Method for removing chlorine from lithium precipitation mother liquor by ion exchange

Abstract

The application discloses a method for removing chlorine in lithium precipitation mother liquor by ion exchange method and belongs to the technical field of purifying solution by ion exchange method. The method comprises the following steps: A) injecting acid into the lithium precipitation mother liquor to remove carbon; B) removing chlorine by exchange adsorption of a sulfate resin column group; C) washing a chlorine resin column; D) eluting and regenerating the chlorine resin column after washing; and E) transforming a hydroxyl resin column into a sulfate resin column after regeneration. The method has the advantages of being online, continuous, simple in operation and maintenance, low in investment and operation cost, high in chlorine ion removal efficiency and high in recovery rate of battery-grade lithium carbonate products.

Description

Technical Field

[0001] This invention relates to a method for efficiently recovering lithium by removing chloride ions from lithium precipitation mother liquor using ion exchange, and in particular, a method for removing chloride ions from lithium precipitation mother liquor by continuous exchange adsorption, intermittent washing, elution, and regeneration of ion exchange resin column groups, belonging to the field of ion exchange method for purifying solutions. Background Technology

[0002] Lithium, the world's lightest metal, is closely intertwined with today's high technology, defense industry, and our daily lives. It is a crucial raw material for the development of high-tech industries such as nuclear power, aerospace, and electronics, and a vital material foundation for people's ever-growing material and cultural well-being. The lithium industry, as a key battery material sector, spans three strategic emerging industries: new materials, new energy, and new information technology. With the support and promotion of industrial policies, the lithium industry is poised for an attractive future.

[0003] Lithium carbonate is the most widely used and most important basic product in the lithium industry. It is divided into two categories based on the raw materials used in its production process: lithium extraction from ore and lithium extraction from brine. Lithium extraction from ore is a mature and stable process with simple technology, suitable for the production of high-purity lithium carbonate and battery-grade lithium carbonate, while lithium extraction from brine is suitable for the preparation of industrial-grade lithium carbonate.

[0004] Lithium extraction from ore refers to the production of lithium carbonate from solid lithium ores such as spodumene and lepidolite. The general process is as follows: First, the solid lithium ore is roasted at high temperature into a clinker, then crushed and leached with water to transfer the soluble lithium sulfate in the clinker into a solution, thus obtaining a lithium sulfate solution. The lithium sulfate solution is purified to remove impurities and concentrated to obtain a lithium-rich solution, which is then reacted with a saturated sodium carbonate solution to produce lithium carbonate precipitate. Solid-liquid separation yields a primary lithium carbonate cake, which is washed, dried, and crushed to obtain a high-purity or battery-grade lithium carbonate product. The solid-liquid separation yields a primary lithium precipitation mother liquor, which is acidified for decarbonation, MVR evaporation, concentration, and crystallization, followed by centrifugal separation to obtain anhydrous sodium sulfate and centrifugal mother liquor. The centrifugal mother liquor is then further purified and reacted with a saturated sodium carbonate solution for a secondary lithium precipitation to produce lithium carbonate precipitate. The secondary lithium carbonate cake and secondary lithium precipitation mother liquor are then combined with the primary lithium precipitation mother liquor, implementing a closed-loop cycle to improve the lithium carbonate recovery rate.

[0005] However, in existing lithium extraction processes, raw materials such as lithium ore and sodium carbonate continuously introduce chloride ions into the system. The current processes lack treatment measures and have no process outlet, leading to the continuous accumulation and enrichment of chloride ions within the system. As the chloride ion concentration increases, it causes significant harm to the entire production system: 1) Chloride ions corrode stainless steel equipment and facilities, reducing their lifespan. Dissolved metal ions severely affect the quality of battery-grade lithium carbonate products and the safety of lithium-ion batteries; 2) During the evaporation and concentration of lithium precipitation mother liquor in MVR (Medium-Voltage Reduction) processes, fine sodium chloride crystals easily precipitate, causing scaling and blockage in the MVR system heat exchangers. This severely affects the formation of sodium sulfate and potassium sulfate crystals, reducing the efficiency of MVR concentration, crystallization, and denitrification, and even making solid-liquid separation impossible using centrifuges, resulting in the MVR system's inability to operate normally and stably; 3) This leads to high sodium, potassium, and sulfate content in battery-grade lithium carbonate products, resulting in substandard products and significantly increasing the cost of secondary purification; 4) Lithium sulfate solutions containing high concentrations of chloride ions can only be sold as substandard products at reduced prices, affecting the recovery rate of battery-grade lithium carbonate products. Therefore, there is an urgent need for an online, continuous, simple-to-operate and maintain dechlorination method with low operating costs in the lithium extraction process from ore.

[0006] The main methods for removing chloride ions from solutions include precipitation, solvent extraction, and ion exchange. Precipitation methods primarily involve silver salt, cuprous salt, and bismuth salt precipitation. Solvent extraction methods mainly include organic-phase liquid-liquid extraction using alkaline extractants. Ion exchange methods primarily involve anion exchange resins. However, these methods are mostly used in water treatment, wastewater treatment, and the removal of chloride ions from zinc sulfate solutions, and are rarely applied in lithium extraction from ores.

[0007] Chinese patent CN101492772A discloses an industrial-scale ion exchange method for removing fluoride and chlorine from wet zinc smelting. This technology involves passing a zinc sulfate solution through an ion exchange resin under acidic conditions with a pH of 2.5–5.5. The resin adsorbs fluoride and chlorine ions, thus removing them from the solution. However, this technology uses a 10% sulfuric acid solution as the eluent, resulting in a perchloric acid solution, which presents significant challenges for water treatment.

