Method for comprehensive utilization of lepidolite

Abstract

The present application belongs to the technical field of lithium ore recycling, and particularly relates to a method for comprehensive utilization of lepidolite, comprising the following steps: (1) leaching the lepidolite ore powder with acid to obtain a leaching solution by filtration; (2) treating the leaching solution by nanofiltration to obtain high-pressure nanofiltration concentrated water, and performing electrodialysis on the high-pressure nanofiltration concentrated water to obtain an electrodialysis alkali liquor; (3) evaporating and concentrating the electrodialysis alkali liquor, cooling and crystallizing, and filtering to obtain lithium hydroxide monohydrate crystals and a crystallization mother liquor, introducing carbon dioxide into the crystallization mother liquor, and filtering to obtain lithium carbonate and a lithium precipitation mother liquor; (4) performing extraction on the lithium precipitation mother liquor to separate and obtain a loaded organic phase, washing the loaded organic phase with a stripping acid to obtain a stripping liquor, evaporating and crystallizing the stripping liquor to produce rubidium salt and cesium salt; (5) adjusting the pH of the metal cation concentrated water liquid generated in the nanofiltration treatment to 6.0-7.0, filtering to obtain potassium fluosilicate and a filtrate, continuously adjusting the pH of the filtrate to alkaline, and filtering to obtain aluminum hydroxide and an aluminum precipitation mother liquor.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ore recycling, and particularly relates to a method for comprehensive utilization of lepidolite. BACKGROUND

[0002] With the approaching of the target period of carbon peak and carbon neutrality of various countries, global environmental protection emission standards will become increasingly stringent, and a large amount of carbon emissions generated by traditional fossil fuel vehicles and thermal power generation will be difficult to meet the requirements of environmental protection, and the power and energy industry is facing the pressure of transformation to clean and energy-saving new industries. Therefore, in recent years, the power battery and lithium battery energy storage system industry has developed rapidly, leading to the increasing demand for lithium and its compounds, which are key raw materials for lithium batteries.

[0003] Natural lithium resources include lithium-containing salt lakes and lithium ores, etc. The advantage of lithium extraction from lithium-containing salt lakes is that the production cost is relatively low, but the corresponding lithium extraction process requires high technical requirements, the water quality of different salt lakes varies greatly, the initial investment is large, the cost recovery period is long, and the exploitation of salt lakes has higher environmental protection requirements due to the fragile natural environment of salt lakes. In comparison with salt lake lithium, ore lithium has the advantages of high grade and simple composition, and is easier to meet product standards after separation and enrichment. The disadvantage is that the production cost is relatively high. Lithium ore is mainly divided into two types of lithium ore and lepidolite. Lithium ore has simple element composition and high lithium grade, and is rich in reserves in China, but the high-cold and high-altitude mining and beneficiation environment to some extent limits its industrialized development and utilization. The lepidolite resource is rich in reserves and relatively low in mining difficulty. Unlike lithium ore, lepidolite has a low lithium grade, a complex chemical composition and fluorine, and is associated with rubidium and cesium. Fluorine elements will cause lithium loss in the lithium extraction process, affect the leaching of lithium, and directly discharge or abandon them to become pollutants. Rubidium and cesium elements have high value, and a supporting recovery process is needed to improve production income and make up for the defects of high production cost of lepidolite lithium extraction.

[0004] The existing lepidolite concentrate leaching process is mainly sulfuric acid method and sulfate method. The sulfuric acid method is to crush the lepidolite concentrate, then defluorinate at a high temperature of 870 DEG C or higher in steam, then mix concentrated sulfuric acid and calcine at 300-450 DEG C to leach lithium and other metal elements, and then produce lithium carbonate, rubidium sulfate and cesium sulfate solution after removing impurities from the leaching solution. The sulfate method needs to add sulfate to the crushed concentrate and calcine at 900 DEG C to convert mica into soluble sulfate, and then leach metal elements with dilute sulfuric acid, and the subsequent process is similar to the sulfuric acid method. The above processes inevitably have the problems of high energy consumption, generation of fluorine-containing waste gas and waste water. SUMMARY

[0005] The present application aims to at least solve one of the technical problems existing in the related art. To this end, the present application provides a method for comprehensive utilization of lepidolite, which can realize efficient leaching of lepidolite, reduce energy consumption and metal loss, and recover and utilize fluorine-containing waste materials, thereby comprehensively producing high-recovery-value metals such as lithium, aluminum, rubidium and cesium, to solve the problems of high production cost, wastewater and hazardous waste treatment inherent in the above process.

[0006] The above technical object of the present application is achieved by the following technical solution:

[0007] A method for comprehensive utilization of lepidolite, comprising the following steps:

[0008] (1) mixing lepidolite powder with leaching acid, leaching, and filtering to obtain leaching liquid and leaching residue;

[0009] (2) sequentially subjecting the leaching liquid obtained in step (1) to nanofiltration acid purification, nanofiltration cation separation and high-pressure nanofiltration concentration to obtain high-pressure nanofiltration fresh water and high-pressure nanofiltration concentrated water, and subjecting the high-pressure nanofiltration concentrated water to electrodialysis to obtain electrodialysis acid liquor and electrodialysis alkali liquor;

[0010] (3) evaporating and concentrating the electrodialysis alkali liquor obtained in step (2), then cooling and crystallizing, and filtering to obtain lithium hydroxide monohydrate crystals and a crystallization mother liquor, introducing carbon dioxide into the crystallization mother liquor, and filtering after reaction to obtain lithium carbonate and a lithium precipitation mother liquor;

