Method for linking rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste for resourceization

Abstract

This invention proposes a method for the integrated resource recovery of rare earth oxalic acid precipitation wastewater and impurity removal slag solid waste. The oxalic acid precipitation wastewater is the precipitate wastewater obtained after adding oxalic acid to ion-type rare earth leaching solutions or purified rare earth solutions to precipitate rare earths, followed by filtration. The impurity removal slag solid waste is a precipitate containing aluminum, small amounts of rare earths, and clay, obtained after pretreatment of the rare earth leaching solution with a purification agent. The method involves adding the impurity removal slag in batches to the oxalic acid precipitation wastewater and stirring until the pH reaches approximately 5.5, causing the rare earths in the slag to dissolve, while the oxalic acid in the solution enters the slag. The rare earths in the filtered clear liquid are recovered using carbonate precipitation, and the oxalic acid in the solution is thoroughly removed. After adjusting the concentration and pH, the solution is used for cyclic leaching of ion-type rare earths. This invention uses the impurity removal slag generated during the metallurgical process to replace external reagents in treating oxalic acid precipitation wastewater, achieving efficient oxalic acid removal while recovering rare earths from the slag, effectively solving the efficiency and cost problems associated with separate treatment of oxalic acid wastewater and impurity removal slag.

Description

Technical Field

[0001] This invention relates to the field of rare earth hydrometallurgy and comprehensive resource utilization technology, and in particular to a method for the integrated resource utilization of rare earth oxalic acid precipitation wastewater and impurity removal slag solid waste. Background Technology

[0002] In traditional processes for developing ion-adsorption rare earth resources, ammonium sulfate is commonly used as a leaching agent to obtain rare earth solution through in-situ leaching, followed by the recovery of rare earth products using oxalic acid or ammonium bicarbonate precipitation. This process is mature and easy to operate, and has long been widely used in the industrial development of ion-adsorption rare earth resources. Although in recent years, my country has vigorously promoted green and efficient new ammonium-free leaching agents and clean production processes in the development of ion-adsorption rare earth resources, greatly reducing or even prohibiting the use of ammonium sulfate and oxalic acid, in some areas rich in medium and heavy rare earth resources, due to limitations in technology and production models, they can only rely on ammonium sulfate, oxalic acid, and ammonium bicarbonate as raw materials to extract ion-adsorption rare earths and achieve the recycling of impurity residues and oxalic acid precipitation wastewater.

[0003] In the process of rare earth precipitation and recovery, excessive oxalic acid is often added in industrial production to ensure the precipitation rate and product quality. This results in a certain concentration of oxalic acid and valuable metals remaining in the mother liquor after precipitation. If discharged directly without effective treatment, it will not only cause water pollution and increase treatment costs, but also lead to the waste of valuable metal resources. At the same time, a certain amount of rare earth also remains in the pretreatment residue generated during the removal of impurities from the rare earth leaching solution, indicating room for further optimization in its resource utilization.

[0004] The book "Ion Adsorption-Type Rare Earth Resources and Green Extraction" introduces the earliest industrially applied method for treating oxalic acid precipitation wastewater and using it for cyclic leaching. Its characteristic is that, based on the content of oxalate and calcium ions in the oxalic acid precipitation wastewater, a method of neutralization with lime and ammonium bicarbonate (ammonia water) is used to cause oxalate and calcium to precipitate and be removed. Under the condition that the calcium ions are not excessive and the oxalate removal rate is sufficient, the leaching agent concentration and pH can be adjusted and the wastewater can be recycled for leaching with very good results.

[0005] Chinese invention patent CN119707070B discloses a method for recycling rare earth oxalic acid precipitation wastewater, comprising the following steps: Under the influence of an external field, oxalic acid precipitation wastewater is mixed with alkaline calcium salts, and rare earth chloride solution is mixed with calcium oxalate precipitate. The former undergoes a neutralization reaction to generate calcium oxalate precipitate and calcium salt solution, while the latter undergoes an ion exchange reaction to obtain rare earth oxalate precipitate and calcium chloride solution. Finally, rare earth sulfate solution is subjected to a precipitation reaction with the aforementioned calcium salt solution and calcium chloride solution to obtain calcium sulfate precipitate and rare earth chloride solution. This method achieves oxalic acid conversion by introducing external calcium salts and displacement agents, and involves multiple process steps and relies on external reagents.

[0006] Chinese invention patent CN103408091B discloses a method for recycling rare earth oxalic acid precipitation wastewater, including the following steps: preparing a mixed solution of rare earth oxalic acid precipitation wastewater and hydrochloric acid, controlling the oxalate concentration in the solution to be 0.01–10 g / L, and H₂O. + The concentration was 3.5–6 mol / L; the resulting mixed solution was used for back-extraction of rare earths from the rare earth-loaded extraction solution. This method, which mixes oxalic acid wastewater with hydrochloric acid for back-extraction, is limited to specific extraction and separation systems and has a limited scope of application.

[0007] Chinese invention patent CN112645413B discloses a method for recycling rare earth oxalic acid precipitation wastewater, comprising the following steps: using a titanium-based ruthenium-coated and ruthenium metal plate or mesh as the anode and a titanium metal plate or mesh as the cathode, with an anion exchange membrane separating the anode and cathode chambers to form an electrolysis device. Electrolysis is performed using the precipitation mother liquor wastewater as the anolyte and the precipitation washing wastewater as the cathode liquid. An oxidation reaction occurs in the anode chamber to oxidize and decompose oxalate ions, simultaneously recovering hydrochloric acid and rare earth elements from the wastewater. Trace amounts of oxalate ions and chloride ions from the precipitation washing wastewater in the cathode chamber migrate to the anode chamber through the anion exchange membrane, achieving the recycling of both types of wastewater. This method uses electrolytic oxidation to decompose oxalate ions, resulting in good treatment efficiency, but the equipment cost is high and energy consumption is large, making it difficult to promote in areas with limited technological conditions.

[0008] Chinese invention patent CN104711424B discloses a method for recovering rare earth impurities from ion-type slag, comprising the following steps: adding an acidic solution to the slag, stirring at 10-70 °C for 4-8 hours, and filtering to obtain a filtrate containing rare earths and aluminum. Adding an alkaline solution to the filtrate to adjust the pH to 5.0-5.5, causing aluminum hydroxide to precipitate, and filtering to separate the aluminum hydroxide precipitate and the rare earth-containing filtrate. Washing the aluminum hydroxide precipitate with water, filtering, and then calcining at high temperature to obtain alumina. Finally, adding an alkaline solution to the rare earth-containing filtrate to adjust the pH to 6.5-8.0, aging for 6-24 hours, filtering, washing, filtering, and drying to obtain the rare earth product. This method separates and recovers rare earths and aluminum from the slag by stepwise pH control, and the process concept is clear, but it requires the separate introduction of acid and alkali reagents, and there is room for further optimization of the resource utilization method.

[0009] Chinese invention patent CN114250367A discloses a method for resource recovery from ion-type rare earth impurity residue, comprising the following steps: Leaching the impurity residue with concentrated sulfuric acid; performing uranium extraction on the leachate to obtain a uranium-loaded organic phase and a raffinate containing rare earth elements, aluminum, and thorium; performing thorium extraction on the raffinate to obtain a thorium-loaded organic phase and a raffinate containing rare earth elements and aluminum; back-extracting the uranium-loaded and thorium-loaded organic phases to obtain a uranium-enriched solution and a thorium-enriched solution, respectively; subjecting the raffinate containing rare earth elements and aluminum to an ammonium-aluminum reaction, cooling and crystallizing, and filtering to obtain ammonium aluminum sulfate and a rare earth-containing mother liquor, which are then washed to obtain the ammonium aluminum sulfate product. This method comprehensively extracts and recovers multiple valuable elements from the impurity residue, achieving a high degree of resource utilization. However, it requires the introduction of a strong acid solution, and the process is complex and demands high-level equipment conditions, making it difficult to promote and apply under ordinary production conditions.

