A method for separating light, medium and heavy rare earths and aluminum by synergic-coupling extraction

Abstract

The application provides a method for cooperatively and coupledly extracting and separating light, medium and heavy rare earths and aluminum. When the concentration of rare earth sulfate in a feed liquid is lower than the concentration of rare earth chloride, medium and heavy rare earths are first cooperatively extracted by P507-N235-kerosene, and light rare earths are extracted by N1923-isooctanol-kerosene to be separated from aluminum, and different concentrations of hydrochloric acid are used to backwash and back-extract the organic phase to obtain medium and heavy rare earth products; the N1923-isooctanol-kerosene organic phase is back-extracted by hydrochloric acid to obtain a light rare earth product; when the concentration of rare earth sulfate in the feed liquid is higher than the concentration of rare earth chloride, medium and heavy rare earths are first extracted by N1923-isooctanol-kerosene, then cooperatively extracted and pre-grouped, and then back-extracted by hydrochloric acid in stages to obtain medium and heavy rare earth pre-grouping products and thulium, ytterbium and lutetium heavy rare earth pre-grouping products. The application realizes the pre-grouping of light, medium and heavy rare earths and the separation of the rare earths from aluminum by coupling extraction of two kinds of organic phases, and realizes efficient chlorination transformation of rare earth sulfate leaching solution by back-extraction.

Description

Technical Field

[0001] This invention relates to the field of rare earth hydrometallurgy technology, and in particular to a method for synergistic-coupled extraction and separation of light, medium and heavy rare earth elements and aluminum. Background Technology

[0002] Solvent extraction is a common method for separating rare earth elements and aluminum in a leaching solution. Aluminum ions often accompany rare earth elements into the leachate, reducing the loading capacity of the rare earth extractant and leading to excessive aluminum impurities in the rare earth product, thus affecting the final product quality. Therefore, developing an extraction system that can efficiently separate rare earth elements and aluminum while simultaneously achieving pre-grouping of rare earth elements is of significant industrial importance. Currently, industrially used extraction systems for separating rare earth elements and aluminum mainly include naphthenic acid extraction, acidic phosphorus extractant methods, and the recently developed synergistic extraction method.

[0003] Naphthenic acids are a class of carboxylic acid extractants that can selectively extract aluminum at relatively high pH values. Chinese patent application CN101979680A discloses a method for aluminum removal using naphthenic acid-alcohol-kerosene extraction. However, this system is prone to hydrolysis and phase separation in practical applications, requires stringent pH control of the feed solution, and exhibits decreased extraction rate and high rare earth loss when aluminum content is low. Acidic phosphorus extractants, represented by P507, are currently the mainstream extractants for rare earth extraction and separation, exhibiting excellent extraction performance for rare earth ions. However, P507 also has a strong extraction ability for aluminum ions, resulting in a significant co-extraction of aluminum during rare earth extraction. This aluminum is dispersed throughout the extraction tanks for light and medium rare earths, leading to decreased rare earth separation efficiency and deterioration of the purity of rare earth carbonate products. More importantly, traditional P507 extraction processes require the use of ammonia or sodium hydroxide for saponification, generating large amounts of ammonia-nitrogen-containing wastewater, posing a significant environmental burden.

[0004] To overcome the above problems, researchers developed a synergistic non-saponification extraction system using P507 and the tertiary amine N235. Chinese invention patent CN10276676A discloses a non-ammonium saponification rare earth extraction and separation process, employing a mixed composite solvent of P507 and N235, which directly extracts rare earths without ammonium saponification, thus avoiding the generation of ammonia-containing wastewater at the source. Furthermore, some progress has been made in separating rare earths and aluminum in sulfate systems using the primary amine N1923. Chinese invention patent CN201611200748.1 discloses a three-inlet fractionation extraction method for separating mixed rare earths, using P507 as the rare earth extractant and the primary amine N1923 as the acid extraction agent to achieve grouping of light, medium, and heavy rare earths. Chinese patent application CN119082462A discloses the use of amine extractants to extract all rare earths from a sulfate rare earth solution into the organic phase, while aluminum remains in the solution, achieving the separation of rare earths and aluminum. However, these methods are all difficult to simultaneously achieve the pre-grouping of light, medium and heavy rare earth elements and their deep separation from aluminum in the same process, as well as the transformation from the sulfate system to the chloride system.

[0005] In summary, existing technologies still have significant shortcomings in the separation of rare earth elements and aluminum: naphthenic acid systems are prone to emulsification and have poor phase separation; aluminum co-extraction in single P507 systems is severe and saponification wastewater is highly polluting; and existing P507-N235 synergistic systems have insufficient research on rare earth pre-grouping, heavy rare earth back-extraction, and deep separation from aluminum. Summary of the Invention

[0006] In view of the above situation, the main objective of this invention is to propose a synergistic-coupled extraction method for separating light, medium, and heavy rare earth elements and aluminum, in order to solve the above-mentioned technical problems.

[0007] This invention proposes a method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum, the method comprising the following steps: When the concentration of rare earth sulfate in the aqueous feed solution is lower than the concentration of rare earth chloride: Step 1: Extract the aqueous phase solution using an extractant to obtain an organic phase loaded with heavy rare earth ions, a first part of light rare earth, a first part of medium rare earth and aluminum raffinate aqueous phase. Step 2: The organic phases loaded with medium and heavy rare earth ions were backwashed and back-extracted using hydrochloric acid of different concentrations to obtain medium and heavy rare earth elements and thulium, ytterbium, and lutetium heavy rare earth elements, respectively. Step 3: Use N1923-isooctanol-kerosene to couple extract the raffinate aqueous phase of light and medium rare earth elements and aluminum to obtain the organic phases of light and medium rare earth elements; use hydrochloric acid to backwash and back-extract the organic phases of light and medium rare earth elements to obtain the second part of light rare earth elements and the second part of medium rare earth elements, respectively. When the concentration of rare earth sulfate in the aqueous feed solution is higher than the concentration of rare earth chloride; Step 1: Extract the aqueous phase solution using N1923-isooctanol-kerosene to obtain the rare earth-loaded organic phase; Step 2: Use hydrochloric acid to back-extract the organic phase loaded with rare earth elements to obtain a mixed medium and heavy rare earth chloride solution and light rare earth elements. Step 3: Extract the mixed medium and heavy rare earth chloride solution with an extractant to obtain an extractable organic phase loaded with medium and heavy rare earths; Step 4: Use hydrochloric acid of different concentrations to backwash and back-extract the organic phases loaded with medium and heavy rare earth elements to obtain medium and heavy rare earth elements and thulium-ytterbium-lutetium heavy rare earth elements, respectively.

