A process for treating waste electrolyte by utilizing waste aluminum alkali liquor for collaborative resource recovery

Abstract

The present invention provides a process for the synergistic resource treatment of waste electrolyte using waste aluminum alkali liquor, belonging to the field of wastewater treatment technology, comprising the following steps: mixing the waste electrolyte with the waste aluminum alkali liquor for reaction, filtering and separating to produce a first filter cake and a first filtrate, acid-washing the first filter cake, filtering to produce a second filter cake and a second filtrate, washing the second filter cake with water, filtering and purifying it, and then acid-leaching and slurrying it, filtering to produce a third filter cake and a third filtrate; washing the third filter cake with water, filtering and purifying it, and then drying it to produce AlF3; mixing the third filtrate with a water-soluble carbonate solution, filtering to produce a fourth filtrate and a fourth filter cake, and discharging the fourth filtrate into a storage tank for storage; washing the fourth filter cake with water, filtering and purifying it, and then drying it to produce Li2CO3. The present invention provides a process for the synergistic resource treatment of waste electrolyte using waste aluminum alkali liquor, utilizing the synergistic treatment of waste aluminum alkali liquor and waste electrolyte to simultaneously dispose of hazardous waste and produce resource products AlF3 and Li2CO3, thereby having good environmental and economic benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and more specifically, relates to a process for treating waste electrolyte by utilizing waste aluminum alkali liquor for collaborative resource recovery. Background Art

[0002] Lithium battery electrolytes primarily consist of organic solvents, lithium salts, and a small amount of additives. The organic solvents are various carbonates, such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and propylene carbonate. The lithium salt is generally lithium hexafluorophosphate, which accounts for 15% of the total electrolyte mass. Waste electrolyte is considered hazardous waste, primarily sourced from losses incurred by electrolyte manufacturers due to improper operation during the production process, and a certain amount of waste electrolyte generated during the lithium battery recycling process. Waste electrolytes are complex in composition, exhibit significant corrosiveness and volatility, are flammable and explosive, and are therefore very difficult to handle.

[0003] Aluminum product manufacturers often use sodium hydroxide solutions in alkaline cleaning of aluminum pipes, aluminum profiles, and molds, as well as in surface treatment processes. This process removes dirt and natural oxide films from the aluminum surface and further activates the base metal surface. For alkaline etching tanks to function properly, the concentrations of free caustic soda and aluminum ions in the solution must be controlled. This necessitates regular discharge and renewal to maintain solution quality. However, the regularly discharged alkali content and aluminum ions pose a serious threat to the ecological environment, and waste aluminum solution is therefore classified as hazardous waste.

[0004] Lithium salts in spent electrolytes contain high-value-added lithium and fluorine. Lithium is the primary raw material for lithium batteries, and fluorine, after being treated with aluminum lye, can be converted into AlF3. AlF3 is an important inorganic chemical product primarily used in the aluminum smelting industry, serving as one of the primary fluoride salt fluxes for electrolytic aluminum. Therefore, recovering lithium and fluorine from spent electrolytes offers significant economic benefits.

[0005] Waste electrolyte is flammable, explosive, and highly corrosive, necessitating significant processing and resource utilization challenges. Currently, the most common treatment methods are co-firing or pre-treatment followed by incineration. In terms of resource utilization, the most popular methods include supercritical extraction and distillation-condensation. This method uses supercritical fluid to recover organic solvents, but requires stringent conditions, involves complex processes, and is costly. The distillation-condensation method, on the other hand, utilizes low-temperature vacuum evaporation, drying, and condensation to separate and recover the electrolyte. This method offers a relatively high recovery rate, but is complex, energy-intensive, and produces low returns.

