Lithium-containing wastewater fluoride removal, lithium precipitation and recycling method

Abstract

The application provides a method for recycling lithium-containing wastewater, 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 defluorination agent for defluorination treatment, performing solid-liquid separation after the reaction is completed, and obtaining a defluorination-after liquid and a defluorination-after defluorination agent; S2: regenerating the defluorination-after defluorination agent in step S1 by using an alkali solution, and obtaining a regenerated defluorination agent and a regeneration-after liquid after solid-liquid separation; S3: performing lithium precipitation treatment on the defluorination-after liquid in step S1, performing solid-liquid separation after the reaction is completed, and obtaining a lithium precipitation-after liquid and lithium carbonate; sequentially using a second defluorination agent and the lithium precipitation-after liquid to remove impurities from the regeneration-after liquid in step S2, and combining and treating the impurity-removed regeneration-after liquid and the defluorination-after liquid in step S1. The method can reduce the production of solid waste residues and the introduction of impurities in the treatment process of the lithium-containing wastewater, improve the lithium yield, and reduce the production cost.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, specifically relating to a method for defluorinating lithium-containing wastewater, precipitating lithium, and recycling it. Background Technology

[0002] Currently, 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 massive wave of retired power batteries, with the amount expected to reach 380 GWh (approximately 3 million tons) by 2030. If these large-scale retired power batteries are not properly disposed of and their value maximized, they will threaten public safety, cause irreversible environmental pollution, and waste valuable metal resources. During the pre-treatment and resource recycling process of waste batteries, a large amount of fluoride ions from the electrolyte and binder are transferred to the ternary lithium-ion battery, resulting in a large amount of fluoride ions in the lithium sulfate raffinate wastewater after the extraction of nickel, cobalt, and manganese from the ternary lithium-ion battery. This lithium sulfate wastewater needs to be defluorinated before being transferred to the MVR (Medium-Voltage Reduction) system for evaporation and concentration. After concentration, soda ash is generally added to recover the lithium element. The lithium-precipitated liquid is then adjusted and transferred back to the MVR system for further concentration, with no further utilization value.

[0003] There are various methods for treating fluoride-containing wastewater. Currently, the most commonly used treatment processes in engineering are chemical precipitation, flocculation precipitation, and adsorption: (1) Chemical precipitation: This method involves adding ions that can react with F ions and generate precipitates to separate F ions from the water. Commonly used precipitants include lime (CaO) and carbide slag [Ca(OH)2]. This process introduces calcium impurities during the defluorination process. After chemical precipitation, the concentration of fluoride ions in the fluoride-containing wastewater only drops to 30~40 mg / L. At the same time, the amount of calcium slag generated after defluorination is large and the lithium content is high, which affects the recovery rate of metallic lithium. (2) Flocculation precipitation: This method is based on chemical precipitation by adding inorganic flocculants such as metal salts or organic flocculants such as macromolecular compounds to the fluoride-containing wastewater. The flocculants complex fluorides to generate a large amount of colloids and insoluble substances. Based on the mechanism of flocculation adsorption charge neutralization or net capture sweeping, the fluorides continuously aggregate and form dense flocs to remove fluoride. Compared with chemical precipitation, this method uses less reagent and has a larger processing capacity. This method is based on chemical precipitation and uses a combination of chemical precipitation and flocculation precipitation to remove fluoride ions from fluoride-containing wastewater. However, the fluoride removal effect of this method is only about 30~40 mg / L, which is far from sufficient. (3) Adsorption method: This method uses porous solid adsorbents to adsorb F ions onto their surface by molecular attraction or chemical bond force, and then desorbs them to achieve separation and enrichment. Adsorption can effectively remove fluoride ions from wastewater, but the reagent cost of this method is too high. It is 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. Fluoride-containing wastewater contains highly reactive fluoride ions, and often contains high concentrations of inorganic salts, making purification difficult. Deep defluorination requires large dosages of traditional reagents, resulting in significant solid waste generation, high disposal and production costs, and substantial environmental pressure. Therefore, given the complex composition and difficulty in treating lithium-containing sodium sulfate wastewater generated during the recycling of waste lithium batteries, the selection of a suitable treatment process is crucial. An inappropriate treatment plan can lead to problems such as failing to meet fluoride ion concentration standards in the effluent, restricting normal production operations; furthermore, it can increase the generation of solid waste, impacting operational and disposal costs and lithium recovery rates, thus significantly increasing production costs. Summary of the Invention

