Continuous crystallization separation method for improving recovery rate of sodium chloride and lithium chloride through mother liquor circulation

Abstract

The invention discloses a continuous crystallization separation method for improving the recovery rate of sodium chloride and lithium chloride through mother liquor circulation. The method comprises the following steps: continuously feeding a raw material solution into a mixing tank to be mixed with a circulating solution, continuously feeding the mixed solution into a lithium chloride reaction crystallization device, feeding crystallized turbid liquid into a continuous centrifugal device from a crystallizer, carrying out solid-liquid separation, feeding a solid lithium carbonate product into a subsequent drying device, and carrying out vacuum drying at 30-40 DEG C for 5-6 hours, the method comprises the following steps: centrifugally separating a lithium-rich solution, performing evaporative crystallization and concentration on the centrifugally separated mother solution, feeding crystallized turbid liquid into a continuous centrifugal device from a crystallizer, performing solid-liquid separation, feeding a solid sodium chloride product into a subsequent drying device, performing vacuum drying for 5-6 hours at 30-40 DEG C, refluxing the concentrated lithium-rich solution into a mixing tank, and performing continuous recovery through mother solution circulation.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical separation, and particularly relates to a continuous crystallization separation method for improving the recovery rates of sodium chloride and lithium chloride through mother liquor circulation. Background Art

[0002] In today's world, environmental protection and sustainable development have become highly regarded issues. Against this backdrop, the booming new energy vehicle industry has spurred the explosive growth of the lithium-ion battery market demand. Lithium-ion batteries have also stood out with their excellent performance, specifically manifested as high energy density, stable discharge platform, weak self-discharge effect, excellent charge and discharge efficiency, and long cycle service life, etc., making them widely used in many important fields such as power batteries, electrochemical energy storage systems, and portable electronic devices. However, with the annual increase in the production and market demand of lithium-ion batteries, the subsequent problem of waste battery disposal has become increasingly severe.

[0003] In recent years, the number of scrapped lithium-ion batteries has shown a sharp upward trend, and the disposal situation of waste lithium batteries has attracted particular attention. If lithium-ion batteries are not properly disposed of, it will bring serious environmental pollution problems. The harmful substances contained in the positive and negative electrode materials and electrolytes of the batteries will not only damage the ecological environment but also pose potential risks to human health. At the same time, the inability to recycle a large amount of precious metals also causes great waste. However, lithium-ion batteries have the characteristic of being completely recyclable. Structurally, it mainly consists of metal components and plastic components. These components can be recycled and reused after being processed through professional recycling processes to manufacture various new products, realizing the secondary development and efficient utilization of resources. Currently, in the field of waste lithium battery recycling, it mainly focuses on the recycling and treatment of the positive electrode materials, and the mainstream recycling methods are solid-phase method and acid leaching-precipitation method, etc. The solid-phase method has significant advantages such as simple process, easy control of process conditions, and streamlined required equipment. However, it cannot be ignored that the regenerated lithium battery positive electrode material by this method has certain limitations in terms of electrochemical performance, still has a gap with the market expectation, and is difficult to meet the quality requirements of the market demand. During the process of recovering lithium elements by the acid leaching-precipitation method, a mixed solution of lithium chloride and sodium chloride will be produced. How to separate sodium chloride and lithium chloride from the mixed solution has become one of the key steps in the recovery of metal elements in waste lithium batteries. Summary of the Invention

[0004] In order to better separate the two salts in the mixed solution of sodium chloride and lithium chloride, the present invention proposes a method of separation by reaction crystallization to separate lithium element in the form of lithium carbonate, then evaporate and crystallize the remaining mother liquor for concentration to recover sodium chloride, and then reflux the concentrated mother liquor to the initial solution for continuous reaction crystallization separation. By this method, on the one hand, the recovery amount of lithium chloride can be increased, and on the other hand, a large amount of high-purity sodium chloride crystals can be recovered. In theory, the complete element recovery of lithium chloride and sodium chloride can be achieved simultaneously. Compared with other reported separation processes for the mixed solution of lithium chloride and sodium chloride, the separation method of the present invention can effectively separate and purify industrial-grade sodium chloride and lithium carbonate, and the products of sodium chloride and lithium carbonate have high purity, large particle size and uniform particle size distribution, and the process is stable.

