Recycling method for fluorine removal and lithium precipitation of lithium-containing wastewater

Abstract

The invention provides a lithium-containing wastewater recycling method which comprises the following steps: S1, mixing lithium-containing wastewater with a sulfuric acid solution, adjusting the pH value of the mixed solution to 4.0-5.0, then adding a first fluorine removal agent for fluorine removal treatment, and after the reaction is completed, carrying out solid-liquid separation to obtain a fluorine-removed solution and a fluorine removal agent; s2, regenerating the fluorine removal agent subjected to fluorine removal in the step S1 by using alkali liquor, and performing solid-liquid separation to obtain a regenerated fluorine removal agent and regenerated liquid; and S3, carrying out lithium precipitation treatment on the fluorine-removed liquid obtained in the step S1, carrying out solid-liquid separation after the reaction is completed to obtain a lithium-precipitated liquid and lithium carbonate, carrying out impurity removal on the regenerated liquid obtained in the step S2 by using a second fluorine removal agent and the lithium-precipitated liquid in sequence, and combining the regenerated liquid subjected to impurity removal with the fluorine-removed liquid obtained in the step S1. According to the method, solid waste residue output and impurity introduction in the lithium-containing wastewater treatment process can be reduced, the lithium yield is increased, and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the field of new energy technology, and specifically relates to a method for removing fluorine from lithium-containing wastewater and precipitating lithium for recycling. Background Art

[0002] At present, under the guidance and promotion of national policies, my country's new energy vehicle industry is developing rapidly, and power batteries are the core of new energy vehicles. The rapid development of new energy vehicles will bring about a large-scale wave of power battery retirement. It is estimated that the scrap volume will reach 380Gwh, about 3 million tons, by 2030. After a large number of power batteries are retired, if they are not properly disposed of and maximized, they will threaten public safety, cause irreversible environmental pollution, and waste precious valuable metal resources. In the process of pre-treatment and resource recovery of waste batteries, a large amount of fluoride ions in the electrolyte and binder are transferred to the ternary black powder, resulting in a large amount of fluoride ions in the lithium-containing sodium sulfate raffinate wastewater after the extraction technology is used to recover nickel, cobalt, manganese and other metals in the ternary black powder. This part of lithium-containing sodium sulfate wastewater needs to be defluorinated before it can be transferred to MVR for evaporation and concentration. After the lithium ions are concentrated, soda ash is generally added to recover the lithium element in it. After the lithium precipitation liquid is adjusted, it is further transferred to the MVR system for concentration, and there is no other utilization value.

