Impurity removal method for rare earth feed liquid

Abstract

The invention relates to an impurity removal method for rare earth feed liquid, and belongs to the technical field of rare earth metallurgy. The impurity removal method of the rare earth feed liquid comprises the following steps: (1) performing oil removal on rare earth extraction raffinate wastewater, and adding an alkaline precipitator for precipitation to obtain an impurity removal agent; (2) adding barium salt into the rare earth feed liquid to obtain primary impurity-removed liquid; (3) adding the impurity removal agent into the primary impurity removal liquid to obtain secondary impurity removal liquid and impurity removal residues; and (4) extracting the secondary impurity removal liquid by adopting an extracting agent to obtain a tertiary impurity removal liquid and raffinate wastewater, and recycling the obtained raffinate wastewater for preparing the impurity removal agent in the step (1). According to the impurity removal method disclosed by the invention, on the premise of not changing the original raffinate wastewater precipitation treatment flow and meeting the original raffinate wastewater discharge water quality, while the raffinate wastewater is treated, the multi-impurity rare earth feed liquid can be effectively subjected to impurity removal, the comprehensive utilization of resources is realized, and the green and healthy development of the rare earth industry is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of rare earth metallurgy technology, and specifically relates to a method for removing impurities from rare earth slurry. Background Technology

[0002] Current ion-adsorption rare earth mining processes mainly focus on the leaching of rare earth elements from the ore body and the recovery of rare earth elements after leaching. Less attention is paid to the removal of non-rare earth impurities that accompany rare earth leaching during the mining process. As a result, after acid dissolution of rare earth concentrate, ion-adsorption rare earth smelting enterprises often obtain rare earth chloride solutions containing non-rare earth ions such as aluminum, iron, thorium, uranium, fluorine, calcium, magnesium, and sulfate. These impurities need to be removed in order to obtain qualified rare earth solutions that meet the requirements for extraction and separation.

[0003] Conventional methods for removing impurities from high-impurity rare earth solutions mainly include alkaline adjustment, ion adsorption, and oxalic acid precipitation. Alkaline adjustment involves adding liquid alkali or ammonia to the high-impurity rare earth solution to adjust the pH to the range where non-rare earth ions hydrolyze. This causes non-rare earth ions such as aluminum, iron, thorium, and uranium, whose hydrolysis pH is lower than that of rare earth ions, to form hydrolysis products, which are then removed. Its advantages are simple process and a certain degree of impurity removal effect. However, its disadvantages include the difficulty in removing the hydrolysis products, leading to unstable impurity removal, significant rare earth loss during the process, and inability to remove impurities with hydrolysis pH values ​​higher than those of rare earth ions. Ion adsorption, on the other hand, utilizes functional groups in resins to react with certain non-rare earth ions. The adsorption and removal of non-rare earth impurities from high-impurity rare earth solutions by binding ions has the advantages of good removal effect and low rare earth loss. The disadvantages are that the resin adsorption capacity is small and it can often only remove one type of non-rare earth ion. The removal of multi-impurity rare earth solutions requires the use of multiple types of resins and multiple removal processes. The oxalic acid precipitation method precipitates rare earths in high-impurity rare earth solutions by precipitating rare earths in oxalic acid. The resulting rare earth oxalate is then roasted and acid-dissolved to obtain a low-impurity rare earth solution. This process is costly and complex, and is usually only used for the purification of high-impurity rare earth solutions that cannot be treated by certain conventional removal methods.

