A method for recovering lithium carbonate from a lithium carbonate solution

Abstract

The application discloses a method for preparing battery-grade lithium carbonate from lithium precipitation mother liquor, which comprises the following steps: carrying out decarburization reaction on the lithium precipitation mother liquor by using calcium oxide to obtain decarburization lithium-containing alkali solution; mixing the decarburization lithium-containing alkali solution with an extractant to obtain a lithium-rich organic phase; adding pure water or centrifugal mother liquor after pyrolysis, and carrying out aeration back extraction by introducing carbon dioxide to obtain lithium bicarbonate solution; sequentially carrying out deep oil removal treatment and calcium-magnesium resin impurity removal treatment to obtain purified lithium bicarbonate solution; and carrying out pyrolysis reaction, and then carrying out filtration, washing and drying to obtain battery-grade lithium carbonate. The application adopts deep oil removal and chelating resin deep calcium-magnesium removal purification process, improves the purity of the prepared lithium carbonate, and meets the requirements of battery-grade lithium carbonate; one-step decarburization and alkali production are realized by using calcium oxide to remove carbonate and generate hydroxyl; meanwhile, calcium slag can be recycled by high-temperature pyrolysis to regenerate calcium oxide, thereby reducing the consumption of lime; and the multi-stage alkaline extraction process is adopted to improve the extraction rate of lithium in the lithium precipitation mother liquor.

Description

Technical Field

[0001] This application relates to the field of battery-grade lithium carbonate preparation technology, and in particular to a method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor. Background Technology

[0002] In the industrial production process of preparing lithium carbonate by adding sodium carbonate to lithium sulfate solution, a large amount of lithium precipitation mother liquor is generated. This mother liquor still contains a certain amount of lithium, and direct discharge not only causes a serious waste of lithium resources but also puts pressure on environmental treatment. Therefore, the recovery and utilization of lithium resources from lithium precipitation mother liquor has significant economic and environmental value.

[0003] Currently, the mainstream process for lithium recovery from lithium precipitation mother liquor is the evaporation and sodium precipitation method: first, dilute sulfuric acid is added to the mother liquor for decarbonation, then caustic soda is added to adjust the pH to neutral, followed by evaporation and concentration to remove sodium sulfate. The mother liquor after sodium precipitation is then added to sodium carbonate for secondary lithium precipitation. This process has significant drawbacks: first, it consumes a large amount of acid and alkali, resulting in high reagent costs; second, it involves a large amount of water evaporation, leading to high steam energy consumption; and third, the purity of the recovered lithium carbonate is only about 98%, which can only be sold at a low price as crude lithium carbonate, resulting in low economic added value.

[0004] Chinese patent CN111943236A discloses a method for multi-stage adsorption of lithium from lithium precipitation mother liquor using a lithium adsorbent. The lithium solution obtained after multi-stage acid desorption is then returned to the system for lithium precipitation. This method requires multi-stage adsorption and desorption equipment, resulting in a long process flow and high equipment investment. Furthermore, the lithium solution obtained from the desorption process has a low concentration and cannot be directly used for lithium precipitation; further evaporation and concentration are required, leading to still high energy consumption.

[0005] Chinese patent CN111945017A discloses a method for lithium extraction from nickel leaching residue of ternary lithium recovery using an extractant. This method requires pretreatment with acid before extraction and saponification of the organic phase with alkali during extraction. The entire process consumes large amounts of acid and alkali, resulting in high reagent costs, and is not suitable for alkaline lithium precipitation mother liquor systems.

[0006] In summary, existing lithium extraction technologies from lithium precipitation mother liquor generally suffer from problems such as high acid and alkali consumption, high evaporation energy consumption, low product purity, high equipment investment, and long process flow. The industry urgently needs to develop a new low-cost, short-process lithium precipitation mother liquor recovery technology that can directly produce battery-grade lithium carbonate. Summary of the Invention

[0007] In order to solve at least one of the above-mentioned technical problems, and to develop a new process for recovering lithium precipitation mother liquor that is low-cost, short-process, and can directly produce battery-grade lithium carbonate, this application provides a method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor.

[0008] On the one hand, this application provides a method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor, comprising the following steps:

[0009] S1. Add calcium oxide to the lithium precipitation mother liquor to carry out the decarbonization reaction. After the reaction is complete, filter and separate to obtain calcium slag and decarbonized alkaline lithium liquor.

[0010] S2. The decarbonized alkaline lithium liquid is mixed with an extractant for extraction, and after phase separation, a lithium-rich organic phase and raffinate are obtained.

[0011] S3. Add pure water or centrifuged mother liquor after pyrolysis to the lithium-rich organic phase, and pass carbon dioxide for aeration and back-extraction. After phase separation, a lithium bicarbonate solution and a blank organic phase are obtained.

[0012] S4. The lithium bicarbonate solution is subjected to deep degreasing treatment and calcium-magnesium resin impurity removal treatment in sequence to obtain purified lithium bicarbonate solution.