[0008] Chinese patent CN117003805A discloses a process for separating and purifying UMP feed solution using a sequential ion exchange method. This sequential continuous ion exchange method consists of three or more resin columns, divided into three zones: I, II, and III, with at least one column in each zone. The feed solution enters from the top of the resin column and flows out from the bottom. Each resin column is filled with anion exchange resin, and adsorption, washing, elution, and regeneration are performed in sequence. However, although this process uses a series of resin columns, it requires alternating operation, failing to achieve online, continuous operation. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide an online, continuous method for removing chloride ions from lithium precipitation mother liquor with low input, simple operation and maintenance, and low cost. This method eliminates the hazards caused by chloride ion accumulation in lithium precipitation mother liquor, such as equipment corrosion, reduced MVR concentration crystallization denitrification efficiency, and excessive sodium, potassium, and sulfate content in secondary lithium carbonate products.

[0010] To address the aforementioned technical problems, this invention provides a method for efficiently recovering lithium by removing chloride ions from lithium precipitation mother liquor via ion exchange, specifically a method for removing chloride ions from lithium precipitation mother liquor through continuous exchange adsorption, intermittent washing, elution, and regeneration of an ion exchange column assembly. The specific technical solution is as follows:

[0011] A method for removing chloride from lithium precipitation mother liquor by ion exchange includes the following steps: A) Sulfuric acid is injected into the lithium precipitation mother liquor, stirred and acidified for decarbonization, cooled, and separated into liquid and solid to produce decarbonized liquid and decarbonized residue. The lithium precipitation mother liquor is the residual liquid from lithium carbonate produced by precipitating lithium sulfate solution with saturated sodium carbonate solution. The decarbonized residue is sent to prepare lithium sulfate solution; B) The decarbonized liquid is injected into a sulfate-type resin column assembly. The sulfate-type resin in the resin column undergoes anion exchange with the decarbonized liquid, and chloride ions in the decarbonized liquid are adsorbed in the resin column to produce an adsorbed liquid and a chloride-type resin column. The adsorbed liquid is sent for concentration, crystallization, and denitrification. After deep purification, lithium is recovered by secondary lithium precipitation with saturated sodium carbonate solution. C) The chloride-form resin column is washed with wash water, producing wash water and washed chloride-form resin columns. Part of the wash water is returned for use in this step, and part is returned to step B and mixed with the decarbonization liquid, then incorporated into the decarbonization liquid; D) The washed chloride-form resin column is eluted and regenerated with eluent, producing eluent and hydroxide resin columns. Part of the eluent is returned for use in this step, and part is sent to a salt chemical treatment plant; E) The hydroxide-form resin column is transformed with a conversion solution, producing a conversion solution and sulfate-form resin columns. Part of the conversion solution is returned for use in this step, and part is returned to step A and mixed with the lithium precipitation mother liquor, then incorporated into the lithium precipitation mother liquor. The sulfate-form resin columns are incorporated into the sulfate-form resin column group in step B.

[0012] The resin column group mentioned in step B is preferably composed of 4 to 5 resin columns connected in series. The decarbonization liquid is injected into the first-stage resin column, then flows through the second-stage resin column, and finally flows out from the last-stage resin column.

[0013] In step B, each resin column in the resin column group is further preferably capable of being short-circuited, separated from the resin column group, and subjected to washing, elution, regeneration, and transformation of the chlorine-form resin column.

[0014] In a further optimized step, the decarbonization solution in step B is injected into the resin column group for anion exchange. The adsorbed liquid sample produced by the last resin column is collected periodically and sent for chloride ion content testing. The chloride ion content of the sample is required to be ≤0.2g / L. If the requirement is not met, the chloride form resin column that is saturated with exchange adsorption is short-circuited in time, and the sulfate form resin column that has completed the transformation is replaced. The chloride form resin column separated by the short circuit is washed, eluted, regenerated, and transformed in time.

[0015] Further preferably, the anion exchange resin packed in the resin column assembly in step B is an environmentally friendly ion exchange resin with trade name success 940.

[0016] Generally, the stirring time for acidification and decarburization in step A is 0.5h to 2.0h, the final pH of the decarburized liquid is 2.0 to 5.0, and the temperature is cooled to 30℃ to 50℃.

[0017] Generally, in step B, the decarbonation solution is injected into a sulfate-type resin column group for anion exchange, and the residence time in the single-stage resin column is 30 min to 45 min.

[0018] Generally, in step C, the chlorinated resin column is washed with wash water. First, the decarbonization liquid in the resin column is drained, and 2BV of primary wash water is injected for 1.0h of circulation washing to produce secondary wash water. Then, fresh water is injected for 1.0h of circulation washing to produce primary wash water. The primary wash water is used for the next round of chlorinated resin column washing. The secondary wash water is returned to step B and mixed with the decarbonization liquid, and then incorporated into the decarbonization liquid.

[0019] Generally, in step D, the washing of the chlorinated resin column involves injecting eluent for elution and regeneration. First, the primary wash water in the resin column is drained, and 2 BV of primary eluent is injected for circulation and regeneration for 1.0 h to produce secondary eluent. Then, sodium hydroxide solution is injected for circulation and washing for 1.0 h to produce primary eluent. The primary eluent is used for the next round of chlorinated resin column elution and regeneration. The concentration of the sodium hydroxide solution is 40.0 g / L to 50.0 g / L.

[0020] Generally, in step E, the hydroxide-type resin column is injected with a conversion solution for conversion. First, the primary eluent in the resin column is drained, and 2 BV of primary conversion solution is injected for 1.0 h of conversion to produce a secondary conversion solution. Then, sulfuric acid solution is injected for 1.0 h of conversion to produce a primary conversion solution. The primary conversion solution is used for the next round of hydroxide-type resin column conversion. The concentration of the sulfuric acid solution is 100.0 g / L to 120.0 g / L. The secondary conversion solution is returned to step A and mixed with the lithium precipitation mother liquor. After the conversion is completed, the sulfate-type resin column is drained of the primary conversion solution and filled with fresh water to submerge the resin column for replacement and operation.