[0006] In terms of recycling and reusing waste aluminum lye, some manufacturers use acid neutralization and then filtration to recycle. Due to the high pH, ​​this will consume a lot of acid. At the same time, the aluminum ion concentration is high, separation is difficult, and the production cost is high. Summary of the Invention

[0007] The purpose of the present invention is to provide a process for treating waste electrolyte by utilizing waste aluminum alkali liquor in a synergistic resource-based manner, aiming to treat waste electrolyte and waste aluminum alkali liquor while recovering the available resources in the two waste liquors to create economic value.

[0008] To achieve the above object, the technical solution adopted by the present invention is to provide a process for treating waste electrolyte by utilizing waste aluminum alkali liquor for resource recovery, comprising the following steps:

[0009] S1: waste electrolyte and waste aluminum alkali solution are mixed and reacted to obtain a first slurry;

[0010] S2: The first slurry is filtered and separated to generate a first filter cake and a first filtrate, and the first filtrate is incinerated;

[0011] S3: acid-washing the first filter cake to obtain a second slurry, filtering the second slurry to generate a second filter cake and a second filtrate, and discharging the second filtrate into a sewage treatment device for treatment;

[0012] S4: washing, filtering and purification of the second filter cake;

[0013] S5: acid leaching the second filter cake to obtain a third slurry, and filtering the third slurry to generate a third filter cake and a third filtrate;

[0014] S6: The third filter cake is washed, filtered, purified, and then dried to obtain AlF3;

[0015] S7: The third filtrate is mixed with a sodium carbonate solution to obtain a fourth slurry;

[0016] S8: The fourth slurry is filtered to generate a fourth filtrate and a fourth filter cake, and the fourth filtrate is discharged into a storage tank for recovery and storage;

[0017] S9: The fourth filter cake is washed with water, filtered, purified, and then dried to obtain Li2CO3.

[0018] In a possible implementation, step S1 includes the following specific steps:

[0019] A1: Calculate the amount of waste aluminum alkali solution based on the treatment volume of waste electrolyte;

[0020] A2: First, all the waste aluminum alkali solution is input into the reactor, and then the waste electrolyte is added dropwise to the waste aluminum alkali solution to form a reaction solution. The waste electrolyte is added dropwise at a rate of 0.3-0.4 kg / h. During the addition of the waste electrolyte, the reaction solution is continuously stirred and the reaction temperature of the reaction solution is controlled between 40-50°C.

[0021] A3: After the addition of the waste electrolyte is completed, the reaction solution continues to react for 2.5-3 hours to obtain the first slurry.

[0022] In one possible implementation, in step S2, the first filter cake needs to undergo two stages of water washing, filtration and purification before entering S3. The filtrate after the first stage of water washing and filtration is directly discharged into the sewage treatment equipment for treatment, and the filtrate after the second stage of water washing and filtration is used as washing water in the first stage of water washing.

[0023] In a possible implementation, in step S3 , the first filter cake is acid-washed with concentrated hydrochloric acid.

[0024] In a possible implementation, in step S5, the second filter cake is acid-leached with industrial sulfuric acid. During the acid-leaching process, the pH value is adjusted to be stable at 1.0 and the leaching temperature is 40°C.

[0025] In one possible implementation, in step S7, a sodium carbonate solution is first added to the lithium precipitation equipment, and then the third filtrate is added dropwise to the sodium carbonate solution to form a mixed liquid. During the mixing process, the temperature in the lithium precipitation equipment is kept above 95°C, and the dripping time of the third filtrate does not exceed 50 minutes. After the third filtrate is added dropwise, the temperature in the lithium precipitation equipment is maintained, and the mixed liquid is allowed to react continuously for 30-40 minutes to obtain a fourth slurry.

[0026] In a possible implementation, in step S4, step S6 and step S9, the second filter cake, the third filter cake and the fourth filter cake are all subjected to multi-stage water washing and filtration treatment.

[0027] In a possible implementation, in step S4, step S6 and step S9, the filtrates generated by washing and filtering the second filter cake, the third filter cake and the fourth filter cake are all discharged into a sewage treatment device for treatment.