[0013] S5. The purified lithium bicarbonate solution is heated to carry out a pyrolysis reaction, and after filtration, washing and drying, battery-grade lithium carbonate is obtained.

[0014] By adopting the above technical solution, and employing deep degreasing and chelating resin deep calcium and magnesium removal purification processes, the purity of the prepared lithium carbonate is improved to meet the requirements of battery-grade lithium carbonate. The purpose of adding calcium oxide to the lithium precipitation mother liquor is to remove carbonate ions from the mother liquor and simultaneously introduce hydroxide ions required for extraction. No additional acid or alkali decarbonation is needed, and no additional alkali saponification is required during the extraction process. The reaction equation is as follows:

[0015] CaO + H₂O = Ca(OH)₂

[0016] Ca(OH)₂ + Na₂CO₃ = CaCO₃↓ + 2NaOH

[0017] Li₂CO₃ + Ca(OH)₂ = CaCO₃↓ + 2LiOH

[0018] The process employs a one-step decarbonization and alkali production method using calcium oxide, simultaneously removing carbonate ions and generating hydroxide ions. This eliminates the need for additional dilute sulfuric acid for decarbonization and for adding alkali to saponify the extracted organic phase. Furthermore, the calcium slag can be recycled by high-temperature pyrolysis to produce regenerable calcium oxide, reducing lime consumption. The multi-stage alkaline extraction process also improves the lithium extraction rate from the lithium precipitation mother liquor.

[0019] Optionally, in S1, the amount of calcium oxide added is 1.3 to 1.4 times the theoretical molar amount of carbonate in the lithium precipitation mother liquor; the temperature of the decarbonization reaction is 75 to 85°C, and the reaction time is 1.5 to 2.5 h.

[0020] By adopting the above technical solution, the complete removal of carbonate ions is ensured while controlling the introduction of excessive calcium impurities, thereby improving reaction efficiency and reducing energy consumption costs.

[0021] Optionally, in S2, the extractant is selected from any one or more combinations of hydroxy ketone extractants, organophosphorus oxide extractants, and β-diketone extractants, and the diluent for the extractant is light white oil or sulfonated kerosene.

[0022] Optionally, the hydroxy ketone extractant is Lix54 or a derivative thereof; the organophosphorus oxide extractant is n-octylphosphine oxide or a derivative thereof; and the β-diketone extractant is benzoyltrifluoroacetone or a derivative thereof.

[0023] By adopting the above technical solution and selecting extractants and diluents suitable for alkaline lithium liquid systems, the lithium selectivity is excellent, the phase separation speed is fast, the organic phase has good chemical stability and low loss.

[0024] Optionally, in S2, the mixed extraction adopts multi-stage countercurrent extraction, with 1 to 5 stages, an extraction temperature of 30 to 40°C, and an oil-to-water ratio of 1:1 to 1.2:1.

[0025] By adopting the above technical solution, the mass transfer driving force is large, the lithium enrichment effect is good, and the single-stage extraction rate is high and stable.

[0026] Optionally, in S3, the lithium-rich organic phase is first subjected to multi-stage countercurrent washing with pure water before back-extraction, with 1 to 3 washing stages and an oil-water ratio of 8:1 to 12:1; the carbon dioxide back-extraction has 1 to 3 stages, and the pH value at the reaction endpoint is controlled to be 7 to 8.

[0027] Optionally, in S4, the deep degreasing treatment includes gravity degreasing of the coalescing filter element and deep degreasing by activated carbon adsorption.

[0028] By adopting the above technical solution, a two-stage deep oil removal process using a coalescing filter element and activated carbon is employed to remove suspended and dissolved trace organic matter, enabling the product to meet the total carbon index requirements for battery-grade products.

[0029] Optionally, in S1, the calcium slag is regenerated into calcium oxide after high-temperature pyrolysis and returned to S1 for recycling; in S2, the blank organic phase is returned to S2 for recycling; in S5, the centrifuged mother liquor generated by the pyrolysis reaction is returned to S3 for recycling.

[0030] By adopting the above technical solutions, calcium slag regeneration, organic phase and pyrolysis mother liquor are recycled, reducing raw material consumption and solid waste discharge, and improving the total lithium recovery rate.

[0031] Optionally, in S5, the pyrolysis reaction is carried out in a boiling state, and the washing is done with hot water at 90~100℃.

[0032] Secondly, this application provides the application of battery-grade lithium carbonate prepared by the above method in the field of lithium batteries.

[0033] By adopting the above technical solution, the obtained battery-grade lithium carbonate can be directly used in the preparation of lithium battery cathode materials without secondary purification.

[0034] In summary, the present invention has at least one of the following beneficial technical effects:

[0035] 1. By using deep degreasing and chelating resin deep calcium and magnesium removal purification processes, the purity of the prepared lithium carbonate is improved to meet the requirements of battery-grade lithium carbonate;

[0036] 2. The process uses calcium oxide for one-step decarbonization and alkali production, simultaneously removing carbonate ions and generating hydroxide ions. This eliminates the need for additional dilute sulfuric acid for decarbonization and for adding alkali to saponify the extracted organic phase. Furthermore, the calcium slag can be recycled by high-temperature pyrolysis to produce calcium oxide, reducing lime consumption.

