Method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate

Abstract

The application discloses a method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate, and belongs to the technical field of chemical industry. The method comprises the following steps: reacting industrial-grade lithium carbonate with a hydrochloric acid solution to generate a lithium chloride solution; adding oxalic acid and a lithium hydroxide solution to remove impurities chemically under the condition of temperature rise; then, performing ultrafiltration and nanofiltration in sequence; treating the lithium chloride nanofiltration permeate liquid with an ion exchange resin to obtain a purified lithium chloride solution; obtaining a lithium hydroxide solution, a dilute hydrochloric acid solution and a dilute lithium chloride solution through bipolar membrane electrodialysis of the purified lithium chloride solution; obtaining a lithium hydroxide concentrate and a dilute lithium hydroxide solution through homogeneous membrane electrodialysis of the lithium hydroxide solution, adding lithium carbonate seed crystals to the lithium hydroxide concentrate, and introducing carbon dioxide gas to generate a lithium carbonate slurry; and obtaining high-purity lithium carbonate products through centrifugal dewatering, washing and drying of the lithium carbonate slurry. The method has high impurity removal rate, widens the limitation of raw materials, guarantees the quality of lithium carbonate, has low three-waste emission, and realizes efficient recycling and utilization of resources.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and particularly relates to a method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate. Background Art

[0002] Lithium carbonate plays a pivotal role among lithium compounds and is widely used in glass, ceramics, medicine, batteries, and other fields. In recent years, with the growing global demand for high-purity lithium salts in new energy and new materials, the demand for 4N high-purity lithium carbonate has also been growing.

[0003] At present, the production process of high-purity lithium carbonate generally adopts industrial-grade lithium carbonate to react with water and carbon dioxide to form a soluble lithium bicarbonate solution, remove insoluble matter by filtration, and then use chelating resin to remove divalent metal ions to obtain pure lithium bicarbonate solution. The lithium bicarbonate solution is heated and decomposed to precipitate battery-grade lithium carbonate. The battery-grade lithium carbonate is slurried with water and reacted with carbon dioxide again to produce soluble lithium bicarbonate. It is filtered, impurities are removed by chelating resin, and high-purity lithium carbonate is obtained by heating and decomposition. This method has the following defects: (1) the quality requirements of industrial-grade lithium carbonate raw materials are high; (2) lithium bicarbonate is unstable and easily precipitates during the process, which is easy to clog pipelines. In particular, during the operation of the resin impurity removal system, the unstable precipitation of lithium bicarbonate causes serious chelating resin hardening, and the resin regeneration and washing consumes a large amount of acid, resulting in a large amount of pickling wastewater; (3) the solubility of lithium bicarbonate solution is low, and the amount of lithium bicarbonate solution required to produce a ton of lithium carbonate is large, resulting in a thermal decomposition process and high steam consumption; (4) the reactor wall is seriously blocked, affecting the heat transfer efficiency; (5) the first-time yield is low and the recovery rate is low.

[0004] Therefore, providing a method for producing high-purity lithium carbonate using industrial-grade lithium carbonate as raw material, which has low requirements for raw materials, high finished product yield, and low three-waste emissions, has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate, wherein the lithium carbonate product obtained by the method has high purity, high lithium recovery rate, low by-products, and an environmentally friendly process. To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] The present invention discloses a method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate, comprising the following steps:

[0007] S1. Dissolution: Industrial-grade lithium carbonate is reacted with hydrochloric acid solution to produce lithium chloride solution;

[0008] S2 chemical impurity removal: The lithium chloride solution obtained in step S1 was heated, oxalic acid and lithium hydroxide solution were added sequentially to react for chemical impurity removal;

[0009] S3 ultrafiltration: The lithium chloride solution in step S2 was subjected to ultrafiltration after chemical impurity removal to obtain lithium chloride ultrafiltration permeate and ultrafiltration concentrate;

[0010] S4 nanofiltration: The lithium chloride ultrafiltration permeate obtained in step S3 was subjected to nanofiltration to obtain lithium chloride nanofiltration permeate and nanofiltration concentrate, respectively;

[0011] S5 ion exchange: The lithium chloride nanofiltration permeate obtained in step S4 is treated with an ion exchange resin to obtain a purified lithium chloride solution;

[0012] S6 bipolar membrane electrodialysis: The lithium chloride purified solution obtained in step S5 was subjected to bipolar membrane electrodialysis to obtain lithium hydroxide solution, dilute hydrochloric acid solution, dilute lithium chloride solution;

[0013] S7. Homogeneous membrane electrodialysis: The lithium hydroxide solution obtained in step S6 is subjected to homogeneous membrane electrodialysis to obtain a lithium hydroxide concentrate and a dilute lithium hydroxide solution.

[0014] S8 carbonization: The lithium hydroxide concentrate obtained in step S7 is added to lithium carbonate seed crystals, and carbon dioxide gas is introduced into the reaction to generate a lithium carbonate slurry;

[0015] S9. Centrifugal separation and drying: The lithium carbonate slurry prepared in step S8 is centrifuged, dehydrated, and washed to obtain wet lithium carbonate and centrifuge mother liquor; the wet lithium carbonate is dried to obtain a high-purity lithium carbonate product.