[0011] (4) subjecting the lithium precipitation mother liquor obtained in step (3) to extraction to separate a loaded organic phase and a raffinate, subjecting the loaded organic phase to back extraction with back extraction acid to obtain back extraction liquid A and a primary back extraction organic phase, further back extracting the primary back extraction organic phase with back extraction acid to obtain back extraction liquid B, evaporating and crystallizing the back extraction liquid A to produce a rubidium salt, and evaporating and crystallizing the back extraction liquid B to produce a cesium salt;

[0012] (5) adjusting the pH of the metal cation concentrated water liquid generated in the nanofiltration cation separation process to 6.0-7.0, and filtering to obtain potassium fluosilicate and a filtrate, and further adjusting the pH of the filtrate to alkaline, and filtering to obtain aluminum hydroxide and an aluminum precipitation mother liquor.

[0013] In an embodiment, the method further comprises the following steps: evaporating the aluminum precipitation mother liquor obtained in step (5) to saturation of sodium salt, and separating sodium salt and potassium salt by stepwise freezing crystallization process.

[0014] In an embodiment, the method further comprises the following steps: collecting distilled water generated by evaporation and concentration of the electrodialysis alkali liquor, evaporation and crystallization of the back extraction liquid A, evaporation and crystallization of the back extraction liquid B, and evaporation of the aluminum precipitation mother liquor, and using the distilled water to dilute the leaching liquid in step (1).

[0015] In an embodiment, the process further comprises the step of: concentrating the at least one of the nanofiltration acid purification concentrated brine, the high pressure nanofiltration brine, the electrodialysis acid solution and the acidic washing water obtained after washing the leaching residue for producing the leaching acid in step (1).

[0016] In an embodiment, the acid concentration refers to concentrating the acidic waste water by one of reverse osmosis concentration process, low temperature evaporation concentration process, falling film evaporation concentration process, so as to obtain H + concentrated acid with a molar concentration of 6-8 mol / L. The acidic waste water is at least one of the nanofiltration acid purification concentrated brine, the high pressure nanofiltration brine, the electrodialysis acid solution and the acidic washing water obtained after washing the leaching residue.

[0017] In an embodiment, in step (1), the leaching acid is mixed by fluorosilicic acid and other inorganic acid, and the other inorganic acid includes at least one of hydrochloric acid, sulfuric acid and phosphoric acid.

[0018] In an embodiment, the mass ratio of the leaching acid to the lepidolite powder is (2-5):1, and the leaching acid needs to be supplemented with other inorganic acid in each cycle, and the supplementing amount is determined by the amount of other metal elements (mainly including potassium, sodium, rubidium and cesium elements) in the lepidolite powder except lithium and aluminum elements, and the supplementing amount is calculated according to 90%-200% wt of the theoretical amount required for complete combination of anions in the other inorganic acid and ions of the other metal elements.

[0019] In an embodiment, in step (1), the leaching temperature is 80-150℃, the pressure is 0.1-1.0 MPa, and the reaction time is 1-4 hours.

[0020] In an embodiment, in step (1), the molar concentration of H + in the leaching solution is 4-6 mol / L.

[0021] In an embodiment, in step (1), the leaching residue is used as a raw material for producing building materials after being washed, and generates acidic washing water, and the main components of the leaching residue are silicon dioxide and a small amount of aluminosilicate (such as sodium aluminosilicate) or fluorosilicate (such as sodium fluorosilicate), phosphosilicate, which are used as raw materials for glass, ceramic, concrete and other building materials.

[0022] In an embodiment, in step (2), the nanofiltration acid purification is performed by nanofiltration membrane on the leaching solution to obtain nanofiltration acid purification concentrated brine and nanofiltration acid purification brine, and the nanofiltration acid purification concentrated brine enters the nanofiltration cation separation step.

[0023] In an embodiment, the nanofiltration acid purification is purified by multi-stage acid-resistant nanofiltration membrane, and the typical operating environment of the acid-resistant nanofiltration membrane in the nanofiltration acid purification is: 20 wt% or less of sulfuric acid solution or hydrochloric acid solution, 30 wt% or less of phosphoric acid solution, the series connection number is 3-7, and the pre-membrane pressure is 1.0-1.5 MPa.

[0024] In an embodiment, in step (2), the nanofiltration cation separation is performed by nanofiltration membrane on the nanofiltration acid purification concentrated water to obtain metal cation dilute water and the metal cation concentrated water, and the metal cation dilute water enters the high-pressure nanofiltration concentration step.

[0025] In an embodiment, in step (2), the metal cation in the metal cation dilute water is monovalent metal cation, and the metal cation in the metal cation concentrated water is high-valence metal cation.

[0026] In an embodiment, the nanofiltration cation separation is concentrated by multi-stage acid-resistant nanofiltration membrane, and the series connection number is 3-7, and the pre-membrane pressure is 1.5-2.5 MPa.

[0027] In an embodiment, in step (2), the high-pressure nanofiltration concentration is performed by nanofiltration membrane on the metal cation dilute water to obtain the high-pressure nanofiltration dilute water and the high-pressure nanofiltration concentrated water.

[0028] In an embodiment, the high-pressure nanofiltration concentration is concentrated by multi-stage acid-resistant nanofiltration membrane, and the series connection number is 3-7, and the pre-membrane pressure is 3-6 MPa.