[0037] 3. Employ a multi-stage alkaline extraction process to improve the lithium extraction rate in the lithium precipitation mother liquor. Attached Figure Description

[0038] Figure 1 This is a process flow diagram of a method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor according to the present invention. Detailed Implementation

[0039] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0040] On the one hand, this application designs a method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor. The method involves decarbonizing the lithium precipitation mother liquor with calcium oxide, filtering and separating it to obtain calcium slag and decarbonized alkaline lithium liquid. The calcium slag can be heated and decomposed to obtain calcium oxide for continued use. The decarbonized alkaline lithium liquid is extracted and separated to obtain a lithium-rich organic phase. Pure water or centrifuged mother liquor after pyrolysis is added, and carbon dioxide is introduced for aeration and back-extraction. After phase separation, a lithium bicarbonate solution is obtained. The solution is then subjected to deep degreasing treatment and calcium-magnesium resin impurity removal treatment to obtain a purified lithium bicarbonate solution. Finally, a pyrolysis reaction is carried out, and the solution is filtered, washed, and dried to obtain battery-grade lithium carbonate.

[0041] This application employs a deep degreasing and chelating resin deep calcium and magnesium removal purification process to improve the purity of the prepared lithium carbonate, meeting the requirements for battery-grade lithium carbonate. The purpose of adding calcium oxide to the lithium precipitation mother liquor is to remove carbonate ions and simultaneously introduce hydroxide ions required for extraction. No additional acid or alkali decarbonation is needed, and no additional alkali saponification is required during the extraction process. The reaction equation is as follows:

[0042] CaO + H₂O = Ca(OH)₂

[0043] Ca(OH)₂ + Na₂CO₃ = CaCO₃↓ + 2NaOH

[0044] Li₂CO₃ + Ca(OH)₂ = CaCO₃↓ + 2LiOH

[0045] The process employs a one-step decarbonization and alkali production method using calcium oxide, simultaneously removing carbonate ions and generating hydroxide ions. This eliminates the need for additional dilute sulfuric acid for decarbonization and for adding alkali to saponify the extracted organic phase. Furthermore, the calcium slag can be recycled by high-temperature pyrolysis to produce regenerable calcium oxide, reducing lime consumption. The multi-stage alkaline extraction process also improves the lithium extraction rate from the lithium precipitation mother liquor.

[0046] On the other hand, this application demonstrates the application of battery-grade lithium carbonate prepared by the above method in the field of lithium batteries. The battery-grade lithium carbonate prepared by the method of this application can be directly used in the preparation of lithium battery cathode materials without secondary purification.

[0047] Unless otherwise specified, the main components involved in the following embodiments of this application are all purchased from commercially available products. Specific Implementation

[0048] Example 1

[0049] This embodiment provides a method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor, as detailed below:

[0050] A certain amount of lithium precipitation mother liquor was taken, and the carbonate content was tested. Calcium oxide was weighed out at 1.3 times the theoretical molar amount of carbonate and added to the mother liquor. Stirring was started, and the reaction temperature was controlled at 80℃. The reaction was carried out under constant temperature stirring for 2 hours. After the reaction was completed, the mixture was separated by pressure filtration to obtain calcium carbonate slag and alkali-containing lithium filtrate. The separated calcium carbonate slag was sent to a rotary kiln for high-temperature pyrolysis treatment at 800℃ to regenerate calcium oxide, which can be recycled for the next batch of decarbonation reaction.

[0051] Light white oil was used as a diluent to prepare an organic phase solution of a hydroxyketone extractant (Lix54). The resulting lithium-containing filtrate and the prepared organic phase solution were fed into a multi-stage countercurrent extraction tank at an oil-to-water ratio of 1.2:1, and the extraction temperature was controlled at 35°C for four stages of countercurrent extraction. After extraction, the phases were separated to obtain a lithium-rich organic phase and raffinate. The raffinate could be sent to the upstream salting process for reuse. The lithium-rich organic phase was then fed into a washing tank and subjected to two stages of countercurrent washing with pure water at an oil-to-water ratio of 10:1 to remove water-soluble impurity ions such as sodium and calcium entrained in the organic phase.

[0052] The washed lithium-rich organic phase is introduced into the back-extraction tank, and the centrifuged mother liquor returned from pyrolysis is added as the back-extraction aqueous phase. Carbon dioxide gas is continuously introduced for aeration, and the pH value of the solution is monitored in real time. Aeration is stopped when the pH value reaches 7-8. After the reaction is completed, the phases are separated by settling to obtain an aqueous lithium bicarbonate solution and a blank organic phase. The blank organic phase can be directly returned to the extraction section for the next batch of extraction operations.

