Method for treating high-COD (Chemical Oxygen Demand) lithium-containing wastewater by electrocatalysis combined alkaline lithium extraction process

Abstract

The invention relates to the technical field of lithium-containing wastewater treatment, in particular to a method for treating high-COD (Chemical Oxygen Demand) lithium-containing wastewater by an electrocatalysis combined alkaline lithium extraction process, which comprises the following steps: S1, carrying out oxidative degradation on the high-COD lithium-containing wastewater by using an electrocatalysis method, and collecting and temporarily storing CO2; s2, adding an extraction agent, a synergistic extraction agent and a diluent into the low-COD lithium-containing wastewater to perform lithium extraction on the wastewater, and separating the low-COD lithium-containing wastewater into a loaded organic phase and raffinate; s3, the loaded organic phase is subjected to reverse extraction, standing and phase splitting are carried out, and a reverse extraction water phase is a high-purity lithium bicarbonate solution; and S4, pyrolyzing the reverse extraction water phase, and drying to obtain the battery-grade lithium carbonate. The whole steps are simple, the treatment effect is excellent, the problems of wastewater treatment and lithium recovery are effectively solved, the electrocatalysis and alkaline lithium extraction combined treatment method is adopted, organic matter degradation, lithium recovery, generated CO2 recycling and organic phase reutilization can be achieved at the same time, and the method has the advantages of being environmentally friendly, capable of saving energy and low in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-containing wastewater treatment, and in particular to a method for treating high-COD lithium-containing wastewater by using an electrocatalytic combined alkaline lithium extraction process. Background Art

[0002] With the growing development of the new energy industry, lithium batteries are widely used. As a large number of lithium batteries expire, they are facing the problem of retirement and scrapping. The recycling of waste lithium batteries has important practical significance. At present, the recycling of waste lithium batteries mainly adopts physical-fire method and wet method. The recycling process will produce a large amount of recycled wastewater. The recycled wastewater is high-salt wastewater containing organic extractants. The recycled wastewater also contains a small amount of valuable metal lithium. Lithium resources are in short supply and the price of lithium carbonate is relatively high. Therefore, the lithium in the recycled wastewater has a certain recovery value.

[0003] Recycled wastewater has the characteristics of high concentration, complex composition, high chroma, strong toxicity, stable chemical properties, difficulty in biodegradation, and long duration. Traditional wastewater treatment methods are difficult to achieve the purpose of lithium recovery while achieving wastewater treatment. Therefore, in view of the characteristics of lithium-containing wastewater, a short-process, low-cost, high-recovery-rate, and high-purity recovery process is urgently needed. Summary of the Invention

[0004] In response to the above problems, the present invention provides a method for treating high COD lithium-containing wastewater by combining an electrocatalytic and alkaline lithium extraction process, so as to solve the problem that traditional wastewater treatment methods are difficult to achieve lithium recovery while treating wastewater.

[0005] To achieve the above object, the present invention provides a method for treating high COD lithium-containing wastewater by an electrocatalytic combined alkaline lithium extraction process, comprising the following steps: S1. Using electrocatalysis to oxidize and degrade high-content organic matter in high-COD lithium-containing wastewater, converting high-COD low-lithium wastewater into low-COD lithium-containing wastewater, and collecting and temporarily storing the CO2 generated during the oxidation and degradation process; S2, adding an extractant, a co-extractant and a diluent to the low COD lithium-containing wastewater to extract lithium from the wastewater, and separating the low COD lithium-containing wastewater into a loaded organic phase and a raffinate; S3, adding pure water to the loaded organic phase, passing the CO2 produced in step S1 into the loaded organic phase, stripping the loaded organic phase, standing for phase separation, and the stripping aqueous phase is a high-purity lithium bicarbonate solution; S4. Pyrolyzing the stripping aqueous phase to generate lithium carbonate and CO2. The lithium carbonate is dried to obtain battery-grade lithium carbonate, and the CO2 is recycled.

[0006] Furthermore, in step S1, the electrocatalytic method is used to oxidize and degrade organic matter, using a BDD electrode as the positive electrode, controlling the current to 8-9 A, and the electrocatalytic time to 3-4 hours.

[0007] Furthermore, in step S2, the extractant is one or more of isooctyl salicylate, n-octyl salicylate, methyl salicylate, butyl salicylate, ethylene glycol salicylate, and isoamyl salicylate, and the extractant concentration is 10-20%; the synergistic agent is one or more of trialkylphosphine oxide, tri-n-butylphosphine oxide, triphenyl phosphate, tributyl phosphate, and trioctylphosphine oxide, and the synergistic agent concentration is 10-20%; the diluent is one or more of sulfonated kerosene, ordinary kerosene, aviation kerosene, ethyl acetate, benzene, heptane, toluene, and amyl acetate; the volume ratio of the total volume of the extractant, synergistic agent and diluent to the low COD lithium-containing wastewater is 0.5-2:1.

[0008] Furthermore, in step S3, the volume ratio of pure water to the loaded organic phase is 5-10:1, the CO2 is introduced for 20-30 minutes, and the phase separation is allowed to stand for 20-30 minutes.

