Method and device for extracting lithium from lithium ore

Abstract

The invention discloses a method and a device for extracting lithium from lithium ore. The method comprises the following steps: carrying out fine grinding, sulfuric acid leaching, primary extraction, secondary extraction, aluminum precipitation, causticization sulfate radical removal, UF impurity removal, lithium adsorption by an aluminum-based adsorbent, sulfate radical conversion by chlorine type ion exchange resin, two-stage NF divalent salt removal, RO concentration, resin calcium and magnesium removal, MVR evaporation, lithium carbonate precipitation and other technological processes on the lithium ore to obtain the battery-grade lithium carbonate. According to the method, the lixivium obtained by a lithium ore concentrated sulfuric acid leaching method is separated and purified by taking a membrane method as a technical core, and causticization reaction and sulfate radical removal by resin are assisted, so that the removal of divalent anion impurities is realized, and the problems of low lithium leaching rate and high sulfate radical content in a lithium carbonate finished product in the process of extracting lithium from the lithium ore are solved; meanwhile, the sulfuric acid is recycled. The method is simple in process, low in energy consumption, high in extraction rate, high in automation degree and low in production cost, and can be applied to large-scale production of extracting lithium from spodumene or lepidolite.

Description

Technical Field

[0001] The invention belongs to the technical field of extracting lithium from ores, and specifically relates to a method and a device for extracting lithium from lithium ore. Background Art

[0002] The production method of lithium carbonate mainly includes three parts: smelting, purification and recovery, of which smelting extracts more than 80% of lithium. The main raw materials for lithium carbonate smelting are spodumene, lepidolite and salt lake brine. Different sources of raw materials also derive different lithium extraction processes. At present, the lithium ore raw materials with industrial mining value and large-scale application are mainly spodumene and lepidolite. Spodumene often coexists with gangue minerals such as quartz and feldspar to form pegmatite spodumene ore, which is the most important and largest lithium ore resource. Spodumene has always been the main raw material for extracting lithium. It has a simple chemical composition and high lithium grade. The theoretical content of Li2O is 8.03%, but due to sodium-potassium substitution, the Li2O content is usually 2.91%-7.66%. Lepidolite, also known as "lepidolite", is a common lithium mineral. It is a basic aluminum silicate of potassium and lithium and a type of mica mineral. Lepidolite has large reserves and complex composition. Its lithium grade is lower than that of spodumene. After mining and selection of lepidolite concentrate, the Li2O content is usually 2.0-3.5%. It often contains rubidium, cesium, etc., and contains 5.9% fluorine in its composition.

[0003] The sulfuric acid method for treating spodumene concentrate is currently the most widely used process for extracting lithium from ore. The process is easy to control and the product quality is stable and reliable. After years of development and improvement, the process has become relatively mature. The basic principle of the process is to calcine the lithium concentrate at high temperature to convert α-type spodumene into β-type spodumene. Then add sulfuric acid for acidification reaction. After the reaction, add an appropriate amount of water to leach lithium sulfate. After impurity removal and concentration, the finished liquid is obtained, which reacts with soda ash to form lithium carbonate, and then demagnetizes, stirs, and dries to obtain battery-grade lithium carbonate. The main methods for extracting lithium from lithium mica include limestone roasting method, sulfuric acid roasting method, sulfate roasting method, chlorination roasting method and pressure cooking method. The current mainstream process is sulfate method. The principle of the lithium mica sulfate method is to calcine lithium mica and sulfate at high temperature in a certain proportion. The lithium in the ore is replaced by potassium or sodium in the sulfate to form soluble lithium sulfate. Then the sintered clinker is separated by water leaching to obtain lithium sulfate solution, and then the lithium carbonate product is obtained through purification, impurity removal, concentration, lithium precipitation and other processes.

[0004] At present, no matter whether the sulfate method or the sulfuric acid method is used by various lithium mining companies for lithium ore, the lithium recovery rate is low, generally between 60-75%. At the same time, the purity of lithium carbonate after extraction is low. The main problem is that the leaching at the front end cannot fully recover lithium, and the lithium loss rate is high during the impurity removal process at the back end. Summary of the invention

[0005] The purpose of the present invention is to provide a method for extracting lithium from lithium ore using an integrated membrane method. The method fully utilizes the technical advantages of the leaching method and membrane separation, significantly improves the recovery rate of lithium leached at the front end, and reduces the loss rate of lithium in the back end impurity removal process. The method has controllability, a high degree of automation, low production cost, low pollution, and a high lithium recovery rate, and can be applied to large-scale production of lithium extraction from ores.

