Fluorine removal agent for leaching solution of zinc hydrometallurgy based on rare earth waste recycling and preparation and application thereof

Abstract

The application discloses a fluorine removal agent for zinc hydrometallurgy leaching liquor based on rare earth waste recovery and preparation and application, relates to the technical field of fluorine removal of zinc hydrometallurgy leaching liquor, and is composed of nano magnetic iron oxide and rare earth carbonate prepared from rare earth waste recovery, wherein the rare earth carbonate is one or more of lanthanum carbonate, cerium carbonate and lanthanum cerium carbonate; the molar ratio of Fe element to rare earth element is 1: (1-10); and the fluorine removal agent is Fe3O4@RE2 (CO3) 3 with a core-shell structure. The fluorine removal agent has high fluorine removal rate, low fluorine removal cost, less zinc loss, and good fluorine removal effect for high-fluorine and low-fluorine solutions. The fluorine removal agent has simple preparation method and low cost.

Description

Technical Field

[0001] This invention relates to the field of defluorination technology for wet zinc smelting leaching solutions, specifically to a defluorination agent for wet zinc smelting leaching solutions based on rare earth waste recycling, its preparation method, and its application. Background Technology

[0002] Fluorine in hydrometallurgical zinc smelting systems originates from raw materials, auxiliary materials, and production water, and continuously accumulates along with the electrolytic waste liquid during the leaching → purification → electrolysis process. The increasing fluorine concentration in the system has several negative consequences: First, it exacerbates equipment corrosion, as fluorine-containing solutions intensify corrosion of agitators, pipelines, and pump impellers during leaching and transportation. Second, it severely impacts production. Increased fluorine concentration inhibits PbO2 formation on the lead anode surface, reduces the density of the PbO2 oxide film, accelerates lead dissolution, and shortens the lifespan of the lead anode plate. Furthermore, fluorine damages the alumina film on the aluminum cathode surface, causing precipitated zinc to adhere to the pits, forming a zinc-aluminum alloy, increasing the difficulty of zinc stripping and the amount of damage to the cathode plate. Third, it threatens the health of workers. The hydrometallurgical zinc smelting industry generally believes that fluorine in the leaching solution... - The concentration must be controlled below 50 mg / L to ensure normal production.

[0003] Currently, the treatment of fluoride in the hydrometallurgical zinc refining system in industry is mainly carried out in two aspects. On the one hand, the zinc material is pretreated for defluorination before the leaching process, and the main processes include alkaline washing and roasting. On the other hand, the zinc sulfate solution after leaching is defluorinated, and the main processes include: (1) chemical precipitation method. This process is simple to operate, but the addition of precipitant causes the pH of the solution to rise, resulting in the defluorination of fluoride. - OH - With Zn 2+ Generate ZnF + The complex ion and Zn(OH)2 precipitation cause incomplete fluoride removal and increase zinc loss. (2) Ion exchange method: the fluoride removal efficiency is affected by multiple factors, and the ion exchange method has a long adsorption and regeneration time, low efficiency, large desorption liquid volume, and high treatment cost. (3) Solvent extraction method: the extractant can be recycled, but the fluoride extraction rate is low, and the extraction process will co-extract zinc, causing zinc loss; the extraction method will cause residual organic phase to cause "plate burning". (4) Adsorption method: the adsorbent includes natural mineral adsorbents and artificial synthetic adsorbents. The fluoride removal capacity of natural minerals is usually low, and chemical modification or external field enhancement is required to improve the adsorption performance. Artificial synthetic adsorbents include carbon-based adsorbents, aluminum-based adsorbents and rare earth adsorbents. Carbon-based adsorbents have weak fluoride removal capacity and are not suitable for deep fluoride removal of zinc electrolyte. Aluminum-based adsorbents have good fluoride removal effect, but SO4 in the solution 2-The defluorination efficiency of adsorbents is significantly affected, and they are prone to forming colloids, making filtration difficult. Rare earth adsorbents have good defluorination efficiency, but the cost is high. The aluminum hydroxide-based carbonate rare earth defluorinating agent disclosed in Chinese patent CN105420754A has a defluorination rate of only 75%. 3+ Hydrolysis produces Al(OH)3 colloid, resulting in significant zinc loss. The rare earth elements used are commercially available carbonate rare earths, leading to high costs. CN117228812A discloses a rare earth element-modified aluminum-iron based defluorinating agent composed of aluminum-iron base materials and rare earth element chlorides. It is mainly used for treating low-concentration fluoride-containing wastewater and may introduce chloride ions. CN120094546A discloses a method for preparing a rare earth composite defluorinating agent, which involves rare earth slag raffinate → heavy metal scavenging agent impurity removal → evaporation concentration → cooling crystallization. This process is lengthy, and the resulting composite defluorinating agent has a high soluble aluminum content, easily hydrolyzing to form aluminum hydroxide during use, leading to difficult liquid-solid separation and a high zinc loss rate. Summary of the Invention