[0003] There are many methods for treating fluoride-containing wastewater. The three most commonly used treatment processes in engineering are chemical precipitation, flocculation precipitation, and adsorption: (1) Chemical precipitation: This method is to separate F ions from water by adding ions that can react with F ions and generate precipitates into fluoride-containing wastewater. Commonly used precipitants are lime (CaO) and carbide slag [Ca(OH)2]. This process introduces impurity calcium during the defluorination process. After chemical precipitation treatment, the fluoride ion concentration in the fluoride-containing wastewater is only reduced to 30~40mg / L. At the same time, the amount of calcium slag produced after defluorination is large and the lithium content is high, which affects the yield of metallic lithium. (2) Flocculation precipitation: This method is based on the chemical precipitation method. Add inorganic flocculants such as metal salts or organic flocculants such as macromolecular compounds to fluoride-containing wastewater, use flocculants to complex fluoride to produce a large amount of colloids and insoluble substances, and based on the mechanism of flocculation adsorption, electrical neutralization or net capture and sweeping, make fluoride continue to aggregate and form tight flocs to remove fluoride. Compared with the chemical precipitation method, this method uses less reagents and has a larger treatment volume. This method is based on the chemical precipitation method, and uses the chemical precipitation method combined with the flocculation precipitation method to remove fluoride ions from fluoride-containing wastewater. However, the fluoride removal effect of this method is only about 30~40mg / L, and the depth of fluoride removal is far from enough. (3) Adsorption method: This method uses porous solid adsorbents to adsorb F ions to its surface by molecular gravity or chemical bond force, and then desorbs them to achieve separation and enrichment. Adsorption defluorination can effectively remove fluoride ions from wastewater, but the reagent cost of this method is too high and it is only suitable for the treatment of low-concentration fluoride-containing wastewater. At the same time, the process of regenerating and backwashing the adsorbent after adsorption generates a large amount of washing wastewater. In summary, when recycling precious metal resources from waste batteries, it is necessary to carry out in-depth treatment of fluoride ions. The fluoride ions contained in fluoride-containing wastewater are highly active. At the same time, the wastewater often contains high concentrations of inorganic salts, which makes it difficult to purify. In deep defluorination, the traditional dosage of reagents is large, the amount of solid waste generated is large, the related disposal costs and production costs are high, and the environmental pressure is obvious. Therefore, in view of the complex and difficult-to-treat water quality of lithium-containing sodium sulfate wastewater generated in the process of recycling waste lithium batteries, the selection of lithium-containing sodium sulfate wastewater treatment process is particularly important. If the treatment plan is not selected properly, on the one hand, it will lead to the problem that the fluoride ion concentration of the external drainage is difficult to meet the standard, which will limit the normal operation of the enterprise's production; on the other hand, it will increase the large amount of solid waste residue generated, which will affect the related operation and disposal costs and lithium recovery rate, resulting in a significant increase in production costs. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a method for removing fluorine from lithium-containing wastewater and precipitating lithium for recycling, which reduces the output of solid waste residue and the introduction of impurities in the process of treating lithium-containing wastewater, improves the yield of lithium and reduces production costs.

[0005] According to a first aspect of the present invention, a method for recycling lithium-containing wastewater is proposed, comprising the following steps: S1: mixing the lithium-containing wastewater with a sulfuric acid solution, adjusting the pH of the mixed solution to 4.0-5.0, then adding a first defluorinating agent for defluorination treatment, and performing solid-liquid separation after the reaction is completed to obtain a defluorinated liquid and a defluorinated defluorinating agent; S2: regenerating the defluorinating agent after defluorination described in step S1 with an alkali solution, and obtaining a regenerated defluorinating agent and a regenerated liquid after solid-liquid separation; S3: subjecting the defluorinated liquid in step S1 to lithium precipitation treatment, performing solid-liquid separation after the reaction is completed to obtain lithium precipitation liquid and lithium carbonate, and sequentially using a second defluorinating agent and the lithium precipitation liquid to remove impurities from the regenerated liquid in step S2, and the regenerated liquid after impurities removal is combined with the defluorinated liquid in step S1 for treatment.

[0006] The lithium-containing wastewater treated by the present invention can be lithium-containing sodium sulfate wastewater or lithium-containing ammonium sulfate wastewater, and is preferably a raffinate produced when recovering metals such as nickel, cobalt, and manganese in ternary black powder in an extraction process, wherein the main component is sodium sulfate, wherein the sodium ion content is 9-15 g / L, the lithium ion content is 2-4 g / L, the fluoride ion content is 40-80 mg / L, and the pH is 5-7.

[0007] In some embodiments, in step S1, the first defluorinating agent is at least one of zirconium oxide or titanium oxide. The present invention introduces a solid regenerable defluorinating agent, which is used for defluorination treatment of lithium-containing wastewater, has a significant defluorination effect, and can reduce the output of lithium-containing slag and improve the lithium recovery rate. The regenerated defluorinating agent can continue to be used for defluorination, reducing production costs. The first defluorinating agent reacts with fluoride ions to form a complex, and the principle is as follows: MeO2+6F - +4H2O→H2[MeF6]+6OH - .

[0008] In some preferred embodiments, the particle size D50 of the first defluorination agent is greater than 25 μm.

