WO2024174341A1 - Method for treating synthesis wastewater of battery positive electrode material precursor - Google Patents

Abstract

The present application relates to the technical field of wastewater treatment, and discloses a method for treating synthesis wastewater of a battery positive electrode material precursor. The method comprises: performing impurity removal and concentration on synthesis wastewater generated in the synthesis process of a battery positive electrode material precursor, preparing an obtained concentrated solution into a suspension, and performing solid-liquid separation to obtain first alkali removal mother liquor; removing sodium bicarbonate in the first alkali removal mother liquor to obtain second alkali removal mother liquor; and evaporating and crystallizing the second alkali removal mother liquor to obtain an ammonium nitrogen fertilizer mainly containing ammonium sulfate. The method can increase the conversion rate of sodium sulfate, enable sodium sulfate generated in the synthesis process of the battery positive electrode material precursor to be effectively utilized, and avoid the generation of solid waste.

Description

A method for treating battery positive electrode material precursor synthesis wastewater Technical Field

The present application relates to the technical field of battery positive electrode material precursor wastewater treatment, and in particular, to a method for treating battery positive electrode material precursor synthesis wastewater.

Background Art

In the production process of lithium/sodium-ion battery positive electrode material precursors, a large amount of wastewater containing sodium sulfate is generated in the precipitation process, and the wastewater of ternary and multi-material precursors also contains ammonia.

According to the chemical reaction formula, about 1.53 tons of sodium sulfate will be produced for every ton of lithium/sodium-ion battery cathode material ternary and multi-element battery cathode material precursors, and about 1.41 tons of sodium sulfate will be produced for every ton of lithium iron phosphate precursors for lithium-ion battery cathode materials. With the rapid development of the electronics industry and the new energy vehicle industry, my country's ternary precursor shipments will reach 618,000 tons in 2021, and iron phosphate shipments will be about 330,000 tons, which means that about 1.41 million tons of sodium sulfate will be produced in 2021. It is predicted that by 2025, the total amount of sodium sulfate produced by the precursor industry will exceed 5 million tons.

Some existing technologies for treating wastewater generated during the production of precursors for positive electrode materials for lithium/sodium ion batteries have problems such as high evaporation energy consumption and large accumulation of byproduct sodium sulfate; some existing technologies convert sodium sulfate in iron phosphate wastewater into byproduct phosphogypsum, resulting in excessive solid waste, which is neither economical nor environmentally friendly. In addition, the conversion rate of sodium sulfate corresponding to the precursor synthesis wastewater treatment method provided in the prior art is relatively low, at about 75%.

In view of this, this application is hereby filed.

Summary of the invention

The purpose of this application is to provide a method for treating wastewater from the synthesis of anode material precursors for batteries, which can improve the conversion rate of sodium sulfate and The sodium sulfate by-product produced in the process is effectively utilized downstream, while also avoiding the generation of solid waste, thereby avoiding pollution and environmental damage.

This application can be implemented as follows:

The present application provides a method for treating wastewater from synthesis of a positive electrode material precursor of a battery, comprising the following steps:

S1: removing impurities from synthetic wastewater containing sodium sulfate generated during the synthesis of a battery positive electrode material precursor to obtain a sodium sulfate solution;

S2: concentrating the sodium sulfate solution to obtain a sodium sulfate concentrate;

S3: preparing a sodium bicarbonate-containing suspension from the sodium sulfate concentrate;

S4: performing solid-liquid separation on the sodium bicarbonate-containing suspension to obtain a first sodium bicarbonate wet-base product and a first de-alkali mother liquor;

S5: concentrating the first de-alkali mother liquor to obtain a concentrated mother liquor; cooling the concentrated mother liquor for crystallization to precipitate a portion of sodium bicarbonate, and then performing solid-liquid separation to obtain a second sodium bicarbonate wet-base product and a second de-alkali mother liquor;

S6: Evaporating and crystallizing the second de-alkali mother liquor to obtain an ammonium nitrogen fertilizer mainly containing ammonium sulfate.

