Process for defluorination of rare earth compounds

Abstract

The present application belongs to the field of rare earth processing technology, and particularly relates to a defluorination process of a rare earth compound. The defluorination process comprises the following steps: pulp preparation, oxidation pretreatment, primary alkali washing for defluorination, secondary alkali washing for defluorination, washing, and grading utilization of wastewater at different levels. The defluorination process and conditions are optimized, and the prepared rare earth compound product has greatly reduced fluorine content, and other impurities such as aluminum and sulfur can also be removed, so that the product quality is good and meets the requirements of rare earth smelting and separation. Meanwhile, the wastewater generated in the process can be reused in different stages after simple treatment, greatly reducing pollution, and the economic and environmental benefits are remarkable.

Description

Technical Field

[0001] This invention belongs to the field of rare earth processing technology, specifically relating to a defluorination process for rare earth compounds. Background Technology

[0002] Rare earth carbonates and oxides are important intermediate products in rare earth hydrometallurgical production, mainly derived from processes such as alkaline decomposition and ammonium bicarbonate precipitation after acid leaching of rare earth concentrates. Ionic rare earth deposits often contain mica, which causes rare earth ions to exchange fluorine from the mica during leaching. While the mother liquor from rare earth leaching typically contains 2-15 mg / L of fluorine, this low concentration, if not removed, will form fluorides during rare earth carbonate precipitation, directly impacting product quality and separation efficiency during rare earth smelting.

[0003] Currently, methods for defluorinating rare earth materials include high-temperature roasting, alkaline roasting-water washing, and acid washing-alkaline boiling. High-temperature roasting requires temperatures of 850-1000℃ to decompose fluorides, resulting in high energy consumption, demanding equipment, and the generation of fluorine-containing exhaust gases, causing pollution and waste. Alkaline roasting-water washing involves roasting a mixture of rare earth materials with alkaline substances to convert fluoride into soluble sodium fluoride, which is then removed by water washing. While this method achieves a high defluorination rate, it also requires high-temperature roasting, leading to high energy consumption and incomplete defluorination. Acid washing-alkaline boiling treats rare earth materials under acidic conditions followed by high-temperature alkaline boiling with a strong alkaline solution for defluorination. This method introduces an acid washing step, increasing the process complexity, and the high-temperature alkaline boiling still requires intense high-temperature, high-alkaline conditions. These existing methods are energy-intensive and have high pH requirements, easily causing secondary pollution, and poor condition control can lead to incomplete defluorination. Therefore, developing a new defluorination process for rare earth compounds is essential. Summary of the Invention

[0004] To address the aforementioned shortcomings, this invention provides a defluorination process for rare earth compounds. This defluorination process utilizes readily available raw materials, is easy to operate, removes fluoride thoroughly, is low in cost, and is more environmentally friendly.

[0005] The purpose of this invention is to provide a defluorination process for rare earth compounds, comprising the following steps: (1) Pulping: The rare earth compound is mixed with water and then crushed or ball-milled to make a slurry; (2) Oxidation pretreatment: Add oxidant to the slurry and stir the reaction at 25-60℃ for 0.5-2h. After the reaction is completed, the preliminary activated rare earth material is obtained. (3) First alkaline washing defluorination: The pre-activated rare earth material is transferred into a stirred reaction tank, and the first alkaline washing working solution is added. The mixture is stirred and reacted at 50-80℃ for 1-1.5h. After the reaction is completed, the solid and liquid are separated to obtain the first washing residue and the first washing filtrate. (4) Secondary alkaline washing and defluorination: Transfer the primary washing residue to another stirred reaction tank, add the secondary alkaline washing working solution, stir and react at 60-90℃ for 0.5-2h, after the reaction is completed, separate the solid and liquid to obtain secondary washing residue and secondary washing filtrate. (5) Washing: The secondary washing residue is washed using a three-stage countercurrent washing method. After washing, solid and liquid are separated, and the rare earth compound filter residue is dried to a moisture content of less than 5% to obtain the defluorinated rare earth compound product.