[0021] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0022] 1) Online, continuous, and simple operation and maintenance: In existing technologies, the main methods for removing chloride ions from solutions include precipitation, solvent extraction, and ion exchange resin methods. Precipitation uses soluble precipitants such as silver salts, cuprous salts, and bismuth salts to react with chloride ions in the solution to produce a precipitate. After liquid-solid separation, the chloride ions are removed. Obviously, this method is not online or continuous. Solvent extraction uses an organic phase containing an alkaline extractant to react with chloride ions in the solution, transferring the chloride ions into the organic phase to remove them from the solution. This method can achieve online and continuous operation. However, solvent extraction units involve multi-stage mixing and separation of organic phases and solutions, conversion between high and low solution levels, oil removal from extraction residues, and regeneration and transformation of organic phases, which obviously makes operation and maintenance complex. Ion exchange resin methods involve single-column operation and multi-column circulation, which are not online or continuous, and moving bed operation and maintenance are complex. This invention employs an ion exchange resin column assembly for continuous exchange adsorption and intermittent washing, elution, regeneration, and transformation to remove chloride ions from lithium precipitation mother liquor. The ion exchange resin column assembly consists of 4 to 5 resin columns. Any resin column that is saturated with exchange adsorption is short-circuited and separated from the resin column assembly for washing, elution, regeneration, and transformation. The remaining resin column assembly, containing 3 to 4 resin columns, operates continuously online. During operation, the liquid after adsorption from the last resin column is periodically sampled to monitor the chloride ion content, thereby periodically selecting the resin column that is saturated with exchange adsorption. Furthermore, it involves only four types of aqueous solution transfer, requires no high-power mechanical operation, and is simple to operate and maintain.

[0023] 2) Low Investment and Operating Costs: Existing technologies for removing chloride ions from solutions involve low investment, requiring only a stirred reaction tank and liquid-solid separation equipment. However, the consumption of soluble precipitants for chloride ions is high, regardless of whether they are silver salts, cuprous salts, or bismuth salts, resulting in high operating costs. Solvent extraction involves fixed investments such as solvent extraction units, high and low temperature storage tanks, mechanical stirring systems, and deoiling systems, leading to relatively high investment costs. It also involves extractants, modifiers, solvent oils, transforming agents, elution regeneration agents, and electricity consumption, resulting in high operating costs. This invention uses ion exchange resin column groups for continuous exchange adsorption and intermittent washing, elution, regeneration, and transformation to remove chloride ions from lithium precipitation mother liquor. This involves fixed investments such as ion exchange resin column groups, ion exchange resins, low-level tanks, and transfer pumps, resulting in relatively low investment costs. It also involves bulk chemicals such as fresh water, sulfuric acid, and sodium hydroxide, resulting in low unit consumption and lower operating costs.

[0024] 3) High Chloride Ion Removal Efficiency: In existing technologies, precipitation methods for removing chloride ions from solutions, with silver salt precipitation achieving the highest removal rate (up to 99.9%), are unsuitable for industrial production due to their high cost. Cuprous and bismuth salt precipitation methods, due to incomplete precipitation of cuprous chloride and bismuth oxychloride, achieve a maximum removal rate of 90%. To improve the removal rate, multi-stage dechlorination processes are recommended, but these complicate operation. Solvent extraction methods can remove chloride ions from solutions, achieving a removal rate of up to 99.0%. Further improvements require multi-stage extraction processes to reduce the operating capacity of the extractant, but this further complicates operation. This invention utilizes a continuous exchange adsorption and intermittent washing and elution regeneration process with ion exchange resin columns to remove chloride ions from lithium precipitation mother liquor, achieving a removal rate exceeding 99.0%. Firstly, the chloride ion load decreases sequentially in each stage of the series-connected resin column group, with the final resin column having a lower chloride ion load, ensuring a low residual chloride ion concentration in the post-adsorption solution. Furthermore, no leakage has been observed during practical operation.

[0025] 4) High Recovery Rate of Battery-Grade Lithium Carbonate: In existing technologies, the recovery rate of battery-grade lithium carbonate from ore-based lithium extraction is only 80.0% after primary lithium carbonate precipitation. Secondary lithium carbonate precipitation after decarbonization, concentration, crystallization, desalination, and deep purification of the lithium precipitation mother liquor only yields industrial-grade lithium carbonate. Furthermore, chloride ions accumulate and enrich in the system during the ore-based lithium extraction process, corroding production equipment, increasing the salt-to-nitrate ratio of the MVR concentrate, reducing the MVR concentration, crystallization, and denitrification efficiency, and harming the quality of the secondary lithium carbonate product. This invention employs a continuous exchange adsorption and intermittent washing and regeneration process using ion exchange resin columns to remove chloride ions from the lithium precipitation mother liquor. After decarbonization, dechlorination, concentration, crystallization, denitrification, and deep purification of the lithium precipitation mother liquor, secondary lithium carbonate precipitation yields battery-grade lithium carbonate, increasing the recovery rate of battery-grade lithium carbonate by more than 15.0%. It also significantly improves corrosion of production equipment and significantly enhances the MVR concentration, crystallization, and denitrification efficiency. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of a method for removing chlorine from lithium precipitation mother liquor by ion exchange. Detailed Implementation

[0027] To enable those skilled in the art to understand and implement the present invention, specific embodiments are described in detail below, with preferred embodiments further illustrating the invention. Admittedly, the selected embodiments are not all embodiments of the present invention, nor are they within the full scope of protection of the claims. Any specific embodiment that follows the scope defined by the claims of the present invention should be included within the protection scope of the present invention.

