Method and system for recovering mother liquor in precursor synthesis process

Abstract

The invention relates to the technical field of wastewater treatment, and provides a mother liquor recovery method and system in a precursor synthesis process. The mother liquor recovery method in the precursor synthesis process comprises the following steps: carrying out pressure filtration on a reaction solution obtained by a coprecipitation method to obtain a pressure filtration mother liquor and a ternary positive electrode material precursor; carrying out first ultrafiltration on the filter pressing mother liquor to obtain a concentrated solution and filtered produced water, and recovering the concentrated solution to a reaction kettle of a coprecipitation method; performing first reverse osmosis on the filtered produced water to obtain concentrated water and reverse osmosis produced water; carrying out deamination and crystallization on the concentrated water to obtain sulfate; the reverse osmosis produced water is used for preparing a reaction material of a coprecipitation method. According to the method, the yield of the ternary precursor in the filter-pressing mother liquor can be increased, the amount of wastewater subsequently generated by the filter-pressing mother liquor is small, and the deamination efficiency is high.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and particularly to a method and system for recovering mother liquor in the process of precursor synthesis, and more particularly to a method and system for recovering mother liquor in the process of synthesizing ternary cathode material precursors. Background Art

[0002] Ternary cathode materials refer to the cathode materials of lithium-ion batteries composed of three elements: nickel (Ni), cobalt (Co), and manganese (Mn), usually abbreviated as NCM. Lithium-ion batteries containing ternary cathode materials have the characteristics of high energy density, high power output, good low-temperature resistance, low internal resistance, and excellent cycle stability, and occupy an important position in the new energy market, being widely used in the fields of AGV trucks, drones, and new energy vehicles. However, with the improvement of the energy density of new iron-lithium batteries and the cost advantage of iron-lithium batteries themselves, the market of lithium-ion batteries containing ternary cathode materials has gradually been occupied by iron-lithium batteries. As the main material of lithium-ion batteries, ternary cathode materials face a very difficult task of cost reduction.

[0003] Ternary cathode material precursors are the key raw materials for preparing ternary cathode materials, with a cost accounting for more than 50% of the total cost of ternary cathode materials, which is the key link for cost reduction of ternary cathode materials. The preparation process of ternary cathode material precursors is to add salt solutions of nickel, cobalt, and manganese (such as sulfates) to a precipitant (such as sodium hydroxide) and a complexing reagent (such as ammonia water), and generate a slurry of reaction solution through coprecipitation. The slurry of the reaction solution is filtered, washed, and dried under pressure to obtain the required ternary cathode material precursors. In the pressure filtration solid-liquid separation process, small-particle-size ternary cathode material precursors (the proportion is generally 1.0 - 2.0% of the total weight of ternary cathode material precursors) pass through the filter cloth and enter the mother liquor, and enter the mother liquor treatment system with the mother liquor, and cannot be used as normal products. Therefore, a more feasible process needs to be designed to recycle the small-particle-size materials passing through the filter online into the system, thereby improving the yield of precursors and avoiding the problem of directly mixing small-particle-size materials into the finished product and affecting the product quality. At the same time, for every ton of ternary cathode material precursors produced, 8 - 12 tons of mother liquor with a concentration of 10 - 12 wt% will be generated. These mother liquors need to be stripped of ammonia and evaporated and crystallized, which consumes a large amount of steam, seriously affecting the treatment cost of the mother liquor. It is necessary to design and optimize the mother liquor treatment to reduce the mother liquor treatment cost, improve the yield of ternary cathode material precursors in the mother liquor, and thus reduce the environmental protection treatment cost of the precursors. Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems in the related technologies to some extent. For this reason, an object of the present invention is to provide a method for recovering mother liquor in the process of precursor synthesis, which can improve the yield of ternary precursors in the pressure filtration mother liquor, and the waste water generated by the subsequent pressure filtration mother liquor is less, and the ammonia stripping efficiency is high.

[0005] To this end, a method for recycling mother liquor in the precursor synthesis process is provided in the first aspect of the present invention, including: pressure filtering the reaction liquid obtained by the coprecipitation method to obtain a pressure-filtered mother liquor and a ternary cathode material precursor; performing a first ultrafiltration on the pressure-filtered mother liquor to obtain a concentrated solution and filtered product water, and recycling the concentrated solution to the reaction kettle of the coprecipitation method; performing a first reverse osmosis on the filtered product water to obtain concentrated water and reverse osmosis product water; deammonifying and crystallizing the concentrated water to obtain sulfates; and using the reverse osmosis product water to prepare the reaction materials for the coprecipitation method.

[0006] According to the method for recycling mother liquor in the precursor synthesis process of the embodiments of the present invention, performing a first ultrafiltration on the pressure-filtered mother liquor realizes the solid-liquid separation of the pressure-filtered mother liquor. The concentrated solution containing the solid-phase ternary cathode material precursor is directly recycled to the reaction kettle for producing the ternary cathode material precursor. Compared with the conventional treatment process, the material loss of the pressure-filtered mother liquor is reduced, and the yield of the ternary cathode material precursor is improved; the main component of the filtered product water generated by the first ultrafiltration is sulfates (such as sodium sulfate and ammonium sulfate, and after deammonification, the sulfate is sodium sulfate). After the first ultrafiltration, in combination with the first reverse osmosis, the first reverse osmosis is used to concentrate the filtered product water, which can increase the concentration of sulfates therein, reduce the amount of concentrated water generated by the first reverse osmosis, reduce the scale of subsequent deammonification, and improve the deammonification efficiency. In summary, the method for recycling mother liquor in the precursor synthesis process proposed by the present invention has a high yield of the ternary cathode material precursor, less waste water generated from the subsequent pressure-filtered mother liquor, and high deammonification efficiency.

[0007] In some embodiments of the present invention, the ultrafiltration membrane for the first ultrafiltration includes one or more of a polytetrafluoroethylene membrane and a ceramic membrane. Optionally, the ultrafiltration membrane for the first ultrafiltration includes a polytetrafluoroethylene membrane.