[0009] In some embodiments, in step S1, the content of the first defluorinating agent in the mixed solution is 1-10 g / L.

[0010] In some embodiments, in step S1, the defluorination treatment includes adding an acid solution to maintain a pH of 4.5 to 5.0; And / or, the temperature of the defluorination treatment is 30-50°C; And / or, the defluorination treatment time is 0.5 to 2 hours; And / or, the stirring speed of the defluorination treatment is 200-300 rpm.

[0011] In some embodiments, in step S2, the regeneration process is: mixing the defluorinated defluorinating agent with water, controlling the liquid-solid ratio to (4-5): 1 mL / g, adding the alkali solution to control the pH to 12-13, reacting for 1-2 hours, and obtaining the regenerated defluorinating agent and the regenerated liquid after solid-liquid separation. The first defluorinating agent used in the present invention can be regenerated by alkali solution treatment, and the principle is as follows: H2[MeF6]+6OH - →MeO2+6F - +4H2O.

[0012] In some embodiments, step S2 further comprises activating the regenerated defluorinating agent, wherein the activation process is as follows: mixing the regenerated defluorinating agent with water, controlling the liquid-solid ratio to (4-5): 1 mL / g, adding sulfuric acid solution to control the pH to 4-5, reacting for 1-2 hours, and obtaining an activated defluorinating agent. Treating the regenerated defluorinating agent under low-acid conditions can increase its molecular activity and improve the defluorination effect.

[0013] In some embodiments, in step S3, the lithium precipitation treatment process is: the defluorinated liquid is concentrated and then a sodium carbonate solution is added, and the molar ratio of sodium carbonate in the sodium carbonate solution to lithium ions in the defluorinated liquid is (1.1-1.2): 1; The temperature of the lithium precipitation treatment is controlled at 85-95°C; And / or, the lithium precipitation treatment time is 1 to 1.5 hours; And / or, the stirring speed in the lithium precipitation treatment is 200~300rpm.

[0014] In some embodiments, the defluorinated liquid is concentrated by step-by-step falling film evaporation using an MVR system.

[0015] In some preferred embodiments, in step S3, the defluorinated liquid is concentrated to a lithium ion concentration of 8-12 g / L.

[0016] In some preferred embodiments, in step S3, the mass percentage concentration of the sodium carbonate solution is 10% to 20%.

[0017] In some embodiments, the second defluorinating agent is at least one of calcium oxide and calcium hydroxide; in step S3, the impurity removal process is: mixing the regenerated liquid described in step S2 with the second defluorinating agent to remove fluorine, then mixing the defluorinated regenerated liquid with the lithium precipitation liquid to remove calcium, and obtaining the de-impurified regenerated liquid after solid-liquid separation; wherein the molar ratio of carbonate ions in the lithium precipitation liquid to calcium ions in the defluorinated regenerated liquid is (1.2~1.5):1. Since the lithium precipitation liquid contains a large amount of CO3 2-Ions can be used to decalcify the regenerated liquid after defluorination of calcium oxide or calcium hydroxide, control the molar ratio of carbonate ions in the lithium precipitation liquid to calcium ions in the regenerated liquid, and reduce the calcium ion concentration in the regenerated liquid after defluorination to 10~20mg / L, thereby reducing production costs.

[0018] In some embodiments, the dosage of the second defluorinating agent is 8-12 kg / m³.

[0019] In some embodiments, the post-lithium precipitation solution contains cations, and the cations include Na + 、 NH4 + At least one of the above, the method further comprises the following steps: saponifying the organic extractant with the lithium precipitation solution described in step S3, wherein the organic extractant contains H + , control the Na in the solution after lithium precipitation + NH4 + The total number of moles of H in the organic extractant + The molar ratio is 1: (2.5~5); after the saponification is completed, the water phase is taken and combined with the lithium-containing wastewater described in step S1 for treatment. + and a higher pH (Na + The content is 10~30g / L, pH is 11~12), which can be used to saponify the organic extractant in the extraction process, control the sodium ions in the solution after lithium precipitation and the H in the organic extractant + The molar ratio can achieve a target saponification rate of 20% to 40%, reducing the amount of liquid alkali used in the extraction process.