[0028] Battery-grade lithium carbonate is mainly produced by reacting a concentrated lithium-rich sulfate solution with a saturated sodium carbonate solution to obtain lithium carbonate and a lithium precipitation mother liquor. Due to the low solubility product of lithium carbonate, lithium cannot be completely precipitated in the system (the precipitation rate is generally 70%–80%). To recover lithium from the lithium precipitation mother liquor, it is generally first neutralized with sulfuric acid to remove carbonate ions. Then, the neutralized lithium precipitation mother liquor is evaporated, concentrated, and crystallized to separate anhydrous sodium sulfate, followed by secondary lithium precipitation. However, because raw materials and auxiliary materials, including lithium ore and sodium carbonate, continuously introduce chloride ions into the system, and the existing production process lacks treatment measures and a process outlet, chloride ions continuously accumulate and enrich within the system. As the chloride ion concentration continues to increase, it brings significant harm to the entire production system: 1) corrosion of stainless steel equipment and facilities; 2) malfunction of the MVR evaporation, concentration, and crystallization system; 3) increased purification costs for battery-grade lithium carbonate products; 4) low recovery rates for battery-grade lithium carbonate products, etc. This is a long-standing and unresolved problem in the lithium carbonate industry. Therefore, there is an urgent need for an online, continuous dechlorination treatment method in lithium carbonate production that is simple to operate and maintain and has low operating costs.

[0029] To eliminate the hazards of chlorine in lithium carbonate production, the inventors continuously summarized and researched in practice, and optimized a method for removing chlorine from lithium precipitation mother liquor using ion exchange. This method is characterized by the use of ion exchange column arrays for continuous exchange adsorption followed by intermittent washing, elution, and regeneration to remove chloride ions from the lithium precipitation mother liquor. This method fully meets the requirements of online operation, continuous processing, simple operation and maintenance, low investment, and low operating costs, and also boasts a high chloride ion removal rate and a high recovery rate of battery-grade lithium carbonate.

[0030] The lithium precipitation mother liquor in lithium carbonate production is generally an alkaline sulfate solution. + 2.0g / L~3.0g / L, Cl - 10.0 g / L~20.0 g / L, pH=9~11, rich in CO3 2- OH - Obviously, this solution cannot be directly used for dechlorination with ion exchange resin. Generally, the lithium precipitation mother liquor is taken and uniformly injected with 98% industrial sulfuric acid (by mass) for decarbonization under stirring. The pH of the solution is adjusted to 2.0–5.0, and the reaction is carried out with thorough stirring for 0.5–2.0 hours until carbon dioxide gas is exhausted and small bubbles on the liquid surface disappear completely. The solution is then cooled to 30–50°C, and liquid-solid separation is performed to obtain decarbonized liquid and decarbonized slag. The decarbonized slag is sent to prepare lithium sulfate solution for further lithium recovery. Liquid-solid separation can be performed using a plate and frame filter press, a box filter press, or a diaphragm filter press, to minimize the moisture content of the decarbonized slag and improve the clarity of the solution. The main chemical reactions in the process are:

[0031] CO3 2- +H₂SO₄=SO₄ 2- +CO2↑+H2O

[0032] 2OH - +H₂SO₄=SO₄ 2- +2H2O

[0033] The decarbonized solution is injected into an ion exchange resin column for adsorption. Chloride ions in the decarbonized solution undergo ion exchange with the sulfate-type ion exchange resin column, and the chloride ions are adsorbed in the resin column. Sulfate ions in the resin enter the solution, thus removing chloride ions from the decarbonized solution and producing an adsorbed solution and a loaded chloride-type resin column. The sulfate-type resin reaches saturation after adsorbing a certain amount of chloride ions and can no longer exchange and adsorb chloride ions. To ensure the throughput of the decarbonized solution by the sulfate-type resin column, a resin column group containing multiple resin columns is set. To ensure online and continuous operation of the decarbonized solution exchange adsorption, it is preferable to use 4 to 5 resin columns connected in series. The decarbonized solution is injected into the first-stage resin column, then flows through the second-stage resin column, and finally flows out from the last-stage resin column. The resin column group has a stepped layout, with the decarbonized solution flowing downstream from the top of the resin column and then injected into the second-stage resin exchange column through the bottom. During operation, the decarbonized solution can completely submerge the resin columns, making it less likely for the flow to be interrupted. Obviously, as long as the resin column stepped layout has a reasonable height difference, continuous and automatic online operation of the decarbonization solution is entirely possible. Generally, to ensure the equilibrium time of the resin column exchange adsorption, the decarbonization solution is injected into the resin column group for anion exchange adsorption, and the residence time in a single resin column is 30 min to 45 min. The main chemical reactions during the process are:

[0034] R3NHSO4+Cl - =R3NCl+HSO4 -

[0035] The adsorption liquid produced by the resin column, also known as the dechlorination liquid, is a weakly acidic solution. Liquid alkali (sodium hydroxide mass fraction 32%–50%) can be added to adjust the pH of the adsorption liquid to 6.5–8.5. This solution is then sent to the MVR system for evaporation, concentration, crystallization, and denitrification. At this point, the concentrated solution has a pH ≥ 12 and a Cl- content of [missing information]. - With a concentration ≤1g / L, the impact of chloride ions on equipment and product quality is essentially eliminated. The lithium ion concentration in the denitrification mother liquor reaches 10.0~20.0g / L, and it is then transferred to subsequent deep purification and lithium precipitation processes.