[0006] This invention's defluorination process first involves grinding rare earth compounds into a slurry, then mixing and reacting it with an oxidant. Utilizing the oxidant's property of decomposing into active oxides in solution, the oxidant attacks the crystal structure surrounding the fluoride, disrupting the bond between the fluoride and the rare earth matrix, releasing fluoride ions for subsequent alkaline washing. Simultaneously, the bubbles and oxidative etching generated during oxidation make the material particle surface porous, facilitating the penetration of the subsequent alkaline washing solution and increasing fluoride release. A mild alkaline washing process using a mixture of strong and weak alkalis not only removes free fluoride and fluoride encapsulated in soluble fluoride salts from the material surface and near the surface, but also, due to the relatively mild alkalinity of the system, avoids the formation of a dense encapsulation layer, facilitating further deep defluorination. A high-concentration secondary alkaline washing working solution further introduces insoluble and deeper encapsulated fluorides into the liquid phase, achieving deep defluorination. Finally, a three-stage countercurrent washing process is employed, resulting in excellent washing performance and increased washing efficiency per unit volume of water. The process of this invention has a good defluorination effect, which can reduce the fluoride content to below 0.1%. At the same time, rare earth compounds exist in solid form during the defluorination process, and the quality is improved after removing other impurities such as aluminum and sulfur.

[0007] Preferably, in step (1) of the above technical solution, the rare earth compound is one or two of rare earth carbonates or rare earth oxides, and the main rare earths are lanthanum, cerium, praseodymium, neodymium, etc.; the mass ratio of the rare earth compound to water is 1:0.8-1.2.

[0008] Preferably, in step (2) of the above technical solution, the oxidant is any one or more of hydrogen peroxide, sodium persulfate, and sodium percarbonate, and the amount added is 0.5-3% of the mass of the rare earth compound. When hydrogen peroxide, sodium persulfate, and sodium percarbonate are mixed with water, they decompose to produce active substances such as hydroxyl radicals. These active substances can attack the rare earth compound, causing its crystal lattice to crack, thereby loosening the bond between fluoride ions and the rare earth matrix, releasing the fluoride ions, and at the same time making the surface of the rare earth compound loose and porous, increasing the specific surface area, which is beneficial for subsequent alkaline cleaning.

[0009] Preferably, in step (3) of the above technical solution, the primary alkaline washing working solution is a mixed solution of sodium bicarbonate and sodium hydroxide or a mixed solution of ammonium bicarbonate and sodium hydroxide, the pH of the reaction system is controlled at 9-11, wherein the concentration of sodium bicarbonate or ammonium bicarbonate is 30-60 g / L, and the concentration of sodium hydroxide is 10-30 g / L; the solid-liquid mass ratio of the alkaline washing is 1:3-5. In this technical solution, a mixed solution of sodium bicarbonate or ammonium bicarbonate and sodium hydroxide is used as the primary alkaline washing working solution, utilizing the OH- provided by sodium hydroxide... - Dissolving fluoride ions in the liquid phase, while using sodium bicarbonate or ammonium bicarbonate as a buffer, not only stabilizes the system pH and prevents localized over-alkalinity from causing rare earth hydroxide flocculation that encapsulates fluoride and hinders fluoride release, but also ensures that the HCO3- - / CO3 2- The system can also help decompose some fluorinated carbonates and promote the dissolution of fluorine.

[0010] Preferably, in step (4) of the above technical solution, the secondary alkaline washing working solution is a mixed solution of sodium hydroxide solution and the oxidant, the pH of the reaction system is controlled at 11-13, the concentration of sodium hydroxide is 20-50 g / L, and the amount of oxidant added is 0.1-0.5% of the mass of the rare earth compound; the solid-liquid mass ratio of the alkaline washing is 1:3-4. This technical solution utilizes high concentrations of OH... - The solution disrupts the rare earth compounds that encapsulate fluorine, and with the addition of a small amount of oxidant, the crystal structure of the rare earth compounds is further disrupted, converting the sparingly soluble fluorides and the encapsulated fluorine into the liquid phase, thereby improving the conversion of fluorine.

