Method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride and high-purity anhydrous lithium chloride

Abstract

The invention discloses a method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride and the high-purity anhydrous lithium chloride. The method comprises the following steps: obtaining a lithium chloride pre-dissolving solution of suspended sulfate impurities; filtering and separating the lithium chloride pre-dissolved solution to obtain a filtered lithium chloride solution; performing evaporative crystallization on the filtered lithium chloride liquid to obtain lithium chloride crystal slurry; performing centrifugal separation on the lithium chloride crystal slurry to obtain clean lithium chloride crystals; cooling and crystallizing the clean lithium chloride crystals to obtain cooled slurry; drying the cooled slurry by a drying machine to obtain dried lithium chloride; carrying out secondary dissolution on the dried lithium chloride so as to obtain a high-purity dissolved solution; and performing anhydrous treatment on the high-purity dissolved solution to obtain the high-purity anhydrous lithium chloride. The whole process does not depend on excessive chemical precipitants, impurity removal is achieved only through physical separation and selective adsorption, and secondary impurity introduction is avoided.

Description

Technical Field

[0001] This application relates to the field of lithium chloride technology, specifically to a method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride, and the high-purity anhydrous lithium chloride. Background Technology

[0002] In the fields of lithium resource recovery and high-purity lithium chloride preparation, crude lithium chloride containing potassium chloride (such as byproducts of lithium extraction from salt lakes and products from industrial waste recovery) is an important raw material. However, existing purification technologies mostly employ single crystallization or simple filtration to remove impurities, failing to fully utilize the solubility differences between lithium chloride and potassium chloride / sulfate for targeted separation. On the one hand, the solubility curves of potassium chloride and lithium chloride are similar, and conventional cooling crystallization can only remove less than 70% of potassium salts, resulting in potassium chloride residues in the product often exceeding 0.05%. On the other hand, impurities such as sulfates easily co-crystallize with lithium chloride, and it is difficult to completely remove them using only a single precipitation process. Consequently, the total impurity content of the final product is difficult to reduce to below 0.05%, failing to meet high-purity standards. Summary of the Invention

[0003] The purpose of this invention is to provide a method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride, thereby solving at least one of the aforementioned technical problems.

[0004] One aspect of the present invention provides a method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride, wherein the method comprises:

[0005] To obtain a pre-dissolved lithium chloride solution containing suspended sulfate impurities;

[0006] The lithium chloride pre-dissolved solution containing suspended sulfate impurities is filtered and separated to obtain the lithium chloride filtrate.

[0007] The filtered lithium chloride solution is evaporated and crystallized to obtain a lithium chloride crystallization slurry.

[0008] The lithium chloride crystallization slurry is centrifuged to obtain clean lithium chloride crystals;

[0009] Clean lithium chloride crystals are cooled and crystallized to obtain a cooled slurry;

[0010] The cooled slurry is dried in a dryer to obtain dried lithium chloride;

[0011] The dried lithium chloride is dissolved a second time to obtain a high-purity dissolved solution;

[0012] The high-purity dissolved solution is anhydrous to obtain high-purity anhydrous lithium chloride.

[0013] Optionally, the lithium chloride pre-dissolution solution for obtaining suspended sulfate impurities includes:

[0014] Take crude lithium chloride crystals containing potassium chloride, add them to deionized water and circulating mother liquor at a mass-volume ratio of crude product:deionized water:circulating mother liquor = 1:2.0:1.2, and mix to form a solid-liquid mixed suspension;

[0015] The solid-liquid mixture suspension is heated to 58-60℃ and stirred at a constant temperature. At the same time, lithium chloride seed crystals are added at 0.5% of the crude product mass, and polyaspartic acid scale inhibitor is added according to the solution mass. The mixture is stirred at a constant temperature for 35 minutes to obtain a high-temperature solution with a lithium chloride concentration of 43%-46%.

[0016] The high-temperature solution was taken under stirring, and the sulfate content was determined by barium turbidimetry. Based on the test results, the following gradient cooling was performed to obtain a suspension at 35°C:

[0017] If the sulfate content is detected to be ≥2.5%, the system temperature is lowered to 35℃ at a rate of 1.5℃ / h, and kept at this temperature for 15 min with stirring at 200r / min.

[0018] If the sulfate content is detected to be <2.5%, the system temperature is lowered to 35℃ at a rate of 2℃ / h, and kept at this temperature for 10 min with stirring at 200r / min.

[0019] Add 0.3% (by mass) of crude potassium chloride seed crystals to a suspension at 35°C, cool to 25°C at a rate of 1°C / h, and keep warm for 20 min with stirring at 180 r / min to obtain a suspension at 25°C.

[0020] The suspension at 25°C was cooled to 20-22°C at a rate of 0.8°C / h, kept at 180 r / min for 15 min with stirring, and then filtered after standing for 10 min to obtain a pre-dissolved lithium chloride solution containing suspended sulfate impurities.

[0021] Optionally, the step of filtering and separating the pre-dissolved lithium chloride solution containing suspended sulfate impurities to obtain the lithium chloride filtrate includes:

[0022] Polyaluminum chloride was added to a lithium chloride pre-dissolved solution containing suspended sulfate impurities at a mass ratio of 0.02%, and the solution was stirred at 150 r / min for 15 min at 25 °C to obtain a suspension containing 5-10 μm flocs.