[0010] It is evident that the aforementioned methods generally suffer from common problems, including separate treatment of oxalic acid wastewater and impurity removal residue, low process coupling, and insufficient resource utilization efficiency. Therefore, addressing the still prominent issues of oxalic acid precipitation wastewater and impurity removal residue, and finding efficient ways to remove oxalic acid from wastewater and improve the recovery efficiency of rare earth and valuable metal resources, is of significant research importance and is key to achieving comprehensive and efficient utilization of rare earth metallurgical resources. Summary of the Invention

[0011] In view of the above situation, the main objective of this invention is to propose a method for the integrated resource utilization of rare earth oxalic acid precipitation wastewater and impurity residue solid waste, so as to solve the above-mentioned technical problems.

[0012] This invention proposes a method for the integrated resource recovery of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste, the method comprising the following steps: Step 1: Add a descaling agent to the ion adsorption type rare earth leachate to cause aluminum, suspended clay and rare earth to precipitate and aggregate, and filter to obtain rare earth pretreatment descaling residue. Step 2: Add oxalic acid to the ion adsorption type rare earth leachate or the rare earth solution after impurity removal to precipitate rare earth, and filter to separate the oxalic acid precipitate wastewater. Step 3: Add the rare earth pretreatment residue to the oxalic acid precipitation wastewater in batches under stirring to react, so that the pH gradually increases to 5.0-5.5, so that oxalic acid and aluminum ions enter the precipitate at the same time and rare earth ions dissolve. Step 4: After the reaction is complete, filter and separate to obtain a rare earth supernatant with low oxalic acid content and a residue containing oxalic acid after impurity removal. Step 5: Add carbonate to the rare earth supernatant with low oxalic acid content to precipitate rare earth, stir, filter, and obtain rare earth carbonate precipitate and precipitate supernatant. Step 6: Rare earth carbonate precipitation is used to recover and prepare rare earth oxide products. After adjusting the concentration of leaching agent and pH of the precipitate supernatant to between 3 and 5, it is used for cyclic leaching of ion-adsorption type rare earth ore.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In existing technologies, the treatment of oxalic acid precipitation wastewater (e.g., lime neutralization, extraction, electrolytic oxidation, etc.) and the resource utilization of the slag (e.g., acid leaching, stepwise precipitation, etc.) are two independent processes, requiring the separate addition of external acid and alkali reagents. This results in low process coupling and high equipment investment and operating costs. This invention creatively combines these two processes, utilizing the slag generated during the rare earth metallurgy process itself to replace external alkaline reagents, directly treating oxalic acid precipitation wastewater. The residual alkaline component (HCO3) in the slag... - OH - The process neutralizes the acidity of the wastewater, and some of the rare earth elements contained within the wastewater are dissolved, released, and recovered during the treatment. Simultaneously, in the circulating leaching stage, the acidity of the oxalic acid precipitation wastewater itself is used to adjust the pH of the supernatant, eliminating the need for external commercial acid. The entire process achieves an internal resource recovery loop of "treating waste with waste," significantly reducing the consumption of external reagents and the wastewater treatment load.

[0014] 2. Existing technologies for treating oxalic acid wastewater or removing impurities often suffer from pH control issues that lead to co-precipitation of rare earth elements and aluminum, resulting in rare earth loss or poor separation. This invention addresses this by adding impurity removal residue in batches, slowly adjusting the system pH to around 5.5. Below pH 5.0, valuable metal ions such as rare earth and aluminum encapsulated in the residue gradually dissolve and enter the liquid phase. At pH 5.0-5.5, aluminum ions hydrolyze and co-precipitate with oxalate, achieving deep removal of oxalic acid (removal rate exceeding 95%) and effective aluminum removal. Meanwhile, the concentration of rare earth ions increases within this pH range, selectively remaining in the liquid phase, resulting in a purified solution low in oxalic acid and aluminum, and rich in rare earth elements. This control strategy cleverly utilizes the differences in hydrolysis and precipitation behavior of aluminum and rare earth elements at different pH ranges, completing the core processes of "dissolution of valuable metal acids" and "co-precipitation separation of impurities" within the same reaction cycle, making the process concise and efficient.

[0015] 3. Existing methods of directly reusing or simply treating oxalic acid wastewater often result in high residual oxalic acid concentrations, leading to the formation of oxalate precipitation in rare earth elements during leaching and reducing leaching efficiency. This invention achieves deep removal of oxalic acid (extremely low residual levels) at a target pH of 5.5. After recovering rare earth elements from the resulting low-oxalic acid rare earth enrichment solution, the resulting alkaline precipitate supernatant is reused as previously prepared. Data from Examples 6 and 7 of the specification confirm that the reused leaching solution treated using this method achieves rare earth leaching efficiencies of 95.59%-99.48% and 98.36%-99.03% in magnesium sulfate and ammonium sulfate systems, respectively, approaching the levels of pure fresh leaching agent (99.89% and 100.83%). In contrast, in the experimental group where oxalic acid precipitate wastewater and impurity removal slag solid waste were reacted to a lower pH (4.0-5.0), the oxalic acid in the treated solution was not deeply removed, resulting in significantly lower rare earth leaching efficiencies when directly used for leaching (93.79% and 87.64%). This indicates that the method of the present invention effectively avoids the inhibitory effect of a large amount of oxalic acid on leaching, and ensures the stable and efficient operation of the recycling process.

[0016] 4. Table 2 of the specification shows that, after treatment by the method of this invention, the oxalic acid-containing residue achieved a reduction rate of 1.97%-4.84% compared to the original pre-treated residue, reducing the amount of solid waste and disposal costs. Simultaneously, the rare earth elements recovered from the wastewater and residue, after precipitation and calcination, yielded rare earth oxide products with a total REO content greater than 92% (Table 1), meeting industry product quality requirements. This invention solves the wastewater treatment problem while simultaneously recovering residual rare earth elements from the residue, improving the overall rare earth recovery rate and demonstrating significant environmental and economic benefits.

[0017] 5. The reagents used in this invention (removal of impurities, oxalic acid wastewater, and conventional precipitants) are all derived from the products of the rare earth metallurgical process itself or from inexpensive and readily available raw materials, and do not rely on electrolysis devices, extraction equipment, or strong acids and bases. Examples 1-4 in the specification respectively verified that two leaching solution systems, magnesium sulfate / ammonium sulfate and two combinations of NaHCO3 / NH4HCO3, achieved good oxalic acid removal and rare earth recovery effects, proving the universality of the method. The process operation only involves conventional unit operations such as room temperature stirring, batch feeding, and filtration separation, with low requirements for equipment materials and automation levels, making it particularly suitable for application scenarios where technical conditions in rare earth mining areas are limited.