[0011] Preferably, in step (5) of the above technical solution, in the three-stage countercurrent washing, the washing water temperature of each stage is controlled at 60-90℃, the washing solid-liquid volume ratio is 1:2-4, and the washing time is 0.5-1h.

[0012] Three-stage countercurrent washing refers to a process where the material and washing water flow in opposite directions: fresh water enters from the third stage, comes into contact with the material, becomes saline wastewater that enters the second stage, and the wastewater from the second stage then enters the first stage, while the material enters from the first stage. This process is repeated three times before the material is discharged. This results in higher washing efficiency per unit volume of water and lower total water consumption. Simultaneously, using hot water for washing increases the solubility of soluble impurities in rare earth compounds (such as NaF, Na₂CO₃, and NaHCO₃), further improving washing efficiency.

[0013] Preferably, in step (5) of the above technical solution, the drying temperature is 80-110℃.

[0014] Preferably, the above technical solution also includes the graded utilization of wastewater at each stage. Specifically, the primary washing filtrate generated in step (3) is added to a defluorinating agent, stirred for 1-2 hours, and then separated into solid and liquid components. The filter residue is fluoride. The filtrate is returned to step (1) as pulping water after pH adjustment to 5-7. The secondary washing filtrate generated in step (4) is evaporated and concentrated, then returned to step (3) or step (4) to prepare an alkaline washing working solution. The condensate enters step (5) as washing water. The washing water generated in step (5) is reused in a counter-current manner. This invention treats and reuses the filtrate, reducing wastewater discharge and improving utilization efficiency. The primary washing filtrate has a high fluoride content, which can be converted into insoluble calcium fluoride for recovery by adding appropriate defluorinating agents such as calcium salts. The filtrate contains sodium carbonate and a small amount of alkali, which can be used as pulping water after pH adjustment. The secondary washing filtrate has a relatively low fluoride content, but its sodium hydroxide content is still high. After concentration, it can be used as the alkali source for the primary or secondary alkaline washing working solution and recycled. The condensate can be used as washing water. The washing water generated in the tertiary countercurrent washing can be used as makeup water for the secondary washing, depending on the countercurrent method. The secondary washing water can be used as makeup water for the primary washing, and the secondary washing water can be used as makeup water for the primary washing. The primary washing water can be added to the primary or secondary washing filtrate. In this way, all process water can be recycled and reused, which is more environmentally friendly.

[0015] Preferably, in the above technical solution, the defluorinating agent is an iron salt, a calcium salt, or a mixed aluminum-iron salt.

[0016] Preferably, in the above technical solution, solid-liquid separation is performed by vacuum dehydration or pressure filtration dehydration.

[0017] Advantages compared to existing technologies: This invention first grinds rare earth compounds into a slurry, which is then mixed with an oxidant to release fluoride ions. Simultaneously, the oxidative etching process makes the surface of the material particles porous, facilitating subsequent alkaline washing. The first defluorination stage uses a mild alkaline wash to remove free fluoride and fluoride encapsulated in soluble fluoride salts from the surface and near-surface of the material, removing most of the fluoride from the rare earth compounds. The mild system also facilitates subsequent deep defluorination. The second defluorination stage uses a high-alkali system combined with a small amount of oxidant to achieve deep defluorination. Finally, a three-stage countercurrent washing process is employed, resulting in excellent washing performance with low water consumption. The obtained rare earth compound product not only has a significantly reduced fluoride content (below 0.1%) but also removes other impurities such as aluminum and sulfur, resulting in high-quality products that meet the requirements for rare earth smelting and separation.

