A method for treating wastewater from the synthesis of a cathode material precursor for a battery

Abstract

The present invention discloses a method for treating synthetic wastewater from the precursor of battery cathode materials, belonging to the technical field of wastewater treatment for the precursor of battery cathode materials. The method includes: removing impurities and concentrating the synthetic wastewater containing sodium sulfate generated during the synthesis of the precursor of battery cathode materials to obtain a sodium sulfate concentrate; preparing the concentrate into a suspension containing sodium bicarbonate, performing solid-liquid separation to obtain a first wet-based sodium bicarbonate product and a first mother liquor after alkali removal; concentrating the first mother liquor after alkali removal, cooling and crystallizing to precipitate part of sodium bicarbonate, and performing solid-liquid separation on the remaining concentrated mother liquor to obtain a second wet-based sodium bicarbonate product and a second mother liquor after alkali removal; evaporating and crystallizing the second mother liquor after alkali removal to obtain an ammonium nitrogen fertilizer mainly containing ammonium sulfate. This method can effectively utilize the by-product sodium sulfate generated during the synthesis of the precursor of battery cathode materials downstream on the premise of improving the conversion rate of sodium sulfate, and at the same time avoid the generation of solid waste, thereby avoiding the problems of pollution and environmental damage.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment for battery cathode material precursors, and more specifically, to a method for treating synthetic wastewater of battery cathode material precursors. Background Art

[0002] During the production process of lithium / sodium ion battery cathode material precursors, a large amount of wastewater containing sodium sulfate is generated in the precipitation process, and the wastewater of ternary and multi-component material precursors also contains ammonia.

[0003] According to chemical reaction formula calculations: for every ton of ternary and multi-component battery cathode material precursors of lithium / sodium ion batteries produced, approximately 1.53 tons of sodium sulfate are generated, and for every 1 ton of lithium iron phosphate precursor of lithium ion battery cathode materials produced, approximately 1.41 tons of sodium sulfate are generated. With the rapid development of the electronics industry and the new energy vehicle industry, the shipment volume of ternary precursors in China reached 618,000 tons in 2021, and the shipment volume of lithium iron phosphate was approximately 330,000 tons. Then, about 1.41 million tons of sodium sulfate were generated in 2021. It is predicted that by 2025, the total amount of sodium sulfate generated by the precursor industry will exceed 5 million tons.

[0004] In some existing technologies, the treatment methods for the wastewater generated during the production process of lithium / sodium ion battery cathode material precursors have problems such as high evaporation energy consumption and a large accumulation of by-product sodium sulfate; in some other existing technologies, by converting sodium sulfate in iron phosphate wastewater into by-product phosphogypsum, there are too much solid waste, which is neither economical nor environmentally friendly. In addition, the conversion rate of sodium sulfate corresponding to the synthetic wastewater treatment method provided in the existing technology is relatively low, about 75%.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for treating synthetic wastewater of battery cathode material precursors, which can effectively utilize the by-product sodium sulfate generated during the synthesis process of battery cathode material precursors downstream on the premise of improving the conversion rate of sodium sulfate, and at the same time avoid the generation of solid waste, thereby avoiding the problems of pollution and environmental damage.

[0007] The present application can be implemented as follows:

[0008] The present application provides a method for treating synthetic wastewater of battery cathode material precursors, including the following steps:

[0009] S1: Remove impurities from the synthetic wastewater containing sodium sulfate generated during the synthesis process of battery cathode material precursors to obtain a sodium sulfate solution;

[0010] S2: Concentrate the sodium sulfate solution to obtain a concentrated sodium sulfate solution;

[0011] S3: Prepare a suspension containing sodium bicarbonate from the concentrated sodium sulfate solution.

[0012] S4: Perform solid-liquid separation on the suspension containing sodium bicarbonate to obtain a first wet-based sodium bicarbonate product and a first mother liquor for alkali removal.

[0013] S5: Concentrate the first mother liquor for alkali removal to obtain a concentrated mother liquor; cool and crystallize the concentrated mother liquor to precipitate part of the sodium bicarbonate, and perform solid-liquid separation on the remaining concentrated mother liquor to obtain a second wet-based sodium bicarbonate product and a second mother liquor for alkali removal.

