Method for preparing battery-grade lithium hydroxide monohydrate by causticizing lithium carbonate

Abstract

The invention belongs to the technical field of lithium salt preparation, and provides a method for preparing battery-grade lithium hydroxide monohydrate by causticizing lithium carbonate. According to the method, raw material washing and ion exchange purification are combined with a multi-stage crystallization impurity removal process including evaporation concentration, rotational flow classification and elutriation to achieve a synergistic effect, so that the impurity content of the product is effectively controlled, and a lithium carbonate component causing scaling is actively removed; therefore, the scaling problem of evaporative crystallization equipment is remarkably relieved while the product purity is improved, and the lithium hydroxide monohydrate meeting the battery-grade quality requirement is stably and continuously produced by taking the industrial-grade lithium carbonate as the raw material.

Description

Technical Field

[0001] This invention relates to the field of lithium salt preparation technology, specifically to a method for preparing battery-grade lithium hydroxide monohydrate by causticizing lithium carbonate. Background Technology

[0002] The causticization process for lithium carbonate, an important technology for converting industrial-grade lithium carbonate into lithium hydroxide monohydrate, has attracted widespread attention due to its simple route and environmental friendliness. This method is particularly suitable for processing substandard industrial-grade lithium carbonate with low main content and high impurity content caused by fluctuations in raw materials or processes, and is an effective path to transform low-value-added lithium salt resources into high-value-added products. In recent years, with the rapid growth in demand for battery-grade lithium salts from the new energy vehicle industry, producing battery-grade lithium hydroxide monohydrate that meets stringent impurity control requirements using this route has become an urgent industry need. However, traditional lithium carbonate causticization processes face numerous challenges in pursuing high product purity.

[0003] While existing technologies can remove some impurities from lithium hydroxide solution obtained through causticization reactions using conventional purification methods, trace amounts of impurity ions, such as lithium carbonate, remaining in the solution are prone to precipitating during thermal concentration in the subsequent critical evaporation and crystallization process. These precipitated impurities not only directly affect the chemical purity of the final product, making it difficult to meet battery-grade standards, but also easily form stubborn scale on the heat transfer surfaces of core equipment such as evaporators and heat exchangers. Even with deep purification technologies that reduce the content of most metallic impurities in the solution and can even produce products with compliant main content, the problem of equipment scaling during production cannot be avoided. The root cause is that the evaporation and crystallization process involves both lithium hydroxide crystallization and lithium carbonate precipitation, and the crystallization operating conditions that improve product purity often exacerbate the deposition of lithium carbonate on the heat exchanger surface. Scale formation significantly reduces equipment heat transfer efficiency and production capacity, increases energy consumption, and frequently leads to production interruptions for cleaning and maintenance, severely restricting the continuous, stable, and efficient operation of the production line. This poses a major obstacle to the large-scale and economical production of battery-grade lithium hydroxide monohydrate through this route. Therefore, there is an urgent need for an improved causticization process that can effectively solve the above-mentioned purity and scaling problems and achieve efficient and continuous production of battery-grade lithium hydroxide monohydrate. Summary of the Invention

[0004] This invention provides a method for preparing battery-grade lithium hydroxide monohydrate using lithium carbonate causticization, thereby solving the problems of low purity of lithium hydroxide monohydrate products prepared by lithium carbonate causticization in the prior art and the inability to efficiently and continuously produce battery-grade lithium hydroxide monohydrate due to scaling of the evaporation and crystallization equipment during the production process.

[0005] In a first aspect, the present invention provides a method for preparing battery-grade lithium hydroxide monohydrate by causticizing lithium carbonate, comprising the following steps:

[0006] (1) Lithium source pretreatment: The lithium source raw material containing lithium carbonate is washed and solid-liquid separated to obtain pretreated material and washing liquid; (2) Causticization reaction: The pretreated material is mixed with an alkaline calcium-containing substance to carry out a causticization reaction to obtain a solid-liquid mixture containing lithium hydroxide; the solid-liquid mixture containing lithium hydroxide is subjected to solid-liquid separation to obtain a lithium hydroxide solution and causticization residue. (3) Ion exchange purification treatment: The lithium hydroxide solution is subjected to ion exchange treatment to obtain a purified solution; (4) Evaporation and concentration and impurity classification: The purified liquid is evaporated and concentrated to obtain a concentrated liquid; the concentrated liquid is subjected to hydrocyclone classification to obtain the first lithium carbonate impurity and the concentrated overflow liquid; wherein, the concentration of lithium hydroxide in the concentrated liquid is 100 g / L~120 g / L. (5) Evaporation crystallization and washing separation: The concentrated overflow liquid is evaporated and crystallized in one step and then separated into solid and liquid to obtain the first lithium hydroxide monohydrate crystal slurry; the first lithium hydroxide monohydrate crystal slurry is washed in the first stage to separate the second lithium carbonate impurity; the slurry after the first stage washing is separated into solid and liquid to obtain crude lithium hydroxide monohydrate and the mother liquor of the first crystallization. (6) Refining and resolution and secondary evaporation crystallization: Crude lithium hydroxide monohydrate is dissolved in water and refined by filtration to obtain a resolution and refined solution; the resolution and refined solution is subjected to secondary evaporation crystallization to obtain a second lithium hydroxide monohydrate slurry; the second lithium hydroxide monohydrate slurry is subjected to a second-stage washing to separate the third lithium carbonate impurity; the slurry after the second-stage washing is subjected to solid-liquid separation to obtain wet refined lithium hydroxide monohydrate and secondary crystallization mother liquor; (7) Drying: The wet refined lithium hydroxide monohydrate is dried to obtain battery-grade lithium hydroxide monohydrate.