[0023] The suspension containing 5-10μm flocs was filtered sequentially through 5μm and 0.2μm ceramic membranes to obtain the lithium chloride filtrate.

[0024] Optionally, the step of evaporating and crystallizing the lithium chloride filtrate to obtain a lithium chloride crystallization slurry includes:

[0025] The lithium chloride filtrate was evaporated at 150°C and at normal pressure to a density of 1.35 g / cm³ to obtain a saturated lithium chloride solution.

[0026] A lithium chloride saturated solution was stirred at 80 r / min for 60 min at a temperature of 110-120℃ to obtain a lithium chloride crystallization slurry.

[0027] Optionally, the centrifugation of the lithium chloride crystallization slurry to obtain clean lithium chloride crystals includes:

[0028] The lithium chloride crystallization slurry was centrifuged at 3200 r / min for 15 s to obtain wet lithium chloride crystals;

[0029] A 48% lithium chloride solution at 120-130℃ is sprayed onto wet lithium chloride crystals, and the solution is centrifuged at 3200 r / min for 10 s to obtain clean lithium chloride crystals.

[0030] Optionally, the cooling and crystallization of clean lithium chloride crystals to obtain a cooled slurry includes:

[0031] Clean lithium chloride crystals are mixed with deionized water at a ratio of 1:0.5 and stirred at 90°C for 20 minutes until completely dissolved. Then, 8% anhydrous ethanol is added. The material is heated by the heat of dissolution to obtain a refined lithium chloride solution with a temperature of 150~160°C.

[0032] The cooled slurry is obtained by staged cooling crystallization, which is carried out through the following steps:

[0033] The temperature was lowered to 130℃ at a rate of 3℃ / h, held for 2 hours, then lowered to 120℃ at a rate of 1.5℃ / h, held for 3 hours, and then lowered to 110℃ at a rate of 0.8℃ / h, held for 1 hour, thus obtaining the cooled slurry.

[0034] Optionally, the step of drying the cooled slurry in a dryer to obtain dried lithium chloride includes:

[0035] The cooled slurry was dried under nitrogen gas for 5 hours at a pulsating cycle of 170-180℃ and a vacuum of -0.095MPa or -0.08MPa to obtain dried lithium chloride.

[0036] Optionally, the step of dissolving the dried lithium chloride a second time to obtain a high-purity dissolved solution includes:

[0037] Dried lithium chloride was mixed with deionized water at a ratio of 1:0.5 and stirred at 45℃-50℃ for 20 min. The mixture was then filtered through a 0.5μm filter membrane to obtain undissolved lithium chloride crystals and a solution containing impurities.

[0038] The impurity-containing solution is passed through a cation exchange column to obtain a purified solution.

[0039] Undissolved lithium chloride crystals were mixed with the purified solution and stirred at 45-50℃ for 30 minutes until completely dissolved. The solution was then filtered through a 0.2μm filter to obtain a high-purity lithium chloride solution.

[0040] Optionally, the step of anhydrousifying the high-purity dissolved solution to obtain high-purity anhydrous lithium chloride includes:

[0041] High-purity anhydrous lithium chloride is obtained by evaporating the solution after dissolving it in high purity at 150-160℃ and -0.05MPa to a solid state.

[0042] This application also provides a high-purity anhydrous lithium chloride, which is produced by the method described above for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride.

[0043] Based on the solubility differences of lithium chloride with potassium chloride and sulfate at different temperatures, this application designs a three-stage impurity removal logic: dual impurity pre-removal + gradient crystallization + ion exchange. In the dissolution stage, high-temperature dissolution followed by gradient cooling utilizes the characteristic of sulfate solubility decreasing rapidly with temperature to achieve pre-precipitation. In the crystallization stage, potassium chloride seed crystals induce the co-crystallization of potassium chloride and lithium chloride, promoting the directional precipitation of potassium salts. In the deep purification stage, selective adsorption by cation exchange resin precisely captures trace metal ions such as calcium and magnesium, fundamentally avoiding impurity residue. The entire process does not rely on excessive chemical precipitants, achieving impurity removal solely through physical separation and selective adsorption, avoiding the introduction of secondary impurities and ensuring product purity from the source. Attached Figure Description

[0044] Figure 1 This is a schematic flowchart of the method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride according to this application.

[0045] Figure 2 This is a schematic diagram comparing the method of producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride of this application with other comparative examples. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0047] like Figure 1 The method shown for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride includes:

[0048] To obtain a pre-dissolved lithium chloride solution containing suspended sulfate impurities;

[0049] The lithium chloride pre-dissolved solution containing suspended sulfate impurities is filtered and separated to obtain the lithium chloride filtrate.

[0050] The filtered lithium chloride solution is evaporated and crystallized to obtain a lithium chloride crystallization slurry.

[0051] The lithium chloride crystallization slurry is centrifuged to obtain clean lithium chloride crystals;

[0052] Clean lithium chloride crystals are cooled and crystallized to obtain a cooled slurry;

[0053] The cooled slurry is dried in a dryer to obtain dried lithium chloride;

[0054] The dried lithium chloride is dissolved a second time to obtain a high-purity dissolved solution;

[0055] The high-purity dissolved solution is anhydrous to obtain high-purity anhydrous lithium chloride.