[0004] The purpose of this invention is to solve the many problems existing in the above-mentioned technologies, and to provide a defluorinating agent for wet zinc smelting leaching solution based on rare earth waste recycling, which has high defluorination rate, low defluorination cost, low zinc loss, and high filtration rate, as well as its preparation method and application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first technical solution of the present invention is to provide a defluorinating agent for wet zinc leaching solution based on rare earth waste recycling. The defluorinating agent is composed of nano-magnetic iron oxide and rare earth carbonates prepared by rare earth waste recycling. The rare earth carbonates are one or more of lanthanum carbonate, cerium carbonate, and lanthanum-cerium carbonate. The molar ratio of Fe element to rare earth element is 1:(1~10). The defluorinating agent is Fe3O4@RE2(CO3)3 with a core-shell structure.

[0007] Furthermore, the particle size of the nano-magnetic iron oxide does not exceed 100 nm.

[0008] Furthermore, in the defluorinating agent, the Fe:La:Ce molar ratio is 1:(1~5):(1~5), and the La / Ce molar ratio is ≥1.

[0009] The second technical solution of the present invention provides a method for preparing the defluorinating agent, the method of which is as follows:

[0010] (1) Iron source activation: Nano-magnetic iron oxide is placed in 0.1~1mol / L HCl solution and stirred at 25~80℃ for 0.2~2h. Then it is washed with water until neutral to obtain activated iron source;

[0011] (2) Rare earth regeneration: Mix rare earth waste at a ratio of H2SO4:rare earth waste = 1: (1~10) mL / g, calcine at 100~600℃ for 1~3h, then soak in water, and filter to obtain rare earth sulfate solution;

[0012] (3) In-situ loading: The activated iron source prepared in step (1) is added to the rare earth sulfate solution prepared in step (2), the molar ratio of Fe: rare earth element is controlled to be 1:(1~10), ammonium carbonate solution is slowly added for neutralization, the pH is adjusted to 4.5-7.5, and the reaction is stirred at 40~60℃ for 2~8h to obtain the neutralized solution;

[0013] (4) Aging and crystallization: The neutralized liquid obtained in step (3) is left to stand at 20~60℃ for 6~12h and then filtered to obtain the defluorinating agent Fe3O4@RE2(CO3)3 with a core-shell structure.

[0014] The third technical solution of the present invention provides the application of the defluorinating agent, which is to add the defluorinating agent to a zinc leaching solution at a temperature of 60~80℃ and pH 4~5.5 at a ratio of 8~15 times the mass of fluorine, react for 0.5~2h, and then apply a magnetic field of 0.5~1.5T to perform solid-liquid separation.