[0007] In an optional embodiment, the method further includes a lithium carbonate recovery and material recycling step: the first lithium carbonate impurity, the second lithium carbonate impurity and the third lithium carbonate impurity are mixed with at least a portion of the primary crystallization mother liquor, carbon dioxide is introduced to carry out a carbonation reaction, and after the reaction, solid-liquid separation is performed to obtain lithium carbonate wet product and lithium carbonate recovery mother liquor; the lithium carbonate wet product is returned to step (2) and used together with the pretreated material for subsequent causticization reaction. And / or, it also includes a lithium chloride preparation step: the washing liquid obtained in step (1) and / or the lithium carbonate recovery mother liquor obtained in the lithium carbonate recovery and material recycling step are reacted with hydrochloric acid to generate lithium chloride and with sodium hydroxide to neutralize, and then concentrated to obtain a lithium chloride product solution.

[0008] In an optional embodiment, the method further includes: returning at least a portion of the secondary crystallization mother liquor obtained in step (6) to step (5), mixing it with the concentrated overflow liquid, and then performing a single evaporation crystallization. And / or, it also includes: reusing the steam condensate generated during the evaporation and concentration process of step (4) and / or the single evaporation and crystallization process of step (5) for the water use step of this method.

[0009] In one alternative implementation, in step (1), the detergent used for washing includes water; And / or, the washing temperature is 85℃~100℃, and the washing time is 15min~60min; And / or, in step (1), during the washing of the lithium source material containing lithium carbonate, the mass ratio of the lithium source material containing lithium carbonate to the detergent is 1:(2~4).

[0010] In one optional embodiment, in step (2), the temperature of the causticizing reaction is 85°C to 98°C, and the reaction time is 1h to 5h. And / or, the causticization reaction is carried out under mechanical stirring at a speed of 90 rpm to 110 rpm; And / or, the molar ratio of lithium carbonate in the pretreated material to that in the alkaline calcium-containing substance, calculated as Ca, is (0.5~1.5):(0.5~1.5).

[0011] In one optional embodiment, in step (2), the alkaline calcium-containing substance includes at least one of calcium hydroxide and calcium oxide; And / or, step (2) further includes: washing and calcining the causticized slag; And / or, in step (3), the ion exchange treatment process includes: passing the lithium hydroxide solution sequentially through a cation exchange resin and an anion chelating resin.

[0012] In this invention, the causticizing reaction in step (2) can be carried out in any of the following ways: Method 1: First, mix calcium oxide and water at a mass ratio of 1:(6~7) and carry out a digestion reaction at 65℃~95℃ for 30~45 minutes to prepare calcium hydroxide slurry; after the digestion reaction is completed, the insoluble large particles (lime residue) can be discharged from the system through a basket filter with a pore size of 750μm~850μm; then mix with the slurry formed by mixing pretreated material and water at a mass ratio of 1:(2~4); Method 2: When calcium oxide is used as the alkaline calcium-containing substance, the process of mixing the pretreated material with the alkaline calcium-containing substance includes: directly mixing the pretreated material, calcium oxide and water, so that the lime digestion and causticization reaction are carried out in the same reactor; the mass ratio of calcium oxide to water is 1:(6~7).

[0013] In one optional embodiment, the washing method is countercurrent washing; wherein the number of washings is ≥2 times, the mass ratio of caustic sludge to water is 1:(2~4) during each washing process, and the washing time is 15min~20min. And / or, the calcination temperature is 1000℃~1200℃, and the calcination time is ≥30min; And / or, the flow rates of the cation exchange resin and the anion chelating resin are each independently 1.5 m / s to 2 m / s.

[0014] In this invention, the resource utilization treatment of caustic slag specifically includes: washing the separated caustic slag (e.g., countercurrent washing), followed by solid-liquid separation to obtain wet calcium carbonate solid and washing liquid. The soluble lithium and calcium components contained in the washing liquid are recycled in step (2) to prepare calcium hydroxide slurry, thereby realizing the recovery and utilization of lithium and calcium elements and the recycling of process water. The wet calcium carbonate (e.g., using a suspension preheater) is calcined at 1000℃~1200℃ for at least 30 minutes to decompose into calcium oxide (CaO) and carbon dioxide (CO2). The generated CaO can be used to prepare calcium hydroxide slurry in a recycling manner, thereby realizing the recovery of calcium source and the recovery of lithium attached to the slag; the generated CO2 can be collected and used in subsequent lithium carbonate recovery processes. This method effectively reduces solid waste and improves raw material utilization.

[0015] In this invention, the cation exchange resin can be selected from strongly acidic styrene-based cation exchange resins (such as gel-type or macroporous type) or weakly acidic acrylic-based cation exchange resins (such as macroporous type or gel-type). Its main function is to remove divalent cation impurities (such as Ca) from the solution. 2+ Mg 2+ The anion chelating resin can be selected from aminomethylphosphonic acid chelating resin, N-methylglucosamine chelating resin, and methine oxime chelating resin. Its main function is to specifically adsorb and remove anionic impurities such as borate from the solution. The resin can be regenerated using conventional methods in the art after use.

[0016] In an optional embodiment, in step (4), the evaporation and concentration are carried out at 60°C to 80°C and 20 kPa to 50 kPa. And / or, the primary evaporation crystallization is carried out at 50°C to 80°C and 20 kPa to 50 kPa.