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

[0005] According to a first aspect of the present invention, a method for recycling lithium-containing wastewater is provided, comprising the following steps:

[0006] S1: Mix lithium-containing wastewater with sulfuric acid solution, adjust the pH of the mixture to 4.0~5.0, then add the first defluorinating agent for defluorination treatment. After the reaction is completed, perform solid-liquid separation to obtain defluorinated liquid and defluorinating agent.

[0007] S2: The defluorinating agent after defluorination in step S1 is regenerated with alkaline solution, and the regenerated defluorinating agent and the regenerated liquid are obtained after solid-liquid separation.

[0008] S3: The defluorinated liquid described in step S1 is subjected to lithium precipitation treatment. After the reaction is completed, solid-liquid separation is performed to obtain the lithium-precipitated liquid and lithium carbonate. The regenerated liquid described in step S2 is then treated with the second defluorinating agent and the lithium-precipitated liquid to remove impurities. The regenerated liquid after impurity removal is then combined with the defluorinated liquid described in step S1 for further treatment.

[0009] The lithium-containing wastewater treated by this invention can be lithium-containing sodium sulfate wastewater or lithium-containing ammonium sulfate wastewater, preferably the raffinate produced during the extraction process when recovering metals such as nickel, cobalt, and manganese from ternary black powder. The main component is sodium sulfate, wherein the sodium ion content is 9~15g / L, the lithium ion content is 2~4g / L, the fluoride ion content is 40~80mg / L, and the pH is 5~7.

[0010] In some embodiments, in step S1, the first defluorinating agent is at least one of zirconium oxide or titanium oxide. This invention introduces a solid, regenerable defluorinating agent for the defluorination treatment of lithium-containing wastewater, exhibiting significant defluorination effects while reducing lithium-containing slag production and improving lithium recovery rates. The regenerated defluorinating agent can be reused for defluorination, reducing production costs. The first defluorinating agent reacts with fluoride ions to form a complex, as follows: MeO2 + 6F - +4H₂O→H₂[MeF₆]+6OH⁻ - .

[0011] In some preferred embodiments, the particle size D50 of the first defluorinating agent is >25 μm.

[0012] In some embodiments, in step S1, the content of the first defluorinating agent in the mixture is 1~10 g / L.

[0013] In some embodiments, step S1 includes adding acid to maintain a pH of 4.5 to 5.0;

[0014] And / or, the temperature of the defluorination treatment is 30~50℃;

[0015] And / or, the defluorination treatment time is 0.5~2h;

[0016] And / or, the stirring speed for the defluorination treatment is 200~300 rpm.

[0017] In some embodiments, in step S2, the regeneration process is as follows: the defluorinating agent after defluorination is mixed with water, the liquid-to-solid ratio is controlled at (4~5):1 mL / g, the alkaline solution is added to control the pH at 12~13, the reaction is carried out for 1~2 hours, and the regenerated defluorinating agent and the regenerated liquid are obtained after solid-liquid separation. The first defluorinating agent used in this invention can be regenerated by alkaline treatment, the principle of which is as follows: H2[MeF6] + 6OH - →MeO2+6F - +4H2O.

[0018] In some embodiments, step S2 further includes activating the regenerated defluorinating agent. The activation process involves mixing the regenerated defluorinating agent with water, controlling the liquid-to-solid ratio at (4-5):1 mL / g, adding sulfuric acid solution to control the pH at 4-5, and reacting for 1-2 hours to obtain an activated defluorinating agent. Treating the regenerated defluorinating agent under low-acid conditions can increase its molecular activity and improve the defluorination effect.

