Comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite

Abstract

The invention provides a comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite. The comprehensive utilization method comprises the following steps: crushing a lepidolite roasting clinker, and leaching at normal temperature; defluorination and suction filtration are carried out on the leachate; adjusting the pH of the filtrate with lime water to remove magnesium; removing calcium by using potassium carbonate; extracting and separating to obtain a lithium-loaded organic phase; performing carbon dioxide reverse extraction on the lithium-loaded organic phase, removing calcium and magnesium from a reverse extraction water phase through resin, and performing pyrolysis to prepare lithium carbonate; and when potassium ions in the raffinate reach a certain concentration, carrying out evaporative crystallization to produce a potassium salt byproduct with high economic value. According to the method, the mica roasting clinker is leached with a large amount of water, the leaching rate of lithium is guaranteed, calcium oxide or potassium hydroxide is adopted for impurity removal, the pH of the solution is increased, and the extraction driving force is met; by adopting carbon dioxide reverse extraction, the quality of lithium carbonate is improved; the clinker is repeatedly leached after the raffinate is deoiled, the concentration of potassium in the solution is improved, the evaporation cost is reduced, and the method for producing lithium carbonate is high in recovery rate, low in energy consumption and low in production cost.

Description

Technical Field

[0001] The present application relates to the technical field of separation and purification, and in particular to a comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite. Background Art

[0002] The recycling method of lepidolite at present is mainly sulfate roasting method, and its production process is lepidolite concentrate batching-sintering-crushing-leaching-impurity purification-concentration-sodium carbonate lithium precipitation-decarbonization and neutralization of lithium precipitation mother liquor-evaporation concentration and salt precipitation, etc. However, the mica concentrate grade is low, and the lithium content of the leachate is low when the existing method leaches the clinker. The low-concentration leachate needs to be evaporated and concentrated to a higher concentration to meet the concentration requirement of lithium precipitation when producing lithium carbonate, resulting in large energy consumption and high production cost. The competitiveness of lepidolite in preparing lithium carbonate is not strong. In addition, lepidolite concentrate contains a large amount of potassium, and the existing method produces a large amount of potassium salt when producing lithium carbonate, which has low economic value. Patent CN118619314A discloses a method for preparing battery-grade lithium compounds, belonging to the technical field of lithium compound preparation methods. The method comprises the following steps: S1, sulfuric acid acidification or sulfate roasting of a lithium-containing raw material, followed by water leaching to obtain a leaching slurry; the lithium-containing raw material is a lithium mineral or waste lithium battery material; S2, calcium oxide or calcium hydroxide is added to the leaching slurry, fully reacted, and then filtered to obtain filtrate A and filter residue A; S3, a calcium ion-removing substance is added to filtrate A, fully reacted, and then filtered to obtain filtrate B and filter residue B; S4, filtrate B is fully contacted with an extractant for extraction, and then separated to obtain a loaded organic phase and a raffinate; S5, the loaded organic phase is reversely extracted to obtain a lithium solution and a blank organic phase; S6, the lithium solution is further processed to obtain a battery-grade lithium compound. However, the method for preparing lithium carbonate from lepidolite ore is cumbersome, requiring multiple precipitation and filtration processes, which takes a long time, has poor calcium and magnesium treatment effects, produces a large amount of residue, makes it difficult to produce high-purity lithium carbonate, and has a low comprehensive utilization rate of potassium salts. Summary of the Invention

[0003] The present application is made in view of the above-mentioned problems, and its purpose is to provide a preparation method for separating and purifying lithium carbonate and potassium in mica from low-grade lepidolite with simple process, convenient operation, low energy consumption, stable preparation process, high recovery rate, low cost, high product purity and high economic value.