[0017] In this invention, the concentration and crystallization process in step (4) has specific technical effects: during the evaporation and concentration of the lithium hydroxide purification solution, a small amount of lithium carbonate particles will precipitate as the concentration increases. At this time, the lithium carbonate concentration in the concentrate may be between 0.7 g / L and 1.0 g / L. After concentration, the concentrate can be sent to a hydrocyclone separator. By adjusting the classification efficiency of the hydrocyclone separator, a portion of the lithium carbonate particles can be controlled to be discharged from the underflow system and sent to the lithium carbonate recovery process; while another portion of fine lithium carbonate particles enters the primary evaporation and crystallization process with the concentrate (overflow). During the primary evaporation and crystallization process, these fine lithium carbonate particles can act as seed crystals, adsorbing the lithium carbonate impurities that continue to precipitate during the crystallization process, thereby significantly reducing the scaling of lithium carbonate on the evaporator and heat exchanger pipes and ensuring the continuity of production.

[0018] In one optional embodiment, crystallization is carried out in a single evaporation until the slurry density reaches 1.2~1.4 g / cm³. 3 .

[0019] In an optional embodiment, to further improve product purity, step (5) further includes: setting a backwashing device at the outlet of the crystallizer during primary evaporation crystallization (e.g., at the salt leg at the bottom of the evaporator, where the salt leg refers to the conical bottom cavity or pipe at the bottom of the evaporator used to collect the solid phase) to perform a backwashing operation on the outlet; wherein, the solid phase material separated by the backwashing operation is returned to step (2) and used together with the pretreated material for subsequent causticization reaction. Utilizing the difference in particle size and settling velocity between lithium hydroxide monohydrate crystals and lithium carbonate impurities, efficient separation is achieved through backwashing, ensuring that the carbonate content of the product meets the standards.

[0020] In one optional embodiment, in step (6), the concentration of lithium hydroxide in the reconstituted liquid is 80 g / L to 120 g / L; And / or, the secondary evaporation crystallization is carried out under conditions of 50℃~80℃ and 20 kPa~50 kPa; And / or, in step (7), the drying temperature is 75°C to 90°C.

[0021] In this invention, the refining process in step (6) may include: dissolving crude lithium hydroxide monohydrate in water and then refining and removing impurities. The refining and removing impurities may include a first filtration (e.g., using a filter press), a second filtration (e.g., using a precision filter), and removal of magnetic impurities (e.g., using a pipeline demagnetizer to control the content of magnetic foreign matter in the final product to meet battery-grade quality standards). The operating temperature during the entire refining and removing process should preferably be controlled below 95°C. After secondary evaporation and crystallization, the lithium hydroxide concentration in the resulting secondary crystallization mother liquor may be 120 g / L~130 g / L, and the lithium carbonate concentration may be 0.6 g / L~1 g / L. This secondary crystallization mother liquor can be returned to step (5) for primary evaporation and crystallization to achieve material recycling. As another optional implementation, the secondary crystallization mother liquor may also be divided into two parts, one part returned to primary evaporation and crystallization, and the other part returned to secondary evaporation and crystallization for internal circulation. By adjusting the ratio of the two parts (for example, the ratio of returning to the primary evaporation crystallization is between 30% and 100%), the total system circulation flow and impurity load of each process can be flexibly controlled to adapt to different production conditions and product requirements. This is also covered by the technical solution of the present invention. Similarly, a backwashing device can also be installed at the evaporator outlet of the secondary evaporation crystallization to further improve product quality.

[0022] In this invention, the process of recycling by-products may include: A. Lithium carbonate recovery: The mother liquor from the first crystallization stage is reacted with carbon dioxide at 90℃~100℃ for 0.5~2.5 hours (reaction formula: 2LiOH+CO2→Li2CO3+H2O). After the reaction, solid-liquid separation is performed to obtain wet lithium carbonate and lithium carbonate recovery mother liquor. The wet lithium carbonate is returned to step (2) and used together with the pretreated material for subsequent causticizing reactions; the lithium carbonate recovery mother liquor can be used for lithium chloride preparation.

[0023] B. Lithium chloride preparation: The washing liquid and / or lithium carbonate recovery mother liquor generated in step (1) are combined, and hydrochloric acid solution is added first to react (Li2CO3+2HCl→2LiCl+CO2+H2O), and then sodium hydroxide solution is added to neutralize the excess hydrochloric acid. After removing impurities by fine filtration, the reaction solution is first concentrated through a membrane to obtain a concentrated solution with a lithium chloride mass fraction of 4%~6%, and then further concentrated through a multi-stage evaporator at 80℃~110℃ and 100 kPa~150 kPa to obtain a lithium chloride solution with a lithium chloride mass fraction of 35%~45%, which is used as a by-product.

[0024] C. Wastewater Treatment: The combined wastewater generated throughout the process can be treated sequentially using membrane concentration and multi-stage vacuum evaporators. Membrane concentration removes salts and impurities, and the condensate from multi-effect evaporation, once it meets the standards, can be reused in production. The remaining small amount of solid waste is then disposed of in compliance with regulations, achieving water conservation and environmentally friendly production.