[0019] In some embodiments, in step S3, the lithium precipitation process is as follows: the defluorinated liquid is concentrated and then a sodium carbonate solution is added, 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;

[0020] The temperature for the lithium deposition process is controlled at 85~95℃;

[0021] And / or, the lithium deposition treatment time is 1~1.5h;

[0022] And / or, the stirring speed in the lithium deposition process is 200~300 rpm.

[0023] In some embodiments, the defluorinated liquid is concentrated by a stepwise falling film evaporation using an MVR system.

[0024] In some preferred embodiments, in step S3, the defluorinated liquid is concentrated to a lithium ion concentration of 8-12 g / L.

[0025] In some preferred embodiments, in step S3, the mass percentage concentration of the sodium carbonate solution is 10% to 20%.

[0026] In some embodiments, the second defluorinating agent is at least one of calcium oxide or calcium hydroxide; in step S3, the impurity removal process is as follows: the regenerated liquid obtained in step S2 is mixed with the second defluorinating agent to remove fluoride, and then the defluorinated regenerated liquid is mixed with the lithium precipitation liquid to remove calcium, and the impurity-removed regenerated liquid is obtained 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. Because 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, and to control the molar ratio of carbonate ions in the lithium precipitation liquid to calcium ions in the regenerated liquid. This can reduce the calcium ion concentration in the regenerated liquid after defluorination to 10~20 mg / L, thereby reducing production costs.

[0027] In some embodiments, the amount of the second defluorinating agent used is 8~12 kg / m³.

[0028] In some embodiments, the post-lithium precipitation solution contains cations, including Na. + NH4 + The method further includes at least one of the following steps: saponifying the organic extractant with the lithium precipitation solution described in step S3, wherein the organic extractant contains H. + Controlling the Na content in the lithium precipitation solution + NH4 + The total number of moles and the H in the organic extractant + The molar ratio is 1:(2.5~5); after saponification, the aqueous phase is taken and combined with the lithium-containing wastewater described in step S1 for treatment. Because the liquid after lithium precipitation contains a large amount of Na... + And the pH is high (Na) + (Concentration of 10~30 g / L, pH 11~12) can be used for saponification of organic extractants in the extraction process, controlling the sodium ions and H+ in the organic extractant in the lithium precipitation solution. + With a molar ratio of 20% to 40%, the target saponification rate can be achieved, reducing the amount of liquid alkali used in the extraction process.

[0029] In some preferred embodiments, the organic extractant is at least one of P204 or P507.

[0030] According to a second aspect of the present invention, the method described in the first aspect of the invention is proposed for the defluorination of lithium-containing wastewater. The method can reduce the fluoride content in the solution after defluorination to below 1 mg / L, and the defluorinated solution can be recycled, effectively reducing production costs.

[0031] According to one embodiment of the present invention, at least the following beneficial effects are achieved:

[0032] The first defluorinating agent used in this invention can efficiently remove fluoride from lithium-containing wastewater without introducing new impurities or producing excess filter residue, thus greatly reducing lithium ion loss. Furthermore, the low concentration of metallic lithium entrained in the defluorinating agent after defluorination further reduces the lithium loss rate. The defluorinating agent maintains stable defluorination performance after regeneration and can be regenerated multiple times. After concentration and lithium precipitation, the defluorinated liquid can be reused in extraction systems and calcium removal systems following defluorination of the regenerated liquid, allowing for recycling and further reducing production costs. Attached Figure Description

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0034] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention. Detailed Implementation

[0035] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention.

[0036] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0037] The lithium-containing sodium sulfate stock solution used in the following examples and comparative examples all came from the production line, with a sodium ion content of 13 g / L, a lithium ion content of 2.036 g / L, a fluoride ion content of 59.4 mg / L, and a pH of 6.0.

[0038] Example 1

[0039] This embodiment provides a method for recycling lithium-containing wastewater, such as... Figure 1 As shown, the specific steps include:

[0040] 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 speed to 200 rpm, and defluorinate at 40℃ for 1 hour. During the reaction, add concentrated sulfuric acid to control the pH at 4.5. After the reaction is complete, filter to obtain the defluorinating agent and the defluorinated solution.

