Method for treating battery discharge wastewater

Abstract

The invention discloses a treatment method of battery discharge wastewater. The treatment method comprises the following steps: S1, filter pressing; s2, performing Fenton oxidation; s3, removing fluorine and impurities; s4, adsorption; s5, evaporative crystallization; and S6, depositing lithium. Through the treatment process of filter pressing, Fenton oxidation, fluorine and impurity removal, adsorption, evaporative crystallization and lithium precipitation, impurities and organic waste in the discharge wastewater can be effectively removed, and valuable Li element and sodium chloride are recycled; the recycled sodium chloride and condensed distilled water are compounded to obtain a discharge salt solution which can be circularly used for battery discharge. The treatment process is high in heat utilization rate and low in overall energy consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery recovery and wastewater treatment, and in particular relates to a method for treating battery discharge wastewater. Background Art

[0002] The efficient recycling of power lithium batteries is a current research hotspot both domestically and internationally. Recycled lithium-ion batteries contain a small amount of charge, and to prevent explosions and fires during subsequent disassembly and crushing, they must be discharged. Common discharge methods include physical and chemical discharge, with salt water discharge being the most widely used. Salt water discharge utilizes the conductive properties of a conductive salt. By soaking retired lithium batteries in a bath of conductive salt water, this creates a short circuit between the positive and negative electrodes, allowing the battery to release any remaining charge.

[0003] Lithium batteries generally consist of a positive electrode, a negative electrode, a separator layer, an electrolyte, a binder, and a casing. The positive electrode is an oxide of transition metals and lithium, while the negative electrode is primarily made of carbon-based materials such as graphite and carbon fiber. The electrolyte contains organic solvents such as LiPF6, ethylene carbonate, propylene carbonate, diethyl carbonate, and dimethyl carbonate. The most commonly used brine for saltwater discharge is sodium chloride solution. Due to the corrosion of chloride ions, LiPF6 and lipid organic matter in the electrolyte leak into the saltwater during discharge, resulting in the production of soluble lipids, alkanes, lithium, and fluorine in the discharged saltwater. Furthermore, the aluminum foil and iron casing corrode with the discharged saltwater, resulting in the production of iron oxide and aluminum oxide impurities. After the salt water is discharged, there will be a lot of impurities and pollutants in the salt water to form discharge wastewater. The discharge wastewater cannot be discharged directly and needs to be further treated. For example, patent CN 116924616A discloses a discharge wastewater treatment process by adsorption, oxidation, phosphate precipitation of lithium, and calcium salt defluorination and phosphorus removal to achieve lithium recovery and sodium chloride recovery in wastewater. However, for high COD wastewater, the adsorption step of the process requires the consumption of a large amount of activated carbon, and the phosphate precipitation step requires heating, which generates additional energy consumption. For another example, patent CN218403896U discloses a discharge wastewater circulation treatment device, which is equipped with sections such as precipitation, defluorination, and oxidation to remove organic matter. The treated wastewater is circulated for salt water discharge. As the wastewater is continuously circulated and concentrated, the lithium enrichment and recovery in the wastewater are not considered, resulting in a waste of resources. Summary of the Invention

[0004] In view of this, an object of the present invention is to provide a method for treating battery discharge wastewater.

[0005] The present invention provides a method for treating battery discharge wastewater, comprising the following steps: S1: filtration: the battery discharge wastewater is filtered to obtain the first filtrate and waste residue 1; S2: Fenton oxidation: After adjusting the acidity of the first filtrate, a catalyst and an oxidant are added to perform Fenton oxidation degradation to obtain degraded wastewater; S3: Fluorine and impurity removal: Calcium hydroxide is added to the degradation wastewater to carry out precipitation reaction. After the reaction is completed, a flocculant is added, and after stirring and mixing, solid-liquid separation is carried out to obtain a second filtrate and waste residue 2; S4: adsorption: adsorbing the second filtrate with activated carbon to obtain a third filtrate; S5: Evaporation and crystallization: The third filtrate is evaporated and crystallized to obtain distilled water, crystallization mother liquor and sodium chloride crystals; S6: lithium precipitation: sodium carbonate solution is added to the crystallization mother liquor to precipitate lithium, and after solid-liquid separation, crude lithium carbonate and lithium precipitation mother liquor are obtained.