[0004] In order to achieve the above-mentioned object, the present application provides a comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite, comprising the following steps: Step S1, mixing lepidolite concentrate with calcium sulfate, potassium sulfate, and calcium carbonate in a certain proportion and roasting to obtain clinker, crushing the roasted clinker, adding a certain amount of water at room temperature, stirring and leaching for 1-2 hours, and filtering to obtain a leachate; Step S2, adding sulfuric acid to the leachate to adjust the pH of the leachate to 3.5-4, and adding 1.5-2.5 g / L of a defluoridating agent to remove fluorine. After reacting for 0.5-1 hour, filter pressing and discharge the filter residue; Step S3, adding calcium oxide or potassium hydroxide to the filter press supernatant of S2 to adjust the pH value of the solution to 11.6-12.5, reacting for 30 minutes, filtering, and discharging the filter residue; Step S4, adding 1 to 1.2 times the molar amount of calcium ions in potassium carbonate solution to the supernatant of S3 filter press, reacting for 1 hour, filtering while hot, and then fine filtering; Step S5, cooling the precise filtrate of S4 to 30-40°C and then extracting the lithium ions in the aqueous phase with the organic phase to obtain a loaded organic phase and a raffinate; the lithium content of the raffinate is less than 20 ppm; the raffinate is deoiled and returned to S1 to leach the clinker; when the total potassium ion in the raffinate is enriched to 80 g / L, evaporation and crystallization are performed to produce potassium sulfate potash fertilizer; Step S6: stripping the loaded organic phase with water and carbon dioxide, so that lithium ions are transferred from the loaded organic phase to the stripping aqueous phase; In steps S7 and S6, the stripping aqueous phase is deoiled and then calcium and magnesium are removed by resin to obtain a stripping supernatant; the stripping supernatant is pyrolyzed, crystallized, and then separated to obtain lithium carbonate solid; the pyrolysis mother liquor after cooling is returned to S6 to strip the loaded organic phase.

[0005] In any embodiment, the mass ratio of the lepidolite concentrate: calcium sulfate: potassium sulfate: calcium carbonate is 1: 0.2-0.3: 0.1-0.3: 0.05-0.1.

[0006] In any embodiment, the lithium oxide content in the calcined lepidolite is 1.2-1.6%.

[0007] In any embodiment, more than 95% of the calcined lepidolite in S1 passes through a 200-mesh sieve after being crushed.

[0008] In any embodiment, the liquid-to-solid ratio in S1 is 2 to 3:1; and the filter residues of S2, S3, and S4 are used for roasting raw materials.

[0009] In any embodiment, the leaching concentration of lithium oxide in the leachate in S1 is 4.2-5.5 g / L.

[0010] The existing lithium oxide concentration is usually greater than 15.

[0011] In any embodiment, in step S4, the filtrate is heated to 85-95°C.

[0012] In any embodiment, the suction filtration in step S4 is 1-5 microns, and the precision filtration is 0.2-0.4 microns.

[0013] In any embodiment, the pH of the filtrate before the S5 extraction is adjusted to 12-13.5 by adding potassium hydroxide. By controlling the above steps, the pH value of the filtrate before the S5 extraction can be controlled at 12-13.5 without adding potassium hydroxide for adjustment, thereby reducing the amount of potassium hydroxide added.

[0014] In any embodiment, the S7 stripping supernatant is heat-exchanged with the pyrolysis mother liquor to increase the temperature of the stripping supernatant, which is then heated to 90-95° C. for pyrolysis.

[0015] Beneficial effects of the present invention: 1) No sodium sulfate is added during sulfate roasting of lepidolite concentrate, ensuring that no sodium salt is produced during leaching, leaving only potassium salt. Subsequent salt separation is unnecessary, increasing the economic value of potassium salt. Large amounts of water can be used during leaching of roasted mica clinker, ensuring high leaching rates of lithium and potassium in the clinker, controlling the leaching concentration of lithium oxide, and reducing the amount of potassium hydroxide used. 2) The leachate is treated with calcium oxide and potassium carbonate to remove impurities, which increases the pH of the solution, satisfies the extraction driving force, and reduces the amount of potassium hydroxide used; 3) The use of carbon dioxide stripping improves the quality of lithium carbonate; after the raffinate is deoiled, it is repeatedly leached into the clinker, increasing the potassium concentration in the solution and reducing evaporation costs. This method produces lithium carbonate with a high recovery rate, low energy consumption, and low production costs, thereby improving the quality of lithium carbonate and potash fertilizer. 4) The leachate is extracted to separate lithium and potassium, and the raffinate can be repeatedly used for clinker leaching. When the potassium concentration of the leachate reaches 80g / L, the extract enters the evaporation crystallization system, which has low energy consumption and high economic value of potassium sulfate.