[0004] Furthermore, the raffinate wastewater generated during rare earth extraction, after oil removal, typically contains calcium and magnesium ions, along with small amounts of heavy metal ions such as lead and cadmium, in addition to the saponifying agent cations. Sometimes, to ensure the purity of the rare earth solution, it may also contain small amounts of rare earth ions such as lanthanum. This type of wastewater is generally treated by lime neutralization and precipitation before discharge, and the resulting solid waste is disposed of by specialized institutions. This disposal process produces a large quantity of highly alkaline solid waste, requiring acid-base adjustment during subsequent solid waste stabilization, resulting in significant resource waste. Therefore, using the raffinate wastewater for the removal of impurities from rare earth solutions is of great significance for the comprehensive utilization of data and the avoidance of resource waste. Summary of the Invention

[0005] The purpose of this invention is to provide a method for removing impurities from rare earth feed solutions based on the characteristics of both extraction wastewater and rare earth feed solutions with multiple impurities. This method can remove impurities from rare earth feed solutions while treating extraction wastewater, without changing the original sedimentation treatment process of extraction wastewater and meeting the original discharge water quality requirements. This achieves comprehensive utilization of resources and is conducive to the green and healthy development of the rare earth industry.

[0006] This invention is achieved through the following technical solution: This invention provides a method for removing impurities from rare earth slurry, comprising the following steps: (1) Remove oil from rare earth extraction wastewater and then add alkaline precipitant to precipitate and obtain impurity removal agent; (2) Add barium salt to the rare earth solution to obtain a primary impurity removal solution; (3) Add the impurity removal agent obtained in step (1) to the primary impurity removal solution obtained in step (2) to obtain the secondary impurity removal solution and the impurity removal residue; (4) The secondary impurity removal solution obtained in step (3) is extracted with an extractant to obtain a tertiary impurity removal solution and raffinate wastewater. The raffinate wastewater is recycled for the preparation of impurity removal agent in step (1).

[0007] Preferably, the method for removing impurities from the rare earth liquid further includes step (5): cross-flow exchange between the impurity-removed residue obtained in step (3) and the new rare earth liquid, followed by water washing, to achieve the recovery of rare earth elements from the impurity-removed residue.

[0008] The present invention utilizes the principle that the hydrolysis pH value of calcium and magnesium ions in the raffinate wastewater is higher than that of rare earth elements. After the raffinate wastewater is treated to remove oil, an alkaline precipitant (such as a calcium or magnesium precipitant) is used to precipitate the calcium, magnesium, rare earth elements and heavy metal ions in the raffinate wastewater, thereby solving the wastewater discharge problem and obtaining an alkaline impurity removal agent. After removing sulfate ions from a rare earth solution containing many impurities with barium salts, an alkaline impurity removal agent is added. Due to the difference in hydrolysis pH, the calcium and magnesium hydrolysis products in the impurity removal agent will undergo an exchange reaction with non-rare earth ions such as aluminum, iron, thorium, and uranium, which have lower hydrolysis pH values. That is, calcium and magnesium dissociate and are released into the solution, while aluminum, iron, thorium, and uranium hydrolyze and enter the impurity removal residue. At the same time, under certain pH conditions, fluorine and non-rare earth cations such as aluminum will form complexes, which will also be complexed and hydrolyzed during the hydrolysis process. Therefore, fluoride ions can also be removed in this process. In addition, the added impurity removal agent and the barium sulfate produced from the previous sulfate removal can both act as adsorption carriers to adsorb and carry the non-rare earth hydrolysis products generated during the impurity removal process, further improving the impurity removal effect. Although the hydrolysis pH of rare earth elements is lower than that of calcium and magnesium, the loss caused by rare earth hydrolysis can be reduced by controlling the pH of the feed solution during the impurity removal process. Furthermore, by cross-flow exchange between the removed residue and a new multi-impurity rare earth solution, and taking advantage of the higher hydrolysis pH of rare earth ions compared to non-rare earth elements such as aluminum, the rare earth elements lost during the aforementioned impurity removal process can be further recovered. Finally, the removed rare earth feed solution is then subjected to extraction separation. Utilizing the difference in separation coefficients, calcium and magnesium can be separated from the rare earth feed solution into the raffinate wastewater, achieving further impurity removal while also enabling the recycling of calcium and magnesium resources.

[0009] Preferably, in step (1), the oil content in the raffinate wastewater after oil removal does not exceed 1 mg / L.