[0029] In an embodiment, in step (2), the electrodialysis is bipolar membrane electrodialysis, and the electrodialysis device used in the bipolar membrane electrodialysis includes a raw solution chamber, an electrodialysis alkali solution chamber, and an electrodialysis acid solution chamber, the electrodialysis alkali solution chamber is separated from the raw solution chamber by a cation membrane, the electrodialysis acid solution chamber is separated from the raw solution chamber by an anion membrane, the electrodes of the bipolar membrane electrodialysis device are titanium coated with ruthenium and iridium electrodes, and the electrode solution is selected from lithium hydroxide solution with a mass percentage concentration of 1%-4%.

[0030] In an embodiment, in the bipolar membrane electrodialysis, OH - When the concentration is increased to 1.8-2.2 mol / L, the alkali solution is discharged.

[0031] In an embodiment, in step (3), after the electrodialysis alkali solution is evaporated and concentrated to saturation of the potassium hydroxide component at room temperature, cooling crystallization is performed.

[0032] In an embodiment, in step (3), the temperature for the cooling crystallization is 10-30℃.

[0033] In an embodiment, in step (3), before the evaporation concentration, the alkali liquor from the electrodialysis is concentrated by a high-pressure reverse osmosis membrane to a lithium content of 32-37 g / L.

[0034] In an embodiment, in step (3), after the washing and drying of the lithium hydroxide monohydrate, a battery-grade lithium hydroxide monohydrate is obtained.

[0035] In an embodiment, in step (3), after the washing and drying of the lithium carbonate, a battery-grade lithium carbonate product is obtained.

[0036] In an embodiment, in step (4), before the evaporation crystallization, the stripping liquor A and the stripping liquor B are both subjected to oil removal pretreatment so that the oil content in the stripping liquor A and the stripping liquor B is reduced to below 5 mg / L.

[0037] In an embodiment, in step (4), the raffinate is subjected to oil removal pretreatment so that the oil content in the raffinate is reduced to below 5 mg / L.

[0038] In an embodiment, in step (5), the pH adjusting agent is at least one of KOH, NaOH and the raffinate.

[0039] In an embodiment, in step (5), adjusting the pH of the filtrate to alkaline refers to adjusting the pH to 8.0-9.0.

[0040] In an embodiment, in step (5), after the impurity removal pretreatment of the aluminum precipitation mother liquor by heavy metal removal resin, the potassium salt obtained by crystallization can be sold as a potassium fertilizer.

[0041] In an embodiment, in step (5), the aluminum precipitation mother liquor is directly evaporated to dryness, and a potassium salt containing a small amount of sodium salt is produced and sold as a potassium fertilizer.

[0042] In an embodiment, a method for comprehensive utilization of lepidolite includes the following steps:

[0043] S1. Leaching: leaching acid is added to lepidolite powder for low-temperature reaction, and after the reaction is completed, distilled water is added for dilution, and the leaching solution and leaching residue are separated by filtration;

[0044] S2. Nanofiltration acid purification: the leaching solution is subjected to acid purification treatment by a nanofiltration membrane to obtain nanofiltration acid purification concentrated water and nanofiltration acid purification fresh water.

[0045] S3. Nanofiltration cation separation: the nanofiltration acid purification concentrated water is subjected to cation separation treatment by a nanofiltration membrane to obtain metal cation fresh water and metal cation concentrated water.

[0046] S4. High-pressure nanofiltration concentration, bipolar membrane electrodialysis: the metal cation fresh water liquid is concentrated by high-pressure nanofiltration membrane to obtain high-pressure nanofiltration fresh water and high-pressure nanofiltration concentrated water, and the high-pressure nanofiltration concentrated water is subjected to bipolar membrane electrodialysis treatment to obtain an electrodialysis acid liquid and an electrodialysis alkali liquid;

[0047] S5. Evaporation concentration, cooling crystallization: the electrodialysis alkali liquid is subjected to evaporation concentration process treatment until the potassium hydroxide component therein is saturated at normal temperature, and then cooling crystallization is performed, and filtration is performed to obtain lithium hydroxide monohydrate crystals and a crystallization mother liquor;

[0048] S6. Carbonation lithium precipitation: carbon dioxide is introduced into the crystallization mother liquor to generate a precipitate, and after filtration, lithium carbonate and a lithium precipitation mother liquor are obtained;

[0049] S7. Multistage extraction separation, stripping: the lithium precipitation mother liquor is subjected to multistage extraction separation process treatment to obtain a loaded organic phase and a raffinate, the loaded organic phase is subjected to stripping with a stripping acid to obtain a stripping liquid A and a primary stripping organic phase, the primary stripping organic phase is further subjected to stripping with a stripping acid to obtain a stripping liquid B, and the raffinate, the stripping liquid A and the stripping liquid B are subjected to oil removal pretreatment;

[0050] S8. Evaporation crystallization: the stripping liquid A is subjected to evaporation crystallization to produce a rubidium salt, and the stripping liquid B is subjected to evaporation crystallization to produce a cesium salt;

[0051] S9. Fluorine removal, aluminum precipitation: a pH adjuster is used to adjust the pH of the metal cation concentrated water liquid to 6.0-7.0, and filtration is performed to obtain potassium fluosilicate; the pH of the filtered metal cation concentrated water liquid is continuously adjusted to be alkaline, and filtration is performed to obtain aluminum hydroxide and an aluminum precipitation mother liquor;