[0018] 6. In summary, this invention uses pre-treated impurity removal slag generated within the rare earth metallurgical process to treat oxalic acid precipitation wastewater, eliminating the need for external precipitants, displacement agents, or electrolysis equipment. The reagents originate from within the production process, fundamentally reducing treatment costs. By adjusting the amount of impurity removal slag added, the pH of the system is controlled, enabling the coordinated treatment of oxalic acid wastewater and the slag. This efficiently removes oxalic acid while recovering rare earth elements from the slag, achieving coupled resource utilization of both types of waste. The resulting treated liquid is then reused for cyclic leaching, constructing a closed-loop process system, reducing wastewater discharge. Furthermore, the process is simple to operate, has low equipment requirements, and is suitable for ion adsorption-based rare earth mining scenarios in areas with limited technological capabilities.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by means of embodiments of the invention. Attached Figure Description

[0020] Figure 1 Figure showing the changes in the concentration of relevant ions in the magnesium sulfate system for adjusting the pH of grass-laden wastewater by adding NaHCO3 residue for impurity removal. Figure 2 Figure showing the changes in the concentration of relevant ions in the pH control system of grass sedimentation wastewater after impurity removal by adding NaHCO3 impurity removal residue to the magnesium sulfate system; Figure 3 Figure showing the changes in the concentration of relevant ions in the pH control system of ammonium sulfate system for grass sedimentation wastewater under the condition of adding NaHCO3 residue for impurity removal; Figure 4 Figure showing the changes in the concentration of relevant ions in the pH control system of grass sedimentation wastewater after impurity removal in the ammonium sulfate system by adding NH4HCO3 impurity removal residue; Figure 5 Relevant data charts for adding a small amount of NaHCO3 to the magnesium sulfate system to remove impurities and using the supernatant for circulating leaching; Figure 6 Data chart showing the use of supernatant precipitate for cyclic leaching after adding a large amount of NaHCO3 to a magnesium sulfate system to remove impurities; Figure 7 Data chart showing the relevant data of the supernatant precipitated from magnesium sulfate after adding a large amount of NaHCO3 to remove impurities, which is then used for circulating leaching. Figure 8 Relevant data charts for adding a small amount of NaHCO3 to the ammonium sulfate system to remove impurities and using the supernatant for circulating leaching; Figure 9 Relevant data graphs show that after adding a large amount of NaHCO3 to the ammonium sulfate system to remove impurities, the supernatant is used for circulating leaching. Figure 10 Relevant data graphs show that after adding a large amount of NH4HCO3 to the ammonium sulfate system to remove impurities, the supernatant after precipitation is used for circulating leaching. Figure 11 This is a flowchart of the method for the integrated resource utilization of rare earth oxalic acid precipitation wastewater and solid waste from impurity removal, as proposed in this invention. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0022] These and other aspects of the embodiments of the present invention will become clear from the following description and accompanying drawings. In these descriptions and drawings, some specific embodiments of the present invention are specifically disclosed to illustrate some ways of implementing the principles of the embodiments of the present invention; however, it should be understood that the scope of the embodiments of the present invention is not limited thereto.

[0023] Example 1 This embodiment provides a method for the integrated resource recovery of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste, the method comprising the following steps: Take 1000 mL of rare earth ion concentration 0.17 g / L, Mg 2+ The concentration was 1.28 g / L, Al 3+ The concentration is 0.03 g / L, F - A 4 mg / L concentration of actual rare earth leaching solution from a mine was placed in a beaker. 500 mL of the leaching solution was directly added to the beaker with an 80 g / L oxalic acid aqueous solution at a mass ratio of oxalic acid to rare earth oxides of 2:1. The solution was filtered to obtain oxalic acid precipitate wastewater A from the magnesium sulfate leaching solution, with a pH of 2.393. Another 500 mL of the leaching solution was pretreated with a 2% NaHCO3 solution to remove impurities, resulting in the removal of residue and supernatant. An 80 g / L oxalic acid aqueous solution was added to the supernatant at a mass ratio of oxalic acid to rare earth oxides of 2:1. The solution was filtered to obtain oxalic acid precipitate wastewater B from the magnesium sulfate leaching solution, with a pH of 2.528.

[0024] Sodium bicarbonate was added to the ion-adsorption type rare earth magnesium sulfate leaching solution from a mine in Fujian Province to remove impurities, causing aluminum, suspended clay, and a small amount of rare earth to precipitate and aggregate. The residue was obtained by filtration after pretreatment with rare earth NaHCO3.

[0025] Take 500 mL of oxalic acid precipitation wastewater A from the magnesium sulfate system into a beaker. Add NaHCO3 pretreatment residue from a magnesium sulfate leaching solution of a mine in Fujian Province to the wastewater for impurity removal. Use a batch addition method: when the pH is below 5.0, each batch adds 2% of the total residue; after the pH reaches 5.0, each batch adds 5% of the total residue. Add the next batch only after the pH has stabilized, allowing the pH of the system to rise slowly. Before the pH gradually rises from the initial value to 5.0, the stirring rate is controlled at 450 r / min; during the target stage of pH rising from 5.0 to 5.4, due to the increased residue volume and solid-liquid ratio, the stirring rate is increased to 600 r / min. During the above process, continuously stir and collect small amounts of supernatant at different pH values. Determine the oxalate ion concentration using potassium permanganate titration and calculate the oxalic acid removal rate. Figure 1 As shown in (a), the fluoride ion concentration was measured using a fluoride ion electrode. Figure 1 As shown in (b), the concentration changes of rare earth ions, aluminum ions, magnesium ions, and uranium ions in the supernatant were determined by ICP-MS as follows: Figure 1 As shown in (cf).

[0026] Depend on Figure 1 As shown in (af), as the pH of the system gradually increased from the initial value to approximately 4.5, the concentrations of aluminum and fluoride ions in the supernatant increased rapidly, while the concentrations of uranium and magnesium ions also showed a certain upward trend, and the concentration of rare earth ions increased relatively slowly. At pH 4.5, the oxalic acid removal rate was only 13.51%. After the pH further increased to above 4.5, the concentrations of each component in the system changed significantly: the concentrations of aluminum, fluoride, and oxalate ions began to decrease rapidly, while the concentration of rare earth ions increased significantly; simultaneously, the concentration of uranium ions gradually decreased after pH approximately 4.8, while the concentration of magnesium ions showed an overall continuous upward trend. With further increases in pH, the oxalic acid removal rate increased to 90.27% at pH 5.1, and reached 98.52% at pH 5.4. At this point, the concentration of rare earth ions in the supernatant was 0.23 g / L, while the concentration of aluminum ions decreased to 0.00135 g / L.

[0027] The above results indicate that pH ≈ 4.5 is the inflection point for changes in the concentrations of various ions in the reaction system and a key dividing point for subsequent comparative experiments. When the pH of the reaction system is below 5.0, the contents of aluminum, fluorine, and uranium in the solution are still relatively high, and the removal rate of oxalic acid is low at this time. However, at the target stage, when the pH of the system is adjusted to around 5.5, deep removal of oxalic acid and effective removal of impurity metals such as aluminum can be achieved, while rare earth ions are still largely retained in the supernatant, providing favorable conditions for the subsequent addition of a precipitant to recover rare earths.

[0028] Example 2 This embodiment provides a method for the integrated resource recovery of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste, the method comprising the following steps: Take 500 mL of oxalic acid precipitation wastewater B from the magnesium sulfate leaching solution prepared in Example 1 into a beaker. Add NaHCO3 pretreatment residue ① from a magnesium sulfate leaching solution of a mine in Fujian Province to the wastewater. Use a batch addition method: when the pH is below 5.0, the amount added per batch is 1% of the total residue; after the pH reaches 5.0, the amount added per batch is 7% of the total residue. Add the next batch only after the pH has stabilized, allowing the pH of the system to rise slowly. Before the pH gradually rises from the initial value to 5.0, the stirring rate is controlled at 350 r / min; during the target stage of pH rising from 5.0 to 5.5, the stirring rate is increased to 550 r / min. During the above process, continuously stir and collect small amounts of supernatant at different pH values. Determine the oxalate ion concentration using potassium permanganate titration and calculate the oxalic acid removal rate as follows: Figure 2 As shown in (a), the fluoride ion concentration was measured using a fluoride ion electrode. Figure 2 As shown in (b), the concentration changes of rare earth ions, aluminum ions, magnesium ions, and uranium ions in the supernatant were determined by ICP-MS as follows: Figure 2 As shown in (cf).