[0008] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention couples extractant synergistic extraction with N1923-isooctanol-kerosene extraction, which can directly extract under acidic conditions of pH 2.0~2.5, greatly improving the extraction capacity and selectivity of medium and heavy rare earths, and the separation coefficient of heavy rare earths and aluminum can reach 6000.

[0009] 2. This invention can achieve efficient back-extraction of heavy rare earth elements using only 2 mol / L hydrochloric acid, solving the problem of difficult back-extraction of heavy rare earth elements in the traditional P507 system.

[0010] 3. By coupling with the N1923-isooctanol-kerosene extraction process, this invention can simultaneously achieve the pre-grouping of light, medium and heavy rare earth elements and their separation from aluminum, and back-extract to obtain rare earth chloride solution, thereby realizing the rare earth chloride transformation of various sulfate rare earth leachates. Attached Figure Description

[0011] Figure 1 A graph showing the effect of different N235 volume fractions on the separation coefficient of rare earth and aluminum. Figure 2 This is a graph showing the effect of aqueous phase pH on the separation coefficient of rare earth elements and aluminum. Figure 3 The graph shows the effect of rare earth elements on the separation coefficient of aluminum. Figure 4 A graph showing the effect of synergistic extraction temperature on the separation coefficient of rare earth and aluminum; Figure 5 A bar chart comparing the effects of aluminum content in the feed liquid on the separation coefficients of rare earth elements and aluminum in the P507-N235 system and the single P507 kerosene system. Figure 6 A bar chart comparing the effects of aluminum content in the feed solution on the separation coefficients of rare earth and aluminum under different N235 addition amounts; Figure 7 A bar chart comparing the effects of aluminum content in the feed solution on the separation coefficients of rare earth elements and aluminum under different aqueous phase pH conditions. Figure 8A bar chart comparing the single-stage back-extraction rates of medium and heavy rare earth elements in the P507-N235 system and the single P507 kerosene system; Figure 9 A schematic diagram showing the effect of the P507-N235 system back-extraction ratio on the single-stage back-extraction rate of medium and heavy rare earth elements. Figure 10 A schematic diagram showing the effect of the number of back-extractions on the back-extraction rate of medium and heavy rare earth elements in the P507-N235 system; Figure 11 This is a schematic diagram of a three-stage countercurrent extraction process. Detailed Implementation

[0012] 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.

[0013] Example 1 This embodiment provides a method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum, the method comprising the following steps: When the concentration of rare earth sulfate in the aqueous feed solution is lower than the concentration of rare earth chloride: Step 1: Prepare an extractant using 30% P507 and sulfonated kerosene; use the extractant to extract the aqueous phase (pH 0.5) (co-extraction ratio O / A 1:2, temperature 0℃) for 10 min to obtain an organic phase loaded with heavy rare earth ions, a first part of light rare earth, a first part of medium rare earth and aluminum raffinate aqueous phase; Step 2: Use hydrochloric acid (1.0 mol / L) to perform a first backwash and back-extraction on the organic phase loaded with medium and heavy rare earth ions for 10 min to obtain medium and heavy rare earths; The organic phase loaded with medium and heavy rare earth ions was subjected to a first backwash and back-extraction for 10 min using hydrochloric acid (4.0 mol / L) to obtain thulium, ytterbium, and lutetium heavy rare earth elements. Step 3: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; use N1923-isooctanol-kerosene to couple extract the raffinate aqueous phase of light and medium rare earth elements and aluminum to obtain the organic phases of light and medium rare earth elements. The organic phases of light and medium rare earth elements were backwashed and back-extracted using hydrochloric acid (0.1 mol / L) to obtain the second part of light rare earth elements and the second part of medium rare earth elements, respectively. When the concentration of rare earth sulfate in the aqueous feed solution is higher than the concentration of rare earth chloride; Step 1: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; use N1923-isooctanol-kerosene to extract the aqueous phase solution (pH 0.5) to obtain the rare earth-loaded organic phase. Step 2: Back-extract the organic phase loaded with rare earth elements using 0.1 mol / L hydrochloric acid to obtain a mixed solution of medium and heavy rare earth chlorides and light rare earth elements. Step 3: Prepare an extractant using 30% P507 and sulfonated kerosene; use the extractant to extract a mixed medium and heavy rare earth chloride solution (co-extraction ratio O / A 1:2, temperature 0℃) for 10 min to obtain an extractable organic phase loaded with medium and heavy rare earths. Step 4: Use hydrochloric acid (1.0 mol / L) to backwash and back-extract the organic phase loaded with medium and heavy rare earth elements to obtain medium and heavy rare earth elements; The organic phase containing the medium and heavy rare earth elements was backwashed and back-extracted using hydrochloric acid (4.0 mol / L) to obtain thulium, ytterbium, and lutetium heavy rare earth elements.

