A process for defluorination of lithium battery wastewater through recycling

Abstract

This invention discloses a process for cyclic defluorination of lithium battery wastewater, belonging to the field of wastewater defluorination. The process includes the following steps: pumping lithium battery wastewater and aluminum salts into a defluorination reactor to form a mixed solution; then pumping an alkaline reagent into the mixed solution to adjust its pH value; after the pH value of the mixed solution stabilizes, separating the pH-stabilized solution through a filter press to obtain a mixture of fluoride-containing aluminum slag and fluoride-containing calcium slag; pumping the mixture into an acid leaching reactor after hot water slurrying; pumping concentrated acid into the acid leaching reactor to adjust its pH value; after the pH value in the acid leaching reactor stabilizes, pumping the alkaline reagent into the acid leaching reactor to adjust its pH value; and finally, after the pH value adjusted by the alkaline reagent stabilizes, separating the fluoride-containing calcium slag precipitate and the aluminum salts through a filter press. This invention achieves the recycling of the defluorinating agent, reducing the industrial defluorination cost of lithium battery wastewater.

Description

Technical Field

[0001] This invention belongs to the field of wastewater defluorination, specifically relating to a process method for the cyclic defluorination of lithium battery wastewater. Background Technology

[0002] Fluorine is chemically highly reactive, interacting with almost all elements. Therefore, fluorine in nature mostly exists in compound form, such as in phosphate rock, fluorite, cryolite, and fluorite. In recent years, the country has vigorously promoted and developed new energy vehicles. Lithium batteries, as a core component of new energy vehicles, have seen significant development and their numbers are increasing daily. The raw materials for lithium battery production mainly include salt lake brine, spodumene, lepidolite, and spent lithium batteries. During the production process, the generation of fluoride-containing wastewater is unavoidable. The standard for fluoride content in industrial wastewater discharge is <10 mg / L, and the standard for fluoride content in drinking water is <1 mg / L. Excessive fluoride content in wastewater not only corrodes equipment, accelerates its aging, and imposes an economic burden on enterprises, but more importantly, if the fluoride in the wastewater is not treated to meet discharge standards, it will not only pollute the ecological water environment but also cause excessive fluoride levels in local drinking water, leading to various fluorosis and brain damage. The main defluorination processes for lithium battery wastewater include adsorption, chemical flocculation and precipitation, electrodialysis, and ion exchange. Adsorption uses adsorbents to adsorb pollutants in the water to purify the wastewater; these mainly include iron-based adsorbents, rare earth adsorbents, and biological adsorbents. Chemical flocculation and precipitation involves using chemical agents, coagulants, and flocculants to react with negative ions in the wastewater to form insoluble precipitates or complexes, thus removing fluoride. Electrodialysis utilizes the selective permeability of ion exchange membranes; under an applied electric field, cations and anions in the aqueous solution move towards the anode and cathode, respectively, achieving separation and concentration through the ion exchange membrane. Ion exchange uses ion exchange resins to separate electrolyte-containing liquid mixtures; some anions in the ion exchange resin can exchange with fluoride ions, thereby adsorbing fluoride from the wastewater.