[0016] 5) The preparation method of the present application has the advantages of low energy consumption, simplified process, low production cost, high product quality, high lithium yield, and convenient treatment of by-products. DETAILED DESCRIPTION

[0017] The following specifically discloses an embodiment of a comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite of the present application. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the following description is provided for those skilled in the art to fully understand the present application and is not intended to limit the subject matter described in the claims.

[0018] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0019] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0020] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0021] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0022] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0023] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0024] A comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite comprises the following steps: Step S1, mixing lepidolite concentrate with calcium sulfate, potassium sulfate, and calcium carbonate in a certain proportion and roasting to obtain clinker, crushing the roasted lepidolite clinker, adding a certain amount of water at room temperature, stirring and leaching for 1-2 hours, and filtering to obtain a leachate; Step S2, adding sulfuric acid to the leachate to adjust the pH of the leachate to 3.5-4, and adding 1.5-2.5g / L of a defluoridating agent to remove fluorine. After reacting for 0.5-1 hour, filter pressing and discharge the filter residue. The present application uses aluminum and lanthanum salts as defluoridating agents, which can achieve a more effective defluoridation effect under the above-mentioned acidic conditions.

[0025] Step S3, adding calcium oxide or potassium hydroxide to the filter press clear liquid of S2, adjusting the pH value of the solution to 11.6-12.5, reacting for 30 minutes, filtering, and discharging the filter residue; the pH value ensures the magnesium removal effect.

[0026] Step S4, adding 1 to 1.2 times the molar amount of calcium ions in potassium carbonate solution to the supernatant of S3 filter press, reacting for 1 hour, filtering while hot, and then fine filtering; Step S5, cooling the precise filtrate of S4 to 30-40°C and then extracting the lithium ions in the aqueous phase with the organic phase to obtain a loaded organic phase and a raffinate; the lithium content of the raffinate is less than 20 ppm; the raffinate is deoiled and returned to S1 to leach the clinker; when the total potassium ion in the raffinate is enriched to 80 g / L, evaporation and crystallization are performed to produce potassium sulfate potash fertilizer; Step S6: stripping the loaded organic phase with water and carbon dioxide, so that lithium ions are transferred from the loaded organic phase to the stripping aqueous phase; In steps S7 and S6, the stripping aqueous phase is deoiled and then calcium and magnesium are removed by resin to obtain a stripping supernatant; the stripping supernatant is pyrolyzed, crystallized, and then separated to obtain lithium carbonate solid; the pyrolysis mother liquor after cooling is returned to S6 to strip the loaded organic phase.

[0027] The lithium carbonate obtained by this method can reach a high-purity level with low potassium and sulfate content. Compared with the sodium carbonate lithium precipitation process, the amount of sodium introduced is less, there are fewer by-products, and the cost is low.

[0028] In some embodiments, the mass ratio of the lepidolite concentrate: calcium sulfate: potassium sulfate: calcium carbonate is 1: 0.2-0.3: 0.1-0.3: 0.05-0.1. Adding too little calcium sulfate can affect the lithium leaching rate, while adding too much can increase costs. Adding too little calcium carbonate can result in poor fluoride removal, while adding too much can increase costs. Adding too little potassium sulfate can affect the lithium leaching rate, while adding too much can affect the quality of lithium carbonate and increase costs.