[0028] In a possible implementation, in step S2 , a candle filter is used to filter the first slurry.

[0029] In a possible implementation, the filtering equipment used in step S3, step S5, step S6, step S8 and step S9 is a plate and frame filter press.

[0030] The beneficial effect of the process provided by the present invention for utilizing waste aluminum alkali liquor to synergistically resource-treat waste electrolyte is that: compared with the prior art, the process of the present invention for utilizing waste aluminum alkali liquor to synergistically resource-treat waste electrolyte, by controlling the ratio of waste aluminum alkali liquor and waste electrolyte, reaction rate and reaction temperature, controls the reaction products, and effectively separates fluorine, phosphorus and other elements in the waste electrolyte. On the one hand, it effectively avoids the presence of a large amount of fluorine and phosphorus elements in the organic filtrate, which leads to corrosion of the incineration equipment. On the other hand, it avoids the organic matter from entering the resource-recycling system, which leads to complicated separation process and incomplete separation, and has high resource utilization rate. The reaction conditions of this process are mild, and normal pressure and 40-50°C are sufficient, which reduces the risks caused by negative pressure or high temperature during the electrolyte treatment process, has high safety and low public works consumption. At the same time, waste aluminum alkali liquor and waste electrolyte are both hazardous wastes. By utilizing waste aluminum alkali liquor and waste electrolyte for synergistic treatment, resource products AlF3 and Li2CO3 are obtained while disposing of hazardous wastes, which has good environmental and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 A process flow chart for the collaborative resource treatment of waste electrolyte using waste aluminum alkali liquor provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] See also Figure 1 The present invention provides a method for treating waste electrolyte by utilizing waste aluminum alkali solution for resource utilization. The method comprises the following steps:

[0035] S1: The waste electrolyte and waste aluminum alkali solution are mixed and reacted to obtain the first slurry. In actual production, the waste electrolyte is processed in batches. Step S1 includes the following specific operating steps: A1: Calculate the amount of waste aluminum alkali solution based on the processing volume of the waste electrolyte; A2: First, all the waste aluminum alkali solution is input into the reactor, and then the waste electrolyte is mixed into the waste aluminum alkali solution by dropwise addition to form a reaction solution at a dropwise addition rate of 0.3-0.4kg / h. During the dropwise addition of the waste electrolyte, the reaction solution is continuously stirred and the reaction temperature of the reaction solution is controlled between 40-50°C; A3: After the waste electrolyte is added, the reaction solution continues to react for 2.5-3 hours to obtain the first slurry.

[0036] Among them, in step A1, the main component of the waste electrolyte is lithium hexafluorophosphate. The lithium hexafluorophosphate reacts with the waste aluminum alkali solution to produce precipitates such as AlF3, LiF, and AlPO4, which can achieve the purpose of removing F and P. Therefore, the amount of waste aluminum alkali solution used can be calculated based on the fluorine content in the waste electrolyte. The specific calculation method is:

[0037] According to the reaction, the molar ratio of aluminum to fluorine is n(Al):n(F) = 1:3-1:6, meaning the molar ratio of aluminum to lithium hexafluorophosphate is n(Al):n(LiPF6) = 1:0.5-1:1. Let's assume the F content in the electrolyte is C1 ppm, the Al content in the waste aluminum caustic is C2 ppm, and if M1 g of electrolyte is used, then at least M2 g of waste aluminum caustic is required.