[0018] This invention allows wastewater generated during the defluorination process to be reused at different stages after simple treatment, greatly reducing pollution and production costs, resulting in significant economic and environmental benefits. Attached Figure Description

[0019] Figure 1This is a flow chart of the defluorination process for rare earth compounds of the present invention. Detailed Implementation

[0020] The above-described technical features of the present invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. However, the present invention is not limited to these embodiments, nor are these embodiments limited in any way.

[0021] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the formulations involved in the following examples are all commercially available products that can be purchased from the market.

[0022] The present invention will be further described in detail below with reference to embodiments: Example 1 A process for removing fluoride from rare earth compounds includes the following steps: (1) Pulping: The rare earth compounds (fluorinated carbonate rare earths that have been pressed and dehydrated, the analysis results are F 0.62%, Al2O3 2.6%, SO4 0.62%), Al2O3 2.6%, SO4 0.62 ... 2- 2.1% (75% loss on ignition) is mixed with water at a mass ratio of 1:1 and then pulverized or ball-milled to form a slurry; (2) Oxidation pretreatment: Add 1% hydrogen peroxide of rare earth compound by mass to the slurry, stir and react at 25°C for 2 hours. After the reaction is completed, the preliminary activated rare earth material is obtained. (3) First alkaline washing and defluorination: The pre-activated rare earth material is transferred into a stirred reaction tank, and a first alkaline washing working solution (sodium bicarbonate concentration of 40 g / L and sodium hydroxide concentration of 20 g / L) is added until the solid-liquid mass ratio is 1:4 and the pH is 9-11. The mixture is stirred and reacted at 60℃ for 1.5 h. After the reaction is completed, the mixture is filtered and dehydrated to obtain the first washing residue and the first washing filtrate. Calcium salt is added to the first washing filtrate and stirred and reacted for 1.5 h. The solid and liquid are separated. The filter residue is calcium fluoride. The filtrate is returned to step (1) as pulping water after the pH is adjusted to 5-7. (4) Secondary alkaline washing and defluorination: Transfer the primary washing residue to another stirred reaction tank, add secondary alkaline washing working solution (sodium hydroxide concentration is 40g / L, hydrogen peroxide addition is 0.2% of the mass of rare earth compound) until the solid-liquid mass ratio is 1:3, pH is 11-13, stir and react at 80℃ for 1.5h, after the reaction is completed, the solid and liquid are separated to obtain secondary washing residue and secondary washing filtrate; the secondary washing filtrate is evaporated and concentrated and returned to step (3) or step (4) to prepare alkaline washing working solution, and the condensate enters step (5) as washing water; (5) Washing: The secondary washing residue is washed using a three-stage countercurrent washing method. The washing water temperature is controlled at 70℃ for each stage, the solid-liquid volume ratio is 1:3, and the washing time is 1h. After washing, the solid and liquid are separated, and the rare earth compound filter residue is dried at 100℃ until the moisture content is less than 5% to obtain the defluorinated rare earth compound product. The washing water is reused, the third-stage washing water is used as the second-stage washing water, the second-stage washing water is used as the first-stage washing water, and the first-stage washing water enters the primary washing filtrate or the secondary washing filtrate.

[0023] The impurity content in the defluorinated rare earth compound product was tested, and the results were: F 0.06%, Al2O3 1.3%, SO4 0.06%, Al2O3 1.3%, SO4 0.06%. 2- 0.05%, loss on ignition rate 73%; wastewater recycling rate is over 90%.