[0029] Depend on Figure 2 As shown in (af), as the pH of the system gradually increased from the initial value to approximately 4.5, the concentrations of aluminum and fluoride ions in the supernatant increased rapidly, while the concentration of rare earth ions increased more slowly. At pH 4.5, the oxalic acid removal rate was only 5.77%. After the pH further increased to above 4.5, the concentrations of aluminum and oxalate ions began to decrease rapidly, while the concentration of rare earth ions increased significantly. In addition, throughout the process, the concentrations of fluoride and uranium ions showed a trend of first increasing and then decreasing significantly at the target stage, while the concentration of magnesium ions consistently increased. Therefore, valuable metals can be recovered to some extent. With further increases in pH, the oxalic acid removal rate increased to 88.46% at pH 5.2, and reached 95.64% at pH 5.5. At this point, the concentration of rare earth ions in the supernatant was 0.12 g / L, while the concentration of aluminum ions was measured to be 0.0076 g / L, indicating almost complete precipitation.

[0030] The above results indicate that pH ≈ 4.5 is the inflection point for changes in the concentrations of various ions in the reaction system and a key dividing point for subsequent comparative experiments. When the pH of the reaction system is below 5.0, the contents of aluminum, fluorine, and uranium in the solution are still relatively high, and the removal rate of oxalic acid is low at this time. However, at the target stage, when the pH of the system is adjusted to around 5.5, deep removal of oxalic acid and effective removal of impurity metals such as aluminum can be achieved, while rare earth ions are still largely retained in the supernatant, providing favorable conditions for the subsequent addition of a precipitant to recover rare earths.

[0031] Example 3 This embodiment provides a method for the integrated resource recovery of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste, the method comprising the following steps: Take 2000 mL of NH4+ with a rare earth ion concentration of 0.30 g / L. + The concentration was 3.42 g / L, Al 3+ The concentration is 0.17 g / L, F - A rare earth leaching solution with a concentration of 5 mg / L was placed in a beaker. 1000 mL of the leaching solution was directly added to the beaker with an oxalic acid aqueous solution at a mass ratio of 2.3:1 (oxalic acid to rare earth oxides). The mixture was filtered to obtain oxalic acid precipitate wastewater C from the ammonium sulfate leaching solution. The pH of the solution at this point was 2.238. Another 1000 mL of the leaching solution was pretreated with a 2% NH4HCO3 solution to remove impurities. The removed residue and supernatant were then separated. An oxalic acid aqueous solution of 80 g / L was added to the supernatant at a mass ratio of 2.3:1 (oxalic acid to rare earth oxides). The mixture was filtered to obtain oxalic acid precipitate wastewater D from the ammonium sulfate leaching solution. The pH of the solution at this point was 2.458.

[0032] Ammonium bicarbonate was added to the ion-adsorption type rare earth simulated ammonium sulfate leaching solution to cause aluminum, suspended clay and a small amount of rare earth to precipitate and aggregate. The residue was obtained by filtration after rare earth NH4HCO3 pretreatment and impurity removal ①.

[0033] 1000 mL of oxalic acid precipitation wastewater C from ammonium sulfate leaching solution was placed in a beaker. NaHCO3 pretreatment residue from magnesium sulfate leaching solution of a mine in Fujian Province was added to this wastewater for impurity removal. A batch addition method was used: when the pH was below 5.0, each batch added 2% of the total residue; after the pH reached 5.0, each batch added 5% of the total residue. Each batch was added only after the pH stabilized, allowing the pH of the system to rise slowly. Before the pH gradually increased to 5.0, the stirring rate was controlled at 500 r / min; during the target stage of increasing the pH from 5.0 to 5.4, the stirring rate was increased to 700 r / min. Throughout the process, continuous stirring was maintained, and small amounts of supernatant were collected at different pH values. The oxalate ion concentration was determined using potassium permanganate titration, and the oxalic acid removal rate was calculated. Figure 3 As shown in (a), the fluoride ion concentration was measured using a fluoride ion electrode. Figure 3 As shown in (b), the concentration changes of rare earth ions, aluminum ions, magnesium ions, and uranium ions in the supernatant were determined by ICP-MS as follows: Figure 3 As shown in (cf).

[0034] Depend on Figure 3As shown in (af), as the pH of the system gradually increases from its initial value to approximately 4.5, the concentrations of aluminum and fluoride ions in the supernatant increase rapidly, while the concentrations of uranium and magnesium ions also show a certain degree of upward trend, and the concentration of rare earth ions increases relatively slowly. At pH 4.5, the oxalic acid removal rate is only 11.63%. After the pH is further increased to above 4.5, the concentrations of each component in the system change significantly: the concentrations of aluminum, fluoride, and oxalate ions begin to decrease rapidly, while the concentration of rare earth ions increases significantly.

[0035] Meanwhile, the uranium ion concentration decreased rapidly after reaching approximately pH 4.9, while the magnesium ion concentration showed a continuous upward trend. With further increases in pH, the oxalic acid removal rate increased to 90.00% at pH 5.1, and reached 97.21% at pH 5.4. At this point, the rare earth ion concentration in the supernatant was 0.41 g / L, while the aluminum ion concentration decreased to 0.00399 g / L.

[0036] The above results indicate that pH ≈ 4.5 is the inflection point for changes in the concentrations of various ions in the reaction system and a key dividing point for subsequent comparative experiments. When the pH of the reaction system is below 5.0, the contents of aluminum, fluorine, and uranium in the solution are still relatively high, and the removal rate of oxalic acid is low at this time. However, at the target stage, when the pH of the system is adjusted to around 5.5, deep removal of oxalic acid and effective removal of impurity metals such as aluminum can be achieved, while rare earth ions are still largely retained in the supernatant, providing favorable conditions for the subsequent addition of a precipitant to recover rare earths.

[0037] Example 4 This embodiment provides a method for the integrated resource recovery of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste, the method comprising the following steps: Take 1000 mL of the oxalic acid precipitation wastewater D from the ammonium sulfate leachate prepared in Example 3 into a beaker. Add NH4HCO3 pretreatment residue ① of the ammonium sulfate leachate to the wastewater for impurity removal. Use a batch addition method: when the pH is below 5.0, the amount added in each batch is 1% of the total residue; after the pH reaches 5.0, the amount added in each batch is 7% of the total residue. Add the next batch only after the pH has stabilized, allowing the pH of the system to rise slowly. Before the pH gradually rises from the initial value to 5.0, the stirring rate is controlled at 400 r / min; during the target stage of pH rising from 5.0 to 5.4, the stirring rate is increased to 650 r / min. During the above process, continuously stir and collect small amounts of supernatant at different pH values. Determine the oxalate ion concentration using potassium permanganate titration and calculate the oxalic acid removal rate as shown below. Figure 4 As shown in (a), the fluoride ion concentration was measured using a fluoride ion electrode. Figure 4 As shown in (b), the concentration changes of rare earth ions, aluminum ions, magnesium ions, and uranium ions in the supernatant were determined by ICP-MS as follows: Figure 4As shown in (cf).

[0038] Depend on Figure 4 As shown in (af), as the pH of the system gradually increases from the initial value to about 4.0, the concentrations of aluminum ions and fluoride ions in the supernatant increase rapidly, while the concentration of rare earth ions increases more slowly. When the pH is 4.5, the oxalic acid removal rate is only 34.03%. After the pH is further increased to above 4.5, the concentrations of aluminum ions, fluoride ions, and oxalate ions begin to decrease rapidly, while the concentration of rare earth ions increases significantly.