[0006] To achieve the above object, the present invention provides the following technical solutions: In a first aspect, the present invention provides a method for extracting lithium from lithium ore, comprising the following steps: S1. Grind the lithium ore into ore powder, add acid solution and catalyst, leaching, solid-liquid separation, and obtain filter residue and leaching solution; S2, extracting the filter residue described in step S1 once, filtering, and extracting the obtained filter residue twice, filtering; S3, subjecting the filtrate obtained by filtering twice in step S2 to aluminum precipitation reaction, and filtering; S4, subjecting the filtrate obtained by filtering after the aluminum precipitation reaction in step S3 to causticization reaction and filtering; S5, the filtrate obtained after the causticizing treatment in step S4 is subjected to ultrafiltration UF, adsorption and analysis, ion exchange, primary nanofiltration NF1, secondary nanofiltration NF1, reverse osmosis RO, calcium and magnesium removal resin treatment and MVR evaporation treatment in sequence; S6. Performing lithium precipitation reaction on the concentrated mother liquor obtained after MVR evaporation in step S5 to obtain lithium carbonate.

[0007] In the above method, in step S1, the leaching solution continues to circulate and leach until a saturated leaching solution is obtained; the saturated leaching solution is subjected to aluminum precipitation reaction and filtered.

[0008] In the above method, in step S5, the concentrated solution obtained by the ultrafiltration UF and the concentrated solution obtained by the primary nanofiltration NF1 are returned for further causticization; and the concentrated solution obtained by the secondary nanofiltration NF2 is returned to the primary nanofiltration NF1.

[0009] In the above method, in step S1, the lithium ore is spodumene and / or lepidolite.

[0010] Table 1 Analysis results of main elements of lepidolite ore

[0011] In the above method, in step S1, the acid solution is concentrated sulfuric acid with a concentration of 30-90%, preferably 70%; the volume ratio of the mineral powder to the acid solution is 1: (1-10).

[0012] In the above method, in step S1, the catalyst is one or more of sodium fluoride, potassium fluoride and calcium fluoride, preferably 1% sodium fluoride; the amount of the catalyst is 1-10% of the mass of the mineral powder.

[0013] In the above method, in step S1, the operating conditions of the leaching are: solid-liquid ratio of 3:1, temperature of 90-150°C, preferably 120-150°C, stirring speed of 80-200 r / min, preferably 100 r / min, and holding time of 1-4h, preferably 90min. Preferably, the hydrogen fluoride gas generated during the leaching process is connected to a device containing sodium hydroxide solution through a gas pipe, and the concentration of the sodium hydroxide solution is 2-10%.

[0014] In the above method, in step S1, the solid-liquid separation method is plate and frame filter press or centrifuge centrifugation.

[0015] In the above method, in step S2, the conditions for the primary extraction are: water extraction, a solid-liquid ratio of (1-4):1, preferably 3:1, a temperature of 60-100°C, preferably 90°C, a stirring speed of 80-200 r / min, preferably 100 r / min, and a holding time of 20-120 min, preferably 60 min.

[0016] In the above method, in step S2, the conditions for the secondary leaching are: leaching with alkali solution, the liquid-to-solid ratio is (1-4):1, preferably 1:1, the temperature is 60-120°C, preferably 95°C, the stirring speed is 80-200 r / min, preferably 100 r / min, and the insulation time is 0.5-3h, preferably 30min; the concentration of the alkali solution is 2-10%, preferably 5%.

[0017] In the above method, in step S3, the conditions for the aluminum precipitation reaction are: adding a base to make the system pH 3-7, preferably 4; the base is one or more of sodium hydroxide, sodium bicarbonate, potassium hydroxide and calcium hydroxide.

[0018] In the above method, in step S4, the conditions of the causticizing reaction are: temperature of 30-100°C, preferably 60°C, stirring speed of 30-120 r / min, preferably 80 r / min, insulation time of 30-120 min, preferably 60 min, and system pH of 11 or above; the reagent used in the causticizing reaction is calcium hydroxide, and its addition amount is 100-150% of the molar amount of sulfate in the solution.