[0036] If elution and regeneration are performed after the sulfate-type resin column group is completely saturated, it will cause an interruption in the ion exchange adsorption production. To eliminate this drawback, a further optimization is to allow each resin column in the resin column group to be short-circuited, separating them from the resin column group for washing, elution, regeneration, and conversion of the loaded chloride-type resin column. In practical operation, the decarbonization liquid exchange adsorption pipeline is set as a continuous pipeline, while the washing, elution, regeneration, and conversion pipelines are set as intermittent pipelines, with the two lines operating independently and in parallel. Wash water, eluent, and conversion solution can all be used to flush the resin columns in both directions.

[0037] To further optimize the process of controlling the continuous exchange adsorption and intermittent washing, elution, regeneration, and transformation of this anion exchange resin column assembly to remove chloride ions from the lithium precipitation mother liquor, the inventors have optimized the method as follows: During ion exchange, when the decarbonization solution is injected into the sulfate-type resin column assembly, samples of the adsorbed liquid produced by the final resin column are periodically collected and sent for chloride ion content testing. The chloride ion content of the sample is required to be ≤0.2 g / L. If this requirement is not met, the saturated single-stage chloride-type resin column is short-circuited, and the transformed sulfate-type resin column is replaced. The short-circuited single-stage chloride-type resin column is then promptly washed, eluted, regenerated, and transformed. Clearly, with a stepped resin column layout, the higher resin columns undergo washing, elution, regeneration, and transformation at higher frequencies, while the lower resin columns undergo these processes at lower frequencies. By setting a specific program, automated control can be easily achieved.

[0038] The removal of chloride ions from lithium precipitation mother liquor using ion exchange involves not only the design of the process, equipment, and methods, but also, crucially, the selection of the ion exchange resin. Commonly available anion exchange resins include strong-base gel resin 201×7 (formerly brand 717) and strong-base macroporous resin D201. Through numerous experiments and studies, the inventors further optimized the anion exchange resin used in the resin column assembly to be an environmentally friendly ion exchange resin, trade name Success 940. This resin exhibits high saturated adsorption capacity, strong weather resistance, and excellent controllability, making it suitable for dechlorination treatment of high-salt lithium precipitation mother liquor solutions.

[0039] Generally, the loaded chlorine-form resin column should be washed with wash water. First, drain the decarbonization liquid from the chlorine-form resin column, then inject 2BV of primary wash water for 1.0h of circulation to produce secondary wash water. Then, inject fresh water for 1.0h of circulation to produce primary wash water. The primary wash water can be used for the next round of loading of the chlorine-form resin column. The secondary wash water is returned to be mixed with the decarbonization liquid and incorporated into the decarbonization liquid.

[0040] After washing, the chlorinated resin column is regenerated by injecting eluent. First, the primary wash water is drained from the column, and then 2 BV of primary eluent is injected for 1.0 h of elution and regeneration, producing a secondary eluent. Then, sodium hydroxide solution is injected for another 1.0 h of elution, producing a primary eluent. This primary eluent is used for the next round of washing and regeneration of the chlorinated resin column. Generally, the concentration of the sodium hydroxide solution is 40.0 g / L to 50.0 g / L. The main chemical reactions during the process are:

[0041] R3NCl + NaOH = R3NOH + NaCl

[0042] After elution and regeneration, the hydroxide-type resin column is injected with a conversion solution for conversion. First, the primary eluent is drained from the hydroxide-type resin column, and 2 BV of primary conversion solution is injected for 1.0 h of circulation conversion, producing a secondary conversion solution. Then, sulfuric acid solution is injected for 1.0 h of circulation conversion, producing a primary conversion solution. This primary conversion solution is used for the next round of hydroxide-type resin column conversion. The concentration of the sulfuric acid solution is generally 100.0 g / L to 120.0 g / L. The secondary conversion solution is returned and mixed with the lithium precipitation mother liquor, and then incorporated into the lithium precipitation mother liquor. After conversion, the sulfate-type resin column is drained of the primary conversion solution, and a new water-flooded resin column is injected for replacement and operation. The main chemical reactions during the process are:

[0043] R3NOH + H2SO4 = R3NHSO4 + H2O

[0044] The mother liquor containing lithium precipitation had a high chloride ion content, which was determined by back titration using the Philhard method.

[0045] The chloride ion content in the adsorbed solution was low, and it was determined by silver chloride turbidimetric method.

[0046] Formula for calculating chloride ion removal rate:

[0047]

[0048] Formula for calculating the recovery rate of battery-grade lithium carbonate:

[0049]

[0050] The chemical composition requirements for battery-grade lithium carbonate and industrial-grade lithium carbonate are shown in Tables 1 and 2.

[0051] Table 1. Chemical Composition Requirements for Battery-Grade Lithium Carbonate (YS / T582-2013)

[0052]

[0053] Table 2 Chemical Composition Requirements for Industrial Grade Lithium Carbonate (GB / T1075-2013)

[0054]

[0055] Control Experiment 1: Preparation of Battery-Grade Lithium Carbonate from Lithium-Precipitated Mother Lithium (Without Dechlorination, One-Step Denitration)

[0056] Take 10.0 L of lithium precipitation mother liquor, Li + 2.45g / L Cl - 12.5 g / L pH 12.5 was injected into a small stirred reaction tank. Stirring was started, and 98% industrial sulfuric acid was injected evenly. The pH of the solution was adjusted to 2.5. The injection of industrial sulfuric acid was stopped, and stirring was continued until the small bubbles on the liquid surface were exhausted and the liquid surface was calm. The reaction was continued for 1.0 h to complete the decarbonization operation.

[0057] After decarbonization, while the solution is still being stirred, industrial liquid alkali (sodium hydroxide mass fraction 40.0%) is injected to adjust the solution pH to 8.0. Then, the injection of liquid alkali is stopped, and the conditioning operation is completed.

[0058] After conditioning, the solution was transferred to a rotary evaporator and concentrated under vacuum at 0.07 MPa–0.06 MPa and 55°C–65°C until approximately 2.0 L of concentrate was obtained. The concentrate was then filtered under vacuum while hot to remove crystals, yielding 1.86 L of concentrated solution. + 12.90g / L Cl - 67.1g / L pH12.5.