[0029] In some embodiments, the lithium oxide content in the calcined lepidolite is 1.2-1.6%.

[0030] In some embodiments, more than 95% of the calcined lepidolite in S1 passes through a 200-mesh sieve after being crushed.

[0031] In some embodiments, the liquid-to-solid ratio in S1 is 2 to 3: 1, and the lithium oxide concentration of the leachate is ensured to be 4.2-5.5 g / L.

[0032] The fluorine removal residue, magnesium removal residue, and calcium removal residue in steps S2, S3, and S4 are returned for roasting. The fluorine removal residue in S2 is mainly composed of aluminum fluoride, lanthanum fluoride precipitates, and aluminum hydroxide and lanthanum hydroxide flocculants. The magnesium removal residue in S3 is mainly composed of magnesium hydroxide and insoluble calcium sulfate. The calcium removal residue in S4 is mainly composed of calcium carbonate precipitates. The residue is mainly composed of calcium carbonate and a small amount of calcium sulfate. By testing the residue content, the residue is added to the roasting raw materials to reduce the amount of calcium carbonate added as a roasting auxiliary material, saving costs and reducing the final residue amount.

[0033] In some embodiments, the lithium oxide concentration of the leachate in S1 is 4.2-5.5 g / L. The lithium ion concentration is 1.48-2.48 g / L. If the lithium oxide concentration is too high, potassium hydroxide must be added during extraction to replenish the hydroxide ions and ensure the driving force of extraction, which increases costs. If the lithium oxide concentration is too low, the extraction agent consumption is high, which is uneconomical.

[0034] The current lithium oxide concentration is about 15g / L, and a high concentration will result in a large subsequent consumption of potassium hydroxide.

[0035] In some embodiments, the filtrate in step S4 is heated to 85-95° C. to ensure that the calcium content in the filtered solution is less than 20 ppm.

[0036] By controlling the temperature, on the one hand, the removal rate of calcium ions is improved, and on the other hand, the hydroxide ions in the filtrate can meet the extraction requirements and the pH value can reach 12.5-13.5, reducing or eliminating the need to add potassium hydroxide to supplement hydroxide.

[0037] In some embodiments, the suction filtration in step S4 is 1-5 microns, and the precision filtration is 0.2-0.4 microns.

[0038] Through two-stage filtration, clogging is reduced and impurity removal is improved.

[0039] In any embodiment, the filtrate before extraction in step S5 is adjusted to pH=12-13.5 by adding potassium hydroxide.

[0040] Add potassium hydroxide to adjust p H, normally there is no need to adjust, it can reach 13 normally.

[0041] In some embodiments, when the total potassium ions in the S5 raffinate reach 80 g / L, evaporation and crystallization are performed to produce potassium sulfate by-product.

[0042] In some embodiments, the S7 stripping supernatant is heat exchanged with the pyrolysis mother liquor to increase the temperature of the stripping supernatant, which is then heated to 90-95° C. for pyrolysis.

[0043] Example Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0044] Example 1 A comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite comprises the following steps: S1. Mixing lepidolite concentrate with calcium sulfate, potassium sulfate, and calcium carbonate in a mass ratio of 1:0.25:0.15:0.08 and roasting the mixture to obtain clinker. The clinker is crushed, and more than 95% of the crushed clinker should pass through a 300-mesh sieve. S2 is to leach the clinker with clean water and raffinate at room temperature to obtain a leachate slurry with a liquid-to-solid ratio of 2:1. The mixture is stirred and leached for 1.5 hours, and filtered to obtain a leachate with a lithium oxide concentration of 4.25 g / L. S3: Add sulfuric acid to the leachate to adjust the pH of the leachate to 3.5, and add 2g / L of defluoridation agent to remove fluorine. After reacting for 0.8 hours, filter press and discharge the residue. S4 adds calcium oxide or potassium hydroxide to the filtered clear liquid of S3 to adjust the pH value of the solution to 12, reacts for 30 minutes, filters, and discharges the filter residue.