[0052] S10. Evaporation crystallization, freeze crystallization: the aluminum precipitation mother liquor is subjected to evaporation crystallization process, and after evaporation to saturation of a sodium salt, potassium salt and evaporation mother liquor are separated by filtration, and a step-by-step freeze crystallization process is used to separate the sodium salt and the potassium salt, and the method for producing the sodium salt and the potassium salt is not limited thereto, and the present application does not limit the process for producing the sodium salt and the potassium salt;

[0053] S11. Distilled water washing: distilled water produced in each evaporation process section is collected and used to dilute the leaching liquid in step S1 and to wash the leaching residue in step S1 (or to prepare saturated solutions of each product to wash each product), and after washing, the leaching residue is obtained and used as a raw material for producing building materials, and acidic washing water is produced;

[0054] S12. Acid concentration: the nanofiltration acid purified fresh water liquid in S2, the high-pressure nanofiltration fresh water and the electrodialysis acid liquid in S4, and the acidic washing water in S11 are respectively or collectively subjected to acid concentration treatment to obtain concentrated acid as leaching acid for reuse in the leaching step S1.

[0055] The process method of step S1 leaching is to use a mixture of fluosilicic acid and other inorganic acids as leaching acid to destroy the structure of lepidolite, so as to realize leaching, avoid high energy consumption problem caused by high temperature roasting, reduce equipment material requirement and improve the leaching rate of each valuable metal. Most of the valuable metals will be converted into soluble salts into the leaching solution, and the main components of the remaining leaching residue are silicon dioxide and a small amount of aluminum silicate (or fluosilicate, silicon phosphate), which can be used as raw materials for manufacturing building materials after washing to remove residual acid.

[0056] There are charged groups on the surface of nanofiltration membranes or in the membranes, which hinder the penetration of multivalent ions through electrostatic interaction. Based on this characteristic, nanofiltration membranes can be used to separate hydrogen ions and metal ions in solution, or to separate high and low valence metal ions, to achieve the purpose of acid purification and separation of metal ions. In order to separate various valuable metals in the leaching solution and avoid the generation of fluorine-containing wastewater, step S2 uses acid-resistant nanofiltration membrane to separate the leaching solution, recovers most of the leaching acid and fluorine element, greatly reduces the alkali consumption for pH adjustment and impurity precipitation, and avoids the problem of high energy consumption of pyrolytic defluorination treatment, reduces the requirement for reaction equipment material, and does not need to increase the fluorine-containing waste gas collection equipment. Step S3 uses acid-resistant nanofiltration membrane to separate metal cation dilute solution and high valence metal cation (mainly aluminum) concentrated solution.

[0057] The main metal elements in the metal cation dilute solution are potassium, lithium, sodium, rubidium and cesium. Step S4 uses high-pressure nanofiltration membrane to further concentrate and uses bipolar membrane electrodialysis process to produce acid solution containing mixed acid and mixed alkali solution. The bipolar membrane electrodialysis process realizes the three purposes of product defluorination purification, lithium salt solution causticization and acid recycling in one step, greatly reduces the amount of defluorination agent and acid-alkali auxiliary materials. The lithium solution after causticization is beneficial to the crystallization separation and carbonization separation of lithium element; the lithium precipitation mother liquor after causticization greatly reduces the alkali consumption for pH adjustment and saponification before extraction, so that the purity of each product is higher; the raffinate after causticization is used for defluorination and aluminum precipitation in step S9 to adjust pH, reducing the alkali consumption.

[0058] Step S5 uses the characteristics of low solubility of lithium hydroxide monohydrate to concentrate the mixed alkali solution by using alkali-resistant reverse osmosis membrane, evaporative concentration, cooling crystallization process to obtain lithium hydroxide monohydrate crystals, which can be washed and dried to prepare battery-grade lithium hydroxide monohydrate product. The crystallization mother liquor returns to the evaporation concentration process section and circulates to potassium hydroxide saturation to obtain saturated crystallization mother liquor.

[0059] Step S6 introduces carbon dioxide into the saturated crystallization mother liquor to carbonize and precipitate lithium to further improve the utilization rate of leached lithium, obtaining lithium carbonate and lithium precipitation mother liquor. The lithium carbonate can be washed and dried to prepare battery-grade lithium carbonate.

[0060] The main components of the lithium precipitation mother liquor are potassium, sodium, rubidium and cesium strong alkali, which is beneficial to improve the extraction efficiency and separation efficiency under high alkalinity conditions. The high-value rubidium salt back-extraction solution and cesium salt back-extraction solution are separated out by multi-stage extraction and back-extraction in step S7.

[0061] The alkaline raffinate is used to adjust the pH of the metal cation concentrated water solution in step S9, remove the fluorine elements in the solution by generating insoluble potassium fluosilicate, avoid the use of additional fluorine removal agent, produce aluminum hydroxide and aluminum precipitation mother liquor, reduce the alkali consumption of readjustment, and reduce the production cost.

[0062] The potassium salt and sodium salt are produced by evaporating the aluminum precipitation mother liquor in step S10. After removing trace heavy metals in the aluminum precipitation mother liquor by heavy metal adsorption resin, the potassium salt can be sold as potassium fertilizer.

[0063] The mixed acid-containing wastewater produced in each nanofiltration process section, bipolar membrane process section and residual acid washing process section can be concentrated by step S12 acid concentration process to produce concentrated acid for back use in the leaching process section, realize the recycling of fluorine elements, and avoid the treatment and discharge problems of fluorine-containing wastewater and waste gas.