[0014] S6: Perform evaporation crystallization on the second mother liquor for alkali removal to obtain an ammonium nitrogen fertilizer mainly containing ammonium sulfate.

[0015] In an optional embodiment, when the battery cathode material precursor is a ternary cathode material precursor and / or a multi-component cathode material precursor, S1 includes:

[0016] Remove ammonia from the synthetic wastewater containing ammonia and sodium sulfate generated during the synthesis of the battery cathode material precursor to obtain a deammoniated waste liquid; remove the metal hydroxide waste residue from the deammoniated waste liquid to obtain a sodium sulfate solution free of ammonia and heavy metal ions.

[0017] In an optional embodiment, it further includes: condense and absorb the ammonia evaporated during the ammonia removal process to prepare ammonia water for returning to the synthesis process for use.

[0018] In an optional embodiment, when the battery cathode material precursor is a lithium iron phosphate cathode material precursor, S1 includes: remove phosphate from the synthetic wastewater containing phosphate and sodium sulfate generated during the synthesis of the battery cathode material precursor to obtain a phosphate-removed sodium sulfate solution.

[0019] In an optional embodiment, the phosphate-removed sodium sulfate solution is obtained by the following method:

[0020] Mix the synthetic wastewater to be treated with a calcium sulfate suspension, and then remove the obtained calcium phosphate precipitate; mix the solution containing calcium ions remaining after removing the calcium phosphate precipitate with a sodium carbonate solution, and then remove the obtained calcium carbonate precipitate to obtain a phosphate-removed sodium sulfate solution.

[0021] In an optional embodiment, the mass concentration of sodium sulfate in the concentrated sodium sulfate solution obtained in S2 is not less than 30 g / L.

[0022] In an optional embodiment, the concentrated sodium sulfate solution is a nearly saturated sodium sulfate solution or a saturated sodium sulfate solution.

[0023] In an optional embodiment, the pure water obtained during the concentration of the sodium sulfate solution is recycled to the front-end process of the precursor synthesis.

[0024] In an alternative embodiment, in S3, the suspension containing sodium bicarbonate is obtained by mixing the concentrated sodium sulfate solution with ammonium bicarbonate, or the suspension containing sodium bicarbonate is obtained by mixing the concentrated sodium sulfate solution with ammonia water and carbon dioxide.

[0025] In an alternative embodiment, the weight ratio of the concentrated sodium sulfate solution to ammonium bicarbonate is 1 - 1.2:1.

[0026] In an alternative embodiment, the concentrated sodium sulfate solution and ammonium bicarbonate are mixed under stirring conditions.

[0027] In an alternative embodiment, the stirring speed is 120 - 600 r / min, and / or the stirring time is not less than 60 min.

[0028] In an alternative embodiment, in S5, the temperature of the cooled concentrated mother liquor is not higher than 20°C.

[0029] In an alternative embodiment, it further includes S7A: drying the first wet sodium bicarbonate product and / or the second wet sodium bicarbonate product for standby.

[0030] In an alternative embodiment, it further includes S7B: roasting and decomposing the first wet sodium bicarbonate product and / or the second wet sodium bicarbonate product to obtain a sodium carbonate product.

[0031] In an alternative embodiment, the temperature of roasting and decomposing is 140 - 210°C; and / or the time of roasting and decomposing is not less than 30 min.

[0032] The beneficial effects of this application include:

[0033] This application removes impurities and concentrates the synthetic wastewater containing sodium sulfate generated during the synthesis process of the battery cathode material precursor, directly preparing a concentrated sodium sulfate solution that can be used for alkali production; by making the concentrated sodium sulfate solution into a suspension containing sodium bicarbonate to further prepare soda ash and ammonium nitrogen fertilizer, the wastewater treatment by-products are changed from sodium sulfate and raw material ammonium bicarbonate to sodium carbonate and ammonium nitrogen fertilizer with higher value, bringing greater economic benefits to the enterprise while solving the dilemma of a large backlog of by-product sodium sulfate by precursor production enterprises, and providing a feasible wastewater treatment method for the lithium / sodium ion battery cathode material precursor production industry.