In an optional embodiment, when the battery positive electrode material precursor is a ternary positive electrode material precursor and/or a multi-element positive electrode material precursor, S1 includes:

The synthetic wastewater containing ammonia and sodium sulfate generated in the synthesis process of the battery positive electrode material precursor is deammonified to obtain a deammonified waste liquid; the metal hydroxide waste residue in the deammonified waste liquid is removed to obtain a sodium sulfate solution free of ammonia and heavy metal ions.

In an optional embodiment, the method further includes: condensing and absorbing ammonia gas evaporated during the ammonia removal process to produce ammonia water for returning to the synthesis step.

In an optional embodiment, when the battery positive electrode material precursor is a lithium iron phosphate positive electrode material precursor, S1 includes: removing phosphate from synthetic wastewater containing phosphate and sodium sulfate generated during the synthesis of the battery positive electrode material precursor to obtain a dephosphorized sodium sulfate solution.

In an optional embodiment, the dephosphorized sodium sulfate solution is obtained by the following method:

The synthetic wastewater to be treated is mixed with a calcium sulfate suspension, and then the resulting calcium phosphate precipitate is removed; the calcium ion-containing solution remaining after the calcium phosphate precipitate is removed is mixed with a sodium carbonate solution, and then the resulting calcium carbonate precipitate is removed to obtain a dephosphorized sodium sulfate solution.

In an optional embodiment, the mass concentration of sodium sulfate in the sodium sulfate concentrate obtained in S2 is not less than 30 g/L.

In an optional embodiment, the sodium sulfate concentrate is a nearly saturated sodium sulfate solution or a saturated sodium sulfate solution.

In an optional embodiment, the pure water obtained in the process of concentrating the sodium sulfate solution is recycled to the front-end process of precursor synthesis.

In an optional embodiment, in S3, the suspension containing sodium bicarbonate is obtained by mixing concentrated sodium sulfate with ammonium bicarbonate, or the suspension containing sodium bicarbonate is obtained by mixing concentrated sodium sulfate with aqueous ammonia and carbon dioxide.

In an optional embodiment, the weight ratio of sodium sulfate concentrate to ammonium bicarbonate is (1-1.2):1.

In an alternative embodiment, the sodium sulfate concentrate and the ammonium bicarbonate are mixed under stirring conditions.

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

In an optional embodiment, in S5, the temperature of the concentrated mother liquor after cooling is not higher than 20°C.

In an optional embodiment, the method further includes S7A: drying the first sodium bicarbonate wet-based product and/or the second sodium bicarbonate wet-based product for standby use.

In an optional embodiment, the method 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.

In an optional embodiment, the temperature of calcination and decomposition is 140-210° C.; and/or the time of calcination and decomposition is not less than 30 min.

The beneficial effects of this application include:

The present invention directly prepares sodium sulfate concentrate that can be used for alkali production by removing impurities and concentrating synthetic wastewater containing sodium sulfate generated during the synthesis of battery positive electrode material precursors; The sodium concentrate is made into a suspension containing sodium bicarbonate to further prepare soda ash and ammonium nitrogen fertilizer, thereby changing the by-products of wastewater treatment from sodium sulfate and raw material ammonium bicarbonate to more valuable sodium carbonate and ammonium nitrogen fertilizer. This not only solves the dilemma of precursor production companies hoarding large amounts of by-product sodium sulfate, but also brings greater economic benefits to the companies, and provides a feasible wastewater treatment method for the lithium/sodium ion battery positive electrode material precursor production industry.

In addition, the scheme uses two concentration processes to separate most of the water, reducing the energy consumption of subsequent evaporation and crystallization to prepare ammonium nitrogen fertilizer; the de-alkali mother liquor is directly evaporated and crystallized to produce ammonium nitrogen fertilizer mainly containing ammonium sulfate, realizing full utilization of nitrogen in the raw materials. In the alkali production process, the first de-alkali mother liquor is further concentrated by using a membrane filtration system, thereby increasing 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

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

FIG1 is a first process flow chart of a method for treating wastewater from synthesis of anode material precursors of a battery provided in the present application;

FIG. 2 is a second process flow chart of the method for treating battery positive electrode material precursor synthesis wastewater provided in the present application.