[0064] The beneficial effects of the present application are:

[0065] (1) The leaching reaction conditions in the method of the present application are mild, the energy consumption is low, the valuable metal leaching rate is high, most of the fluorine-containing leaching acid is collected and reused, no additional equipment is needed for pyrolysis of leaching liquid and collection and treatment of fluorine-containing waste gas, and the alkali consumption of readjustment and impurity removal by precipitation is greatly reduced.

[0066] (2) The bipolar membrane electrodialysis process in the method of the present application realizes the three purposes of product liquid defluorination, lithium salt solution causticization and separation acid reuse in one step, greatly reduces the amount of various auxiliary materials, and reduces the production cost of lepidolite.

[0067] (3) In the method of the present application, each valuable metal in lepidolite is extracted as much as possible and prepared into qualified products, the metal loss of each mother liquor and waste liquid is extremely small, and the unit lepidolite production benefit is improved.

[0068] (4) In the method of the present application, each process product is effectively disposed, there is no fluorine-containing wastewater and waste gas discharged to the outside for treatment, each pollution element is fixed in solid material, as a product to produce economic value, green environmental protection, and friendly to the natural environment. BRIEF DESCRIPTION OF DRAWINGS

[0069] Figure 1 It is a flowchart of Example 1 of the present application;

[0070] Figure 2 It is an XRD graph of the solid waste obtained in Example 1 of the present application;

[0071] Figure 3XRD pattern of the solid waste obtained in Example 6 of the present application. DETAILED DESCRIPTION

[0072] The present application is further described below in conjunction with specific examples.

[0073] The main components of the lepidolite raw material used in the examples of the present application are shown in Table 1:

[0074] Table 1. Main components of lepidolite

[0075]

[0076] Example 1:

[0077] A method for comprehensive utilization of lepidolite, as shown in Figure 1 , comprises the following steps:

[0078] S1. Low-temperature leaching: 100-mesh lepidolite ore powder is added with leaching acid having a hydrogen ion concentration of 8 mol / L, the leaching acid is prepared by mixing fluorosilicic acid having a mass percentage concentration of 30% with concentrated sulfuric acid having a mass percentage concentration of 50%, the amount of use is 5 times the mass of the lepidolite ore powder, the reaction is carried out at 95°C and 0.2 MPa for 3 h, after the reaction is completed, the temperature is cooled to room temperature, and distilled water is added for dilution to a hydrogen ion concentration of 5 mol / L, and filtration separation is performed to obtain a leaching solution and a leaching residue;

[0079] S2. Nanofiltration acid purification: the leaching solution is subjected to acid purification using a 5-stage AR40-35 nanofiltration membrane, the pressure before the nanofiltration membrane is maintained at 1.5 MPa, and a nanofiltration acid purification concentrated water solution and a nanofiltration acid purification fresh water solution are obtained;

[0080] S3. Nanofiltration cation separation: the nanofiltration acid purification concentrated water solution is subjected to cation separation treatment using a 3-stage AR50-35 nanofiltration membrane, the pressure before the nanofiltration membrane is maintained at 2.5 MPa, and a monovalent metal cation fresh water solution and a high-valence metal cation concentrated water solution are obtained;

[0081] S4. High-pressure nanofiltration concentration and bipolar membrane electrodialysis: the monovalent metal cation fresh water solution is concentrated after high-pressure nanofiltration using a 7-stage AR10-35 high-pressure nanofiltration membrane to obtain high-pressure nanofiltration fresh water and high-pressure nanofiltration concentrated water, and the high-pressure nanofiltration concentrated water is subjected to bipolar membrane electrodialysis, the electrodialysis device used contains a raw solution chamber, an electrodialysis alkali solution chamber and an electrodialysis acid solution chamber, the electrodialysis alkali solution chamber is separated from the raw solution chamber by a cation membrane, the electrodialysis acid solution chamber is separated from the raw solution chamber by an anion membrane, the cation membrane and the anion membrane are alternately arranged, each pair of cation and anion membranes is separated by a bipolar membrane, the electrodes of the bipolar membrane electrodialysis device are titanium-coated ruthenium-iridium electrodes, and the electrode solution is lithium hydroxide solution having a mass percentage concentration of 2%, and the current density is 250 A / m 2 , after 3 h of electrodialysis, the OH -The molar concentration reaches 2.2 mol / L, and the electrodialysis acid solution and the electrodialysis alkali solution are obtained;

[0082] S5. Evaporation concentration, cooling crystallization: the electrodialysis alkali solution is treated by an evaporation concentration process, the solution volume is reduced by 60%, and after the potassium hydroxide component is saturated at room temperature, the evaporation concentrated solution is cooled to 20 DEG C, and lithium hydroxide monohydrate crystals and a crystallization mother liquor are obtained by filtration. The lithium hydroxide monohydrate crystals are washed twice with saturated lithium hydroxide solution, and dried at 90 DEG C to obtain battery-grade lithium hydroxide monohydrate with a main content of 56.9% of lithium hydroxide;

[0083] S6. Carbonization and lithium precipitation: carbon dioxide is introduced into the crystallization mother liquor until the lithium content in the filtrate is less than 100 mg / L, and after filtration, lithium carbonate and a lithium precipitation mother liquor are obtained. The lithium carbonate is washed with nitrilotriacetic acid (NTA) solution, and battery-grade lithium carbonate products with a purity of 99.5% are obtained after drying at 120 DEG C;