[0019] In the above method, in step S5, ultrafiltration (UF) is used to remove suspended matter from the filtrate, and the ultrafiltration clear liquid is used to adsorb and analyze lithium using an aluminum-based adsorbent, and the analytical liquid is used to further remove sulfate using a chlorine-type ion exchange resin to convert lithium sulfate into lithium chloride, and the lithium chloride solution is used to remove divalent ions using NF1 and NF2 two-stage nanofiltration.

[0020] The ultrafiltration membrane used in the ultrafiltration UF is one or more of a hollow fiber membrane, a tubular membrane, a ceramic membrane and a spiral membrane, the pore size of the membrane element is 20-100 nm, preferably 50 nm, and the filtration method is a continuous cross-flow method. The operating conditions in the ultrafiltration UF unit are: the inlet pressure is maintained within 5 bar.

[0021] In the above method, in step S5, the adsorption conditions are: rotating disk adsorption, the rate is 1-3 BV / h, preferably 2BV / h, and the adsorbent is an aluminum-based adsorbent; preferably, the main material of the aluminum-based adsorbent is Li2SO4.2Al(OH)3.nH2O or LiCl.2Al(OH)3.nH2O.

[0022] In the above method, in step S5, the analysis conditions are: the rate is 2-5 BV / h, preferably 3 BV / h, and the analysis liquid is water, and its conductivity is ≤10 μs / cm.

[0023] In the above method, in step S5, the conditions for the ion exchange are: using a chloride-type ion exchange resin, preferably a D72 type anion resin; an adsorption rate of 1-2 BV / h, and a resin regeneration rate of 1-2 BV / h.

[0024] In the above method, in step S5, the conditions of the primary nanofiltration NF1 and the secondary nanofiltration NF2 are: using a spiral membrane, the molecular weight cutoff of the membrane element is 100-1000Da, preferably 400Da, and the material of the membrane element is one or more of polyethersulfone, polyamide, polypropylene, polyester, polyurethane, polyvinylidene fluoride and cellulose acetate. The retention rate of monovalent salts is ≤30%, the retention rate of divalent salts is ≥98%, and the surface charge of the membrane is positive or negative; preferably, it is a Suez nanofiltration membrane.

[0025] In the above method, in step S5, water filtration is used in the treatment of the primary nanofiltration NF1 and the secondary nanofiltration NF2, and the amount of water used is 1 / 6-1 / 2 of the amount of influent water.

[0026] In the above method, in step S5, the clear liquid produced by NF2 is concentrated with lithium by reverse osmosis (RO), and the concentrated liquid is sent to the calcium and magnesium removal resin to remove the residual calcium and magnesium in the reverse osmosis concentrate, and the water produced by the resin system is concentrated with the mechanical evaporation and recompression technology (MVR) to concentrate the lithium in the resin produced water. The membrane element used in the reverse osmosis RO unit is a high-pressure reverse osmosis membrane, and the material of the membrane element is a polyamide material. The membrane element is selected with a wide flow channel, a withstand pressure of <80bar, and a retention rate of monovalent salt greater than 99%. The preferred brand is any one of Dow, Suez, and Minard.

[0027] In the above method, in step S5, the resin used for the calcium and magnesium removal resin treatment is a chelating macroporous weakly acidic cation exchange resin with an aminomethylphosphine functional group, preferably model CH-93.

[0028] In the above method, in step S5, the lithium concentration in the concentrated mother liquor obtained by the MVR evaporation treatment is 10-30 g / L.

[0029] In the above method, in step S6, the conditions of the lithium precipitation reaction are: temperature of 60-95°C, stirring rate of 60-120 r / min, insulation time of 0.5-3h, system pH of 8-9, and concentration of sodium carbonate solution of 150-300 g / L.

[0030] According to one of the specific embodiments of the present invention, the extraction method further comprises: subjecting the lithium carbonate aqueous solution obtained by the lithium precipitation reaction to centrifugation, water washing, and drying to obtain high-purity lithium carbonate powder; the drying device can be a spray dryer, a disc dryer, a flash dryer, a vacuum dryer, etc. After the drying, the lithium carbonate powder is obtained, and its purity reaches more than 99.5%.

[0031] In a second aspect, the present invention provides an extraction device for implementing the above method, comprising the following units connected in sequence: a grinding unit, a leaching unit, a solid-liquid separation unit, a primary leaching unit, a secondary leaching unit, an aluminum precipitation unit, a causticizing unit, an ultrafiltration UF unit, an adsorption unit, a chlorine-type ion exchange resin unit, a primary nanofiltration NF1 unit, a secondary nanofiltration NF2 unit, a reverse osmosis RO unit, a calcium and magnesium removal resin unit, an MVR evaporation unit, and a lithium precipitation reaction unit; The saturated leaching solution outlet of the solid-liquid separation unit is connected to the inlet pipeline of the aluminum precipitation unit; The filtrate outlet of the primary leaching unit is connected to the inlet pipeline of the aluminum precipitation unit.