[0059] After concentration and desalination, the filtrate was subjected to conventional deep purification, lithium precipitation, washing, drying, and pulverization to obtain 95.5g of lithium carbonate, containing 99.12% lithium carbonate, 0.11% sodium, 0.008% chloride, and 0.058% sulfate. It was determined to be industrial-grade lithium carbonate No. 1. The lithium recovery rate of the lithium precipitation mother liquor was 73.24%, and the recovery rate of battery-grade lithium carbonate was 0%.

[0060] Control Experiment 2: Preparation of Battery-Grade Lithium Carbonate from Lithium-Precipitated Mother Lithium (without Dechlorination, Secondary Denitration)

[0061] Take 20.0 L of lithium precipitation mother liquor, Li + 2.45g / L Cl - 12.5 g / L pH 12.5 was injected into a small stirred reaction tank. Stirring was started, and 98% industrial sulfuric acid was injected evenly. The pH of the solution was adjusted to 2.5. The injection of industrial sulfuric acid was stopped, and stirring was continued until the small bubbles on the liquid surface were exhausted and the liquid surface was calm. The reaction was continued for 1.0 h to complete the decarbonization operation.

[0062] After decarbonization, the solution was stirred continuously, and then industrial liquid alkali (40.0% sodium hydroxide by mass) was added to adjust the pH to 8.0. The addition of liquid alkali was then stopped, completing the conditioning process. The conditioned solution was then transferred to a rotary evaporator and concentrated under vacuum at 0.07-0.06 MPa and 55-65°C until approximately 2.0 L of concentrate was obtained. Concentration was stopped, and the solution was filtered under vacuum while hot to remove crystals, yielding 2.1 L of concentrated solution. + 22.86g / L Cl - 119.0g / L PH13.0.

[0063] The concentrated desalinated filtrate was placed in a refrigerated crystallizer for freeze crystallization at 3.0℃~5.0℃ for 24.0h. While still cold, it was then vacuum filtered to remove crystals, yielding 1.86L of crystalline denitrified filtrate. + 25.30g / L Cl - 134.2g / LPH13.0.

[0064] After conventional deep purification, lithium precipitation, washing, drying, and pulverization, 187.5g of lithium carbonate was obtained, containing 99.32% lithium carbonate, 0.068% sodium, 0.008% chloride, and 0.048% sulfate. It was determined to be industrial-grade lithium carbonate #0. The lithium recovery rate of the lithium precipitation mother liquor was 71.90%, and the recovery rate of battery-grade lithium carbonate was 0%.

[0065] Example 1: Removal of chlorine from lithium precipitation mother liquor by ion exchange method

[0066] Take the lithium mother liquor, Li + 2.1g / L Cl - 10.5 g / L pH 12.5 was injected into a small stirred reaction tank. Stirring was started, and 98% industrial sulfuric acid was injected evenly. The pH of the solution was adjusted to 2.0. The injection of industrial sulfuric acid was stopped, and stirring was continued until the small bubbles on the liquid surface were exhausted and the liquid surface was calm. The reaction was continued for 0.5 hours to complete the decarbonization operation. The solution was allowed to stand and cool down to 50°C. The decarbonized liquid was obtained by vacuum filtration, and the decarbonized residue was returned to the production for recycling.

[0067] The decarbonation solution was placed in a high-level tank and injected into a resin column assembly consisting of three 500mL sulfate-type resin columns connected in series in a stepped arrangement. The decarbonation solution flowed downstream from the top of the first-stage resin column, then through the bottom to the top of the second-stage resin column, and then through the bottom to the top of the final-stage resin column, exiting from the highest point of the resin packing layer in the final-stage resin column. The post-adsorption flow rate of the final-stage resin column was controlled at 11mL / min, and the residence time of the decarbonation solution in the single-stage resin column was 45min. The resin columns were filled with Success940 environmentally friendly ion exchange resin, which had been regenerated and converted to sulfate-type after washing and elution.

[0068] The chloride ion content in the post-adsorption liquid was determined periodically using the silver chloride turbidimetric method. The chloride ion detection results in the post-adsorption liquid are shown in Table 3.

[0069] Table 3 Results of liquid chloride ion adsorption.

[0070]

[0071] After 5.0 hours of adsorption, the chlorine content of the sample reached 0.20 g / L. Injection of the decarbonization solution was stopped, and 3.3 L of the post-adsorption solution was collected. The combined sample Li... + 2.10g / L Cl - At 0.05 g / L and pH 2.5, the chloride ion removal rate is 99.52%.

[0072] The saturated chloride-form resin column was removed and replaced with another 500mL sulfate-form Success940 resin column, with the tubing connected. Simultaneously, another 500mL sulfate-form Success940 environmentally friendly resin column was added after the final resin column, forming a series of four 500mL resin columns arranged in a stepped configuration. As before, the decarbonization solution flowed downstream from the top of the new first-stage resin column, then through the bottom to the top of the second-stage resin column, then through the bottom to the top of the next-second-stage resin column, and finally out through the highest point of the resin packing layer in the final-stage resin column. The post-adsorption flow rate of the final-stage resin column was controlled at 17mL / min, and the residence time of the decarbonization solution in the single-stage resin column was 30min.

[0073] The chloride ion content in the post-adsorption liquid was determined periodically using the silver chloride turbidimetric method. The chloride ion detection results in the post-adsorption liquid are shown in Table 4.

[0074] Table 4 Results of liquid chloride ion adsorption.