[0034] In addition, through two concentration processes in this solution, most of the water is separated by concentration, reducing the energy consumption for subsequent evaporation and crystallization to prepare ammonium nitrogen fertilizer; the defluorination mother liquor is directly evaporated and crystallized to produce ammonium nitrogen fertilizer mainly containing ammonium sulfate, realizing the full utilization of nitrogen in the raw materials. During the alkali production process, the first defluorination mother liquor is further concentrated by using a membrane filtration system, improving the yield of sodium bicarbonate and the conversion rate of sodium sulfate, and the conversion rate of sodium sulfate can reach more than 85%. Brief Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following accompanying drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related accompanying drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is the first process flow diagram of the method for treating the synthesis wastewater of the battery cathode material precursor provided by the present application;

[0037] Figure 2 It is the second process flow diagram of the method for treating the synthesis wastewater of the battery cathode material precursor provided by the present application. Detailed Embodiments

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those conditions not specified in the embodiments, they shall be carried out according to conventional conditions or conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0039] The method for treating the synthesis wastewater of the battery cathode material precursor provided by the present application will be specifically described below.

[0040] Please refer to Figure 1 and Figure 2 together. The present application proposes a method for treating the synthesis wastewater of the battery cathode material precursor, including the following steps:

[0041] S1: Remove impurities from the synthesis wastewater containing sodium sulfate generated during the synthesis of the battery cathode material precursor to obtain a sodium sulfate solution.

[0042] The above battery cathode material can be a lithium-ion battery cathode material or a sodium-ion battery cathode material.

[0043] The cathode material precursor can be a ternary cathode material precursor or a multi-component cathode material precursor, or a lithium iron phosphate cathode material precursor (such as iron phosphate).

[0044] In some alternative embodiments, such as Figure 1 , the battery cathode material precursor is a ternary cathode material precursor and / or a multi-component cathode material precursor. Correspondingly, S1 includes:

[0045] Ammonia is removed from the synthetic wastewater containing ammonia and sodium sulfate generated during the synthesis process of the cathode material precursor of the battery to obtain deammoniated waste liquid; the metal hydroxide waste residue in the deammoniated waste liquid is removed to obtain a sodium sulfate solution free of ammonia and heavy metal ions.

[0046] The above process can be carried out in a distillation column.

[0047] Furthermore, after ammonia removal, the ammonia evaporated during the ammonia removal process can be condensed and absorbed (for example, condensed and absorbed through the top condenser of the distillation column) to obtain ammonia water for return to the synthesis process for use.

[0048] The deammoniated waste liquid after ammonia removal can be discharged from the bottom of the distillation column, filtered after heat exchange to remove the metal hydroxide waste residue precipitated due to ammonia removal (wherein the metal can include, for example, nickel, cobalt, manganese, and / or iron, etc.), and a sodium sulfate solution free of ammonia and heavy metal ions is obtained.

[0049] It should be noted that the specific molecular formula of the above ternary cathode material precursor or / and multi-component cathode material precursor can refer to the relevant prior art and will not be elaborated and limited one by one here.

[0050] In some other alternative embodiments, such as Figure 2 , the cathode material precursor of the battery is the precursor of lithium iron phosphate cathode material (this precursor is for the scheme of precipitating iron phosphate with sodium phosphate), correspondingly, S1 includes:

[0051] Phosphate is removed from the synthetic wastewater containing phosphate and sodium sulfate generated during the synthesis process of the cathode material precursor of the battery to obtain a sodium sulfate solution with phosphorus removed.

[0052] Specifically, the above sodium sulfate solution with phosphorus removed can be obtained by the following method:

[0053] The synthetic wastewater to be treated is mixed with a calcium sulfate suspension, and the excess phosphate in the wastewater precipitates in the form of calcium phosphate. Subsequently, the obtained calcium phosphate precipitate is removed (for example, by filtration). The solution containing calcium ions remaining after removing the calcium phosphate precipitate is mixed with a sodium carbonate solution to precipitate the excess calcium ions in the form of calcium carbonate. Subsequently, the obtained calcium carbonate precipitate is removed (for example, by filtration) to obtain a sodium sulfate solution with phosphorus removed.