[0005] The technical solution of the present invention is as follows:

[0006] A continuous crystallization separation method for improving the recovery rates of sodium chloride and lithium chloride by circulating mother liquor, comprising the following steps:

[0007] Step 1: The raw material liquid continuously enters the mixing tank and is mixed with the circulating solution;

[0008] Step 2: The mixed solution continuously enters the lithium chloride reaction crystallization device for crystallization;

[0009] Step 3: The crystallized suspension enters the continuous centrifugation device for solid-liquid separation. The solid lithium carbonate enters the subsequent drying device and is vacuum dried at 30-40 °C for 5-6 hours;

[0010] Step 4: The mother liquor after centrifugal separation enters the evaporation crystallization for concentration;

[0011] Step 5: The crystallized suspension enters the continuous centrifugation device from the crystallizer for solid-liquid separation. The solid sodium chloride enters the subsequent drying device and is vacuum dried at 30-40 °C for 5-6 hours;

[0012] Step 6: The concentrated lithium-rich solution is refluxed into the mixing tank for continuous recovery through the circulation of the mother liquor.

[0013] Further, in the raw material liquid in Step 1, the sodium chloride content is about 5-8%, and the lithium chloride content is about 40-50%.

[0014] Further, the average residence time of the solution in the lithium chloride reaction crystallization device in Step 2 is 4-6 hours.

[0015] Further, the vacuum degree of the drying conditions in Steps 3 and 5 is 0.07-0.08 MPa.

[0016] Further, the evaporation crystallization concentration temperature in Step 4 is 70 °C.

[0017] Further, the ratio of the raw material liquid to the refluxed lithium-rich solution is 5 - 8.

[0018] Based on the NaCl-LiCl-H2O ternary phase diagram and combined with the specific composition of the mixed solution of lithium chloride and sodium chloride, the present invention studies the optimal crystallization principle and successfully applies it to the separation and purification of the mixed solution of lithium chloride and sodium chloride, obtaining industrial-grade sodium chloride and lithium carbonate. This is the technical innovation of the present invention. The present invention evaporates and crystallizes the raw material liquid, centrifugally separates part of the sodium chloride, then reacts and crystallizes the solution to separate the lithium carbonate product. After evaporating and crystallizing the sodium chloride product, through the mother liquor circulation, the reaction crystallization separation of lithium chloride and the evaporation separation of sodium chloride are realized by evaporating the solvent. Therefore, the separation process of the present invention can not only obtain industrial-grade sodium chloride and lithium carbonate products, but also maximize the treatment of the mixed solution. After treatment, the remaining solution can be recycled and recovered, and the mixed solution can be maximally treated to reduce resource waste.

[0019] Using the continuous crystallization separation method of the mixed solution of sodium chloride and lithium chloride described in the present invention, industrial-grade lithium carbonate products can be prepared, with a purity of over 98.5%, and the primary recovery rate of lithium chloride can reach over 85%; at the same time, the separation of sodium chloride in the solution can be realized, with a purity of over 99.0%; at the same time, the process is a continuous operation, with good process stability, stable product quality and no batch-to-batch differences. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the process flow chart of the present invention;

[0021] Figure 2 is the recovered lithium carbonate crystal diagram of Example 1;

[0022] Figure 3 is the recovered sodium chloride crystal diagram of Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] As Figure 1 shown, the continuous crystallization separation method for improving the recovery rates of sodium chloride and lithium chloride by mother liquor circulation of the present invention includes the following steps:

[0024] Step 1, the raw material liquid continuously enters the mixing tank and is mixed with the circulating solution;

[0025] Step 2, the mixed solution continuously enters the lithium chloride reaction crystallization device for crystallization;

[0026] Step 3, the crystallized suspension enters the continuous centrifugation device for solid-liquid separation. The solid lithium carbonate enters the subsequent drying device and is vacuum dried at 30 - 40 degrees for 5 - 6 hours;

[0027] Step 4, the mother liquor after centrifugal separation enters the evaporation crystallization for concentration;

[0028] Step 5: The crystallized suspension enters the continuous centrifugation device from the crystallizer for solid-liquid separation. The solid sodium chloride enters the subsequent drying device and is vacuum-dried at 30 - 40°C for 5 - 6 hours.