[0020] In some preferred embodiments, the organic extractant is at least one of P204 or P507.

[0021] According to the second aspect of the present invention, the application of the method described in the first aspect of the present invention in the defluorination of lithium-containing wastewater is proposed. The fluorine content in the solution after defluorination by this method can be reduced to less than 1 mg / L, and the defluorinated solution can be recycled, effectively reducing production costs.

[0022] According to one embodiment of the present invention, there are at least the following beneficial effects: The first defluorinating agent used in the present invention can efficiently defluorinate lithium-containing wastewater, does not introduce new impurities during the defluorination process, and has no excess filter residue output, which greatly reduces the loss of lithium ions. At the same time, the concentration of metallic lithium entrained by the defluorinating agent after defluorination is low, which can further reduce the loss rate of lithium. The defluorination effect is stable after the defluorinating agent is regenerated, and it can be regenerated and used multiple times. After the defluorinated liquid is concentrated and lithium is precipitated, it can be reused in the extraction system, and the decalcification system after the defluorinated liquid after the defluorinating agent is regenerated can be recycled, which can reduce production costs again. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a process flow chart of Example 1 of the present invention. DETAILED DESCRIPTION

[0024] The concept and technical effects of the present invention will be clearly and completely described below in conjunction with embodiments to fully understand the purpose, features and effects of the present invention.

[0025] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0026] The lithium-containing sodium sulfate stock solution used in the following examples and comparative examples is all from the production line, wherein the sodium ion content is 13 g / L, the lithium ion content is 2.036 g / L, the fluoride ion content is 59.4 mg / L, and the pH is 6.0.

[0027] Example 1 This embodiment provides a method for recycling lithium-containing wastewater, such as Figure 1 As shown, the specific steps include: S1: Add concentrated sulfuric acid solution to the lithium-containing sodium sulfate stock solution, and the pH of the mixed solution is 5.0. Add zirconium oxide, adjust the stirring rate to 200rpm, and defluorinate at 40°C for 1h. During the reaction, add concentrated sulfuric acid to control the pH to 4.5. After the reaction is completed, filter to obtain the defluorinated defluoridation agent and defluorinated liquid. In the above process, different amounts of zirconium oxide were used to make its content in the mixed solution 1 g / L, 2 g / L, 3 g / L, 6 g / L, 8 g / L, and 10 g / L, respectively. The fluoride ion content and lithium ion content in the corresponding defluorinated liquid were measured, and the results are shown in Table 1.

[0028] Table 1

[0029] Among them, fluoride ion removal rate = (fluoride ion content in the original solution - fluoride ion content in the solution after defluorination) / fluoride ion content in the original solution. It can be seen that with the increase of zirconium oxide defluoridation agent content, the defluoridation effect gradually increases, while the lithium ion content does not change significantly, that is, the lithium entrained by the defluoridation agent after defluorination is low.

[0030] The conventional defluorination process uses calcium oxide to perform two-stage defluorination on fluoride-containing wastewater, so two batches of defluorination slag are produced, each batch of defluorination slag has a water content of about 40%, and the lithium content is 0.1%. It can be seen that the present invention effectively reduces the loss of lithium while achieving a better defluorination effect.

[0031] S2: Add the defluorinated defluorinating agent in step S1 to pure water, control the liquid-solid ratio to 4:1 mL / g, add 32% mass percentage of liquid alkali to control the pH to 12, and react for 1 hour to defluorinate and regenerate. Press filter to obtain the regenerated defluorinating agent and the regenerated liquid. Add the regenerated defluorinating agent to pure water, control the liquid-solid ratio to 4:1 mL / g, add concentrated sulfuric acid to control the pH to 4, and react for 1 hour to activate. After activation, press filter to obtain the activated defluorinating agent.