[0024] Example 2 A process for removing fluoride from rare earth compounds includes the following steps: (1) Pulping: The rare earth compounds (fluorinated carbonate rare earths that have been pressed and dehydrated, with analytical results of F 0.65%, Al2O3 2.0%, SO4 0.65%), were pulped. 2- 2.5% (loss on ignition 72%) is mixed with water at a mass ratio of 1:1.1 and then pulverized or ball-milled to form a slurry; (2) Oxidation pretreatment: Add 2% hydrogen peroxide of rare earth compound by mass to the slurry, stir and react at 50°C for 1 hour. After the reaction is completed, the preliminary activated rare earth material is obtained. (3) First alkaline washing and defluorination: The pre-activated rare earth material is transferred into a stirred reaction tank, and a first alkaline washing working solution (ammonium bicarbonate concentration of 60 g / L and sodium hydroxide concentration of 10 g / L) is added until the solid-liquid mass ratio is 1:3 and the pH is 9-10. The mixture is stirred and reacted at 80℃ for 1 h. After the reaction is completed, the mixture is filtered and dehydrated to obtain the first washing residue and the first washing filtrate. Calcium salt is added to the first washing filtrate, and the mixture is stirred and reacted for 1 h. The solid and liquid are separated, and the filter residue is calcium fluoride. The filtrate is returned to step (1) as pulping water after the pH is adjusted to 5-7. (4) Secondary alkaline washing and defluorination: Transfer the primary washing residue to another stirred reaction tank, add secondary alkaline washing working solution (sodium hydroxide concentration is 50g / L, hydrogen peroxide addition is 0.2% of the mass of rare earth compound) until the solid-liquid mass ratio is 1:4, pH is 12-13, stir and react at 90℃ for 0.5h, after the reaction is completed, the solid and liquid are separated to obtain secondary washing residue and secondary washing filtrate; the secondary washing filtrate is evaporated and concentrated and returned to step (3) or step (4) to prepare alkaline washing working solution, and the condensate enters step (5) as washing water; (5) Washing: The secondary washing residue is washed using a three-stage countercurrent washing method. The washing water temperature is controlled at 90℃ for each stage, the solid-liquid volume ratio is 1:2, and the washing time is 1h. After washing, the solid and liquid are separated, and the rare earth compound filter residue is dried at 80℃ until the moisture content is less than 5% to obtain the defluorinated rare earth compound product. The washing water is reused, the third-stage washing water is used as the second-stage washing water, the second-stage washing water is used as the first-stage washing water, and the first-stage washing water enters the primary washing filtrate or the secondary washing filtrate.

[0025] The impurity content in the defluorinated rare earth compound product was tested, and the results were: F 0.07%, Al2O3 1.2%, SO4 0.07%, Al2O3 1.2%, SO4 0.07%. 2- 0.04%, loss on ignition rate 74%; wastewater recycling rate is over 90%.

[0026] Example 3 A process for removing fluoride from rare earth compounds includes the following steps: (1) Pulping: The rare earth compounds (fluorine-containing rare earth oxides that have been pressed and dehydrated, with analysis results of F 0.54%, Al2O3 2.5%, SO4 0.54%), were pulped. 2- 2% (loss on ignition 75%) is mixed with water at a mass ratio of 1:0.9 and then pulverized or ball-milled to form a slurry; (2) Oxidation pretreatment: Add sodium persulfate of 3% by mass of rare earth compound to the slurry, stir and react at 25°C for 2 hours. After the reaction is completed, the preliminary activated rare earth material is obtained. (3) First alkaline washing and defluorination: The pre-activated rare earth material is transferred into a stirred reaction tank, and a first alkaline washing working solution (sodium bicarbonate concentration is 30 g / L, sodium hydroxide concentration is 30 g / L) is added until the solid-liquid mass ratio is 1:3 and the pH is 10-11. The mixture is stirred and reacted at 50℃ for 1.5 h. After the reaction is completed, the mixture is filtered and dehydrated to obtain the first washing residue and the first washing filtrate. Calcium salt is added to the first washing filtrate, and the mixture is stirred and reacted for 2 h. The solid and liquid are separated, and the filter residue is calcium fluoride. The filtrate is returned to step (1) as pulping water after the pH is adjusted to 5-7. (4) Secondary alkaline washing and defluorination: Transfer the primary washing residue to another stirred reaction tank, add secondary alkaline washing working solution (sodium hydroxide concentration is 20g / L, sodium persulfate is added at 0.5% of the mass of rare earth compound) until the solid-liquid mass ratio is 1:4, pH is 11-13, stir and react at 60℃ for 2h. After the reaction is completed, the solid and liquid are separated to obtain secondary washing residue and secondary washing filtrate; the secondary washing filtrate is evaporated and concentrated and returned to step (3) or step (4) to prepare alkaline washing working solution, and the condensate enters step (5) as washing water; (5) Washing: The secondary washing residue is washed using a three-stage countercurrent washing method. The washing water temperature is controlled at 60℃ for each stage, the solid-liquid volume ratio is 1:4, and the washing time is 1h. After washing, the solid and liquid are separated, and the rare earth compound filter residue is dried at 110℃ until the moisture content is less than 5% to obtain the defluorinated rare earth compound product. The washing water is reused, the third-stage washing water is used as the second-stage washing water, the second-stage washing water is used as the first-stage washing water, and the first-stage washing water enters the primary washing filtrate or the secondary washing filtrate.