[0010] There are no restrictions on the method of oil removal from the raffinate wastewater; those skilled in the art can routinely choose common methods in the field.

[0011] Specifically, in step (1), the rare earth leaching wastewater is the leaching wastewater produced during the rare earth extraction and separation process, and the rare earth extraction and separation method includes at least one of the following: integrated mining leaching and extraction process and extraction and separation process of rare earth smelting plant.

[0012] Specifically, the concentration of calcium ions in the rare earth extraction wastewater is 100 mg / L-10000 mg / L, and the concentration of magnesium ions is 100 mg / L-10000 mg / L.

[0013] Preferably, in step (1), the endpoint of precipitation by the alkaline precipitant is when the pH value of the solution is 10-13.

[0014] Specifically, in step (1) of this invention, the precipitation method can be conventional stirring. The pH value at the precipitation endpoint can be controlled between 10 and 13 depending on the alkaline precipitant added. After precipitation, the impurity removal agent obtained does not need to be washed. Rare earth ions, aluminum, iron, thorium, uranium, lead, cadmium and other non-rare earth ions in the precipitated wastewater have been basically removed, leaving only a small amount of calcium and magnesium ions, which can meet the water quality standards of the original precipitated wastewater after lime neutralization.

[0015] Preferably, in step (1), the alkaline precipitant includes at least one of calcium oxide, magnesium oxide, calcium hydroxide, and magnesium hydroxide.

[0016] Preferably, in step (2), the barium salt includes barium chloride.

[0017] Preferably, in step (2), the amount of barium salt added is 0.8-1.2 times the molar amount of sulfate in the rare earth solution, more preferably 0.9-1.1 times.

[0018] Preferably, in step (3), the pH value of the primary impurity removal solution obtained in step (2) is first adjusted to 1.5-3.0, and then the impurity removal agent obtained in step (1) is added until the pH value of the solution is 4.0-5.0, so as to obtain the secondary impurity removal solution and the impurity removal residue.

[0019] More preferably, in step (3), the pH value of the primary impurity removal solution obtained in step (2) is first adjusted to 2.0-2.5, and then the impurity removal agent obtained in step (1) is added until the pH value of the solution is 4.3-4.6, so as to obtain the secondary impurity removal solution and the impurity removal residue.

[0020] Specifically, the pH value of the primary impurity removal solution obtained in step (2) is adjusted by using an acid (such as hydrochloric acid) or a base (such as calcium oxide, magnesium oxide, etc.).

[0021] Preferably, in step (4), the extractant includes an organophosphorus extractant, which includes 2-ethylhexyl phosphate mono-2-ethylhexyl ester (p507).

[0022] Specifically, in step (4), the extractant is a mixture of organophosphorus extractant and kerosene. There are no special requirements on the volume ratio of the organophosphorus extractant and kerosene, and those skilled in the art can choose conventionally.

[0023] Preferably, in step (4), the extractant is a saponified extractant, and the molar charge of the saponified extractant is 0.95-1.2 times the molar charge of rare earth elements in the secondary impurity removal solution; the saponification agent used in the saponification is at least one of calcium oxide, magnesium oxide, calcium hydroxide, magnesium hydroxide, calcium carbonate, or magnesium bicarbonate.

[0024] This invention involves saponifying an acidic organophosphorus extractant to convert it into a metal salt form. Rare earth elements in the secondary impurity removal solution are then extracted via cation exchange. Therefore, limiting the molar charge of the saponified extractant to 0.95-1.2 times the molar charge of the rare earth elements in the secondary impurity removal solution enables effective extraction of rare earth elements and improves the impurity removal effect.

[0025] Specifically, the present invention does not limit the degree of saponification of the extractant after saponification, and those skilled in the art can choose it conventionally; optionally, the degree of saponification of the extractant after saponification does not exceed 36%.

[0026] More preferably, in step (4), the molar charge of the saponified extractant is 1.05-1.1 times the molar charge of the rare earth element in the secondary impurity removal solution.