[0084] S7. Multi-stage extraction separation and stripping: t-BAMBP and sulfonated kerosene are mixed to form an extraction organic phase with a mass ratio of 35:65, and the lithium precipitation mother liquor is subjected to 6-stage countercurrent extraction with an extraction phase ratio (oil-water ratio) of 1.2:1 at 25 DEG C to obtain a preliminary loaded organic phase and a raffinate. The preliminary loaded organic phase is subjected to a 3-stage water washing process with a water washing phase ratio (oil-water ratio) of 1:1 to obtain a water-washed loaded organic phase and washing water. The washing water is mixed into the raffinate. The water-washed loaded organic phase is subjected to a 2-stage stripping process with a stripping phase ratio (oil-water ratio) of 2:1, and the 1st and 2nd stage stripping acids are 2 mol / L and 4 mol / L hydrochloric acid, respectively. After the 1st stage stripping, a stripping solution A is obtained, and after the 2nd stage stripping, a stripping solution B is obtained. The raffinate, the stripping solution A and the stripping solution B are subjected to oil removal pretreatment with activated carbon until the oil content is less than 5 mg / L;

[0085] S8. Evaporation crystallization: the stripping solutions A and B are subjected to evaporation crystallization to produce corresponding rubidium chloride and cesium chloride products with purities of 99.4% and 99.1%, respectively;

[0086] S9. Fluorine removal and aluminum precipitation: the raffinate after oil removal and KOH are used to adjust the pH of the high-valence metal cation concentrated water solution to 6.5 to produce potassium fluosilicate precipitate, and the precipitate is removed by filtration to obtain a fluorine-removed filtrate, and the fluorine content in the fluorine-removed filtrate is reduced to 76 mg / L. Sodium hydroxide is used to adjust the pH of the fluorine-removed filtrate to 9, and aluminum hydroxide and an aluminum precipitation mother liquor are obtained by filtration;

[0087] S10. Evaporation crystallization and freeze crystallization: the aluminum precipitation mother liquor is subjected to evaporation crystallization until the solution volume is reduced by 84%, and potassium sulfate is obtained by filtration. The K2O mass fraction in the potassium sulfate is 51%, and the freeze evaporation mother liquor is cooled to 0 DEG C for preservation and filtration to obtain sodium sulfate decahydrate crystals. Meta alum is obtained by heating the sodium sulfate decahydrate crystals to 100 DEG C for dehydration;

[0088] S11. Distilled water washing: Collect the distilled water produced in each evaporation process section, and use it to dilute the leaching solution in step S1, or to wash the leaching residue in step S1, to obtain solid waste and acidic washing water. The XRD pattern of the obtained solid waste is shown in FIG. 1, and the crystal thereof is mainly SiO2 and Na2SiF6, which is detected by XRD. The solid waste is used as a raw material for producing building materials. Figure 2

[0089] S12. Acid concentration: Perform falling film evaporation on the nanofiltration acid purified fresh water, high-pressure nanofiltration fresh water, electrodialysis acid liquid, and acidic washing water, to obtain a mixed acid liquid with a mass percentage of 33% as leaching acid for reuse to step S1.

[0090] The recovery rates of lithium, potassium, rubidium, cesium, and aluminum in a single cycle process reach 92%, 91%, 97%, 96%, and 79%, respectively.

[0091] Example 2:

[0092] A method for comprehensive utilization of lepidolite, which is performed according to the steps in Example 1, with the only difference being that:

[0093] The number of nanofiltration membrane stages in step S2 is 7;

[0094] The number of nanofiltration membrane stages in step S3 is 5;

[0095] The oil removal process in step S7 is an ozone oxidation and activated carbon combined oil removal process, and the raffinate, back-extraction liquid A, and back-extraction liquid B are pretreated for oil removal to an oil content of less than 1 mg / L;

[0096] The purity of the obtained rubidium chloride and cesium chloride products in step S8 is improved to 99.8% and 99.5%, respectively.

[0097] The recovery rates of lithium, potassium, rubidium, cesium, and aluminum in a single cycle process reach 93%, 90%, 97%, 97%, and 82%, respectively.

[0098] Example 3:

[0099] A method for comprehensive utilization of lepidolite, which is performed according to the steps in Example 1, with the only difference being that:

[0100] The low-temperature leaching reaction conditions in step S1 are 140°C, 0.4 MPa, and a reaction time of 1.5 h;

[0101] The oil removal process in step S7 is an ozone oxidation and activated carbon combined oil removal process, and the raffinate, back-extraction liquid A, and back-extraction liquid B are pretreated for oil removal to an oil content of less than 1 mg / L;

[0102] The purity of the obtained rubidium chloride and cesium chloride products in step S8 is improved to 99.7% and 99.5%, respectively.

[0103] ​In step S9, the pH of the high-valence metal cation concentrated solution after oil removal is adjusted to 7 using the raffinate to produce potassium fluosilicate precipitation, and the precipitation is removed by filtration, and the fluorine in the solution is reduced to 72 mg / L;

[0104] The recovery rates of lithium, potassium, rubidium, cesium and aluminum in the single-cycle process are 95%, 91%, 97%, 97% and 84%, respectively.

[0105] Example 4:

[0106] A method for comprehensive utilization of lepidolite, which is performed according to the steps in Example 1, with the only difference being that:

[0107] In step S2, the number of nanofiltration membrane stages is 3;

[0108] In step S5, the alkali-resistant reverse osmosis membrane is used to concentrate the electrodialysis alkali liquor to a lithium content of 34.7 g / L, and then evaporation concentration is performed to reduce the solution volume by 67%. After cooling the concentrated solution to 0°C, lithium hydroxide monohydrate crystals are obtained by filtration.