[0032] The leaching liquid outlet of the solid-liquid separation unit is connected to the inlet pipeline of the leaching unit; The concentrated solution outlet of the ultrafiltration UF unit is connected to the inlet pipeline of the causticization reaction; The concentrate outlet of the primary nanofiltration NF1 unit is connected to the inlet pipeline of the causticizing reaction; The concentrate outlet of the secondary nanofiltration NF2 unit is connected to the inlet pipeline of the primary nanofiltration NF1 unit.

[0033] Compared with the prior art, the present invention has the following beneficial effects: In the present invention, the lithium ore is subjected to the process of grinding, sulfuric acid leaching, primary leaching, secondary leaching, aluminum precipitation, causticizing to remove sulfate radicals, UF impurity removal, aluminum-based adsorbent adsorption of lithium, conversion of sulfate radicals by chlorine-type ion exchange resin, removal of divalent salts by two-stage NF, RO concentration, resin removal of calcium and magnesium, MVR evaporation and precipitation of lithium carbonate. The whole system has strong stability, high controllability and high automation. Compared with the prior art, the method has the advantages of low energy consumption, low investment, high recovery rate and high purity of lithium carbonate, realizes the extraction of battery-grade lithium carbonate from lithium ore, provides a new process for lithium extraction technology from ore, solves the existing technical problems and creates higher value for lithium resource development at home and abroad. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A process diagram of a method for extracting lithium using an integrated membrane method using lithium ore leaching solution as a raw material provided by the present invention. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0036] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0037] Unless otherwise specified, the reagents, materials, instruments, etc. used in the following examples can be obtained from commercial sources.

[0038] Example 1: A device for extracting lithium from lithium ore The device comprises the following units connected in sequence: a grinding unit, a leaching unit, a solid-liquid separation unit, a primary leaching unit, a secondary leaching unit, an aluminum precipitation unit, a causticizing unit, an ultrafiltration UF unit, an adsorption unit, a chlorine-type ion exchange resin unit, a primary nanofiltration NF1 unit, a secondary nanofiltration NF2 unit, a reverse osmosis RO unit, a calcium and magnesium removal resin unit, an MVR evaporation unit, and a lithium precipitation reaction unit; wherein: The leachate outlet of the solid-liquid separation unit is connected to the inlet pipeline of the leaching unit; the saturated leachate outlet of the solid-liquid separation unit is connected to the inlet pipeline of the aluminum precipitation unit; the filtrate outlet of the primary leaching unit is connected to the inlet pipeline of the aluminum precipitation unit; the concentrate outlet of the ultrafiltration UF unit is connected to the inlet pipeline of the causticizing reaction; the concentrate outlet of the primary nanofiltration NF1 unit is connected to the inlet pipeline of the causticizing reaction; the concentrate outlet of the secondary nanofiltration NF2 unit is connected to the inlet pipeline of the primary nanofiltration NF1 unit.

[0039] In the device: The ultrafiltration membrane used in the ultrafiltration UF unit is one or more of a hollow fiber membrane, a tubular membrane, a ceramic membrane and a spiral membrane. The pore size of the membrane element is 20-100 nm, preferably 50 nm. The filtration method is a continuous cross-flow method.

[0040] The adsorption device used in the adsorption unit is a rotary disc adsorption device, and the adsorption device is filled with an aluminum-based adsorbent; preferably, the main material of the aluminum-based adsorbent is Li2SO4.2Al(OH)3.nH2O or LiCl.2Al(OH)3.nH2O.

[0041] The resin used in the chloride-type ion exchange resin unit is an anion resin, preferably a D72 anion resin.

[0042] The membrane elements used in the primary nanofiltration NF1 unit and the secondary nanofiltration NF2 unit are rolled membranes, the filtration method is continuous cross-flow, the membrane element has a molecular weight cutoff of 100-1000Da, preferably 400Da, and the material is one or more of polyethersulfone, polyamide, polypropylene, polyester, polyurethane, polyvinylidene fluoride and cellulose acetate; the retention rate of monovalent salts is ≤30%, the retention rate of divalent salts is ≥98%, and the surface charge of the membrane is positive or negative; preferably, it is a Suez nanofiltration membrane.