[0003] Patent CN103058419A discloses a defluoridation process for drinking water. This process involves adding polyaluminum chloride, diatomaceous earth, kaolin, and attapulgite to water and mixing them thoroughly. The mixture is then filtered through granular hydroxyapatite filter media and fiber ball filters to obtain treated drinking water. This method requires strict control of the pH value of the water being treated. If the pH value is too acidic, the hydroxyapatite will easily dissolve and lose its filtering effect. Patent CN111547804B discloses a composite defluoridator for industrial wastewater and its preparation method. This composite defluoridator utilizes silicate as a defluorination spatial framework, introducing some aluminum atoms to replace silicon atoms to form aluminum-silicon-oxygen tetrahedra, and then introducing divalent cations into the tetrahedra. These cations form chemical bonds with fluoride ions, firmly fixing the fluoride ions inside the defluoridator. However, this composite defluoridator can only be used to remove fluoride from wastewater with a fluoride concentration of less than 100 mg / L. Industrial wastewater often has a fluoride concentration far exceeding 100 mg / L. In such cases, directly using this composite defluoridator cannot achieve the desired defluorination, requiring pretreatment of the high-concentration fluoride wastewater to a low-concentration level, increasing the process steps. Patent CN111732114A discloses a method for removing fluoride ions from lithium sulfate solution. Specifically, it involves adding a substance containing La to the fluoride-containing lithium sulfate solution. 3+ Or Y 3+ The precipitant removes fluoride ions by forming lanthanum fluoride or yttrium fluoride precipitates with them. However, this process uses lanthanum-containing precipitants... 3+ Or Y 3+ The precipitant used is a rare earth precipitant, which is expensive and cannot be recycled. Patent CN112250090A discloses a production method for deep defluorination of lithium sulfate solution. This method uses magnesium-based substances such as magnesium oxide, magnesium sulfate, magnesium nitrate, or magnesium chloride as defluorinating agents to adsorb and fix fluoride ions in a strongly alkaline solution. However, magnesium-based substances are prone to precipitation reactions in strongly alkaline solutions, which reduces the concentration of magnesium ions and hinders the binding of magnesium ions with fluoride ions.

[0004] In conclusion, establishing a low-cost defluorination process that allows for the recycling of defluorinating agents is of great significance for the treatment of fluoride in industrial wastewater. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention utilizes an aluminum salt to chemically react with fluoride and sodium ions in lithium battery wastewater to generate a water-insoluble Na3AlF6 complex, thereby removing fluoride ions from the wastewater. However, due to the acidic nature of aluminum salts, a solution with a low pH prevents aluminum ions from forming aluminum hydroxide precipitate to complex with fluoride and sodium ions. By adjusting the pH to a specific value using calcium oxide, aluminum ions can form aluminum hydroxide precipitate to remove fluoride ions. Furthermore, the calcium ions from the added calcium oxide react with fluoride ions to generate CaF2, further removing fluoride ions and the introduced calcium ions. The generated Na3AlF6 complex, after treatment with concentrated acid, displaces aluminum ions back to form aluminum salts. These displaced aluminum salts can then be reintroduced into the lithium battery wastewater solution to perform fluoride removal, thus solving the problems mentioned in the background art. Specifically, the technical solution of this invention includes the following:

[0006] A process for defluorinating lithium battery wastewater through recycling, characterized in that the method includes the following steps:

[0007] Lithium battery wastewater and aluminum salts are pumped into a defluorination reactor to form a mixed solution, and then an alkaline reagent is pumped into the mixed solution to adjust the pH value of the mixed solution.

[0008] After the pH value of the mixed solution stabilizes, the pH-stabilized mixed solution is separated by a filter press to obtain a mixture of fluorinated aluminum slag and fluorinated calcium slag. The mixture is then pumped into an acid leaching kettle after being slurried with hot water, and concentrated acid is pumped into the acid leaching kettle to adjust the pH value.

[0009] After the pH value in the acid leaching kettle stabilizes, the alkaline reagent is pumped into the acid leaching kettle to adjust the pH value. After the pH value adjusted by the alkaline reagent stabilizes, the fluorine-containing calcium slag precipitate and the aluminum salt are separated by a filter press.

[0010] Furthermore, the volume ratio of the lithium battery wastewater to the aluminum salt is 100:1 to 5.

[0011] Furthermore, the aluminum salt includes aluminum sulfate or aluminum nitrate, preferably aluminum sulfate.