[0014] Example 2 This embodiment provides a method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum, the method comprising the following steps: When the concentration of rare earth sulfate in the aqueous feed solution is lower than the concentration of rare earth chloride: Step 1: Prepare an extractant using 30% P507 (volume fraction), 15% N235 (volume fraction), and sulfonated kerosene. Use the extractant to extract the aqueous phase (pH 1.5) (co-extraction ratio O / A 1:1, temperature 27.5℃) for 10 min to obtain an organic phase loaded with heavy rare earth ions, a first part of light rare earth, a first part of medium rare earth, and an aqueous raffinate containing aluminum. Step 2: Use hydrochloric acid (1.5 mol / L) to perform a first backwash and back-extraction on the organic phase loaded with medium and heavy rare earth ions for 10 min to obtain medium and heavy rare earths; The organic phase loaded with medium and heavy rare earth ions was subjected to a first backwash and back-extraction for 10 min using hydrochloric acid (4.5 mol / L) to obtain thulium ytterbium lutetium heavy rare earth elements. Step 3: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; use N1923-isooctanol-kerosene to couple extract the raffinate aqueous phase of light and medium rare earth elements and aluminum to obtain the organic phases of light and medium rare earth elements. The organic phases of light and medium rare earth elements were backwashed and back-extracted using hydrochloric acid (0.3 mol / L) to obtain the second part of light rare earth elements and the second part of medium rare earth elements, respectively. When the concentration of rare earth sulfate in the aqueous feed solution is higher than the concentration of rare earth chloride; Step 1: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; extract the aqueous phase solution (pH 1.5) using N1923-isooctanol-kerosene to obtain the rare earth-loaded organic phase. Step 2: Back-extract the organic phase loaded with rare earth elements using 0.3 mol / L hydrochloric acid to obtain a mixed medium and heavy rare earth chloride solution and light rare earth elements. Step 3: Prepare an extractant using 30% P507 (volume fraction), 15% N235 (volume fraction), and sulfonated kerosene; use the extractant to extract a mixed medium and heavy rare earth chloride solution (co-extraction ratio O / A 1:1, temperature 27.5℃) for 10 min to obtain an extractable organic phase loaded with medium and heavy rare earths. Step 4: Use hydrochloric acid (1.5 mol / L) to backwash and back-extract the organic phase loaded with medium and heavy rare earth elements to obtain medium and heavy rare earth elements. The organic phase containing the medium and heavy rare earth elements was backwashed and back-extracted using hydrochloric acid (4.5 mol / L) to obtain thulium, ytterbium, and lutetium heavy rare earth elements.

[0015] Example 3 This embodiment provides a method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum, the method comprising the following steps: When the concentration of rare earth sulfate in the aqueous feed solution is lower than the concentration of rare earth chloride: Step 1: Prepare an extractant using 30% P507 (volume fraction), 30% N235 (volume fraction), and sulfonated kerosene. Use the extractant to extract the aqueous phase (pH 2.5) (co-extraction ratio O / A 2:1, temperature 55℃) for 10 min to obtain an organic phase loaded with heavy rare earth ions, a first part of light rare earth, a first part of medium rare earth, and an aqueous raffinate containing aluminum. Step 2: Use hydrochloric acid (2.0 mol / L) to perform a first backwash and back-extraction on the organic phase loaded with medium and heavy rare earth ions for 10 min to obtain medium and heavy rare earths; The organic phase loaded with medium and heavy rare earth ions was subjected to a first backwash and back-extraction for 10 min using hydrochloric acid (5.0 mol / L) to obtain thulium, ytterbium, and lutetium heavy rare earth elements. Step 3: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; use N1923-isooctanol-kerosene to couple extract the raffinate aqueous phase of light and medium rare earth elements and aluminum to obtain the organic phases of light and medium rare earth elements. The organic phases of light and medium rare earth elements were backwashed and back-extracted using hydrochloric acid (0.5 mol / L) to obtain the second part of light rare earth elements and the second part of medium rare earth elements, respectively. When the concentration of rare earth sulfate in the aqueous feed solution is higher than the concentration of rare earth chloride; Step 1: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; extract the aqueous phase solution (pH 2.5) using N1923-isooctanol-kerosene to obtain the rare earth-loaded organic phase. Step 2: Back-extract the organic phase loaded with rare earth elements using 0.5 mol / L hydrochloric acid to obtain a mixed medium and heavy rare earth chloride solution and light rare earth elements. Step 3: Prepare an extractant using 30% P507, 30% N235 and sulfonated kerosene; use the extractant to extract a mixed medium and heavy rare earth chloride solution (co-extraction ratio O / A 2:1, temperature 55℃) for 10 min to obtain an extractable organic phase loaded with medium and heavy rare earths. Step 4: Use hydrochloric acid (2.0 mol / L) to backwash and back-extract the organic phase loaded with medium and heavy rare earth elements to obtain medium and heavy rare earth elements; The organic phase containing the medium and heavy rare earth elements was backwashed and back-extracted using hydrochloric acid (5.0 mol / L) to obtain thulium, ytterbium, and lutetium heavy rare earth elements.

[0016] Example 4 This embodiment provides a method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum, the method comprising the following steps: When the concentration of rare earth sulfate in the aqueous feed solution is lower than the concentration of rare earth chloride: Step 1: Prepare an extractant using 30% P507 and sulfonated kerosene; use the extractant to extract the aqueous phase (pH 0.5) (co-extraction ratio O / A 2:4, temperature 0℃) for 10 min to obtain an organic phase loaded with heavy rare earth ions, a first part of light rare earth, a first part of medium rare earth and aluminum raffinate aqueous phase; Step 2: Use hydrochloric acid (1.5 mol / L) to perform a first backwash and back-extraction on the organic phase loaded with medium and heavy rare earth ions for 10 min to obtain medium and heavy rare earths; The organic phase loaded with medium and heavy rare earth ions was subjected to a first backwash and back-extraction for 10 min using hydrochloric acid (4.5 mol / L) to obtain thulium ytterbium lutetium heavy rare earth elements. Step 3: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; use N1923-isooctanol-kerosene to couple extract the raffinate aqueous phase of light and medium rare earth elements and aluminum to obtain the organic phases of light and medium rare earth elements. The organic phases of light and medium rare earth elements were backwashed and back-extracted using hydrochloric acid (0.7 mol / L) to obtain the second part of light rare earth elements and the second part of medium rare earth elements, respectively. When the concentration of rare earth sulfate in the aqueous feed solution is higher than the concentration of rare earth chloride; Step 1: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; use N1923-isooctanol-kerosene to extract the aqueous phase solution (pH 0.5) to obtain the rare earth-loaded organic phase. Step 2: Back-extract the organic phase loaded with rare earth elements using 0.7 mol / L hydrochloric acid to obtain a mixed medium and heavy rare earth chloride solution and light rare earth elements. Step 3: Prepare an extractant using 30% P507 and sulfonated kerosene; use the extractant to extract a mixed medium and heavy rare earth chloride solution (co-extraction ratio O / A 2:4, temperature 0℃) for 10 min to obtain an extractable organic phase loaded with medium and heavy rare earths. Step 4: Use hydrochloric acid (1.5 mol / L) to backwash and back-extract the organic phase loaded with medium and heavy rare earth elements to obtain medium and heavy rare earth elements. The organic phase containing the medium and heavy rare earth elements was backwashed and back-extracted using hydrochloric acid (4.5 mol / L) to obtain thulium, ytterbium, and lutetium heavy rare earth elements.