[0009] Furthermore, the pyrolysis temperature is 70~90°C, the pyrolysis time is 2~5 hours, the drying temperature is 90~105°C, and the drying time is 2~4 hours.

[0010] Beneficial effects of the present invention: The present invention has simple overall steps, excellent treatment effect, and effectively solves the problems of wastewater treatment and lithium recovery; The present invention adopts a combined treatment method of electrocatalysis and alkaline lithium extraction, which can effectively degrade organic matter in wastewater and recover lithium at the same time; The present invention recycles the generated CO2 and reuses the organic phase, which has the advantages of environmental protection, energy saving and low cost. The battery-grade lithium carbonate recovered in the present invention has high product purity and quality, is economically beneficial, and fully recycles and utilizes valuable metals in wastewater, so that the wastewater can better meet emission standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments or descriptions 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.

[0012] Figure 1 It is a process flow chart. DETAILED DESCRIPTION

[0013] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention. Example 1

[0014] In this embodiment, a method for treating high COD lithium-containing wastewater using an electrocatalytic combined alkaline lithium extraction process comprises the following steps: S1. Use electrocatalysis to degrade organic pollutants in 1L of high COD lithium-containing wastewater, and degrade the high COD lithium-containing wastewater into low COD lithium-containing wastewater. The COD content in the high COD lithium-containing wastewater is 2.4g / L, the oil content is 95.08mg / L, the lithium content is 400mg / L, and the pH is 4. 5.76, the electrocatalytic method uses the BDD electrode as the positive electrode and the Pt electrode as the negative electrode, controls the current to 8.25A, and degrades for 2 hours. The COD content in the low-COD lithium-containing wastewater is reduced to 245 mg / L, the oil content is reduced to below 5 mg / L, and the pH of the solution is increased to 13; the BDD positive electrode produces CO2 and water in the process of degrading organic matter, and the CO2 produced in the process of organic matter degradation is collected and temporarily stored. While directly degrading organic matter, the BDD positive electrode directly degrades the organic matter adsorbed on the electrode surface, and produces CO2 and water in the process of degrading organic matter, and the CO2 is collected and temporarily stored. When the voltage exceeds 2.5V, the BDD positive electrode will also undergo a water electrolysis reaction to generate hydrogen and free OH. The free OH provides alkaline power for the extraction process in the subsequent step S2; S2, according to the ratio of 12% salicylic acid isooctyl ester, 12% trioctyl phosphine oxide and 76% sulfonated kerosene, the organic phase was added to the low COD lithium-containing wastewater for extraction, the volume ratio of the extraction phase to the low COD lithium-containing wastewater was 1: 1, stirred for 5 min at room temperature, allowed to stand, and the low COD lithium-containing wastewater was separated into a loaded organic phase and a raffinate, a portion of lithium entered the loaded organic phase, and the extraction rate of the single-stage extraction was 60.75%. After the first extraction, the lithium content in the raffinate was reduced to below 157 mg / L, and the raffinate was subjected to multi-stage extraction until the lithium content was reduced to below 10 mg / L; S3, adding pure water to the loaded organic phase, the volume ratio of pure water to the loaded organic phase is 7:1, the CO2 collected in step S1 is passed into the loaded organic phase, the loaded organic phase is stripped, and the phases are allowed to stand and separate. The aqueous phase is a high-purity lithium bicarbonate solution, and the organic phase can be reused; S4. The aqueous phase in step S3 is pyrolyzed at 90° C. The lithium bicarbonate is pyrolyzed to produce wet lithium carbonate, which is then dried at 105° C. for 2 h to produce battery-grade lithium carbonate with a lithium carbonate content of 99.66%. The CO2 generated during the preparation of wet lithium carbonate by pyrolysis of lithium bicarbonate is collected and recycled. Example 2

[0015] In this embodiment, a method for treating high COD lithium-containing wastewater using an electrocatalytic combined alkaline lithium extraction process comprises the following steps: S1. Degradation of organic pollutants in 1L of high-COD lithium-containing wastewater by electrocatalysis to degrade the high-COD lithium-containing wastewater into low-COD lithium-containing wastewater. The COD content in the high-COD lithium-containing wastewater was 3g / L, the oil content was 84.06mg / L, the lithium content was 570mg / L, and the pH was 5.76. The electrocatalytic method used a BDD electrode as the positive electrode and a Pt electrode as the negative electrode. The current was controlled at 8.25A and the degradation lasted for 3h. The COD content in the low-COD lithium-containing wastewater was reduced to 266mg / L, the oil content was reduced to below 1mg / L, and the pH of the solution was increased to 13.26. The BDD positive electrode produced CO2 in the process of degrading organic matter, and the CO2 generated during the degradation of organic matter was collected and temporarily stored. S2, according to the ratio of 12% salicylic acid isooctyl ester, 12% trioctyl phosphine oxide and 76% sulfonated kerosene, the organic phase was added to the low COD lithium-containing wastewater for extraction, the volume ratio of the extraction phase to the low COD lithium-containing wastewater was 1: 1, stirred for 5 min at room temperature, allowed to stand, and the low COD lithium-containing wastewater was separated into a loaded organic phase and a raffinate, a portion of the lithium entered the loaded organic phase, and the extraction rate of the single-stage extraction was 49.29%. After the first extraction, the lithium content in the raffinate was reduced to below 289 mg / L, and the raffinate was subjected to multi-stage extraction until the lithium content was reduced to below 10 mg / L; S3, add pure water to the loaded organic phase, the volume ratio of pure water to the loaded organic phase is 5:1, the CO2 collected in step S1 is passed into the loaded organic phase, the loaded organic phase is stripped, and the phases are allowed to stand and separate. The aqueous phase is a high-purity lithium bicarbonate solution, and the organic phase can be reused; S4. The aqueous phase in step S3 is pyrolyzed at 90° C. The lithium bicarbonate is pyrolyzed to produce wet lithium carbonate, which is then dried at 105° C. for 2 h to produce battery-grade lithium carbonate with a lithium carbonate content of 99.59%. The CO2 generated by the pyrolysis of the lithium bicarbonate is collected and recycled.