[0016] In some embodiments of the present invention, the lithium concentration in the lithium chloride solution generated in S1 is 11-16 g / L;

[0017] Preferably, the concentration of the hydrochloric acid solution in step S1 is 1.5-2 mol / L.

[0018] In some embodiments of the present invention, in S2, the lithium chloride solution is heated to 40-60°C;

[0019] Preferably, the reaction endpoint controls the c(C2O4 2- )1.5~2.5g / L, c(OH - )1~3g / L; Preferably, in step S2, the lithium hydroxide solution produced by bipolar membrane electrodialysis is added for chemical impurity removal.

[0020] In the present invention, by controlling the C2O4 2- and OH - content, ensuring the removal effect of impurities while taking into account the cost of impurity removal and the impact on subsequent use.

[0021] In some embodiments of the present invention, in S3, the pore size of the ultrafiltration membrane is 0.02 to 0.2 μm;

[0022] Preferably, the ultrafiltration concentrate enters the plate and frame filter press for filtration, the clear liquid obtained by filtration is returned to the ultrafiltration raw material tank, and the plate and frame filter press residue is discharged from the system.

[0023] In some embodiments of the present invention, in S4, the nanofiltration concentrate is returned to step S2 for chemical impurity removal again;

[0024] Preferably, the pH value of the lithium chloride ultrafiltration permeate is adjusted to 4 to 7 before the nanofiltration treatment.

[0025] The nanofiltration concentrate is enriched with a large amount of oxalate, calcium, magnesium and other ions. Therefore, the pH value of the lithium chloride ultrafiltration permeate needs to be adjusted to 4-7 before nanofiltration treatment to avoid oxalate precipitation. The excess oxalate can replace part of the oxalic acid and be used as an impurity remover for S2.

[0026] In some embodiments of the present invention, in S5, the lithium chloride purified solution has Ca≤0.02ppm, Mg≤0.01ppm, B≤5ppm, and Si≤1ppm;

[0027] Preferably, the ion exchange resin is composed of a chelating resin for removing calcium and magnesium and a chelating resin for removing boron; the ion exchange process is to remove calcium and magnesium first and then remove boron.

[0028] Preferably, the pH of the lithium chloride nanofiltration permeate is adjusted to 8.5-9.5 before entering the ion exchange resin; more preferably, the lithium hydroxide solution produced by the bipolar membrane is used to adjust the pH of the lithium chloride nanofiltration permeate to 8.5-9.5.

[0029] In some embodiments of the present invention, the concentration of the lithium hydroxide solution obtained in S6 is 36 to 50 g / L; the concentration of the dilute hydrochloric acid solution is 1.5 to 2 mol / L, and the lithium concentration in the dilute lithium chloride solution is 3 to 5 g / L;

[0030] Preferably, the dilute hydrochloric acid solution is returned to step S1 for use;

[0031] Preferably, the dilute lithium chloride solution is subjected to acid-resistant reverse osmosis treatment to obtain a lithium chloride concentrate and a lithium chloride permeate. More preferably, the lithium concentration in the lithium chloride concentrate is 6 to 10 g / L, and the lithium concentration in the lithium chloride permeate is 0.6 to 1 g / L. More preferably, the lithium chloride concentrate is returned to step S6 and mixed with the lithium chloride purification solution to serve as the feed solution for bipolar membrane electrodialysis. More preferably, the lithium chloride permeate serves as the receiving solution for the dilute hydrochloric acid generated by the bipolar membrane electrodialysis.

[0032] In some embodiments of the present invention, the concentration of the lithium hydroxide concentrate obtained in S7 is 75 to 96 g / L;

[0033] Preferably, the concentration of the lithium hydroxide dilute solution obtained in S7 is 10 to 20 g / L;

[0034] Preferably, the lithium hydroxide dilute solution obtained in step S7 is returned to the alkali circulation tank of the bipolar membrane electrodialysis in step S6 to serve as a receiving solution for the lithium hydroxide produced by the bipolar membrane electrodialysis.

[0035] In some embodiments of the present invention, in S8, the concentrated lithium hydroxide solution is heated to 50-60° C., and high-purity lithium carbonate is added as a seed crystal;

[0036] Preferably, the carbon dioxide includes the carbon dioxide produced in step S1;

[0037] Preferably, in said S8, during the carbonization reaction, the reaction temperature is controlled to be 50-60°C;

[0038] Preferably, the addition rate of lithium hydroxide and carbon dioxide is controlled to maintain the hydroxide concentration in the reaction system at 15 to 30 g / L;

[0039] Preferably, the amount of seed crystals added is 1 to 10% of the mass of the generated lithium carbonate.