[0045] S5: heating the filter press liquid to 90°C, adding a potassium carbonate solution with a molar amount of 1.1 times the amount of calcium ions, reacting for 1 hour, filtering while hot, and then precision filtering with a precision of 0.2 microns. The pH of the solution is controlled at 13, so that the hydroxide ions in the solution meet the extraction requirements, and the filtered residue is discharged; S6: The precise filtrate is cooled to 35°C and then extracted. The organic phase extracts lithium ions in the aqueous phase to obtain a loaded organic phase and a raffinate. The lithium content of the raffinate is 15ppm. The raffinate is deoiled and returned to S1 for leaching clinker. When the total potassium ion in the raffinate is enriched to 80g / L, it is evaporated and crystallized to produce potassium sulfate fertilizer. S7 uses pure water, cooled pyrolysis mother liquor, and carbon dioxide to strip the loaded organic phase, so that lithium ions are transferred from the loaded organic phase to the stripping aqueous phase; the stripping aqueous phase is deoiled and then passed through a resin to remove calcium and magnesium, thereby obtaining a stripping clear liquid; S8: Heat exchange is performed between the stripping supernatant and the pyrolysis mother liquor to increase the temperature of the stripping supernatant, which is then heated to 93°C to pyrolyze and crystallize the lithium bicarbonate solution, and then separate to obtain lithium carbonate solid.

[0046] Example 2 A comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite comprises the following steps: S1. Mix lepidolite concentrate with calcium sulfate, potassium sulfate, and calcium carbonate in a mass ratio of 1:0.2:0.1:0.05 and roast to obtain clinker. The clinker is crushed. The crushed clinker should be -74µm@100% and -45µm@85%; S2 is to leach the clinker with clean water and raffinate at room temperature to obtain a leachate slurry, the liquid-to-solid ratio of the leaching is 3:1, the leaching is stirred for 1 hour, and the leaching is performed by pressure filtration. After pressure filtration, a leachate is obtained, and the lithium oxide concentration of the leachate is controlled at 3.2 g / L; S3: Add sulfuric acid to the leachate to adjust the pH of the leachate to 4, and add 1.5g / L of defluoridation agent to remove fluorine. After reacting for 1 hour, filter press and discharge the filter residue; S4 adds calcium oxide or potassium hydroxide to the filtered clear liquid of S3 to adjust the pH value of the solution to 12.5, reacts for 30 minutes, filters, and discharges the filter residue.

[0047] S5: heating the filter press liquid to 95°C, adding 1.05 times the molar amount of potassium carbonate solution of calcium ions, reacting for 1 hour, filtering while hot, and then precision filtering with a precision of 0.2 microns. The pH of the solution is controlled at 13.5 to ensure that the hydroxide ions in the solution meet the extraction requirements, and the filtered residue is discharged; S6: The precise filtrate is cooled to 35°C and then extracted. The organic phase extracts lithium ions in the aqueous phase to obtain a loaded organic phase and a raffinate. The lithium content of the raffinate is 20 ppm. The raffinate is deoiled and returned to S1 for leaching clinker. When the total potassium ion in the raffinate is enriched to 80 g / L, it is evaporated and crystallized to produce potassium sulfate fertilizer. S7 uses pure water, cooled pyrolysis mother liquor, and carbon dioxide to strip the loaded organic phase, so that lithium ions are transferred from the loaded organic phase to the stripping aqueous phase; the stripping aqueous phase is deoiled and then passed through a resin to remove calcium and magnesium to obtain a stripping clear liquid; the fluorine removal slag, magnesium removal slag, and calcium removal slag in S3, S4, S5, and S6 are returned for roasting; S8: Heat exchange is performed between the stripping supernatant and the pyrolysis mother liquor to increase the temperature of the stripping supernatant, which is then heated to 95°C to pyrolyze and crystallize the lithium bicarbonate solution, and then separate to obtain lithium carbonate solid.