[0025] The technical solution of this invention has the following advantages: 1. A method for preparing battery-grade lithium hydroxide monohydrate by causticizing lithium carbonate, comprising the following steps: (1) lithium source pretreatment: washing and solid-liquid separation of lithium source raw materials containing lithium carbonate to obtain pretreated material and washing liquid; (2) causticizing reaction: mixing the pretreated material with an alkaline calcium-containing substance for causticizing reaction to obtain a solid-liquid mixture containing lithium hydroxide; performing solid-liquid separation of the solid-liquid mixture containing lithium hydroxide to obtain lithium hydroxide solution and causticizing residue; (3) ion exchange purification treatment: performing ion exchange treatment on the lithium hydroxide solution to obtain purified liquid; (4) evaporation concentration and impurity classification: evaporating and concentrating the purified liquid to obtain concentrated liquid; performing hydrocyclone classification treatment on the concentrated liquid to obtain the first lithium carbonate impurity and concentrated overflow liquid; wherein, the concentration of lithium hydroxide in the concentrated liquid is 100 g / L~120 g / L. g / L; (5) First evaporation crystallization and washing separation: The concentrated overflow liquid is subjected to first evaporation crystallization and solid-liquid separation to obtain the first lithium hydroxide monohydrate slurry; the first lithium hydroxide monohydrate slurry is subjected to first-stage washing to separate the second lithium carbonate impurity; the slurry after the first-stage washing is subjected to solid-liquid separation to obtain crude lithium hydroxide monohydrate and first crystallization mother liquor; (6) Refining resolution and second evaporation crystallization: The crude lithium hydroxide monohydrate is dissolved in water and refined by filtration to obtain resolution refined liquid; the resolution refined liquid is subjected to second evaporation crystallization to obtain the second lithium hydroxide monohydrate slurry; the second lithium hydroxide monohydrate slurry is subjected to second-stage washing to separate the third lithium carbonate impurity; the slurry after the second-stage washing is subjected to solid-liquid separation to obtain wet refined lithium hydroxide monohydrate and second crystallization mother liquor; (7) Drying: The wet refined lithium hydroxide monohydrate is dried to obtain battery-grade lithium hydroxide monohydrate.

[0026] This invention effectively removes soluble sulfate and chloride ions from industrial-grade lithium carbonate raw materials through the washing pretreatment in step (1), reducing the impurity load of subsequent processes from the source. The ion exchange treatment in step (3) further removes cations such as calcium and magnesium, as well as anions such as borate, laying the foundation for high product purity. In step (4), by evaporating and concentrating the purified solution, the lithium hydroxide concentration is increased to 100-120 g / L, reducing the lithium ions (Li...) in the solution. + ) and carbonate ions (CO3) 2-The concentration increases synchronously. Due to the relatively low solubility of lithium carbonate, its ion product first reaches supersaturation and precipitates, thus achieving pre-separation of impurities. Subsequently, the first lithium carbonate impurity is separated by cyclone fractionation, and the remaining lithium carbonate microcrystals enter step (5) with the concentrated overflow liquid. During the first evaporation crystallization process, these lithium carbonate microcrystals can act as seed crystals to adsorb the lithium carbonate that continues to precipitate during the crystallization process, thereby reducing its deposition on the equipment surface. The first-stage washing set in step (5) further separates the second lithium carbonate impurity, effectively improving the purity of the crude product. Step (6) achieves deep purification of the product by remelting, refining filtration and secondary evaporation crystallization of the crude product, combined with the second-stage washing to remove the third lithium carbonate impurity. The above steps work together systematically to achieve deep removal of impurities, while effectively controlling the precipitation and adhesion behavior of lithium carbonate through fractionation and washing operations, thereby simultaneously solving the problems of low product purity and easy scaling of equipment, ensuring the efficient and continuous production of battery-grade lithium hydroxide monohydrate.

[0027] 2. This invention achieves effective recovery of lithium and calcium resources entrained in the causticizing slag produced by the causticizing reaction through washing, solid-liquid separation, and calcination. The calcium oxide generated from the calcined slag can be recycled for the preparation of alkaline calcium-containing substances required for the causticizing reaction, while the carbon dioxide generated during calcination can be further used for the recovery and preparation of lithium carbonate. This not only reduces the generation of solid waste but also achieves a highly efficient closed-loop recycling of materials, significantly improving the utilization rate of raw materials and the green and environmentally friendly level of the production process, while reducing production costs.

[0028] 3. This invention further recovers and reuses the mother liquor and / or washing liquid from the primary crystallization process for the preparation of lithium carbonate and lithium chloride, respectively. By controlling conditions, such as introducing carbon dioxide to precipitate lithium carbonate, or preparing lithium chloride solution through acidification, neutralization, and concentration steps, the invention achieves full-process, multi-product recovery of lithium elements. This not only avoids the loss of valuable components but also enriches the product line and improves the economic efficiency and resource utilization efficiency of the entire process. It is particularly suitable for processing industrial-grade lithium carbonate raw materials with large fluctuations in composition.

[0029] 4. This invention achieves efficient separation of the target product, lithium hydroxide monohydrate crystals, and impurities (such as lithium carbonate) by setting backwashing devices at the crystallizer outlets (e.g., the salt leg) in each evaporation and crystallization stage (e.g., steps (4) and (5)). This physical separation method further enhances the purification effect of the product, especially by controlling the carbonate content in the product, ensuring that the final product can consistently meet the stringent requirements of battery-grade quality standards.

[0030] 5. The process steps of this invention are rationally designed, with close connections between each stage, enabling continuous and automated operation throughout the entire process. From raw material pretreatment, causticization reaction, and ion exchange purification to multi-stage evaporation crystallization and product drying, all are suitable for integration using continuous equipment (such as continuous reactors, continuous filter presses, MVR evaporation crystallization systems, continuous dryers, etc.). This continuous production mode not only significantly improves production efficiency and equipment utilization but also facilitates stable control of the production process and uniformity of product quality, providing a reliable technical solution for the large-scale, low-cost industrial production of battery-grade lithium hydroxide monohydrate. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 This is a flowchart of the causticizing reaction in Example 1; Figure 2 This is a flowchart illustrating the preparation process of lithium hydroxide monohydrate in Example 1; Figure 3 This is a flowchart illustrating the preparation of the by-product lithium chloride solution in Example 1; Figure 4 This is a flowchart of the causticizing reaction in Example 2; Figure 5 This is a flowchart illustrating the preparation process of lithium hydroxide monohydrate in Example 3. Detailed Implementation

[0033] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0034] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0035] The requirements for D1 grade (battery grade) in GB / T 26008-2020 are as follows: 1. Product chemical composition:

[0036] 2. Magnetic foreign matter content in the product: not more than 50 micrograms per kilogram.