[0040] In some embodiments of the present invention, the centrifugal mother liquor obtained in S9 is subjected to nanofiltration treatment to obtain nanofiltration concentrate of the centrifugal mother liquor and nanofiltration permeate of the centrifugal mother liquor, respectively;

[0041] Preferably, the concentrated water from the centrifuged mother liquor is returned to step S2 to replace part or all of the lithium hydroxide for lithium chloride impurity removal;

[0042] Preferably, the alkaline circulation tank of the bipolar membrane electrodialysis of the centrifuged mother liquor nanofiltration permeate step S6 serves as the receiving liquid for the lithium hydroxide produced by the bipolar membrane electrodialysis;

[0043] Preferably, the nanofiltration membrane used for centrifuging the mother liquor is an alkali-resistant nanofiltration membrane, and the cut-off molecular weight of the membrane is 100 to 1000 Daltons.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The present invention is scientifically designed and ingeniously conceived. It combines chemical impurity removal, membrane separation impurity removal, chelate resin impurity removal and other methods to achieve a high impurity removal rate, broaden the limitations of raw materials, and ensure the quality of lithium carbonate. The introduction of membrane separation impurity removal in the present invention greatly reduces the load of resin impurity removal, reduces the frequency of resin regeneration, and reduces the amount of regeneration wastewater. The lithium chloride purification solution used for bipolar membrane electrodialysis in the present invention has a low impurity content, wherein Ca≤0.02ppm, Mg≤0.01ppm, B≤5ppm, and Si≤1ppm; reducing the deposition of these impurities inside the membrane is beneficial to improving the electrical efficiency and service life of the membrane. The lithium hydroxide solution prepared using a low-impurity lithium chloride solution bipolar membrane is of better quality, and the quality of the lithium carbonate produced is higher. The present invention uses lithium hydroxide solution carbonization to produce lithium carbonate, which has the advantages of fast reaction speed and high production capacity of a single set of equipment. In the production process of the present invention, the three wastes are discharged at low levels, and resources are recycled and reused efficiently.

[0046] Compared with the traditional process of producing high-purity lithium carbonate from industrial-grade lithium carbonate, the method of the present invention is simpler and more convenient. It does not require first purifying industrial-grade lithium carbonate into battery-grade lithium carbonate, and then purifying battery-grade lithium carbonate into high-purity lithium carbonate; it broadens the restrictions on raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Attachment Figure 1 is a process flow chart of the present invention;

[0048] Attachment Figure 2 Schematic diagram of the bipolar membrane electrodialysis process of the present invention; wherein the corresponding names of the figure marks are: 1-alkali circulation pump, 2-acid circulation pump, 3-brine circulation pump. DETAILED DESCRIPTION

[0049] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0050] As attached Figure 1 As shown, the present invention discloses a method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate, which specifically comprises the following steps:

[0051] S1. Dissolution: React industrial-grade lithium carbonate with a 1.5-2 mol / L dilute hydrochloric acid solution to form a lithium chloride solution with a lithium concentration of 11-16 g / L.

[0052] S2 chemical impurity removal: the lithium chloride solution obtained in step S1 was heated to 40 ~ 60 ℃, followed by adding oxalic acid, lithium hydroxide solution for 30 to 60 minutes, for chemical impurity removal; the reaction endpoint control solution c (C2O42- )1.5~2.5g / L, c(OH - )1~3g / L; Preferably, in step S2, the lithium hydroxide solution produced by bipolar membrane electrodialysis is added for chemical impurity removal.

[0053] In the method of the present invention, oxalic acid and lithium hydroxide are added to precipitate metal impurities such as calcium, magnesium, iron, manganese, and barium;

[0054] S3 ultrafiltration: The lithium chloride solution subjected to chemical impurity removal treatment in step S2 was ultrafiltered to obtain lithium chloride ultrafiltration permeate and ultrafiltration concentrate; wherein the pore size of the ultrafiltration membrane was 0.02 to 0.2 μm; the ultrafiltration concentrate was filtered into a plate and frame filter press, and the supernatant obtained by the filtration was returned to the ultrafiltration feed tank, and the plate and frame filter press residue was discharged from the system;

[0055] S4. Nanofiltration: The lithium chloride ultrafiltration permeate obtained in step S3 is adjusted to a pH of 4 to 7 with hydrochloric acid and then subjected to nanofiltration to obtain a lithium chloride nanofiltration permeate and a nanofiltration concentrate, respectively. The nanofiltration concentrate is returned to step S2 for further chemical removal. The nanofiltration membrane in step S4 is an acid-resistant nanofiltration membrane with a molecular weight cutoff of 100 to 1000 Daltons.

[0056] In step S4 of the present invention, the pH of the lithium chloride ultrafiltration permeate is adjusted to 4-7 to avoid the divalent ions on the concentrated solution side from enriching and reacting with oxalate to form oxalate precipitation to block the membrane during the nanofiltration process; at the same time, the C2O4 2- 、SO4 2- A trace amount of Si, Al, Ca, Mg, B and other ions are intercepted in the nanofiltration concentrate, and the nanofiltration concentrate returns to step S2 for impurity removal reaction.

[0057] S5. Ion exchange: The lithium chloride nanofiltration permeate obtained in step S4 is treated with an ion exchange resin to obtain a purified lithium chloride solution; the purified lithium chloride solution contains Ca≤0.02ppm, Mg≤0.01ppm, B≤5ppm, and Si≤1ppm;

[0058] The ion exchange resin is composed of a chelating resin for removing calcium and magnesium and a chelating resin for removing boron. The ion exchange process is to pass the lithium chloride nanofiltration permeate through the chelating resin for removing calcium and magnesium and the chelating resin for removing boron in turn for ion exchange treatment, first removing calcium and magnesium and then removing boron.

[0059] Preferably, the pH of the lithium chloride nanofiltration permeate is adjusted to 8.5-9.5 before entering the ion exchange resin; more preferably, the lithium hydroxide solution produced by the bipolar membrane is used to adjust the pH of the lithium chloride nanofiltration permeate to 8.5-9.5.

