Preparation method of high-purity lithium carbonate

Abstract

The invention discloses a method for preparing high-purity lithium carbonate. The method comprises the following steps: slowly dropping a saturated lithium sulfate solution into a saturated calcium bicarbonate solution, stirring while dropping, to obtain a lithium bicarbonate solution; adding barium bicarbonate into the lithium bicarbonate solution for reaction, filtering to obtain a filtrate, and then adding Li 2 C 2 O 4 The reaction is carried out, and the second filtrate is filtered for the second time to obtain a second filtrate; the second filtrate is loaded into an ion exchange device with a selective resin to obtain a lithium bicarbonate clean liquid; the lithium bicarbonate clean liquid is heated to boiling and maintained, and a lithium carbonate wet material is obtained by filtration; the lithium carbonate wet material is heated to boiling with deionized water and stirred and washed, and a lithium carbonate stirred and washed wet material is obtained after filtration; the lithium carbonate stirred and washed wet material is dried and packaged to obtain high-purity lithium carbonate. The present invention does not require hydrogenation, and lithium bicarbonate can be directly generated by the reaction of lithium sulfate and calcium bicarbonate, without the need for lithium hydroxide or lithium carbonate to pass CO 2 The production of lithium bicarbonate saves operating steps and shortens the process time by 1‑2 h.

Description

Technical Field

[0001] The invention relates to the technical field of lithium carbonate extraction, and in particular to a method for preparing high-purity lithium carbonate. Background Art

[0002] Lithium carbonate is an important lithium salt with a wide range of uses and strong market application value. According to relevant national and industry standards such as GB / T11075-2003, GB10576-89, and YS / T582-2006, lithium carbonate can be divided into four grades: industrial grade Li 2 CO 3 Content <99.50%, battery grade Li 2 CO 3 Satisfy 99.50%≤Li 2 CO 3 Content <99.90%, high purity 3N grade Li 2 CO 3 Satisfy 99.90%≤Li 2 CO 3 Content <99.99%, high purity 4N grade Li 2 CO 3 The above meets Li 2 CO 3 Content ≥99.99%. However, at present, most domestic lithium carbonate manufacturers can only provide relatively low-end industrial-grade lithium carbonate. Some stronger manufacturers can provide battery-grade lithium carbonate, but their actual application value is far less than that of high-purity lithium carbonate, which makes my country's lithium carbonate industry lack international competitiveness.

[0003] At present, the uses of high-purity lithium carbonate are mainly in two aspects:

[0004] 1) Used to synthesize high-purity lithium fluoride, and then synthesize lithium hexafluorophosphate, which is used as the electrolyte of lithium batteries;

[0005] 2) Some high-quality battery positive electrode materials will also use high-purity lithium carbonate as raw material to improve battery performance.

[0006] In addition, high-purity lithium carbonate also has certain applications in some optical materials. With the development of the lithium battery industry, some manufacturers have higher and higher requirements for the quality of lithium batteries. In the production of lithium batteries, the level of impurities in the raw materials seriously affects the battery capacity, service life and safety of lithium batteries. Therefore, the use of high-purity lithium carbonate will be more widely used.

[0007] The Chinese invention patent with publication number CN108423695A discloses a method for preparing lithium carbonate, which comprises adding EDTA and polyethylene glycol dissolved in a pure lithium sulfate solution to obtain a lithium carbonate solution. 2 CO 3The solution is filtered, washed and dried to obtain battery-grade lithium carbonate. 4 2- If it is not removed in advance, the obtained lithium carbonate contains a large amount of SO 4 2- Package, and SO 4 2- It is difficult to reduce the content to an acceptable level by water washing, and the resulting lithium carbonate cannot reach a high-purity level; in addition, due to the use of EDTA, the filtrate cannot be recycled or reused multiple times, which can easily lead to the enrichment of metal ions, resulting in a decrease in the grade of lithium carbonate, a low lithium yield, and a large amount of waste salt in the wastewater, which increases the treatment cost.