[0053] The obtained lithium bicarbonate solution is first passed through a coalescing filter for gravity oil removal, and then through an activated carbon adsorption column for deep oil removal, completely removing trace amounts of organic phase entrained in the solution. The deoiled lithium bicarbonate solution is then passed through a calcium-magnesium chelating resin column to remove trace amounts of calcium and magnesium impurity ions, yielding a high-purity lithium bicarbonate purified solution.

[0054] The purified lithium bicarbonate solution was fed into a pyrolysis reactor and heated to boiling for pyrolysis. After pyrolysis, the mixture was filtered, and the solid filter cake was washed with 95°C hot water. The washed cake was then dried in a drying apparatus to obtain battery-grade lithium carbonate. All pyrolysis centrifugal mother liquor generated during filtration was collected and recycled back to the back-extraction section.

[0055] In the method of this embodiment, the lithium extraction rate is 99.2%, and the purity of the prepared lithium carbonate is 99.62%, which meets the national standard requirements for battery-grade lithium carbonate.

[0056] Example 2

[0057] This embodiment provides a method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor. The difference between this method and Embodiment 1 is that the extraction process parameters are different: the oil-to-water ratio is 1:1 and the number of extraction stages is 3-stage countercurrent extraction.

[0058] A certain amount of lithium precipitation mother liquor was taken, and the carbonate content was tested. Calcium oxide was weighed out at 1.3 times the theoretical molar amount of carbonate and added to the mother liquor. Stirring was started, and the reaction temperature was controlled at 80℃. The reaction was carried out under constant temperature stirring for 2 hours. After the reaction was completed, the mixture was separated by pressure filtration to obtain calcium carbonate slag and alkali-containing lithium filtrate. The separated calcium carbonate slag was sent to a rotary kiln for high-temperature pyrolysis treatment at 800℃ to regenerate calcium oxide, which can be recycled for the next batch of decarbonation reaction.

[0059] Light white oil was used as a diluent to prepare an organic phase solution of a hydroxyketone extractant (Lix54). The resulting lithium-containing filtrate and the prepared organic phase solution were then introduced into a multi-stage countercurrent extraction tank at an oil-to-water ratio of 1:1. The extraction temperature was controlled at 35°C, and three stages of countercurrent extraction were performed. After extraction, the phases were separated to obtain a lithium-rich organic phase and a raffinate. The raffinate could be sent to the upstream salting process for reuse. The lithium-rich organic phase was then introduced into a washing tank and subjected to two stages of countercurrent washing with pure water at an oil-to-water ratio of 10:1 to remove water-soluble impurity ions such as sodium and calcium entrained in the organic phase.

[0060] The washed lithium-rich organic phase is introduced into the back-extraction tank, and the centrifuged mother liquor returned from pyrolysis is added as the back-extraction aqueous phase. Carbon dioxide gas is continuously introduced for aeration, and the pH value of the solution is monitored in real time. Aeration is stopped when the pH value reaches 7-8. After the reaction is completed, the phases are separated by settling to obtain an aqueous lithium bicarbonate solution and a blank organic phase. The blank organic phase can be directly returned to the extraction section for the next batch of extraction operations.

[0061] The obtained lithium bicarbonate solution is first passed through a coalescing filter for gravity oil removal, and then through an activated carbon adsorption column for deep oil removal, completely removing trace amounts of organic phase entrained in the solution. The deoiled lithium bicarbonate solution is then passed through a calcium-magnesium chelating resin column to remove trace amounts of calcium and magnesium impurity ions, yielding a high-purity lithium bicarbonate purified solution.

[0062] The purified lithium bicarbonate solution was fed into a pyrolysis reactor and heated to boiling for pyrolysis. After pyrolysis, the mixture was filtered, and the solid filter cake was washed with 95°C hot water. The washed cake was then dried in a drying apparatus to obtain battery-grade lithium carbonate. All pyrolysis centrifugal mother liquor generated during filtration was collected and recycled back to the back-extraction section.

[0063] Testing showed that the lithium extraction rate in this embodiment was 98.7%, and the purity of the prepared lithium carbonate was 99.58%, which meets the national standard requirements for battery-grade lithium carbonate.

[0064] Example 3

[0065] This embodiment provides a method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor, as detailed below:

[0066] A certain amount of lithium precipitation mother liquor was taken, and the carbonate content was tested. Calcium oxide was weighed out at 1.3 times the theoretical molar amount of carbonate and added to the mother liquor. Stirring was started, and the reaction temperature was controlled at 80℃. The reaction was carried out under constant temperature stirring for 2 hours. After the reaction was completed, the mixture was separated by pressure filtration to obtain calcium carbonate slag and alkali-containing lithium filtrate. The separated calcium carbonate slag was sent to a rotary kiln for high-temperature pyrolysis treatment at 800℃ to regenerate calcium oxide, which can be recycled for the next batch of decarbonation reaction.

