 1 hour, the solution is filtered while hot, and the filter cake is washed twice in countercurrent, and then pulped, carbonized and pyrolyzed to obtain battery-grade lithium carbonate.

[0015] S3, post-treatment and reuse of the purified mother liquor: sodium phosphate is added to the purified liquid and sodium lithium phosphate precipitate is filtered out to obtain a purified mother liquor. The filtrate obtained after solid-liquid separation of the purified mother liquor is subjected to processes such as phosphorus removal, calcium removal, evaporation concentration and freezing sodium precipitation. The obtained sodium hydroxide ice crystals are remelted and reused for slurrying ingredients before high-temperature leaching. The remaining alkaline mother liquor is subjected to a multi-stage carbonation process and solid-liquid separation to obtain products such as sodium carbonate, sodium bicarbonate, potassium bicarbonate and rubidium-cesium mother liquor; In S3, the mass fraction of sodium hydroxide after evaporation is controlled to be 37%-40%, and the evaporated liquid is cooled to 30°C and sent to the freezing sodium precipitation process. It is further cooled to 0°C-5°C. Most of the sodium hydroxide is crystallized and separated in the form of hydrates. The overflow clear liquid of the freezing crystallizer is sent to the carbonation device, and carbon dioxide is introduced to reduce the pH of the solution. The pH at the reaction end is controlled to be 11-12. After evaporation and concentration, sodium carbonate crystals are obtained by hot filtration. After the remaining filtrate is cooled, carbon dioxide is continued to be introduced to control the pH at the reaction end to be 8. It is cooled to 10°C and potassium bicarbonate precipitate is obtained by solid-liquid separation. The remaining mother liquor is evaporated and concentrated, and bicarbonate is filtered out, and it is circulated back to the first carbonation. After a period of circulation, the rubidium element in the mother liquor is enriched to more than 6g / L, and part of the mother liquor can be discharged from the system and sent to the extraction process or sold as a rubidium-cesium mother liquor product.

[0016] Furthermore, the high-temperature leaching step in S1 is carried out in a strong alkaline system with the presence of lime. After the mica is dissolved, calcium aluminosilicate and other precipitates are generated. In addition to the alkali metal elements, some aluminum and silicon elements are also leached into the filtrate. The filter residue separated from the leaching solution is washed and the iron concentrate is separated by magnetic separation.

[0017] Furthermore, after solid-liquid separation in S1, purified slag is obtained. The liquid obtained after secondary washing of the purified slag is mixed with sodium hydroxide solution and slaked lime and recycled for slurry preparation. The effective ingredient in the returned purified slag is calcium oxide. The ratio of lithium mica, sodium hydroxide and calcium oxide is controlled to be 1:1.23:0.3, and the concentration of sodium hydroxide solution is 30%, which is obtained by mixing caustic soda flakes, recycled alkali solution and supplementary water.

[0018] Furthermore, the phosphorus slag obtained after filtration in the causticizing step in S2 is acidified with sulfuric acid, filtered and separated to obtain regenerated phosphoric acid, which is reused in the lithium phosphate precipitation step. The reused phosphoric acid reacts with the alkali in the purified liquid to generate sodium phosphate, which can also participate in the sodium lithium phosphate precipitation reaction.

[0019] Furthermore, the phosphorus slag obtained after filtration in the causticizing step in S2 is acidified with sulfuric acid, subjected to solid-liquid separation, and washed twice to obtain calcium sulfate.

[0020] Furthermore, lime milk and sodium carbonate solution are added to the purified mother liquor obtained in S3 to remove phosphorus and calcium, and then the mother liquor is evaporated and concentrated, and cooled to below 15°C, and enters the freezing and de-sodiuming process, sodium hydroxide is crystallized from the mother liquor, and after solid-liquid separation, the obtained sodium hydroxide hydrate is heated and remelted to obtain a sodium hydroxide solution, which is reused for the slurry batching before high-temperature leaching.

[0021] Furthermore, after freezing and removing sodium to separate sodium hydroxide in S3, carbon dioxide is introduced into the filtrate. After multi-stage carbonation and solid-liquid separation, part of the mother liquor obtained withdraws from the circulation and is used as rubidium and cesium mother liquor for extraction process; the remaining mother liquor is evaporated and concentrated and then recycled to the first-stage carbonation stage.