[0016] In the process of electrocatalytic degradation of organic matter in wastewater in the above-mentioned Example 1 and Example 2, the relationship between COD and oil content and electrolysis time is as follows Table 1: Table 1 Relationship between COD and oil content and electrolysis time

[0017] The technical indicators of the battery-grade lithium carbonate finally obtained in the above-mentioned Example 1 and Example 2 are as follows: Table 2 Technical indicators of battery-grade lithium carbonate

[0018] In summary, according to the data in Table 1 and Table 2, electrocatalysis can effectively degrade COD and oil in wastewater; extraction of low-COD lithium-containing wastewater that has undergone electrocatalytic treatment can achieve efficient separation of lithium, and lithium bicarbonate solution is obtained by back extraction with carbon dioxide, which is then used to obtain battery-grade lithium carbonate through pyrolysis and drying. The obtained battery-grade lithium carbonate has a high lithium carbonate content and a low impurity content, and the content of each component meets the relevant standards for battery-grade lithium carbonate.

[0019] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. 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 method for treating high COD lithium-containing wastewater by electrocatalysis combined with alkaline lithium extraction process, characterized in that: The steps include: S1. Using electrocatalysis to oxidize and degrade high-content organic matter in high-COD lithium-containing wastewater, converting high-COD low-lithium wastewater into low-COD lithium-containing wastewater, and collecting and temporarily storing the CO2 generated during the oxidation and degradation process; S2, adding an extractant, a co-extractant and a diluent to the low COD lithium-containing wastewater to extract lithium from the wastewater, and separating the low COD lithium-containing wastewater into a loaded organic phase and a raffinate; S3, adding pure water to the loaded organic phase, passing the CO2 produced in step S1 into the loaded organic phase, stripping the loaded organic phase, standing for phase separation, and the stripping aqueous phase is a high-purity lithium bicarbonate solution; S4. Pyrolyzing the stripping aqueous phase to generate lithium carbonate and CO2. The lithium carbonate is dried to obtain battery-grade lithium carbonate, and the CO2 is recycled.

2. The method for treating high COD lithium-containing wastewater by an electrocatalytic combined alkaline lithium extraction process according to claim 1, characterized in that: In step S1, the electrocatalytic method is used to oxidize and degrade organic matter, using a BDD electrode as the positive electrode, controlling the current to 8-9 A, and the electrocatalytic time to 3-4 hours.

3. The method for treating high COD lithium-containing wastewater by an electrocatalytic combined alkaline lithium extraction process according to claim 1, characterized in that: In step S2, the extractant is one or more of isooctyl salicylate, n-octyl salicylate, methyl salicylate, butyl salicylate, ethylene glycol salicylate, and isoamyl salicylate, and the concentration of the extractant is 10-20%; the synergistic extractant is one or more of trialkylphosphine oxide, tri-n-butylphosphine oxide, triphenyl phosphate, tributyl phosphate, and trioctylphosphine oxide, and the concentration of the synergistic extractant is 10-20%; the diluent is one or more of sulfonated kerosene, ordinary kerosene, aviation kerosene, ethyl acetate, benzene, heptane, toluene, and amyl acetate; the volume ratio of the total volume of the extractant, the synergistic extractant, and the diluent to the low COD lithium-containing wastewater is 0.5-2:

1.

4. The method for treating high COD lithium-containing wastewater by an electrocatalytic combined alkaline lithium extraction process according to claim 1, characterized in that: In step S3, the volume ratio of pure water to loaded organic phase is 5-10:1, the CO2 is introduced for 20-30 min, and the phase separation is allowed to stand for 20-30 min.

5. The method for treating high COD lithium-containing wastewater by an electrocatalytic combined alkaline lithium extraction process according to claim 1, characterized in that: In step S4, the pyrolysis temperature is 70-90° C., the pyrolysis time is 2-5 hours, the drying temperature is 90-105° C., and the drying time is 2-4 hours.

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