[0015] After the synthesis of nanomaterials, impurities inevitably adsorb or remain on the particle surface, such as incompletely reacted iron salt precursors, neutralizing agents, and organic anions like citrate used for pH stabilization. These impurities occupy active sites on the surface, hindering subsequent functionalization modifications. This invention uses a low concentration of hydrochloric acid to treat nano-magnetic iron oxide for a short time. Through ion exchange and acid dissolution, these physically adsorbed or weakly chemically bound impurities are efficiently removed without significantly damaging the crystal framework of nano-Fe3O4, providing a clean active surface for subsequent steps. This process is a typical material cleaning and purification process; by controlling the appropriate hydrochloric acid concentration and treatment time, it is possible to ensure that impurities are effectively removed while the loss of the main material is minimal.

[0016] Furthermore, hydrochloric acid selectively and slightly dissolves / etches iron atoms on the Fe3O4 surface, thus "roughening" the nanoparticle surface through gentle chemical etching to increase its specific surface area and expose more iron active sites. The rate and extent of this reaction are strictly limited by the hydrochloric acid concentration, temperature, and processing time. Under the parameters defined in this invention, namely using a 0.1~1 mol / L HCl solution and stirring at 25~80℃ for 0.2~2 h, the reaction occurs only on the outermost layer of the nanoparticles. The effect is to roughen the smooth surface, even creating nanoscale pores or steps, without dissolving the entire particle.

[0017] This invention recovers rare earth from rare earth waste through a sulfation roasting-water leaching process, and then loads it in situ with activated nano-magnetic iron oxide to prepare a core-shell structured defluorinating agent with high adsorption capacity. Assisted magnetic filtration further enhances sedimentation and filtration rates, thereby increasing the defluorination rate, reducing defluorination costs, minimizing zinc loss, and improving filtration speed.

[0018] Compared with the prior art, the main beneficial effects of the present invention are as follows:

[0019] 1. The rare earth carbonates used in this invention are derived from rare earth waste, which are inexpensive and have low defluorination costs;

[0020] 2. This invention uses nano-magnetic iron oxide and rare earth solution to prepare a defluorinating agent in situ, which has a large adsorption capacity, good defluorinating effect, fast sedimentation rate and low main metal loss rate.

[0021] 3. This invention cleverly utilizes the inherent magnetism of the defluorinating agent to effectively accelerate the liquid-solid separation rate through magnetic filtration.

[0022] 4. The defluorinating agent preparation method of the present invention is simple, requires low investment in production equipment, and the prepared defluorinating agent has wide adaptability and is easy to use. It has a good defluorinating effect on both high-fluoride and low-fluoride solutions. Detailed Implementation

[0023] The present invention will be further explained below with reference to the embodiments. The following embodiments do not limit the scope of protection of the present invention in any way. All technical solutions obtained by equivalent substitution are within the scope of protection of the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions. Example 1

[0024] A defluorinating agent for wet zinc smelting leaching solutions based on rare earth waste recycling is composed of nano-magnetic iron oxide and rare earth carbonates prepared from recycled rare earth waste. The nano-magnetic iron oxide is Fe3O4 with a particle size of approximately 50 nm, and the rare earth waste is rare earth polishing powder waste, whose main components are La2O3 30 wt% and CeO2 23 wt%. This rare earth waste can be recycled to prepare lanthanum carbonate (La2(CO3)3), cerium carbonate (Ce2(CO3)3), and lanthanum-cerium carbonate (LaCe(CO3)3), with a Fe:(La+Ce) molar ratio of 1:4.

[0025] The method for preparing the defluorinating agent in this embodiment is as follows:

[0026] (1) Iron source activation: Nano-magnetic iron oxide was stirred in an HCl solution with a concentration of 0.5 mol / L at a temperature of 60℃ for 0.5 h, and then washed with water until neutral to obtain an activated iron source;

[0027] (2) Rare earth regeneration: The polishing powder waste was mixed with H2SO4 at a molar ratio of 1:10 and then calcined at 400℃ for 2 hours. The mixture was then soaked in water to obtain a mixed solution of La2(SO4)3 and Ce2(SO4)3.