[0041] 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 defluorination solution were measured, and the results are shown in Table 1.

[0042] Table 1

[0043]

[0044] The fluoride ion removal rate is calculated as follows: (fluoride ion content in the original solution - fluoride ion content in the defluorinated solution) / fluoride ion content in the original solution. It can be seen that the defluorination effect gradually increases with the increase of the zirconium oxide defluorinating agent content, while the lithium ion content does not change significantly, meaning that the lithium entrained by the defluorinating agent after defluorination is relatively low.

[0045] Conventional defluorination processes use calcium oxide for two-stage defluorination of fluoride-containing wastewater, resulting in two batches of defluorination residue. Each batch of residue contains approximately 40% water and 0.1% lithium. Therefore, this invention effectively reduces lithium loss while achieving good defluorination results.

[0046] S2: Add the defluorinating agent from step S1 to pure water, controlling the liquid-to-solid ratio at 4:1 mL / g. Add 32% (w / w) liquid alkali to control the pH at 12, and react for 1 hour to regenerate the defluorinating agent. Filter by pressure to obtain the regenerated defluorinating agent and the regenerated liquid. Add the regenerated defluorinating agent to pure water, controlling the liquid-to-solid ratio at 4:1 mL / g. Add concentrated sulfuric acid to control the pH at 4, and react for 1 hour to activate the agent. After activation, filter by pressure to obtain the activated defluorinating agent.

[0047] The activated defluorinating agent was mixed with pure water to form a slurry, with a liquid-to-solid ratio of 4:1 mL / g. Concentrated sulfuric acid was added to control the pH at 4.5. The slurry-formed defluorinating agent was then added to the lithium sodium sulfate stock solution, controlling the defluorinating agent content in the mixture to 3 g / L. During the reaction, concentrated sulfuric acid was added to maintain the pH at 4.5. This reduced the fluoride content of the lithium sodium sulfate stock solution from 59.4 mg / L to 4.42 mg / L, achieving a fluoride ion removal rate of 92.56%. This demonstrates that the regenerated defluorinating agent can still maintain high defluorination efficiency.

[0048] S3: The defluorinated liquid from step S1 is fed into an MVR system and concentrated through a series of falling films. When the lithium ion concentration reaches 10 g / L, the concentrated lithium solution is transferred to a lithium precipitation tank, and a 15% (w / w) sodium carbonate solution is added for reaction. The molar ratio of sodium carbonate in the added sodium carbonate solution to lithium ions in the concentrated lithium solution is 1.15:1. The reaction temperature is controlled at 90℃, the reaction time is 1.5 h, and the stirring speed is 200 rpm. After the reaction is complete, the reaction solution is centrifuged to obtain solid crude lithium carbonate and the lithium precipitation liquid. The Na in the lithium precipitation liquid... + The content is approximately 23 g / L, CO3 2- The content is approximately 8 g / L, and the pH is approximately 11.

[0049] S4: Take the regenerated liquid from step S2, and apply it at a rate of 10 kg / m³. 3 Calcium oxide was added to remove fluoride, and after filtration, the regenerated solution after fluoride removal was obtained (where Ca... 2+Approximately 0.27 g / L) was mixed with the lithium precipitation solution from step S3, and the molar ratio of carbonate ions in the lithium precipitation solution to calcium ions in the defluorinated regenerated solution was controlled at 1.3:1. After the reaction was completed, the calcium ion concentration in the defluorinated regenerated solution decreased to 15 mg / L. This regenerated solution can be combined with the defluorinated solution from step S1 for further treatment.

[0050] S5: Take the lithium-precipitated liquid from step S3 and saponify the organic extractant P204 in the extraction system. Control the molar ratio of sodium ions in the lithium-precipitated liquid to hydrogen ions in the organic extractant to be 1:2.5. The organic saponification rate was measured to be 40%. After saponification, allow the mixture to stand and separate into layers. The aqueous phase can be combined with the lithium-containing sodium sulfate stock solution for further treatment.

[0051] It is evident that after the defluorination liquid is concentrated and lithium is precipitated, it can be reused in the extraction system and the calcium removal system of the defluorination agent regeneration-calcium oxide defluorination liquid, thus achieving recycling and effectively reducing production costs.