[0017] Example 5 This embodiment provides a method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum, the method comprising the following steps: When the concentration of rare earth sulfate in the aqueous feed solution is lower than the concentration of rare earth chloride: Step 1: Prepare an extractant using 30% P507 (volume fraction), 10% N235 (volume fraction), and sulfonated kerosene. Use the extractant to extract the aqueous phase (pH 1.0) (co-extraction ratio O / A 3:4, temperature 25℃) for 10 min to obtain an organic phase loaded with heavy rare earth ions, a first part of light rare earth, a first part of medium rare earth, and an aqueous raffinate containing aluminum. Step 2: Use hydrochloric acid (1.5 mol / L) to perform a first backwash and back-extraction on the organic phase loaded with medium and heavy rare earth ions for 10 min to obtain medium and heavy rare earths; The organic phase loaded with medium and heavy rare earth ions was subjected to a first backwash and back-extraction for 10 min using hydrochloric acid (4.5 mol / L) to obtain thulium ytterbium lutetium heavy rare earth elements. Step 3: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; use N1923-isooctanol-kerosene to couple extract the raffinate aqueous phase of light and medium rare earth elements and aluminum to obtain the organic phases of light and medium rare earth elements. The organic phases of light and medium rare earth elements were backwashed and back-extracted using hydrochloric acid (0.9 mol / L) to obtain the second part of light rare earth elements and the second part of medium rare earth elements, respectively. When the concentration of rare earth sulfate in the aqueous feed solution is higher than the concentration of rare earth chloride; Step 1: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; use N1923-isooctanol-kerosene to extract the aqueous phase solution (pH 1.0) to obtain the rare earth-loaded organic phase. Step 2: Back-extract the organic phase loaded with rare earth elements using 0.9 mol / L hydrochloric acid to obtain a mixed medium and heavy rare earth chloride solution and light rare earth elements. Step 3: Prepare an extractant using 30% P507 (volume fraction), 10% N235 (volume fraction), and sulfonated kerosene; use the extractant to extract a mixed medium and heavy rare earth chloride solution (co-extraction ratio O / A 1:2~2:1, temperature 25℃) for 10 min to obtain an extractable organic phase loaded with medium and heavy rare earths. Step 4: Use hydrochloric acid (1.5 mol / L) to backwash and back-extract the organic phase loaded with medium and heavy rare earth elements to obtain medium and heavy rare earth elements. The organic phase containing the medium and heavy rare earth elements was backwashed and back-extracted using hydrochloric acid (4.5 mol / L) to obtain thulium, ytterbium, and lutetium heavy rare earth elements.

[0018] Example 6 This embodiment provides a method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum, the method comprising the following steps: When the concentration of rare earth sulfate in the aqueous feed solution is lower than the concentration of rare earth chloride: Step 1: Prepare an extractant using 30% P507 (volume fraction), 20% N235 (volume fraction), and sulfonated kerosene. Use the extractant to extract the aqueous phase (pH 1.5) (co-extraction ratio O / A 4:4, temperature 35℃) for 10 min to obtain an organic phase loaded with heavy rare earth ions, a first part of light rare earth, a first part of medium rare earth, and an aqueous raffinate containing aluminum. Step 2: Use hydrochloric acid (1.5 mol / L) to perform a first backwash and back-extraction on the organic phase loaded with medium and heavy rare earth ions for 10 min to obtain medium and heavy rare earths; The organic phase loaded with medium and heavy rare earth ions was subjected to a first backwash and back-extraction for 10 min using hydrochloric acid (4.5 mol / L) to obtain thulium ytterbium lutetium heavy rare earth elements. Step 3: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; use N1923-isooctanol-kerosene to couple extract the raffinate aqueous phase of light and medium rare earth elements and aluminum to obtain the organic phases of light and medium rare earth elements. The organic phases of light and medium rare earth elements were backwashed and back-extracted using hydrochloric acid (1.1 mol / L) to obtain the second part of light rare earth elements and the second part of medium rare earth elements, respectively. When the concentration of rare earth sulfate in the aqueous feed solution is higher than the concentration of rare earth chloride; Step 1: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; extract the aqueous phase solution (pH 1.5) using N1923-isooctanol-kerosene to obtain the rare earth-loaded organic phase. Step 2: Back-extract the organic phase loaded with rare earth elements using 1.1 mol / L hydrochloric acid to obtain a mixed medium and heavy rare earth chloride solution and light rare earth elements. Step 3: Prepare an extractant using 30% P507 (volume fraction), 20% N235 (volume fraction), and sulfonated kerosene; use the extractant to extract a mixed medium and heavy rare earth chloride solution (co-extraction ratio O / A 4:4, temperature 35℃) for 10 min to obtain an extractable organic phase loaded with medium and heavy rare earths. Step 4: Use hydrochloric acid (1.5 mol / L) to backwash and back-extract the organic phase loaded with medium and heavy rare earth elements to obtain medium and heavy rare earth elements. The organic phase containing the medium and heavy rare earth elements was backwashed and back-extracted using hydrochloric acid (4.5 mol / L) to obtain thulium, ytterbium, and lutetium heavy rare earth elements.