[0067] Light white oil was used as a diluent to prepare an organic phase solution of n-octyl phosphorus oxide extractant. The resulting lithium-containing filtrate and the prepared organic phase solution were then introduced into a multi-stage countercurrent extraction tank at an oil-to-water ratio of 1.2:1. The extraction temperature was controlled at 35°C, and four stages of countercurrent extraction were performed. After extraction, the phases were separated to obtain a lithium-rich organic phase and raffinate. The raffinate could be sent to the upstream salting process for reuse. The lithium-rich organic phase was then introduced into a washing tank and subjected to two stages of countercurrent washing with pure water at an oil-to-water ratio of 10:1 to remove water-soluble impurity ions such as sodium and calcium entrained in the organic phase.

[0068] The washed lithium-rich organic phase is introduced into the back-extraction tank, and the centrifuged mother liquor returned from pyrolysis is added as the back-extraction aqueous phase. Carbon dioxide gas is continuously introduced for aeration, and the pH value of the solution is monitored in real time. Aeration is stopped when the pH value reaches 7-8. After the reaction is completed, the phases are separated by settling to obtain an aqueous lithium bicarbonate solution and a blank organic phase. The blank organic phase can be directly returned to the extraction section for the next batch of extraction operations.

[0069] The obtained lithium bicarbonate solution is first passed through a coalescing filter for gravity oil removal, and then through an activated carbon adsorption column for deep oil removal, completely removing trace amounts of organic phase entrained in the solution. The deoiled lithium bicarbonate solution is then passed through a calcium-magnesium chelating resin column to remove trace amounts of calcium and magnesium impurity ions, yielding a high-purity lithium bicarbonate purified solution.

[0070] The purified lithium bicarbonate solution was fed into a pyrolysis reactor and heated to boiling for pyrolysis. After pyrolysis, the mixture was filtered, and the solid filter cake was washed with 95°C hot water. The washed cake was then dried in a drying apparatus to obtain battery-grade lithium carbonate. All pyrolysis centrifugal mother liquor generated during filtration was collected and recycled back to the back-extraction section.

[0071] In the method of this embodiment, the lithium extraction rate is 99.2%, and the purity of the prepared lithium carbonate is 99.62%, which meets the national standard requirements for battery-grade lithium carbonate.

[0072] Example 4

[0073] This embodiment provides a method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor, as detailed below:

[0074] A certain amount of lithium precipitation mother liquor was taken, and the carbonate content was tested. Calcium oxide was weighed out at 1.3 times the theoretical molar amount of carbonate and added to the mother liquor. Stirring was started, and the reaction temperature was controlled at 80℃. The reaction was carried out under constant temperature stirring for 2 hours. After the reaction was completed, the mixture was separated by pressure filtration to obtain calcium carbonate slag and alkali-containing lithium filtrate. The separated calcium carbonate slag was sent to a rotary kiln for high-temperature pyrolysis treatment at 800℃ to regenerate calcium oxide, which can be recycled for the next batch of decarbonation reaction.

[0075] Light white oil was used as a diluent to prepare an organic phase solution of benzoyltrifluoroacetone extractant. The resulting lithium-containing filtrate and the prepared organic phase solution were then introduced into a multi-stage countercurrent extraction tank at an oil-to-water ratio of 1.2:1. The extraction temperature was controlled at 35°C, and four stages of countercurrent extraction were performed. After extraction, the phases were separated to obtain a lithium-rich organic phase and raffinate. The raffinate could be sent to the upstream salting process for reuse. The lithium-rich organic phase was then introduced into a washing tank and subjected to two stages of countercurrent washing with pure water at an oil-to-water ratio of 10:1 to remove water-soluble impurity ions such as sodium and calcium entrained in the organic phase.

[0076] The washed lithium-rich organic phase is introduced into the back-extraction tank, and the centrifuged mother liquor returned from pyrolysis is added as the back-extraction aqueous phase. Carbon dioxide gas is continuously introduced for aeration, and the pH value of the solution is monitored in real time. Aeration is stopped when the pH value reaches 7-8. After the reaction is completed, the phases are separated by settling to obtain an aqueous lithium bicarbonate solution and a blank organic phase. The blank organic phase can be directly returned to the extraction section for the next batch of extraction operations.

[0077] The obtained lithium bicarbonate solution is first passed through a coalescing filter for gravity oil removal, and then through an activated carbon adsorption column for deep oil removal, completely removing trace amounts of organic phase entrained in the solution. The deoiled lithium bicarbonate solution is then passed through a calcium-magnesium chelating resin column to remove trace amounts of calcium and magnesium impurity ions, yielding a high-purity lithium bicarbonate purified solution.

[0078] The purified lithium bicarbonate solution was fed into a pyrolysis reactor and heated to boiling for pyrolysis. After pyrolysis, the mixture was filtered, and the solid filter cake was washed with 95°C hot water. The washed cake was then dried in a drying apparatus to obtain battery-grade lithium carbonate. All pyrolysis centrifugal mother liquor generated during filtration was collected and recycled back to the back-extraction section.

[0079] In the method of this embodiment, the lithium extraction rate is 99.2%, and the purity of the prepared lithium carbonate is 99.62%, which meets the national standard requirements for battery-grade lithium carbonate.