[0008] In some embodiments of the present invention, the cut-off pore size of the ultrafiltration membrane for the first ultrafiltration is 0.05 μm to 0.2 μm.

[0009] In some embodiments of the present invention, the working pressure of the first ultrafiltration is 4 bar - 8 bar.

[0010] In some embodiments of the present invention, the ultrafiltration element for the first ultrafiltration is a columnar ultrafiltration membrane module. A hollow ultrafiltration membrane is provided inside the columnar ultrafiltration membrane module, and the hollow ultrafiltration membrane is fixed in the columnar ultrafiltration membrane module in a manner that can swing at the bottom; preferably, the columnar ultrafiltration membrane module has a differential packaging structure with the upper part integrally packaged and the lower part independently packaged with single filaments.

[0011] In some embodiments of the present invention, the solid content of the pressure-filtered mother liquor is 0.5% to 2.0%.

[0012] In some embodiments of the present invention, the solid content of the concentrated solution is 3% to 8%.

[0013] In some embodiments of the present invention, in the filtered product water, the total mass ratio of ammonium sulfate and sodium sulfate is 5% to 10%.

[0014] In some embodiments of the present invention, recycling the concentrated solution to the reaction kettle of the co-precipitation method includes: adjusting the particle size of the ternary cathode material precursor in the concentrated solution and recycling it to the reaction kettle of the co-precipitation method.

[0015] In some embodiments of the present invention, the average particle size of the ternary cathode material precursor in the concentrated solution is adjusted from 0.5 μm to 3 μm to 3 μm to 5 μm.

[0016] In some embodiments of the present invention, the rejection rate of the reverse osmosis membrane of the first reverse osmosis is 80% to 90%.

[0017] In some embodiments of the present invention, the operating pressure of the first reverse osmosis is 60 bar to 80 bar.

[0018] In some embodiments of the present invention, in the concentrated water, the total mass ratio of ammonium sulfate and sodium sulfate is 15% to 20%.

[0019] In some embodiments of the present invention, the reverse osmosis membrane of the first reverse osmosis includes one or more of polytetrafluoroethylene membranes and ceramic membranes.

[0020] In some embodiments of the present invention, the step of pressure filtering the reaction liquid obtained by the co-precipitation method to obtain a pressure-filtered mother liquor and a ternary cathode material precursor includes:

[0021] Pressure filtering the reaction liquid obtained by the co-precipitation method to obtain a pressure-filtered mother liquor and solids;

[0022] Washing, drying, batch mixing, sieving to remove iron, and packaging the solids to obtain a ternary cathode material precursor;

[0023] Performing a second ultrafiltration on the washing liquid obtained by the washing to obtain impurities and ultrafiltration product water;

[0024] Performing a second reverse osmosis on the ultrafiltration product water, and the obtained product water is used to prepare the reaction materials of the co-precipitation method.

[0025] In some embodiments of the present invention, the washing liquid obtained by the washing is directly subjected to second ultrafiltration and second reverse osmosis treatment without cooling, wherein the working temperature ranges of both the second ultrafiltration and the second reverse osmosis are not lower than 50 °C.

[0026] In some embodiments of the present invention, the ultrafiltration membrane used in the second ultrafiltration includes one or more of a ceramic membrane, polyvinylidene chloride, polyvinyl chloride, and a polysulfone / polyethersulfone composite membrane. The operating temperature range of the ultrafiltration membrane is 50°C - 150°C, and the operating pressure is 15 bar - 25 bar.

[0027] In some embodiments of the present invention, the reverse osmosis membrane used in the second reverse osmosis includes one or more of a ceramic membrane, a polyamide composite membrane, and a polyethersulfone composite membrane. The operating temperature range of the reverse osmosis membrane is 50°C - 90°C, and the operating pressure is 15 bar - 25 bar.

[0028] In some embodiments of the present invention, the temperature of the washing liquid obtained from washing is 50°C to 80°C.

[0029] In some embodiments of the present invention, the concentrated water obtained from the second reverse osmosis is subjected to deammoniation treatment.

[0030] In a second aspect of the present invention, the present invention provides a mother liquor recovery system for the precursor synthesis process. The mother liquor recovery system for the ternary cathode material precursor synthesis process is used to implement the method described in the first aspect.

[0031] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, where:

[0033] Figure 1 shows a schematic flow diagram of the mother liquor recovery method for the precursor synthesis process according to an embodiment of the present invention;

[0034] Figure 2 shows a detailed process diagram of the mother liquor recovery method for the precursor synthesis process according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] Embodiments of the present invention will be described in detail below. The embodiments described below are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0036] It should be noted that the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. Further, in the description of the present invention, unless otherwise specified, the meaning of "plural" is two or more.

[0037] In the first aspect of the present invention, a method for recycling the mother liquor in the precursor synthesis process is proposed. Please refer to Figure 1 , and the method includes:

[0038] S1. Filter press the reaction liquid obtained by the coprecipitation method to obtain a filter press mother liquor and a ternary cathode material precursor.

[0039] Specifically, in this step, three raw materials, namely a soluble nickel source (such as nickel sulfate), a soluble cobalt source (cobalt sulfate), and a soluble manganese source (such as manganese sulfate), and a precipitating agent, liquid caustic soda, and a complexing agent, ammonia water, are proportioned in a certain ratio, and coprecipitation reaction is carried out in a reaction kettle to synthesize a ternary cathode material precursor. The separated liquid forms a filter press mother liquor.

[0040] The reaction kettle discharge is separated by a filter press into solid and liquid. The separated solid is washed, dried, batch-mixed, sieved to remove iron, and packaged into a ternary cathode material precursor product.

[0041] It can be understood that the precursor of the ternary cathode active material may have the chemical formula Ni x Co y Mn (1-x-y-a) M a (OH) 2 , where 0.5 ≤ x ≤ 1, 0.05 ≤ y ≤ 0.2, 0 ≤ a ≤ 0.1, and M may include one or more of Al, Ti, Zr, Mo, Cr, W, B, Mg, Ba, Nb, and Sr. As an example, x may be 0.5, 0.7, 0.9, 1, etc.; y may be 0.05, 0.1, 0.15, 0.2, etc.; x may be 0, 0.05, 0.1, etc.