[0054] In some other alternative embodiments, the synthetic wastewater of the cathode material precursor of the battery to be treated includes at least two of the synthetic wastewater of the ternary cathode material precursor, the synthetic wastewater of the multi-component cathode material precursor, and the synthetic wastewater of the precursor of lithium iron phosphate cathode material. In this case, the different synthetic wastewaters are treated according to S1 corresponding to the above different cathode material precursors of the battery, and then the obtained sodium sulfate solutions are combined for subsequent steps.

[0055] S2: Concentrate the sodium sulfate solution to obtain a concentrated sodium sulfate solution (which can be used for alkali production).

[0056] Exemplarily but not limitedly, this step can be carried out using a membrane filtration system.

[0057] For reference, the mass concentration of sodium sulfate in the obtained concentrated sodium sulfate solution is not less than 30 g / L, and can be, for example, 30.4 g / L, 32 g / L, 35.5 g / L, or 47.6 g / L, etc.

[0058] Preferably, the concentrated sodium sulfate solution is a nearly saturated sodium sulfate solution or a saturated sodium sulfate solution to facilitate the improvement of the conversion rate of sodium sulfate.

[0059] Furthermore, the pure water obtained during the concentration of the sodium sulfate solution can be recycled to the front-end process of precursor synthesis.

[0060] S3: Prepare a suspension containing sodium bicarbonate from the concentrated sodium sulfate solution.

[0061] This step can be carried out in a reaction kettle.

[0062] In some embodiments, the above suspension containing sodium bicarbonate can be obtained by mixing the concentrated sodium sulfate solution with ammonium bicarbonate. In other embodiments, the above suspension containing sodium bicarbonate is also obtained by mixing the concentrated sodium sulfate solution with ammonia water and carbon dioxide.

[0063] For reference, the weight ratio of the concentrated sodium sulfate solution to ammonium bicarbonate can be 1 - 1.2:1, such as 1:1, 1.05:1, 1.08:1, 1.1:1, 1.12:1, 1.15:1, or 1.2:1, etc., and can also be any other value within the range of 1 - 1.2:1.

[0064] Preferably, the concentrated sodium sulfate solution and ammonium bicarbonate are mixed under stirring conditions to enable the two to react quickly and uniformly to completion.

[0065] Exemplarily, the stirring speed can be 120 - 600 r / min (preferably 400 r / min). The stirring time is preferably not less than 60 min.

[0066] S4: Perform solid-liquid separation on the suspension containing sodium bicarbonate to obtain a first wet-based sodium bicarbonate product and a first mother liquor for alkali removal (i.e., Figure 1 the mother liquor for alkali removal I in

[0067] For reference, the above solid-liquid separation can be carried out in a vacuum filter. After solid-liquid separation, the separated solid can also be washed.

[0068] S5: Concentrate the first mother liquor after alkali removal to obtain a concentrated mother liquor; cool and crystallize the concentrated mother liquor to precipitate part of the sodium bicarbonate, and perform solid-liquid separation on the remaining concentrated mother liquor to obtain a second wet-based sodium bicarbonate product and a second mother liquor after alkali removal (i.e., the mother liquor II after alkali removal in Figure 1 ).

[0069] In this step, the concentration is carried out using a membrane filtration system.

[0070] Exemplarily, the volume of the first mother liquor after alkali removal can be concentrated to 45%, 50%, or 62% etc. of the volume of the added sodium sulfate solution.

[0071] Preferably, the temperature of the concentrated mother liquor after cooling is not higher than 20°C, such as 20°C, 18°C, 15°C, 12°C, 10°C, or 9°C etc.

[0072] By controlling the temperature of the concentrated mother liquor after cooling, on the one hand, the concentration of the mother liquor I after alkali removal can be made close to saturation to facilitate the improvement of the sodium conversion rate. On the other hand, the concentration of ammonium sulfate can be effectively controlled at this concentration to avoid its synchronous precipitation and entrainment into the precipitated sodium bicarbonate during this process.

[0073] S6: Evaporate and crystallize the second mother liquor after alkali removal to obtain an ammonium nitrogen fertilizer mainly containing ammonium sulfate (which can be sold externally).

[0074] In some embodiments, the above method for treating the wastewater from the synthesis of the battery cathode material precursor may further include S7A: drying the first wet-based sodium bicarbonate product and / or the second wet-based sodium bicarbonate product for standby (which can be sold externally).