[0075]

[0076] After 5.0 hours of adsorption, the chlorine content in the sample reached 0.18 g / L. Injection of the decarbonization solution was stopped, and 4.7 L of the post-adsorption solution was collected. The combined sample Li... + 2.10g / L Cl - At 0.08 g / L and pH 2.5, the chloride ion removal rate was 99.23%.

[0077] Remove the saturated chloride-type resin column from the secondary adsorption stage and replace it with another 500mL sulfate-type Success940 resin column. Connect the tubing to form a series of four 500mL resin columns arranged in a stepped configuration, ready for carbon removal liquid exchange adsorption.

[0078] Similarly, the constructed resin column group can be used to systematically replace the saturated chloride-form resin columns at each stage based on the detection results of chloride ions after adsorption, thus maintaining the online and continuous operation of the decarbonization liquid.

[0079] Example 2: Washing of a loaded chlorinated resin column

[0080] Take any 500mL chlorinated resin column that is saturated with adsorption as described in Example 1. First, drain the decarbonization solution from the resin column. Prepare 1000mL of fresh water (approximately twice the resin volume, i.e., 2 BV). Introduce the water from the top or bottom of the resin column, and drain the water from the top or bottom of the column using either forward or reverse flow. Circulate and wash for 1.0h to produce secondary wash water. Prepare another 1000mL of fresh water and circulate and wash for another 1.0h to produce primary wash water. Mix the secondary wash water with the decarbonization solution and add it to the decarbonization solution.

[0081] Take another 500mL chlorinated resin column saturated with the adsorption solution from Example 1. First, drain the decarbonization solution from the resin column. Then, introduce 1000mL of the first wash water (approximately twice the resin volume, i.e., 2 BV) from the top or bottom of the resin column. Drain the water from the top or bottom of the resin column using either forward or reverse flow. Circulate and wash for 1.0 h to produce the second wash water. Prepare another 1000mL of fresh water and circulate and wash for another 1.0 h to produce the first wash water. Mix the second wash water with the decarbonization solution and add it to the decarbonization solution.

[0082] Example 3: Washing load, chlorinated resin column elution and regeneration

[0083] Take any 500mL loaded chlorinated resin column from Example 2 after washing. First, drain the primary wash water from the resin column. Prepare 1000mL of 40.0g / L sodium hydroxide solution (approximately twice the resin volume, i.e., 2BV). Introduce the solution from the top or bottom of the resin column, and drain the water from the top or bottom of the column using either forward or reverse flow. Circulate and regenerate for 1.0h to produce a secondary eluent. Then prepare 1000mL of 50.0g / L sodium hydroxide solution and circulate and regenerate for another 1.0h to produce a primary eluent. The secondary eluent is an alkaline brine and is sent to a salt chemical plant for further treatment.

[0084] Take another 500mL loaded chlorine-form resin column after washing in Example 2. First, drain the primary wash water from the resin column. Then, introduce 1000mL of the primary eluent (approximately twice the resin volume, i.e., 2 BV) from the top or bottom of the resin column. Drain the eluent through either forward or reverse flow from the top or bottom of the resin column, and circulate the eluent for 1.0 h to produce a secondary eluent. Next, prepare 1000mL of 40.0g / L sodium hydroxide solution and circulate the eluent for another 1.0 h to produce a primary eluent. As above, the secondary eluent is an alkaline brine and is sent to a salt chemical plant for further processing.

[0085] Example 4: Elution and regeneration of hydroxide ion-type resin column transformation

[0086] Take any 500mL hydroxide-type resin column after elution and regeneration as in Example 3. First, drain the primary eluent from the resin column. Prepare 1000mL of 120.0g / L sulfuric acid solution (approximately twice the resin volume, i.e., 2BV). Introduce the solution from the top or bottom of the resin column, and drain the solution from the top or bottom of the column using either forward or reverse flow. Circulate for 1.0h to produce the secondary conversion solution. Then prepare another 1000mL of 120.0g / L sulfuric acid solution and circulate for another 1.0h to produce the primary conversion solution. Mix the secondary conversion solution with the lithium precipitation mother liquor and add it to the lithium precipitation mother liquor.

[0087] Take another 500mL hydroxide-type resin column after elution and regeneration in Example 3. First, drain the primary eluent from the resin column. Then, introduce 1000mL of the primary conversion solution (approximately twice the resin volume, i.e., 2BV) into the resin column from either the top or bottom. Drain the solution from the top or bottom of the column using either forward or reverse flow. Circulate the conversion solution for 1.0h to produce the secondary conversion solution. Next, prepare 1000mL of 100.0g / L sulfuric acid solution and circulate it for another 1.0h to produce the primary eluent. As above, the secondary eluent is an alkaline brine and is sent to a salt chemical plant for further processing.

[0088] Example 5: Preparation of battery-grade lithium carbonate from dechlorination solution (primary denitration)

[0089] Take 8.0 L of the dechlorination solution after two adsorption cycles in Example 1, and combine the sample Li + 2.10g / L Cl - 0.068 g / L pH 2.5, with stirring, inject industrial liquid alkali (sodium hydroxide mass fraction 40.0%), adjust the solution pH to 8.0, stop injecting liquid alkali, and the conditioning operation is completed.

[0090] After conditioning, the solution was transferred to a rotary evaporator and concentrated under vacuum at 0.07 MPa–0.06 MPa and 55°C–65°C until approximately 1.5 L of concentrate was obtained. The solution was then filtered under vacuum while hot to remove crystals, yielding 1.4 L of concentrated solution. + 12.0g / L Cl - 0.39g / L pH12.0.

[0091] After concentration and desalination, the filtrate was subjected to conventional deep purification, lithium precipitation, washing, drying, and pulverization to obtain 68.2g of lithium carbonate, containing 99.62% lithium carbonate, 0.018% sodium, 0.0015% chloride, and 0.053% sulfate. This was determined to be battery-grade lithium carbonate. The lithium recovery rate of the dechlorination solution was 76.28%, and the battery-grade lithium carbonate recovery rate was also 76.28%. Conventionally, the lithium content in the lithium precipitation mother liquor is approximately 20%–25% of that in lithium ore. Based on this calculation, the battery-grade lithium carbonate yield will be increased by more than 15.25%.