DETAILED DESCRIPTION

In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

The following is a detailed description of the method for treating battery positive electrode material precursor synthesis wastewater provided in this application.

Please refer to FIG. 1 and FIG. 2 together. The present application proposes a method for treating wastewater from synthesis of a positive electrode material precursor of a battery, comprising the following steps:

S1: removing impurities from synthetic wastewater containing sodium sulfate generated during the synthesis of battery positive electrode material precursors to obtain a sodium sulfate solution.

The above-mentioned battery positive electrode material can be a lithium ion battery positive electrode material or a sodium ion battery positive electrode material.

The positive electrode material precursor may be a ternary positive electrode material precursor or a multi-element positive electrode material precursor, or may be a lithium iron phosphate positive electrode material precursor (such as iron phosphate).

In some optional embodiments, as shown in FIG1 , the battery positive electrode material precursor is a ternary positive electrode material precursor and/or a multi-element positive electrode material precursor, and accordingly, S1 includes:

The synthetic wastewater containing ammonia and sodium sulfate generated in the synthesis process of the battery positive electrode material precursor is deammonified to obtain a deammonified waste liquid; the metal hydroxide waste residue in the deammonified waste liquid is removed to obtain a sodium sulfate solution free of ammonia and heavy metal ions.

The above process can be carried out in a distillation tower.

Furthermore, after the ammonia is removed, the ammonia gas evaporated during the ammonia removal process can be condensed and absorbed (for example, condensed and absorbed by the top condenser of the distillation tower) to produce ammonia water for return to the synthesis process.

The deammoniation waste liquid after ammonia removal can be discharged from the bottom of the distillation tower, filtered after heat exchange, and the metal hydroxide waste residue precipitated by deammoniation (wherein the metal may include nickel, cobalt, manganese and/or iron, etc.) is removed to obtain a sodium sulfate solution for deammoniation and removal of heavy metal ions.

It should be noted that the specific molecular formula of the above-mentioned ternary positive electrode material precursor and/or multi-element positive electrode material precursor can be referred to the relevant existing technology, and will not be expanded or limited one by one here.

In some other optional embodiments, as shown in FIG. 2 , the positive electrode material precursor of the battery is a positive electrode material precursor of lithium iron phosphate (the precursor is for the solution of using sodium phosphate to precipitate iron phosphate), and the corresponding The S1 includes:

The phosphate radicals in the synthetic wastewater containing phosphate radicals and sodium sulfate generated in the synthesis process of the battery positive electrode material precursor are removed to obtain a dephosphorized sodium sulfate solution.

Specifically, the above-mentioned sodium sulfate solution for dephosphorization can be obtained by the following method:

The synthetic wastewater to be treated is mixed with a calcium sulfate suspension, and the excess phosphate in the wastewater is precipitated in the form of calcium phosphate, and then the obtained calcium phosphate precipitate is removed (for example, by filtering). The solution containing calcium ions remaining after the calcium phosphate precipitate is removed is mixed with a sodium carbonate solution to precipitate the excess calcium ions in the form of calcium carbonate, and then the obtained calcium carbonate precipitate is removed (for example, by filtering) to obtain a dephosphorized sodium sulfate solution.

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

S2: Concentrate the sodium sulfate solution to obtain a sodium sulfate concentrate (which can be used to make alkali).

This step can be performed by, for example but not by way of limitation, using a membrane filtration system.

For reference, the mass concentration of sodium sulfate in the obtained sodium sulfate concentrate is not less than 30 g/L, such as 30.4 g/L, 32 g/L, 35.5 g/L or 47.6 g/L.

Preferably, the sodium sulfate concentrate is a nearly saturated sodium sulfate solution or a saturated sodium sulfate solution, so as to improve the conversion rate of sodium sulfate.

Furthermore, the pure water obtained in the process of concentrating the sodium sulfate solution can be recycled to the front-end process of precursor synthesis.

S3: preparing a sodium bicarbonate-containing suspension from the sodium sulfate concentrate.

This step can be carried out in a reactor.