[0075] In other embodiments, the above method for treating the wastewater from the synthesis of the battery cathode material precursor may further include S7B: further including: roasting and decomposing the first wet-based sodium bicarbonate product and / or the second wet-based sodium bicarbonate product to obtain a sodium carbonate product (which can be sold externally).

[0076] Exemplarily, the temperature of the roasting and decomposition can be 140 - 210°C (such as 140°C, 150°C, 180°C, 200°C, or 210°C etc., preferably 160°C); and / or, the time of the roasting and decomposition can be not less than 30 min (such as 30 min, 60 min, or 90 min etc., preferably 65 min).

[0077] It should be noted that according to actual needs, part of the first sodium bicarbonate wet-based product can be used for step S7A, and the remaining part of the first sodium bicarbonate wet-based product can be used for step S7B; similarly, part of the second sodium bicarbonate wet-based product can be used for step S7A, and the remaining part of the second sodium bicarbonate wet-based product can be used for step S7B. It is also possible to use all of the first sodium bicarbonate wet-based product for step S7A and all of the second sodium bicarbonate wet-based product for step S7B; similarly, it is also possible to use all of the second sodium bicarbonate wet-based product for step S7A and all of the first sodium bicarbonate wet-based product for step S7B.

[0078] Continuing from the above, in the method for treating the synthetic wastewater of the battery cathode material precursor provided in this application, a sodium sulfate solution that can be used for alkali production is directly prepared through impurity removal and membrane concentration. By concentrating the sodium sulfate solution and preparing a suspension containing sodium bicarbonate, soda ash and ammonium nitrogen fertilizer can be further prepared. The wastewater treatment by-products change from sodium sulfate and raw material ammonium bicarbonate to sodium carbonate and ammonium nitrogen fertilizer with higher value, bringing greater economic benefits to the enterprise while solving the dilemma of a large backlog of by-product sodium sulfate by precursor production enterprises, and providing a feasible wastewater treatment method for the lithium / sodium ion battery cathode material precursor production industry.

[0079] In addition, this solution concentrates the wastewater and the alkali-making mother liquor through a two-stage membrane filtration system, and most of the water is separated by the membrane, reducing the energy consumption for subsequent evaporation and crystallization to prepare ammonium nitrogen fertilizer. The alkali-making mother liquor is directly evaporated and crystallized to produce ammonium nitrogen fertilizer mainly containing ammonium sulfate, realizing the full utilization of nitrogen in the raw materials. During the alkali-making process, the first alkali-making mother liquor is further concentrated by using a membrane filtration system, improving the yield of sodium bicarbonate and the conversion rate of sodium sulfate, and the conversion rate of sodium sulfate can reach more than 85%.

[0080] The features and properties of the present invention will be further described in detail below in conjunction with the embodiments.

[0081] Example 1

[0082] Please refer to Figure 1 , this example provides a method for treating the synthetic wastewater of the lithium-ion battery cathode material precursor, including the following steps:

[0083] S1: The synthetic wastewater of the lithium-ion battery cathode material precursor - nickel cobalt manganese hydroxide (the wastewater contains ammonia, sodium sulfate, nickel, cobalt, manganese, etc.) is directly introduced into a rectifying tower for ammonia removal. The evaporated ammonia gas is condensed and absorbed by a condenser at the top of the tower to obtain ammonia water, and the ammonia water is returned to the synthesis process for use; the deammoniated waste liquid at the bottom of the tower is heat-exchanged with the synthetic wastewater, and the precipitate (mainly composed of complexed nickel, cobalt, and manganese precipitated as hydroxides due to ammonia removal) is filtered off to obtain a sodium sulfate solution without ammonia and heavy metal ions.

[0084] S2: Concentrate the obtained sodium sulfate solution using a membrane filtration system to obtain a concentrated sodium sulfate solution (with a sodium sulfate mass concentration of 47.6 g / L). The pure water separated during this process is recycled to the front-end process of precursor synthesis.