[0008] The Chinese invention patent with publication number CN114105172A discloses a method for producing high-purity lithium carbonate by lime causticization and carbonization of crude lithium carbonate. The method uses crude lithium carbonate solids after washing and impurities removal to undergo causticization reaction with water and quicklime, and obtains lithium hydroxide solution by filtration and separation. Due to the low solubility of lithium carbonate, the process is very slow and the conversion rate is not high. In addition, a large amount of lithium carbonate will be lost by filtration, and the lithium yield will decrease. In addition, the lithium hydroxide solution is hydrogenated to obtain a lithium bicarbonate solution, which consumes a large amount of CO. 2 The hydrogenation process is relatively slow, which greatly reduces the production efficiency, and needs to be carried out under certain pressure conditions, which poses certain safety risks.

[0009] In summary, the existing methods for producing lithium carbonate have the disadvantages of low yield, low production efficiency, high waste liquid discharge and high cost. Summary of the invention

[0010] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for preparing high-purity lithium carbonate. The method uses lithium sulfate to prepare high-purity lithium carbonate, with an actual yield of more than 95%. The product quality can reach the industry standard of 99.99% for high-purity lithium carbonate, and is more suitable for industrialization.

[0011] In order to achieve the above-mentioned purpose, the technical solution designed by the present invention is:

[0012] The present invention provides a method for preparing high-purity lithium carbonate, comprising the following steps:

[0013] 1) At room temperature, Ca(HCO 3 ) 2 Dissolve in water and stir to obtain Ca(HCO 3 ) 2 Saturated solution;

[0014] 2) Li 2 SO 4 Stir and dissolve to obtain Li 2 SO 4 Saturated solution;

[0015] 3) Li 2 SO 4 The saturated solution was slowly added dropwise to the Ca(HCO 3 ) 2 Add the saturated solution dropwise while stirring for 1-2 hours to produce a large amount of white precipitate CaSO 4 , filtered to obtain LiHCO 3 Solution and by-product CaSO 4 plaster;

[0016] 4) To LiHCO 3 Ba(HCO) was added to the solution 3 ) 2 The reaction was carried out, and the filtrate was filtered to obtain the filtrate, and Li 2 C 2 O 4 reacting, and filtering for a second time to obtain a second filtrate;

[0017] 5) The second filtrate is charged into an ion exchange device with a selective resin to obtain LiHCO 3 Clean liquid;

[0018] 6) LiHCO 3 The clean liquid was heated to boiling and maintained, and Li 2 CO 3 Wet material and Li 2 CO 3 Mother liquor, Li 2 CO 3 The mother liquor is recycled to step 1) in which Ca(HCO 3 ) 2 Dissolve and / or use in step 2) for Li 2 SO 4 Dissolve;

[0019] 7)Li 2 CO 3 The wet material was heated to boiling with deionized water and stirred, and then filtered to obtain Li 2 CO 3 The wet material and the filtrate are stirred and washed, and the filtrate is recycled to step 1) in which Ca(HCO 3 ) 2 Dissolve and / or use in step 2) for Li 2 SO 4 Dissolve;

[0020] 8)Li 2 CO 3 The wet material is dried and packaged to obtain high-purity Li 2 CO 3 .

[0021] Furthermore, in step 3), Li 2 SO 4 Li in saturated solution 2 SO 4 With Ca(HCO 3 ) 2 Ca(HCO) in saturated solution 3 ) 2 The molar ratio is: 1:0.95-1.05.

[0022] Furthermore, in step 3), Li 2 SO 4 Li in saturated solution 2 SO 4 With Ca(HCO 3 ) 2 Ca(HCO) in saturated solution 3 ) 2 The molar ratio is: 1:1.

[0023] Furthermore, in step 4), LiHCO 3 SO in solution 4 2- With Ba(HCO 3 ) 2 The molar ratio is: 1:1-1.5.

[0024] Furthermore, in step 4), LiHCO 3 SO in solution 4 2- With Ba(HCO 3 ) 2 The molar ratio is: 1:1.

[0025] Furthermore, in step 4), the Ca in the filtrate 2+ With Li 2 C 2 O 4 The molar ratio is: 1:1-1.5.

[0026] Furthermore, in step 4), the Ca in the filtrate 2+ With Li 2 C 2 O 4 The molar ratio is: 1:1.

[0027] Furthermore, in step 5), the flow rate of the ion exchange device is 1 ml / min.

[0028] Furthermore, in step 6), LiHCO 3The heating rate of the clean liquid from room temperature to boiling is 1-3°C / min, and the boiling maintenance time is 30-60min.

[0029] Furthermore, in step 7), Li 2 CO 3 The mass ratio of wet material to deionized water is 1:3-4, and the stirring and washing time is 30-60 minutes.