[0056] In this embodiment, the lithium chloride pre-dissolution solution for obtaining suspended sulfate impurities includes:

[0057] Take crude lithium chloride crystals containing potassium chloride, add them to deionized water and circulating mother liquor at a mass-volume ratio of crude product:deionized water:circulating mother liquor = 1:2.0:1.2, and mix to form a solid-liquid mixed suspension;

[0058] The solid-liquid mixture suspension is heated to 58-60℃ and stirred at a constant temperature. At the same time, lithium chloride seed crystals are added at 0.5% of the crude product mass, and polyaspartic acid scale inhibitor is added according to the solution mass. The mixture is stirred at a constant temperature for 35 minutes to obtain a high-temperature solution with a lithium chloride concentration of 43%-46%.

[0059] The high-temperature solution was taken under stirring, and the sulfate content was determined by barium turbidimetry. Based on the test results, the following gradient cooling was performed to obtain a suspension at 35°C:

[0060] If the sulfate content is detected to be ≥2.5%, the system temperature is lowered to 35℃ at a rate of 1.5℃ / h, and kept at this temperature for 15 min with stirring at 200r / min.

[0061] If the sulfate content is detected to be <2.5%, the system temperature is lowered to 35℃ at a rate of 2℃ / h, and kept at this temperature for 10 min with stirring at 200r / min.

[0062] Add 0.3% (by mass) of crude potassium chloride seed crystals to a suspension at 35°C, cool to 25°C at a rate of 1°C / h, and keep warm for 20 min with stirring at 180 r / min to obtain a suspension at 25°C.

[0063] The suspension at 25°C was cooled to 20-22°C at a rate of 0.8°C / h, kept at 180 r / min for 15 min with stirring, and then filtered after standing for 10 min to obtain a pre-dissolved lithium chloride solution containing suspended sulfate impurities.

[0064] In this embodiment, the step of filtering and separating the lithium chloride pre-dissolved solution containing suspended sulfate impurities to obtain the lithium chloride filtrate includes:

[0065] Polyaluminum chloride was added to a lithium chloride pre-dissolved solution containing suspended sulfate impurities at a mass ratio of 0.02%, and the solution was stirred at 150 r / min for 15 min at 25 °C to obtain a suspension containing 5-10 μm flocs.

[0066] The suspension containing 5-10μm flocs was filtered sequentially through 5μm and 0.2μm ceramic membranes to obtain the lithium chloride filtrate.

[0067] In this embodiment, the step of evaporating and crystallizing the lithium chloride filtrate to obtain a lithium chloride crystallization slurry includes:

[0068] The lithium chloride filtrate was evaporated at 150°C and -0.05 MPa to a density of 1.35 g / cm³ to obtain a saturated lithium chloride solution.

[0069] A lithium chloride saturated solution was stirred at 80 r / min for 60 min at a temperature of 110-120℃ to obtain a lithium chloride crystallization slurry.

[0070] In this embodiment, the centrifugation of the lithium chloride crystallization slurry to obtain clean lithium chloride crystals includes:

[0071] The lithium chloride crystallization slurry was centrifuged at 3200 r / min for 15 s to obtain wet lithium chloride crystals;

[0072] A 48% lithium chloride solution at 120-130℃ is sprayed onto wet lithium chloride crystals, and the solution is centrifuged at 3200 r / min for 10 s to obtain clean lithium chloride crystals.

[0073] In this embodiment, the cooling and crystallization of clean lithium chloride crystals to obtain a cooled slurry includes:

[0074] Clean lithium chloride crystals were mixed with deionized water at a ratio of 1:0.5, stirred at 35°C for 20 minutes until completely dissolved, and then 8% anhydrous ethanol was added to obtain a refined lithium chloride solution.

[0075] The cooled slurry is obtained by staged cooling crystallization, which is carried out through the following steps:

[0076] The temperature was lowered to 130℃ at a rate of 3℃ / h, held for 2 hours, then lowered to 120℃ at a rate of 1.5℃ / h, held for 3 hours, and then lowered to 110℃ at a rate of 0.8℃ / h, held for 1 hour, thus obtaining the cooled slurry.

[0077] In this embodiment, the step of drying the cooled slurry in a dryer to obtain dried lithium chloride includes:

[0078] The cooled slurry was dried under nitrogen gas for 5 hours at a pulsating cycle of 170-180℃ and a vacuum of -0.095MPa or -0.08MPa to obtain dried lithium chloride.

[0079] In this embodiment, the secondary dissolution of the dried lithium chloride to obtain a high-purity dissolved solution includes:

[0080] Dried lithium chloride was mixed with deionized water at a ratio of 1:0.5 and stirred at 45℃-50℃ for 20 min. The mixture was then filtered through a 0.5μm filter membrane to obtain undissolved lithium chloride crystals and a solution containing impurities.

[0081] The impurity-containing solution is passed through a cation exchange column to obtain a purified solution.

[0082] Undissolved lithium chloride crystals were mixed with the purified solution and stirred at 45-50℃ for 30 minutes until completely dissolved. The solution was then filtered through a 0.2μm filter to obtain a high-purity lithium chloride solution.

[0083] In this embodiment, the step of anhydrousifying the high-purity dissolved solution to obtain high-purity anhydrous lithium chloride includes:

[0084] High-purity anhydrous lithium chloride is obtained by evaporating the solution after dissolving it in high purity at 150-160℃ and -0.05MPa to a solid state.

[0085] This application also provides a high-purity anhydrous lithium chloride, which is produced by the method described above for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride.

