A method for reducing potassium in a battery single water lithium hydroxide one evaporation high potassium mother liquor

Abstract

The application discloses a method for producing battery single-water lithium hydroxide and reducing potassium in one evaporation high-potassium mother liquor, and relates to the technical field of lithium salt production, and comprises the following steps: tangentially introducing one evaporation mother liquor with potassium ions greater than or equal to 20 g / L into a conical bottom stirring tank, and keeping the temperature at 75 DEG C to 95 DEG C; gradient cooling is performed, calcium sulfate crystals are first precipitated, and then potassium mirabilite is precipitated by further cooling; after standing and sedimentation, clear liquid and crystal slurry are separated, and low-potassium clear liquid is returned to the system for reuse. The potassium removal rate is about 41%, the calcium removal rate is greater than or equal to 93%, the lithium recovery rate is greater than or equal to 95%, the finished product impurities can be significantly reduced, and the equipment fouling can be slowed down, the process flow is short, and the method is suitable for industrialized continuous production.

Description

Technical Field

[0001] This invention relates to the field of lithium salt production technology, and in particular to a method for reducing potassium in a high-potassium mother liquor produced from lithium hydroxide monohydrate for batteries. Background Technology

[0002] In the freeze-crystallization process for preparing battery-grade lithium hydroxide monohydrate (LiOH·H2O) from spodumene, a large amount of recycled mother liquor is generated during the first evaporation crystallization (single evaporation). The main components of this recycled mother liquor are sodium sulfate and lithium sulfate, with potassium ions continuously accumulating. When this high-potassium mother liquor is returned to the main system, it easily leads to excessive potassium impurities in the finished lithium hydroxide product, affecting the yield of battery-grade products. Traditional potassium removal methods often involve freezing sodium precipitation followed by waste discharge or lithium precipitation to prepare mixed salts, which suffer from problems such as significant lithium loss, long process time, high cost, and inefficient mother liquor recycling. Therefore, there is an urgent need to develop a single-evaporation mother liquor potassium removal process that is highly efficient in potassium removal, has a high lithium recovery rate, and can be continuously operated industrially. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for reducing potassium in the production of high-potassium mother liquor for battery monohydrate lithium hydroxide by single distillation.

[0004] To solve the above technical problems, the technical solution of the present invention is as follows: A method for reducing potassium in a single-distillation high-potassium mother liquor for producing lithium hydroxide monohydrate for batteries includes the following steps: Step S1: Obtain a single-distilled high-potassium mother liquor with a potassium ion concentration ≥20g / L. Feed the mother liquor tangentially along the wall of a conical bottom stirring tank, control the temperature inside the tank to 75℃-95℃, and stir. Step S2: Start the crystal slurry circulation pump at the bottom of the cone to provide seed crystals, and perform gradient cooling at a rate of 4℃ / h-8℃ / h. First, cool down to 55℃ to precipitate calcium sulfate, and then cool down to 23℃-35℃ to crystallize potassium sulfate. Step S3: Stop stirring and circulating pump, let stand and settle for 20-28 hours, then discharge the clear liquid from the clear liquid outlet at 1 / 3 height from the bottom of the tank, and perform solid-liquid separation on the crystal slurry discharged from the cone bottom; Step S4: Return the separated clear liquid to the mixing mother liquor preparation tank of the sodium sulfate section for reuse.

[0005] As a preferred embodiment of the method for reducing potassium in the single-distillation high-potassium mother liquor for producing lithium hydroxide monohydrate of batteries according to the present invention, the tank is a cylindrical conical bottom tank, the mother liquor is fed tangentially, and the clear liquid outlet is set perpendicular to the tank wall.

[0006] As a preferred embodiment of the method for reducing potassium in the single-distillation high-potassium mother liquor for producing lithium hydroxide monohydrate of batteries according to the present invention, in step S1, the feeding is stopped when the mother liquor level reaches the high alarm value of the tank, and the stirring speed is 3-6 r / min.

[0007] As a preferred embodiment of the method for reducing potassium in the single-distillation high-potassium mother liquor for producing lithium hydroxide monohydrate of batteries according to the present invention, wherein: in step S1, the stirring speed is 5 r / min.

[0008] As a preferred embodiment of the method for reducing potassium in the single-distillation high-potassium mother liquor for producing lithium hydroxide monohydrate of batteries according to the present invention, in step S2, the cooling rate is 5℃ / h, the final temperature is reduced to 28℃, and the mixture is stirred at this temperature for 1h.

[0009] As a preferred embodiment of the method for reducing potassium in the single-distillation high-potassium mother liquor for producing lithium hydroxide monohydrate of batteries according to the present invention, in step S3, the settling time is 24 hours, and after the settling is completed, the potassium ion concentration in the clear liquid is sampled and tested. When the potassium ion concentration is ≤13g / L, the clear liquid is discharged.