[0012] Furthermore, the alkaline reagent is preferably calcium oxide. If liquid alkali or sodium carbonate is used to adjust the pH of the solution, the sodium ion content in the wastewater increases, requiring additional process steps to remove sodium ions. Moreover, the calcium ions in calcium oxide can combine with fluoride ions in lithium battery wastewater to form calcium fluoride precipitate, which plays a synergistic role in removing fluoride and reduces the amount of aluminum salt used.

[0013] Furthermore, the alkaline reagent adjusts the pH of the mixed solution to 5.5–8.0. If the pH is too low, aluminum salt cannot form aluminum hydroxide precipitate in this pH environment, and instead combines with fluoride ions in the form of aluminum ions to form aluminum fluoride precipitate, making it difficult to retain aluminum ions through acid treatment. If the pH is too high, due to the amphoteric nature of aluminum hydroxide, it will continue to react with hydroxide ions to form salt, reducing the efficiency of aluminum sulfate in forming aluminum hydroxide and thus removing fluoride. In addition, an excessively high pH will cause hydroxide ions to competitively combine with calcium ions, reducing the synergistic effect of calcium ions in removing fluoride.

[0014] Furthermore, the concentrated acid includes sulfuric acid or nitric acid, preferably sulfuric acid.

[0015] Furthermore, the concentrated acid adjusts the pH value to 1.5–2.5. Under these acidic conditions, the mixture of fluorinated aluminum slag and fluorinated calcium slag can be completely dissolved, facilitating the subsequent pH adjustment with alkaline reagents for the separation of aluminum and calcium.

[0016] Furthermore, the pH value of the acid leaching kettle is adjusted to 4.5-5.0 by pumping in the alkaline reagent. The pH value of the solution after concentrated acid treatment is increased by the alkaline reagent calcium oxide, so that calcium ions can react with fluoride ions in the solution to form calcium fluoride precipitate, thereby removing fluoride ions and additional calcium ions. At the same time, the lower weak acid environment makes it difficult for aluminum ions to form aluminum hydroxide precipitate, thus retaining aluminum ions to the maximum extent, so that they can be recycled into the next lithium battery wastewater defluorination process, thereby realizing the recycling of aluminum defluorinating agent.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] (1) This invention uses aluminum salt as a defluorinating agent and adjusts the pH value of the mixed solution of lithium battery wastewater and aluminum salt by alkaline reagent calcium oxide. This controls the aluminum ions in the aluminum salt to form aluminum hydroxide precipitate, which reacts with fluoride ions and sodium ions in the lithium battery wastewater in the form of aluminum hydroxide to form water-insoluble Na3AlF6 complex. In addition, while adjusting the pH, the alkaline reagent calcium oxide can react with fluoride ions in the lithium battery wastewater to form calcium fluoride precipitate, which plays a synergistic role in removing fluoride ions and at the same time reduces the amount of aluminum salt used.

[0019] (2) The fluorine-containing aluminum slag and fluorine-containing calcium slag obtained by the filter press are treated with concentrated acid and then redissolved into a solution. The pH value of the solution after concentrated acid treatment is adjusted to a weakly acidic environment by calcium oxide. This ensures that calcium ions form calcium fluoride precipitate with fluoride ions in the solution, while aluminum ions do not easily form aluminum hydroxide precipitate. This maximizes the retention of aluminum ions, allowing them to enter the next defluorination process and realize the recycling of aluminum salts.

[0020] (3) The concentrated acid treatment step of the present invention can redissolve the lithium fluoride precipitate formed by lithium ions and fluoride ions in lithium battery waste liquid, creatively solving the problem of lithium ion loss caused by lithium ions in lithium battery waste liquid being able to combine with fluoride ions to form lithium fluoride precipitate, and providing a way to recover lithium, the core material of lithium batteries, from lithium battery waste liquid.

[0021] (4) Compared with expensive defluorinating agents such as rare earth mixed defluorinating agents, the aluminum salt defluorinating agent combined with the cyclic defluorinating process used in this invention can greatly reduce the cost of industrial treatment of lithium battery wastewater, and provides a research direction for exploring other industrial wastewater removal while reducing costs. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below through embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise stated, all raw materials and reagents used in this invention are commercially available or can be prepared by known methods.