[0037] Example 1 This embodiment provides a method for preparing battery-grade lithium hydroxide monohydrate using lithium carbonate causticization. The causticization reaction process of this embodiment is as follows: Figure 1 As shown (where TG Li2CO3 refers to industrial-grade lithium carbonate); the complete preparation process of lithium hydroxide monohydrate is as follows: Figure 2 As shown; the preparation process of the by-product lithium chloride solution is as follows: Figure 3 As shown, the specific steps are as follows: (1) Lithium source pretreatment: 1.6t of industrial-grade lithium carbonate (purity 99.11%) and 4.8t of water (mass ratio 1:3) were added to a steam-jacketed washing tank for washing. The washing temperature was controlled at 90℃ and the washing time was 20min. After washing, solid-liquid separation was performed using a centrifuge to obtain 4.7t of pretreated material and washing liquid.

[0038] (2) Causticization reaction: 1.7t of pretreated material was mixed with 4.94t of water (mass ratio 1:2.9) to obtain lithium carbonate slurry. 1.64t of quicklime and 11t of water (mass ratio approximately 1:6.7) were digested in a lime digester at 90°C for 30 min. After digestion, insoluble large particles (i.e., lime residue) were removed through a basket filter with a pore size of 800μm to obtain calcium hydroxide slurry. The calcium hydroxide slurry was pumped to a causticization reactor and mixed with the lithium carbonate slurry at a molar ratio of lithium carbonate to calcium hydroxide of 1:1. The causticization reaction was carried out at 95°C for 3 h under mechanical stirring (100 rpm) and steam coil heating to obtain a solid-liquid mixture containing lithium hydroxide (i.e., lithium hydroxide slurry). Subsequently, the lithium hydroxide slurry was subjected to solid-liquid separation using a vertical filter press to obtain a lithium hydroxide solution and approximately 3.5t of causticization residue (calcium carbonate).

[0039] The causticized slag was subjected to two countercurrent washes, each using 11 tons of water (water to causticized slag mass ratio approximately 3.1:1) for 18 minutes. After washing, a diaphragm filter press was used for solid-liquid separation to obtain a solid (wet calcium carbonate) and a washing liquid. The washing liquid was reused to prepare calcium hydroxide slurry. The wet calcium carbonate was placed in a suspension preheater and calcined at 1100°C for 30 minutes, decomposing to produce calcium oxide (CaO) and carbon dioxide (CO2). The obtained CaO was used to prepare the calcium hydroxide slurry, and the CO2 was collected for later use.

[0040] (3) Ion exchange purification treatment: The lithium hydroxide solution obtained in step (2) is first passed through an exchange column packed with strong acid styrene-based cation exchange resin (purchased from Lijiang Biotechnology) at a flow rate of 1.8 m / s. At this time, the Ca in the solution... 2+ Mg2+ The concentration was reduced to below 5 ppm; then the solution was passed through an exchange column packed with SY-905 type (amine type, boron removal resin, purchased from Sany Resin) anion chelating resin at a flow rate of 1.8 m / s. At this point, the boron concentration in the solution was reduced to below 5 ppm, and the purified solution was obtained.

[0041] (4) Evaporation and Concentration: The purified liquid obtained in step (3) is evaporated and concentrated using an MVR evaporator at 70°C and 30 kPa until the lithium hydroxide concentration reaches 110 g / L, resulting in a concentrated liquid. A small amount of lithium carbonate precipitates during this process, and the lithium carbonate concentration in the concentrated liquid is approximately 0.8 g / L. The concentrated liquid is then pumped to a hydrocyclone separator for hydrocyclone classification. By adjusting the classification efficiency, most of the precipitated lithium carbonate particles are controlled to be discharged from the underflow as the first lithium carbonate impurity and collected for later use. The remaining concentrated overflow containing fine lithium carbonate particles is discharged from the topflow and enters the subsequent process.

[0042] The concentrated overflow liquid was subjected to a single evaporation and crystallization at 70°C and 30 kPa to obtain a solution with a density of approximately 1.3 g / cm³. 3 The first lithium hydroxide monohydrate slurry was prepared. A backwashing device (i.e., first-stage washing) was installed at the salt leg of the evaporator outlet during the primary evaporation crystallization process. Utilizing the difference in particle size and settling velocity between lithium hydroxide monohydrate and lithium carbonate, the second lithium carbonate impurity was separated and collected for later use. The washed slurry was then centrifuged to obtain crude lithium hydroxide monohydrate and primary crystallization mother liquor.

[0043] (5) Refining and crystallization: The crude lithium hydroxide monohydrate obtained in step (4) is mixed with water and refined and purified by passing it through a filter press (first filtration), a precision filter (second filtration) and a pipeline demagnetizer (to remove magnetic impurities) at a temperature not higher than 95°C, to obtain a reconstituted refined solution with a lithium hydroxide concentration of 120 g / L.

[0044] The reconstituted and refined liquid was subjected to secondary evaporation and crystallization at 80℃ and 50 kPa. A backwashing device (i.e., a second-stage washing) was also installed at the salt leg of the evaporator outlet to separate the third lithium carbonate impurity and collect it for later use. The washed material was centrifuged to obtain wet refined lithium hydroxide monohydrate and secondary crystallization mother liquor. The lithium hydroxide concentration in the secondary crystallization mother liquor was about 130 g / L and the lithium carbonate concentration was about 1 g / L. All of it was returned to step (4) for a first evaporation and crystallization.