[0039] Furthermore, throughout the process, the uranium ion concentration initially increased, then gradually decreased, and finally stabilized, while the magnesium ion concentration showed a slight but continuous upward trend. With further increases in pH, the oxalic acid removal rate reached 96.53% at pH 5.0, and 98.19% at pH 5.4. At this point, the rare earth ion concentration in the supernatant was 1.20 g / L, while the aluminum ion concentration was measured at 0.00258 g / L, indicating almost complete precipitation.

[0040] The above results indicate that pH ≈ 4.5 is the inflection point for changes in the concentrations of various ions in the reaction system and a key dividing point for subsequent comparative experiments. When the pH of the reaction system is below 5.0, the contents of aluminum, fluorine, and uranium in the solution are still relatively high, and the removal rate of oxalic acid is low at this time. However, at the target stage, when the pH of the system is adjusted to around 5.5, deep removal of oxalic acid and effective removal of impurity metals such as aluminum can be achieved, while rare earth ions are still largely retained in the supernatant, providing favorable conditions for the subsequent addition of a precipitant to recover rare earths.

[0041] Example 5 like Figure 11 As shown in the figure, this embodiment provides a method for the integrated resource utilization of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste. The method includes rare earth product preparation and impurity removal residue reduction analysis. The specific steps are as follows: Take 1000 mL of oxalic acid precipitation wastewater A from the magnesium sulfate leaching solution prepared in Example 1 into a beaker, and add NaHCO3 pretreatment residue ① from a magnesium sulfate leaching solution of a mine in Fujian to the wastewater for impurity removal. The addition is done in batches. When the pH is below 5.0, the amount added in each batch is 2% of the total residue. When the pH reaches 5.0, the amount added in each batch is 5% of the total residue. Each batch is added after the pH stabilizes, so that the pH of the system rises slowly. When the pH is below 5.0, the stirring rate is controlled at 500 r / min. After the pH reaches 5.0, the stirring rate is increased to 700 r / min, and the pH of the reaction system is adjusted to 5.4. After the pH reaches 5.4, the stirring reaction is continued for 45 min. The mixture is filtered to separate the rare earth supernatant with low oxalic acid and the oxalic acid-containing residue ②. 6% NaHCO3 solution is slowly added to the rare earth supernatant at a stirring rate of 500 r / min to precipitate the rare earth. The pH of the precipitate is controlled at 7.2. After filtration and washing, the precipitate supernatant and rare earth carbonate precipitate are obtained. The dried rare earth carbonate is calcined in a muffle furnace at 950 ℃ for 60 min (Note: the drying temperature in this part is a well-known temperature in the industry, with a temperature range of 800-1000 ℃. To maintain the consistency of the experimental results, the subsequent temperature is 950 ℃). After cooling, rare earth oxide product 1 is obtained. 3 mol / L The sulfate ion concentration was determined by the barium chromate colorimetric method and the concentrations of rare earth ions, aluminum ions, magnesium ions, and calcium ions were determined by ICP-MS. The calculated results are shown in Table 1 for Product 1. Additionally, 0.5 g of the oxalic acid-containing impurity-removing residue ② was dissolved under heating conditions of HNO3 and H2O2, and the volume was adjusted to 50 mL. The fluoride ion concentration was determined by the fluoride ion electrode, and the concentrations of rare earth ions and aluminum ions were determined by ICP-MS. The calculated results are shown in Table 2 for Sample 2.

[0042] Take 1000 mL of oxalic acid precipitation wastewater B from the magnesium sulfate leaching solution prepared in Example 1 into a beaker, and add NaHCO3 pretreatment residue ① from a magnesium sulfate leaching solution from a mine in Fujian to the wastewater. The addition is done in batches. When the pH is below 5.0, the amount added in each batch is 1% of the total residue. When the pH reaches 5.0, the amount added in each batch is 5% of the total residue. Each batch is added after the pH stabilizes, so that the pH of the system rises slowly. When the pH is below 5.0, the stirring rate is controlled at 400 r / min. After the pH reaches 5.0, the stirring rate is increased to 600 r / min, and the pH of the reaction system is adjusted to 5.5. After the pH reaches 5.5, the stirring reaction is continued for 45 min. The mixture is filtered to separate the rare earth supernatant with low oxalic acid and the oxalic acid-containing residue ②. 6% NaHCO3 precipitant solution is slowly added to the rare earth supernatant at a stirring rate of 500 r / min to precipitate the rare earth. The pH of the precipitate is controlled at 7.0. After filtration and washing, the precipitate supernatant and rare earth carbonate precipitate are obtained. The dried rare earth carbonate is calcined in a muffle furnace at 950 ℃ for 60 min. After cooling, rare earth oxide product 2 is obtained. It is dissolved and diluted to 50 mL with 3 mol / L HCl. The concentration of sulfate ions is determined by barium chromate colorimetry, and the concentrations of rare earth ions, aluminum ions, magnesium ions, and calcium ions are determined by ICP-MS. The results are shown in Table 1 for product 2. In addition, 0.5 g of the oxalic acid-containing impurity-removing residue ② was dissolved under heating conditions of HNO3 and H2O2, and the volume was adjusted to 50 mL. The concentration of fluoride ions was measured using a fluoride ion electrode, and the concentrations of rare earth ions and aluminum ions were measured by ICP-MS. The calculated results are shown in sample 3 in Table 2.

[0043] Take 1000 mL of the oxalic acid precipitation wastewater C from the ammonium sulfate leaching solution prepared in Example 3 into a beaker. Add NaHCO3 pretreatment residue ① from a magnesium sulfate leaching solution of a mine in Fujian to the wastewater. Add in batches, with each batch adding 2% of the total residue when the pH is below 5.0, and 7% of the total residue when the pH reaches 5.0. Add the next batch only after the pH has stabilized, allowing the pH of the system to rise slowly. Adjust the pH of the reaction system to 5.4. After reaching pH 5.4, continue stirring for 45 min. Filter to separate the low-oxalic acid rare earth supernatant and the oxalic acid-containing residue ②. Slowly add 6% NH4HCO3 precipitant solution to the rare earth supernatant at a stirring rate of 500 r / min for precipitation, controlling the precipitation pH to 7.2. Filter and wash to obtain the precipitate supernatant and rare earth carbonate precipitate. Calcinate the dried rare earth carbonate in a muffle furnace at 950 ℃ for 60 minutes. After cooling, rare earth oxide product 3 was obtained. It was dissolved in 3 mol / L HCl and brought to a final volume of 50 mL. The sulfate ion concentration was determined using the barium chromate colorimetric method, and the concentrations of rare earth ions, aluminum ions, magnesium ions, and calcium ions were determined by ICP-MS. The calculated results are shown in Table 1 for product 3. Additionally, 0.5 g of the oxalic acid-containing impurity-removing residue ② was dissolved under heating conditions of HNO3 and H2O2, filtered, and brought to a final volume of 50 mL. The fluoride ion concentration was determined using a fluoride ion electrode, and the concentrations of rare earth ions and aluminum ions were determined by ICP-MS. The calculated results are shown in Table 2 for sample 4.