[0024] The relevant reagents and raw materials information are as follows:

[0025] Aluminum sulfate was purchased from Zibo Zhongshi Chemical Co., Ltd.

[0026] Aluminum nitrate and calcium oxide were both purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0027] Both concentrated sulfuric acid and concentrated nitric acid were purchased from Huafu Chemical Co., Ltd.

[0028] The acid leaching vessel mentioned in the text is a reaction vessel for acid treatment, and hot water slurrying refers to heat-treating the fluorine-containing filter residue into a suspension to facilitate subsequent reactions.

[0029] Example 1:

[0030] A process for defluorinating lithium battery wastewater through recycling specifically includes the following steps:

[0031] The lithium battery wastewater with a fluoride content of 1500 mg / L was treated according to a 50m³ standard. 3 Pumping 50m at a flow rate of / h 3 The volume of the solution was added to the defluorination reactor, and the dissolved aluminum sulfate solution was added at a rate of 1 m³ / min. 3 Pumping 1m at a flow rate of / h 3The volume of the solution was added to the defluorination reactor. Simultaneously, dissolved calcium oxide emulsion was pumped into the reactor for mixing and stirring. The pH value in the reactor was monitored online using an online pH meter. Once the pH value stabilized at 5.5, the addition of calcium oxide emulsion was stopped. The solid-liquid mixture in the reactor was then separated using a filter press to obtain solids containing fluorinated aluminum slag and fluorinated calcium slag, as well as an aqueous solution. The fluorine content of the aqueous solution separated by the filter press was measured to be 10.3 mg / L. The mixture of fluorinated aluminum slag and fluorinated calcium slag was then pumped into an acid leaching reactor after being slurried with hot water. Concentrated sulfuric acid was added and mixed. The pH value in the acid leaching reactor was monitored online using an online pH meter. When the pH of the solution stabilized at 1.5, the addition of concentrated sulfuric acid was stopped. The solution in the acid leaching vessel was tested and found to contain 3.55 g / L lithium, 20.3 g / L aluminum, 1.48 g / L fluorine, and 0.42 g / L calcium. At this point, calcium oxide emulsion was added to the acid leaching vessel to raise the pH of the mixed solution to 4.5. The addition of calcium oxide emulsion was then stopped. The solid-liquid mixture in the acid leaching vessel was then separated by a filter press to obtain a mixture containing fluorine-containing calcium slag and aluminum sulfate. The mixture containing aluminum sulfate was tested and found to contain 3.23 g / L lithium, 15.9 g / L aluminum, less than 0.005 g / L fluorine, and 0.01 g / L calcium.

[0032] Example 2:

[0033] A process for defluorinating lithium battery wastewater through recycling specifically includes the following steps:

[0034] The dissolved aluminum sulfate solution from Example 1 was replaced with the aluminum sulfate-containing mixture obtained at the end of Example 1, and the amount of aluminum sulfate added was reduced to 0.5 mg. 3 The fluoride content of the aqueous solution separated by the filter press was measured to be 14.5 mg / L. The pH value of the acid leaching vessel was adjusted to 2.5 with concentrated sulfuric acid as in Example 1, and the lithium content, aluminum content, fluoride content, and calcium content in the acid leaching vessel were measured to be 3.24 g / L, 15.3 g / L, fluoride content, and calcium content, respectively. The pH value of the acid leaching vessel was then adjusted to 5.0 with calcium oxide as in Example 1, and the lithium content, aluminum content, fluoride content, and calcium content in the mixed solution containing aluminum sulfate were measured to be 3.11 g / L, 13.6 g / L, fluoride content, and calcium content, respectively.