[0080] Comparative Example 1

[0081] This comparative example uses a standard industry-standard lithium precipitation mother liquor recovery process, and the specific steps are as follows:

[0082] Take the same batch of lithium precipitation mother liquor as in Example 1, and slowly add 20% by mass of dilute sulfuric acid at room temperature with stirring to carry out the decarbonation reaction. Monitor the pH value of the solution in real time. Stop adding acid when the pH stabilizes at 4.0 at the end of the reaction, and continue stirring for 30 minutes to remove carbonate ions from the solution.

[0083] Add solid sodium hydroxide flakes to the decarbonized liquid, adjust the pH of the solution to 7.0, and stir until the sodium hydroxide flakes are completely dissolved; send the neutralized liquid to an evaporator for evaporation and concentration, concentrate to 1 / 3 of the original volume, filter while hot to separate the precipitated sodium sulfate crystals, and obtain sodium precipitation mother liquor.

[0084] Anhydrous sodium carbonate was added to the sodium precipitation mother liquor. The amount added was calculated as 1.3 times the theoretical molar amount of lithium in the mother liquor. The sodium carbonate solution was slowly added to the sodium precipitation mother liquor using the reverse addition method. The reaction temperature was controlled at 95℃, and the reaction was stirred for 1 hour. After the reaction was completed, the mixture was filtered while hot. The filter cake was washed with 95℃ hot water and dried to obtain crude lithium carbonate product. The precipitated mother liquor was collected.

[0085] Comparative Example 2

[0086] Compared to Example 1, this comparative example omits the deep degreasing and resin impurity removal processes of the back-extraction solution; the remaining steps are the same, as detailed below:

[0087] Take the same batch of lithium precipitation mother liquor as in Example 1, add calcium oxide at 1.3 times the theoretical molar amount of carbonate, stir and react at 80°C for 2 hours, separate calcium carbonate residue and decarbonized alkaline lithium liquor by pressure filtration; regenerate calcium oxide by high-temperature pyrolysis of calcium residue at 800°C.

[0088] Lix54 alkaline extractant diluted with light white oil was used, and the oil-to-water ratio O / A was controlled at 1.2:1. Four-stage countercurrent extraction was carried out at 35℃. The lithium-rich organic phase was washed with pure water in two stages of countercurrent washing, with an oil-to-water ratio O / A of 10:1.

[0089] After washing, pure water was added to the organic phase, and carbon dioxide was introduced for aeration and back-extraction. When the pH of the solution reached 7-8, the aeration was stopped, and the phases were separated to obtain a lithium bicarbonate solution and a blank organic phase.

[0090] The obtained lithium bicarbonate solution was directly heated to boiling to carry out the pyrolysis reaction, and the mixture was continuously stirred until no obvious bubbles were generated. The mixture was filtered while hot, the filter cake was washed with 95°C hot water, dried and the lithium carbonate product was obtained. The pyrolysis centrifugal mother liquor was collected.

[0091] Comparative Example 3

[0092] The difference between this comparative example and Example 1 is that only the deep degreasing process is retained, while the calcium-magnesium resin impurity removal step is omitted. The remaining processes are the same as in Example 1, and the specific steps are as follows:

[0093] Take the same batch of lithium precipitation mother liquor as in Example 1, add calcium oxide at 1.3 times the theoretical molar amount of carbonate, stir and react at 80°C for 2 hours, separate calcium carbonate residue and decarbonized alkaline lithium liquor by pressure filtration; regenerate calcium oxide by high-temperature pyrolysis of calcium residue at 800°C.

[0094] Lix54 alkaline extractant diluted with light white oil was used, and the oil-to-water ratio O / A was controlled at 1.2:1. Four-stage countercurrent extraction was carried out at 35℃. The lithium-rich organic phase was washed with pure water in two stages of countercurrent washing at an oil-to-water ratio O / A of 10:1 to remove water-soluble impurities such as sodium and calcium entrained in the organic phase.

[0095] Pure water was added to the washed organic phase, and carbon dioxide was continuously introduced for aeration and back-extraction. The pH value of the solution was monitored in real time. When the pH stabilized at 7-8, the aeration was stopped, and the phases were separated to obtain an aqueous lithium bicarbonate solution and a blank organic phase. The blank organic phase was transferred to the next batch of extraction for recycling.

[0096] The obtained lithium bicarbonate solution was sequentially passed through a coalescing filter for gravity oil removal and then through an activated carbon adsorption column for deep oil removal, resulting in a de-oiled lithium bicarbonate solution; the calcium magnesium chelate resin impurity removal process is omitted in this comparative example.

[0097] The degreased lithium bicarbonate solution was heated to boiling to carry out a pyrolysis reaction, and stirred continuously until no obvious bubbles escaped; it was filtered while hot, the filter cake was washed with 95°C hot water, dried to obtain lithium carbonate product, and the pyrolysis centrifugal mother liquor was collected.