[0086] The present application and comparative examples are described in detail below by way of examples. In the following examples, the premises of each embodiment and comparative example are as follows: all embodiments or comparative examples use crude lithium chloride (bagged, 50kg / bag) as a by-product of lithium extraction from salt lakes. The basic components are uniformly controlled as follows: lithium chloride purity 85%-88%, impurities are mainly potassium chloride and sulfate, and calcium and magnesium ions are trace accompanying impurities; the solvent is industrial-grade deionized water (pipeline transport, resistivity ≥18MΩ・cm); the auxiliary reagents are all industrial-grade (polyaluminum chloride PAC: 25% content, liquid; lithium chloride seed crystals: 99.9% purity, powder; cation exchange resin: 001×7 strong acid, spherical).

[0087] Example 1:

[0088] Crude lithium chloride: fed at a constant speed via belt conveyor + loss-in-weight feeder (accuracy ±0.5%), with a feed rate of 1000 kg per hour (24 tons per day).

[0089] Solvent: Industrial deionized water is simultaneously delivered to a 10m³ continuous dissolving tank via a metering pump (flow rate 2000L / h) and circulating mother liquor via a variable frequency pump (flow rate 1200L / h), ensuring that the ratio of crude product:deionized water:circulating mother liquor is 1:2.0:1.2 (mass-volume ratio).

[0090] Raw material composition: lithium chloride purity 85%, potassium chloride 3%, sulfate 1%, total calcium and magnesium ion content 0.3%, other insoluble matter 1%.

[0091] Temperature control of the dissolving tank: 58℃ constant temperature water is introduced into the jacket (the temperature is precisely controlled by the steam heat exchanger, with fluctuations of ±0.3℃), and the propeller agitator is set to 380r / min (to form an axial flow field and prevent solid deposition).

[0092] Auxiliary reagent addition: Lithium chloride seed crystals (50% concentration suspension, added at 0.5% of the crude product feed rate, i.e., 5 kg / h) and polyaspartic acid scale inhibitor (1% concentration solution, added at 50 ppm of the total solution, i.e., 210 g / h) are continuously added via metering pump.

[0093] Insulation and degassing: Maintain a residence time of 35 minutes in the dissolving tank (feed rate controlled by liquid level), and simultaneously open the vacuum degassing valve on the top of the tank (vacuum degree -0.07MPa) to remove HCl gas and air generated during dissolution;

[0094] Sulfate detection and cooling control: Before the solution enters the buffer tank, the online XRF detector detects the sulfate content in real time (displaying 1.2%), triggering the cooling program. The solution is cooled to 35°C at a rate of 2°C / h through a shell-and-tube cooler and then held in a 35°C insulated tank for 10 minutes (stirring rate 200r / min).

[0095] After cooling, the solution enters a crystallization buffer tank, and potassium chloride seed crystals (30% concentration suspension, added at 0.3% of the crude product feed rate, i.e., 3 kg / h) are added. The solution is cooled to 25°C at a rate of 1°C / h (hold for 20 min), and then cooled to 20°C at a rate of 0.8°C / h (hold for 15 min). Finally, it is filtered through a rotary drum filter (filtration area 5 m²) to obtain a lithium chloride pre-dissolved solution.

[0096] Flocculation-gradient membrane filtration for impurity removal:

[0097] Flocculation reaction: The pre-dissolved liquid enters a 10m³ flocculation tank, and PAC (25% concentration, i.e., 10kg / h) is added at 0.02% of the total solution volume. The mixture is stirred at 150r / min for 15min at 25℃ (the residence time is controlled by the tank volume and the feed rate).

[0098] Gradient membrane filtration: After flocculation, the solution is pumped into a ceramic membrane filter unit, first through a 5μm pore size membrane (operating pressure 0.28MPa, cross-flow velocity 1.8m / s), then through a 0.2μm pore size membrane (operating pressure 0.3MPa, cross-flow velocity 1.8m / s). The permeate is the lithium chloride filtration solution (online turbidity meter shows ≤0.5NTU). The retained filter cake is transported by a screw pump to the waste residue treatment system (after lithium recovery by hydrochloric acid dissolution, it is treated by pressure filtration).

[0099] Vacuum evaporation - constant temperature crystal growth:

[0100] Vacuum evaporation: The filtered liquid is fed into a falling film vacuum evaporator, and the heating temperature is controlled at 150℃ and atmospheric pressure to evaporate to a solution density of 1.35 g / cm³ (monitored in real time by an online density meter) to obtain a saturated lithium chloride solution;

[0101] Constant temperature crystal growth: The saturated solution is introduced into a 20m³ crystallization tank and maintained at 120℃ (temperature controlled by jacket hot water). The mixture is stirred at 80r / min for 60min (residence time 60min) to form a crystallization slurry containing large particles of 600-800μm (particle size is monitored by an online particle counter).

[0102] Centrifugation - Washing with the same concentration:

[0103] Initial centrifugation: The crystallized slurry is fed into a horizontal spiral sedimentation centrifuge and centrifuged at 3200 r / min for 15 s (processing capacity 3 m³ / h). The separated saturated mother liquor (lithium chloride concentration 50%-52%) is sent to the mother liquor storage tank for circulation.

[0104] Washing at the same concentration: The wet crystals (5% water content) in the centrifuge are sprayed into a refined lithium chloride solution at 120℃ and 48% concentration (the amount used is 15% of the crystal mass, precisely controlled by a metering pump) through a spray device, and centrifuged for another 10 seconds to obtain clean lithium chloride crystals (5% water content, offline detection purity 98.5%). The washing mother liquor is added to the saturated mother liquor storage tank.