[0030] Principle of the present invention:

[0031] 1. Ca(HCO 3 ) 2 The concentration of saturated solution is 1.02mol / L. The saturated solution is to reduce the discharge of mother liquor. CaSO 4 It is slightly soluble. Using a saturated solution is more conducive to precipitation. The remaining Ca in the solution 2+ with SO 4 2- The amount of impurity removal reagents used in the subsequent step is minimal.

[0032] 2. In the method of the present invention, lithium sulfate is added dropwise to calcium bicarbonate to reduce SO 4 2- The packaging of Li+ makes LiHCO 3 Medium SO 4 2- On the contrary, when calcium bicarbonate is added to lithium sulfate, the reaction occurs in the presence of a large amount of SO 4 2- The conditions are more conducive to SO 4 2- Compared with monovalent ions, divalent ions have a stronger attraction to opposite charges and are not easy to wash away.

[0033] 3. In the method of the present invention, calcium, magnesium and other divalent ions are removed by the adsorption of calcium and magnesium by resin to obtain LiHCO 3 The resin can be used repeatedly after regeneration. The typical exchange reaction of the resin is as follows:

[0034] Ca 2+ (Solution)+2Na + R→CaR+2Na + (Solution)

[0035] Mg 2+ (Solution)+2Na + R→MgR+2Na + (Solution)

[0036] In the above formula, R represents the skeleton of the ion exchanger.

[0037] 4. LiHCO3 Principle of clean liquid pyrolysis:

[0038] 2LiHCO 3 =Li 2 CO 3 +CO 2 +H 2 O.

[0039] Beneficial effects of the present invention:

[0040] 1. Compared with the traditional method of preparing lithium carbonate from lithium sulfate, the method of the present invention does not require hydrogenation and can directly prepare lithium carbonate from lithium sulfate. 2 SO 4 With Ca(HCO 3 ) 2 The reaction produces LiHCO 3 , without the need for LiOH or Li 2 CO 3 CO 2 Formation of LiHCO 3 , saving operation steps and shortening the process time by 1-2h.

[0041] 2. The patent has low sulfate content and is easy to pass. The traditional process is to use lithium sulfate and sodium carbonate to precipitate lithium carbonate first. The wet lithium carbonate contains a large amount of sulfate. Since sulfate is a divalent ion, it has a stronger attraction to the opposite charge and is not easy to wash away. The method of the present invention is to first add calcium salt and barium salt to the solution in sequence, remove sulfate to a qualified level (remove insoluble sulfate), and obtain lithium bicarbonate after filtration. The lithium bicarbonate is pyrolyzed and filtered to obtain lithium carbonate (remove soluble sulfate). This process ensures the qualification of sulfate, and high-purity lithium carbonate can be obtained by one-step reaction. However, due to the high sulfate content, the traditional process cannot produce high-purity lithium carbonate by one-step reaction.

[0042] 3. Compared with the traditional method of preparing lithium carbonate from lithium sulfate, the method of the present invention has less waste salt in the waste liquid. In the waste liquid of the traditional process, there is a large amount of sodium sulfate waste salt in each reaction, which is difficult to handle, causing environmental pressure and increased processing costs. This patent only recycles the lithium carbonate mother liquor that cannot be recycled for the last time after multiple times, and the waste liquid discharge is much less.

[0043] In summary, the present invention utilizes calcium salt to remove sulfate, thereby greatly reducing the content of sulfate, avoiding the common problem that high-purity lithium carbonate cannot be produced due to excessively high sulfate content, and the use of calcium bicarbonate can achieve the purpose of killing two birds with one stone. DETAILED DESCRIPTION

[0044] The present invention is further described in detail below in conjunction with specific embodiments so that those skilled in the art can understand.