[0098] Comparative Example 4

[0099] Compared to Example 1, this comparative example retains only the calcium-magnesium resin impurity removal process, omitting the deep degreasing step. The remaining processes are the same as in Example 1, and the specific steps are as follows:

[0100] Take the same batch of lithium precipitation mother liquor as in Example 1, add calcium oxide at 1.3 times the theoretical molar amount of carbonate, stir and react at 80°C for 2 hours, separate calcium carbonate residue and decarbonized alkaline lithium liquor by pressure filtration; regenerate calcium oxide by high-temperature pyrolysis of calcium residue at 800°C.

[0101] Lix54 alkaline extractant diluted with light white oil was used, and the oil-to-water ratio O / A was controlled at 1.2:1. Four-stage countercurrent extraction was carried out at 35℃. The lithium-rich organic phase was washed with pure water in two stages of countercurrent washing at an oil-to-water ratio O / A of 10:1 to remove water-soluble impurities such as sodium and calcium entrained in the organic phase.

[0102] Pure water was added to the washed organic phase, and carbon dioxide was continuously introduced for aeration and back-extraction. The pH value of the solution was monitored in real time. When the pH stabilized at 7-8, the aeration was stopped, and the phases were separated to obtain an aqueous lithium bicarbonate solution and a blank organic phase. The blank organic phase was transferred to the next batch of extraction for recycling.

[0103] The obtained lithium bicarbonate solution was directly passed into a calcium-magnesium chelate resin column for deep impurity removal. The flow rate was controlled to ensure full contact between the solution and the resin. The effluent was the lithium bicarbonate solution after resin impurity removal. This comparative example omits the coalescing filter and activated carbon deep oil removal process.

[0104] The purified lithium bicarbonate solution was heated to boiling to carry out the pyrolysis reaction, and the mixture was stirred continuously until no obvious bubbles escaped. The mixture was filtered while hot, the filter cake was washed with 95°C hot water, dried and the lithium carbonate product was obtained. The pyrolysis centrifugal mother liquor was collected.

[0105] Comparative Example 5

[0106] The difference between this comparative example and Example 1 is that sodium carbonate chemical precipitation is used instead of calcium magnesium resin for impurity removal, while retaining the deep degreasing process. The remaining processes are the same as in Example 1, and the specific steps are as follows:

[0107] Take the same batch of lithium precipitation mother liquor as in Example 1, add calcium oxide at 1.3 times the theoretical molar amount of carbonate, stir and react at 80°C for 2 hours, separate calcium carbonate residue and decarbonized alkaline lithium liquor by pressure filtration; regenerate calcium oxide by high-temperature pyrolysis of calcium residue at 800°C.

[0108] Lix54 alkaline extractant diluted with light white oil was used, and the oil-to-water ratio O / A was controlled at 1.2:1. Four-stage countercurrent extraction was carried out at 35℃. The lithium-rich organic phase was washed with pure water in two stages of countercurrent washing at an oil-to-water ratio O / A of 10:1 to remove water-soluble impurities such as sodium and calcium entrained in the organic phase.

[0109] Pure water was added to the washed organic phase, and carbon dioxide was continuously introduced for aeration and back-extraction. The pH value of the solution was monitored in real time. When the pH stabilized at 7-8, the aeration was stopped, and the phases were separated to obtain an aqueous lithium bicarbonate solution and a blank organic phase. The blank organic phase was transferred to the next batch of extraction for recycling.

[0110] The obtained lithium bicarbonate solution was sequentially passed through a coalescing filter for gravity oil removal and an activated carbon adsorption column for deep oil removal. Then, anhydrous sodium carbonate was added to the deoiled solution, and the mixture was stirred for 30 minutes to allow calcium and magnesium ions to form carbonate precipitates for removal. The calcium carbonate and magnesium carbonate precipitates were then removed by filtration to obtain a chemically purified lithium bicarbonate solution.

[0111] The lithium bicarbonate solution, after chemical purification, was heated to boiling to carry out a pyrolysis reaction, and stirred continuously until no obvious bubbles escaped. The solution was filtered while hot, the filter cake was washed with 95°C hot water, dried, and the lithium carbonate product was obtained. The pyrolysis centrifugal mother liquor was collected.

[0112] The lithium content of the mother liquor, raffinate, and precipitate mother liquor of the tested examples and comparative examples was determined, and the purity of the obtained lithium carbonate was also determined. The results are shown in Table 1.

[0113] Table 1

[0114] As can be seen from the comparison of the above embodiments and comparative examples, the method of preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor of the present invention has a stable lithium carbonate product purity of over 99.5%, and can directly produce battery-grade lithium carbonate.

[0115] A comparison of Examples 1 and 2 shows that the number of extraction stages and the oil-to-water ratio directly affect the lithium extraction rate. Under identical conditions, the extraction rate of the 4-stage countercurrent extraction scheme with an oil-to-water ratio of 1.2:1 is approximately 2.5 percentage points higher than that of the 3-stage extraction scheme with an oil-to-water ratio of 1:1, and the lithium residue in the raffinate decreases from 0.085 g / L to 0.005 g / L. This indicates that increasing the number of extraction stages and appropriately increasing the proportion of the organic phase can significantly reduce lithium loss. Both process parameters achieve the required product purity; in actual production, the choice should be made based on capacity and cost considerations.