[0045] (6) Drying: The wet refined lithium hydroxide monohydrate obtained in step (5) is dried at 85°C using a continuous vacuum belt dryer to obtain approximately 1.69t of battery-grade lithium hydroxide monohydrate product.

[0046] (7) Byproduct recovery and waste treatment: The washing liquid generated in step (1) and the lithium carbonate recovery mother liquor generated in step (4) are combined (total mass approximately 7.3t). First, 0.25t of 31% hydrochloric acid solution is added and reacted at 50℃ for 30min; then, 0.02t of 50% sodium hydroxide solution is added and reacted at 50℃ for 30min for neutralization. After fine filtration, the reaction solution is concentrated using a membrane concentration process to obtain a 5% lithium chloride concentrate, which is then further concentrated using a triple-effect evaporator at 110℃ and 130 kPa to obtain a 40% lithium chloride solution as a byproduct.

[0047] The collected first lithium hydrochloride impurity, second lithium carbonate impurity, and third lithium carbonate impurity were mixed with the mother liquor from the first crystallization. CO2 was introduced into this mixture, and the mixture was reacted at 95°C for 40 minutes to carry out a carbonation reaction. After the reaction, the mixture was separated by centrifugation to obtain wet lithium carbonate and lithium carbonate recovery mother liquor. The wet lithium carbonate was returned to step (2) and used together with the pretreated material for the causticization reaction; the lithium carbonate recovery mother liquor was used to prepare lithium chloride.

[0048] The combined wastewater generated from the entire process is treated by a reverse osmosis membrane concentration unit. The resulting industrial water is reused in production, while the concentrated wastewater undergoes further treatment in a multi-effect vacuum evaporation crystallizer. The resulting condensate is reused, and the solid waste is ultimately disposed of in compliance with regulations.

[0049] The lithium hydroxide monohydrate and byproduct lithium chloride solution prepared in this embodiment were subjected to quality testing. The content of lithium hydroxide monohydrate (LiOH·H2O) was determined by ion chromatography, metallic impurities were determined by inductively coupled plasma optical emission spectrometry (ICP-OES), and other impurities were determined by spectrophotometry. The content of magnetic foreign matter was determined according to the method specified in Appendix B of GB / T 26008-2020. The results are shown in Table 1. All indicators of the product meet the D1 grade (battery grade) requirements of GB / T 26008-2020. The composition of the lithium chloride solution is shown in Table 2 and can be sold as a byproduct.

[0050] Production stability observation: During a continuous 72-hour production test, the evaporator, heat exchanger, and other equipment involved in this embodiment operated stably, with no significant decrease in inlet and outlet temperature difference or heat exchange efficiency. No obvious lithium carbonate scale was found during shutdown inspection.

[0051] Table 1. Quality test results of lithium hydroxide monohydrate in Example 1 (content: wt%)

[0052] Table 2. Quality test results of lithium chloride solution in Example 1

[0053] As shown in Table 2, the lithium chloride solution contains 40% lithium chloride by mass, along with 15% sodium chloride, and impurities such as calcium (0.15%), sulfate (1.35%), magnesium (0.15%), and potassium (0.43%). The pH value is 7.2. This byproduct lithium chloride has some recycling value, but further purification processes (such as impurity removal and separation) are needed to reduce the impurity content and meet the purity requirements of lithium chloride in different application scenarios.

[0054] Lithium recovery rate calculation: Based on industrial-grade lithium carbonate (99.11% purity) as raw material, the total lithium input is approximately 0.2979t. The lithium recovery rate in the product lithium hydroxide monohydrate is approximately 95.6%, and the lithium recovery rate in the by-product lithium chloride is approximately 2.5%, resulting in a total lithium recovery rate as high as 98.1%.

[0055] Example 2 This embodiment provides a method for preparing battery-grade lithium hydroxide monohydrate using lithium carbonate causticization, which is basically the same as that in Example 1, except for the causticization reaction method in step (2): the pretreated material obtained in step (1) is directly added to the causticization reactor for mixing with quicklime and water. All other conditions are the same as in Example 1. The causticization reaction process of this embodiment is as follows: Figure 4 As shown.

[0056] The quality test results of the obtained lithium hydroxide monohydrate product are shown in Table 3. It still meets the D1 grade requirements of GB / T 26008-2020, and the lithium recovery rate is comparable to that of Example 1.

[0057] Production stability observation: During a continuous 72-hour production test, the evaporator, heat exchanger, and other equipment involved in this embodiment operated stably, with no significant decrease in inlet and outlet temperature difference or heat exchange efficiency. No obvious lithium carbonate scale was found during shutdown inspection.

[0058] Table 3. Quality test results of lithium hydroxide monohydrate in Example 2 (content: wt%)

[0059] Example 3 This embodiment provides a method for preparing battery-grade lithium hydroxide monohydrate using lithium carbonate causticization, which is basically the same as that in Embodiment 1, except for the recycling method of the secondary crystallization mother liquor in step (5): the secondary crystallization mother liquor is divided into two parts, one half of which is returned to step (4) for a first evaporation crystallization, and the other half is returned to the secondary evaporation crystallization process in step (5) for internal circulation. All other conditions are the same as in Embodiment 1. The preparation process of lithium hydroxide monohydrate in this embodiment is as follows: Figure 5 As shown.

[0060] The quality test results of the obtained lithium hydroxide monohydrate product are shown in Table 4, and it still meets the battery-grade requirements.

[0061] Production stability observation: During a continuous 72-hour production test, the evaporator, heat exchanger, and other equipment involved in this embodiment operated stably, with no significant decrease in inlet and outlet temperature difference or heat exchange efficiency. No obvious lithium carbonate scale was found during shutdown inspection.