In some embodiments, the suspension containing sodium bicarbonate can be obtained by mixing sodium sulfate concentrate with ammonium bicarbonate. In other embodiments, the suspension containing sodium bicarbonate can also be obtained by mixing sodium sulfate concentrate with ammonium bicarbonate. It is obtained by mixing sodium persulfate concentrate with ammonia water and carbon dioxide.

For reference, the weight ratio of sodium sulfate concentrate 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, or any other value within the range of (1-1.2):1.

Preferably, the sodium sulfate concentrate and the ammonium bicarbonate are mixed under stirring conditions so that the two react quickly and evenly.

For example, the stirring speed may be 120-600 r/min (preferably 400 r/min). The stirring time is preferably not less than 60 min.

S4: The sodium bicarbonate-containing suspension is subjected to solid-liquid separation to obtain a first sodium bicarbonate wet-base product and a first de-alkali mother liquor (i.e., the de-alkali mother liquor I in FIG. 1 ).

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

S5: Concentrating the first de-alkali mother liquor to obtain a concentrated mother liquor; cooling the concentrated mother liquor for crystallization to precipitate a portion of sodium bicarbonate, and then performing solid-liquid separation to obtain a second sodium bicarbonate wet-base product and a second de-alkali mother liquor (i.e., the de-alkali mother liquor II in FIG. 1 ).

In this step, concentration is carried out using a membrane filtration system.

For example, the volume of the first de-alkali mother liquor can be concentrated to 45%, 50% or 62% of the volume of the added sodium sulfate solution.

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.

By controlling the temperature of the concentrated mother liquor after cooling, on the one hand, the concentration of the de-alkali mother liquor I can be made close to saturation, so as to improve the conversion rate of sodium. On the other hand, the concentration of ammonium sulfate can be effectively controlled at this concentration to avoid its simultaneous precipitation in the process and being brought into the precipitated sodium bicarbonate.

S6: Evaporating and crystallizing the second alkali-removed mother liquor to obtain an ammonium nitrogen fertilizer mainly containing ammonium sulfate (which can be sold externally).

In some embodiments, the above-mentioned battery positive electrode material precursor synthesis wastewater treatment method can also The method comprises the steps of: drying the first sodium bicarbonate wet-based product and/or the second sodium bicarbonate wet-based product for standby use (the product can be sold externally).

In other embodiments, the above-mentioned battery positive electrode material precursor synthesis wastewater treatment method may also include S7B: also including: 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 (which can be sold externally).

Exemplarily, the calcination decomposition temperature 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 calcination decomposition time can be not less than 30 min (such as 30 min, 60 min or 90 min, etc., preferably 65 min).

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.

As mentioned above, in the method for synthesizing wastewater of battery positive electrode material precursor provided in the present application, a sodium sulfate solution that can be used for alkali production is directly prepared by impurity removal and membrane concentration, and soda ash and ammonium nitrogen fertilizer can be further prepared by concentrating the sodium sulfate solution and preparing it into a suspension containing sodium bicarbonate. The by-products of wastewater treatment are changed from sodium sulfate and raw material ammonium bicarbonate to more valuable sodium carbonate and ammonium nitrogen fertilizer, which not only solves the dilemma of precursor production enterprises hoarding a large amount of by-product sodium sulfate, but also brings greater economic benefits to the enterprises, and provides a feasible wastewater treatment method for the lithium/sodium ion battery positive electrode material precursor production industry.

In addition, the scheme uses two membrane filtration systems to concentrate wastewater and alkali mother liquor, and most of the water is separated by the membrane, which reduces the energy consumption of subsequent evaporation and crystallization to prepare ammonium nitrogen fertilizer. The de-alkali 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. In the alkali production process, the first de-alkali mother liquor is further concentrated by using a membrane filtration system, which improves the carbonation rate. The yield of sodium hydrogen and the conversion rate of sodium sulfate can reach more than 85%.

The features and performance of the present application are further described in detail below in conjunction with the embodiments.