[0032] The activated defluorinating agent was mixed with pure water to make pulp, the liquid-solid ratio was controlled to be 4:1 mL / g, concentrated sulfuric acid was added to control the pH to 4.5, the defluorinating agent after pulping was added to the lithium-containing sodium sulfate stock solution, the defluorinating agent content in the mixed solution was controlled to be 3g / L, and concentrated sulfuric acid was added during the reaction to control the pH to 4.5, which can reduce the fluorine content of the lithium-containing sodium sulfate stock solution from 59.4mg / L to 4.42mg / L, and the fluoride ion removal rate is 92.56%. It can be seen that the regenerated defluorinating agent can still maintain a high defluorination efficiency.

[0033] S3: The defluorinated liquid in step S1 is sent to the MVR system, and after step-by-step falling film concentration, when the lithium ion concentration reaches 10g / L, the concentrated lithium liquid is transferred to the lithium precipitation tank and a sodium carbonate solution with a mass percentage concentration of 15% is added thereto for reaction. The molar ratio of sodium carbonate in the added sodium carbonate solution to lithium ions in the concentrated lithium liquid is 1.15:1. The reaction temperature is controlled at 90°C, the reaction time is 1.5h, and the stirring speed is 200rpm. After the reaction is completed, the reaction liquid is transferred to a centrifuge for centrifugation to obtain solid crude lithium carbonate and lithium precipitation liquid. The Na + The content is about 23g / L, CO3 2- The content is about 8g / L and the pH is about 11.

[0034] S4: Take the regenerated liquid in step S2 and heat it at 10kg / m 3 Calcium oxide is added in an amount of 100% to remove fluorine, and the regenerated liquid after defluorination is obtained after filtration (wherein Ca 2+ The molar ratio of carbonate ions in the lithium precipitation liquid to calcium ions in the regeneration liquid after defluorination is controlled to be 1.3:1. After the reaction is completed, the calcium ion concentration in the regeneration liquid after defluorination is reduced to 15 mg / L. The regeneration liquid can be combined with the defluorination liquid in step S1 for treatment.

[0035] S5: Take the post-lithium precipitation liquid in step S3, saponify the organic extractant P204 in the extraction system, control the molar ratio of sodium ions in the post-lithium precipitation liquid to hydrogen ions in the organic extractant to be 1:2.5, and measure the organic saponification rate to be 40%. After the saponification is completed, stand and separate, and the aqueous phase can be combined with the lithium-containing sodium sulfate stock solution for treatment.

[0036] It can be seen that after the defluoridated liquid is concentrated and lithium is precipitated, it can be recycled to the extraction system and the defluoridation agent regeneration-calcification system of the defluoridated liquid of calcium oxide for circular use, which effectively reduces the production cost.

[0037] Comparative Example 1 The only difference from Example 1 is that in step S1, the lithium-containing sodium sulfate stock solution is not mixed with the concentrated sulfuric acid solution, and the defluorination experiment is directly carried out, and the pH is not adjusted during the reaction.

[0038] In the above process, different amounts of zirconium oxide defluoridation agent were used to make its content in the mixed solution 1g / L, 2g / L, and 3g / L, respectively. The fluoride ion content and lithium ion content in the corresponding defluoridated liquid were measured. The comparison of the defluoridation effect with that of Example 1 is shown in Table 2.

[0039] Table 2

[0040] It can be seen that in Comparative Example 1, the pH value was not adjusted during the defluorination process. When the same content of zirconium oxide defluorinating agent was used, the fluoride ion removal rate was lower than that of Example 1, while the lithium ion content did not change significantly.