[0109] The recovery rates of lithium, potassium, rubidium, cesium and aluminum in the single-cycle process are 88%, 93%, 96%, 95% and 80%, respectively.

[0110] Example 5:

[0111] A method for comprehensive utilization of lepidolite, which is performed according to the steps in Example 1, with the only difference being that:

[0112] In step S1, the hydrogen ion concentration of the leaching acid is 6 mol / L, the leaching acid is prepared by mixing 30% fluosilicic acid with 37.5% hydrochloric acid, the amount of leaching acid is 3.5 times the mass of lepidolite powder, and the leaching reaction conditions are 100°C, 0.3 MPa, and 2 h.

[0113] In step S10, the aluminum precipitation mother liquor is subjected to evaporation crystallization to reduce the solution volume by 62%, and potassium chloride is produced as a salt. The remaining mother liquor is a mixed solution of potassium chloride and sodium chloride.

[0114] In step S12, the mixed acid is subjected to falling film evaporation to obtain a mixed acid solution with a mass percentage concentration of 29%.

[0115] The recovery rates of lithium, potassium, rubidium, cesium and aluminum in the single-cycle process are 93%, 85%, 97%, 96% and 82%, respectively.

[0116] Example 6:

[0117] A method for comprehensive utilization of lepidolite, which is performed according to the steps in Example 1, with the only difference being that:

[0118] The concentration of hydrogen ion in the leaching acid in step S1 is 8 mol / L, the leaching acid is prepared by mixing fluorosilicic acid with a mass percentage of 30% and phosphoric acid with a mass percentage of 85%, the mass of the leaching acid is twice the mass of the lepidolite powder, the leaching reaction conditions are 80°C, 0.2 MPa, and the reaction time is 4 h;

[0119] After the pH is adjusted to 6.5 in step S9, the precipitate is a mixture of aluminum phosphate and potassium fluorosilicate. After the pH is adjusted to 9, only a small amount of aluminum hydroxide containing aluminum phosphate is produced;

[0120] In step S10, the aluminum precipitation mother liquor is evaporated to produce potassium phosphate as a potassium phosphate fertilizer. The sodium salt is sodium phosphate dodecahydrate produced by cooling crystallization;

[0121] After washing in step S11, the XRD pattern of the solid waste is shown in Figure 3 The XRD detection shows that the main crystal components are silicon dioxide and silicon phosphate;

[0122] In step S12, the falling film evaporation is used to concentrate the mixed acid to a mass percentage of 32%.

[0123] The single-cycle process has a lithium, potassium, rubidium, cesium, and aluminum recovery rate of 90%, 93%, 95%, 93%, and 45%, respectively.

[0124] Comparative Example 1:

[0125] A method for comprehensive utilization of lepidolite, comprising the following steps:

[0126] S1. High-temperature calcination to remove fluorine and leaching: 10% of water is added to the lepidolite powder of Example 1, then calcined at 800°C for 1 h, the calcined product is ball milled to 100 mesh, 50% water is added to the calcined product to make a slurry, the theoretical amount of 120% nitric acid is added to the slurry, and the reaction is carried out at 100°C for 1 h, then the leaching residue and leaching solution are separated by filtration;

[0127] S2. Washing of leaching residue: the leaching residue obtained in S1 is washed and used as building materials or solid waste treatment;

[0128] S3. Nanofiltration separation: the leaching solution obtained in S1 is treated by cation separation using a 3-stage AR50-35 nanofiltration membrane, the pressure before the nanofiltration membrane is maintained at 2.5 MPa, and after the nanofiltration membrane separation, a monovalent ion nitrate solution and a multivalent ion nitrate solution are obtained;

[0129] S4. Purification of monovalent ion nitrate solution: t-BAMBP and sulfonated kerosene are mixed at a mass ratio of 35:65 to form an extraction organic phase, and the monovalent ion nitrate solution obtained in S3 is subjected to 6-stage countercurrent extraction at 25°C with an extraction phase ratio (oil / water ratio) of 1.2:1 to obtain a loaded organic phase and a raffinate. The loaded organic phase is subjected to 2-stage stripping treatment with a stripping phase ratio (oil / water ratio) of 2:1, and 4 mol / L hydrochloric acid is used as the stripping acid to obtain a stripping solution. After the stripping solution is neutralized with potassium hydroxide, the neutralized stripping solution is further purified by a two-stage selective ion exchange resin purification process to obtain a potassium adsorption solution, a rubidium-containing first resin desorption solution, a cesium-containing resin desorption solution, and a raffinate which is a lithium nitrate solution.

[0130] S5. Impurity removal of polyvalent ion nitrate solution: The polyvalent ion nitrate solution in S3 is heated to 40°C, and magnesium oxide or calcium oxide is added to adjust the pH to 7, and aluminum hydroxide is produced as a precipitate which can be used in an aluminum plant. The remaining liquid is concentrated by evaporation to obtain a calcium magnesium nitrate solution, and calcium oxide or magnesium oxide is added to adjust the concentration and proportion of the system, and then concentrated and spray granulated to produce calcium magnesium nitrate fertilizer.

[0131] S6. Bipolar membrane separation: The lithium nitrate solution obtained in S4 is concentrated, enriched, and precisely filtered, and then subjected to separation treatment by a bipolar membrane to obtain dilute nitric acid and lithium hydroxide solution. The dilute nitric acid is concentrated and recycled for use in the leaching process, and the lithium hydroxide solution is evaporated and concentrated to crystallize high-purity lithium hydroxide product.