Example 1

Referring to FIG. 1 , this embodiment provides a method for treating wastewater from synthesis of positive electrode material precursors for lithium-ion batteries, comprising the following steps:

S1: The synthetic wastewater (wastewater containing ammonia, sodium sulfate, nickel, cobalt and manganese, etc.) of the precursor of the positive electrode material of lithium-ion batteries, namely nickel-cobalt-manganese hydroxide, is directly introduced into a distillation tower for ammonia removal. The evaporated ammonia gas is condensed and absorbed by the top condenser to obtain ammonia water, which is returned to the synthesis process for use. The deammoniation waste liquid at the bottom of the tower is heat exchanged with the synthetic wastewater, and then filtered to remove the precipitate (mainly composed of complexed nickel, cobalt and manganese precipitated as hydroxide due to deammoniation) to obtain a sodium sulfate solution free of ammonia and heavy metal ions.

S2: The sodium sulfate solution obtained above is concentrated using a membrane filtration system to obtain a sodium sulfate concentrate (sodium sulfate mass concentration is 47.6 g/L). The pure water separated in this process is reused in the front-end process of precursor synthesis.

S3: Add the obtained sodium sulfate concentrate and ammonium bicarbonate into the reaction kettle to obtain a suspension containing sodium bicarbonate, wherein the mass ratio of the sodium sulfate concentrate to the ammonium bicarbonate is about 1.12:1. The stirring speed is 250 r/min and the stirring time is 120 min.

S4: The 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 sodium bicarbonate wet-base product and a first de-alkali mother liquor (i.e., de-alkali mother liquor I).

S5: Concentrating the first de-alkali mother liquor by using a membrane filtration system (concentrating the volume of the first de-alkali mother liquor to 62% of the volume of the added sodium sulfate solution) to obtain a concentrated mother liquor; cooling the concentrated mother liquor for crystallization to obtain a concentrated solution in which sodium bicarbonate is precipitated; and then sending it to a vacuum filter for solid-liquid separation and washing to obtain a second sodium bicarbonate wet-based product and a second de-alkali mother liquor (i.e., de-alkali mother liquor II).

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

S6: Evaporating and crystallizing the second alkali-removed mother liquor to obtain an ammonium nitrogen fertilizer mainly containing ammonium sulfate.

S7: roasting and decomposing the first sodium bicarbonate wet-based product and the second sodium bicarbonate wet-based product obtained above (roasting temperature is 200° C., roasting time is 30 min) to prepare sodium carbonate products and then sell them; or, drying the first sodium bicarbonate wet-based product and the second sodium bicarbonate wet-based product and directly selling them.

According to calculation, the conversion rate of sodium sulfate corresponding to this method is about 88%.

Example 2

Referring to FIG. 2 , this embodiment provides a method for treating wastewater from synthesis of positive electrode material precursors for lithium-ion batteries, comprising the following steps:

S1: Add an appropriate amount of calcium sulfate suspension to the synthetic wastewater (wastewater containing sodium sulfate and sodium phosphate) of the precursor of the positive electrode material of lithium-ion batteries, so that the sodium phosphate and calcium sulfate react to form a calcium phosphate precipitate, and filter out the calcium phosphate precipitate; then add an appropriate amount of sodium carbonate solution to precipitate excess calcium ions into calcium carbonate, and then filter out the calcium carbonate precipitate to obtain a dephosphorized sodium sulfate solution.

S2: The sodium sulfate solution obtained above is concentrated using a membrane filtration system to obtain a sodium sulfate concentrate (sodium sulfate mass concentration is 35.5 g/L). The pure water separated in this process is reused in the front-end process of precursor synthesis.

S3: Add the obtained sodium sulfate concentrate and ammonium bicarbonate into the reaction kettle to obtain a suspension containing sodium bicarbonate, wherein the mass ratio of the sodium sulfate concentrate to the ammonium bicarbonate is about 1.08:1. The stirring speed is 600 r/min and the stirring time is 60 min.

S4: The 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 sodium bicarbonate wet-base product and a first de-alkali mother liquor (i.e., de-alkali mother liquor I).