[0044] Take 1000 mL of the oxalic acid precipitation wastewater D from the ammonium sulfate leaching solution prepared in Example 3 into a beaker, and add ammonium sulfate leaching solution NH4HCO3 pretreatment to remove impurities ①. The addition is done in batches. When the pH is below 5.0, the amount added in each batch is 1% of the total amount of residue. After the pH reaches 5.0, the amount added in each batch is 7% of the total amount of residue. Each batch is added after the pH stabilizes, so that the pH of the system rises slowly. When the pH is below 5.0, the stirring rate is controlled at 500 r / min. After the pH reaches 5.0, the stirring rate is increased to 700 r / min, and the pH of the reaction system is adjusted to 5.4. After the pH reaches 5.4, the stirring reaction is continued for 45 min. The mixture is filtered to separate the rare earth supernatant with low oxalic acid and the oxalic acid-containing impurity residue ②. 6% NH4HCO3 solution is slowly added to the rare earth supernatant at a stirring rate of 500 r / min to precipitate the rare earth. The pH of the precipitate is controlled at 7.0. After filtration and washing, the precipitate supernatant and rare earth carbonate precipitate are obtained. The dried rare earth carbonate is calcined in a muffle furnace at 950 ℃ for 60 min. After cooling, rare earth oxide product 4 is obtained. It is dissolved and diluted to 50 mL with 3 mol / L HCl. The concentration of sulfate ions is determined by the barium chromate colorimetric method, and the concentrations of rare earth ions, aluminum ions, magnesium ions and calcium ions are determined by ICP-MS. The results are shown in Table 1 for product 4. In addition, 0.5 g of the oxalic acid-containing impurity-removing residue ② was dissolved under heating conditions of HNO3 and H2O2, and the volume was adjusted to 50 mL. The fluoride ion concentration was measured using a fluoride ion electrode, and the rare earth ion and aluminum ion concentrations were measured by ICP-MS. The calculated results are shown in sample 6 in Table 2.

[0045] Take 0.5 g of the NaHCO3 pretreated residue ① of magnesium sulfate leaching solution from a mine in Fujian and the NH4HCO3 pretreated residue ① of ammonium sulfate leaching solution. Dissolve them under heating conditions of HNO3 and H2O2, and bring the volume to 50 mL. Use a fluoride ion electrode to determine the fluoride ion concentration, and ICP-MS to determine the rare earth ion and aluminum ion concentrations. The calculated results are shown in Table 2 for samples 1 and 5, respectively.

[0046] Table 1. Elemental Content Analysis of Rare Earth Oxide Products

[0047] Table 2. Elemental content analysis of pretreated impurity-removing slag before and after reaction.

[0048] As shown in Table 1, the total rare earth oxide content of the four rare earth oxide products obtained is all above 92%, indicating that rare earth is recovered while effectively removing oxalic acid, thus verifying the feasibility of this method in oxalic acid removal and rare earth recovery.

[0049] As shown in Table 2, after the NaHCO3 pretreatment residue ① of magnesium sulfate leachate and the NH4HCO3 pretreatment residue ① of ammonium sulfate leachate were combined with rare earth oxalic acid precipitation wastewater, the rare earth content in the resulting oxalic acid-containing residue ② decreased by 6.25%-19.40% compared to before treatment, and the residue mass reduction was 1.97%-4.84%. Meanwhile, the contents of impurities such as aluminum and fluorine increased accordingly. This indicates that rare earth elements were effectively released from the residue and entered the recovery process, and oxalic acid was simultaneously removed, achieving the synergistic goal of reducing the volume of solid waste from the residue and recovering rare earth resources. The resulting oxalic acid-containing residue ② still retains a certain amount of alkaline components. Where resource conditions permit, it can be further utilized as needed to continuously realize its potential value in the recovery of rare earth and oxalic acid.

[0050] Example 6 This embodiment provides a comparative verification experiment of cyclic leaching in a resource recovery method that combines rare earth oxalic acid precipitation wastewater with impurity removal slag solid waste. The specific steps are as follows: Take 500 mL of oxalic acid precipitation wastewater A from the magnesium sulfate leaching solution prepared in Example 1 into a beaker. Add a small amount of NaHCO3 pretreatment residue ① from a magnesium sulfate leaching solution of a mine in Fujian Province to the wastewater. Add the residue in batches, with each batch being 1% of the total residue. Add the next batch only after the pH has stabilized. The stirring rate is controlled at 400 r / min, and the pH of the system is adjusted to 4.5. After the pH reaches 4.5, continue stirring for 45 min. Filter to separate the supernatant containing oxalic acid and the residue with low oxalic acid content. Measure the magnesium ion concentration and oxalic acid concentration in the supernatant. Under a magnesium ion equivalent concentration gradient of 0.12N-0.36N, dilute the supernatant or add magnesium sulfate according to the required concentration at a liquid-to-solid ratio of 0.7:1 for cyclic leaching of ion-adsorption type rare earth ores. The resulting rare earth leaching efficiency is as follows: Figure 5 As shown in (a), the concentrations of aluminum ions, magnesium ions, fluorine content, oxalic acid concentration and loss rate, and pH changes in the leachate are as follows: Figure 5 As shown in (bf).

[0051] Take 250 mL of the supernatant obtained from the reaction system of magnesium sulfate leaching solution and oxalic acid precipitation wastewater A from Example 5 with magnesium sulfate leaching solution pretreated with NaHCO3 to remove impurities ① from a mine in Fujian, and place it in a beaker. Under the condition of room temperature and stirring speed of 500 r / min, add the oxalic acid precipitation wastewater A prepared in Example 1 to adjust the pH of the solution to between 3 and 5 (to ensure the consistency of experimental results, the pH is adjusted to 4.5 in this invention). Then, measure the magnesium ion concentration and oxalic acid concentration in the solution. Under the gradient of magnesium ion equivalent concentration of 0.12N-0.36N, according to the liquid-solid ratio of 0.7:1, dilute the supernatant or add magnesium sulfate according to the required concentration and use it for cyclic leaching of ion adsorption type rare earth ores. The obtained rare earth leaching efficiency is as follows: Figure 6 As shown in (a), the concentrations of aluminum ions, magnesium ions, fluorine content, oxalic acid concentration and loss rate, and pH changes in the leachate are as follows: Figure 6 As shown in (bf).

[0052] Take 250 mL of the supernatant obtained from the reaction system of magnesium sulfate leaching solution oxalic acid precipitation wastewater B from Example 5 and magnesium sulfate leaching solution from a mine in Fujian Province after NaHCO3 pretreatment to remove impurities ①, and place it in a beaker. Under the condition of room temperature and stirring speed of 500 r / min, add the oxalic acid precipitation wastewater B prepared in Example 1 to the beaker to adjust the pH of the solution to between 3 and 5. Measure the magnesium ion concentration and oxalic acid concentration in the solution. Under the gradient of magnesium ion equivalent concentration of 0.12N-0.36N, according to the liquid-solid ratio of 0.7:1, dilute the supernatant or add magnesium sulfate according to the required concentration and use it for cyclic leaching of ion-adsorption type rare earth ores. The obtained rare earth leaching efficiency is as follows: Figure 7 As shown in (a), the concentrations of aluminum ions, magnesium ions, fluorine content, oxalic acid concentration and loss rate, and pH changes in the leachate are as follows: Figure 7 As shown in (bf).

[0053] Depend on Figure 5 (a) Figure 6 (a) Figure 7 (a) The comparison shows that when using only 0.36N magnesium sulfate as the leaching agent, the rare earth leaching efficiency can reach 99.89%. In the comparative experimental group where the supernatant of the reaction system, after dissolving impurities and adjusting the pH to 4.5 using oxalic acid precipitation wastewater, was directly used for circulating ore leaching, the rare earth leaching efficiency decreased to 93.79% when the magnesium sulfate concentration in the leaching agent was 0.36N and the original rare earth content in the leaching agent was deducted. However, when the pH of the reaction system was adjusted to the target stage of around 5.5, with the same magnesium sulfate concentration of 0.36N in the leaching agent and the original rare earth content in the leaching agent deducted, the rare earth leaching efficiency could reach 95.59% and 99.48%, respectively. This shows that the rare earth leaching efficiency is high at the target stage, and valuable metals are effectively recycled.