Claims

1. A method for removing chlorine from lithium precipitation mother liquor by ion exchange, characterized in that, The process includes the following steps: A) Sulfuric acid is injected into the lithium precipitation mother liquor, and the mixture is stirred, acidified, and decarbonized. The mixture is then cooled, and liquid-solid separation is performed to produce a decarbonated liquid and a decarbonated slag. The lithium precipitation mother liquor is the residual liquid from the precipitation of lithium carbonate using a saturated sodium carbonate solution. The decarbonated slag is sent to prepare a lithium sulfate solution. B) The decarbonated liquid is injected into a sulfate-type resin column assembly. The sulfate-type resin in the column undergoes anion exchange with the decarbonated liquid, and chloride ions in the decarbonated liquid are adsorbed into the resin column, producing an adsorbed liquid and a chloride-type resin column. The adsorbed liquid is sent for concentration, crystallization, and denitrification. After deep purification, lithium is recovered by secondary lithium precipitation using a saturated sodium carbonate solution. C) Wash water is injected into the chloride-type resin column for washing, producing wash water and a washed chloride-type resin column. Part of the wash water is returned for use in this step, and part is returned to step B to mix with the decarbonated liquid and incorporated into the decarbonated liquid. D) Wash the chloride-type resin column by injecting eluent to regenerate it, producing eluent and hydroxide resin column. Part of the eluent is returned for use in this step, and part is sent to salt chemical treatment; E) Inject the hydroxide-type resin column with conversion solution to convert it, producing conversion solution and sulfate-type resin column. Part of the conversion solution is returned for use in this step, and part is returned to step A to be mixed with lithium precipitation mother liquor and incorporated into the lithium precipitation mother liquor. The sulfate-type resin column is incorporated into the sulfate-type resin column group in step B for operation. The resin column group described in step B consists of 4 to 5 resin columns connected in series. The decarbonization liquid is injected into the first resin column, then flows through the second resin column, and finally flows out from the last resin column. In step B, each resin column in the resin column group can be short-circuited to separate it from the resin column group for washing, elution, regeneration, and conversion of the chlorine form resin column.

2. The method for removing chlorine from lithium precipitation mother liquor by ion exchange according to claim 1, characterized in that, In step B, the decarbonization solution is injected into the resin column group for anion exchange. The adsorbed liquid sample produced by the last resin column is collected periodically and sent for chloride ion content testing. The chloride ion content of the sample is required to be ≤0.2g / L. If the requirement is not met, the saturated chloride form resin column is short-circuited in time and replaced with a sulfate form resin column that has completed the transformation. The chloride form resin column separated by the short circuit is washed, eluted, regenerated and transformed in time.

3. The method for removing chlorine from lithium precipitation mother liquor by ion exchange according to claim 2, characterized in that... The anion exchange resin packed in the resin column assembly in step B is an environmentally friendly ion exchange resin.

4. The method for removing chlorine from lithium precipitation mother liquor by ion exchange according to any one of claims 1 to 3, characterized in that, In step A, the stirring time for acidification and decarburization is 0.5h to 2.0h, the final pH of the decarburized liquid is 2.0 to 5.0, and the temperature is cooled to 30℃ to 50℃.

5. The method for removing chlorine from lithium precipitation mother liquor by ion exchange according to any one of claims 1 to 3, characterized in that, In step B, the decarbonation solution is injected into a sulfate-type resin column for anion exchange, and the residence time in the single-stage resin column is 30 min to 45 min.

6. The method for removing chlorine from lithium precipitation mother liquor by ion exchange according to any one of claims 1 to 3, characterized in that, In step C, the chlorinated resin column is washed with wash water. First, the decarbonization liquid in the resin column is drained, and 2BV of primary wash water is injected for 1.0h of circulation washing to produce secondary wash water. Then, fresh water is injected for 1.0h of circulation washing to produce primary wash water. The primary wash water is used for the next round of chlorinated resin column washing. The secondary wash water is returned to step B and mixed with the decarbonization liquid, and then incorporated into the decarbonization liquid.

7. The method for removing chlorine from lithium precipitation mother liquor by ion exchange according to any one of claims 1 to 3, characterized in that, In step D, the chlorinated resin column is washed and regenerated by injecting eluent. First, the primary wash water in the resin column is drained, and 2 BV of primary eluent is injected for 1.0 h of elution and regeneration, producing secondary eluent. Then, sodium hydroxide solution is injected for 1.0 h of elution and washing, producing primary eluent. The primary eluent is used for the next round of chlorinated resin column elution and regeneration. The concentration of the sodium hydroxide solution is 40.0 g / L to 50.0 g / L.

8. The method for removing chlorine from lithium precipitation mother liquor by ion exchange according to any one of claims 1 to 3, characterized in that, In step E, the hydroxide-type resin column is transformed by injecting a transformation solution. First, the primary eluent in the resin column is drained, and 2 BV of primary transformation solution is injected for 1.0 h of transformation to produce a secondary transformation solution. Then, sulfuric acid solution is injected for 1.0 h of transformation to produce a primary transformation solution. The primary transformation solution is used for the next round of hydroxide-type resin column transformation. The concentration of the sulfuric acid solution is 100.0 g / L to 120.0 g / L. The secondary transformation solution is returned to step A and mixed with the lithium precipitation mother liquor. After the transformation is completed, the primary transformation solution is drained from the sulfate-type resin column, and fresh water is injected to submerge the resin column for replacement and operation.

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