[0027] The impurity content in the defluorinated rare earth compound product was tested, and the results were: F 0.06%, Al2O3 1.6%, SO4 0.06%. 2- 0.1%, loss on ignition rate 73%; wastewater recycling rate is over 90%.

[0028] Comparative Example 1 A process for removing fluoride from rare earth compounds differs from Example 1 in that it omits the oxidation pretreatment step (2), while the other steps are the same as in Example 1.

[0029] The impurity content in the defluorinated rare earth compound product was tested, and the results were: F 0.30%, Al2O3 2.4%, SO4 ... 2- 0.9%, loss on ignition 75%.

[0030] Comparative Example 2 A defluorination process for rare earth compounds differs from Example 1 in that the alkaline washing working solution in step (3) is only sodium hydroxide with a concentration of 20 g / L, while the other steps are the same as in Example 1.

[0031] The impurity content in the defluorinated rare earth compound product was tested, and the results were: F 0.21%, Al2O3 2.0%, SO4 ... 2- 0.7%, loss on ignition 74%.

[0032] Comparative Example 3 A defluorination process for rare earth compounds differs from Example 1 in that the alkaline washing working solution in step (3) is only sodium bicarbonate with a concentration of 40 g / L, while the other steps are the same as in Example 1.

[0033] The impurity content in the defluorinated rare earth compound product was tested, and the results were: F 0.32%, Al2O3 2.2%, SO4 ... 2- 0.6%, loss on ignition 75%.

[0034] Comparative Example 4 A defluorination process for rare earth compounds differs from Example 1 in that the secondary alkaline washing working solution in step (4) is only sodium hydroxide (without oxidant) with a concentration of 40 g / L, while the other steps are the same as in Example 1.

[0035] The impurity content in the defluorinated rare earth compound product was tested, and the results were: F 0.14%, Al2O3 1.7%, SO4 ... 2- 0.2%, loss on ignition 73%.

[0036] Comparative Example 5 A defluorination process for rare earth compounds differs from Example 1 in that the secondary alkaline washing working solution in step (4) is only sodium bicarbonate with a concentration of 40 g / L, while the other steps are the same as in Example 1.

[0037] The impurity content in the defluorinated rare earth compound product was tested, and the results were: F 0.16%, Al2O3 1.8%, SO4 ... 2- 0.3%, loss on ignition 74%.

[0038] Comparative Example 6 A process for removing fluoride from rare earth compounds differs from Example 1 in that, in step (4), the reaction is stirred at room temperature (25°C) for 1.5 hours, while the other steps are the same as in Example 1.

[0039] The impurity content in the defluorinated rare earth compound product was tested, and the results were: F 0.11%, Al2O3 1.5%, SO4 ... SO4 0.5%, SO4 0.11%, SO4 0.5%, SO4 0.11%, SO4 0.11%, SO4 0.11%, SO4 0.11%, SO4 0.11%, SO4 2- 0.1%, loss on ignition 75%.