[0043] The reverse osmosis membrane used in the reverse osmosis RO unit is a high-pressure reverse osmosis membrane. The material of the membrane element is polyamide material. The membrane element is selected with a wide flow channel, the withstand pressure is <80bar, the retention rate of monovalent salt is greater than 99%, and the brand is Dow.

[0044] The calcium-magnesium-removal resin used in the calcium-magnesium-removal resin unit is a chelating macroporous weakly acidic cation exchange resin with an aminomethylphosphine functional group, preferably model CH-93.

[0045] Example 2: A method for extracting lithium using an integrated membrane process using lithium ore leachate as a raw material Process flow such as Figure 1 As shown, the following steps are included: S1. Grinding-leaching: The lithium mica ore is ground by a ball mill to control the particle size to -200 mesh to obtain lithium mica ore powder; Pour the mineral powder into the reactor of the leaching unit, which is lined with polytetrafluoroethylene. Add 70% concentrated sulfuric acid, control the solid-liquid ratio to 3:1, and add 1% sodium fluoride as a catalyst. Seal the reactor, open the exhaust gas outlet of the reactor, use 5% sodium hydroxide solution to absorb the hydrogen fluoride gas produced by the reaction, and use silicone oil to heat the reactor to control the temperature between 120-150°C. Turn on the reactor stirring device, control the stirring speed at 100r / min, and keep the reactor warm for 90min to obtain a mixture of leaching solution and slag.

[0046] S2, solid-liquid separation - primary leaching - secondary leaching - aluminum precipitation: The mixture is separated by centrifugation to obtain a leachate and a filter residue; the filter residue is sent to a primary leaching unit and a secondary leaching unit for leaching, and the leachate is monitored in real time. If the content of lithium ions in the leachate is not saturated, it is returned to the leaching unit to continue leaching the ore powder. After repeating this process 6-7 times, the content of lithium ions in the leachate reaches saturation, and a saturated leachate is obtained, which is sent to a primary leaching unit and a secondary leaching unit; The filter residue slag is mixed with pure water in a solid-liquid ratio of 3:1 for primary leaching, the pure water temperature is 90°C, and a reactor is used at a stirring speed of 100 r / min and a holding time of 60 min to obtain a mixture of a primary filtrate and slag; after centrifugal separation, the primary leached slag is mixed with 5% sodium hydroxide solution in a liquid-solid ratio of 1:1 for secondary leaching, and a reactor is used at a stirring speed of 100 r / min, the alkali solution temperature is controlled at 95°C, and the holding time is 30 min to obtain a mixture of a secondary filtrate and secondary leached slag.

[0047] The filtrates obtained from the two times are mixed with the saturated leaching solution, and sent to an aluminum precipitation unit to add sodium bicarbonate to perform an aluminum precipitation step, and the pH is adjusted to 4 to obtain a mixed solution containing aluminum hydroxide precipitation, which is subjected to solid-liquid separation to obtain a lithium sulfate mixed filtrate containing a small amount of potassium sulfate and sodium sulfate; S3, causticization-UF: The obtained lithium sulfate mixed filtrate is sent to a causticizing unit, and a calcium hydroxide solution is added. The amount of calcium hydroxide added is calculated according to the amount of calcium required for all the generated calcium sulfate. Considering the solubility of calcium hydroxide, it is actually added at 120%. The obtained solution is stirred at 60°C and a stirring speed of 80r / min for 60 minutes, and solid-liquid separation is performed by centrifugation or plate and frame filter pressing. The sulfate removal rate is achieved by this method to be above 90%; the pH of the filtrate after solid-liquid separation reaches above 11, and small suspended matter remains; The filtrate is sent to the ultrafiltration UF unit, and is directly clarified by a tubular membrane (UF) made of PTFE (polytetrafluoroethylene). The selected membrane pore size is 50nm, and the filtration method adopted by the entire membrane device is continuous cross-flow. The inlet pressure is maintained within 5bar; after clarification by the tubular membrane, tubular membrane clear liquid and tubular membrane concentrated liquid are obtained. Part of the lithium sulfate is retained in the tubular membrane concentrated liquid, and the tubular membrane concentrated liquid is returned to the reactor of the causticizing unit to increase the recovery rate of lithium.