[0006] Preferably, in step S1, the sodium chloride concentration in the battery discharge wastewater is 1-10 wt%, the COD is 500-5000 mg / L, the lithium content is 1.0-2.0 g / L, and the fluorine content is 30-80 mg / L.

[0007] Preferably, in step S1, the filter press uses a filter with a pore size of no more than 1 μm.

[0008] Preferably, in step S2, hydrochloric acid is used to adjust the pH of the first filtrate to 4-5; the catalyst is ferrous chloride; the oxidant is hydrogen peroxide, and the concentration of hydrogen peroxide is 20-30wt%; the ratio of the mass of the oxidant to the mass of COD in the first filtrate is (6-10):1; and the ratio of the mass of the catalyst to the mass of COD in the first filtrate is (0.3-0.8):1.

[0009] Preferably, in step S2, the Fenton oxidation degradation time is 4 to 6 hours.

[0010] Preferably, in step S3, calcium hydroxide solution is added to adjust the pH to 9-10; the flocculant is polyacrylamide (PAM), and the amount of flocculant added is 1-3 mg per liter of solution.

[0011] Preferably, in step S3, the precipitation reaction time is 20 to 30 minutes; and the stirring and mixing time is 5 to 10 minutes.

[0012] Preferably, in step S3, the COD of the second filtrate is less than 700 mg / L.

[0013] Preferably, in step S4, the adsorption method using activated carbon is: passing the second filtrate through an activated carbon filter for adsorption; wherein: the adsorption residence time of the second filtrate is 10 to 30 minutes.

[0014] Preferably, in step S4, the COD of the third filtrate is less than 100 mg / L.

[0015] Preferably, in step S5, the evaporation crystallization temperature is 90-100°C.

[0016] Preferably, in step S5, the temperature of the distilled water condensed by distillation is between 50° C. and 60° C., and the distilled water is directly compounded with the recovered sodium chloride crystals to obtain a sodium chloride discharge solution.

[0017] Preferably, in step S6, the concentration of the sodium carbonate solution is 300-350 g / L; the sodium carbonate solution is added according to a molar ratio of sodium carbonate to lithium ions in the crystallization mother liquor of (2.05-2.1):1; the lithium precipitation time is 20-30 min; and plate pressure filtration is used for solid-liquid separation.

[0018] Preferably, in step S6, the lithium precipitation mother liquor is returned to the first filtrate of step S2.

[0019] The above one or more technical solutions of the present invention can achieve at least one of the following beneficial effects: The present invention utilizes a treatment process involving filtration, Fenton oxidation, fluorine and impurity removal, adsorption, evaporative crystallization, and lithium precipitation to effectively remove impurities and organic waste from discharge wastewater, recovering valuable lithium and sodium chloride. The lithium recovery rate is above 82%. The recovered sodium chloride is then compounded with condensed distilled water to produce a discharge salt solution, which can be recycled for battery discharge. The treatment process has high heat utilization and low overall energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 4 is a process flow chart of the method of the present invention. DETAILED DESCRIPTION

[0021] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0022] As mentioned above, the present invention provides a method for treating battery discharge wastewater, comprising the following steps: S1: filtration: the battery discharge wastewater is filtered to obtain the first filtrate and waste residue 1; S2: Fenton oxidation: After adjusting the acidity of the first filtrate, a catalyst and an oxidant are added to perform Fenton oxidation degradation to obtain degraded wastewater; S3: Fluorine and impurity removal: Calcium hydroxide is added to the degradation wastewater to carry out precipitation reaction. After the reaction is completed, a flocculant is added, and after stirring and mixing, solid-liquid separation is carried out to obtain a second filtrate and waste residue 2; S4: adsorption: adsorbing the second filtrate with activated carbon to obtain a third filtrate; S5: Evaporation and crystallization: The third filtrate is evaporated and crystallized to obtain distilled water, crystallization mother liquor and sodium chloride crystals; S6: lithium precipitation: sodium carbonate solution is added to the crystallization mother liquor to precipitate lithium, and after solid-liquid separation, crude lithium carbonate and lithium precipitation mother liquor are obtained.