[0045] Example 1

[0046] A method for preparing high-purity lithium carbonate 1 comprises the following steps:

[0047] 1) Weigh 327.3 g of Ca(HCO 3 ) 2 (content 99%), added to 2L deionized water (circulation time Li 2 CO 3 The mother liquor and the washing filtrate were used as supplementary solvents for deionized water to dissolve Ca(HCO 3 ) 2 ), stirred and dissolved at room temperature to obtain Ca(HCO 3 ) 2 Saturated solution;

[0048] 2) Weigh 222.2 g of Li 2 SO 4 (content 99%); add 640ml deionized water (circulation time Li 2 CO 3 The mother liquor and the filtrate were used as supplementary solvents for dissolving Li 2 SO 4 ), stirred and dissolved at room temperature to obtain Li 2 SO 4 Saturated solution;

[0049] 3) Press Li 2 SO 4 With Ca(HCO 3 ) 2 Li was added at a molar ratio of 1:1 2 SO 4 The saturated solution was slowly added dropwise to the Ca(HCO 3 ) 2 Add the solution dropwise while stirring for 1 hour to produce a large amount of white precipitate CaSO 4 , filtered to obtain LiHCO 3 Solution and by-product CaSO 4 plaster;

[0050] 4) Sampling and testing of LiHCO 3 Ca in solution 2+ 、SO 4 2- Mg 2+ The contents were 0.6g / L, 1.4g / L, and 0.005g / L respectively;

[0051] 5) Press LiHCO 3 SO in solution 4 2- With Ba(HCO 3 )2 The molar ratio of 1:1 to LiHCO 3 Ba(HCO) was added to the solution 3 ) 2 The reaction was carried out, and the filtrate was filtered to obtain the filtrate. Then, the Ca 2+ With Li 2 C 2 O 4 The molar ratio is 1:1. Li is added to the filtrate. 2 C 2 O 4 reacting, and filtering for a second time to obtain a second filtrate;

[0052] 6) The second filtrate is charged into an ion exchange device with a chelating resin at a flow rate of 1 ml / min. The removal rate of calcium in the primary ion exchange is 80%, and the removal rate of calcium in the secondary ion exchange is 99% (the divalent ions such as calcium and magnesium are removed by the adsorption of the resin on calcium and magnesium, and the resin can be used repeatedly after regeneration) to obtain LiHCO 3 Clean liquid;

[0053] 7) LiHCO 3 The clean solution was heated from room temperature to boiling at a heating rate of 2°C / min and maintained for 30 min. Li 2 CO 3 Wet material and Li 2 CO 3 Mother liquor, Li 2 CO 3 The mother liquor is recycled to step 1) in which Ca(HCO 3 ) 2 Dissolve and / or use in step 2) for Li 2 SO 4 Dissolve;

[0054] 8) Press Li 2 CO 3 The mass ratio of wet material to deionized water is 1:4. 2 CO 3 The wet material was heated to boiling with deionized water and stirred for 30 min. After filtration, Li 2 CO 3 The wet material and the filtrate are stirred and washed, and the filtrate is recycled to step 1) in which Ca(HCO 3 ) 2 Dissolve and / or use in step 2) for Li 2 SO 4 Dissolve;

[0055] 9)Li 2 CO 3 The wet material is dried and packaged to obtain high-purity Li 2 CO3 Product 1.

[0056] Example 2

[0057] A method for preparing high-purity lithium carbonate 2 comprises the following steps:

[0058] 1) Weigh 327.3 g of Ca(HCO 3 ) 2 (content 99%), added to 2L deionized water (circulation time Li 2 CO 3 The mother liquor and the washing filtrate were used as supplementary solvents for deionized water to dissolve Ca(HCO 3 ) 2 ), stirred and dissolved at room temperature to obtain Ca(HCO 3 ) 2 Saturated solution;

[0059] 2) Weigh 222.2 g of Li 2 SO 4 (content 99%); add 640ml deionized water (circulation time Li 2 CO 3 The mother liquor and the filtrate were used as supplementary solvents for dissolving Li 2 SO 4 ), stirred and dissolved at room temperature to obtain Li 2 SO 4 Saturated solution;

[0060] 3) Press Li 2 SO 4 With Ca(HCO 3 ) 2 The molar ratio of Li is 1:1.05 2 SO 4 The saturated solution was slowly added dropwise to the Ca(HCO 3 ) 2 Add the solution dropwise while stirring for 1 hour to produce a large amount of white precipitate CaSO 4 , filtered to obtain LiHCO 3 Solution and by-product CaSO 4 plaster;

[0061] 4) Sampling and testing of LiHCO 3 Ca in solution 2+ 、SO 4 2- Mg 2+ The contents were 0.78g / L, 1.21g / L, and 0.0048g / L respectively;