[0029] Step 6: The concentrated lithium-rich solution flows back into the mixing tank and is continuously recovered through the mother liquor circulation.

[0030] Example 1

[0031] The raw material solution contains approximately 8% sodium chloride and approximately 40% lithium chloride. The raw material solution continuously enters the mixing tank and is mixed with the recycled lithium-rich solution. The mixed solution continuously enters the lithium carbonate reaction crystallization device. The suspension after 5 hours of reaction crystallization enters the continuous centrifugation device from the crystallizer for solid-liquid separation. The separated solid lithium carbonate product enters the subsequent drying device and is vacuum-dried at a vacuum degree of 0.07 MPa and a temperature of 30°C for 6 hours. The purity of the obtained lithium carbonate product is 98.5%, and the primary recovery rate is 85.7%. The mother liquor after the above centrifugation separation continuously enters the evaporation crystallization concentration device and is subjected to evaporation crystallization at 70°C. The suspension after evaporation crystallization enters the continuous centrifugation device from the crystallizer for solid-liquid separation. The separated solid sodium chloride product enters the subsequent drying device and is vacuum-dried at a vacuum degree of 0.07 MPa and a temperature of 30°C for 5 hours. The purity of the obtained sodium chloride product is 99.2%, and the primary recovery rate is 55.2%. The evaporated solution flows back into the mixing tank. The reflux ratio of the raw material solution to the recycled lithium-rich solution is 5, realizing the concentration and reflux of lithium chloride in the solution.

[0032] The recovered lithium carbonate crystals and sodium chloride crystals are as Figure 2 shown in the figure.

[0033] Example 2

[0034] The sodium chloride content in the raw material liquid is about 7%, and the lithium chloride content is about 43%. The raw material liquid continuously enters the mixing tank to be mixed with the circulating lithium-rich solution. The mixed solution continuously enters the lithium carbonate reaction crystallization device. The suspension after 4 hours of reaction crystallization enters the continuous centrifugation device from the crystallizer for solid-liquid separation. The separated solid lithium carbonate product enters the subsequent drying device and is vacuum-dried at a vacuum degree of 0.08 MPa and a temperature of 30°C for 6 hours. The purity of the obtained lithium carbonate product is 98.7%, and the primary recovery rate is 85.5%. The mother liquor after the above centrifugation separation continuously enters the evaporation crystallization concentration device and undergoes evaporation crystallization at 70°C. The suspension after evaporation crystallization enters the continuous centrifugation device from the crystallizer for solid-liquid separation. The separated solid sodium chloride product enters the subsequent drying device and is vacuum-dried at a vacuum degree of 0.08 MPa and a temperature of 30°C for 5 hours. The purity of the obtained sodium chloride product is 99.4%, and the primary recovery rate is 57.4%. The evaporated solution flows back into the mixing tank, and the reflux ratio of the raw material liquid to the reflux is 6, realizing the concentration and reflux of lithium chloride in the solution.

[0035] Example 3

[0036] The sodium chloride content in the raw material liquid is about 6%, and the lithium chloride content is about 47%. The raw material liquid continuously enters the mixing tank to be mixed with the circulating lithium-rich solution. The mixed solution continuously enters the lithium carbonate reaction crystallization device. The suspension after 5.5 hours of reaction crystallization enters the continuous centrifugation device from the crystallizer for solid-liquid separation. The separated solid lithium carbonate product enters the subsequent drying device and is vacuum-dried at a vacuum degree of 0.08 MPa and a temperature of 30°C for 5 hours. The purity of the obtained lithium carbonate product is 98.9%, and the primary recovery rate is 85.3%. The mother liquor after the above centrifugation separation continuously enters the evaporation crystallization concentration device and undergoes evaporation crystallization at 70°C. The suspension after evaporation crystallization enters the continuous centrifugation device from the crystallizer for solid-liquid separation. The separated solid sodium chloride product enters the subsequent drying device and is vacuum-dried at a vacuum degree of 0.08 MPa and a temperature of 30°C for 6 hours. The purity of the obtained sodium chloride product is 99.5%, and the primary recovery rate is 59.7%. The evaporated solution flows back into the mixing tank, and the reflux ratio of the raw material liquid to the reflux is 7, realizing the concentration and reflux of lithium chloride in the solution.