[0042] In some embodiments of the present invention, the pore size of the filter cloth for filter pressing is 1.2 - 3 μm. In the related art, during the synthesis process, small-sized ternary cathode material precursors will pass through the filter cloth and enter the filter press mother liquor, resulting in material loss. If the pore size of the filter cloth is reduced, it will affect the operating pressure of the filter press, increase the filtration time, reduce the production efficiency, and increase the energy consumption. In the prior art, filter cloth with a pore size of 1.2 - 3 μm is usually selected for filter pressing, but this will cause about 1.0 - 2.0% of the total weight of the ternary cathode material precursor to enter the filter press mother liquor. This part of the material will be lost during the water treatment process along with the filter press mother liquor, which will also cause material loss and increase the production cost. The prior art attempts to directly inject the filter press mother liquor obtained by solid-liquid separation by the filter press into the reaction kettle of the coprecipitation method to recover small particle precursor materials, but the water content of the mother liquor is too high, which does not meet the material ratio of the reaction kettle. Direct injection into the reaction kettle will disrupt the reaction process of the precursor and reduce the production quality of the precursor.

[0043] In some embodiments of the present invention, step S1 includes:

[0044] S11. Filter press the reaction liquid obtained by coprecipitation to obtain a filter-pressed mother liquor and solids.

[0045] S12. Wash, dry, batch mix, screen out iron, and package the solids to obtain a ternary cathode material precursor.

[0046] S13. Perform a second ultrafiltration on the washing liquid obtained from the washing to obtain impurities and ultrafiltration product water.

[0047] S14. Perform a second reverse osmosis on the ultrafiltration product water, and the obtained product water is used to prepare the reaction materials for the coprecipitation method.

[0048] Thus, by performing a second ultrafiltration and a second reverse osmosis on the washing liquid, the recycling of the washing liquid can be realized, and the production cost can be further reduced.

[0049] In some embodiments of the present invention, the washing liquid obtained from the washing is directly subjected to a second ultrafiltration and a second reverse osmosis treatment without cooling, wherein the operating temperature ranges of the second ultrafiltration and the second reverse osmosis are both not lower than 50°C.

[0050] In the field of the production of the precursor of the cathode material, the washing water is mainly pure water with a conductivity requirement of less than 10 μs / cm and a temperature of 50 - 80°C; the water after washing the product also has heat. In the embodiments of the present application, the washing liquid is directly subjected to ultrafiltration and reverse osmosis filtration (second ultrafiltration and second reverse osmosis) at a temperature not lower than 80°C without cooling, which can avoid the loss of the heat of the washing water, make the obtained product water have a certain stability, thus accelerating the dissolution when preparing the reaction materials required for the coprecipitation method, and also being beneficial to the subsequent coprecipitation reaction, effectively utilizing the heat of the production line, and further reducing the production cost.

[0051] The existing reverse osmosis generally uses a temperature lower than 40°C, so it cannot work effectively under high-temperature conditions. Since the temperature of the washing liquid is 50 - 80°C, if the existing reverse osmosis means are directly used to treat the washing liquid, the desalination performance of the membrane will rapidly decline, resulting in a reduction in the membrane flux and the desalination rate, thus affecting the quality of the product water; the embodiments of the present application adopt high-temperature ultrafiltration and reverse osmosis treatment (temperature not lower than 80°C), which can avoid the energy consumption loss of the washing wastewater and achieve the purpose of reducing costs and increasing efficiency in the production process. And the use of a high-temperature reverse osmosis membrane eliminates the cooling time of the high-temperature washing water, does not require waiting for the washing water to be reduced to below 40°C, saves the process, and the effluent of the reverse osmosis can be directly used for the preparation of raw materials, reducing the energy consumption.

[0052] The washing liquid first passes through a high-temperature ultrafiltration (second ultrafiltration) membrane to remove impurities. The produced water of the high-temperature ultrafiltration enters the high-temperature reverse osmosis membrane (second reverse osmosis). The produced water of the high-temperature reverse osmosis membrane is used to prepare the reaction materials for the coprecipitation method, that is, the dissolution of sulfates, effectively utilizing the heat of the washing liquid. The concentrated water of the high-temperature reverse osmosis membrane enters the ammonia stripping tower for ammonia stripping.

[0053] In some embodiments of the present invention, the ultrafiltration membrane used in the second ultrafiltration includes one or more of a ceramic membrane, polyvinylidene chloride, polyvinyl chloride, and a polysulfone / polyethersulfone composite membrane. The ultrafiltration membrane of the above materials can be used under relatively high temperatures (50°C to 80°C), and at high temperatures, it can continuously have good ultrafiltration performance.

[0054] In some embodiments of the present invention, the working temperature range of the ultrafiltration membrane used in the second ultrafiltration is 50°C - 150°C, and the operating pressure is 1 bar - 5 bar. As an example, the working temperature of the ultrafiltration membrane can be 50°C, 90°C, 100°C, 120°C, 150°C, etc., and the operating pressure can be 1 bar, 3 bar, 5 bar, etc. Controlling the working temperature and pressure of the ultrafiltration membrane within the above ranges can improve the durability of the ultrafiltration membrane and avoid energy consumption losses of the washing liquid, achieving the purpose of cost reduction and efficiency improvement in the production process.

[0055] In some embodiments of the present invention, the reverse osmosis membrane used in the second reverse osmosis includes one or more of a ceramic membrane, a polyamide composite membrane, and a polyethersulfone composite membrane. The reverse osmosis membrane of the above materials can be used under relatively high temperatures (50°C to 80°C), and at high temperatures, the reverse osmosis membrane can continuously maintain a high desalination performance, maintaining a high membrane flux and desalination rate, and ensuring good produced water quality.