[0023] In the treatment method of the present invention, organic matter, fluorine, phosphorus, heavy metals and other impurities in battery discharge wastewater can be efficiently removed, and lithium and sodium chloride salts in the discharge wastewater can be recovered and reused.

[0024] The present invention uses a combined Fenton oxidation and adsorption process to remove organic matter from wastewater. Organic matter in battery discharge wastewater includes lipids, aldehydes, ketones, benzene rings, alkanes, and amides. However, Fenton oxidation has poor oxidative degradation capabilities for benzene rings and alkanes. Therefore, the Fenton oxidation process can only degrade organic matter other than alkanes and benzene rings in the wastewater. To improve the removal of organic matter, the present invention further utilizes an adsorption process, which can remove alkanes and benzene rings from the wastewater. Therefore, the combination of these two processes can reduce the COD in the wastewater to below 100 mg / L, achieving an organic matter removal rate exceeding 95%.

[0025] In the present invention, after Fenton oxidation, the phosphorus and fluorine in the discharge wastewater are converted into phosphate and fluoride ions, and the complex metals are oxidized to ionic states. Therefore, in the defluorination and impurity removal step, calcium hydroxide is added to the degradation wastewater. The calcium hydroxide reacts with impurity ions to form precipitates such as calcium phosphate, calcium fluoride, iron hydroxide, manganese hydroxide, and aluminum hydroxide, thereby achieving simultaneous dephosphorization, defluorination, and heavy metal removal. In addition, since the calcium fluoride precipitate is relatively fine and precipitates slowly, the addition of a flocculant helps the precipitate to quickly agglomerate, thereby improving the subsequent solid-liquid separation effect and avoiding the occurrence of filtration. The second filtrate after the defluorination and impurity removal step is clear and transparent, with low turbidity, less than 2 mg / L of suspended solids in the water, and the fluoride ion concentration is reduced to below 10 mg / L; this can delay the subsequent clogging of the activated carbon.

[0026] The present invention uses evaporative crystallization to recover refined sodium chloride and distilled water. The distilled water and refined sodium chloride crystals are then compounded into a solution, thereby avoiding the problem of impurity enrichment. Furthermore, sodium chloride salt solutions of varying concentrations can be configured as needed, providing convenience and flexibility. The prepared sodium chloride solution can be reused in the battery discharge process. After the evaporative crystallization process, a high-temperature crystallization mother liquor is formed. Sodium carbonate can be directly reacted with the high-temperature crystallization mother liquor to precipitate lithium, eliminating the need for an additional heat source. This allows for efficient recovery of lithium carbonate resources while fully utilizing the heat source.

[0027] Preferably, in step S1, the sodium chloride concentration in the battery discharge wastewater is 1-10 wt%, the COD is 500-5000 mg / L, the lithium content is 1.0-2.0 g / L, and the fluorine content is 30-80 mg / L.

[0028] Preferably, in step S1, the filter press uses a filter with a pore size of no more than 1 μm.

[0029] Preferably, in step S2, hydrochloric acid is used to adjust the pH of the first filtrate to 4-5; the catalyst is ferrous chloride; the oxidant is hydrogen peroxide, and the concentration of hydrogen peroxide is 20-30wt%; the ratio of the mass of the oxidant to the mass of COD in the first filtrate is (6-10):1; and the ratio of the mass of the catalyst to the mass of COD is (0.3-0.8):1.

[0030] In the Fenton oxidation process of the present invention, hydrochloric acid is used to adjust the pH, hydrogen peroxide is used as the oxidant, and ferrous chloride is used as the catalyst, thereby avoiding the introduction of other impurity anions in the process and affecting the recovery purity of the sodium chloride salt.

[0031] In the present invention, by controlling the addition amount of the catalyst and the oxidant, the oxidation degradation effect can be improved and the COD value can be reduced.