[0048] Example 3 A comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite comprises the following steps: S1. Mix lepidolite concentrate with calcium sulfate, potassium sulfate, and calcium carbonate in a mass ratio of 1:0.3:0.2:0.1 and roast to obtain clinker. The clinker is crushed. The crushed clinker should be -74µm@100% and -45µm@85%; S2 is to leach the clinker with clean water and raffinate at room temperature to obtain a leachate slurry, the liquid-to-solid ratio of the leaching is 1:1, the leaching is stirred for 2 hours, and the leaching is performed by pressure filtration. After pressure filtration, a leachate is obtained, and the lithium oxide concentration of the leachate is controlled at 5.35 g / L; S3: Add sulfuric acid to the leachate to adjust the pH of the leachate to 3.5, and add 2.5g / L of defluoridation agent to remove fluorine. After reacting for 0.5 hours, filter press and discharge the residue. S4 adds calcium oxide or potassium hydroxide to the filtered clear liquid of S3 to adjust the pH value of the solution to 11.6, reacts for 30 minutes, filters, and discharges the filter residue.

[0049] S5: heating the filter press liquid to 85°C, adding a potassium carbonate solution with a molar amount of 1.2 times that of calcium ions, reacting for 1 hour, filtering while hot, and then precision filtering with a precision of 0.2 microns. The pH of the solution is controlled at 12.5, so that the hydroxide ions in the solution meet the extraction requirements, and the filtered residue is discharged; S6: The precise filtrate is cooled to 40°C and then extracted. The organic phase extracts lithium ions in the aqueous phase to obtain a loaded organic phase and a raffinate. The lithium content of the raffinate is 10 ppm. The raffinate is deoiled and returned to S1 for leaching clinker. When the total potassium ion in the raffinate is enriched to 80 g / L, it is evaporated and crystallized to produce potassium sulfate fertilizer. S7 uses pure water, cooled pyrolysis mother liquor, and carbon dioxide to strip the loaded organic phase, so that lithium ions are transferred from the loaded organic phase to the stripping aqueous phase; the stripping aqueous phase is deoiled and then passed through a resin to remove calcium and magnesium to obtain a stripping clear liquid; the fluorine removal slag, magnesium removal slag, and calcium removal slag in S3, S4, S5, and S6 are returned for roasting; S8: Heat exchange is performed between the stripping supernatant and the pyrolysis mother liquor to increase the temperature of the stripping supernatant, which is then heated to 95°C to pyrolyze and crystallize the lithium bicarbonate solution, and then separate to obtain lithium carbonate solid.

[0050] Comparative Example 1 Step S5 is modified to add a sodium carbonate solution with a molar amount of 1.2 times the calcium ion to the filter press clear liquid, and then finely filter it with a fine filtration accuracy of 0.2 microns. The pH of the solution is controlled at 12.5 so that the hydroxide ions in the solution meet the extraction requirements, and the filtered residue is discharged; other conditions are the same as in Example 1.

[0051] Comparative Example 2 The S6 precise filtrate is first passed through a resin to remove calcium and magnesium, and the aqueous phase of the S7 stripping is removed for oil removal and then passed through a resin to remove calcium and magnesium. The other steps are the same as those in Example 1.

[0052] Comparative Example 3 The S2 clinker was leached with clean water and raffinate at room temperature to obtain a leaching slurry with a liquid-to-solid ratio of 0.8:1. The mixture was stirred and leached for 2 hours, and filtered to obtain a leachate with a lithium oxide concentration of 7.5 g / L. S6: Cool the precise filtrate to 35°C and then extract it. The organic phase extracts lithium ions in the aqueous phase to obtain a loaded organic phase and a raffinate. The lithium content of the raffinate is 80 ppm. The other steps are the same as in Example 1.

[0053] As lithium oxide concentration increases, insufficient hydroxide ions lead to a significant decrease in lithium extraction efficiency, with lithium oxide levels in the raffinate reaching 80 ppm, impacting extraction efficiency. Only by increasing the amount of potassium hydroxide can lithium oxide levels in the raffinate be kept below 20 ppm, which increases production costs.