[0085] S3: Add the obtained concentrated sodium sulfate solution and ammonium bicarbonate into a reaction kettle to obtain a suspension containing sodium bicarbonate. Among them, the mass ratio of ammonium bicarbonate to sodium sulfate is approximately 1.12:1. The stirring speed is 250 r / min, and the stirring time is 120 min.

[0086] S4: Perform solid-liquid separation on the above suspension of sodium bicarbonate and send it to a vacuum filter for solid-liquid separation and washing to obtain a first wet-based sodium bicarbonate product and a first mother liquor for alkali removal (i.e., mother liquor I for alkali removal).

[0087] S5: Concentrate the above first mother liquor for alkali removal using a membrane filtration system (concentrate the volume of the first mother liquor for alkali removal to 62% of the volume of the added sodium sulfate solution) to obtain a concentrated mother liquor; cool and crystallize the concentrated mother liquor to obtain a concentrated solution from which sodium bicarbonate precipitates; send the remaining concentrated mother liquor to a vacuum filter for solid-liquid separation and washing to obtain a second wet-based sodium bicarbonate product and a second mother liquor for alkali removal (i.e., mother liquor II for alkali removal).

[0088] After cooling, the temperature of the concentrated mother liquor is 10°C, and the ammonium sulfate concentration is approximately 71.4 g / L.

[0089] S6: Perform evaporation crystallization on the above second mother liquor for alkali removal to obtain an ammonium-based nitrogen fertilizer mainly containing ammonium sulfate.

[0090] S7: Roast and decompose the above obtained first wet-based sodium bicarbonate product and second wet-based sodium bicarbonate product (roasting temperature is 200°C, roasting time is 30 min) to prepare sodium carbonate products for sale; or, dry the first wet-based sodium bicarbonate product and second wet-based sodium bicarbonate product directly for sale.

[0091] After calculation, the conversion rate of sodium sulfate corresponding to this method is approximately 88%.

[0092] Example 2

[0093] Please refer to Figure 2 , this example provides a method for treating wastewater from the synthesis of a precursor for a lithium-ion battery cathode material, including the following steps:

[0094] S1: Add the synthetic wastewater of the lithium-ion battery cathode material precursor, iron phosphate (the wastewater contains sodium sulfate and sodium phosphate), to an appropriate amount of calcium sulfate suspension so that sodium phosphate reacts with calcium sulfate to form calcium phosphate precipitate, and filter to remove the calcium phosphate precipitate; then add an appropriate amount of sodium carbonate solution to precipitate the excess calcium ions as calcium carbonate, and then filter to remove the calcium carbonate precipitate to obtain a sodium sulfate solution with phosphorus removed.

[0095] S2: Concentrate the obtained sodium sulfate solution using a membrane filtration system to obtain a concentrated sodium sulfate solution (the mass concentration of sodium sulfate is 35.5 g / L), and the pure water separated in this process is recycled to the front-end process of precursor synthesis.

[0096] S3: Add the obtained concentrated sodium sulfate solution and ammonium bicarbonate to a reaction kettle to obtain a suspension containing sodium bicarbonate. Among them, the mass ratio of ammonium bicarbonate to sodium sulfate is about 1.08:1. The stirring speed is 600 r / min, and the stirring time is 60 min.

[0097] S4: Perform solid-liquid separation on the above suspension of sodium bicarbonate and send it to a vacuum filter for solid-liquid separation and washing to obtain a first wet-based sodium bicarbonate product and a first mother liquor for alkali removal (i.e., mother liquor I for alkali removal).

[0098] S5: Concentrate the above first mother liquor for alkali removal using a membrane filtration system (concentrate the volume of the first mother liquor for alkali removal to 45% of the volume of the added sodium sulfate solution) to obtain a concentrated mother liquor; cool and crystallize the concentrated mother liquor to obtain a concentrated solution with precipitated sodium bicarbonate; send the remaining concentrated mother liquor to a vacuum filter for solid-liquid separation and washing to obtain a second wet-based sodium bicarbonate product and a second mother liquor for alkali removal (i.e., mother liquor II for alkali removal).

[0099] After cooling, the temperature of the concentrated mother liquor is 20 °C, and the ammonium sulfate concentration is approximately 73.4 g / L.

[0100] S6: Evaporate and crystallize the above second mother liquor for alkali removal to obtain an ammonium nitrogen fertilizer mainly containing ammonium sulfate.