[0032] Preferably, in step S2, the Fenton oxidation degradation time is 4 to 6 hours.

[0033] Preferably, in step S3, calcium hydroxide solution is added to adjust the pH to 9-10; the flocculant is polyacrylamide (PAM), and the amount of flocculant added is 1-3 mg per liter of solution; Preferably, in step S3, the precipitation reaction time is 20 to 30 minutes; and the stirring and mixing time is 5 to 10 minutes.

[0034] Preferably, in step S3, the COD of the second filtrate is less than 700 mg / L.

[0035] Preferably, in step S4, the adsorption method using activated carbon is: passing the second filtrate through an activated carbon filter for adsorption; wherein: the adsorption residence time of the second filtrate is 10 to 30 minutes.

[0036] Preferably, in step S4, the COD of the third filtrate after adsorption is less than 100 mg / L.

[0037] Preferably, in step S5, the evaporation crystallization temperature is 90-100°C.

[0038] Preferably, in step S5, the temperature of the distilled water condensed by distillation is between 50° C. and 60° C., and the distilled water is directly compounded with the recovered sodium chloride crystals to obtain a sodium chloride discharge solution.

[0039] In the present invention, the waste heat of distilled water is used to compound the obtained sodium chloride, so that sodium chloride discharge wastewater can be obtained without heating, thereby realizing the recycling of sodium chloride.

[0040] Preferably, in step S6, the concentration of the sodium carbonate solution is 300-350 g / L; the sodium carbonate solution is added according to a molar ratio of sodium carbonate to lithium ions in the crystallization mother liquor of (2.05-2.1):1; the lithium precipitation time is 20-30 min; and plate pressure filtration is used for solid-liquid separation.

[0041] Preferably, in step S6, the lithium precipitation mother liquor is returned to the first filtrate of step S2.

[0042] In the present invention, the lithium precipitation mother liquor is returned to the filtrate of step S2, so that the residual lithium can be returned to the system, thereby improving the recovery rate of lithium.

[0043] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0044] The process flow of a method for treating battery discharge wastewater in the present invention is as follows: Figure 1 The specific steps can be found in the embodiments.

[0045] Example 1 The data of impurity content in the discharge wastewater in this embodiment can be seen in Table 1. The treatment method of the discharge wastewater is as follows: S1: Filtration and slag removal: The battery discharge wastewater is passed through a plate and frame filter press with a filter cloth pore size of 0.1 μm to perform solid-liquid separation to obtain the first filtrate and waste residue.

[0046] S2: Fenton oxidation: 10 wt% hydrochloric acid was added to the first filtrate in step S1 to adjust the pH of the filtrate to about 4, and then ferrous chloride catalyst (the mass ratio of catalyst to COD was 0.5:1) was added. After stirring evenly, 27 wt% hydrogen peroxide (the mass ratio of hydrogen peroxide to COD was 6:1) was added and oxidative degradation was carried out for 4 hours to obtain degraded wastewater.

[0047] S3: Fluorine removal and impurity removal: 10 wt% calcium hydroxide solution was added to the degradation wastewater in step S2 to adjust the pH to about 9, and a precipitation reaction was carried out for 20 minutes. After the reaction was completed, polyacrylamide (added in an amount of 1 mg / L) was added, stirred for 5 minutes, and then entered into a filter press for solid-liquid separation to obtain a second filtrate and waste residue. The COD in the second filtrate was 670.5 mg / L, and the fluorine content was less than 10 mg / L.

[0048] S4: Adsorption: The second filtrate in step S3 is passed through an activated carbon filter for adsorption, and the adsorption residence time is controlled to be 20 minutes to obtain a third filtrate; S5: Evaporation and crystallization: The third filtrate in step S4 is evaporated and crystallized, the evaporation temperature is controlled at 95°C, the water vapor is condensed and distilled water is collected, the sodium chloride slurry in the crystallizer is passed through a thickener and a centrifuge for dehydration to obtain sodium chloride crystals and evaporation crystallization mother liquor; the distilled water and sodium chloride crystals are recovered and compounded into a 5wt% solution for reuse in the battery discharge process.