[0105] Solvent cooling crystallization:

[0106] Ethanol dissolution: Clean crystals and deionized water are mixed at a mass-to-volume ratio of 1:0.5 (crystal feed rate 800 kg / h, deionized water 400 L / h), and stirred in a dissolving tank at 90°C for 20 min until completely dissolved. Then, 8% of the solution mass of industrial anhydrous ethanol (purity 99.5%, i.e., 243 L / h) is added to obtain a refined lithium chloride solution.

[0107] Segmented cooling crystallization: The refined solution enters a three-stage cooling crystallizer (total volume 3m³). The first stage cools the solution to 130℃ at 3℃ / h (hold for 2h), the second stage cools the solution to 120℃ at 1.5℃ / h (hold for 3h), and the third stage cools the solution to 110℃ at 0.8℃ / h (hold for 1h). The stirring rate is 50r / min throughout the process to form a cooled slurry.

[0108] Vacuum pulse drying:

[0109] Filtration and solidification: After cooling, the slurry is filtered by a centrifuge (filter cloth pore size 100μm) to obtain cooled crystalline crystals (water content of about 5%). The mother liquor is sent to the ethanol recovery tower (ethanol is recovered by distillation and then recycled).

[0110] Vacuum drying: The crystallized crystals are fed into a vacuum disc dryer, and the drying temperature is controlled at 170℃. The vacuum degree is pulsatingly cyclically at -0.095MPa (10min → -0.08MPa (5min)). At the same time, 99.99% nitrogen gas (flow rate 2m³ / h) is introduced and dried for 5h (continuous feeding, residence time 5h) to obtain dried lithium chloride (offline detection moisture ≤0.08%, purity 99.3%).

[0111] Secondary dissolution - ion exchange purification:

[0112] Reverse dissolution filtration: After drying, lithium chloride and deionized water are mixed at a mass-to-volume ratio of 1:0.5 (crystal feed rate 600 kg / h, deionized water 300 L / h), stirred in a dissolution tank at 92℃ for 20 min, and filtered through a 0.5 μm precision filter membrane to separate undissolved high-purity lithium chloride crystals from impurity-containing solution.

[0113] Ion exchange purification: The impurity-containing solution (lithium chloride concentration 5%-8%) is pumped into a dual parallel cation exchange resin column (single column volume 5m³) at a controlled flow rate of 15m / h. When the calcium and magnesium ion concentration in the effluent is ≤0.001g / L (monitored by an online ion detector), the purified solution is collected. Redissolution and filtration: Undissolved lithium chloride crystals are mixed with the purified solution and stirred in a redissolution tank at 92℃ for 30min until completely dissolved. The solution is then filtered through a 0.2μm precision filter membrane to obtain a high-purity lithium chloride solution (offline detection purity ≥99.95%).

[0114] Anhydrous final treatment:

[0115] Vacuum evaporation and solidification: High-purity lithium chloride solution is fed into a titanium vacuum evaporator, with the temperature controlled at 150℃ and the vacuum degree at -0.05MPa, until it is completely evaporated into solid crystals (to avoid hydrolysis); Screening and packaging: The solid crystals are screened by a 300-mesh vibrating screen (processing capacity 500kg / h) to remove agglomerated particles. Qualified crystals are sent to a clean packaging room and packaged in vacuum aluminum foil bags (25kg / bag) to obtain battery-grade anhydrous lithium chloride finished product (output 480kg per hour, daily capacity 11.52t).

[0116] Example 2 (only the differences from Example 1 are listed):

[0117] Raw material differences: The crude lithium chloride contains 4% potassium chloride and 2% sulfate (other components are the same as in Example 1), and the daily feed rate remains 24t;

[0118] Dissolution-pre-removal differences: Online XRF detection showed a sulfate content of 2.1%, the trigger cooling rate was adjusted to 1.8℃ / h (instead of 2℃ / h in Example 1), the 35℃ holding time was extended to 12 min (instead of 10 min), and the cooling endpoint temperature was 21℃ (instead of 20℃).

[0119] Other steps: The evaporation temperature was adjusted to 155℃, the drying temperature was adjusted to 175℃, and the remaining equipment parameters, reagent dosages, and operating procedures were completely consistent with those in Example 1.

[0120] Example 3 (only the differences from Example 1 are listed):

[0121] Raw material differences: The crude lithium chloride contains 5% potassium chloride and 3% sulfate (other components are the same as in Example 1), with a daily feed rate of 24t;

[0122] Dissolution-pre-removal differences: Online XRF detection showed a sulfate content of 2.8%, the trigger cooling rate was adjusted to 1.5℃ / h (instead of 2℃ / h in Example 1), the 35℃ holding time was extended to 15 min (instead of 10 min), and the cooling endpoint temperature was 22℃ (instead of 20℃).

[0123] Other steps: The evaporation temperature was adjusted to 158℃, the drying temperature was adjusted to 180℃, and the flow rate of the ion exchange resin column was reduced to 14m / h (to ensure thorough removal of calcium and magnesium ions). The remaining equipment parameters, reagent dosages, and operating procedures were completely consistent with those in Example 1.