[0060] S6. Bipolar membrane electrodialysis: The purified lithium chloride solution obtained in step S5 is subjected to bipolar membrane electrodialysis to obtain a lithium hydroxide solution with a concentration of 36 to 50 g / L, a dilute hydrochloric acid solution with a concentration of 1.5 to 2 mol / L, and a dilute lithium chloride solution with a lithium concentration of 3 to 5 g / L.

[0061] As attached Figure 2 As shown, the bipolar membrane electrodialysis device described in the present invention is a three-compartment electrodialysis device, which includes an alkali chamber, a salt chamber, and an acid chamber. The alkali chamber is connected to the alkali circulation tank through an alkali circulation pump, the salt chamber is connected to the salt circulation tank through a brine circulation pump, and the acid chamber is connected to the acid circulation tank through an acid circulation pump.

[0062] A dilute hydrochloric acid solution with a concentration of 1.5 to 2 mol / L is produced from the acid circulation tank, a lithium hydroxide solution with a concentration of 36 to 50 g / L is produced from the alkali circulation tank, and a dilute lithium chloride solution with a lithium concentration of 3 to 5 g / L is produced from the salt circulation tank.

[0063] The dilute hydrochloric acid solution is returned to step S1 for use;

[0064] A dilute lithium chloride solution with a lithium concentration of 3 to 5 g / L is subjected to acid-resistant reverse osmosis treatment to obtain a lithium chloride concentrate with a lithium concentration of 6 to 10 g / L and a lithium chloride permeate with a lithium concentration of 0.6 to 1 g / L. The lithium chloride concentrate with a lithium concentration of 6 to 10 g / L is returned to step S6 and mixed with the purified lithium chloride solution to serve as the feed solution for bipolar membrane electrodialysis. The lithium chloride permeate with a lithium concentration of 0.6 to 1 g / L enters the acid circulation tank and serves as the receiving solution for the dilute hydrochloric acid. The alkaline circulation tank is replenished with pure water as the receiving solution.

[0065] S7. Homogeneous membrane electrodialysis: The concentration of 36 to 50 g / L lithium hydroxide solution obtained in step S6 is subjected to homogeneous membrane electrodialysis to obtain a lithium hydroxide concentrate having a concentration of 75 to 96 g / L and a lithium hydroxide concentrate having a concentration of 10 to 20 g / L. A dilute lithium hydroxide solution is obtained.

[0066] The lithium hydroxide dilute solution is returned to the alkali circulation tank of the bipolar membrane electrodialysis in step S6 and mixed with pure water to serve as the receiving solution for the lithium hydroxide produced by the bipolar membrane electrodialysis;

[0067] S8. Carbonization: Add the lithium hydroxide concentrate obtained in step S7 to a reactor and heat it to 50-60°C, add high-purity lithium carbonate as a seed crystal, and introduce carbon dioxide gas to react to generate a lithium carbonate slurry; the carbon dioxide gas includes the carbon dioxide produced in step S1; during the carbonization reaction, control the reaction temperature to 50-60°C; control the addition rate of lithium hydroxide and carbon dioxide to maintain the hydroxide concentration in the reaction system at 15-30g / L; the amount of seed crystal added is 1-10% of the mass of the generated lithium carbonate.

[0068] S9. Centrifugal separation and drying: The lithium carbonate slurry prepared in step S8 is centrifuged, dehydrated, and washed to obtain wet lithium carbonate and centrifuge mother liquor; the wet lithium carbonate is dried to obtain a high-purity lithium carbonate product.

[0069] S10. The centrifuged mother liquor obtained in S9 was subjected to nanofiltration to obtain a centrifuged mother liquor nanofiltration concentrate and a centrifuged mother liquor nanofiltration permeate;

[0070] The concentrated water from the centrifuged mother liquor is returned to step S2 to replace part or all of the lithium hydroxide for lithium chloride impurity removal. After the alkali-resistant nanofiltration treatment, a small amount of carbonate ions are intercepted in the concentrated water from the nanofiltration, preventing the carbonate ions from entering the bipolar membrane electrodialysis to form lithium carbonate precipitation and clogging the membrane;

[0071] The centrifuged mother liquor nanofiltration permeate is returned to the alkali circulation tank of the bipolar membrane electrodialysis in step S6 as the receiving liquid for the lithium hydroxide produced by the bipolar membrane;

[0072] The nanofiltration membrane used for centrifuging the mother liquor is an alkali-resistant nanofiltration membrane with a cutoff molecular weight of 100 to 1000 Daltons.

[0073] Example 1

[0074] This embodiment discloses a method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate of the present invention, which specifically comprises the following steps:

[0075] S1. Dissolution: Add 200 kg of industrial-grade lithium carbonate with a main content of 99.2 wt.% to a 3000 L reactor, and slowly add 1.5 mol / L dilute hydrochloric acid to the reactor to form a lithium chloride solution with a lithium concentration of 15.5 g / L.

[0076] S2. Chemical impurity removal: Lithium chloride solution was heated to 42°C, oxalic acid and lithium hydroxide solution were added in sequence and reacted for 30 minutes. The reaction endpoint was controlled by c(C2O4 2- )1.5g / L, c(OH - )1g / L.