[0056] In some embodiments of the present invention, the working temperature range of the reverse osmosis membrane used in the second reverse osmosis is 50°C - 90°C, and the operating pressure is 15 bar - 25 bar. As an example, the working temperature of the reverse osmosis membrane can be 50°C, 80°C, 85°C, 90°C, etc., and the operating pressure can be 15 bar, 20 bar, 25 bar, etc. Controlling the working temperature and pressure of the reverse osmosis membrane within the above ranges can improve the durability of the reverse osmosis membrane and avoid energy consumption losses of the washing liquid, achieving the purpose of cost reduction and efficiency improvement in the production process.

[0057] In some embodiments of the present invention, the temperature of the washing liquid obtained by washing is 50°C to 80°C. For example, the temperature of the washing liquid can be 50°C, 60°C, 70°C, 80°C, etc. Controlling the temperature of the washing liquid within the above ranges and directly performing the second ultrafiltration and the second reverse osmosis can avoid energy consumption losses of the washing liquid, achieving the purpose of cost reduction and efficiency improvement in the production process.

[0058] In some embodiments of the present invention, the concentrated water obtained from the second reverse osmosis is subjected to deammoniation treatment.

[0059] In some embodiments of the present invention, during deammoniation, the bottom temperature of the deammoniation tower is 103 - 105 °C, the pressure of the deammoniation tower is 0 - 10 kPa, the liquid level of the deammoniation tower is 1.3 - 1.5 m, and the feeding rate is 25 - 45 m 3 / h. As an example, the bottom temperature of the deammoniation tower can be 103 °C, 104 °C, 105 °C, etc., the pressure of the deammoniation tower can be 0 kPa, 2 kPa, 5 kPa, 7 kPa, 10 kPa, etc., the liquid level of the deammoniation tower can be 1.3 m, 1.4 m, 1.5 m, etc., and the feeding rate can be 25 m 3 / h, 30 m 3 / h, 40 m 3 / h, 45 m 3 / h, etc.

[0060] S2. Perform first ultrafiltration on the filter press mother liquor to obtain concentrated liquid and filtered product water, and recycle the concentrated liquid to the reaction kettle for the coprecipitation method.

[0061] In this step, first ultrafiltration is used for solid-liquid separation to obtain concentrated liquid and filtered product water. The main component in the concentrated liquid is small particles of the ternary cathode material precursor, and the main solute in the filtered product water is sulfate. Performing first ultrafiltration on the filter press mother liquor realizes the solid-liquid separation of the filter press mother liquor. The separated concentrated liquid containing the solid-phase ternary cathode material precursor is directly recycled to the reaction kettle for producing the ternary cathode material precursor. Compared with the conventional treatment process, this step reduces the material loss of the filter press mother liquor, improves the recovery rate of the ternary cathode material precursor. At the same time, the solid content of the concentrated liquid after ultrafiltration is high. Recycling it to the reaction kettle for continuous production will not only not affect the reaction process of the conventional precursor, but also help the small particle precursors to continue to grow into precursors that meet the particle size requirements in the reaction kettle, thereby improving the production quality.

[0062] In some embodiments of the present invention, the ultrafiltration membrane for the first ultrafiltration includes one or more of polytetrafluoroethylene membrane and ceramic membrane. The ultrafiltration membranes of the above materials have good solid-liquid separation effects. In some other embodiments of the present invention, the ultrafiltration membrane for the first ultrafiltration includes polytetrafluoroethylene membrane (PTFE membrane). The filter press mother liquor generated by the ternary cathode material precursor is alkaline, with a pH value of 11 - 13, and the PTFE membrane has strong alkali resistance. In addition, the outer surface of the PTFE membrane element is smooth, pollutants are not easily deposited on the membrane surface, the service life is long, and the energy consumption of the PTFE membrane is low, and the cost is low, which can further reduce the cost of recycling the filter press mother liquor.

[0063] In some embodiments of the present invention, the cut-off pore size of the ultrafiltration membrane of the first ultrafiltration is 0.05 μm to 0.2 μm. For example, the cut-off pore size of the ultrafiltration membrane of the first ultrafiltration can be 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, etc. Controlling the cut-off pore size of the ultrafiltration membrane of the first ultrafiltration within the above range is sufficient to retain the ternary cathode material precursor in the pressure filtration mother liquor in the concentrate, and the solid content in the concentrate is concentrated 4 to 6 times compared to the pressure filtration mother liquor, and it will not cause the cut-off pore size to be too small to affect the operating pressure and increase the ultrafiltration time. It can further improve the recovery rate of the ternary precursor in the pressure filtration mother liquor, and the amount of wastewater generated by the pressure filtration mother liquor subsequently is small, and the ammonia removal efficiency is high.

[0064] In some embodiments of the present invention, the working pressure of the first ultrafiltration is 4 bar - 8 bar. For example, the pressure of the first ultrafiltration can be 4 bar, 5 bar, 6 bar, 7 bar, 8 bar, etc. Controlling the pressure of the first ultrafiltration within the above range can accelerate the first ultrafiltration process, reduce the time of the first ultrafiltration, and will not damage the structure of the ultrafiltration membrane due to too high pressure.

[0065] In some embodiments of the present invention, the ultrafiltration element of the first ultrafiltration is a columnar ultrafiltration membrane module. A hollow ultrafiltration membrane is provided inside the columnar ultrafiltration membrane module, and the hollow ultrafiltration membrane is fixed in the columnar ultrafiltration membrane module in a manner that can swing at the bottom; preferably, the columnar ultrafiltration membrane module has a differential encapsulation structure with the upper part integrally encapsulated and the lower part independently encapsulated with single filaments. The ultrafiltration element of the first ultrafiltration is a membrane module with a bottom single-filament encapsulation structure. In terms of the encapsulation structure, the conventional ultrafiltration element has an end-encapsulation structure, and pollutants are likely to accumulate at the bottom, and there are dead corners in the membrane shell during the discharge process, and the pollutants cannot be completely discharged; the present application uses a membrane module with a bottom single-filament encapsulation structure, and the bottom is in a bulk state, and pollutants are not easily accumulated; and due to the bottom single-filament encapsulation, the membrane shell has no glued end face, and there is no dead corner during the evacuation process, which can further improve the ultrafiltration effect and increase the recovery rate of the ternary cathode active material precursor.