[0038] If the experiment is conducted according to n(Al):n(F)=1:6, and the aluminum excess is 20%, then M2 needs to be:

[0039]

[0040] If the experiment is conducted according to n(Al):n(F)=1:3, and the aluminum excess is 20%, then M2 needs to be:

[0041]

[0042] Among them, in step A2, the corrosive gas and violent heat release generated by the decomposition of lithium hexafluorophosphate in the electrolyte are avoided by controlling the droplet acceleration rate; at the same time, the solid phase and organic phase components are controlled within this droplet acceleration rate range, so that the fluorine and phosphorus elements can be precipitated to the greatest extent. On the one hand, the composition of the solid phase product is simple, and the subsequent resource separation process is efficient and simple; on the other hand, the production of the by-product LiP2F2 is reduced. LiP2F2 will dissolve in organic matter and enter the incineration system, causing problems such as corrosion of the incineration equipment and difficulty in handling fluoride ions in the flue gas.

[0043] During this process, the reaction solution needs to be continuously stirred. The purpose of stirring is, on the one hand, to promote the reaction between the aluminum ions in the waste aluminum lye and the fluoride ions and phosphate ions in the waste electrolyte. On the other hand, the above reaction is an exothermic reaction, and the optimal reaction temperature required for the above reaction is 40-50°C. In order to stabilize the reaction temperature, the reaction temperature is controlled by providing circulating cooling water. Continuous stirring of the reaction solution promotes heat exchange between the reaction solution and the circulating water, improving the cooling efficiency. In addition, in step A3, after the waste electrolyte is added, the reaction solution continues to react for 2.5-3 hours, and the reaction temperature of the reaction solution is still controlled between 40-50°C.

[0044] S2: The first slurry is filtered and separated to generate a first filter cake and a first filtrate, and the first filtrate is incinerated. The first slurry obtained by step S1 is mainly composed of solid precipitate and organic solvent, wherein the solid precipitate is a mixture mainly composed of AlF3, AlPO4 and LiF, etc. In step S2, the first slurry is pumped into the filtration equipment for filtration, and the precipitate in the first slurry is filtered to obtain the first filter cake, and the organic solvent and the like form the first filtrate. In this embodiment, the filtration equipment used in step S2 is a candle filter, which has good airtightness and low filtrate leakage rate, thereby reducing the impact of the filtrate on the on-site environment. The separated filtrate is a solution containing esters, which has a high organic matter concentration and a high calorific value, and is sent to incineration and other related treatment facilities for incineration.

[0045] In this step, in order to reduce the content of organic matter in the first filter cake, the first filter cake needs to undergo two-stage water washing, filtration and purification treatment before entering S3. The filters used in the two-stage water washing and filtration treatment are all plate and frame filter presses, which have good purification effects. In the two-stage water washing process, the filtrate after the first-stage water washing and filtration is directly discharged into the sewage treatment equipment for treatment, and the filtrate after the second-stage water washing and filtration is directly used as washing water in the first-stage water washing treatment for secondary use. This arrangement can save part of the washing water and reduce the process treatment cost.

[0046] S3: Pickling the first filter cake to obtain a second slurry, filtering the second slurry to generate a second filter cake and a second filtrate, and discharging the second filtrate into a sewage treatment device for treatment.

[0047] In this step, the first filter cake is pickled with concentrated hydrochloric acid. At room temperature, the AlPO4 present in the first filter cake reacts with the concentrated hydrochloric acid to produce AlCl3 and H3PO4. However, the AlF3 and LiF present in the first filter cake do not react with concentrated hydrochloric acid at room temperature and pressure. After the pickling reaction, the first filter cake is treated to produce a second slurry. At this point, the solid precipitate in the second slurry is primarily AlF3 and LiF, while the liquid portion is primarily a mixed solution of AlCl3 and H3PO4. In this step, the second slurry is filtered using a plate and frame filter press. The solid precipitate in the second slurry forms a second filter cake, and the liquid portion forms a second filtrate, which is directly discharged into a wastewater treatment facility for treatment.

[0048] S4: The second filter cake is washed, filtered, and purified. In this step, the second filter cake is subjected to multi-stage water washing and filtration. This multi-stage water washing effectively removes residual AlCl3 and H3PO4 in the second filter cake, thereby improving the purity of the second filter cake. In this step, the filter used is a plate and frame filter press, and the filtrate produced in this step is sent to a sewage treatment facility for treatment.