[0077] S3. Ultrafiltration: The lithium chloride solution after chemical impurity removal is ultrafiltered through an ultrafiltration membrane with a pore size of 0.05 μm to obtain lithium chloride ultrafiltration permeate and lithium chloride ultrafiltration concentrate. The lithium chloride ultrafiltration concentrate enters a plate and frame filter press for filtration. The clear liquid obtained by filtration is returned to the ultrafiltration raw material tank, and the filtration residue is discharged from the system.

[0078] S4. Nanofiltration: The ultrafiltration permeate was adjusted to pH 4.5 with dilute hydrochloric acid produced by bipolar membrane electrodialysis, and then nanofiltration was performed through a 100 Dalton alkali-resistant nanofiltration membrane to obtain lithium chloride nanofiltration permeate and nanofiltration concentrate, respectively; the nanofiltration concentrate was returned to the chemical impurity removal reactor in step S2, and the lithium chloride nanofiltration permeate entered the ion exchange system;

[0079] S5. Ion exchange: The lithium chloride nanofiltration permeate was adjusted to pH 8.8 using a bipolar membrane to produce a lithium hydroxide solution, and then ion exchange treatment was performed by a calcium and magnesium chelating resin and a boron removal resin to obtain a purified lithium chloride solution having Ca≤0.02ppm, Mg≤0.01ppm, B≤5ppm, and Si≤1ppm.

[0080] S6. The purified lithium chloride solution enters bipolar membrane electrodialysis treatment to obtain a lithium hydroxide solution with a concentration of 36 g / L, a dilute hydrochloric acid solution with a concentration of 1.5 mol / L, and a dilute lithium chloride solution with a lithium concentration of 4.5 g / L.

[0081] The dilute hydrochloric acid solution returns to step S1 to dissolve industrial lithium carbonate;

[0082] The dilute lithium chloride solution is treated with acid-resistant reverse osmosis to obtain a lithium chloride concentrate with a lithium concentration of 9.0 g / L and a lithium chloride permeate with a lithium concentration of 0.8 g / L. The lithium chloride concentrate is mixed with the lithium chloride purified solution and used as the raw liquid for bipolar membrane electrodialysis and enters the salt circulation tank; the lithium chloride permeate enters the acid circulation tank;

[0083] S7 homogeneous membrane electrodialysis: The lithium hydroxide solution obtained in step S6 was concentrated by homogeneous membrane electrodialysis to obtain a concentration of 76g / L of lithium hydroxide concentrate and a concentration of 15.8g / L of a dilute lithium hydroxide solution, the dilute lithium hydroxide solution returns to the alkaline circulation tank of the bipolar membrane electrodialysis S6, as the receiving solution of lithium hydroxide produced by the bipolar membrane;

[0084] S8. Carbonization: The 76 g / L lithium hydroxide concentrate obtained in step S7 was added to a carbonization reactor and heated to 52°C. Lithium carbonate seed crystals were added to form 1 wt.% of the mass of lithium carbonate to be generated. Carbon dioxide gas was introduced to react and generate a lithium carbonate slurry. The reaction temperature was controlled at 52°C by cooling water to maintain the hydroxide concentration in the reaction system at 15.5 g / L.

[0085] S9. Centrifugal separation and drying: The lithium carbonate slurry is centrifuged, dehydrated, and washed to obtain wet lithium carbonate and mother liquor. The wet lithium carbonate is dried to obtain high-purity lithium carbonate product.

[0086] S10. After the centrifuged mother liquor is treated by alkali-resistant nanofiltration with a molecular weight cutoff of 100 Daltons, the obtained lithium hydroxide concentrated water is returned to the chemical impurity removal process in step S2, and the alkali-resistant nanofiltration permeate is returned to the alkaline circulation tank of the bipolar membrane electrodialysis for reuse.

[0087] Example 2

[0088] This embodiment discloses a method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate of the present invention, which specifically comprises the following steps:

[0089] S1. Dissolution: Add 180 kg of industrial-grade lithium carbonate with a main content of 99.0 wt.% to a 3000 L reactor, and slowly add 1.8 mol / L dilute hydrochloric acid to the reactor to react to form a lithium chloride solution with a lithium concentration of 13.5 g / L.

[0090] S2. Chemical impurity removal: Lithium chloride solution was heated to 55°C, oxalic acid and lithium hydroxide solution were added in sequence and reacted for 43 minutes. The reaction endpoint was controlled by c(C2O4 2- )2.1g / L, c(OH - )1.9g / L.

[0091] S3. Ultrafiltration: The lithium chloride solution after chemical impurity removal is ultrafiltered through an ultrafiltration membrane with a pore size of 0.1 μm to obtain lithium chloride ultrafiltration permeate and lithium chloride ultrafiltration concentrate. The lithium chloride ultrafiltration concentrate enters a plate and frame filter press for filtration. The clear liquid obtained by filtration is returned to the ultrafiltration raw material tank, and the filtration residue is discharged from the system.