[0066] In some embodiments of the present invention, the hollow ultrafiltration membrane is an ultrafiltration membrane composed of hollow fibers. The outer diameter of the hollow fiber is 0.5 - 2.0 mm, and the inner diameter is 0.3 - 1.4 mm. As an example, the outer diameter of the hollow fiber can be 0.5 mm, 1 mm, 1.5 mm, 2 mm, etc., and the inner diameter can be 0.3 mm, 0.5 mm, 0.8 mm, 1 mm, 1.4 mm, etc. The wall of the hollow fiber is covered with micropores, and the pore size can be expressed by the molecular weight of the substance that can be intercepted. The upper part of the hollow fiber single filament is fixed at the top of the columnar ultrafiltration membrane module, and the free end swings at the lower part of the ultrafiltration membrane module.

[0067] It can be understood that for the membrane module with a bottom single-filament encapsulation structure used in the first ultrafiltration, its specific structure can be obtained by those skilled in the art according to the description.

[0068] In some embodiments of the present invention, the solid content of the filter press mother liquor is 0.5% to 2.0%. It can be understood that the solid content of the filter press mother liquor refers to the mass ratio of the ternary cathode active material precursor in the filter press mother liquor. As an example, the solid content of the filter press mother liquor can be 0.5%, 1%, 1.5%, 2.0%, etc. After ultrafiltration, the solid content in the concentrated liquid can be concentrated 4 to 6 times compared to the filter press mother liquor, realizing the recycling of the ternary cathode active material precursor in the filter press mother liquor.

[0069] In some embodiments of the present invention, the solid content of the concentrated liquid is 3% to 8%. It can be understood that the solid content of the concentrated liquid refers to the mass ratio of the ternary cathode active material precursor in the concentrated liquid. As an example, the solid content of the concentrated liquid can be 3%, 5%, 6%, 8%, etc. The concentrated liquid after ultrafiltration and concentration, compared to the filter press mother liquor, can be recycled to the reaction kettle of the coprecipitation method, reducing the influence on the previous reaction process due to excessive water content and ensuring high-quality ternary cathode material precursors in the reaction kettle of the coprecipitation method.

[0070] In some embodiments of the present invention, recycling the concentrated liquid to the reaction kettle of the coprecipitation method includes: adjusting the particle size of the ternary cathode material precursor in the concentrated liquid and recycling it to the reaction kettle of the coprecipitation method.

[0071] In some embodiments of the present invention, to adjust the particle size of the ternary cathode material precursor in the concentrated liquid, a thickener can be used to enlarge the small particle size of the cathode active material precursor in the concentrated liquid to a relatively larger particle size. After recycling to the reaction kettle of the coprecipitation method, it can reduce the influence of the small particle size ternary cathode material precursor on the overall particle size and particle size distribution of the obtained ternary cathode material precursor, and then inherit the particle size characteristics of the ternary cathode material precursor to the ternary cathode material, reducing the generation of too small particles in the ternary cathode material, reducing the generation of side reactions during the battery cycle containing the ternary cathode material, and maintaining the excellent cycle life of the battery.

[0072] In some embodiments of the present invention, the average particle size of the ternary cathode material precursor in the concentrated liquid is adjusted from 0.5 μm to 3 μm to 3 μm to 5 μm. For example, the average particle size of the ternary cathode material before adjustment can be 0.5 μm, 1 μm, 2 μm, 3 μm, etc., and the average particle size after adjustment can be 3 μm, 4 μm, 5 μm, etc. Enlarging the average particle size of the ternary cathode material precursor to 3 μm to 5 μm can reduce the influence of the recycled small particle size ternary cathode material precursor on the quality of the ternary cathode active material precursor generated in the reaction kettle of the coprecipitation method, and form high-quality ternary cathode material precursors on the premise of ensuring high recovery rate.

[0073] S3. Perform first reverse osmosis on the filtered produced water to obtain concentrated water and reverse osmosis produced water.

[0074] In this step, reverse osmosis is adopted. The filtered produced water generated by the first ultrafiltration mainly contains sulfates (such as sodium sulfate and ammonium sulfate). After the first ultrafiltration, first reverse osmosis is carried out on the filtered produced water. Concentrating the filtered produced water by first reverse osmosis can increase the concentration of sulfates therein, reduce the amount of concentrated water (waste water subsequently generated from the pressure filter mother liquor) generated by the first reverse osmosis, thereby reducing the amount of waste water to be treated, reducing the scale of subsequent deammoniation, and improving the deammoniation efficiency.

[0075] In some embodiments of the present invention, the rejection rate of the reverse osmosis membrane for the first reverse osmosis is 80% - 90%. For example, the rejection rate of the reverse osmosis membrane for the first reverse osmosis can be 80%, 82%, 85%, 88%, 90%, etc. Specifically, the rejection rate of a conventional reverse osmosis membrane is generally above 98%. In this application, by controlling the rejection rate within 80% - 90%, the conductivity of the reverse osmosis produced water is increased compared to a reverse osmosis with a relatively high rejection rate. Thereby, the osmotic pressure difference of the concentrated water is reduced, and at the same time, the feed amount of the deammoniation tower for subsequent deammoniation is reduced, the amount of concentrated water (waste water subsequently generated from the pressure filter mother liquor) generated by the first reverse osmosis is reduced, thereby reducing the amount of waste water to be treated and improving the deammoniation efficiency of the deammoniation tower.

[0076] It can be understood that in the embodiments of this application, the reverse osmosis membrane processes the filtered produced water of the first ultrafiltration to obtain the treated concentrated water and reverse osmosis produced water. After reverse osmosis, the salt concentration in the reverse osmosis produced water is increased and the conductivity is also relatively high, and it can directly enter the reaction kettle of the coprecipitation method to prepare the bottom liquid. Compared with a reverse osmosis membrane with a high rejection rate, the amount of the treated concentrated water with a low rejection rate in this application is reduced, and the concentration of the concentrated water is also reduced. When entering the subsequent deammoniation tower, compared with the filtered produced water without reverse osmosis treatment or a reverse osmosis membrane with a high rejection rate, under the same working conditions, the deammoniation efficiency is improved, that is, under the same conditions, the amount of concentrated water (waste water) to be treated is reduced.