[0010] As a preferred embodiment of the method for reducing potassium in the single-distillation high-potassium mother liquor for producing battery monohydrate lithium hydroxide according to the present invention, in step S3, the solid-liquid separation is carried out by a filter press; the filter cake obtained by filter press is discharged or used as potassium resource recovery, and the filtrate is returned to the next cycle and combined with the single-distillation high-potassium mother liquor for treatment.

[0011] The beneficial effects of this invention are: (1) This invention employs a gradient cooling crystallization design: during the first-stage cooling to 55°C, the solubility of calcium sulfate decreases sharply within the cooling range of 75-95°C to 55°C, causing calcium ions to preferentially precipitate as calcium sulfate dihydrate. These fine calcium sulfate crystals act as "bridging seeds" for subsequent crystallization. During the second-stage cooling to 23-35°C, potassium ions combine with sodium and sulfate ions to form potassium sulfate, which precipitates in large quantities on and around the calcium sulfate seed crystals, forming composite salt particles. After settling, the potassium ion concentration in the clarified liquid can be stably reduced to below 13 g / L, with a potassium removal rate of approximately 41%; the calcium ion concentration decreases from 0.30 g / L to below 0.02 g / L, with a calcium removal rate ≥93%. The finished lithium hydroxide monohydrate contains ≤0.003% potassium impurities, fully meeting battery-grade standards (typically requiring ≤0.005% potassium).

[0012] (2) The selective sedimentation principle of this invention is only for the removal of calcium sulfate and potassium sulfate. Lithium ions remain in a dissolved state throughout the entire cooling process from 75-95℃ to 23-35℃ and hardly participate in any crystallization precipitation. The lithium ion concentration in the clear liquid only slightly decreases from 51.84 g / L before treatment to 50.84 g / L, and the lithium recovery rate is ≥95%, which is much higher than the traditional freezing sodium precipitation waste discharge or lithium precipitation mixed salt process (usually the lithium recovery rate is only 70-85%), and greatly reduces lithium loss in production.

[0013] (3) In traditional processes, after the high-calcium mother liquor enters the evaporator, calcium ions easily form calcium sulfate scale on the surface of the heat exchange tubes, leading to decreased heat transfer efficiency and increased energy consumption. Typically, the evaporator needs to be shut down for cleaning every 3-5 days. This invention removes calcium ions in the form of calcium sulfate dihydrate at the front end, reducing the calcium content in the clear liquid to below 0.02 g / L, significantly reducing the scaling tendency of the evaporator and pipelines. Practical application verification shows that after 15 days of continuous operation, there is no significant scaling on the evaporator heat exchange tubes, and the equipment operation and cleaning cycle can be extended by more than 3 times. Detailed Implementation

[0014] To make the content of this invention easier to understand, the invention will be further described in detail below based on specific embodiments.

[0015] Example 1: This example provides a method for reducing potassium content in a single-distillation high-potassium mother liquor for producing lithium hydroxide monohydrate for batteries. The method specifically includes the following steps: Step S1: Mother liquor collection and temperature control.

[0016] The high-potassium mother liquor from the first evaporation crystallization process in the production system for battery-grade lithium hydroxide monohydrate from spodumene, maintained at 75-95℃, was analyzed and its composition is as follows: Li + 51.84 g / L; K + 21.00 g / L; Ca 2+ : 0.30 g / L.

[0017] The mother liquor is fed tangentially along the wall of a cylindrical-conical-bottomed stirred tank, with the inlet positioned at 3 / 5 of the tank's height. Feeding is stopped when the liquid level reaches the tank's high mark. The agitator is then started, with the stirring speed controlled at 5 r / min. The temperature of the mother liquor inside the tank is maintained at 75-95℃ to bring the sodium sulfate concentration close to saturation. A clear liquid outlet is located at 1 / 3 of the tank's height from the bottom for subsequent solid-liquid separation.

[0018] Step S2: Gradient cooling crystallization.

[0019] Start the cone-bottom crystal slurry circulation pump to circulate the bottom crystal slurry within the tank, providing seed crystals to promote the nucleation and growth of potassium mirabilite. Employ gradient cooling at a rate controlled at 5℃ / h. First-stage cooling: the temperature is reduced from 75-95℃ to 55℃. During this process, calcium ions are released as seed crystals encapsulated in the form of calcium sulfate dihydrate (CaSO4·2H2O). Secondary cooling: Continue cooling to 28℃ and stir at this temperature for 1 hour. Potassium ions combine with sodium and sulfate ions to form potassium mirabilite (K3Na(SO4)2) which is precipitated in large quantities.