[0062] 5) Press LiHCO 3SO in solution 4 2- With Ba(HCO 3 ) 2 The molar ratio of 1:1.5 to LiHCO 3 Addition of Ba(HCO 3 ) 2 The reaction was carried out, and the filtrate was filtered to obtain the filtrate. Then, the Ca 2+ With Li 2 C 2 O 4 The molar ratio is 1:1.5. Li is added to the filtrate. 2 C 2 O 4 reacting, and filtering for a second time to obtain a second filtrate;

[0063] 6) The second filtrate is charged into an ion exchange device with a chelating resin at a flow rate of 1 ml / min. The removal rate of calcium in the primary ion exchange is 80%, and the removal rate of calcium in the secondary ion exchange is 99% (the divalent ions such as calcium and magnesium are removed by the adsorption of the resin on calcium and magnesium, and the resin can be used repeatedly after regeneration) to obtain LiHCO 3 Clean liquid;

[0064] 7) LiHCO 3 The clean solution was heated from room temperature to boiling at a heating rate of 1°C / min and maintained for 60 min. Li 2 CO 3 Wet material and Li 2 CO 3 Mother liquor, Li 2 CO 3 The mother liquor is recycled to step 1) in which Ca(HCO 3 ) 2 Dissolve and / or use in step 2) for Li 2 SO 4 Dissolve;

[0065] 8) Press Li 2 CO 3 The mass ratio of wet material to deionized water is 1:3. 2 CO 3 The wet material was heated to boiling with deionized water and stirred for 60 min. After filtration, Li 2 CO 3 The wet material and the filtrate are stirred and washed, and the filtrate is recycled to step 1) in which Ca(HCO 3 ) 2 Dissolve and / or use in step 2) for Li 2 SO 4 Dissolve;

[0066] 9)Li2 CO 3 The wet material is dried and packaged to obtain high-purity Li 2 CO 3 Product 2.

[0067] Example 3

[0068] A method for preparing high-purity lithium carbonate 3 comprises the following steps:

[0069] 1) Weigh 327.3 g of Ca(HCO 3 ) 2 (content 99%), added to 2L deionized water (circulation time Li 2 CO 3 The mother liquor and the washing filtrate were used as supplementary solvents for deionized water to dissolve Ca(HCO 3 ) 2 ), stirred and dissolved at room temperature to obtain Ca(HCO 3 ) 2 Saturated solution;

[0070] 2) Weigh 222.2 g of Li 2 SO 4 (content 99%); add 640ml deionized water (circulation time Li 2 CO 3 The mother liquor and the filtrate were used as supplementary solvents for dissolving Li 2 SO 4 ), stirred and dissolved at room temperature to obtain Li 2 SO 4 Saturated solution;

[0071] 3) Press Li 2 SO 4 With Ca(HCO 3 ) 2 The molar ratio of Li is 1:0.95 2 SO 4 The saturated solution was slowly added dropwise to the Ca(HCO 3 ) 2 Add the solution dropwise while stirring for 1 hour to produce a large amount of white precipitate CaSO 4 , filtered to obtain LiHCO 3 Solution and by-product CaSO 4 plaster;

[0072] 4) Sampling and testing of LiHCO 3 Ca in solution 2+ 、SO 4 2- Mg 2+The contents were 0.49g / L, 1.92g / L, and 0.0057g / L respectively;

[0073] 5) Press LiHCO 3 SO in solution 4 2- With Ba(HCO 3 ) 2 The molar ratio of 1:1.2 to LiHCO 3 Ba(HCO) was added to the solution 3 ) 2 The reaction was carried out, and the filtrate was filtered to obtain the filtrate. Then, the Ca 2+ With Li 2 C 2 O 4 The molar ratio is 1:1.2. Li is added to the filtrate. 2 C 2 O 4 reacting, and filtering for a second time to obtain a second filtrate;

[0074] 6) The second filtrate is charged into an ion exchange device with a chelating resin at a flow rate of 1 ml / min. The removal rate of calcium in the primary ion exchange is 80%, and the removal rate of calcium in the secondary ion exchange is 99% (the divalent ions such as calcium and magnesium are removed by the adsorption of the resin on calcium and magnesium, and the resin can be used repeatedly after regeneration) to obtain LiHCO 3 Clean liquid;

[0075] 7) LiHCO 3 The clean solution was heated from room temperature to boiling at a heating rate of 3°C / min and maintained for 40 min. Li 2 CO 3 Wet material and Li 2 CO 3 Mother liquor, Li 2 CO 3 The mother liquor is recycled to step 1) in which Ca(HCO 3 ) 2 Dissolve and / or use in step 2) for Li 2 SO 4 Dissolve;