[0035] Example 3:

[0036] A process for defluorinating lithium battery wastewater through recycling specifically includes the following steps:

[0037] The amount of dissolved aluminum sulfate added in Example 1 was increased to 2.5 mg. 3In Example 1, the pH of the defluorination reactor was adjusted to 6.5, and the fluoride content of the effluent separated by the filter press was measured to be 12.6 mg / L. In Example 2, the pH of the concentrated sulfuric acid treatment remained unchanged, and the lithium content, aluminum content, fluoride content, and calcium content of the solution in the acid leaching reactor were measured to be 3.43 g / L, 19.2 g / L, fluoride content, and 0.46 g / L. In Example 3, the pH of the acid leaching reactor was adjusted to 5.0 with calcium oxide, and the lithium content, aluminum content, fluoride content, and calcium content of the mixed solution containing aluminum sulfate were measured to be 3.36 g / L, 13.7 g / L, fluoride content, and 0.012 g / L.

[0038] Example 4:

[0039] A process for defluorinating lithium battery wastewater through recycling specifically includes the following steps:

[0040] In Example 1, aluminum sulfate was replaced with aluminum nitrate, and the pH of the defluorination reactor was increased to 8.0. The fluoride content of the aqueous solution separated by the filter press was measured to be 13.6 mg / L. In Example 1, concentrated sulfuric acid was replaced with concentrated nitric acid, and the lithium content in the acid leaching reactor was measured to be 3.22 g / L, aluminum content to be 16.4 g / L, fluoride content to be 1.46 g / L, and calcium content to be 0.48 g / L. In Example 1, calcium oxide was used to adjust the pH of the acid leaching reactor to be 5.0, and the lithium content in the mixed solution containing aluminum sulfate was measured to be 2.85 g / L, aluminum content to be 12.8 g / L, fluoride content to be less than 0.011 g / L, and calcium content to be 0.06 g / L.

[0041] As can be seen from the data in the above embodiments, the cyclic defluorination process designed in this invention can not only remove fluoride ions from lithium battery wastewater, but also retain lithium ions, the core component of lithium batteries, in the wastewater to the greatest extent in the aluminum salt solution through acid treatment. This has guiding significance for the subsequent development of extracting lithium ions from aluminum salt solution for the preparation of lithium batteries.

[0042] The embodiments described above have been used to illustrate the technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A process for defluorinating lithium battery wastewater through recycling, characterized in that, The method includes the following steps: Lithium battery wastewater and aluminum salts are pumped into a defluorination reactor to form a mixed solution, and then an alkaline reagent is pumped into the mixed solution to adjust the pH value of the mixed solution to 5.5~8.0; After the pH value of the mixed solution stabilizes, the pH-stabilized mixed solution is separated by a filter press to obtain a mixture of fluorinated aluminum slag and fluorinated calcium slag. The mixture is then pumped into an acid leaching kettle after being slurried with hot water, and concentrated acid is pumped into the acid leaching kettle to adjust the pH value to 1.5~2.

5. After the pH value in the acid leaching kettle stabilizes, the alkaline reagent is pumped into the acid leaching kettle to adjust the pH value to 4.5~5.

0. After the pH value adjusted by the alkaline reagent stabilizes, the fluorine-containing calcium slag precipitate and the aluminum salt are separated by a filter press.

2. The process for defluorination of lithium battery wastewater according to claim 1, characterized in that, The volume ratio of the lithium battery wastewater to the aluminum salt is 100:1~5.

3. The process for defluorination of lithium battery wastewater according to claim 1, characterized in that, The aluminum salts include aluminum sulfate or aluminum nitrate.

4. The process for defluorination of lithium battery wastewater according to claim 1, characterized in that, The alkaline reagent is calcium oxide.

5. The process for defluorination of lithium battery wastewater according to claim 1, characterized in that, The concentrated acid includes sulfuric acid or nitric acid.

6. The application of the process for defluorination of lithium battery wastewater according to any one of claims 1 to 5 in the field of defluorination.