S5: Concentrating the first de-alkali mother liquor by using a membrane filtration system (concentrating the volume of the first de-alkali mother liquor to 45% of the volume of the added sodium sulfate solution) to obtain a concentrated mother liquor; cooling the concentrated mother liquor for crystallization to obtain a concentrated solution in which sodium bicarbonate is precipitated; and then sending it to a vacuum filter for solid-liquid separation and washing to obtain a second sodium bicarbonate wet-based product and a second de-alkali mother liquor (i.e., de-alkali mother liquor II).

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

S6: Evaporating and crystallizing the second alkali-removed mother liquor to obtain an ammonium nitrogen fertilizer mainly containing ammonium sulfate.

S7: roasting and decomposing the first sodium bicarbonate wet-based product and the second sodium bicarbonate wet-based product obtained above (roasting temperature is 190° C., roasting time is 40 min) to prepare sodium carbonate products and then sell them; or, drying the first sodium bicarbonate wet-based product and the second sodium bicarbonate wet-based product and directly selling them.

According to calculation, the conversion rate of sodium sulfate corresponding to this method is about 87%.

Example 3

Referring to FIG. 1 , this embodiment provides a method for treating sodium ion battery positive electrode material precursor synthesis wastewater, comprising the following steps:

S1: The synthetic wastewater (wastewater containing ammonia, sodium sulfate, nickel, iron and manganese, etc.) of the precursor of the positive electrode material of sodium ion battery - nickel iron manganese hydroxide is directly introduced into the distillation tower for ammonia removal. The evaporated ammonia gas is condensed and absorbed by the top condenser to obtain ammonia water, which is returned to the synthesis process for use. The deammoniation waste liquid at the bottom of the tower is heat exchanged with the synthetic wastewater, and then filtered to remove the precipitate (mainly composed of complexed nickel, iron and manganese precipitated as hydroxide due to deammoniation) to obtain a sodium sulfate solution free of ammonia and heavy metal ions.

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

S3: Add the obtained sodium sulfate concentrate and ammonium bicarbonate into the reaction kettle to obtain a suspension containing sodium bicarbonate. The mass ratio of the sodium sulfate concentrate to the ammonium bicarbonate is about 1.10:1. The stirring speed is 150r/min and the stirring time is 180min.

S4: The 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 sodium bicarbonate wet-base product and a first de-alkali mother liquor (i.e., de-alkali mother liquor I).

S5: The first de-alkali mother liquor is concentrated by a membrane filtration system (the volume of the first de-alkali mother liquor is concentrated 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 in which sodium bicarbonate is precipitated; and then the concentrated solution is sent to a vacuum filter for solidification. The mixture is separated and washed to obtain a second sodium bicarbonate wet-base product and a second de-alkali mother liquor (i.e., de-alkali mother liquor II).

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

S6: Evaporating and crystallizing the second alkali-removed mother liquor to obtain an ammonium nitrogen fertilizer mainly containing ammonium sulfate.

S7: roasting and decomposing the first sodium bicarbonate wet-based product and the second sodium bicarbonate wet-based product obtained above (roasting temperature is 175° C., roasting time is 50 min) to prepare sodium carbonate products and then sell them; or, drying the first sodium bicarbonate wet-based product and the second sodium bicarbonate wet-based product and directly selling them.

According to calculation, the conversion rate of sodium sulfate corresponding to this method is about 85%.

In summary, the method for treating battery positive electrode material precursor synthesis wastewater provided in the present application can, under the premise of improving the sodium sulfate conversion rate, enable the sodium sulfate produced as a byproduct in the synthesis process of battery positive electrode material precursor to be effectively utilized downstream, while also avoiding the generation of solid waste, thereby avoiding pollution and environmental damage.