[0049] S5: The second filter cake is treated by acid leaching and slurrying to obtain a third slurry, and the third slurry is filtered to generate a third filter cake and a third filtrate. In this step, the second filter cake is first input into the acid leaching equipment, and the acid leaching equipment is first added with bottom water, and then industrial sulfuric acid is added for slurrying. The pH is adjusted to be stable at 1.0, and the leaching temperature is 40°C, wherein the leaching temperature is obtained by indirect heating with steam. The second filter cake reacts with industrial sulfuric acid to form a third slurry. At this time, the main component of the solid precipitate in the third slurry is AlF3, and the liquid part in the third slurry is mainly a mixed solution of H2SO4 and Li2SO4. The third slurry is filtered through a plate and frame filter to obtain a third filter cake. The obtained third filtrate can be temporarily stored in a liquid storage tank for standby use.

[0050] S6: The third filter cake is washed, filtered, purified, and then dried to obtain AlF3. In this step, the third filter cake is subjected to multi-stage water washing and filtration. This multi-stage water washing effectively removes the residual H2SO4 and Li2SO4 in the third filter cake, thereby improving the purity of the third filter cake. In this step, the filter used is a plate and frame filter press. The filtrate produced in this step is sent to a sewage treatment plant for treatment. The third filter cake is purified and dried to obtain crude AlF3.

[0051] S7: The third filtrate is mixed with a soluble carbonate solution to obtain a fourth slurry. Soluble carbonate can be selected from sodium carbonate or potassium carbonate. In this embodiment, sodium carbonate solution is selected and added to the lithium precipitation equipment, and then the third filtrate (the main component is Li2SO4 solution) is added dropwise to the sodium carbonate solution to form a mixed solution. The temperature in the lithium precipitation equipment is kept above 95°C during the mixing process. The dripping time of the third filtrate does not exceed 50 minutes. After the third filtrate is added dropwise, the temperature in the lithium precipitation equipment is maintained, and the mixed solution is allowed to react continuously for 30-40 minutes to obtain a fourth slurry. In this step, the main component of the solid precipitate in the fourth slurry is Li2CO3, and the main component of the liquid part in the fourth slurry is Na2SO4 solution.

[0052] S8: The fourth slurry is filtered to produce a fourth filtrate and a fourth filter cake, which is then discharged into a storage tank for recovery and storage. In this step, the fourth slurry is filtered using a plate and frame filter press. The Li₂CO₃ precipitate in the fourth slurry forms a fourth filter cake, and the Na₂SO₄ solution in the fourth slurry forms a fourth filtrate. Since the Na₂SO₄ solution has a certain economic value, it can be discharged into a storage tank for recovery.

[0053] S9: The fourth filter cake is washed, filtered, purified, and then dried to obtain Li2CO3. In this step, the fourth filter cake is subjected to multi-stage water washing and filtration. The multi-stage water washing can effectively remove the residual Na2SO4 in the fourth filter cake and improve the purity of the fourth filter cake. In this step, the filter used is a plate and frame filter press. The filtrate produced in this step is sent to a sewage treatment plant for treatment. The fourth filter cake is purified and dried to obtain crude Li2CO3.