[0076] 8) Press Li 2 CO 3 The mass ratio of wet material to deionized water is 1:3. 2 CO 3 The wet material was heated to boiling with deionized water and stirred for 40 min. After filtration, Li 2 CO 3 The wet material and the filtrate are stirred and washed, and the filtrate is recycled to step 1) in which Ca(HCO 3 ) 2Dissolve and / or use in step 2) for Li 2 SO 4 Dissolve;

[0077] 9)Li 2 CO 3 The wet material is dried and packaged to obtain high-purity Li 2 CO 3 Product 3.

[0078] Comparative Example 1

[0079] 1) Take 1L of Na 2 CO 3 Solution (where Na 2 CO 3 The solution content is 298g / L, the Mg content is 20mg / L, and the Ca content is 5mg / L; 0.15g EDTA is dissolved), added to the reaction kettle, and the temperature is raised to 90°C;

[0080] 2) Take 1.5L of lithium sulfate purified solution, and then add the lithium sulfate purified solution to Na 2 CO 3 Solution, in which Li 2 SO 4 with Na 2 CO 3 The molar ratio is 1:1.

[0081] 3) After adding the purified lithium sulfate solution, the temperature was raised to 100° C., the mixture was kept boiling and stirred for 50 min, and filtered to obtain 192.4 g of wet lithium carbonate.

[0082] 4) The filter cake was then washed thoroughly with 770 mL of pure water at 90° C. (liquid-to-solid ratio 4:1), and then the obtained lithium carbonate filter cake (containing 13.5% of attached water) was dried at 150° C. to obtain the lithium carbonate product.

[0083] Comparative Example 2

[0084] 1) Add 200 g of crude lithium carbonate (containing 60% lithium carbonate) into a beaker, wash with water and filter;

[0085] 2) adding quicklime and water, the liquid-to-solid ratio is 3:1, the molar ratio of quicklime to lithium carbonate is 1.1:1, the stirring reaction temperature is 90°C, and the reaction time is 2 hours;

[0086] 3) filtering and separating the causticized calcium carbonate residue to obtain a lithium hydroxide solution (containing 14 g / L lithium and 11.2 g / L sulfate);

[0087] 4) concentrating the lithium hydroxide solution to obtain a lithium hydroxide solution containing 16 g / L of lithium, stirring and reacting the added barium hydroxide with oxalic acid, wherein the molar ratio of barium hydroxide to sulfate ion is 1:1.5, the amount of oxalic acid is 5 g / L, and filtering to obtain a refined lithium hydroxide solution;

[0088] 5) half of the lithium hydroxide refined liquid is added to a carbonization reactor and carbon dioxide gas is introduced for carbonization. The carbonization temperature is 30° C., the pressure is 0.1 MPa, the carbonization time is 1 h, and the reaction end point pH is 7.5;

[0089] 6) After the carbonization reaction is completed, the lithium bicarbonate solution is filtered to obtain a solution, and the solution is mixed with the other half of the refined lithium hydroxide solution to precipitate lithium. The reaction temperature is 30° C. and the reaction endpoint pH is 8.5;

[0090] 7) After centrifugation, lithium precipitation mother liquor and wet lithium carbonate solid were obtained, and 96.7g of product was obtained after drying.

[0091] Comparative Example 3

[0092] 1) Preparation of NaHCO 3 Saturated solution and Li 2 SO 4 Saturated solution;

[0093] 2) Press Li 2 SO 4 With NaHCO 3 Li was added at a molar ratio of 1:2 2 SO 4 The saturated solution was added to NaHCO 3 A mixed solution is obtained from the saturated solution;

[0094] 3) Add BaCl to the mixed solution 2 , where SO 4 2- With BaCl 2 The molar ratio is 1:1, and a first filtrate is obtained after filtration;

[0095] 4) Detection of SO in the first filtrate 4 2- , Ba 2+ The concentrations are 1.4*10 -3 g / L, 1.9*10 -3 g / L;

[0096] 5) The first filtrate was heated from room temperature to boiling at a heating rate of 2°C / min and maintained for 30 min, and Li 2 CO 3 Wet material, mother liquor is recycled to step 1) for preparing Li 2 SO 4 Saturated solution;

[0097] 6) Press Li 2 CO 3 The mass ratio of wet material to deionized water is 1:4. 2 CO 3 The wet material was heated to boiling with deionized water and stirred twice for 30 min. After filtering, Li 2 CO 3 Agitate and wash the wet material and agitate the filtrate, and the agitate and wash filtrate is recycled to step 1) for use;

[0098] 7)Li 2 CO 3 The wet material is dried and packaged to obtain Li 2 CO 3 product.