[0062] Table 4. Quality test results of lithium hydroxide monohydrate in Example 3 (content: wt%)

[0063] Comparative Example 1 This comparative example provides a method for preparing lithium hydroxide monohydrate by causticizing lithium carbonate. The only difference between this method and Example 1 is that the "lithium source pretreatment" (i.e., water washing step) in step (1) is omitted. All other conditions are exactly the same as in Example 1.

[0064] Tests and Results: The quality test results of the obtained lithium hydroxide monohydrate product are shown in Table 5. Compared with Example 1, the chloride ion content (Cl) in the product... - ) and sulfate (SO4) 2- The content of soluble anionic impurities increased significantly, exceeding the D1 grade standard of GB / T 26008-2020, proving that water washing pretreatment is crucial for removing soluble anionic impurities and ensuring the purity of the final product. Meanwhile, due to the absence of water washing wastewater, the yield of by-product lithium chloride was extremely low (approximately 1%), resulting in a decrease in the total lithium recovery rate.

[0065] Production stability observation: Due to excessive impurities (especially chloride and sulfate ions), this comparative example failed to obtain qualified products and long-term continuous operation testing was not conducted. However, based on process inference, the lack of water washing pretreatment and high impurity load in the system may exacerbate the potential scaling risk in subsequent processes.

[0066] Table 5. Quality test results of lithium hydroxide monohydrate in Comparative Example 1 (content: wt%)

[0067] Comparative Example 2 This comparative example provides a method for preparing lithium hydroxide monohydrate using lithium carbonate causticization. The only difference between this method and Example 1 is that the "evaporation and concentration" sub-step of step (4) is omitted. That is, the "purified liquid" obtained in step (3) is directly used as the "concentrated liquid" in the subsequent "first-stage evaporation and crystallization" process without evaporation and concentration. All other conditions are exactly the same as in Example 1.

[0068] Tests and Results: The quality test results of the obtained lithium hydroxide monohydrate product are shown in Table 6. Compared with Example 1, the carbonate (CO3) content in the product is lower. 2- The content of 0.55% is seriously excessive and does not meet the battery-grade standard.

[0069] Production stability observation: During the experiment, it was observed that the heat exchange efficiency of the evaporator in the first evaporation crystallization process began to decrease significantly after about 10 hours of operation, while the operating pressure increased. Inspection after shutdown revealed a large amount of hard, white scale on the heat exchange tube walls and the inner wall of the crystallizer. Analysis showed that its main component was lithium carbonate.

[0070] Table 6. Quality test results of lithium hydroxide monohydrate in Comparative Example 2

[0071] Comparative Example 3 This comparative example provides a method for preparing lithium hydroxide monohydrate by causticizing lithium carbonate. The only difference between this method and Example 1 is that the concentration of lithium hydroxide in the concentrate in step (4) is 85 g / L, while all other conditions are exactly the same as in Example 1.

[0072] Tests and Results: The quality test results of the obtained lithium hydroxide monohydrate product are shown in Table 7. Compared with Example 1, the carbonate (CO3) content in the product is lower. 2- The content of ) increased significantly (0.38%), but it met the battery-grade standard.

[0073] Production Stability Observation: During a 24-hour continuous operation test, the heat exchange efficiency of the evaporator in the first evaporation crystallization process showed a slow but continuous downward trend, while the operating pressure increased. Inspection after shutdown revealed a thin, loose white scale adhering to the heat exchange tube walls and the inner wall of the crystallizer. Analysis showed that the main component of this scale was still lithium carbonate. This indicates that although evaporation and concentration were performed, the amount of lithium carbonate precipitated was relatively small. Furthermore, the lithium carbonate crystals precipitated at lower supersaturation levels were generally finer. Although most of the precipitated lithium carbonate was separated by cyclone fractionation, the separation efficiency for fine particles was limited, resulting in some fine-grained lithium carbonate being used in subsequent processes, and a high residual concentration of lithium carbonate in the solution. In the subsequent evaporation crystallization process, the newly generated lithium carbonate was difficult to grow rapidly and orderly on the fine particles, causing the newly precipitated lithium carbonate to tend to nucleate heterogeneously on the heat transfer surface of the equipment, thus exacerbating the scaling phenomenon.

[0074] Table 7. Quality test results of lithium hydroxide monohydrate in Comparative Example 3

[0075] Based on the product quality and production stability test results of the above embodiments and comparative examples, it can be seen that the method for preparing battery-grade lithium hydroxide monohydrate using lithium carbonate causticization provided by the present invention can stably and continuously produce products that fully meet the quality requirements of GB / T26008-2020 D1 grade (battery grade). However, Comparative Example 1, due to the omission of the "lithium source pretreatment" (water washing) step, resulted in significantly excessive chloride and sulfate content in the product, verifying the necessity of this step for removing soluble anionic impurities from the source and ensuring product purity. Comparative Example 2, due to the omission of the "evaporation and concentration" step, not only resulted in severely excessive carbonate content in the product but also directly caused severe scaling problems in the evaporation crystallization equipment, making continuous production impossible. This fully demonstrates the crucial role of the "evaporation and concentration" step in the present invention in pre-precipitating lithium carbonate seeds, guiding the directional precipitation of impurities to reduce equipment scaling, and ultimately controlling the carbonate content in the product. Although the product purity of Comparative Example 3 met the battery-grade quality requirements, obvious scaling signs appeared in the equipment during the production process.