[0041] The above is a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A method for recycling lithium-containing wastewater, characterized in that: The following steps are involved: S1: mixing the lithium-containing wastewater with a sulfuric acid solution, adjusting the pH of the mixed solution to 4.0-5.0, then adding a first defluorinating agent for defluorination treatment, and performing solid-liquid separation after the reaction is completed to obtain a defluorinated liquid and a defluorinated defluorinating agent; S2: regenerating the defluorinating agent after defluorination described in step S1 with an alkali solution, and obtaining a regenerated defluorinating agent and a regenerated liquid after solid-liquid separation; S3: subjecting the defluorinated liquid in step S1 to lithium precipitation treatment, performing solid-liquid separation after the reaction is completed to obtain lithium precipitation liquid and lithium carbonate, and sequentially using a second defluorinating agent and the lithium precipitation liquid to remove impurities from the regenerated liquid in step S2, and the regenerated liquid after impurities removal is combined with the defluorinated liquid in step S1 for treatment.

2. The method according to claim 1, characterized in that In step S1, the first defluorinating agent is at least one of zirconium oxide or titanium oxide.

3. The method according to claim 1, characterized in that In step S1, the content of the first defluorinating agent in the mixed solution is 1-10 g / L.

4. The method according to claim 1, characterized in that: In step S1, the defluorination treatment includes adding acid solution to maintain the pH at 4.5-5.0; And / or, the temperature of the defluorination treatment is 30-50°C; And / or, the defluorination treatment time is 0.5 to 2 hours; And / or, the stirring speed of the defluorination treatment is 200-300 rpm.

5. The method according to claim 1, characterized in that In step S2, the regeneration process is: mixing the defluorinated defluorinating agent with water, controlling the liquid-solid ratio to (4-5): 1 mL / g, adding the alkali solution to control the pH to 12-13, reacting for 1-2 hours, and obtaining the regenerated defluorinating agent and the regenerated liquid after solid-liquid separation.

6. The method according to claim 1, characterized in that Step S2 also includes activating the regenerated defluorinating agent, and the activation process is: mixing the regenerated defluorinating agent with water, controlling the liquid-solid ratio to (4~5): 1 mL / g, adding sulfuric acid solution to control the pH to 4~5, reacting for 1~2 hours, and obtaining an activated defluorinating agent.

7. The method according to claim 1, characterized in that In step S3, the lithium precipitation treatment process is: the defluorinated liquid is concentrated and then added with a sodium carbonate solution, wherein the molar ratio of sodium carbonate in the sodium carbonate solution to lithium ions in the defluorinated liquid is (1.1-1.2):1; The temperature of the lithium precipitation treatment is controlled at 85-95°C; And / or, the lithium precipitation treatment time is 1 to 1.5 hours; And / or, the stirring speed in the lithium precipitation treatment is 200~300rpm.

8. The method according to claim 1, characterized in that The second defluorinating agent is at least one of calcium oxide and calcium hydroxide; in step S3, the impurity removal process is: mixing the regenerated liquid described in step S2 with the second defluorinating agent to remove fluorine, and then mixing the defluorinated regenerated liquid with the lithium precipitation liquid to remove calcium, and obtaining the de-impurified regenerated liquid after solid-liquid separation; wherein the molar ratio of carbonate ions in the lithium precipitation liquid to calcium ions in the defluorinated regenerated liquid is (1.2~1.5):

1.

9. The method according to claim 1, characterized in that: The solution after lithium precipitation contains cations, including Na + 、 NH4 + At least one of the above, the method further comprises the following steps: saponifying the organic extractant with the lithium precipitation solution described in step S3, wherein the organic extractant contains H + , control the Na in the solution after lithium precipitation + NH4 + The total number of moles of H in the organic extractant + The molar ratio is 1: (2.5~5); after the saponification is completed, the water phase is taken and combined with the lithium-containing wastewater described in step S1 for treatment.

10. Use of the method according to any one of claims 1 to 9 in defluorination of lithium-containing wastewater.

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