[0040] Comparative Example 7 A process for removing fluoride from rare earth compounds differs from Example 1 in that step (4) is omitted, while the other steps are the same as in Example 1.

[0041] The impurity content in the defluorinated rare earth compound product was tested, and the results were: F 0.19%, Al2O3 2.0%, SO4 ... 2- 0.4%, loss on ignition 75%.

[0042] Comparative Example 8 A defluorination process for rare earth compounds differs from that in Example 1 in that the washing water temperature in step (5) is room temperature (25°C), while the other steps are the same as in Example 1.

[0043] The impurity content in the defluorinated rare earth compound product was tested, and the results were: F 0.08%, Al2O3 1.7%, SO4 0.08%. 2- 0.3%, loss on ignition 75%.

[0044] Comparative Example 9 A process for removing fluoride from rare earth compounds differs from Example 1 in that steps (2), (3), and (4) are combined as follows: 1.2% hydrogen peroxide by mass of rare earth compounds is added to the slurry, along with sodium bicarbonate (concentration of 40 g / L) and sodium hydroxide (concentration of 60 g / L) to achieve a solid-liquid mass ratio of 1:4, pH of 10-13, and the mixture is stirred and reacted at 60°C for 3 hours. After the reaction is completed, the mixture is filtered and dehydrated to obtain washing residue. Other steps are the same as in Example 1.

[0045] The impurity content in the defluorinated rare earth compound product was tested, and the results were: F 0.20%, Al2O3 2.0%, SO4 0.20%, Al2O3 2.0%, SO4 0.20%. 2- 0.4%, loss on ignition 74%.

[0046] Conclusion Analysis: The results of Examples 1-3 show that the defluorination method of the present invention can reduce the fluoride content in rare earth compounds to below 0.1%, achieving high defluorination efficiency. It also removes most of the alumina and sulfate ions, resulting in high product quality and high wastewater recycling rate. In contrast, in Comparative Example 1, the lack of oxidation pretreatment meant the rare earth crystal structure was not destroyed, affecting subsequent fluoride elution. In Comparative Example 2, the first alkaline wash used only strong alkali sodium hydroxide, which easily formed dense coatings on the surface of rare earth compounds, affecting subsequent deep defluorination. In Comparative Example 3, the first alkaline wash used only weak alkali sodium bicarbonate, resulting in incomplete elution and directly affecting the overall elution effect. In Comparative Example 4, the second alkaline wash did not add an oxidant, preventing the elution of insoluble fluorides or coated fluoride, affecting the overall defluorination effect. In Comparative Example 5, the second alkaline wash used only weak alkali sodium bicarbonate, resulting in even worse defluorination. In Example 6, the secondary alkaline wash was performed at room temperature, resulting in weak diffusion of hydroxide ions and the inability to remove residual fluorine inside the particle pores, thus affecting the defluorination effect. In Comparative Example 7, only one alkaline defluorination was performed, which was not thorough. In Comparative Example 8, the final wash was performed with room temperature water, which had little impact on defluorination, but other impurities were not easily washed out. In Comparative Example 9, the oxidant, sodium bicarbonate, and sodium hydroxide were simultaneously subjected to one alkaline wash. Although the alkalinity was achieved, the reaction was relatively vigorous and uneven, and some rare earth elements were trapped, affecting the release of fluorine, resulting in a less than ideal defluorination effect.

[0047] In summary, this invention optimizes the defluorination process by first subjecting the ground rare earth compounds to oxidation pretreatment, followed by a first alkaline washing defluorination, a second alkaline washing defluorination, and finally washing. The resulting defluorinated rare earth compound product has a fluorine content of less than 0.1% and few other impurities, exhibiting excellent quality and meeting the requirements for rare earth smelting and separation. Simultaneously, the waste liquid is recycled, significantly reducing pollution and costs, resulting in substantial economic and environmental benefits.