[0077] In some embodiments of the present invention, the operating pressure of the first reverse osmosis is 60 bar - 80 bar. For example, the operating pressure can be 60 bar, 70 bar, 80 bar, etc. Controlling the operating pressure of the first reverse osmosis within the above range facilitates achieving a rejection rate of 80% - 90% for the reverse osmosis membrane, reduces the scale of subsequent deammoniation, improves the deammoniation efficiency, increases the treatment amount of the filtered produced water, and thereby increases the treatment amount of the mother liquor.

[0078] In some embodiments of the present invention, in the filtered product water, the total mass ratio of ammonium sulfate and sodium sulfate is 5% to 10%. For example, in the filtered product water, the total mass ratio of ammonium sulfate and sodium sulfate can be 5%, 7%, 9%, 10%, etc. It can be understood that the total mass ratio of ammonium sulfate and sodium sulfate refers to the sum of the mass ratios of ammonium sulfate and sulfate. The concentration of sulfate in the filtered product water is relatively low, and the energy consumption for direct deammoniation and crystallization is relatively high. After reverse osmosis concentration, the amount of concentrated water treatment can be further reduced, and the deammoniation efficiency can be improved.

[0079] In some embodiments of the present invention, in the concentrated water, the total mass ratio of ammonium sulfate and sodium sulfate is 15% to 20%. For example, it can be 15%, 17%, 19%, 20%, etc. By controlling the sulfate content in the concentrated water obtained by reverse osmosis within the above range, the osmotic pressure difference of the concentrated water is reduced, and at the same time, the feed amount of the deammoniation tower for subsequent deammoniation is reduced, and the deammoniation efficiency of the deammoniation tower is improved.

[0080] In some embodiments of the present invention, the reverse osmosis membrane of the first reverse osmosis includes one or more of polytetrafluoroethylene membranes and ceramic membranes. The reverse osmosis membranes of the above materials have good alkali resistance and low cost, and can further reduce the cost of pressure filtration mother liquor recovery.

[0081] S4. Deammoniate and crystallize the concentrated water to obtain sulfate.

[0082] S5. Use the reverse osmosis product water to prepare the reaction materials for the coprecipitation method.

[0083] In summary, the mother liquor recovery method for the synthesis process of ternary cathode material precursors proposed in this application performs the first ultrafiltration on the pressure filtration mother liquor, realizing the solid-liquid separation of the pressure filtration mother liquor. The concentrated liquid containing the solid-phase ternary cathode material precursor separated is directly recycled to the reaction kettle for producing ternary cathode material precursors. Compared with the conventional treatment process, the material loss of the pressure filtration mother liquor is reduced, and the yield of the ternary cathode material precursor is improved; the main component of the filtered product water generated by the first ultrafiltration is sulfate (such as sodium sulfate and ammonium sulfate, and after deammoniation, the sulfate is sodium sulfate). After the first ultrafiltration, in combination with the first reverse osmosis, the first reverse osmosis is used to concentrate the filtered product water, which can increase the concentration of sulfate therein, reduce the amount of concentrated water generated by the first reverse osmosis, reduce the scale of subsequent deammoniation, and improve the deammoniation efficiency. In summary, the mother liquor recovery method for the synthesis process of ternary cathode material precursors proposed in the present invention has a high yield of ternary cathode material precursors, less waste water generated from the subsequent pressure filtration mother liquor, and high deammoniation efficiency.

[0084] Figure 2 Shows the detailed process diagram of the mother liquor recovery method for the precursor synthesis process of an embodiment of the present invention. Please refer to Figure 2 :

[0085] S0. Three raw materials, nickel sulfate, cobalt sulfate, and manganese sulfate, and liquid caustic soda and ammonia water are proportioned in a one-to-one ratio and reacted at 60 °C in a reaction kettle to synthesize the precursor of the ternary cathode material;

[0086] S1. The discharge from the reaction kettle is separated into solid and liquid by a filter press. The separated solid is washed, dried, batch-mixed, sieved to remove iron, and packaged into the product, the precursor of the ternary cathode active material;

[0087] S2. The mother liquor of the filter press is filtered by ultrafiltration (the first ultrafiltration, Figure 2 with a ceramic membrane). The effluent of the ultrafiltration includes the concentrated liquid and the filtered product water. The concentrated liquid goes to a thickener to adjust the particle size; the discharge of the thickener goes to the reaction kettle for co-precipitation synthesis;

[0088] S3. The filtered product water of the ultrafiltration has an inorganic salt concentration of 5% - 10%, and the main components are ammonium sulfate and sodium sulfate. The filtered product water of the ultrafiltration is concentrated by the first reverse osmosis ( Figure 2 membrane concentration in it). The effluent of the reverse osmosis includes the concentrated water and the reverse osmosis product water.

[0089] S4. The concentrated water goes to a deammoniation tower for deammoniation, and the material after deammoniation goes to evaporation and crystallization. The crystalline solid is mainly sulfate (generally sodium sulfate, Glauber's salt),

[0090] S5. The condensate of the evaporation and crystallization and the reverse osmosis product water go to the batching before the reaction kettle in step S0.

[0091] The washing water is mainly pure water with a conductivity below 10 μs / cm and a temperature of 50 - 80 °C; the water after product washing is also at a high temperature. The system uses high-temperature ultrafiltration ( Figure 2 the ultrafiltration in it) and high-temperature reverse osmosis ( Figure 2 the membrane concentration in it) for filtration. The washing water first passes through a high-temperature ultrafiltration membrane to remove impurities. The product water of the high-temperature ultrafiltration membrane enters the high-temperature reverse osmosis membrane. The product water of the high-temperature reverse osmosis membrane and the product water of the first reverse osmosis membrane in the mother liquor treatment system are used together for the preparation of the bottom liquid, that is, the dissolution of sulfate, effectively utilizing the heat of the washing water. The concentrated water of the high-temperature reverse osmosis membrane enters the deammoniation tower for deammoniation treatment.