[0020] Step S3: Settling and separation.

[0021] Turn off the agitator and circulation pump, and allow the mixture to settle for 24 hours. Under the bridging effect of calcium seed crystals, the composite salt particles settle rapidly. After settling, samples were taken to measure the potassium ion concentration in the supernatant, and the K0.05 was determined. + The concentration is 12.37 g / L (≤13 g / L). The clear liquid is discharged from the outlet at 1 / 3 of the tank height from the bottom for later use. A mixed crystal slurry containing potassium sulfate and calcium sulfate is discharged from the bottom of the cone and sent to a filter press for solid-liquid separation. The filter cake is discharged or used for potassium resource recovery; the filtrate is recovered into the system and combined with the high-potassium mother liquor for the next cycle.

[0022] Step S4: Reuse of the clarified liquid.

[0023] The composition of the treated clarified liquid is as follows: Li+: 50.84 g / L; K+: 12.37 g / L; Ca2+: 0.02 g / L. The calculated values ​​are: Potassium removal rate = (21.00 - 12.37) / 21.00×100% = 41.10%; Calcium removal rate = (0.30 - 0.02) / 0.30×100% = 93.3%; Lithium recovery rate = 50.84 / 51.84×100%≈98.1% (>95%).

[0024] The resulting clear liquid is returned to the mixing mother liquor preparation tank in the sodium sulfate section, where it is mixed with other mother liquors in the system and then recycled back into the lithium hydroxide monohydrate production system.

[0025] Therefore, the technical solution of this application uses a combination process of "collection-gradient cooling crystallization-sedimentation separation-system reuse" to achieve efficient removal of potassium and calcium by taking advantage of solubility differences and synergistic sedimentation principles, while maximizing the retention of lithium, reducing losses, and ensuring stable product quality.

[0026] In addition to the above embodiments, the present invention may have other implementation methods; all technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for reducing potassium in a single-distillation high-potassium mother liquor for producing lithium hydroxide monohydrate for batteries, characterized in that: Includes the following steps: Step S1: Obtain a single-distilled high-potassium mother liquor with a potassium ion concentration ≥20g / L. Feed the mother liquor tangentially along the wall of a conical bottom stirring tank, control the temperature inside the tank to 75℃-95℃, and stir. Step S2: Start the crystal slurry circulation pump at the bottom of the cone to provide seed crystals, and perform gradient cooling at a rate of 4℃ / h-8℃ / h. First, cool down to 55℃ to precipitate calcium sulfate, and then cool down to 23℃-35℃ to crystallize potassium sulfate. Step S3: Stop stirring and circulating pump, let stand and settle for 20-28 hours, then discharge the clear liquid from the clear liquid outlet at 1 / 3 height from the bottom of the tank, and perform solid-liquid separation on the crystal slurry discharged from the cone bottom; Step S4: Return the separated clear liquid to the mixing mother liquor preparation tank of the sodium sulfate section for reuse.

2. The method for reducing potassium in the single-distillation high-potassium mother liquor for producing battery-grade lithium hydroxide monohydrate according to claim 1, characterized in that: The tank is a cylindrical conical bottom tank, the mother liquor is fed tangentially, and the clear liquid outlet is set perpendicular to the tank wall.

3. The method for reducing potassium in the single-distillation high-potassium mother liquor for producing battery-grade lithium hydroxide monohydrate according to claim 1, characterized in that: In step S1, feeding is stopped when the mother liquor level reaches the high alarm value of the tank, and the stirring speed is 3-6 r / min.

4. The method for reducing potassium in the single-distillation high-potassium mother liquor for producing battery-grade lithium hydroxide monohydrate according to claim 3, characterized in that: In step S1, the stirring speed is 5 r / min.

5. The method for reducing potassium in the single-distillation high-potassium mother liquor for producing battery-grade lithium hydroxide monohydrate according to claim 1, characterized in that: In step S2, the cooling rate is 5℃ / h, the final temperature is reduced to 28℃, and the mixture is stirred at this temperature for 1h.

6. The method for reducing potassium in the single-distillation high-potassium mother liquor for producing battery-grade lithium hydroxide monohydrate according to claim 1, characterized in that: In step S3, the settling time is 24 hours, and after the settling is completed, the potassium ion concentration in the clear liquid is measured. When the potassium ion concentration is ≤13g / L, the clear liquid is discharged.

7. The method for reducing potassium in the single-distillation high-potassium mother liquor for producing battery-grade lithium hydroxide monohydrate according to claim 1, characterized in that: In step S3, the solid-liquid separation is carried out using a filter press; the filter cake obtained by filter press is discharged or recovered as potassium resource, and the filtrate is returned to the next cycle and combined with the first distillation high potassium mother liquor for treatment.