[0101] S7: Roast and decompose the above obtained first wet-based sodium bicarbonate product and second wet-based sodium bicarbonate product (the roasting temperature is 190 °C, and the roasting time is 40 min) to prepare sodium carbonate products for sale; or, dry the first wet-based sodium bicarbonate product and second wet-based sodium bicarbonate product directly for sale.

[0102] Calculated, the conversion rate of sodium sulfate corresponding to this method is approximately 87%.

[0103] Example 3

[0104] Please refer to Figure 1, this embodiment provides a method for treating wastewater from the synthesis of a sodium-ion battery cathode material precursor, which includes the following steps:

[0105] S1: The synthesis wastewater of the sodium-ion battery cathode material precursor - nickel-iron-manganese hydroxide (the wastewater contains ammonia, sodium sulfate, nickel, iron, manganese, etc.) is directly introduced into a distillation column for ammonia removal. The evaporated ammonia is condensed and absorbed by a condenser at the top of the column to obtain ammonia water, which is returned to the synthesis process for use; the deammoniated waste liquid at the bottom of the column is heat-exchanged with the synthesis wastewater, and then filtered to remove the precipitate (mainly composed of complexed nickel, iron, and manganese precipitating as hydroxides due to ammonia removal), obtaining a sodium sulfate solution without ammonia and heavy metal ions.

[0106] S2: The obtained sodium sulfate solution is concentrated using a membrane filtration system to obtain a sodium sulfate concentrate (the mass concentration of sodium sulfate is 30.4 g / L). The pure water separated in this process is recycled to the front-end process of precursor synthesis.

[0107] S3: The obtained sodium sulfate concentrate and ammonium bicarbonate are added into a reaction kettle together to obtain a suspension containing sodium bicarbonate. Among them, the mass ratio of ammonium bicarbonate to sodium sulfate is about 1.10:1. The stirring speed is 150 r / min, and the stirring time is 180 min.

[0108] S4: The above suspension of sodium bicarbonate is subjected to solid-liquid separation and sent to a vacuum filter for solid-liquid separation and washing to obtain a first wet-based sodium bicarbonate product and a first mother liquor for alkali removal (i.e., mother liquor I for alkali removal).

[0109] S5: The above first mother liquor for alkali removal is concentrated using a membrane filtration system (concentrating the volume of the first mother liquor for alkali removal to 50% of the volume of the added sodium sulfate solution) to obtain a concentrated mother liquor; the concentrated mother liquor is cooled and crystallized to obtain a concentrated solution with precipitated sodium bicarbonate; the remaining concentrated mother liquor is sent to a vacuum filter for solid-liquid separation and washing to obtain a second wet-based sodium bicarbonate product and a second mother liquor for alkali removal (i.e., mother liquor II for alkali removal).

[0110] After cooling, the temperature of the concentrated mother liquor is 9 °C, and the concentration of ammonium sulfate is approximately 56.5 g / L.

[0111] S6: The above second mother liquor for alkali removal is subjected to evaporation crystallization to obtain an ammonium nitrogen fertilizer mainly containing ammonium sulfate.

[0112] S7: The above first wet-based sodium bicarbonate product and second wet-based sodium bicarbonate product are roasted and decomposed (the roasting temperature is 175 °C, and the roasting time is 50 min) to prepare sodium carbonate products for sale; or, the first wet-based sodium bicarbonate product and second wet-based sodium bicarbonate product are dried and sold directly.

[0113] After calculation, the conversion rate of sodium sulfate corresponding to this method is approximately 85%.

[0114] In summary, the method for treating the wastewater generated in the synthesis of the battery cathode material precursor provided by the present application can effectively utilize the by-product sodium sulfate generated in the synthesis process of the battery cathode material precursor downstream on the premise of improving the conversion rate of sodium sulfate, and at the same time avoid the generation of solid waste, thereby avoiding the problems of environmental pollution and damage.