[0092] In the second aspect of the present invention, the present invention proposes a mother liquor recovery system for the precursor synthesis process. The mother liquor recovery system for the precursor synthesis process is used to execute the method described in the first aspect. Thus, the mother liquor recovery system for the synthesis process of the ternary cathode material precursor proposed by the present invention has all the beneficial effects of the above method, which will not be elaborated here one by one.

[0093] The solutions of the present disclosure will be explained below in conjunction with embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. For those embodiments where specific technologies or conditions are not indicated, the technologies or conditions described in the literature in the art or according to the product specifications are followed. For the reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchases.

[0094] Example 1

[0095] S0. Nickel sulfate, cobalt sulfate, and manganese sulfate are formulated according to a mass ratio of 3:1:1 to prepare a mixed salt with a density ρ = 1.25 - 1.35 g / cm 3 . Liquid alkali (NaOH, mass percentage 32%) and ammonia water (mass percentage 25%) are added respectively. Co-precipitation reaction is carried out in a reaction kettle according to V(mixed salt) = 500 ± 10 L / h: V(liquid alkali) = 190 ± 5 L / h: V(ammonia water) = 30 ± 3 L / h. The reaction temperature is 60 ± 10 °C, the stirring speed is 120 - 130 rpm, and the ternary cathode material precursor Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 ;

[0096] S1. The material discharged from the reaction kettle is separated by a filter press into solid and liquid. The separated solid is washed, dried, batch-mixed, sieved to remove iron, and packaged into the product ternary cathode active material precursor;

[0097] The washing water is mainly pure water with a conductivity below 10 μs / cm and a temperature of 75 °C; the water after product washing is also at a high temperature (temperature of 75 °C), and is filtered by high-temperature ultrafiltration (the second ultrafiltration, the ultrafiltration membrane material is polyvinylidene chloride membrane, the working temperature is 75 °C, and the operating pressure is 3 bar) and high-temperature reverse osmosis (the second reverse osmosis, the reverse osmosis membrane material is a ceramic membrane, the working temperature is 75 °C, and the operating pressure is 20 bar). The washing water first passes through the high-temperature ultrafiltration membrane to remove impurities, and the water produced by the high-temperature ultrafiltration membrane enters the high-temperature reverse osmosis membrane. The water produced by the high-temperature reverse osmosis membrane has a temperature not lower than 70 °C, and is used together with the water produced by the first reverse osmosis membrane in the mother liquor treatment system for the preparation of the bottom liquid, that is, the dissolution of sulfates. The concentrated water of the high-temperature reverse osmosis membrane enters the deammoniation tower for deammoniation treatment;

[0098] S2. The pressure-filtered mother liquor (solid content 1.2%) is filtered by ultrafiltration (the first ultrafiltration, with a polytetrafluoroethylene (PTFE) membrane, a cut-off pore size of 0.1 μm, a column-type ultrafiltration element, a hollow ultrafiltration membrane inside, and an upper encapsulation and lower single-filament encapsulation structure). The working pressure of the first ultrafiltration is controlled at 5 bar to obtain the effluent of ultrafiltration including concentrated liquid (solid content 4%) and filtered product water. The concentrated liquid goes to a thickener to adjust the particle size (the average particle size of the ternary cathode material precursor is adjusted from 0.8 μm to 5 μm); the discharge from the thickener goes to a co-precipitation synthesis reactor;

[0099] S3. The filtered product water of ultrafiltration contains ammonium sulfate and sodium sulfate with a total mass ratio of 10%. It is concentrated by the first reverse osmosis (the reverse osmosis membrane material is a ceramic membrane, the rejection rate is 85%, and the operating pressure is 70 bar). The reverse osmosis effluent includes concentrated water (the total mass ratio of ammonium sulfate and sodium sulfate is 16.5%) and reverse osmosis product water.

[0100] S4. The concentrated water goes to a deammoniation tower for deammoniation. The temperature at the bottom of the deammoniation tower is 103 °C, the pressure of the deammoniation tower is 5 Kpa, the liquid level of the deammoniation tower is 1.3 m, and the feeding rate is 30 m 3 / h. After deammoniation, the material goes to evaporation and crystallization, and the crystalline solid is mainly sodium sulfate (sodium sulfate anhydrous);

[0101] S5. The condensate of evaporation and crystallization and the reverse osmosis product water go to the S0 step for batching.

[0102] The steps of Examples 2-9 and Comparative Examples 1-2 are the same as those of Example 1, except for the specific parameters, as shown in Table 1.

[0103] Table 1

[0104]

[0105] In Examples 1-9 and Comparative Examples 1-2, the parameters of the materials obtained in steps S2 and S3 are shown in Table 2:

[0106] Table 2

[0107]

[0108]

[0109] The following measurements are carried out on Examples 1-9 and Comparative Examples 1-2:

[0110] 1. Determination of the yield of the ternary cathode material precursor in step S2: Weigh the amount of the ternary cathode precursor obtained by the above method. Then, the yield of the ternary cathode material precursor = the amount of the actually obtained ternary cathode material precursor ÷ the theoretically calculated amount of the ternary cathode material precursor according to the feeding ratio × 100%.

[0111] 2. Measurement of the amount of concentrated water in step S3: Taking the filtered product water in step S3 as 12 m 3 / ton, perform the first reverse osmosis, and use a flow meter to measure the amount of concentrated water obtained in step S3. The measurement results are shown in Table 3.