[0027] Preferably, in step (4), an extractant is used to extract the secondary impurity removal solution obtained in step (3) to obtain an organic phase and raffinate wastewater, and hydrochloric acid is used to back-extract the organic phase to obtain a tertiary impurity removal solution.

[0028] Most of the sulfate, aluminum, iron, thorium, uranium, and fluoride ions in the secondary impurity removal solution have been removed, but calcium and magnesium ions with hydrolysis pH values ​​higher than those of rare earth ions still remain. A third impurity removal is carried out using a rare earth extractant. During the extraction and separation process, calcium and magnesium are relatively difficult to extract compared to rare earth ions, so they will return to the extraction wastewater during the rare earth extraction and separation process, and new impurity removal agents can be prepared for a new round of recycling.

[0029] Preferably, in step (5), the solid-liquid ratio of the impurity slag to the new rare earth liquid in the cross-flow exchange process is 1:1-4, preferably 1:2-3, and the number of cross-flow exchanges is 1-4 times, preferably 2-3 times.

[0030] Preferably, in step (5), the solid-liquid ratio of the water washing is 1:(1-4), more preferably 1:(2-3), and the number of water washings is 1-4 times, more preferably 2-3 times.

[0031] During the cross-flow exchange process, the rare earth hydroxides and oxyhydrogen ions in the residue will exchange with non-rare earth cations such as aluminum, iron, thorium, and uranium in the new high-impurity rare earth feed solution, whose hydrolysis pH is lower than that of rare earths. This process dissolves rare earth ions while simultaneously removing some impurity ions from the new high-impurity rare earth feed solution, reducing the amount of impurity removal reagents needed in subsequent reactions and improving their utilization rate. Furthermore, the residue after cross-flow exchange also contains a small amount of rare earth feed solution, which can be recovered through washing.

[0032] The present invention has the following beneficial effects: Based on the characteristics of both raffinate wastewater and multi-impurity rare earth feed solutions, this invention proposes a method for removing impurities from multi-impurity rare earth feed solutions. First, it utilizes the principle of sulfate ions reacting with barium ions to form insoluble barium sulfate to remove sulfate ions from the multi-impurity rare earth feed solution. Then, it uses a removal agent prepared from the raffinate wastewater to remove aluminum, iron, thorium, uranium, and fluoride ions. Finally, it removes calcium and magnesium ions through extraction separation. Without altering the original raffinate wastewater sedimentation treatment process and meeting the original raffinate wastewater discharge quality requirements, this method simultaneously treats the raffinate wastewater and removes non-rare earth ions such as aluminum, iron, thorium, uranium, fluoride, calcium, magnesium, and sulfate ions from the multi-impurity rare earth feed solution in stages. This achieves comprehensive resource utilization and is conducive to the green and healthy development of the rare earth industry. Attached Figure Description

[0033] Figure 1 This is a schematic flowchart of the method for removing impurities from rare earth slurry in Example 1. Detailed Implementation

[0034] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0035] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0036] Example 1 A method for removing impurities from a rare earth liquid, the process flow diagram of which is shown below. Figure 1 As shown, the specific steps include: (1) The rare earth smelting wastewater of a rare earth smelting enterprise was de-oiled. After the de-oiling pretreatment, the composition analysis results of the smelting wastewater are shown in Table 1. Then, calcium oxide was added to adjust the pH value to 13.0 for precipitation to obtain the impurity removal agent. Table 1. Main components (mg / L) of raffinate wastewater after oil removal pretreatment (2) The composition analysis results of a rare earth feed solution with many impurities are shown in Table 2; 100 mL of this rare earth feed solution with many impurities was measured and first analyzed according to SO4. 2- Add 1.0 times the molar amount of BaCl2·2H2O to remove impurities and obtain a first-stage impurity-removed solution; Table 2 Main Components of Rare Earth Feed Solution (3) Add hydrochloric acid to the primary impurity removal solution obtained in step (2) to adjust the pH value to 2.25, and then add the impurity removal agent obtained in step (1) to adjust the pH value of the rare earth material solution to 4.30. Filter to obtain secondary impurity removal solution and impurity removal residue. (4) The secondary impurity removal solution obtained in step (3) is saponified with calcium carbonate as the extraction saponifying agent in the p507-kerosene mixed extractant system. The saponified extractant and the secondary impurity removal solution are subjected to liquid-liquid extraction. The molar charge of the saponified extractant is 0.98 times the molar charge of rare earth in the secondary impurity removal solution. The loaded organic phase and raffinate wastewater are obtained. The raffinate wastewater can be recycled for the preparation of impurity removal agent in step (1). The loaded organic phase is back-extracted with 5.34 mol / L hydrochloric acid to obtain the tertiary impurity removal solution. The impurity ions in the tertiary impurity removal solution have been basically removed and can be directly used for rare earth extraction and separation.