[0019] Example 7 This embodiment provides a method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum, the method comprising the following steps: When the concentration of rare earth sulfate in the aqueous feed solution is lower than the concentration of rare earth chloride: Step 1: Prepare an extractant using 30% P507 (volume fraction), 25% N235 (volume fraction), and sulfonated kerosene. Use the extractant to extract the aqueous phase (pH 2.0) (co-extraction ratio O / A 6:4, temperature 45℃) for 10 min to obtain an organic phase loaded with heavy rare earth ions, a first part of light rare earth, a first part of medium rare earth, and an aqueous raffinate containing aluminum. Step 2: Use hydrochloric acid (1.5 mol / L) to perform a first backwash and back-extraction on the organic phase loaded with medium and heavy rare earth ions for 10 min to obtain medium and heavy rare earths; The organic phase loaded with medium and heavy rare earth ions was subjected to a first backwash and back-extraction for 10 min using hydrochloric acid (4.5 mol / L) to obtain thulium ytterbium lutetium heavy rare earth elements. Step 3: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; use N1923-isooctanol-kerosene to couple extract the raffinate aqueous phase of light and medium rare earth elements and aluminum to obtain the organic phases of light and medium rare earth elements. The organic phases of light and medium rare earth elements were backwashed and back-extracted using hydrochloric acid (1.5 mol / L) to obtain the second part of light rare earth elements and the second part of medium rare earth elements, respectively. When the concentration of rare earth sulfate in the aqueous feed solution is higher than the concentration of rare earth chloride; Step 1: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; use N1923-isooctanol-kerosene to extract the aqueous phase solution (pH 2.0) to obtain the rare earth-loaded organic phase. Step 2: Back-extract the organic phase loaded with rare earth elements using 1.5 mol / L hydrochloric acid to obtain a mixed medium and heavy rare earth chloride solution and light rare earth elements. Step 3: Prepare an extractant using 30% P507 (volume fraction), 25% N235 (volume fraction), and sulfonated kerosene; use the extractant to extract a mixed medium and heavy rare earth chloride solution (co-extraction ratio O / A 6:4, temperature 45℃) for 10 min to obtain an extractable organic phase loaded with medium and heavy rare earths. Step 4: Use hydrochloric acid (1.5 mol / L) to backwash and back-extract the organic phase loaded with medium and heavy rare earth elements to obtain medium and heavy rare earth elements. The organic phase containing the medium and heavy rare earth elements was backwashed and back-extracted using hydrochloric acid (4.5 mol / L) to obtain thulium, ytterbium, and lutetium heavy rare earth elements.

[0020] Example 8 This embodiment provides a method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum, the method comprising the following steps: When the concentration of rare earth sulfate in the aqueous feed solution is lower than the concentration of rare earth chloride: Step 1: Prepare an extractant using 30% P507 (volume fraction), 30% N235 (volume fraction), and sulfonated kerosene. Use the extractant to extract the aqueous phase (pH 2.5) (co-extraction ratio O / A 8:4, temperature 55℃) for 10 min to obtain an organic phase loaded with heavy rare earth ions, a first part of light rare earth, a first part of medium rare earth, and an aqueous raffinate containing aluminum. Step 2: Use hydrochloric acid (1.5 mol / L) to perform a first backwash and back-extraction on the organic phase loaded with medium and heavy rare earth ions for 10 min to obtain medium and heavy rare earths; The organic phase loaded with medium and heavy rare earth ions was subjected to a first backwash and back-extraction for 10 min using hydrochloric acid (4.5 mol / L) to obtain thulium ytterbium lutetium heavy rare earth elements. Step 3: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; use N1923-isooctanol-kerosene to couple extract the raffinate aqueous phase of light and medium rare earth elements and aluminum to obtain the organic phases of light and medium rare earth elements. The organic phases of light and medium rare earth elements were backwashed and back-extracted using hydrochloric acid (2 mol / L) to obtain the second part of light rare earth elements and the second part of medium rare earth elements, respectively. When the concentration of rare earth sulfate in the aqueous feed solution is higher than the concentration of rare earth chloride; Step 1: Prepare N1923-isooctanol-kerosene using N1923, isooctanol and kerosene in a ratio of 2:1:7; extract the aqueous phase solution (pH 2.5) using N1923-isooctanol-kerosene to obtain the rare earth-loaded organic phase. Step 2: Use 2 mol / L hydrochloric acid to back-extract the organic phase loaded with rare earth elements to obtain a mixed medium and heavy rare earth chloride solution and light rare earth elements. Step 3: Prepare an extractant using 30% P507, 30% N235 and sulfonated kerosene; use the extractant to extract a mixed medium and heavy rare earth chloride solution (co-extraction ratio O / A 8:4, temperature 55℃) for 10 min to obtain an extractable organic phase loaded with medium and heavy rare earths. Step 4: Use hydrochloric acid (1.5 mol / L) to backwash and back-extract the organic phase loaded with medium and heavy rare earth elements to obtain medium and heavy rare earth elements. The organic phase containing the medium and heavy rare earth elements was backwashed and back-extracted using hydrochloric acid (4.5 mol / L) to obtain thulium, ytterbium, and lutetium heavy rare earth elements.

[0021] Please see Figure 1 Through Examples 4 to 8, the effects of varying N235 volume fractions on the separation coefficient of rare earth elements and aluminum were investigated under the condition of a fixed P507 volume fraction of 30%. Figure 1 It is known that the single P507 kerosene system has a relatively low maximum separation coefficient between rare earth and aluminum, around 1500. However, the addition of N235 can improve the separation coefficient between some medium rare earth (Sm, Eu, Gd, Tb, Dy) and heavy rare earth and aluminum. When the N235 content is 25~30%, the separation coefficient between heavy rare earth and aluminum is the highest. At this point, the phase separation rate and performance are good, and the separation coefficient between Tm and Lu is as high as 6000. Therefore, the optimal N235 addition amount can be controlled at 25~30%.