[0124] III. Comparative Examples:

[0125] Comparative Example 1 (Traditional Dissolution-Precipitation-Single-Effect Evaporation Process)

[0126] Raw materials: Same as in Example 1 (potassium chloride 3%, sulfate 1%, calcium and magnesium ions 0.3%); differences in core processes (industrial equipment and operation):

[0127] Dissolution: A 5m³ intermittent dissolution tank (without jacket temperature control, room temperature dissolution) is used. The crude product and deionized water are mixed at a mass-to-volume ratio of 1:3 (1000kg crude product to 3000L water), with a stirring rate of 200r / min, and dissolved for 30min (without seed crystals or scale inhibitors).

[0128] Impurity removal: Add excess barium chloride solution (1.5 times the molar amount of sulfate) to remove sulfate, let stand for 30 minutes, then add excess sodium carbonate solution (2 times the molar amount of calcium and magnesium ions) to remove calcium and magnesium, and filter with plate and frame (filter cloth pore size 5μm).

[0129] Evaporation crystallization: A single-effect atmospheric pressure evaporator (heating temperature 170℃, no heat pump) was used. After evaporation to saturation, the evaporator was naturally cooled (cooling rate 5℃ / h, no constant temperature crystal growth) and centrifuged at 3000r / min for 10s (no washing with the same concentration).

[0130] Drying: Use a hot air circulating dryer (170℃, normal pressure, without nitrogen protection) to dry for 8 hours, and discharge the mother liquor directly.

[0131] Comparative Example 2 (Fixed Parameter Crystallization - Simplified Impurity Removal Process)

[0132] Raw materials: Same as in Example 2 (4% potassium chloride, 2% sulfate, 0.3% calcium and magnesium ions); Key process differences (industrial equipment and operation):

[0133] Dissolution: Dissolved at a constant temperature of 60℃ (with temperature control), but without circulating mother liquor (all deionized water is used) and without seed induction;

[0134] Crystallization: Fixed cooling rate of 2℃ / h (without adjustment based on impurity content), directly cooling to 110℃ (without segmented heat preservation);

[0135] Impurity removal: The ion exchange resin column is operated as a single column (without parallel switching), the resin dosage is 50% of that in Example 1, and the flow rate is 20 m / h (too fast will result in incomplete impurity removal).

[0136] Drying: Vacuum drying without pulsation (vacuum degree fixed at -0.05MPa), drying time 6h; only part of the mother liquor is circulated (circulation rate 50%).

[0137] See Figure 2 ,from Figure 2 As can be seen from this, the various embodiments of this application have the following advantages compared to the comparative examples:

[0138] This application employs a three-stage process: sulfate gradient cooling pre-precipitation (utilizing the rapid decrease in sulfate solubility at low temperatures, holding at 35℃ for 10-15 min to achieve a sulfate precipitation rate of 45%-55%), potassium chloride seed induction (100-150μm seed crystals provide directional growth sites, resulting in a potassium salt precipitation rate exceeding 60%), and ion exchange deep adsorption. Even with 5% potassium chloride and 3% sulfate in the raw materials, the final product still retains ≤0.005% impurities.

[0139] Comparative Example 1 uses a single chemical precipitation process of excess barium chloride to precipitate sulfate and excess sodium carbonate to precipitate calcium and magnesium, without pre-removal and seed induction; and after precipitation, it directly evaporates and crystallizes without considering the similarity of solubility between potassium chloride and lithium chloride, resulting in potassium chloride residue of 0.082% and calcium and magnesium ions of 0.035%.

[0140] This application returns the crystallization mother liquor (containing 50%-52% lithium chloride) to the dissolution stage, replacing 30% of deionized water, thereby reducing the loss of lithium chloride with the mother liquor. By controlling the density at the end of evaporation (1.35 g / cm³) and the cooling rate (0.8-3℃ / h), excessive precipitation or residue of lithium chloride is avoided, and the final total yield of lithium chloride reaches 98.0%-98.5%.

[0141] Comparative Example 1 uses a process without mother liquor recycling, where the crystallization mother liquor is directly discharged, resulting in a lithium chloride loss rate of 14%-15% with the mother liquor; there is no density monitoring during evaporation (the endpoint is judged based on experience), and the cooling rate is 5℃ / h (too fast leads to impurity encapsulation), resulting in a yield of only 85.2%.

[0142] This application designs an adaptive process that links impurity content detection with process parameters: by rapidly detecting sulfate content (1.2% → 2℃ / h cooling, 2.8% → 1.5℃ / h cooling), the cooling rate and holding time are dynamically adjusted; even if the impurity content of the raw materials fluctuates by 3%-5% (potassium chloride) and 1%-3% (sulfate), the purity of the finished product still fluctuates by ≤±0.02%.

[0143] Comparative Example 2 uses a fixed parameter process: regardless of the impurity content of the raw materials, the temperature is lowered by 2℃ / h and crystallized at the final temperature of 20℃; when the potassium chloride content of the raw material increases from 3% to 5%, the purity of the finished product decreases from 99.7% to 99.5%, with a fluctuation of ±0.13%.

[0144] This application employs a pre-removal process: ① Removing 45%-55% of sulfate and 15%-20% of potassium salt before evaporation and crystallization, reducing the impurity load and energy consumption during subsequent evaporation and crystallization; ② Solvent-co-crystallization process: Introducing ethanol (8% by mass) to lower the lithium chloride crystallization temperature (from 160℃ to 110℃), reducing evaporation; ③ Excess reagent-free process: Reagents are added according to metering (PAC 0.02%, scale inhibitor 50ppm), with no excess residue, reducing wastewater treatment energy consumption. The final unit product energy consumption (equivalent to standard coal) is 75-80 kg / t, with no process wastewater discharge.