[0037] To determine the impurity removal effect, the obtained three impurity removal solutions and the residual wastewater were sent for testing together. The analysis results are shown in Table 3, where " / " indicates that no test was performed.

[0038] Table 3. Component analysis results of the three-stage impurity removal solution and raffinate wastewater As shown in Table 3, after three impurity removal processes, the aluminum, iron, thorium, uranium, fluorine, calcium, magnesium, and sulfate ions contained in the multi-impurity rare earth feed solution can be reduced to a lower level.

[0039] (5) Mix 50 g of the impurity slag obtained in step (3) with a new multi-impurity rare earth material solution at a solid-liquid ratio of 1:2 and stir to allow the damaged hydrogen, oxygen, and rare earth ions in the impurity slag to undergo cross-flow exchange with non-rare earth ions. The number of exchange times is 3. After the resulting filter residue is washed with water at a solid-liquid ratio of 1:2 3 times, the rare earth content in the washing residue is less than 0.5%, and the rare earth element recovery rate in the impurity slag is 98%.

[0040] Example 2 A method for removing impurities from a rare earth liquid sample includes the following steps: (1) The rare earth smelting wastewater of a rare earth smelting enterprise in Example 1 was de-oiled. After the de-oiling pretreatment, magnesium oxide was added to adjust the pH value to 10.0 and precipitation was carried out to obtain the impurity removal agent. (2) Measure 100 mL of the rare earth solution with many impurities from Example 1, and first prepare it according to SO4. 2- Add 0.9 times the molar amount of BaCl2·2H2O to remove impurities and obtain a first-stage impurity-removed solution; (3) Add hydrochloric acid to the primary impurity removal solution obtained in step (2) to adjust the pH value to 2.0, and then add the impurity removal agent obtained in step (1) to adjust the pH value of the rare earth material solution to 4.60. Filter to obtain secondary impurity removal solution and impurity removal residue. (4) The secondary impurity removal solution obtained in step (3) is saponified with magnesium bicarbonate as the extraction saponifying agent in the p507-kerosene mixed extractant system. The saponified extractant and the secondary impurity removal solution are subjected to liquid-liquid extraction. The molar charge of the saponified extractant is 1.05 times the molar charge of rare earth in the secondary impurity removal solution. The obtained raffinate wastewater can be recycled for the preparation of impurity removal agent in step (1). The obtained loaded organic phase is back-extracted with 5.37 mol / L hydrochloric acid to obtain the tertiary impurity removal solution. The impurity ions in the obtained tertiary impurity removal solution have been basically removed and can be directly used for rare earth extraction and separation.

[0041] To determine the impurity removal effect, the obtained three impurity removal solutions were back-extracted with hydrochloric acid and sent for testing together with the raffinate wastewater. The analysis results are shown in Table 4.

[0042] Table 4. Component analysis results of the three-stage impurity removal solution and raffinate wastewater As shown in Table 4, after three impurity removal processes, the aluminum, iron, thorium, uranium, fluorine, calcium, magnesium, and sulfate ions in the multi-impurity rare earth feed solution can be reduced to a lower level.