[0076] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing battery-grade lithium hydroxide monohydrate using lithium carbonate causticization, characterized in that, Includes the following steps: (1) Lithium source pretreatment: The lithium source raw material containing lithium carbonate is washed and solid-liquid separated to obtain pretreated material and washing liquid; (2) Causticization reaction: The pretreated material is mixed with an alkaline calcium-containing substance to carry out a causticization reaction to obtain a solid-liquid mixture containing lithium hydroxide; the solid-liquid mixture containing lithium hydroxide is subjected to solid-liquid separation to obtain a lithium hydroxide solution and causticization residue. (3) Ion exchange purification treatment: The lithium hydroxide solution is subjected to ion exchange treatment to obtain a purified solution; (4) Evaporation and concentration and impurity classification: The purified liquid is evaporated and concentrated to obtain a concentrated liquid; the concentrated liquid is subjected to hydrocyclone classification to obtain the first lithium carbonate impurity and the concentrated overflow liquid; wherein, the concentration of lithium hydroxide in the concentrated liquid is 100 g / L~120 g / L. (5) Evaporation crystallization and washing separation: The concentrated overflow liquid is evaporated and crystallized in one step and then separated into solid and liquid to obtain the first lithium hydroxide monohydrate crystal slurry; the first lithium hydroxide monohydrate crystal slurry is washed in the first stage to separate the second lithium carbonate impurity; the slurry after the first stage washing is separated into solid and liquid to obtain crude lithium hydroxide monohydrate and the mother liquor of the first crystallization. (6) Refining and resolution and secondary evaporation crystallization: Crude lithium hydroxide monohydrate is dissolved in water and refined by filtration to obtain a resolution and refined solution; the resolution and refined solution is subjected to secondary evaporation crystallization to obtain a second lithium hydroxide monohydrate slurry; the second lithium hydroxide monohydrate slurry is subjected to a second-stage washing to separate the third lithium carbonate impurity; the slurry after the second-stage washing is subjected to solid-liquid separation to obtain wet refined lithium hydroxide monohydrate and secondary crystallization mother liquor; (7) Drying: The wet refined lithium hydroxide monohydrate is dried to obtain battery-grade lithium hydroxide monohydrate.

2. The method according to claim 1, characterized in that, It also includes lithium carbonate recovery and material recycling steps: the first lithium carbonate impurity, the second lithium carbonate impurity and the third lithium carbonate impurity are mixed with at least part of the primary crystallization mother liquor, carbon dioxide is introduced to carry out carbonation reaction, and solid-liquid separation is carried out after the reaction to obtain lithium carbonate wet product and lithium carbonate recovery mother liquor; the lithium carbonate wet product is returned to step (2) and used together with the pretreated material for subsequent causticization reaction. And / or, it also includes a lithium chloride preparation step: the washing liquid obtained in step (1) and / or the lithium carbonate recovery mother liquor obtained in the lithium carbonate recovery and material recycling step are reacted with hydrochloric acid to generate lithium chloride and with sodium hydroxide to neutralize, and then concentrated to obtain a lithium chloride product solution.

3. The method according to claim 1 or 2, characterized in that, Also includes: At least a portion of the secondary crystallization mother liquor obtained in step (6) is returned to step (5), mixed with the concentrated overflow liquid, and then subjected to a first evaporation crystallization. And / or, it also includes: reusing the steam condensate generated during the evaporation and concentration process of step (4) and / or the single evaporation and crystallization process of step (5) for the water use step of this method.

4. The method according to claim 1 or 2, characterized in that, In step (1), the detergent used for washing includes water; And / or, the washing temperature is 85℃~100℃, and the washing time is 15min~60min; And / or, in step (1), during the washing of the lithium source material containing lithium carbonate, the mass ratio of the lithium source material containing lithium carbonate to the detergent is 1:(2~4).

5. The method according to claim 1 or 2, characterized in that, In step (2), the temperature of the causticizing reaction is 85℃~98℃, and the reaction time is 1h~5h; And / or, the molar ratio of lithium carbonate in the pretreated material to that in the alkaline calcium-containing substance, calculated as Ca, is (0.5~1.5):(0.5~1.5).

6. The method according to claim 1 or 2, characterized in that, In step (2), the alkaline calcium-containing substance includes at least one of calcium hydroxide and calcium oxide; And / or, step (2) further includes: washing and calcining the causticized slag; And / or, in step (3), the ion exchange treatment process includes: passing the lithium hydroxide solution sequentially through a cation exchange resin and an anion chelating resin.

7. The method according to claim 6, characterized in that, The washing method is countercurrent washing; wherein, the number of washings is ≥2 times, the mass ratio of caustic sludge to water is 1:(2~4) during each washing process, and the washing time is 15min~20min. And / or, the calcination temperature is 1000℃~1200℃, and the calcination time is ≥30min; And / or, the flow rates of the cation exchange resin and the anion chelating resin are each independently 1.5 m / s to 2 m / s.

8. The method according to claim 1 or 2, characterized in that, In step (4), the evaporation and concentration are carried out at 60℃~80℃ and 20 kPa~50 kPa. And / or, the primary evaporation crystallization is carried out at 50°C to 80°C and 20 kPa to 50 kPa.

9. The method according to claim 1 or 2, characterized in that, Step (5) further includes: setting a backwashing device at the outlet of the crystallizer for primary evaporation crystallization to perform backwashing operation on the discharge; wherein, the solid material separated by the backwashing operation is returned to step (2) and used together with the pretreated material for subsequent causticization reaction.

10. The method according to claim 1 or 2, characterized in that, In step (6), the concentration of lithium hydroxide in the reconstituted and purified solution is 80 g / L to 120 g / L; And / or, the secondary evaporation crystallization is carried out under conditions of 50℃~80℃ and 20 kPa~50 kPa; And / or, in step (7), the drying temperature is 75°C to 90°C.

Images