[0092] S4. Nanofiltration: The ultrafiltration permeate was adjusted to pH 5.3 with dilute hydrochloric acid produced by bipolar membrane electrodialysis, and then filtered through a 400 Dalton alkali-resistant nanofiltration membrane to obtain lithium chloride nanofiltration permeate and nanofiltration concentrate, respectively; the lithium chloride nanofiltration concentrate was returned to the chemical impurity removal reactor in step S2, and the nanofiltration permeate entered the ion exchange system;

[0093] S5. Ion exchange: The lithium chloride nanofiltration permeate was adjusted to pH 9.0 using lithium hydroxide solution and then subjected to ion exchange treatment by calcium and magnesium chelating resin and boron removal resin to obtain a purified lithium chloride solution having Ca≤0.02ppm, Mg≤0.01ppm, B≤5ppm, and Si≤1ppm;

[0094] S6. The purified lithium chloride solution enters bipolar membrane electrodialysis treatment to obtain a lithium hydroxide solution with a concentration of 43.2 g / L, a dilute hydrochloric acid solution with a concentration of 1.8 mol / L, and a dilute lithium chloride solution with a lithium concentration of 3.5 g / L.

[0095] The dilute hydrochloric acid solution returns to step S1 to dissolve industrial lithium carbonate;

[0096] The dilute lithium chloride solution is treated with acid-resistant reverse osmosis to obtain a lithium chloride concentrate with a lithium concentration of 8.4 g / L and a lithium chloride permeate with a lithium concentration of 0.8 g / L. The lithium chloride concentrate is mixed with the lithium chloride purified solution and used as the raw liquid for bipolar membrane electrodialysis and enters the salt circulation tank; the lithium chloride permeate enters the acid circulation tank;

[0097] S7 homogeneous membrane electrodialysis: The lithium hydroxide solution obtained in step S6 was concentrated by homogeneous membrane electrodialysis to obtain a concentration of 84g / L of lithium hydroxide concentrate and a concentration of 18.3g / L of a dilute lithium hydroxide solution, the dilute lithium hydroxide solution was returned to the alkaline circulation tank of the bipolar membrane electrodialysis S6, as a receiving solution of lithium hydroxide produced by the bipolar membrane;

[0098] S8. Carbonization: The 84 g / L lithium hydroxide concentrate obtained in step S7 was added to a carbonization reactor and heated to 58°C. Lithium carbonate seed crystals of 5 wt.% of the mass of lithium carbonate to be generated were added, and carbon dioxide gas was introduced to react to generate a lithium carbonate slurry. The reaction temperature was controlled at 58°C by cooling water to maintain the hydroxide concentration in the reaction system at 23 g / L.

[0099] S9. Centrifugal separation and drying: The lithium carbonate slurry is centrifuged, dehydrated, and washed to obtain wet lithium carbonate and mother liquor. The wet lithium carbonate is dried to obtain high-purity lithium carbonate product.

[0100] S10. The centrifuged mother liquor is treated by alkali-resistant nanofiltration with a molecular weight cutoff of 200 Daltons, and the obtained lithium hydroxide concentrated water is returned to the chemical impurity removal process in step S2. The alkali-resistant nanofiltration permeate is returned to the alkaline circulation tank of the bipolar membrane electrodialysis for reuse.

[0101] Example 3

[0102] This embodiment discloses a method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate of the present invention, which specifically comprises the following steps:

[0103] S1. Dissolution: 160 kg of 98.0 wt.% industrial-grade lithium carbonate was added to a 3000 L reactor, and 1.5 mol / L dilute hydrochloric acid was slowly added to the reactor to form a lithium chloride solution with a lithium concentration of 12 g / L.

[0104] S2. Chemical impurity removal: Lithium chloride solution was heated to 50°C, oxalic acid and lithium hydroxide solution were added in sequence and reacted for 60 minutes. The reaction endpoint was controlled by c(C2O4 2- )2.4g / L, c(OH - )2.8g / L.

[0105] S3. Ultrafiltration: The lithium chloride solution after chemical impurity removal is ultrafiltered through an ultrafiltration membrane with a pore size of 0.2 μm to obtain lithium chloride ultrafiltration permeate and lithium chloride ultrafiltration concentrate. The lithium chloride ultrafiltration concentrate enters a plate and frame filter press for filtration, and the clear liquid obtained by filtration is returned to the ultrafiltration raw material tank, and the filtration residue is discharged from the system.

[0106] S4. Nanofiltration: The ultrafiltration permeate was adjusted to pH 6.5 with dilute hydrochloric acid produced by bipolar membrane electrodialysis, and then filtered through a 1000 Dalton alkali-resistant nanofiltration membrane to obtain lithium chloride nanofiltration permeate and nanofiltration concentrate, respectively; the nanofiltration concentrate was returned to the chemical impurity removal reactor in step S2, and the lithium chloride nanofiltration permeate entered the ion exchange system;

[0107] S5. Ion exchange: The lithium chloride nanofiltration permeate was adjusted to pH 9.3 using lithium hydroxide solution and then subjected to ion exchange treatment by calcium and magnesium chelating resin and boron removal resin to obtain a purified lithium chloride solution having Ca≤0.02ppm, Mg≤0.01ppm, B≤5ppm, and Si≤1ppm;

[0108] S6. The purified lithium chloride solution enters bipolar membrane electrodialysis treatment to obtain a lithium hydroxide solution with a concentration of 50 g / L, a dilute hydrochloric acid solution with a concentration of 2 mol / L, and a dilute lithium chloride solution with a lithium concentration of 3.0 g / L.