[0145] Comparative Example 1: No pre-removal process: all impurities enter the evaporation stage, increasing the evaporation load by 20%-25% and raising energy consumption; Excess reagent process: barium chloride and sodium carbonate are in excess by 50%-100%, and residual reagents need to be treated additionally (increasing wastewater treatment energy consumption); Solvent-free auxiliary process: all-aqueous phase crystallization requires a higher evaporation rate, with energy consumption reaching 128 kg standard coal / t, and a large amount of wastewater discharge.

[0146] This application employs a seed-induced impurity removal process: lithium chloride seed crystals (50-100μm) guide the directional dissolution of lithium chloride, preventing impurity adsorption; potassium chloride seed crystals (100-150μm) induce the directional precipitation of potassium salts, preventing co-crystallization with lithium chloride; and an ion exchange deep impurity removal process, resulting in calcium and magnesium ion residues ≤0.001%. The final product purity is ≥99.95%.

[0147] Comparative Example 1: No seed-induced process: Impurities crystallize freely with lithium chloride, easily forming co-crystallization; No deep impurity removal process: Relying solely on chemical precipitation, trace amounts of calcium and magnesium ions cannot be removed, resulting in a purity of only 99.40%.

[0148] This application has the following advantages:

[0149] To address issues such as concentration fluctuations and uneven crystal growth during the dissolution-crystallization process, a dual approach of seed induction and precise parameter control is employed: lithium chloride seed crystals provide a directional template for crystal growth, preventing the formation of fine and impurity crystals; segmented control of key parameters such as dissolution temperature, cooling rate, and stirring rate maintains the thermodynamic stability of the system, ensuring a consistent crystal growth environment and reducing batch-to-batch variations.

[0150] Each core step is equipped with a sampling and testing closed-loop system for dynamic control to promptly correct process deviations, avoid product fluctuations caused by rough operations such as uneven local concentrations and excessively rapid cooling, and ensure the consistency of physicochemical indicators for each batch of products.

[0151] A closed-loop circulating mother liquor system is introduced, which utilizes the existing lithium chloride concentration in the mother liquor to form a "common ion effect," thereby reducing the amount of deionized water used, enhancing the precipitation of impurities, and reducing the loss of lithium chloride in the mother liquor. Vacuum pulsed drying and inert gas protection are adopted to improve dehydration efficiency by destroying the saturated water vapor film on the crystal surface, reducing energy consumption in the drying stage, and avoiding high-temperature oxidation and hydrolysis losses.

[0152] Precise dosing of scale inhibitors and optimized flow field design inhibit sulfate deposition on equipment walls, reduce equipment cleaning frequency and reagent consumption, extend continuous production time, and indirectly reduce the overall energy consumption and resource waste per unit product.

[0153] Abandoning the fixed process parameter mode, a mechanism for impurity content detection and adaptive adjustment of process parameters is established: by rapidly detecting the content of key impurities such as sulfate in crude products, the cooling rate and holding time are dynamically matched to ensure that the process parameters are accurately adapted to the characteristics of raw material impurities, thus avoiding incomplete impurity removal or product loss due to batch differences in raw materials.

[0154] The complementary design of the multi-stage impurity removal system allows for the pre-removal of most easily treatable impurities in the front stage and the deep removal of trace amounts of difficult-to-remove impurities in the back stage, creating a tolerance space. Even if the impurity content of the raw materials fluctuates within a certain range, the product quality can still be guaranteed through the synergistic effect of the multi-stage system.

[0155] The impurity removal reagents (polyaluminum chloride, scale inhibitor, and ion exchange resin) are all added precisely according to the reaction measurement. Polyaluminum chloride is only used to prevent impurity agglomeration. The scale inhibitor inhibits scaling through adsorption. The ion exchange resin can be regenerated and recycled. There is no excess reagent residue throughout the process, and no new chemical pollutants will be introduced.

[0156] The mother liquor, washing water, and drying exhaust gas condensate are all recycled in a closed loop, with no process wastewater discharge; solid impurities are disposed of in compliance with regulations after lithium recovery, maximizing resource utilization and meeting the core requirements of green production.

[0157] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride, characterized in that, The method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride includes: To obtain a pre-dissolved lithium chloride solution containing suspended sulfate impurities; The lithium chloride pre-dissolved solution containing suspended sulfate impurities is filtered and separated to obtain the lithium chloride filtrate. The filtered lithium chloride solution is evaporated and crystallized to obtain a lithium chloride crystallization slurry. The lithium chloride crystallization slurry is centrifuged to obtain clean lithium chloride crystals; Clean lithium chloride crystals are cooled and crystallized to obtain a cooled slurry; The cooled slurry is dried in a dryer to obtain dried lithium chloride; The dried lithium chloride is dissolved a second time to obtain a high-purity dissolved solution; The high-purity dissolved solution is anhydrous to obtain high-purity anhydrous lithium chloride.