[0028] (3) In-situ loading: The mixed solution from step (2) and the activated iron source were mixed by molar ratio Fe:La:Ce=1:3:1. Under stirring conditions, ammonium carbonate solution was added for neutralization, pH was adjusted to 7, and the reaction was carried out at 50℃ for 3h to obtain lanthanum and cerium carbonate slurry with nano-magnetic iron oxide as the core. Lanthanum and cerium carbonate precipitate was formed in the slurry.

[0029] (4) Aging and crystallization: The lanthanum and cerium carbonate slurry obtained from the neutralization in step (3) was left to stand at 45°C for 8 hours to allow the particles to grow further and become more tightly packed. After aging, the slurry was filtered to obtain a defluorinating agent with a core-shell structure.

[0030] Take the wet zinc leaching solution that needs to be defluorinated, its F - The concentration is 85 mg / L, Zn 2+ The concentration is 125 g / L, SO4 2- Concentration 180 g / L. Adjust the pH of the leachate to approximately 5.0 and heat to 75°C, then proceed according to F. - Add 12 times the mass of the defluorinating agent prepared above, react for 1.5 hours, and then perform magnetic filtration while maintaining a magnetic field strength of 1.0 T. Detect the fluoride content (F) in the defluorinated liquid. - Concentration. After testing, the defluorinated solution F... - The concentration was 5.0 mg / L, the fluoride removal rate was 94.1%, the zinc loss rate was 0.18%, and the sedimentation rate was 4.8 cm / min. Example 2

[0031] A defluorinating agent for wet zinc smelting leaching solutions based on rare earth waste recycling is composed of nano-magnetic iron oxide and rare earth carbonates prepared from recycled rare earth waste. The nano-magnetic iron oxide is Fe3O4 with a particle size of approximately 95 nm, and the rare earth waste is the same as in Example 1. The molar ratio of Fe to (La+Ce) is 1:8.

[0032] The method for preparing the defluorinating agent in this embodiment is as follows:

[0033] (1) Iron source activation: Nano-magnetic iron oxide was stirred in an HCl solution with a temperature of 60℃ and a concentration of 0.5mol / L for 1.5h, and then washed with water until neutral to obtain an activated iron source;

[0034] (2) Rare earth regeneration: The polishing powder waste was mixed with H2SO4 at a molar ratio of 1:8 and then calcined at 400℃ for 2 hours. The mixture was then soaked in water to obtain a mixed solution of La2(SO4)3 and Ce2(SO4)3.

[0035] (3) In-situ loading: The RE2(SO4)3 solution and the activated iron source were mixed in a molar ratio of Fe:La:Ce=1:5:3. Under stirring conditions, ammonium carbonate solution was added for neutralization, the pH was adjusted to 7, and the reaction was carried out at 50℃ for 5h to obtain lanthanum cerium carbonate slurry with nano magnetic iron oxide as the core.

[0036] (4) Aging and crystallization: The lanthanum and cerium carbonate slurry obtained from the neutralization in step (3) is left to stand at 45°C for 10 hours and then filtered to obtain a defluorinating agent with a core-shell structure.

[0037] Take the wet zinc leaching solution that needs to be defluorinated, its F - The concentration is 480 mg / L, Zn 2+ The concentration is 125 g / L, SO4 2- Concentration 180 g / L. Adjust the pH of the leachate to approximately 5.0 and heat to 75°C, then proceed according to F. - Add 15 times the mass of the defluorinating agent prepared above, react for 1.5 hours, and then perform magnetic filtration while maintaining a magnetic field strength of 1.0 T. Detect the fluoride content (F) in the defluorinated liquid. - Concentration. After testing, the defluorinated solution F... - The concentration was 22 mg / L, the fluoride removal rate was 95.4%, and the zinc loss rate was 0.31%. Example 3

[0038] A defluorinating agent for wet zinc smelting leaching solutions based on rare earth waste recovery is composed of nano-magnetic iron oxide and rare earth carbonates prepared from the recovered rare earth waste. The nano-magnetic iron oxide is Fe3O4 with a particle size of approximately 80 nm, and the rare earth waste is a mixed rare earth concentrate recovered from tailings, whose main components are 25 wt% La2O3 and 30 wt% CeO2. The molar ratio of Fe to (La+Ce) is 1:2.