[0054] Depend on Figure 5(bf), Figure 6 (bf), Figure 7 (bf) indicates that when the supernatant with the pH adjusted to 4.5 is directly used for circulating leaching, the fluoride content in the leachate is also higher due to the high fluoride content in the leaching agent. However, when the supernatant with the pH adjusted to around 5.5 is used for circulating leaching, the fluoride content in the leachate is close to that of pure magnesium sulfate, meaning there are fewer fluoride ion impurities. Furthermore, at this target stage, while effectively removing oxalic acid without affecting the environment, the aluminum ion content and pH in the circulating leaching leachate are close to those of pure magnesium sulfate leaching agent. The magnesium ion concentration is increased due to the dissolution of magnesium from the impurity slag. This suggests that the system using oxalic acid precipitation wastewater to adjust the pH for circulating leaching at this target stage is stable and generally meets the leaching requirements.

[0055] The above results indicate that when the pH of the reaction system is directly adjusted to 4.5, the rare earth leaching efficiency during recycling is low. Therefore, this condition is not recommended as a recycling method. In contrast, at the target stage, when the system pH is adjusted to around 5.5, it is possible to achieve deep removal of oxalic acid, recycling of valuable metals, and reduction of solid waste from impurity removal, while maintaining a high rare earth leaching efficiency during recycling. This has positive implications for the comprehensive utilization of rare earth resources and environmentally friendly development. Therefore, this condition can be considered a preferred method for the coordinated resource-based treatment and recycling of oxalic acid precipitation wastewater and solid waste from impurity removal.

[0056] Example 7 This embodiment provides a comparative verification experiment of cyclic leaching in a resource recovery method that combines rare earth oxalic acid precipitation wastewater with impurity removal slag solid waste. The specific steps are as follows: Take 500 mL of the oxalic acid precipitation wastewater C from the ammonium sulfate leaching solution prepared in Example 3 into a beaker. Add a small amount of NaHCO3 pretreatment residue ① from a magnesium sulfate leaching solution from a mine in Fujian to the wastewater. Add in batches, with each batch being 2% of the total residue. Add the next batch only after the pH has stabilized. The stirring rate is controlled at 450 r / min, and the pH of the system is adjusted to 4.5. After the pH reaches 4.5, continue stirring for 45 min. Filter to separate the supernatant containing oxalic acid and the residue with low oxalic acid. Determine the concentrations of ammonium ions and oxalic acid in the supernatant. The concentration of ammonium ions is determined using Nessler's reagent spectrophotometry. Under a gradient of ammonium ion equivalent concentrations of 0.12N-0.36N, at a liquid-to-solid ratio of 0.7:1, dilute the supernatant according to the required concentration or add ammonium sulfate for cyclic leaching of ion-adsorption type rare earth ores. The resulting rare earth leaching efficiency is as follows: Figure 8 As shown in (a), the concentrations of aluminum ions, magnesium ions, fluorine content, oxalic acid concentration and loss rate, and pH changes in the leachate are as follows: Figure 8 As shown in (bf).

[0057] Take 250 mL of the supernatant obtained from the reaction system of ammonium sulfate leaching solution and oxalic acid precipitation wastewater C from Example 5 with magnesium sulfate leaching solution pretreated with NaHCO3 to remove impurities ① from a mine in Fujian Province, and place it in a beaker. Under the condition of room temperature and stirring speed of 500 r / min, add oxalic acid precipitation wastewater C prepared in Example 3 to adjust the pH of the solution to between 3 and 5. Measure the concentration of ammonium ions and oxalic acid in the supernatant. The concentration of ammonium ions is determined by Nessler's reagent spectrophotometry. Under the gradient of ammonium ion equivalent concentration of 0.12N-0.36N, according to the liquid-solid ratio of 0.7:1, dilute the supernatant or add ammonium sulfate according to the required concentration and use it for cyclic leaching of ion-adsorption type rare earth ores. The obtained rare earth leaching efficiency is as follows: Figure 9 As shown in (a), the concentrations of aluminum ions, magnesium ions, fluorine content, oxalic acid concentration and loss rate, and pH changes in the leachate are as follows: Figure 9 As shown in (bf).

[0058] Take 250 mL of the supernatant obtained from the reaction system of ammonium sulfate leaching solution and oxalic acid precipitation wastewater D in Example 5 with ammonium sulfate leaching solution pretreated with NH4HCO3 to remove impurities ①, and place it in a beaker. Under the condition of room temperature and stirring speed of 500 r / min, add oxalic acid precipitation wastewater D prepared in Example 3 to the beaker to adjust the pH of the solution to between 3 and 5. Measure the concentration of ammonium ions and oxalic acid in the supernatant. The concentration of ammonium ions is determined by Nessler's reagent spectrophotometry. Under the gradient of ammonium ion equivalent concentration of 0.12N-0.36N, according to the liquid-solid ratio of 0.7:1, dilute the supernatant or add ammonium sulfate according to the required concentration and use it for cyclic leaching of ion-adsorption type rare earth ores. The obtained rare earth leaching efficiency is as follows: Figure 10 As shown in (a), the concentrations of aluminum ions, magnesium ions, fluorine content, oxalic acid concentration and loss rate, and pH changes in the leachate are as follows: Figure 10 As shown in (bf).

[0059] Depend on Figure 8 (a) Figure 9 (a) Figure 10 (a) The comparison shows that when using only 0.36N ammonium sulfate as the leaching agent, the rare earth leaching efficiency can reach 100.83%. In the comparative experimental group where the supernatant of the reaction system, after dissolving impurities and adjusting the pH to 4.5 using oxalic acid precipitation wastewater, was directly used for circulating ore leaching, the rare earth leaching efficiency decreased to 87.64% when the ammonium sulfate concentration in the leaching agent was 0.36N and the original rare earth content in the leaching agent was deducted. However, when the pH of the reaction system was adjusted to the target stage of 5.5, with the same ammonium sulfate concentration of 0.36N in the leaching agent and the original rare earth content in the leaching agent deducted, the rare earth leaching efficiency could reach 98.36% and 99.03%, respectively. It can be seen that the rare earth leaching efficiency at the target stage is relatively high, and the valuable metals are well recycled.

[0060] Depend on Figure 8 (bf), Figure 9 (bf), Figure 10 (bf) indicates that when the supernatant with the pH adjusted to 4.5 is directly used for circulating leaching, the fluoride content in the leachate is also higher due to the high fluoride content in the leaching agent. However, when the supernatant with the pH adjusted to 5.5 is used for circulating leaching, the fluoride content in the leachate is close to that of pure ammonium sulfate, meaning there are fewer fluoride ion impurities. Furthermore, at this target stage, while effectively removing oxalic acid without affecting the environment, the aluminum ion content and pH in the circulating leaching leachate are close to those of pure ammonium sulfate leaching agent. The magnesium ion concentration is increased due to the dissolution of magnesium from the impurity slag. This suggests that the system using oxalic acid precipitation wastewater to adjust the pH for circulating leaching at this target stage is stable and generally meets the leaching requirements.

[0061] The above results indicate that when the pH of the reaction system is directly adjusted to 4.5, the rare earth leaching efficiency during recycling is low. Therefore, this condition is not recommended as a recycling method. In contrast, at the target stage, when the system pH is adjusted to 5.5, it is possible to achieve deep removal of oxalic acid, recycling of valuable metals, and reduction of solid waste from impurity removal, while maintaining a high rare earth leaching efficiency during recycling. This has positive implications for the comprehensive utilization of rare earth resources and environmentally friendly development. Therefore, this condition can be considered a preferred method for the coordinated resource-based treatment and recycling of oxalic acid precipitation wastewater and solid waste from impurity removal.