[0054] Comparative Example 4 A method for preparing battery-grade lithium carbonate comprises the following steps: S1: Roast the lepidolite concentrate with potassium sulfate and calcium sulfate to obtain clinker, which is then leached with water to obtain a leaching slurry. The main active ingredient of the leaching slurry is lithium sulfate, with a lithium ion concentration of 0.5g / L. S2-1: Calcium oxide is added to the leached slurry, and the pH of the leached slurry is adjusted to 8.5. Filtering is performed to obtain filtrate A' and filter residue A'. To fully recover the small amount of lithium entrained in filter residue A', filter residue A' is added to water and stirred to form a slurry. The slurry is filtered to obtain a residue and a washing liquid. The washing liquid is returned to step S1 for water leaching, and the residue is discharged. S2-2 adds calcium oxide to the filtrate A', adjusts the pH value to 12.7, and filters after sufficient reaction to obtain filtrate A and filter residue A. This step mainly converts lithium sulfate into lithium hydroxide, introduces hydroxide into the system, and also removes iron ions, ferrous ions and most magnesium ions. The main component of filtrate A is lithium hydroxide, and also includes soluble impurities formed after water immersion; the main component of filter residue A is calcium sulfate, and there may also be excess calcium oxide or calcium hydroxide. In order to fully recover the small amount of lithium entrained in filter residue A and utilize the excess calcium oxide or calcium hydroxide in filter residue A, filter residue A is returned to step S1 for leaching. S3: The mother liquor obtained in step S6 is added to filtrate A. After sufficient reaction, the mixture is filtered to obtain filtrate B and filter residue B. Since calcium sulfate is slightly soluble in water, the addition of the mother liquor obtained in step S6 converts the water-soluble calcium sulfate into sparingly soluble calcium carbonate, removing most of the calcium ions. To fully recover the small amount of lithium entrained in filter residue B, filter residue B is returned to step S1 for water leaching. S4: Filtrate B is subjected to extensive calcium and magnesium removal using an adsorption resin. The filtrate is then subjected to extensive contact extraction with an extractant to separate the loaded organic phase and the raffinate. Cyanex 923 and LIX 54 are mixed to form a composite extractant, with a volume ratio of Cyanex 923 to LIX 54 of 2:1. Sulfonated kerosene is used as the diluent, and the composite extractant accounts for 15% of the extraction system by volume. The extraction process separates lithium ions from monovalent metal ions (primarily potassium). The raffinate is directly returned to step S1 for water leaching. When the potassium ion concentration in the raffinate reaches the set value, the raffinate is deoiled and concentrated and evaporated to crystallize potassium sulfate. The evaporated water is returned to step S2-1 and added to the filter residue A' and stirred into a slurry. In step S5, carbonic acid is added to strip the loaded organic phase to obtain a lithium bicarbonate solution and a blank organic phase. During the stripping process, carbon dioxide and water are continuously introduced into the loaded organic phase to form a gas-liquid-liquid three-phase phase extraction. The blank organic phase is returned to step S4 for extraction. The volume ratio of the aqueous phase to the organic phase during stripping is controlled so that the lithium ion concentration in the lithium bicarbonate solution after stripping reaches about 8 g / L. S6 removes the oil from the lithium bicarbonate solution and deeply removes calcium and magnesium, and pyrolyzes it to obtain lithium carbonate slurry and carbon dioxide, and the carbon dioxide returns to step S5 for stripping. After the pyrolysis device has been running for a period of time, in order to prevent the scaling of lithium bicarbonate formed in the device, carbon dioxide is introduced into the device to convert the lithium carbonate into soluble lithium bicarbonate. The lithium carbonate slurry is separated into solid and liquid to obtain lithium carbonate precipitate and mother liquor. Since lithium carbonate is slightly soluble in water, the main component of the mother liquor is dissolved lithium carbonate. Part of the mother liquor returns to step S3 as an aqueous solution of carbonate, and part returns to step S5. The lithium carbonate reacts with carbon dioxide and water to generate lithium bicarbonate, so that the lithium in the mother liquor can be fully recovered. The lithium carbonate precipitate is dried to obtain lithium carbonate solid, which is then crushed and packaged by air flow to form a lithium carbonate product, which meets the requirements of the industry standard "YS / T 582-2023 Battery Grade Lithium Carbonate". Table 1 shows the product purity, lithium recovery rate, energy consumption and cost data of the preparation methods of the above embodiments and comparative examples.