[0054] The present invention provides a process for the coordinated resource treatment of waste electrolyte using waste aluminum alkali liquor. Compared with the existing technology, the process utilizes waste aluminum alkali liquor and waste electrolyte for coordinated treatment, obtains resource products AlF3 and Li2CO3 while disposing of hazardous waste, and has better environmental and economic benefits.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A process for treating waste electrolyte by utilizing waste aluminum alkali liquor for resource recovery, characterized in that: The following steps are involved: S1: waste electrolyte and waste aluminum alkali solution are mixed and reacted to obtain a first slurry, wherein the waste electrolyte mainly contains lithium hexafluorophosphate; S2: The first slurry is filtered and separated to generate a first filter cake and a first filtrate, and the first filtrate is incinerated; S3: washing the first filter cake with concentrated hydrochloric acid to obtain a second slurry, filtering the second slurry to produce a second filter cake and a second filtrate, and discharging the second filtrate into a sewage treatment plant for treatment; S4: washing, filtering and purification of the second filter cake; S5: acid leaching the second filter cake with industrial sulfuric acid, adjusting the pH value to be stable at 1.0 and the leaching temperature to 40° C. during the acid leaching process to obtain a third slurry, and filtering the third slurry to generate a third filter cake and a third filtrate; S6: The third filter cake is washed, filtered, purified, and then dried to obtain AlF3; S7: mixing the third filtrate with the soluble carbonate solution to obtain a fourth slurry; S8: The fourth slurry is filtered to generate a fourth filtrate and a fourth filter cake, and the fourth filtrate is discharged into a storage tank for recovery and storage; S9: The fourth filter cake is washed with water, filtered, purified, and then dried to obtain Li2CO3.

2. The process for treating waste electrolyte by utilizing waste aluminum alkali liquor for resource utilization according to claim 1, characterized in that: Step S1 includes the following specific steps: A1: Calculate the amount of waste aluminum alkali solution based on the treatment volume of waste electrolyte; A2: First, all the waste aluminum alkali solution is input into the reactor, and then the waste electrolyte is added dropwise to the waste aluminum alkali solution to form a reaction solution. The dropwise addition rate of the waste electrolyte is 0.3-0.4 kg / h. During the dropwise addition of the waste electrolyte, the reaction solution is continuously stirred and the reaction temperature of the reaction solution is controlled between 40-50°C. A3: After the addition of the waste electrolyte is completed, the reaction solution continues to react for 2.5-3 hours to obtain the first slurry.

3. The process for treating waste electrolyte by utilizing waste aluminum alkali liquor for resource utilization according to claim 1, characterized in that: In step S2, the first filter cake needs to undergo two-stage water washing, filtration and purification before entering S3. The filtrate after the first-stage water washing and filtration is directly discharged into the sewage treatment equipment for treatment, and the filtrate after the second-stage water washing and filtration is used as washing water in the first-stage water washing.

4. The process for treating waste electrolyte by utilizing waste aluminum alkali liquor for resource utilization according to claim 1, characterized in that: In step S7, the soluble carbonate solution is first added to the lithium precipitation equipment, and then the third filtrate is mixed into the soluble carbonate solution in a dropwise manner to form a mixed solution. The mixing process maintains the temperature in the lithium precipitation equipment above 95°C, and the dripping time of the third filtrate does not exceed 50 minutes. After the third filtrate is added, the temperature in the lithium precipitation equipment is maintained, and the mixed solution is allowed to react continuously for 30-40 minutes to obtain a fourth slurry.

5. The process for treating waste electrolyte by utilizing waste aluminum alkali liquor for resource utilization according to claim 1, characterized in that: In step S4, step S6 and step S9, the second filter cake, the third filter cake and the fourth filter cake are all subjected to multi-stage water washing and filtration treatment.

6. The process for treating waste electrolyte by utilizing waste aluminum alkali liquor for resource utilization according to claim 5, characterized in that: In step S4, step S6 and step S9, the filtrates generated by washing and filtering the second filter cake, the third filter cake and the fourth filter cake are discharged into a sewage treatment device for treatment.

7. The process for treating waste electrolyte by utilizing waste aluminum alkali liquor for resource utilization according to claim 1, characterized in that: In step S2 , the first slurry is filtered using a candle filter.

8. The process for treating waste electrolyte by utilizing waste aluminum alkali liquor for resource utilization according to claim 1, characterized in that: The filtering equipment used in step S3, step S5, step S6, step S8 and step S9 is a plate and frame filter press.

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