[0043] (5) Mix 50 g of the impurity-removed residue obtained in step (3) with a new multi-impurity rare earth material solution at a solid-liquid ratio of 1:3 and stir to allow the damaged hydrogen, oxygen, and rare earth ions in the impurity-removed residue to undergo cross-flow exchange with non-rare earth ions. The number of exchange times is 3. After the resulting filter residue is washed with water at a solid-liquid ratio of 1:3 3 times, the rare earth content in the washing residue is less than 0.5%, and the rare earth element recovery rate in the impurity-removed residue is 98.3%.

[0044] Example 3 A method for removing impurities from a rare earth liquid sample includes the following steps: (1) The rare earth smelting wastewater of a rare earth smelting enterprise in Example 1 was de-oiled. After the de-oiling pretreatment, magnesium hydroxide was added to adjust the pH value to 10.5 for precipitation to obtain the impurity removal agent. (2) Measure 100 mL of the rare earth solution with many impurities from Example 1, and first prepare it according to SO4. 2- Add 1.1 times the molar amount of BaCl2·2H2O to remove impurities and obtain a first-stage impurity-removed solution; (3) Add hydrochloric acid to the primary impurity removal solution obtained in step (2) to adjust the pH value to 2.5, and then add the impurity removal agent obtained in step (1) to adjust the pH value of the rare earth material solution to 4.40. Filter to obtain secondary impurity removal solution and impurity removal residue. (4) The secondary impurity removal solution obtained in step (3) is saponified with magnesium bicarbonate as the extraction saponifying agent in the p507-kerosene mixed extractant system. The saponified extractant and the secondary impurity removal solution are subjected to liquid-liquid extraction. The molar charge of the saponified extractant is 1.0 times the molar charge of rare earth in the secondary impurity removal solution. The loaded organic phase and raffinate wastewater are obtained. The raffinate wastewater can be recycled for the preparation of impurity removal agent in step (1). The loaded organic phase is back-extracted with 5.34 mol / L hydrochloric acid to obtain the tertiary impurity removal solution. The impurity ions in the tertiary impurity removal solution have been basically removed and can be directly used for rare earth extraction and separation.

[0045] To determine the impurity removal effect, the obtained three impurity removal solutions were back-extracted with hydrochloric acid and sent for testing together with the raffinate wastewater. The analysis results are shown in Table 5.

[0046] Table 5. Component analysis results of the three-stage impurity removal solution and raffinate wastewater As shown in Table 5, after three impurity removal processes, the aluminum, iron, thorium, uranium, fluorine, calcium, magnesium, and sulfate ions in the multi-impurity rare earth feed solution can be reduced to a lower level.

[0047] (5) Mix 50 g of the impurity-removed residue obtained in step (3) with a new multi-impurity rare earth material solution at a solid-liquid ratio of 1:3 and stir to allow the damaged hydrogen, oxygen, and rare earth ions in the impurity-removed residue to undergo cross-flow exchange with non-rare earth ions. The number of exchange times is 3. After the resulting filter residue is washed with water at a solid-liquid ratio of 1:3 3 times, the rare earth content in the washing residue is less than 0.5%, and the rare earth element recovery rate in the impurity-removed residue is 98.4%.

[0048] Comparative Example 1 A method for removing impurities from a rare earth liquid sample includes the following steps: (1) The composition analysis results of a rare earth feed solution with many impurities are shown in Table 2; 100 mL of this rare earth feed solution with many impurities was measured and first analyzed according to SO4 2- Add 1.0 times the molar amount of BaCl2·2H2O to remove impurities and obtain a first-stage impurity-removed solution; Add hydrochloric acid to the primary impurity removal solution obtained in step (1) to adjust the pH value to 2.25, then add sodium hydroxide, an alkaline impurity removal agent, to adjust the pH value of the rare earth material solution to 4.30, and filter to obtain secondary impurity removal solution and impurity removal residue; To determine the impurity removal effect, the obtained secondary impurity removal solution was sent for testing. The analysis results are shown in Table 6, where " / " indicates no detection.