[0049] S6: Lithium precipitation process: Add a 300g / L sodium carbonate solution to the 90-90°C evaporation crystallization mother liquor in step S5 (at a molar ratio of sodium carbonate to lithium ions in the evaporation crystallization mother liquor of (2.05-2.1):1). Lithium precipitation is carried out for 25 minutes at a stirring speed of 350r / min to precipitate lithium carbonate crystals. After solid-liquid separation using a filter press, crude lithium carbonate and a lithium precipitation mother liquor are obtained. The crude lithium carbonate has a purity of 94% and a recovery rate of 90%. The lithium precipitation mother liquor is returned to the first filtrate in step S2. The results of the test at each stage can be seen in Table 1.

[0050] Table 1 Water quality effects of different process sections in Example 1 In this embodiment, the COD value in the third filtrate is reduced to below 100 mg / L, indicating that the Fenton oxidation and carbon adsorption filtration in the present invention can effectively reduce the COD value in water; in addition, the purity of the crude lithium carbonate in this embodiment reaches 94%, indicating that the impurity ions are removed more thoroughly during the defluorination and de-impurity process, and thus the recovered lithium carbonate has a higher purity.

[0051] Example 2 The method is basically the same as Example 1, except that the amounts of hydrogen peroxide and catalyst added in step S2 are different, as shown in Table 2. In this embodiment, multiple parallel experiments were conducted, and the ratios of hydrogen peroxide to COD were 2:1, 4:1, 8:1, and 10:1, respectively. The relevant test data of hydrogen peroxide and COD can be seen in Table 2.

[0052] Table 2 Effect of hydrogen peroxide dosage on COD removal From the data in Table 2, it can be seen that when the mass ratio of hydrogen peroxide to COD reaches 6:1, there will be a better oxidation effect. However, when the ratio exceeds 8:1, the oxidation effect will no longer be significantly improved if hydrogen peroxide is continued to be added.

[0053] Example 3 The results are basically the same as those in Example 1, except that the amount of catalyst added in step S2 is different, as shown in Table 3. In this example, multiple parallel experiments were conducted, with the catalyst to COD ratios being 0.8:1, 0.66:1, 0.44:1, and 0.4:1, respectively; the measured relevant data can be seen in Table 3.

[0054] From the data in Table 3, it can be seen that the amount of catalyst added has little effect on the oxidation effect. Overall, when the mass ratio of catalyst to COD is greater than 0.5:1, the oxidation effect will be better, but when the mass ratio is greater than 0.66:1, the oxidation effect basically does not increase.

[0055] Table 3 Example 4 The data of impurity content in the discharge wastewater in this embodiment can be seen in Table 4. The treatment method of the discharge wastewater is as follows: S1: Filtration and slag removal: The battery discharge wastewater is passed through a plate and frame filter press with a filter cloth pore size of 0.1 μm to perform solid-liquid separation to obtain the first filtrate and waste residue.

[0056] S2: Fenton oxidation: Add 10 wt% hydrochloric acid to the first filtrate in step S1, adjust the pH of the filtrate to about 5, then add ferrous chloride catalyst (the mass ratio of catalyst to COD is 0.66:1), stir evenly, and then add 20 wt% hydrogen peroxide (the mass ratio of hydrogen peroxide to COD is 8:1) and carry out oxidative degradation for 5 hours to obtain degraded wastewater.

[0057] S3: Fluorine removal and impurity removal: 10 wt% calcium hydroxide solution was added to the degradation wastewater in step S2 to adjust the pH to about 10, and a precipitation reaction was carried out for 25 minutes. After the reaction was completed, polyacrylamide (added in an amount of 2 mg / L) was added, stirred for 10 minutes, and then entered into a filter press for solid-liquid separation to obtain a second filtrate and waste residue. The COD content in the second filtrate was 489 mg / L, and the fluorine content was less than 10 mg / L.

[0058] S4: Adsorption: The second filtrate in step S3 is passed through an activated carbon filter for adsorption, and the adsorption residence time is controlled to be 10 minutes to obtain a third filtrate.