[0037] Example 4

[0038] The content of sodium chloride in the raw material liquid is about 5%, and the content of lithium chloride is about 50%. The raw material liquid continuously enters the mixing tank to be mixed with the circulating lithium-rich solution. The mixed solution continuously enters the lithium carbonate reaction crystallization device. The suspension after 6 hours of reaction crystallization enters the continuous centrifugation device from the crystallizer for solid-liquid separation. The separated solid lithium carbonate product enters the subsequent drying device and is vacuum dried at a vacuum degree of 0.08 MPa and a temperature of 30°C for 5 hours. The purity of the obtained lithium carbonate product is 99.1%, and the primary recovery rate is 85.1%. The mother liquor after the above centrifugal separation continuously enters the evaporation crystallization concentration device and undergoes evaporation crystallization at 70°C. The suspension after evaporation crystallization enters the continuous centrifugation device from the crystallizer for solid-liquid separation. The separated solid sodium chloride product enters the subsequent drying device and is vacuum dried at a vacuum degree of 0.08 MPa and a temperature of 30°C for 5 hours. The purity of the obtained sodium chloride product is 99.6%, and the primary recovery rate is 61.4%. The solution after evaporation flows back into the mixing tank, and the reflux ratio of the raw material liquid to the reflux is 8, realizing the concentration and reflux of lithium chloride in the solution.

[0039] The crystallization separation method of the lithium chloride and sodium chloride mixed solution disclosed and proposed in the present invention can be realized by those skilled in the art by referring to the content herein and appropriately changing links such as raw materials and process parameters. The method and product of the present invention have been described through preferred embodiments. Those skilled in the art can obviously make changes or appropriate modifications and combinations to the methods and products described herein without departing from the content, spirit and scope of the present invention to implement the technology of the present invention. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all regarded as included in the spirit, scope and content of the present invention.

Claims

1. A continuous crystallization separation method for improving the recovery rates of sodium chloride and lithium chloride by circulating mother liquor, characterized in that It includes the following steps: Step 1: The raw material liquid continuously enters the mixing tank and is mixed with the circulating solution; Step 2: The mixed solution continuously enters the lithium chloride reaction crystallization device for crystallization; Step 3: The crystallized suspension enters the continuous centrifugal device for solid-liquid separation. The solid lithium carbonate enters the subsequent drying device and is vacuum dried at 30 - 40 °C for 5 - 6 hours; Step 4: The mother liquor after centrifugal separation enters the evaporation crystallization for concentration; Step 5: The crystallized suspension enters the continuous centrifugal device from the crystallizer for solid-liquid separation. The solid sodium chloride enters the subsequent drying device and is vacuum dried at 30 - 40 °C for 5 - 6 hours; Step 6: The concentrated lithium-rich solution is refluxed into the mixing tank and continuously recovered through the mother liquor circulation.

2. The continuous crystallization separation method for improving the recovery rates of sodium chloride and lithium chloride by mother liquor circulation as described in claim 1, characterized in that: In step 1, the sodium chloride content in the raw material liquid is about 5 - 8%, and the lithium chloride content is about 40 - 50%.

3. The continuous crystallization separation method for improving the recovery rates of sodium chloride and lithium chloride by mother liquor circulation as described in claim 1, characterized in that: In step 2, the average residence time of the solution in the lithium chloride reaction crystallization device is 4 - 6 hours.

4. The continuous crystallization separation method for improving the recovery rates of sodium chloride and lithium chloride by mother liquor circulation as described in claim 1, characterized in that: The vacuum degree of the drying conditions in steps 3 and 5 is 0.07 - 0.08 MPa.

5. The continuous crystallization separation method for improving the recovery rates of sodium chloride and lithium chloride by mother liquor circulation as described in claim 1, characterized in that: In step 4, the evaporation crystallization concentration temperature is 70 °C.

6. The continuous crystallization separation method for improving the recovery rates of sodium chloride and lithium chloride by mother liquor circulation as described in claim 1, characterized in that: The ratio of the raw material liquid to the refluxed lithium-rich solution is 5 - 8.

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