[0109] The dilute hydrochloric acid solution returns to step S1 to dissolve industrial lithium carbonate;

[0110] The dilute lithium chloride solution is treated with acid-resistant reverse osmosis to obtain a lithium chloride concentrate with a lithium concentration of 7.0 g / L and a lithium chloride permeate with a lithium concentration of 0.6 g / L. The lithium chloride concentrate is mixed with the lithium chloride purified solution and used as the raw liquid for bipolar membrane electrodialysis and enters the salt circulation tank; the lithium chloride permeate enters the acid circulation tank;

[0111] S7 homogeneous membrane electrodialysis: The lithium hydroxide solution obtained in step S6 was concentrated by homogeneous membrane electrodialysis to obtain a concentration of 96g / L of lithium hydroxide concentrate and a concentration of 20g / L of a dilute lithium hydroxide solution, the dilute lithium hydroxide solution returned to the alkaline circulation tank of the bipolar membrane electrodialysis S6 as a receiving solution of lithium hydroxide produced by the bipolar membrane;

[0112] S8. Carbonization: The 96 g / L lithium hydroxide concentrate obtained in step S7 is added to a carbonization reactor and heated to 58°C. Lithium carbonate seed crystals are added to form 5 wt.% of the mass of lithium carbonate to be generated. Carbon dioxide gas is introduced into the reactor to react and generate a lithium carbonate slurry. The reaction temperature is controlled at 60°C by cooling water to maintain the hydroxide concentration in the reaction system at 28 g / L.

[0113] S9. Centrifugal separation and drying: The lithium carbonate slurry is centrifuged, dehydrated, and washed to obtain wet lithium carbonate and mother liquor. The wet lithium carbonate is dried to obtain high-purity lithium carbonate product.

[0114] S10. After the centrifuged mother liquor is treated by alkali-resistant nanofiltration with a molecular weight cutoff of 100 Daltons, the obtained lithium hydroxide concentrated water is returned to the chemical impurity removal process in step S2, and the alkali-resistant nanofiltration permeate is returned to the alkaline circulation tank of the bipolar membrane electrodialysis for reuse.

[0115] Test Example 1

[0116] The high-purity lithium carbonate obtained in Examples 1-3 was subjected to sample testing and analysis, and the test results are as follows:

[0117] Table 1 Test results of high-purity lithium carbonate obtained in Examples 1-3

[0118]

[0119]

[0120] The % in the above table indicates mass percentage.

[0121] It can be seen from the above table that lithium carbonate with a purity greater than 99.99% can be obtained by the method of the present invention.

[0122] Comparative Example 1

[0123] This comparative example involves adding water and carbon dioxide to industrial-grade lithium carbonate to form a soluble lithium bicarbonate solution. Insoluble matter is removed by filtration, and then a chelating resin is used to remove divalent metal ions to obtain a pure lithium bicarbonate solution. The lithium bicarbonate solution is then heated and decomposed to precipitate lithium carbonate. The specific steps are as follows:

[0124] 105 kg of technical-grade lithium carbonate (98.0 wt. %) and 2500 L of pure water were added to a 3000 L reactor, and carbon dioxide was introduced for 2 hours to make the solution clear. The solution was then filtered through a plate and frame filter press with a filtration accuracy of 0.2 μm and then passed through a chelating resin tower to remove calcium, magnesium, and boron to obtain 2500 L of lithium bicarbonate purified liquid with a lithium content of 7.5 g / L.

[0125] Transfer the purified lithium bicarbonate liquid into a stainless steel reactor, start stirring, and heat to 90-95°C to thermally decompose and precipitate lithium carbonate and release carbon dioxide.

[0126] The lithium carbonate wet material was centrifuged and washed, and then dried to obtain the lithium carbonate product. A pyrolysis mother liquor with a lithium content of 2.3 g / L was obtained.

[0127] The lithium carbonate content obtained in this comparative example is shown in Table 2.

[0128] Table 2

[0129]

[0130]