[0048] S4, adsorption-chlorine type ion exchange resin replacement: The obtained tubular membrane clear liquid is sent to the adsorption device of the adsorption unit. The device is a turntable type, and the device is filled with an aluminum-based adsorbent. The adsorbent has specific adsorption for lithium ions, and the adsorption amount of lithium can reach 5 mg / g. After 10 cycles of use, the dissolution rate of the adsorbent is less than 5%; after the tubular membrane clear liquid enters the adsorption device, the adsorption rate of the adsorption device is controlled at 2BV / h. During the adsorption process, the lithium ion content in the solution flowing out of the adsorption outlet is monitored to determine whether the adsorbent is saturated. When the resin adsorption is saturated, desorption begins, and the adsorbent after adsorption is desorbed using pure water. The conductivity of the pure water used in this step is ≤10μs / cm, and the desorption rate is 3BV / h. The sulfate content in the solution desorbed by the adsorbent is reduced to 10% of the original; The lithium sulfate analysis solution (water produced by the adsorption device) is continuously fed into the ion resin column of the chlorine-type ion resin unit, and the sulfate in the desorption solution is replaced by anion resin. The anion resin is of model D72, and the resin is converted by brine to a chlorine-type resin. After the lithium sulfate analysis solution passes through the anion resin, the sulfate in the solution is adsorbed, and the chlorine on the resin is exchanged out, and exists in the solution as chloride ions to form a lithium chloride solution. After the adsorbed resin is regenerated by 5% brine, the resin can be reused. The adsorption rate of this step is controlled at 1BV / h, and the resin regeneration rate is controlled at 1BV / h. After the chlorine-type ion resin is treated, the removal rate of sulfate reaches 99%. The step of adsorbing sulfate by the chlorine-type anion ion resin is placed after the aluminum-based adsorption, and the main purpose is to reduce the processing volume of the ion resin.

[0049] S5, NF1-NF2-RO-calcium and magnesium removal resin: The lithium chloride solution is sent to the first-level nanofiltration NF1 unit, and the monovalent / divalent salts are separated by a nanofiltration membrane. The membrane surface is negatively charged, the material is polyamide, the molecular weight cutoff is 400Da (Dalton), the monovalent salt interception rate is ≤30%, and the divalent salt interception rate is ≥98%. The membrane brand is Suez. The device uses cross-flow filtration to filter the solution. The operating pressure of the device is 25bar, and the temperature is controlled at 25-30℃. The clear liquid on the permeation side of the nanofiltration membrane and the concentrated liquid on the interception end are collected separately, and the recovery rate of the clear liquid is controlled between 70-80%. Pure water is added to dialyze the lithium chloride in the concentrated liquid while filtering to increase the recovery rate of lithium chloride. The amount of pure water added is 1 / 3 of the water intake of the first-level nanofiltration. The concentrated liquid produced by NF1 treatment is returned to the causticizing reactor to improve the recovery rate of lithium. The sulfate content in the clear liquid produced by NF1 treatment is less than 50mg / L, the calcium ion content is less than 10mg / L, and the recovery rate of lithium chloride is greater than 95%.

[0050] The obtained primary nanofiltration clear liquid is sent to the secondary nanofiltration NF2 unit to remove the residual divalent ions. The secondary nanofiltration NF2 unit uses nanofiltration membrane elements of the same material and molecular weight cutoff as NF1, and the operating pressure and recovery rate are the same as NF1. The concentrated liquid produced by the NF2 membrane system is mixed with the influent water of NF1 and processed together; The clear liquid produced by NF2 is concentrated with lithium chloride using a reverse osmosis RO unit to reduce the energy consumption required for subsequent evaporation. The reverse osmosis system uses a high-pressure reverse osmosis membrane that can withstand up to 80 bar and has a monovalent salt retention rate greater than 99%. The membrane element brand is Dow. The NF2 clear liquid is concentrated using RO, and the concentration multiple is controlled at about 3 times. The operating pressure of the RO system is between 30-50 bar; The concentrated solution produced by the concentrated solution end of the RO system is sent to the calcium and magnesium removal resin system for de-hardening treatment. The main purpose of this step is to finely remove impurities to improve the quality of lithium carbonate. The resin selected for the calcium and magnesium removal resin system is a chelated macroporous weakly acidic cation exchange resin with aminomethylphosphine functional groups, model CH-93. The calcium and magnesium content in the produced water after resin treatment is less than 1mg / L.