[0059] S5: Evaporation and crystallization: The third filtrate in step S4 is subjected to evaporation and crystallization, and the evaporation temperature is controlled at 98°C. The water vapor is condensed and distilled water is collected. The sodium chloride slurry in the crystallizer is dehydrated through a thickener and a centrifuge to obtain sodium chloride crystals and evaporation crystallization mother liquor; the distilled water and sodium chloride crystals are recovered and compounded into a 5wt% solution for reuse in the battery discharge process.

[0060] S6: Lithium precipitation process: Add 320g / L sodium carbonate solution to the 90-98°C evaporation crystallization mother liquor in step S5 (the molar ratio of sodium carbonate to lithium ions in the evaporation crystallization mother liquor is (2.05-2.1):1). Lithium precipitation is carried out for 20 minutes at a stirring speed of 400r / min to precipitate lithium carbonate crystals. After solid-liquid separation using a filter press, crude lithium carbonate and lithium precipitation mother liquor are obtained. The crude lithium carbonate has a purity of 91% and a recovery rate of 85%. The lithium precipitation mother liquor is returned to the first filtrate in step S2. The test results of each stage can be seen in Table 4.

[0061] Table 4 Water quality effects of different process sections in Example 4 In this embodiment, the COD value in the third filtrate is reduced to below 50 mg / L, indicating that the Fenton oxidation and carbon adsorption filtration in the present invention can effectively reduce the COD value in water; in addition, the purity of the crude lithium carbonate in this embodiment reaches 91%, indicating that the impurity ions are removed more thoroughly during the defluorination and de-impurity process, and thus the recovered lithium carbonate has a higher purity.

[0062] Example 5 The data of impurity content in the discharge wastewater in this embodiment can be seen in Table 5. The treatment method of the discharge wastewater is as follows: S1: Filtration and slag removal: The battery discharge wastewater is passed through a plate and frame filter press with a filter cloth pore size of 0.1 μm to perform solid-liquid separation to obtain the first filtrate and waste residue.

[0063] S2: Fenton oxidation: 10 wt% hydrochloric acid was added to the first filtrate in step S1 to adjust the pH of the filtrate to about 4, and then ferrous chloride catalyst (the mass ratio of catalyst to COD was 0.66:1) was added. After stirring evenly, 30 wt% hydrogen peroxide (the mass ratio of hydrogen peroxide to COD was 8:1) was added and oxidative degradation was carried out for 6 hours to obtain degraded wastewater.

[0064] S3: Fluorine removal and impurity removal: 10 wt% calcium hydroxide solution was added to the degradation wastewater in step S2 to adjust the pH to about 9.5, and a precipitation reaction was carried out for 30 minutes. After the reaction was completed, polyacrylamide (added in an amount of 3 mg / L) was added, stirred for 8 minutes, and then entered into a filter press for solid-liquid separation to obtain a second filtrate and waste residue. The COD in the second filtrate was 238.2 mg / L, and the fluorine content was less than 10 mg / L.

[0065] S4: Adsorption: The second filtrate in step S3 is adsorbed through the activated carbon filter, and the adsorption residence time is controlled to be 30 minutes to obtain the third filtrate S5: Evaporation and crystallization: The third filtrate in step S4 is subjected to evaporation and crystallization, the evaporation temperature is controlled at 90°C, the water vapor is condensed and distilled water is collected, the sodium chloride slurry in the crystallizer is dehydrated through a thickener and a centrifuge to obtain sodium chloride crystals and evaporation crystallization mother liquor; the distilled water and sodium chloride crystals are recovered and compounded into a 5wt% solution for reuse in the battery discharge process.

[0066] S6: Lithium precipitation process: Add 350g / L sodium carbonate solution to the 85-90°C evaporation crystallization mother liquor in step S5 (the molar ratio of sodium carbonate to lithium ions in the evaporation crystallization mother liquor is (2.05-2.1):1). Lithium precipitation is carried out for 30 minutes at a stirring speed of 400r / min to precipitate lithium carbonate crystals. After solid-liquid separation using a filter press, crude lithium carbonate and lithium precipitation mother liquor are obtained. The crude lithium carbonate has a purity of 96% and a recovery rate of 82%. The lithium precipitation mother liquor is returned to the first filtrate in step S2. The test results of each stage can be seen in Table 5.