[0112] Table 3

[0113]

[0114]

[0115] As can be seen from Table 2, compared with Examples 1-9, in Comparative Example 1, the filtered product water was not subjected to reverse osmosis treatment and directly entered the deammoniation tower for treatment. Correspondingly, the amount of concentrated water entering the deammoniation tower in Examples 1-9 increased significantly. This is because the filtered product water was not subjected to membrane concentration, and the amount of water to be deammoniated did not decrease significantly; in Comparative Example 2, the filter press mother liquor was directly subjected to the first reverse osmosis treatment without the first ultrafiltration, that is, the ternary cathode material precursor in the filter press mother liquor was not recovered. Therefore, the recovery rate of the ternary cathode material precursor was low; compared with Example 1, in Example 4, the cut-off pore size of the ultrafiltration membrane in the first ultrafiltration was too large, resulting in a decrease in the recovery rate of the ternary cathode material precursor. This is because the cut-off pore size of the ultrafiltration filter element was large, and some small particle materials passed through the filter, resulting in less recovery; compared with Example 1, in Example 5, the cut-off pore size of the ultrafiltration membrane in the first ultrafiltration was too small, resulting in a high recovery rate of the ternary cathode material precursor. However, in actual production, the treatment efficiency of the filter press mother liquor was very low; compared with Example 1, in Example 6, the concentrated liquid did not enter the thickener to adjust the particle size and was directly recovered. As a result, the particle size of the obtained ternary cathode active material precursor was small and the specific surface area was large. Although the recovery rate was high, it might affect the quality of the ternary cathode active material precursor. Compared with Example 1, in Example 9, the rejection rate of the reverse osmosis membrane in the first reverse osmosis was too high, which not only required a higher operating pressure, but also significantly increased the amount of concentrated water. Moreover, the salt ion concentration in the obtained reverse osmosis product water was low, and the output of the reverse osmosis product water was small. The excessive amount of concentrated water would also increase the workload of subsequent deammoniation and reduce the deammoniation efficiency.

[0116] In the description of this specification, the descriptions with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", "some implementation schemes" or "some examples" etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0117] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for recovering mother liquor in a precursor synthesis process, characterized in that: include: The reaction liquid obtained by the co-precipitation method is filtered to obtain the filter press mother liquid and the ternary positive electrode material precursor; The filter press mother liquor is subjected to a first ultrafiltration to obtain a concentrated solution and filtered water, and the concentrated solution is recovered to a reactor of a co-precipitation method; The filtered water is subjected to a first reverse osmosis to obtain concentrated water and reverse osmosis water; Deaminate and crystallize the concentrated water to obtain sulfate; The reverse osmosis produced water is used to prepare the reaction materials of the co-precipitation method.

2. The method according to claim 1, characterized in that The ultrafiltration membrane of the first ultrafiltration includes one or more of a polytetrafluoroethylene membrane, a ceramic membrane, and a cellulose acetate membrane. Optionally, the ultrafiltration membrane of the first ultrafiltration includes a polytetrafluoroethylene membrane; and / or, The cut-off pore size of the ultrafiltration membrane of the first ultrafiltration is 0.05 μm to 0.2 μm; and / or, The working pressure of the first ultrafiltration is 4 bar-8 bar.

3. The method according to claim 1 or 2, characterized in that: The ultrafiltration element of the first ultrafiltration is a columnar ultrafiltration membrane assembly, which has a hollow ultrafiltration membrane inside; preferably, the packaging structure of the columnar ultrafiltration membrane assembly adopts upper packaging and lower monofilament packaging; and / or, The solid content of the filter press mother liquid is 0.5% to 2.0%; and / or, The solid content of the concentrate is 3% to 8%; and / or, In the filtered water, the total mass proportion of ammonium sulfate and sodium sulfate is 5% to 10%.

4. The method according to claim 1 or 2, characterized in that: Recycling the concentrated solution to the reactor of the co-precipitation method includes: adjusting the particle size of the ternary positive electrode material precursor in the concentrated solution, and recycling it to the reactor of the co-precipitation method.

5. The method according to claim 4, characterized in that The average particle size of the ternary cathode material precursor in the concentrated solution is adjusted from 0.5 μm to 3 μm to 3 μm to 5 μm.

6. The method according to claim 1 or 2, characterized in that: The rejection rate of the reverse osmosis membrane of the first reverse osmosis is 80% to 90%; and / or, The operating pressure of the first reverse osmosis is 60 bar to 80 bar; and / or, In the concentrated water, the total mass proportion of ammonium sulfate and sodium sulfate is 15% to 20%.

7. The method according to claim 1 or 2, characterized in that: The reverse osmosis membrane of the first reverse osmosis includes one or more of a polytetrafluoroethylene membrane, a ceramic membrane, and a cellulose acetate membrane.

8. The method according to claim 1 or 2, characterized in that: The step of filtering the reaction liquid obtained by the coprecipitation method to obtain a filter press mother liquid and a ternary positive electrode material precursor comprises: Filtering the reaction liquid obtained by the coprecipitation method to obtain a filter press mother liquid and a solid; The solid is washed, dried, batch mixed, sieved to remove iron, and packaged to obtain a ternary positive electrode material precursor; The washing liquid obtained by the washing is subjected to a second ultrafiltration to obtain impurities and ultrafiltration product water; The ultrafiltration produced water is subjected to a second reverse osmosis, and the produced water obtained is used to prepare the reaction materials of the co-precipitation method.

9. The method according to claim 8, characterized in that The washing liquid obtained by the washing is subjected to a second ultrafiltration and a second reverse osmosis in sequence without being cooled.

10. The method according to claim 9, characterized in that The ultrafiltration membrane used in the second ultrafiltration includes one or more of a ceramic membrane, polyvinylidene chloride, polyvinyl chloride, and a polysulfone / polyethersulfone composite membrane; and / or, The operating temperature of the ultrafiltration membrane used in the second ultrafiltration is 50°C-150°C, and the operating pressure is 1 bar-5 bar; and / or, The reverse osmosis membrane used in the second reverse osmosis comprises one or more of a ceramic membrane, a polyamide composite membrane, and a polyethersulfone composite membrane; and / or, The reverse osmosis membrane used in the second reverse osmosis has an operating temperature range of 50°C-90°C and an operating pressure of 15bar-25bar; and / or, The temperature of the washing liquid obtained by washing is 50° C. to 80° C.; and / or, The concentrated water obtained by the second reverse osmosis is subjected to deammoniation treatment.

11. A mother liquor recovery system for a precursor synthesis process, characterized in that: The mother liquor recovery system of the precursor synthesis process is used to perform the method according to any one of claims 1-10.

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