[0062] In the oxalic acid precipitation step of this invention, the functional unit in which oxalic acid plays a role is the oxalate ion (C2O4). 2- ) and hydrogen ions (H + Various types of oxalic acid provide the same oxalate ions (C2O4) when dissolved in water. 2- ) and hydrogen ions (H + ).

[0063] Therefore, regardless of the form of oxalic acid used, such as anhydrous oxalic acid, oxalic acid dihydrate, or one or more aqueous solutions of oxalic acid, it participates in the precipitation reaction as oxalate ions and hydrogen ions after entering the rare earth leachate. The presence or absence of water of crystallization only affects the conversion of the dosage (the mass ratio needs to be adjusted according to the molecular weight), without changing the reaction pathway, the composition of the product, or the chemical nature of the oxalic acid precipitation wastewater. Those skilled in the art, based on common knowledge, can select any form of oxalic acid according to actual procurement or inventory conditions without any creative effort.

[0064] In the rare earth precipitation and recovery process, the functional unit of the precipitant is the carbonate ion (CO3-). 2- ) or bicarbonate ions (HCO3) - ).

[0065] Ammonium bicarbonate, sodium bicarbonate, sodium carbonate, and the cations of ammonium carbonate (NH4+) + Or Na + Both are strong acid salt cations, and under the pH conditions (6.8-8.0) for rare earth carbonate precipitation, they do not react with CO32-. 2- It forms a poorly soluble precipitate and does not compete with rare earth ions for reaction; it also remains in the supernatant of the precipitate and enters the circulating leaching system with the recycled liquid.

[0066] Example 5 in the instruction manual simultaneously verified the effectiveness of NaHCO3 and NH4HCO3 as precipitants (REO of products 1-4 was >92%), proving that the type of cation has no significant effect on the rare earth precipitation rate and product purity.

[0067] When the pH of the system is controlled between 6.8 and 8.0, CO3 is present in the solution regardless of whether a normal salt or an acid salt is initially added. 2- and HCO3 - Both can form rare earth carbonate precipitates with rare earth ions. The only difference is: Normal salts are highly alkaline, so a slightly smaller amount is needed to achieve the same pH. Acidic salts have weaker alkalinity, allowing for smoother pH control and easier operation.

[0068] All four precipitants described above primarily function by providing carbonate / bicarbonate ions; the cations do not participate in the precipitation reaction. Carbonates and bicarbonates exist in chemical equilibrium within the precipitation pH range, achieving the same precipitation effect. Those skilled in the art, based on common knowledge, are fully capable of selecting any one or more combinations according to actual needs.

[0069] Examples 1-4 in the instruction manual directly verify the effectiveness of sodium bicarbonate and ammonium bicarbonate in removing impurities. When sodium carbonate and ammonium carbonate are used as impurity removers, their reaction mechanism is the same as that of bicarbonate—during the impurity removal process, they react with impurity ions such as aluminum and iron to form hydroxides or basic carbonate precipitates, leaving only the residual alkaline components (CO3). 2- HCO3 - These substances also exist in the slag. Therefore, sodium carbonate slag and ammonium carbonate slag are completely identical to the two verified slag functional units and are direct equivalent replacements under the same technical concept.

[0070] Sodium carbonate, ammonium carbonate, magnesium oxide, calcium oxide, sodium hydroxide, potassium hydroxide, and ammonia water are all based on the same neutralization mechanism. Therefore, regardless of the source of the impurity removal agent, their essential characteristic in this invention is that they contain unreacted alkaline components, which can undergo a neutralization reaction when acidic oxalic acid wastewater is added, thereby increasing the pH of the system.

[0071] Although these different types of impurity removal residues differ in their specific chemical composition, in the method of this invention, their functions (neutralizing acid, adjusting pH) and the chemical reaction pathways they undergo (acid dissolution and precipitation → co-precipitation removal) are completely consistent. Those skilled in the art, based on common knowledge, can reasonably expect that using any one or more of the above-mentioned impurity removal residues can achieve the technical effects of oxalic acid removal and rare earth recovery under the stepwise pH control conditions of this invention.

[0072] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for the integrated resource utilization of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste, characterized in that, The method includes the following steps: Step 1: Add a descaling agent to the ion adsorption type rare earth leachate to cause aluminum, suspended clay and rare earth to precipitate and aggregate, and filter to obtain rare earth pretreatment descaling residue. Step 2: Add oxalic acid to the ion adsorption type rare earth leachate or the rare earth solution after impurity removal to precipitate rare earth, and filter to separate the oxalic acid precipitate wastewater. Step 3: Add the rare earth pretreatment residue to the oxalic acid precipitation wastewater in batches under stirring to react, so that the pH gradually increases to 5.0-5.5, so that oxalic acid and aluminum ions enter the precipitate at the same time and rare earth ions dissolve. Step 4: After the reaction is complete, filter and separate to obtain a rare earth supernatant with low oxalic acid content and a residue containing oxalic acid after impurity removal. Step 5: Add carbonate to the rare earth supernatant with low oxalic acid content to precipitate rare earth, stir, filter, and obtain rare earth carbonate precipitate and precipitate supernatant. Step 6: Rare earth carbonate precipitation is used to recover and prepare rare earth oxide products. After adjusting the concentration of leaching agent and pH of the precipitate supernatant to between 3 and 5, it is used for cyclic leaching of ion-adsorption type rare earth ore.

2. The method for the integrated resource utilization of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste according to claim 1, characterized in that, In step 3, the rare earth pretreatment residue is added to the oxalic acid precipitation wastewater in batches, with each batch containing 1%-7% of the total required residue. The reaction is stirred until the pH stabilizes before adding the next batch, so that the pH of the system slowly rises to the target range.

3. The method for the integrated resource utilization of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste according to claim 1 or 2, characterized in that, The stirring rate during the reaction process is adjusted according to the pH changes of the reaction system.

4. The method for the integrated resource utilization of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste according to claim 3, characterized in that, The stirring rate is adjusted according to the pH change of the reaction system. When the pH is below 5.0, the stirring rate is controlled at 350-500 r / min. When the pH of the reaction system reaches 5.0-5.5, the stirring rate is increased to 500-700 r / min. After the reaction reaches the target value, the stirring reaction continues for 30-60 min.

5. The method for the integrated resource utilization of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste according to claim 4, characterized in that, The precipitant used in step 5 is one or more of ammonium bicarbonate, sodium bicarbonate, sodium carbonate, and ammonium carbonate.

6. The method for the integrated resource utilization of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste according to claim 5, characterized in that, In step 5, the precipitation process is carried out at a stirring rate of 500 r / min, a pH of 6.8-8.0, and a rare earth carbonate calcination temperature of 800-1000 ℃.

7. The method for the integrated resource utilization of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste according to claim 6, characterized in that, The pretreatment impurity removal agent in step 1 is one or more of the following: ammonium bicarbonate, sodium bicarbonate, sodium carbonate, ammonium carbonate, magnesium oxide, calcium oxide, sodium hydroxide, potassium hydroxide, and ammonia water.

8. The method for the integrated resource utilization of rare earth oxalic acid precipitation wastewater and impurity removal residue solid waste according to claim 7, characterized in that, The oxalic acid used in the steps is one or more of anhydrous oxalic acid, oxalic acid dihydrate, and aqueous oxalic acid solution.

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