[0051] S4, MVR evaporation-lithium precipitation: The produced water from the calcium and magnesium removal resin system is sent to the MVR evaporation unit for evaporation and concentration. The evaporation material temperature of the MVR evaporation unit is 95°C, the secondary steam temperature is 86°C, the condensed water outlet temperature is 65°C, and the evaporation pressure is -40kpa. The concentration multiple of the system is 2-3 times, and the lithium ion content in the obtained evaporation mother liquor solution is 10000-20000 mg / L.

[0052] The obtained evaporated mother liquor solution is sent to the device of the lithium precipitation reaction unit for lithium precipitation reaction, 250g / L sodium carbonate solution is added to the lithium precipitation device, and the pH is adjusted to 9, which is judged as the lithium precipitation end point. At the same time, the lithium precipitation device has stirring and heat preservation functions. When lithium precipitation is carried out, the stirring rate is required to be 80r / min, the temperature is controlled at 90°C, and the heat preservation time is 40min; The obtained mixed solution containing lithium carbonate precipitate is dehydrated by plate and frame filter pressing, and pure water is added for washing during the filtration to remove the sodium chloride wrapped in lithium carbonate, and the washed solution is returned to the MVR water inlet. The obtained lithium carbonate solid is sent to the flash dryer for drying, and the drying temperature of the dryer is controlled at 120°C to finally obtain lithium carbonate powder; MVR evaporation condensate and RO produced water are used as NF1 filter washing water and washing water in lithium carbonate solution plate and frame filter pressing.

[0053] After testing, the purity of lithium carbonate powder is ≥99.5%, and the impurity content meets the battery grade requirements. The recovery rate of lithium using the above method is over 90%.

[0054] The above is a detailed introduction to the present invention, which provides a method for extracting lithium by membrane method using lithium ore leachate as raw material. Specific process technology is applied in this article to describe the principle and implementation mode of the present invention. The above example description is only to help understand the core idea and method of the present invention. It should be pointed out that the technicians in this technical field can improve and modify the present invention without departing from the principle of the present invention, but these improvements and modifications are also within the scope of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims, including other implementation cases that the technicians in this technical field can think of.

Claims

1. A method for extracting lithium from lithium ore, comprising the following steps: S1. Grind the lithium ore to obtain ore powder, add acid solution and catalyst, leaching, solid-liquid separation, and obtain filter residue and leaching solution; S2, extracting the filter residue in step S1 once, filtering, and extracting the obtained filter residue twice, filtering; S3, subjecting the filtrate obtained by the first leaching and filtering and the second leaching and filtering in step S2 to aluminum precipitation reaction and filtering; S4, subjecting the filtrate obtained by filtering after the aluminum precipitation reaction in step S3 to causticization reaction and filtering; S5, the filtrate obtained after the causticizing treatment in step S4 is subjected to ultrafiltration UF, adsorption and analysis, ion exchange, primary nanofiltration NF1, secondary nanofiltration NF1, reverse osmosis RO, calcium and magnesium removal resin treatment and MVR evaporation treatment in sequence; S6. Performing lithium precipitation reaction on the concentrated mother liquor obtained after MVR evaporation in step S5 to obtain lithium carbonate.

2. The method according to claim 1, characterized in that: In step S1, the leaching solution continues to circulate and leach until a saturated leaching solution is obtained; the saturated leaching solution is subjected to aluminum precipitation reaction and filtered; In step S5, the concentrated solution obtained by the ultrafiltration UF and the concentrated solution obtained by the primary nanofiltration NF1 are returned for further causticization; and the concentrated solution obtained by the secondary nanofiltration NF2 is returned to the primary nanofiltration NF1.

3. The method according to claim 1 or 2, characterized in that: The conditions in step S1 are as follows: The lithium ore is spodumene and / or lepidolite; The particle size of the mineral powder is less than 200 mesh; The acid solution is concentrated sulfuric acid with a concentration of 30-90%; the volume ratio of the mineral powder to the acid solution is 1:(1-10); The catalyst is one or more of sodium fluoride, potassium fluoride and calcium fluoride, and the amount of the catalyst is 1-10% of the mass of the ore powder; The leaching conditions are: solid-liquid ratio of 3:1, temperature of 90-150°C, stirring speed of 80-200 r / min, and insulation time of 1-4h; The solid-liquid separation method is plate and frame filter press or centrifuge.