[0022] Please see Figure 2 Examples 4 to 8 illustrate the effect of aqueous phase pH on the separation coefficient of rare earth elements and aluminum. Figure 2It can be seen that under aqueous phase pH conditions of 0.5, 1.0, 1.5, 2.0, and 2.5, the separation coefficients of rare earth elements (La~Gd) and aluminum are all close to 0, indicating that effective separation of rare earth elements and aluminum is not possible. With increasing pH, the separation coefficients of rare earth elements (Tb to Lu) and yttrium (Y) gradually and significantly increase, generally following the order: pH = 2.0 > pH = 2.5 > pH = 1.5 > pH = 1.0 > pH = The separation coefficients of medium and heavy rare earth components reach their peak at pH 2.0, with optimal selective separation of rare earth and aluminum. As pH increases to 2.5, the separation coefficients decrease slightly but remain at a high level, ensuring stable aluminum removal from rare earth. Below pH 2.0, excessively high hydrogen ion concentrations inhibit rare earth extraction, and excessive co-extraction of aluminum ions leads to low separation coefficients and substandard separation. Above pH 2.5, aluminum hydrolysis generates aluminum hydroxide colloids, causing emulsification of the extraction system and loss of rare earth hydrolysis precipitation. Considering both separation performance and extraction process stability, the optimal pH control range for the system is determined to be 2.0–2.5.

[0023] Please see Figure 3 Examples 4 to 8 illustrate the effect of comparison on the separation coefficient of rare earth and aluminum; Figure 3 It can be seen that, compared with the conditions of 2:4, 3:4, 4:4, 6:4, and 8:4, the separation coefficients of rare earth elements (La~Gd) and aluminum in light rare earth elements are close to 0, and effective separation cannot be achieved. The separation coefficients of medium and heavy rare earth elements (Tb to Lu and Y) gradually increase with the increase of the organic phase ratio, in the order of 8:4 > 6:4 > 4:4 > 3:4 > 2:4. Compared with the ratio of less than 1:1, the amount of organic phase is insufficient, the rare earth extraction is incomplete, and the separation effect is poor. Compared with the ratio of more than 1:1, although the separation coefficient is slightly improved, the consumption of extractant increases significantly, the production cost increases, and problems such as poor phase separation and organic phase entrainment loss are also likely to occur. When the ratio is 1:1 (4:4), a high rare earth-aluminum separation coefficient can be maintained to ensure the impurity removal effect, while controlling the consumption of extractant and ensuring normal stratification of the two phases. Considering the separation performance and industrial economics, the optimal ratio is determined to be 1:1.

[0024] Please see Figure 4 Examples 4 to 8 illustrate the effect of temperature on the separation coefficient of rare earth elements and aluminum. Figure 4It can be seen that under temperature conditions of 0℃, 25℃, 35℃, 45℃, and 55℃, the separation coefficients of rare earth elements (La-Gd) and aluminum are close to 0, making effective separation of rare earth elements and aluminum impossible. The separation coefficients of medium and heavy rare earth elements (Tb-Lu) and yttrium (Y) components first increase and then decrease with increasing temperature, reaching their maximum value at 25℃ and maintaining a relatively high separation level at 35℃. Below 25℃, the extraction rate is low, resulting in a low rare earth extraction rate and relatively weak separation effect. Above 35℃, the extraction selectivity decreases, and the separation coefficient gradually declines. Considering the rare earth-aluminum separation performance, process stability, and industrial operating costs, the optimal operating temperature range is determined to be 25–35℃.

[0025] Please see Figure 5 Examples 4 and 5 illustrate the effect of aluminum content in the feed solution of the P507-N235 system and the single P507 kerosene system on the separation coefficient of rare earth elements and aluminum. Figure 5 It was found that within the aluminum concentration range of 2-15 g / L in the feed solution, the separation coefficients of rare earth elements and aluminum in the P507-N235 system were significantly higher than those in the single P507 kerosene system. Furthermore, as the aluminum content in the feed solution increased, the separation coefficient of the single P507 system showed limited improvement, while the separation coefficient of the P507-N235 system continuously increased, demonstrating outstanding resistance to aluminum interference. This indicates that introducing N235 into the P507 extraction system can effectively enhance the selective separation of rare earth elements and aluminum. This synergistic extraction system can meet the aluminum removal requirements of rare earth chloride feed solutions with high aluminum content, thus having a wider range of industrial applications.

[0026] Please see Figure 6 Examples 6 and 8 illustrate the effect of aluminum content in the feed solution on the separation coefficient of rare earth elements and aluminum under different N235 addition amounts. Figure 6 It can be seen that in low-aluminum feed systems with aluminum concentrations of 2 g / L and 5 g / L, the 30% P507 + 30% N235 system has a higher rare earth separation coefficient and better separation effect. When the aluminum concentration of the feed solution increases to 10 g / L and 15 g / L, the 30% P507 + 20% N235 system not only has a significantly higher separation coefficient and stronger rare earth aluminum removal advantage, but also has a better two-phase separation effect. The appropriate extractant combination ratio can be flexibly selected according to the aluminum impurity content of the feed solution.

[0027] Please see Figure 7 The effect of aluminum content in the feed solution on the separation coefficient of rare earth elements and aluminum under different aqueous phase pH conditions was investigated. Figure 7 It can be seen that within the range of aluminum concentration in the liquid feed of 2 to 15 g / L, the rare earth and aluminum separation coefficient corresponding to pH=2.0 is always higher than that of pH=3.0. Regardless of the aluminum impurity content in the liquid feed, a pH of 2.0 can achieve a better rare earth and aluminum separation effect.