[0022] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for comprehensive utilization of low-grade lepidolite, characterized in that: The steps are as follows: S1, leaching purification: the lepidolite is mixed with sodium hydroxide solution and slaked lime to prepare slurry, and then sent to a high-pressure dissolver for pressure cooking and dissolution, and a mixed alkaline slurry containing lithium, potassium, rubidium and cesium is obtained by reaction at 240-290°C. After solid-liquid separation, the filtrate is subjected to the steps of removing aluminum, silicon, fluorine and impurities to obtain a purified liquid; S2, lithium phosphate precipitation: adding sodium phosphate solution to the purified liquid to precipitate lithium ions to achieve preliminary separation of lithium and sodium, obtaining sodium dilithium phosphate precipitate, subjecting the precipitate to causticizing with a causticizing agent to obtain a lithium hydroxide solution, adding sodium carbonate solution to precipitate lithium after evaporation and concentration, and then washing the lithium carbonate precipitate twice and performing solid-liquid separation again, and the precipitate obtained is pulped, carbonized and pyrolyzed to obtain battery-grade lithium carbonate; S3. Post-treatment and reuse of the purified mother liquor: Sodium phosphate is added to the purified liquid and sodium lithium phosphate precipitate is filtered out to obtain a purified mother liquor. The filtrate obtained after solid-liquid separation of the purified mother liquor is subjected to processes such as phosphorus removal, calcium removal, evaporation concentration and freezing sodium precipitation. The obtained sodium hydroxide ice crystals are remelted and reused as slurry ingredients before high-temperature leaching. The remaining alkaline mother liquor is subjected to a multi-stage carbonation process and solid-liquid separation to obtain products such as sodium carbonate, sodium bicarbonate, potassium bicarbonate and rubidium-cesium mother liquor.

2. The method for comprehensive utilization of low-grade lepidolite according to claim 1, characterized in that: The high-temperature leaching step in S1 is carried out in a strong alkaline system with the presence of lime. After the mica is dissolved, calcium aluminosilicate and other precipitates are generated. In addition to alkali metal elements, some aluminum and silicon elements are also leached into the filtrate. The filter residue separated from the leaching liquid is washed and then separated into iron concentrate by magnetic separation.

3. The method for comprehensive utilization of low-grade lepidolite according to claim 1, characterized in that: After solid-liquid separation in S1, purified slag is obtained. The liquid obtained after secondary washing of the purified slag is mixed with sodium hydroxide solution and slaked lime and then recycled for slurry preparation.

4. The method for leaching lepidolite in an alkaline system according to claim 1, characterized in that: The phosphorus slag obtained after filtration in the causticizing step in S2 is acidified with sulfuric acid, filtered and separated to obtain regenerated phosphoric acid, which is reused in the lithium phosphate precipitation step. The reused phosphoric acid reacts with the alkali in the purified liquid to generate sodium phosphate, which can also participate in the sodium lithium phosphate precipitation reaction.

5. The method for leaching lepidolite in an alkaline system according to claim 1, characterized in that: The phosphorus slag obtained after filtration in the causticizing process in S2 is acidified with sulfuric acid, subjected to solid-liquid separation, and washed twice to obtain calcium sulfate.

6. The method for leaching lepidolite in an alkaline system according to claim 1, characterized in that: Lime milk and sodium carbonate solution are added to the purified mother liquor obtained in S3 to remove phosphorus and calcium, and then the mother liquor is evaporated and concentrated, and cooled to below 15°C, and enters the freezing and sodium removal process, sodium hydroxide is crystallized from the mother liquor, and after solid-liquid separation, the obtained sodium hydroxide hydrate is heated and remelted to obtain sodium hydroxide solution, which is reused for slurry preparation before high-temperature leaching.

7. The method for leaching lepidolite in an alkaline system according to claim 1, characterized in that: After freezing and removing sodium to separate sodium hydroxide in S3, carbon dioxide is introduced into the filtrate. After multi-stage carbonation and solid-liquid separation, part of the mother liquor is withdrawn from the circulation and used as rubidium and cesium mother liquor for extraction. The remaining mother liquor is evaporated and concentrated and then recycled to the first-stage carbonation.

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