[0099] The high purity Li prepared by the methods of Examples 1 to 3 2 CO 3 Content testing of products 1 to 3 and the comparative product:

[0100] Table 1 Content of each substance in the product

[0101] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Detection Methods <![CDATA[Li 2 CO 3 ]]> 99.996％ 99.995％ 99.994％ 99.65％ 99.88％ 99.79％ Difference method Pb 0.1ppm 0.2ppm 0.27ppm 0.31ppm 9.2ppm 0.22ppm ICP method Cu 0.2ppm 0.12ppm 0.23ppm 0.57ppm 4.9ppm 0.18ppm ICP method Co 0.06ppm 0.12ppm 0.23ppm 0.21ppm 3.4ppm 0.22ppm ICP method Ni - - - 0.21ppm 4.9ppm - ICP method Fe 1.3ppm 2.5ppm 2.1ppm 4.38ppm 3.1ppm 1.7ppm ICP method Al 1.9ppm 1.4ppm 2.5ppm 3.4ppm 5.1ppm 2.1ppm ICP method Mn 0.04ppm 0.07ppm 0.12ppm 0.26ppm 2.4ppm 0.11ppm ICP method Zn 1.2ppm 1.4ppm 2.1ppm 5.6ppm 3.7ppm 1.3ppm ICP method Cd - - - 0.21ppm 0.32ppm - ICP method Cr - - - 0.12ppm 0.23ppm - ICP method Mg 3.1ppm 2.8ppm 3.2ppm 7.7ppm 7.2ppm 3.1ppm ICP method Ba 1.8ppm 1.2ppm 1.1ppm 1.9ppm 33ppm 5.6ppm ICP method Ca 0.6ppm 0.8ppm 1.2ppm 7.8ppm 58ppm 1.1ppm ICP method Sr - - - - - - ICP method Na 4.5ppm 6.2ppm 7.1ppm 312ppm 88.2ppm 455ppm ICP method K 2.7ppm 4.3ppm 5.2ppm 3.8ppm 76.1ppm 4.4ppm ICP method R - - - - 2.4ppm - ICP method Cs - - - - 5.6ppm - ICP method Si 7.2ppm 4.5ppm 8.2ppm 9.3ppm 10.2ppm 6.1ppm ICP method <![CDATA[SO 4 2- ]]> 6.1ppm 7.2ppm 8.2ppm 1600ppm 89ppm 10.4ppm Ion chromatography Cl 1.5ppm 2.1ppm 1.1ppm 2ppm 29ppm 375ppm Ion chromatography

[0102] Note: ICP method is inductively coupled plasma detection method.

[0103] From the above table, we can see that: Comparative Example 1 uses the method due to SO 4 2- If it is not removed in advance, the obtained lithium carbonate contains a large amount of SO 4 2- Wrapping, high-purity lithium carbonate cannot be produced, and the sodium sulfate waste liquid obtained cannot be recycled, the waste liquid discharge is large, and the treatment cost is high;

[0104] In Comparative Example 2, the conversion rate of the causticization reaction was not high due to the low solubility of lithium carbonate, and some lithium carbonate was lost in the filter residue, the lithium yield was not high, only 80.6%, and the Ca, SO 4 2- The content is not low, and high-purity lithium carbonate cannot be produced; lithium hydroxide needs to pass CO 2 Hydrogenation reduces production efficiency.

[0105] In Comparative Example 3, due to the use of NaHCO 3 Replacement of Ca(HCO 3 ) 2Although hydrogenation is not required, a large amount of Na elements are introduced, and a large amount of barium salts are introduced at the same time. Barium salts are toxic and cannot be used too much. Since the lithium carbonate wet material contains a large amount of NaCl, it needs to be washed with water many times to reduce the production to a lower level, and it cannot reach a high-purity level. In addition, there is a large amount of NaCl in the mother liquor, which cannot be recycled many times.