[0039] The method for preparing the defluorinating agent in this embodiment is as follows:

[0040] (1) Iron source activation: 80 nm magnetic iron oxide nanoparticles were placed in 0.1 mol / L HCl and stirred at 25 °C for 2 h. The mixture was then washed with water until neutral.

[0041] (2) Rare earth regeneration: Mix H2SO4: waste at a ratio of 1:1 (mL / g), calcine at 100℃ for 3 hours, and leach in water to obtain a rare earth sulfate solution;

[0042] (3) In-situ loading: Fe:RE = 1:1, add activated iron source to ammonium carbonate to adjust pH = 4.5, react at 40℃ for 8h to obtain lanthanum cerium carbonate slurry with nano magnetic iron oxide as the core;

[0043] (4) Aging and crystallization: The slurry obtained from the neutralization in step (3) is left to stand at 20°C for 12 hours, then filtered and dried to obtain the defluorinating agent.

[0044] Take the wet zinc leaching solution that needs to be defluorinated, its F - Concentration of 90 mg / L, Zn 2+ Concentration of 130 g / L, SO4 2- Concentration 198 g / L. Adjust the pH of the leachate to approximately 4.0 and heat to 60°C, then proceed according to F. - Add 8 times the mass of the defluorinating agent prepared above, react for 2 hours, and then perform magnetic filtration while maintaining a magnetic field strength of 0.5T. Detect the fluoride content (F) in the defluorinated liquid. - Concentration. After testing, the defluorinated solution F... - With a concentration of 12 mg / L, the fluoride removal rate was 86.7%, and the zinc loss rate was 0.55%. Example 4

[0045] A defluorinating agent for wet zinc smelting leaching solutions based on rare earth waste recycling is composed of nano-magnetic iron oxide and rare earth carbonates prepared from recycled rare earth waste. The nano-magnetic iron oxide is Fe3O4 with a particle size of approximately 100 nm, and the rare earth waste is the same as in Example 3. The molar ratio of Fe to (La+Ce) is 1:10.

[0046] The method for preparing the defluorinating agent in this embodiment is as follows:

[0047] (1) Iron source activation: Nano-magnetic iron oxide (100 nm) was activated in 1 mol / L HCl at 80 °C for 0.2 h;

[0048] (2) Rare earth regeneration: Mix H2SO4: waste = 1:10, calcine at 600℃ for 1 hour, and leach in water to obtain rare earth sulfate solution;

[0049] (3) In-situ loading: The activated iron source was added to the rare earth sulfate solution obtained in step (2), and the Fe:La:Ce=1:5:5 was controlled. Ammonium carbonate solution was added under stirring to adjust the pH to 7.5. The reaction was carried out at 60℃ for 2 hours to obtain lanthanum and cerium carbonate slurry with nano magnetic iron oxide as the core.

[0050] (4) Aging and crystallization: The lanthanum and cerium carbonate slurry obtained in step (3) is left to stand at 60°C for 6 hours, filtered and dried to obtain the defluorinating agent.