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

Claims (10)

A method for treating wastewater from synthesis of a battery positive electrode material precursor, characterized in that it comprises the following steps: S1: removing impurities from synthetic wastewater containing sodium sulfate generated during the synthesis of a battery positive electrode material precursor to obtain a sodium sulfate solution; S2: concentrating the sodium sulfate solution to obtain a sodium sulfate concentrate; S3: preparing the sodium sulfate concentrate into a suspension containing sodium bicarbonate; S4: performing solid-liquid separation on the sodium bicarbonate-containing suspension to obtain a first sodium bicarbonate wet-base product and a first de-alkali mother liquor; S5: concentrating the first de-alkali mother liquor to obtain a concentrated mother liquor; cooling the concentrated mother liquor to crystallize to precipitate a portion of sodium bicarbonate, and then performing solid-liquid separation to obtain a second sodium bicarbonate wet-base product and a second de-alkali mother liquor; S6: Evaporating and crystallizing the second de-alkali mother liquor to obtain an ammonium nitrogen fertilizer mainly containing ammonium sulfate. The method for treating battery positive electrode material precursor synthesis wastewater according to claim 1, characterized in that when the battery positive electrode material precursor is a ternary positive electrode material precursor and/or a multi-element positive electrode material precursor, S1 comprises: The synthetic wastewater containing ammonia and sodium sulfate generated during the synthesis of the battery positive electrode material precursor is subjected to ammonia removal to obtain a deammonified waste liquid; the metal hydroxide waste residue in the deammonified waste liquid is removed to obtain a sodium sulfate solution free of ammonia and heavy metal ions. The method for treating wastewater from synthesis of battery positive electrode material precursors according to claim 2 is characterized in that it also includes: condensing and absorbing the ammonia gas evaporated during the ammonia removal process to produce ammonia water for return to the synthesis process. The method for treating wastewater from synthesis of a positive electrode material precursor of a battery according to claim 1, wherein when the positive electrode material precursor of the battery is a lithium iron phosphate positive electrode material precursor, S1 comprises In summary: the phosphate-containing synthetic wastewater generated during the synthesis of the battery positive electrode material precursor and sodium sulfate is subjected to phosphate removal to obtain a dephosphorized sodium sulfate solution. The method for treating wastewater from synthesis of anode material precursors of a battery according to claim 4, characterized in that the dephosphorized sodium sulfate solution is obtained by the following method: The synthetic wastewater to be treated is mixed with a calcium sulfate suspension, and then the resulting calcium phosphate precipitate is removed; the calcium ion-containing solution remaining after the calcium phosphate precipitate is removed is mixed with a sodium carbonate solution, and then the resulting calcium carbonate precipitate is removed to obtain a dephosphorized sodium sulfate solution. The method for treating battery positive electrode material precursor synthesis wastewater according to any one of claims 1 to 5, characterized in that the mass concentration of sodium sulfate in the sodium sulfate concentrate obtained in S2 is not less than 30 g/L; Preferably, the sodium sulfate concentrate is a saturated sodium sulfate solution; Preferably, the pure water obtained in the process of concentrating the sodium sulfate solution is recycled to the front-end process of precursor synthesis. The method for treating wastewater from synthesis of a positive electrode material precursor for a battery according to claim 6, characterized in that, in S3, the suspension containing sodium bicarbonate is obtained by mixing a concentrated sodium sulfate solution with ammonium bicarbonate, or the suspension containing sodium bicarbonate is obtained by mixing a concentrated sodium sulfate solution with aqueous ammonia and carbon dioxide; Preferably, the weight ratio of the sodium sulfate concentrate to the ammonium bicarbonate is (1-1.2):1; Preferably, the sodium sulfate concentrate and the ammonium bicarbonate are mixed under stirring conditions; Preferably, the stirring speed is 120-600 r/min, and/or the stirring time is not less than 60 min. The method for treating battery positive electrode material precursor synthesis wastewater according to any one of claims 1 to 5, characterized in that, in S5, the temperature of the concentrated mother liquor after cooling is not higher than 20°C. The method for treating battery positive electrode material precursor synthesis wastewater according to any one of claims 1 to 5, characterized in that it also includes S7A: drying the first sodium bicarbonate wet-based product and/or the second sodium bicarbonate wet-based product for standby use. Treatment of battery positive electrode material precursor synthesis wastewater according to any one of claims 1 to 5 The method is characterized in that it further comprises 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; Preferably, the calcination and decomposition temperature is 140-210° C.; and/or the calcination and decomposition time is not less than 30 min.