[0067] Table 5 Water quality effects of different process sections in Example 5 In this embodiment, the COD value in the third filtrate is reduced to below 50 mg / L, indicating that the Fenton oxidation and carbon adsorption filtration in the present invention can effectively reduce the COD value in water; in addition, the purity of the crude lithium carbonate in this embodiment reaches 96%, indicating that the impurity ions are removed more thoroughly during the defluorination and de-impurity process, and thus the recovered lithium carbonate has a higher purity.

[0068] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent variations or additions based on the spirit and substance of the present invention are intended to be encompassed within the scope of protection of the present invention.

Claims

1. A method for treating battery discharge wastewater, characterized in that: The following steps are involved: S1: filtration: the battery discharge wastewater is filtered to obtain the first filtrate and waste residue 1; S2: Fenton oxidation: After adjusting the acidity of the first filtrate, a catalyst and an oxidant are added to perform Fenton oxidation degradation to obtain degraded wastewater; S3: Fluorine and impurity removal: Calcium hydroxide is added to the degradation wastewater to carry out precipitation reaction. After the reaction is completed, a flocculant is added, and after stirring and mixing, solid-liquid separation is performed to obtain a second filtrate and waste residue 2; S4: adsorption: adsorbing the second filtrate with activated carbon to obtain a third filtrate; S5: Evaporation and crystallization: The third filtrate is evaporated and crystallized to obtain distilled water, crystallization mother liquor and sodium chloride crystals; S6: lithium precipitation: sodium carbonate solution is added to the crystallization mother liquor to precipitate lithium, and after solid-liquid separation, crude lithium carbonate and lithium precipitation mother liquor are obtained.

2. The method for treating battery discharge wastewater according to claim 1, characterized in that: In step S1, the concentration of sodium chloride in the battery discharge wastewater is 1-10 wt %, the COD is 500-5000 mg / L, the lithium content is 1.0-2.0 g / L, and the fluorine content is 30-80 mg / L.

3. The method for treating battery discharge wastewater according to claim 1, characterized in that: In step S2, the acid adjustment is to adjust the pH of the first filtrate to 4-5 using hydrochloric acid; The catalyst is ferrous chloride; The oxidant is hydrogen peroxide, and the concentration of hydrogen peroxide is 20~30wt%; The ratio of the mass of the oxidant to the mass of COD in the first filtrate is (6-10):1; the ratio of the mass of the catalyst to the mass of COD in the first filtrate is (0.3-0.8):

1.

4. The method for treating battery discharge wastewater according to claim 1 or 3, characterized in that: In step S2, the Fenton oxidation degradation time is 4 to 6 hours.

5. The method for treating battery discharge wastewater according to claim 1, characterized in that: In step S3, calcium hydroxide solution is added to adjust the pH to 9-10; the flocculant is polyacrylamide, and the amount of flocculant added is 1-3 mg per liter of solution.

6. The method for treating battery discharge wastewater according to claim 1 or 5, characterized in that: In step S3, the precipitation reaction time is 20 to 30 minutes; and the stirring and mixing time is 5 to 10 minutes.

7. The method for treating battery discharge wastewater according to claim 1, characterized in that: In step S4, the activated carbon adsorption method is: passing the second filtrate through an activated carbon filter for adsorption; wherein: the adsorption residence time of the second filtrate is 10 to 30 minutes.

8. The method for treating battery discharge wastewater according to claim 1, characterized in that: In step S5, the evaporation crystallization temperature is 90-100°C.

9. The method for treating battery discharge wastewater according to claim 1, characterized in that: In step S6, sodium carbonate solution is added according to a molar ratio of sodium carbonate to lithium ions in the crystallization mother liquor of (2.05-2.1):1; and the lithium precipitation time is 20-30 minutes.

10. The method for treating battery discharge wastewater according to claim 1, characterized in that: In step S6, the lithium precipitation mother liquor is returned to the first filtrate of step S2.

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