[0052] Comparative Example 1

[0053] The only difference from Example 1 is that in step S1, the lithium-containing sodium sulfate stock solution was not mixed with concentrated sulfuric acid solution and the defluorination experiment was carried out directly, and the pH was not adjusted during the reaction process.

[0054] In the above process, different amounts of zirconium oxide defluorinating agent were used to make their contents in the mixed solution 1 g / L, 2 g / L and 3 g / L, respectively. The fluoride ion content and lithium ion content in the defluorinated solution were measured. The defluorination effect is compared with that of Example 1 in Table 2.

[0055] Table 2

[0056]

[0057] It can be seen that Comparative Example 1 did not adjust the pH during the defluorination process. When using the same amount of zirconium oxide defluorinating agent, the fluoride ion removal rate was lower than that of Example 1, while the lithium ion content did not change significantly.

[0058] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for recycling lithium-containing wastewater, characterized in that, Includes the following steps: S1: Mix lithium-containing wastewater with sulfuric acid solution, adjust the pH of the mixture to 4.0~5.0, then add the first defluorinating agent for defluorination treatment. After the reaction is completed, perform solid-liquid separation to obtain defluorinated liquid and defluorinating agent. S2: The defluorinating agent after defluorination in step S1 is regenerated with alkaline solution, and the regenerated defluorinating agent and the regenerated liquid are obtained after solid-liquid separation. S3: The defluorinated liquid described in step S1 is subjected to lithium precipitation treatment. After the reaction is completed, solid-liquid separation is performed to obtain the lithium precipitation liquid and lithium carbonate. The regenerated liquid described in step S2 is then treated with the second defluorinating agent and the lithium precipitation liquid to remove impurities. The regenerated liquid after impurity removal is then combined with the defluorinated liquid described in step S1 for further treatment. The lithium precipitation process is as follows: the defluorinated liquid is concentrated and then a sodium carbonate solution is added; The second defluorinating agent is at least one of calcium oxide or calcium hydroxide.

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 mixture is 1~10g / L.

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

5. The method according to claim 1, characterized in that, In step S2, the regeneration process is as follows: the defluorinating agent after defluorination is mixed with water, the liquid-solid ratio is controlled at (4~5):1 mL / g, the alkaline solution is added to control the pH=12~13, the reaction is carried out for 1~2 hours, and the regenerated defluorinating agent and the regenerated liquid are obtained after solid-liquid separation.

6. The method according to claim 1, characterized in that, Step S2 also includes activating the regenerated defluorinating agent. The activation process is as follows: the regenerated defluorinating agent is mixed with water, the liquid-solid ratio is controlled at (4~5):1 mL / g, sulfuric acid solution is added to control the pH=4~5, and the reaction is carried out for 1~2 hours to obtain the activated defluorinating agent.

7. The method according to claim 1, characterized in that, In step S3, the molar ratio of sodium carbonate in the sodium carbonate solution to lithium ions in the defluorinated solution is (1.1~1.2):1; The temperature for the lithium deposition process is controlled at 85~95℃; And / or, the lithium deposition treatment time is 1~1.5h; And / or, the stirring speed in the lithium deposition process is 200~300 rpm.

8. The method according to claim 1, characterized in that, In step S3, the impurity removal process is as follows: the regenerated liquid obtained in step S2 is mixed with the second defluorinating agent to remove fluoride, and then the defluorinated regenerated liquid is mixed with the lithium precipitation liquid to remove calcium. After solid-liquid separation, the impurity-removed regenerated liquid is obtained; 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 lithium precipitation solution contains cations, including Na. + NH4 + The method further includes at least one of the following steps: saponifying the organic extractant with the lithium precipitation solution described in step S3, wherein the organic extractant contains H. + Controlling the Na content in the lithium precipitation solution + NH4 + The total number of moles and the H in the organic extractant + The molar ratio is 1:(2.5~5); after saponification, the aqueous phase is taken and combined with the lithium-containing wastewater described in step S1 for treatment.

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

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