4. The method according to any one of claims 1 to 3, characterized in that The conditions in step S2 are as follows: The conditions of the primary extraction are: using water for extraction, the solid-liquid ratio is (1-4): 1, the temperature is 60-100°C, the stirring speed is 80-200 r / min, and the insulation time is 20-120min; The conditions for the secondary extraction are: leaching with alkali solution, a liquid-to-solid ratio of (1-4):1, a temperature of 60-120°C, a stirring speed of 80-200 r / min, and a heat preservation time of 0.5-3h; the concentration of the alkali solution is 2-10%.

5. The method according to any one of claims 1 to 4, characterized in that The conditions in step S3 are as follows: The conditions of the aluminum precipitation reaction are: adding alkali to make the system pH 3-7; The alkali is one or more of sodium hydroxide, sodium bicarbonate, potassium hydroxide and calcium hydroxide.

6. The method according to any one of claims 1 to 5, characterized in that The conditions in step S4 are as follows: The causticizing reaction conditions are: temperature of 30-100°C, stirring speed of 30-120 r / min, insulation time of 30-120 min, and system pH of 11 or above; The reagent used in the causticizing reaction is calcium hydroxide, and its addition amount is 100-150% of the molar amount of sulfate in the solution.

7. The method according to any one of claims 1 to 6, characterized in that The conditions in step S5 are as follows: The conditions of the ultrafiltration UF are: the inlet pressure is maintained within 5 bar, the ultrafiltration membrane is one or more of a hollow fiber membrane, a tubular membrane, a ceramic membrane and a spiral membrane, and the pore size of the membrane element is 20-100 nm; The adsorption conditions are: rotating disk adsorption, rate of 1-3 BV / h, and the adsorbent is an aluminum-based adsorbent; The conditions for the analysis are: a rate of 2-5 BV / h, the analysis liquid is water, and its conductivity is ≤10μs / cm; The conditions of the ion exchange are: using chlorine-type ion exchange resin, the adsorption rate is 1-2BV / h, and the resin regeneration rate is 1-2BV / h; The conditions of the primary nanofiltration NF1 and the secondary nanofiltration NF2 are: using a spiral membrane, the molecular weight cutoff of the membrane element is 100-1000Da, and the material of the membrane element is one or more of polyethersulfone, polyamide, polypropylene, polyester, polyurethane, polyvinylidene fluoride and cellulose acetate; using water for filtration, and the amount used is 1 / 6-1 / 2 of the water intake; The reverse osmosis RO conditions are: using a high-pressure reverse osmosis membrane, and the material of the membrane element is a polyamide material; The conditions for the calcium and magnesium removal resin treatment are as follows: the resin is a chelated macroporous weakly acidic cation exchange resin with an aminomethylphosphine functional group; The lithium concentration in the concentrated mother liquor obtained by the MVR evaporation process is 10-30 g / L.

8. The method according to any one of claims 1 to 7, characterized in that The conditions in step S6 are as follows: The conditions of the lithium precipitation reaction are: temperature of 60-95°C, stirring rate of 60-120 r / min, insulation time of 0.5-3h, system pH of 8-9, and concentration of sodium carbonate solution of 150-300 g / L.

9. An extraction device for implementing the method according to any one of claims 1 to 8, comprising the following units connected in sequence: a grinding unit, a leaching unit, a solid-liquid separation unit, a primary leaching unit, a secondary leaching unit, an aluminum precipitation unit, a causticizing unit, an ultrafiltration UF unit, an adsorption unit, a chlorine-type ion exchange resin unit, a primary nanofiltration NF1 unit, a secondary nanofiltration NF2 unit, a reverse osmosis RO unit, a calcium and magnesium removal resin unit, an MVR evaporation unit, and a lithium precipitation reaction unit; The saturated leaching solution outlet of the solid-liquid separation unit is connected to the inlet pipeline of the aluminum precipitation unit; The filtrate outlet of the primary leaching unit is connected to the inlet pipeline of the aluminum precipitation unit.

10. The extraction device according to claim 9, characterized in that The extraction liquid outlet of the solid-liquid separation unit is connected to the inlet pipeline of the leaching unit; The concentrated solution outlet of the ultrafiltration UF unit is connected to the inlet pipeline of the causticization reaction; The concentrate outlet of the primary nanofiltration NF1 unit is connected to the inlet pipeline of the causticizing reaction; The concentrate outlet of the secondary nanofiltration NF2 unit is connected to the inlet pipeline of the primary nanofiltration NF1 unit.

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