[0132] The recovery rates of lithium, potassium, rubidium, cesium, and aluminum in a single cycle are 80%, 86%, 81%, 82%, and 87%, respectively.

[0133] In the comparative example 1, a large amount of alkali is consumed for the extraction separation of the monovalent ion nitrate solution, and the residual acid is not effectively recovered. The cost of magnesium oxide is high for the impurity removal of the polyvalent ion solution. The overall acid recovery rate is low, and the cost of adding chemicals is high. In the example, most of the residual acid is recovered by multi-stage nanofiltration separation. After the bipolar membrane separation, lithium carbonate is produced, and the lithium precipitation mother liquor is extracted to separate rubidium and cesium, two high-value metals, which reduces the operating cost of the extraction system. The sodium and potassium raffinate is directly used as a pH regulator, which reduces the consumption of alkali for impurity removal.

[0134] As can be seen from the above example and comparative example, the method improves the recovery rate of valuable metals, eliminates the calcination cost, and significantly reduces the cost of adding chemicals. No waste gas is produced, and the method has significant advantages in overall production cost and environmental friendliness.

Claims

1. A method for comprehensive utilization of lepidolite, characterized in that: Includes the following steps: (1) After mixing lepidolite powder with leaching acid, leach it and filter it to obtain leachate and leaching residue; (2) The leachate obtained in step (1) is sequentially purified by nanofiltration acid, separated by nanofiltration cation and concentrated by high pressure nanofiltration to obtain high pressure nanofiltration desalinated water and high pressure nanofiltration concentrated water. The high pressure nanofiltration concentrated water is subjected to electrodialysis to obtain electrodialysis acid solution and electrodialysis alkali solution. (3) The electrodialysis alkaline solution obtained in step (2) is evaporated and concentrated, then cooled and crystallized. The solution is filtered to obtain lithium hydroxide monohydrate crystals and crystallization mother liquor. Carbon dioxide is introduced into the crystallization mother liquor, and after reaction, the solution is filtered to obtain lithium carbonate and lithium precipitation mother liquor. (4) Extract the lithium precipitation mother liquor obtained in step (3) to separate the loaded organic phase and the raffinate. Use back-extraction acid to back-extract the loaded organic phase to obtain back-extraction liquid A and preliminary back-extraction organic phase. Use back-extraction acid to further back-extract the preliminary back-extraction organic phase to obtain back-extraction liquid B. Evaporate and crystallize the back-extraction liquid A to produce rubidium salt, and evaporate and crystallize the back-extraction liquid B to produce cesium salt. (5) Adjust the pH of the concentrated metal cation solution produced by the nanofiltration cation separation to 6.0-7.0, filter to obtain potassium fluorosilicate and filtrate, continue to adjust the pH of the filtrate to alkaline, filter to obtain aluminum hydroxide and aluminum precipitation mother liquor; evaporate the aluminum precipitation mother liquor obtained in step (5) to sodium salt saturation, and then use a stepwise freeze crystallization process to separate sodium salt and potassium salt. The method also includes the following steps: collecting the distilled water generated from the evaporation and concentration of the electrodialysis alkaline solution, the evaporation and crystallization of the back-extraction solution A, the evaporation and crystallization of the back-extraction solution B, and the evaporation of the aluminum precipitation mother liquor, and using it to dilute the leaching solution in step (1); and acid-concentrating at least one of the nanofiltration acid purification solution, the high-pressure nanofiltration solution, the electrodialysis acid solution, and the acidic wash water obtained after washing the leaching residue to prepare the leaching acid in step (1).

2. The method for comprehensive utilization of lithium mica according to claim 1, characterized in that: In step (1), the leaching acid is a mixture of fluorosilicic acid and other inorganic acids, including at least one of hydrochloric acid, sulfuric acid and phosphoric acid.

3. The method for comprehensive utilization of lithium mica according to claim 1, characterized in that: In step (1), the leaching temperature is 80-150℃, the leaching pressure is 0.1-1.0MPa, and the leaching reaction time is 1-4 hours.

4. The method for comprehensive utilization of lithium mica according to claim 1, characterized in that: In step (2), the nanofiltration acid purification is performed by acid purification of the leachate through a nanofiltration membrane to obtain nanofiltration acid purified concentrate and nanofiltration acid purified desalinated solution. The nanofiltration acid purified concentrate then enters the nanofiltration cation separation step.

5. A method for comprehensive utilization of lithium mica according to claim 4, characterized in that: In step (2), the nanofiltration cation separation is performed by using a nanofiltration membrane to separate the cations in the nanofiltration acid purification concentrate to obtain a metal cation desalination solution and the metal cation concentrate. The metal cation desalination solution then enters the high-pressure nanofiltration concentration step.

6. A method for comprehensive utilization of lithium mica according to claim 1, characterized in that: In step (4), both the back-extraction solution A and the back-extraction solution B are subjected to oil removal pretreatment before evaporation and crystallization, so that the oil content in the back-extraction solution A and the back-extraction solution B is reduced to below 5 mg / L.

7. A method for comprehensive utilization of lithium mica according to claim 1, characterized in that: In step (5), the pH adjuster is at least one of KOH, NaOH and the raffinate, and adjusting the pH of the filtrate to alkaline means adjusting the pH to 8.0-9.0.

Images