[0116] The three alkaline extractants selected in Examples 1 and 3-4 can all achieve high extraction rates and product purity, and the process of this application has a wide range of extractant options.

[0117] Comparative Example 1 uses a conventional route of decarbonization with dilute sulfuric acid, sodium evaporation, and lithium precipitation with sodium carbonate. The total lithium recovery rate is only 71.37%, and the product purity is only 95%. This process eliminates the evaporation and concentration stage, which not only significantly improves the lithium yield but also upgrades the product from crude lithium carbonate to battery-grade lithium, resulting in a significant difference in economic value.

[0118] Comparative Example 2 completely skipped the oil and impurity removal process and directly pyrolyzed the back-extraction liquid. The product purity was only 98.56%, which did not meet the industrial-grade standard. This was mainly due to excessive organic matter and calcium and magnesium impurities.

[0119] Comparative Example 3 only performed oil removal without resin removal of calcium and magnesium, and the purity was increased to 99.01%, which is just up to industrial grade, but the calcium and magnesium residue still exceeded the standard and did not meet the battery grade requirements.

[0120] Comparative Example 4 only underwent resin impurity removal without oil removal, resulting in a purity of 99.27%. However, excessive organic residue resulted in a purity that barely met industrial-grade standards and did not meet battery-grade requirements.

[0121] Comparative Example 5 used degreasing and sodium carbonate chemical precipitation to remove calcium and magnesium instead of resin, resulting in a product with a purity of 99.21%, which did not meet the purity requirements for battery-grade lithium carbonate. The chemical precipitation method used in Comparative Example 5 had limited removal depth of calcium and magnesium.

[0122] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor, characterized in that, Includes the following steps: S1. Add calcium oxide to the lithium precipitation mother liquor to carry out the decarbonization reaction. After the reaction is complete, filter and separate to obtain calcium slag and decarbonized alkaline lithium liquor. S2. The decarbonized alkaline lithium liquid is mixed with an extractant for extraction, and after phase separation, a lithium-rich organic phase and raffinate are obtained. S3. Add pure water or centrifuged mother liquor after pyrolysis to the lithium-rich organic phase, and pass carbon dioxide for aeration and back-extraction. After phase separation, a lithium bicarbonate solution and a blank organic phase are obtained. S4. The lithium bicarbonate solution is subjected to deep degreasing treatment and calcium-magnesium resin impurity removal treatment in sequence to obtain purified lithium bicarbonate solution. S5. The purified lithium bicarbonate solution is heated to carry out a pyrolysis reaction, and after filtration, washing and drying, battery-grade lithium carbonate is obtained.

2. The method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor according to claim 1, characterized in that, In S1, the amount of calcium oxide added is 1.3 to 1.4 times the theoretical molar amount of carbonate in the lithium precipitation mother liquor; the temperature of the decarbonization reaction is 75 to 85°C, and the reaction time is 1.5 to 2.5 h.

3. The method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor according to claim 1, characterized in that, In S2, the extractant is selected from any one or more combinations of hydroxy ketone extractants, organophosphorus oxide extractants, and β-diketone extractants, and the diluent for the extractant is light white oil or sulfonated kerosene.

4. The method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor according to claim 3, characterized in that, The hydroxy ketone extractant is Lix54 or a derivative thereof; the organophosphorus oxide extractant is n-octylphosphine oxide or a derivative thereof; and the β-diketone extractant is benzoyltrifluoroacetone or a derivative thereof.

5. The method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor according to claim 1, characterized in that, In S2, the mixed extraction adopts multi-stage countercurrent extraction with 1 to 5 stages, an extraction temperature of 30 to 40°C, and an oil-to-water ratio of 1:1 to 1.2:

1.

6. The method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor according to claim 1, characterized in that, In S3, the lithium-rich organic phase is first subjected to multi-stage countercurrent washing with pure water before back-extraction. The number of washing stages is 1 to 3, and the washing oil-water ratio is 8:1 to 12:

1. The number of carbon dioxide back-extraction stages is 1 to 3, and the pH value at the reaction endpoint is controlled to be 7 to 8.

7. The method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor according to claim 1, characterized in that, In S4, the deep degreasing treatment includes gravity degreasing of the coalescing filter element and deep degreasing by activated carbon adsorption.

8. The method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor according to claim 1, characterized in that, In S1, the calcium slag is regenerated into calcium oxide after high-temperature pyrolysis and returned to S1 for recycling; in S2, the blank organic phase is returned to S2 for recycling; in S5, the centrifuged mother liquor generated by the pyrolysis reaction is returned to S3 for recycling.

9. The method for preparing battery-grade lithium carbonate by recovering lithium precipitation mother liquor according to claim 1, characterized in that, In S5, the pyrolysis reaction is carried out in a boiling state, and the washing is done with hot water at 90~100℃.

10. The application of the method of claim 1 to prepare battery-grade lithium carbonate in the field of lithium batteries.

Images