[0051] Take the wet zinc leaching solution that needs to be defluorinated, its F -Concentration of 500 mg / L, Zn 2+ The concentration is 125 g / L, SO4 2- Concentration 188 g / L. Adjust the pH of the leachate to approximately 5.5 and heat to 80°C, then proceed according to F. - Add 15 times the mass of the defluorinating agent prepared above, react for 2 hours, and then perform magnetic filtration while maintaining a magnetic field strength of 1.5T. Detect the fluoride content (F) in the defluorinated liquid. - Concentration. After testing, the defluorinated solution F... - The concentration was 25 mg / L, the fluoride removal rate was 95%, and the zinc loss rate was 0.35%. Example 5

[0052] A defluorinating agent for wet zinc leaching based on rare earth waste recycling is composed of nano-magnetic iron oxide and rare earth carbonates prepared from recycled rare earth waste. The nano-magnetic iron oxide is Fe3O4 with a particle size of approximately 50 nm, and the rare earth waste is the same as in Example 3. The molar ratio of Fe to (La+Ce) is 1:3.

[0053] The method for preparing the defluorinating agent in this embodiment is as follows:

[0054] (1) Iron source activation: Nano-magnetic iron oxide was stirred in an HCl solution with a temperature of 40℃ and a concentration of 0.5mol / L for 1.0h, and then washed with water until neutral to obtain an activated iron source;

[0055] (2) Rare earth regeneration: The rare earth mixed concentrate was mixed with H2SO4 at a molar ratio of 1:5 (mL / g), and then roasted at 300℃ for 2h. The mixture was then leached in water to obtain a mixed solution of La2(SO4)3 and Ce2(SO4)3.

[0056] (3) In-situ loading: control Fe:La:Ce=1:1:1, add the activated iron source to the mixed solution obtained in step (2), add ammonium carbonate solution under stirring, adjust pH to 6.0, and react at 50℃ for 5h to obtain liquid-solid mixed slurry;

[0057] (4) Aging and crystallization: The liquid-solid mixture obtained in step (3) is left to stand at 40°C for 9 hours, then filtered and dried to obtain the defluorinating agent.

[0058] Take the wet zinc leaching solution that needs to be defluorinated, its F - Concentration of 150 mg / L, Zn 2+ The concentration is 125 g / L, SO4 2- Concentration 188 g / L. Adjust the pH of the leachate to approximately 4.8 and heat to 70°C, then proceed according to F. - Add 10 times the mass of the defluorinating agent prepared above, react for 1 hour, and then perform magnetic filtration while maintaining a magnetic field strength of 1.0 T. Detect the fluoride content (F) in the defluorinated liquid.- Concentration. After testing, the defluorinated solution F... - With a concentration of 6 mg / L, the fluoride removal rate was 96%, and the zinc loss rate was 0.20%. Comparative Example 1

[0059] Al₂(SO₄)₃ was added to the wet zinc smelting leaching solution described in Example 1 to remove fluoride, controlling the mass ratio of Al:F = 12:1, pH = 5.0, and reacting at 75°C for 1.5 h before filtration. After fluoride removal, F was detected in the leaching solution. - The concentration was 18 mg / L, and the fluoride removal rate was 78.8%. Due to Al... 3+ Hydrolysis leads to an increase in solution pH, the formation of Zn4SO4(OH)6 precipitate, a zinc loss rate of 1.92%, and the production of colloidal residue, making solution filtration difficult. Comparative Example 2

[0060] A commercially available rare earth adsorbent, lanthanum carbonate with a purity >99%, was added to the same wet zinc smelting leaching solution as in Example 1, and the same defluorination conditions were controlled as in Example 1 (adjusting the pH of the leaching solution to ≈5.0 and heating to 75°C, according to F...). - Add 12 times the mass of the defluorinating agent and react for 1.5 hours. After defluorination, the defluorination rate was measured to be 92.3%, the zinc loss rate was 0.46%, and the sedimentation rate was 0.3 cm / min. Comparative Example 3

[0061] Other operating procedures are the same as those described in Example 1, but the solid-liquid separation for the defluorination operation uses ordinary filtration. The sedimentation rate is reduced to 0.8 cm / min, the filtration time is extended by 3 times, and the zinc loss rate increases to 0.25%. Comparative Example 4

[0062] Commercial LaCe(CO3)3 was mechanically mixed with unactivated micron-sized Fe3O4 to obtain a Fe:RE=1:4 composite defluorinating agent.