[0048] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for removing fluoride from rare earth compounds, characterized in that, Includes the following steps: (1) Pulping: The rare earth compound is mixed with water and then crushed or ball-milled to make a slurry; (2) Oxidation pretreatment: Add oxidant to the slurry and stir the reaction at 25-60℃ for 0.5-2h. After the reaction is completed, the preliminary activated rare earth material is obtained. (3) First alkaline washing defluorination: The pre-activated rare earth material is transferred into a stirred reaction tank, and the first alkaline washing working solution is added. The mixture is stirred and reacted at 50-80℃ for 1-1.5h. After the reaction is completed, the solid and liquid are separated to obtain the first washing residue and the first washing filtrate. (4) Secondary alkaline washing and defluorination: Transfer the primary washing residue to another stirred reaction tank, add the secondary alkaline washing working solution, stir and react at 60-90℃ for 0.5-2h, after the reaction is completed, separate the solid and liquid to obtain secondary washing residue and secondary washing filtrate. (5) Washing: The secondary washing residue is washed using a three-stage countercurrent washing method. After washing, solid and liquid are separated, and the rare earth compound filter residue is dried to a moisture content of less than 5% to obtain the defluorinated rare earth compound product.

2. The defluorination process for rare earth compounds according to claim 1, characterized in that, In step (1), the rare earth compound is one or two of rare earth carbonates or rare earth oxides; the mass ratio of the rare earth compound to water is 1:0.8-1.

2.

3. The defluorination process for rare earth compounds according to claim 1, characterized in that, In step (2), the oxidant is any one or more of hydrogen peroxide, sodium persulfate, and sodium percarbonate, and the amount added is 0.5-3% of the mass of the rare earth compound.

4. The defluorination process for rare earth compounds according to claim 1, characterized in that, In step (3), the working solution for the first alkaline washing is a mixed solution of sodium bicarbonate and sodium hydroxide or a mixed solution of ammonium bicarbonate and sodium hydroxide. The pH of the reaction system is controlled at 9-11, wherein the concentration of sodium bicarbonate or ammonium bicarbonate is 30-60 g / L and the concentration of sodium hydroxide is 10-30 g / L; the solid-liquid mass ratio of the alkaline washing is 1:3-5.

5. The defluorination process for rare earth compounds according to claim 1, characterized in that, In step (4), the secondary alkaline washing working solution is a mixed solution of sodium hydroxide solution and the oxidant. The pH of the reaction system is controlled at 11-13, the concentration of sodium hydroxide is 20-50 g / L, and the amount of oxidant added is 0.1-0.5% of the mass of rare earth compound. The solid-liquid mass ratio of the alkaline washing is 1:3-4.

6. The defluorination process for rare earth compounds according to claim 1, characterized in that, In step (5), during the three-stage countercurrent washing, the water temperature of each stage is controlled at 60-90℃, the solid-liquid volume ratio is 1:2-4, and the washing time is 0.5-1h.

7. The defluorination process for rare earth compounds according to claim 1, characterized in that, In step (5), the drying temperature is 80-110℃.

8. The defluorination process for rare earth compounds according to claim 1, characterized in that, It also includes the graded utilization of wastewater at all levels. In this case, the primary washing filtrate generated in step (3) is added to a defluorinating agent and stirred for 1-2 hours to separate the solid and liquid. The filter residue is fluoride. The filtrate is returned to step (1) as pulping water after the pH is adjusted to 5-7. The secondary washing filtrate generated in step (4) is returned to step (3) or step (4) to prepare alkaline washing working solution after evaporation and concentration. The condensate enters step (5) as washing water. The washing water generated in step (5) is reused in a countercurrent manner.

9. The defluorination process for rare earth compounds according to claim 8, characterized in that, The defluorinating agent is an iron salt, a calcium salt, or a mixed aluminum-iron salt.

10. The defluorination process for rare earth compounds according to claim 1, characterized in that, Solid-liquid separation is achieved by vacuum dehydration or pressure filtration dehydration.

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