[0049] Table 6. Component analysis results of the three-stage impurity removal solution and raffinate wastewater As shown in Table 6, adding conventional alkaline reagent sodium hydroxide to adjust to the same pH value as in this embodiment significantly reduces the removal efficiency of aluminum, iron, thorium, uranium, and fluorine compared to this invention. Furthermore, the rare earth concentration in the secondary impurity removal solution after impurity removal in this invention is lower.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for removing impurities from a rare earth liquid, characterized in that, Includes the following steps: (1) Remove oil from rare earth extraction wastewater and then add alkaline precipitant to precipitate and obtain impurity removal agent; (2) Add barium salt to the rare earth solution to obtain a primary impurity removal solution; (3) Add the impurity removal agent obtained in step (1) to the primary impurity removal solution obtained in step (2) to obtain the secondary impurity removal solution and the impurity removal residue; (4) The secondary impurity removal solution obtained in step (3) is extracted with an extractant to obtain a tertiary impurity removal solution and raffinate wastewater. The raffinate wastewater is recycled for the preparation of impurity removal agent in step (1).

2. The method for removing impurities from rare earth slurry according to claim 1, characterized in that, In step (1), the oil content in the residual wastewater after oil removal does not exceed 1 mg / L.

3. The method for removing impurities from rare earth slurry according to claim 1, characterized in that, In step (1), the alkaline precipitant includes at least one of calcium oxide, magnesium oxide, calcium hydroxide, and magnesium hydroxide.

4. The method for removing impurities from rare earth slurry according to claim 1, characterized in that, In step (1), the endpoint of precipitation by the alkaline precipitant is a pH value of 10-13 in the solution; and / or, in step (2), the barium salt includes barium chloride.

5. The method for removing impurities from rare earth slurry according to claim 1, characterized in that, In step (2), the amount of barium salt added is 0.8-1.2 times the molar amount of sulfate in the rare earth solution.

6. The method for removing impurities from rare earth slurry according to claim 1, characterized in that, In step (3), the pH value of the primary impurity removal solution obtained in step (2) is first adjusted to 1.5-3.0, and then the impurity removal agent obtained in step (1) is added until the pH value of the solution is 4.0-5.0, so as to obtain the secondary impurity removal solution and the impurity removal residue.

7. The method for removing impurities from rare earth slurry according to claim 1, characterized in that, In step (4), the extractant includes an organophosphorus extractant, which includes 2-ethylhexyl phosphate mono-2-ethylhexyl ester.

8. The method for removing impurities from rare earth slurry according to claim 1, characterized in that, In step (4), the extractant is a saponified extractant, and the molar charge of the saponified extractant is 0.95-1.2 times the molar charge of rare earth elements in the secondary impurity removal solution; the saponification agent used in the saponification is at least one of calcium oxide, magnesium oxide, calcium hydroxide, magnesium hydroxide, calcium carbonate, or magnesium bicarbonate.

9. The method for removing impurities from rare earth slurry according to claim 1, characterized in that, In step (4), an extractant is used to extract the secondary impurity removal liquid obtained in step (3) to obtain an organic phase and raffinate wastewater. Hydrochloric acid is used to back-extract the organic phase to obtain a tertiary impurity removal liquid. And / or, the method for removing impurities from the rare earth feed liquid further includes step (5): cross-flow exchange of the impurity removal residue obtained in step (3) with a new rare earth feed liquid, followed by water washing, to achieve the recovery of rare earth elements from the impurity removal residue.

10. The method for removing impurities from rare earth slurry according to claim 9, characterized in that, The solid-liquid ratio of the impurity residue to the new rare earth feed solution in the cross-flow exchange process is 1:1-4; and / or, the number of cross-flow exchanges is 1-4 times; and / or, the solid-liquid ratio of the water washing is 1:(1-4); and / or, the number of water washings is 1-4 times.

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