[0028] Please see Figure 8 Examples 4 and 8 illustrate the comparison of single-stage back-extraction rates of medium and heavy rare earth elements between the P507-N235 system and the single P507 kerosene system; Figure 8 It can be seen that for most medium rare earth components, the single-stage back-extraction rates of the two extraction systems are not significantly different, and both can maintain a high level of back-extraction. Within the dashed box, the single-stage back-extraction rates of the three heavy rare earths, Tm, Yb, and Lu, are low in the single P507 system, with Yb's back-extraction rate being only about 42% and Lu's as low as about 31%, indicating that the back-extraction of heavy rare earths is extremely insufficient. However, after adopting the P507-N235 synergistic system, the back-extraction rate of heavy rare earths in this range is significantly improved, with Tm's back-extraction rate increasing from 64% to over 88%, and Yb and Lu's back-extraction rates increasing to over 60% and 39%, respectively. The synergistic system significantly improves the shortcoming of the difficulty in back-extracting heavy rare earths, and the recovery efficiency of heavy rare earths is significantly improved. It should be noted that, Figure 8 The dashed box in the middle defines the range of three difficult-to-re-extract heavy rare earth elements: Tm, Yb, and Lu.

[0029] Please see Figure 9 This reflects the impact of the P507-N235 system back-extraction ratio on the single-stage back-extraction rate of medium and heavy rare earth elements; through... Figure 9 It can be seen that, overall, as the back-extraction ratio gradually increases, the single-stage back-extraction rate of most heavy rare earth elements increases synchronously. The back-extraction rates of rare earths such as Tb, Dy, Ho, and Er can be stably maintained above 85% under all three ratios, with limited improvement. However, the heavy rare earths Tm, Yb, and Lu are more affected by the ratio change. The back-extraction rate of Lu is less than 50% when O / A = 1:1, but increases to 75% when O / A = 1:2. Tm and Yb also show a significant increase simultaneously. Adjusting the back-extraction ratio can solve the problem of low recovery rate of difficult-to-back-extract heavy rare earths.

[0030] Please see Figure 10 The results reflect the influence of the number of back-extractions on the back-extraction rate of medium and heavy rare earth elements in the P507-N235 system; through... Figure 10 It can be seen that the Sm, Eu, and Gd components can achieve a back-extraction rate of over 98% with only one back-extraction, essentially achieving complete back-extraction; the Tb, Dy, Ho, Er, and Y rare earth components all have a single back-extraction rate of over 95%, and can achieve complete back-extraction after two back-extractions; the Yb single back-extraction rate is only 57%, which increases to 97% after two back-extractions; Lu is the most difficult element to back-extract, with a single back-extraction rate of only 34%, but the total back-extraction rate increases to 75% after two back-extractions. Therefore, it is evident that the two-stage back-extraction process can significantly improve the recovery efficiency of difficult-to-back-extract heavy rare earth elements.

[0031] It should be noted that, Figure 10 The dashed box in the middle defines the range of three difficult-to-re-extract heavy rare earth elements: Tm, Yb, and Lu.

[0032] Furthermore, take the ammonium chloride rare earth feed solution A from the factory, with a pH of 1.76, a total rare earth content of approximately 2.77 g / L, and an aluminum content of approximately 0.82 g / L; The extractant was prepared by combining 30% P507 with different volume fractions of N235 (0%, 10%, 15%, 20% and 25%, respectively) and using kerosene as a diluent; then, the total organic phase volume was fixed and the ammonium chloride rare earth feed solution A was extracted at a ratio of 1:1 for 10 min in a single stage to obtain the raffinate. The elemental composition of the raffinate was determined, and then the organic phase was back-extracted for 10 min with 2 mol / L hydrochloric acid at a ratio of 1:1. The elemental composition of the back-extracted solution was determined, and the results are shown in Table 1 and Table 2. Tables 1 and 2 together verify the pre-grouping ability and aluminum removal effect of the P507-N235 synergistic system on light and heavy rare earth elements in actual plant feed solutions. Table 1 shows that the total proportion of light rare earth elements (La+Ce+Pr+Nd) in the original feed solution was 23.74%, Y was 44.70%, and medium and heavy rare earth elements (Sm~Lu+Y) totaled 76.26%. After single-stage extraction, as the N235 volume fraction increased from 0% to 25%, the La proportion in the raffinate increased from 10.14% in the original feed solution to over 31.59%, the Nd proportion increased from 20.90% to 26.98%, and Ce and Pr remained basically at the 4%–6% level, indicating that light rare earth elements were gradually enriched in the raffinate; medium and heavy rare earth elements were preferentially extracted into the organic phase. The aluminum concentration in the raffinate remained at 0.72–0.80 g / L, which was basically the same as that of the original feed (0.82 g / L), indicating that most of the aluminum was not extracted and remained in the raffinate aqueous phase.

[0033] As shown in Table 2, after back-extraction with 2 mol / L hydrochloric acid, the Y content in the back-extraction solution increased from 44.70% to 48.10%–57.87%, and the Dy content increased from 8.04% to 9.46%–10.45%, indicating effective enrichment of heavy rare earth elements. Meanwhile, the light rare earth element La decreased from 10.14% to 1.97%–3.89%, and Nd decreased from 9.33% to 4.95%–8.94%, further confirming the selective separation of light and heavy rare earth elements. More importantly, the aluminum concentration in the back-extraction solution decreased from 0.82 g / L to 0.01–0.12 g / L, with only 0.01 g / L under 15% N235 conditions, achieving an aluminum removal rate of over 98.8%. This fully demonstrates that this synergistic system can achieve a high degree of separation between rare earth elements and aluminum throughout the extraction-back-extraction process.

[0034] Combining Tables 1 and 2, single-stage extraction can achieve the initial grouping of light and heavy rare earth elements, while the back-extraction process further enriches Y and medium and heavy rare earth elements and significantly reduces the aluminum content, indicating that this synergistic system has the potential for industrial application.