[0063] Take the wet zinc leaching solution that needs to be defluorinated, its F - The concentration is 85 mg / L, Zn 2+ The concentration is 125 g / L, SO4 2- Concentration 180 g / L. Adjust the pH of the leachate to approximately 5.0 and heat to 75°C, then proceed according to F. - Add 12 times the mass of the defluorinating agent prepared above, react for 1.5 hours, and then perform magnetic filtration while maintaining a magnetic field strength of 1.0 T. Detect the fluoride content (F) in the defluorinated liquid. - Concentration. After testing, the defluorinated solution F... - The concentration was 18 mg / L, the fluoride removal rate was 78.5%, the zinc loss rate was 1.05%, and the sedimentation rate was 0.5 cm / min. Comparative Example 5

[0064] The iron source activation step in Example 1 is omitted, and raw Fe3O4 is used directly for loading. The remaining preparation steps are the same as in Example 1.

[0065] The defluorination conditions were the same as those described in Example 1, and the defluorination rate was reduced to 82.3%.

[0066] As can be seen from the comparative examples, compared with the defluorinating agents commonly used in the prior art, the defluorinating agent of the present invention has a significantly improved defluorination rate under the same defluorination conditions.

Claims

1. A defluorinating agent for wet zinc smelting leaching solution based on rare earth waste recycling, characterized in that, The fluoride removal agent is composed of nano-magnetic iron oxide and rare earth carbonate prepared from rare earth waste recycling, the rare earth carbonate is one or more of lanthanum carbonate, cerium carbonate and lanthanum cerium carbonate; the molar ratio of Fe element to rare earth element is 1:(1-10); the fluoride removal agent is Fe3O4@RE2(CO3)3 with core-shell structure.

2. The defluorination agent for a leaching solution of a zinc hydrometallurgy based on rare earth scrap recycling according to claim 1, characterized in that, The particle size of the nano-magnetic iron oxide is not more than 100 nm.

3. The defluorination agent for a leaching solution of a zinc hydrometallurgy based on rare earth scraps according to claim 1 or 2, characterized in that, In the fluoride removal agent, the molar ratio of Fe: La: Ce is 1:(1-5):(1-5), and the molar ratio of La / Ce is greater than or equal to 1.

4. The method for preparing the defluorinating agent as described in claim 1, 2, or 3, characterized in that, The method is as follows: (1) Iron source activation: place the nano-magnetic iron oxide in a 0.1-1 mol / L HCl solution, stir and activate at 25-80℃ for 0.2-2 h, then wash with water until neutral to obtain an activated iron source; (2) Rare earth regeneration: mix the rare earth waste according to the molar ratio H2SO4: rare earth waste = 1:(1-10), calcine at 100-600℃ for 1-3 h, then immerse in water, filter to obtain a rare earth sulfate solution; (3) In-situ loading: add the activated iron source prepared in step (1) to the rare earth sulfate solution prepared in step (2), control the molar ratio of Fe: rare earth element to be 1:(1-10), slowly add an ammonium carbonate solution for neutralization, adjust the pH to 4.5-7.5, stir and react at 40-60℃ for 2-8 h to obtain a neutralization liquid; (4) Aging and crystallization: filter the neutralization liquid obtained in step (3) after standing and aging at 20-60℃ for 6-12 h to obtain the fluoride removal agent Fe3O4@RE2(CO3)3 with core-shell structure.

5. Use of the fluorine removal agent according to claim 1 or 2 or 3, characterized in that, Add the fluoride removal agent to a zinc leaching solution with a temperature of 60-80℃ and a pH of 4-5.5, the mass of fluoride is 8-15 times of the fluoride removal agent, react for 0.5-2 h, then apply a magnetic field of 0.5T-1.5T for solid-liquid separation.