2. The method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride as described in claim 1, characterized in that, The lithium chloride pre-dissolution solution for obtaining suspended sulfate impurities includes: Take crude lithium chloride crystals containing potassium chloride, add them to deionized water and circulating mother liquor at a mass-volume ratio of crude product:deionized water:circulating mother liquor = 1:2.0:1.2, and mix to form a solid-liquid mixed suspension; The solid-liquid mixture suspension is heated to 58-60℃ and stirred at a constant temperature. At the same time, lithium chloride seed crystals are added at 0.5% of the crude product mass, and polyaspartic acid scale inhibitor is added according to the solution mass. The mixture is stirred at a constant temperature for 35 minutes to obtain a high-temperature solution with a lithium chloride concentration of 43%-46%. The high-temperature solution was taken under stirring, and the sulfate content was determined by barium turbidimetry. Based on the test results, the following gradient cooling was performed to obtain a suspension at 35°C: If the sulfate content is detected to be ≥2.5%, the system temperature is lowered to 35℃ at a rate of 1.5℃ / h, and kept at this temperature for 15 min with stirring at 200r / min. If the sulfate content is detected to be <2.5%, the system temperature is lowered to 35℃ at a rate of 2℃ / h, and kept at this temperature for 10 min with stirring at 200r / min. Add 0.3% (by mass) of crude potassium chloride seed crystals to a suspension at 35°C, cool to 25°C at a rate of 1°C / h, and keep warm for 20 min with stirring at 180 r / min to obtain a suspension at 25°C. The suspension at 25°C was cooled to 20-22°C at a rate of 0.8°C / h, kept at 180 r / min for 15 min with stirring, and then filtered after standing for 10 min to obtain a pre-dissolved lithium chloride solution containing suspended sulfate impurities.

3. The method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride as described in claim 2, characterized in that, The process of filtering and separating the pre-dissolved lithium chloride solution containing suspended sulfate impurities to obtain the lithium chloride filtrate includes: Polyaluminum chloride was added to a lithium chloride pre-dissolved solution containing suspended sulfate impurities at a mass ratio of 0.02%, and the solution was stirred at 150 r / min for 15 min at 25 °C to obtain a suspension containing 5-10 μm flocs. The suspension containing 5-10μm flocs was filtered sequentially through 5μm and 0.2μm ceramic membranes to obtain the lithium chloride filtrate.

4. The method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride as described in claim 3, characterized in that, The process of evaporating and crystallizing the lithium chloride filtrate to obtain a lithium chloride crystallization slurry includes: The lithium chloride filtrate was evaporated at 150°C and atmospheric pressure to a density of 1.35 g / cm³ to obtain a saturated lithium chloride solution. A lithium chloride saturated solution was stirred at 80 r / min for 60 min at a temperature of 110-120℃ to obtain a lithium chloride crystallization slurry.

5. The method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride as described in claim 4, characterized in that, The process of centrifuging the lithium chloride crystallization slurry to obtain clean lithium chloride crystals includes: The lithium chloride crystallization slurry was centrifuged at 3200 r / min for 15 s to obtain wet lithium chloride crystals; A 48% lithium chloride solution at 120-130℃ is sprayed onto wet lithium chloride crystals, and the solution is centrifuged at 3200 r / min for 10 s to obtain clean lithium chloride crystals.

6. The method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride as described in claim 5, characterized in that, The cooling and crystallization of clean lithium chloride crystals to obtain a cooled slurry includes: Clean lithium chloride crystals are mixed with deionized water at a ratio of 1:0.5 and stirred at 90°C for 20 minutes until completely dissolved. Then, 8% anhydrous ethanol is added. The material is heated by the heat of dissolution to obtain a refined lithium chloride solution at a temperature of 150-160°C. The cooled slurry is obtained by staged cooling crystallization, which is carried out through the following steps: The temperature was lowered to 130℃ at a rate of 3℃ / h and held for 2 hours, then lowered to 120℃ at a rate of 1.5℃ / h and held for 3 hours, and then lowered to 110℃ at a rate of 0.8℃ / h and held for 1 hour to obtain the cooled slurry.

7. The method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride as described in claim 6, characterized in that, The step of drying the cooled slurry in a dryer to obtain dried lithium chloride includes: The cooled slurry was dried under nitrogen gas for 5 hours at a pulsating cycle of 170-180℃ and a vacuum of -0.095MPa or -0.08MPa to obtain dried lithium chloride.

8. The method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride as described in claim 7, characterized in that, The process of dissolving the dried lithium chloride a second time to obtain a high-purity dissolved solution includes: Dried lithium chloride was mixed with deionized water at a ratio of 1:0.5 and stirred at 45℃-50℃ for 20 min. The mixture was then filtered through a 0.5μm filter membrane to obtain undissolved lithium chloride crystals and a solution containing impurities. The impurity-containing solution is passed through a cation exchange column to obtain a purified solution. Undissolved lithium chloride crystals were mixed with the purified solution and stirred at 45-50℃ for 30 minutes until completely dissolved. The solution was then filtered through a 0.2μm filter to obtain a high-purity lithium chloride solution.

9. The method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride as described in claim 8, characterized in that, The process of anhydrousizing the high-purity dissolved solution to obtain high-purity anhydrous lithium chloride includes: High-purity anhydrous lithium chloride is obtained by evaporating the solution after dissolving it in high purity at 150-160℃ and -0.05MPa to a solid state.

10. A high-purity anhydrous lithium chloride, characterized in that, The high-purity anhydrous lithium chloride is produced by the method for producing high-purity anhydrous lithium chloride from crude lithium chloride containing potassium chloride as described in any one of claims 1 to 9.

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