[0055] Table 1

[0056] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite, characterized in that: The following steps are involved: Step S1, mixing lepidolite concentrate with calcium sulfate, potassium sulfate, and calcium carbonate in a certain proportion and roasting to obtain clinker, crushing the roasted lepidolite clinker, adding a certain amount of water at room temperature, stirring and leaching for 1-2 hours, and filtering to obtain a leachate; Step S2, adding sulfuric acid to the leachate to adjust the pH of the leachate to 3.5-4, and adding 1.5-2.5 g / L of a defluoridating agent to remove fluorine. After reacting for 0.5-1 hour, filter pressing and discharge the filter residue; Step S3, adding calcium oxide or potassium hydroxide to the filter press supernatant of S2 to adjust the pH value of the solution to 11.6-12.5, reacting for 30 minutes, filtering, and discharging the filter residue; Step S4, adding 1 to 1.2 times the molar amount of calcium ions in potassium carbonate solution to the supernatant of S3 filter press, reacting for 1 hour, filtering while hot, and then fine filtering; Step S5, cooling the precise filtrate of S4 to 30-40°C and then extracting the lithium ions in the aqueous phase with the organic phase to obtain a loaded organic phase and a raffinate; the lithium content of the raffinate is less than 20 ppm; the raffinate is deoiled and returned to S1 to leach the clinker; when the total potassium ion in the raffinate is enriched to 80 g / L, evaporation and crystallization are performed to produce potash fertilizer; Step S6: stripping the loaded organic phase with water and carbon dioxide, so that lithium ions are transferred from the loaded organic phase to the stripping aqueous phase; In steps S7 and S6, the stripping aqueous phase is deoiled and then calcium and magnesium are removed by resin to obtain a stripping supernatant; the stripping supernatant is pyrolyzed, crystallized, and then separated to obtain lithium carbonate solid; the pyrolysis mother liquor after cooling is returned to S6 to strip the loaded organic phase.

2. The comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite according to claim 1, characterized in that: The mass ratio of the lepidolite concentrate: calcium sulfate: potassium sulfate: calcium carbonate is 1: 0.2-0.3: 0.1-0.3: 0.05-0.

1.

3. The comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite according to claim 1, characterized in that: The lithium oxide content in the calcined lepidolite clinker is 1.2-1.6%.

4. The comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite according to claim 1, characterized in that: More than 95% of the calcined lepidolite in S1 passed through a 200-mesh sieve after being crushed.

5. The comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite according to claim 1 or 4, characterized in that: The liquid-to-solid ratio in the S1 is 2-3:1; the filter residues of the S2, S3 and S4 are used for roasting raw materials.

6. The comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite according to claim 5, characterized in that: The leaching concentration of lithium oxide in the leachate in S1 is 4.2-5.5 g / L.

7. The comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite according to claim 1, characterized in that: In step S4, the filtrate is heated to 85-95°C.

8. The comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite according to claim 1 or 7, characterized in that: In step S4, the suction filtration is 1-5 microns, and the precision filtration is 0.2-0.4 microns.

9. The comprehensive utilization method for separating and purifying lithium carbonate and potassium from low-grade lepidolite according to claim 1, characterized in that: The filtrate before the S5 extraction was adjusted to pH 12-13.5 by adding potassium hydroxide.

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