[0131] The above description is merely a preferred embodiment of the present invention and is intended to be illustrative of the present invention, rather than limiting the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made by those skilled in the art to the technical solution of the present invention should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate, characterized in that: The steps include: S1 dissolution: industrial-grade lithium carbonate reacts with hydrochloric acid solution to generate a lithium chloride solution having a lithium concentration of 11-16 g / L; S2. Chemical impurity removal: The lithium chloride solution obtained in step S1 is heated to 40~60°C, and oxalic acid and lithium hydroxide solution are added in sequence to react for chemical impurity removal. The reaction endpoint controls the concentration of c (C2O4 2- )1.5~2.5g / L, c(OH - ) 1~3g / L; S3 ultrafiltration: The lithium chloride solution in step S2 was subjected to ultrafiltration after chemical impurity removal treatment to obtain lithium chloride ultrafiltration permeate and ultrafiltration concentrate; S4 nanofiltration: The ultrafiltration permeate obtained in step S3 was adjusted to a pH of 4 to 7 and then subjected to nanofiltration to obtain lithium chloride nanofiltration permeate and nanofiltration concentrate, respectively; S5 ion exchange: The lithium chloride nanofiltration permeate obtained in step S4 was treated with an ion exchange resin to obtain a purified lithium chloride solution; lithium chloride purified solution Ca≤0.02ppm, Mg≤0.01ppm, B≤5ppm, Si≤1ppm; S6 bipolar membrane electrodialysis: The lithium chloride purified solution obtained in step S5 was subjected to bipolar membrane electrodialysis to obtain a lithium hydroxide solution having a concentration of 36 to 50 g / L, a dilute hydrochloric acid solution having a concentration of 1.5 to 2 mol / L, a dilute lithium chloride solution having a lithium concentration of 3 to 5 g / L; S7 homogeneous membrane electrodialysis: The lithium hydroxide solution obtained in step S6 was subjected to homogeneous membrane electrodialysis to obtain a concentration of 75 to 96 g / L of lithium hydroxide concentrate and a concentration of 10 to 20 g / L of lithium hydroxide dilute solution; S8 carbonization: The lithium hydroxide concentrate obtained in step S7 was added to lithium carbonate seed crystals, and carbon dioxide gas was introduced into the reaction to generate a lithium carbonate slurry; S9. Centrifugation and drying: The lithium carbonate slurry prepared in step S8 is centrifuged and dehydrated, washed to obtain wet lithium carbonate and centrifuged mother liquor; the wet lithium carbonate is dried to obtain a high-purity lithium carbonate product.

2. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1, wherein The concentration of the hydrochloric acid solution in step S1 is 1.5-2 mol / L.

3. A method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, characterized in that, In step S2, the lithium hydroxide solution produced by bipolar membrane electrodialysis is added for chemical impurity removal.

4. A method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, characterized in that, In step S3, the pore size of the ultrafiltration membrane is 0.02-0.2 μm.

5. A method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, characterized in that, In step S3, the ultrafiltration concentrate enters the plate and frame filter press for filtration, the clear liquid obtained by filtration is returned to the ultrafiltration raw material tank, and the plate and frame filter press residue is discharged from the system.

6. A method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, characterized in that, In step S4, the nanofiltration concentrate is returned to step S2 for chemical impurity removal.

7. A method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, characterized in that: In step S5, the ion exchange resin is composed of a chelating resin for removing calcium and magnesium and a chelating resin for removing boron; the ion exchange process is to remove calcium and magnesium first and then remove boron.

8. A method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, characterized in that, In step S5, the pH of the lithium chloride nanofiltration permeate is adjusted to 8.5-9.5 before entering the ion exchange resin.

9. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 8, wherein In step S5, the lithium hydroxide solution produced by the bipolar membrane is used to adjust the pH of the lithium chloride nanofiltration permeate to 8.5-9.

5.

10. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, wherein: The dilute hydrochloric acid solution obtained in step S6 is returned to step S1 for use.

11. A method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, characterized in that: The dilute lithium chloride solution obtained in step S6 is subjected to acid-resistant reverse osmosis treatment to obtain a lithium chloride concentrate and a lithium chloride permeate, wherein the lithium concentration in the lithium chloride concentrate is 6-10 g / L, and the lithium concentration in the lithium chloride permeate is 0.6-1 g / L.

12. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 11, wherein: The lithium chloride concentrated solution returns to step S6 and is mixed with the lithium chloride purified solution to serve as the raw material solution for bipolar membrane electrodialysis.

13. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 11, wherein: The lithium chloride permeate is used as the receiving liquid for the dilute hydrochloric acid produced by bipolar membrane electrodialysis.

14. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, wherein: The lithium hydroxide dilute solution obtained in step S7 is returned to the alkali circulation tank of the bipolar membrane electrodialysis in step S6 to serve as a receiving solution for the lithium hydroxide produced by the bipolar membrane electrodialysis.

15. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, wherein: In step S8, the lithium hydroxide concentrate is heated to 50-60° C., and high-purity lithium carbonate is added as a seed crystal.

16. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, wherein: In step S8, the carbon dioxide includes the carbon dioxide produced in step S1.

17. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, wherein: In step S8, during the carbonization reaction, the reaction temperature is controlled to be 50-60°C.

18. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, wherein: In step S8, the addition rate of lithium hydroxide and carbon dioxide is controlled to maintain the hydroxide concentration in the reaction system at 15-30 g / L.

19. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, characterized in that: In step S8, the amount of seed crystal added is 1-10% of the mass of the generated lithium carbonate.

20. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 1 or 2, characterized in that: The centrifugal mother liquor obtained in step S9 is subjected to nanofiltration treatment to obtain centrifugal mother liquor nanofiltration concentrated water and centrifugal mother liquor nanofiltration permeate, respectively.

21. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 20, wherein: The concentrated water from the centrifuged mother liquor is returned to step S2 to replace part or all of the lithium hydroxide for lithium chloride impurity removal.

22. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 20, wherein: The nanofiltration permeate of the centrifuged mother liquor is returned to the alkali circulation tank of the bipolar membrane electrodialysis in step S6 to serve as a receiving liquid for the lithium hydroxide produced by the bipolar membrane electrodialysis.

23. The method for preparing high-purity lithium carbonate from industrial-grade lithium carbonate according to claim 20, wherein: The nanofiltration membrane used for centrifuging the mother liquor is an alkali-resistant nanofiltration membrane with a molecular weight cutoff of 100 to 1000 Daltons.

Images