[0115] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for treating synthetic wastewater of a battery cathode material precursor, characterized in that, it comprises the following steps: S1: Remove impurities from the synthetic wastewater containing sodium sulfate generated during the synthesis of the battery cathode material precursor to obtain a sodium sulfate solution; S2: Concentrate the sodium sulfate solution to obtain a concentrated sodium sulfate solution; S3: Prepare the concentrated sodium sulfate solution into a suspension containing sodium bicarbonate; S4: Perform solid-liquid separation on the suspension containing sodium bicarbonate to obtain a first wet-based sodium bicarbonate product and a first alkali-removing mother liquor; S5: Concentrate the first alkali-removing mother liquor to obtain a concentrated mother liquor; cool and crystallize the concentrated mother liquor to precipitate part of the sodium bicarbonate, and perform solid-liquid separation on the remaining concentrated mother liquor to obtain a second wet-based sodium bicarbonate product and a second alkali-removing mother liquor; S6: Perform evaporation crystallization on the second alkali-removing mother liquor to obtain an ammonium nitrogen fertilizer mainly containing ammonium sulfate; When the battery cathode material precursor is a ternary cathode material precursor and / or a multi-component cathode material precursor, S1 includes: removing ammonia from the synthetic wastewater containing ammonia and sodium sulfate generated during the synthesis of the battery cathode material precursor to obtain a deammoniated waste liquid; removing metal hydroxide waste residues from the deammoniated waste liquid to obtain a sodium sulfate solution without ammonia and heavy metal ions; When the battery cathode material precursor is a lithium iron phosphate cathode material precursor, S1 includes: removing phosphate from the synthetic wastewater containing phosphate and sodium sulfate generated during the synthesis of the battery cathode material precursor to obtain a phosphate-removed sodium sulfate solution; The concentrated sodium sulfate solution obtained in S2 is a nearly saturated sodium sulfate solution or a saturated sodium sulfate solution; In S3, the suspension containing sodium bicarbonate is obtained by mixing the concentrated sodium sulfate solution with ammonium bicarbonate; In S5, the temperature of the concentrated mother liquor after cooling is not higher than 20°C.

2. The method for treating synthetic wastewater of a battery cathode material precursor according to claim 1, characterized in that, it further includes: Condensing and absorbing the ammonia gas evaporated during the ammonia removal process to prepare ammonia water for returning to the synthesis process for use.

3. The method for treating synthetic wastewater of a battery cathode material precursor according to claim 1, characterized in that, The phosphate-removed sodium sulfate solution is obtained by the following method: Mix the synthetic wastewater to be treated with a calcium sulfate suspension, and then remove the obtained calcium phosphate precipitate; mix the solution containing calcium ions remaining after removing the calcium phosphate precipitate with a sodium carbonate solution, and then remove the obtained calcium carbonate precipitate to obtain a phosphate-removed sodium sulfate solution.

4. The method for treating synthetic wastewater of a battery cathode material precursor according to claim 1, characterized in that, The pure water obtained during the concentration of the sodium sulfate solution is recycled to the front-end process of precursor synthesis.

5. The method for treating synthetic wastewater of a battery cathode material precursor according to claim 1, characterized in that, The weight ratio of the concentrated sodium sulfate solution to the ammonium bicarbonate is 1-1.2:

1.

6. The method for treating synthetic wastewater of a battery cathode material precursor according to claim 1, characterized in that, The concentrated sodium sulfate solution and the ammonium bicarbonate are mixed under stirring conditions.

7. The method for treating the wastewater from the synthesis of the cathode material precursor of a battery according to claim 6, characterized in that, the stirring speed is 120 - 600 r / min, and / or the stirring time is not less than 60 min.

8. The method for treating the wastewater from the synthesis of the cathode material precursor of a battery according to any one of claims 1 - 3, characterized in that, it further includes S7A: drying the first sodium bicarbonate wet-based product and / or the second sodium bicarbonate wet-based product for standby.

9. The method for treating the wastewater from the synthesis of the cathode material precursor of a battery according to any one of claims 1 - 3, characterized in that, it further includes S7B: roasting and decomposing the first sodium bicarbonate wet-based product and / or the second sodium bicarbonate wet-based product to obtain a sodium carbonate product.

10. The method for treating the wastewater from the synthesis of the cathode material precursor of a battery according to claim 9, characterized in that, the temperature for roasting and decomposing is 140 - 210 °C; and / or the time for roasting and decomposing is not less than 30 min.

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