[0106] The method of the present invention uses Ca 2+ , Ba 2+ Will SO 4 2- Removed, there is no SO after pyrolysis 4 2- Wrapping can produce high-purity lithium carbonate (more than 99.99%), and the lithium carbonate mother liquor after pyrolysis can be recycled, and the discharge of waste liquid is greatly reduced. Among them, the effect of embodiment 1 is the best.

[0107] Although the above embodiments have been described in detail, they are only a part of the embodiments of the present invention, not all of them. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all belong to the protection scope of the present invention.

Claims

1. A method for preparing high-purity lithium carbonate, Features: The following steps are involved: 1) At room temperature, Ca(HCO 3 ) 2 Stir and dissolve to obtain Ca(HCO 3 ) 2 Saturated solution; 2) Li 2 SO 4 Stir and dissolve to obtain Li 2 SO 4 Saturated solution; 3) Li 2 SO 4 The saturated solution was slowly added dropwise to the Ca(HCO 3 ) 2 Add the saturated solution dropwise while stirring for 1-2 hours to produce a large amount of white precipitate CaSO 4 , filtered to obtain LiHCO 3 Solution and by-product CaSO 4 plaster; 4) To LiHCO 3 Ba(HCO) was added to the solution 3 ) 2 The reaction was carried out, and the filtrate was filtered to obtain the filtrate, and Li 2 C 2 O 4 reacting, and filtering for a second time to obtain a second filtrate; 5) The second filtrate is charged into an ion exchange device with a selective resin to obtain LiHCO 3 Clean liquid; 6) LiHCO 3 The clean liquid was heated to boiling and maintained, and Li 2 CO 3 Wet material and Li 2 CO 3 Mother liquor, Li 2 CO 3 The mother liquor is recycled to step 1) in which Ca(HCO 3 ) 2 Dissolve and / or use in step 2) for Li 2 SO 4 Dissolve; 7)Li 2 CO 3 The wet material was heated to boiling with deionized water and stirred, and then filtered to obtain Li 2 CO 3 The wet material and the filtrate are stirred and washed, and the filtrate is recycled to step 1) in which Ca(HCO 3 ) 2 Dissolve and / or use in step 2) for Li 2 SO 4 Dissolve; 8)Li 2 CO 3 The wet material is dried and packaged to obtain high-purity Li 2 CO 3 .

2. The method for preparing high-purity lithium carbonate according to claim 1, Features: In the step 3), Li 2 SO 4 Li in saturated solution 2 SO 4 With Ca(HCO 3 ) 2 Ca(HCO) in saturated solution 3 ) 2 The molar ratio is: 1:0.95-1.

05.

3. The method for preparing high-purity lithium carbonate according to claim 1 or 2, Features: In the step 3), Li 2 SO 4 Li in saturated solution 2 SO 4 With Ca(HCO 3 ) 2 Ca(HCO) in saturated solution 3 ) 2 The molar ratio is: 1:

1.

4. The method for preparing high-purity lithium carbonate according to claim 1, Features: In the step 4), LiHCO 3 SO in solution 4 2- With Ba(HCO 3 ) 2 The molar ratio is: 1:1-1.

5.

5. The method for preparing high-purity lithium carbonate according to claim 1 or 4, Features: In the step 4), LiHCO 3 SO in solution 4 2- With Ba(HCO 3 ) 2 The molar ratio is: 1:

1.

6. The method for preparing high-purity lithium carbonate according to claim 1, Features: In the step 4), the Ca in the filtrate 2+ With Li 2 C 2 O 4 The molar ratio is: 1:1-1.

5.

7. The method for preparing high-purity lithium carbonate according to claim 1 or 6, Features: In the step 4), the Ca in the filtrate 2+ With Li 2 C 2 O 4 The molar ratio is: 1:

1.

8. The method for preparing high-purity lithium carbonate according to claim 1 or 6, Features: In the step 5), the flow rate of the ion exchange device is 1 ml / min.

9. The method for preparing high-purity lithium carbonate according to claim 1, Features: In the step 6), LiHCO 3 The heating rate of the clean liquid from room temperature to boiling is 1-3°C / min, and the boiling maintenance time is 30-60min.

10. The method for preparing high-purity lithium carbonate according to claim 1, Features: In the step 7), Li 2 CO 3 The mass ratio of wet material to deionized water is 1:3-4, and the stirring and washing time is 30-60 minutes.