[0035] Table 1. Comparison of N235 content in the organic phase with the fractionation of rare earth chloride feed solution A before and after extraction.

[0036] Table 2. Comparison of rare earth distribution results of the original and back-extraction aqueous phases of ammonium chloride rare earth feed solution A in the factory.

[0037] Furthermore, a multi-stage countercurrent extraction experiment was conducted using simulated rare earth chloride solution B (total rare earth content approximately 20.9 g / L, aluminum content approximately 3.8 g / L). The organic phase used was 30% P507 + 30% N235 + 40% kerosene. Figure 11 The diagram shows a three-stage countercurrent extraction process; the specific operating procedure is as follows: At a ratio of 1:1, rare earth chloride solution (A1) and blank organic phase (O1) were added to separatory funnel No. 1. After extraction equilibrium, the mixture was allowed to stand and separate into layers. The resulting raffinate aqueous phase was transferred to separatory funnel No. 2 and extracted with added O2. At the same time, A2 was added to separatory funnel No. 1 to continue extraction. After rebalancing, the organic phase in separatory funnel No. 2 is mixed with the raffinate aqueous phase produced in separatory funnel No. 1 for extraction. The raffinate aqueous phase is then transferred to separatory funnel No. 3 and O3 is added for extraction. At the same time, A3 is added to separatory funnel No. 1 for the next stage of extraction. Subsequently, the raffinate from each stage was collected, and the changes in the content of rare earth and aluminum elements were determined. The results are shown in Table 3. After a single-stage extraction, the proportions of La, Ce, Pr, and Nd in the raffinate of aqueous phase A1 increased from the initial 3.45%, 5.75%, 6.75%, and 6.16% to 20.90%, 24.19%, 19.93%, and 19.43%, respectively, while the proportion of heavy rare earth elements decreased to below 1%. Then, a new organic phase O2 was added for a second-stage extraction. The raffinate contained almost no Dy or subsequent heavy rare earth elements, but still contained small amounts of Sm, Eu, and Tb. After a third-stage extraction, a new organic phase O3 was added. The proportion of La in the raffinate reached 40.53%, while the proportions of Pr and Nd decreased. At this point, the raffinate contained only La, Ce, Pr, Nd, and a small amount of Gd. As the number of extraction stages increased, a small portion of the aluminum in the feed solution was extracted into the organic phase. For the newly added aqueous phase A2, the next stage of extraction was carried out with the organic phases O1, O2, and O3 in sequence. The results are shown in Table 4. The same pattern as in Result 1 is observed. The proportions of La, Ce, Pr, and Nd are all increased, while the proportions of Tb and subsequent rare earth elements decrease to almost nothing. This indicates that in this extraction system, through multi-stage extraction, preliminary grouping of light and heavy rare earth elements can be achieved on the basis of separating rare earth elements from aluminum.

[0038] Table 3. Results of rare earth fractionation and aluminum concentration in multi-stage countercurrent extraction of the P507-N235 system.

[0039] Table 4. Results of rare earth fractionation and aluminum concentration in multi-stage countercurrent extraction of the P507-N235 system.

[0040] Further, the rare earth concentrate from the factory was dissolved in deionized water at a solid-liquid ratio of 1:2, and then dissolved in 3 mol / L hydrochloric acid with stirring until the pH reached 2.0. Extraction and back-extraction were performed using an organic phase of 30% P507 combined with 20% N235, and the concentrations of rare earth and aluminum in the raffinate and back-extraction solution were determined. The separation coefficient was then calculated. The results are shown in Table 5. The concentration ratio of aluminum to rare earth elements in the original feed solution was 0.29. After single-stage extraction with P507-N235, it can be seen from the concentration of rare earth elements and aluminum in the raffinate that most of the rare earth elements were transferred to the organic phase, while most of the aluminum remained in the aqueous raffinate. After back-extraction, the concentration of aluminum in the back-extraction solution was only 0.11 g / L, and the concentration of rare earth elements was 17.98 g / L. At this time, the concentration ratio of aluminum to rare earth elements in the feed solution was 0.0061, which was about 47 times lower than that in the feed solution. The separation coefficient during the extraction process was 129.54. This extraction system played a role in separating aluminum and enriching rare earth elements.

[0041] Table 5. Extraction and back-extraction results of acid-dissolving rare earth aluminum material solution P507-235 from the plant enrichment.

[0042] Furthermore, a simulated rare earth chloride leaching solution was prepared, which contained 15 rare earth elements and aluminum; the concentration of each rare earth element was controlled at around 2.0 g / L, the total concentration of rare earth elements was 32.47 g / L, the concentration of aluminum was 5.50 g / L, and the pH of the leaching solution was adjusted to 2.0. The feed solution was subjected to single-stage extraction with P507-N235 to obtain an organic phase loaded with medium and heavy rare earth elements, and a raffinate containing light rare earth elements and aluminum was also obtained. Then, a second-stage extraction was performed using the organic phase N1923 to obtain an organic phase containing light and medium rare earth elements. The two organic phases were back-extracted using 2 mol / L HCl solution, and the fractionation of each aqueous phase was calculated. The results are shown in Tables 6 and 7. As can be seen from Table 6, the rare earth fractionation of the original feed solution is relatively uniform (approximately 5% to 7.5%). After primary extraction with P507-N235, the proportions of light rare earth elements La, Ce, Pr, and Nd in the raffinate significantly increased to 17.81%, 16.97%, 17.50%, and 19.21%, respectively, while the extraction rates of each light rare earth element were extremely low (La was almost unextracted, and the extraction rates of Ce, Pr, and Nd were 0.59%, 0.21%, and 1.40%, respectively), indicating that the light rare earth elements remained primarily in the aqueous raffinate phase. Conversely, the extraction rates of heavy rare earth elements Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y were as high as 92.98%, 96.62%, 98.07%, 98.44%, 98.71%, 99.69%, 99.65%, and 90.87%, respectively, and their proportions in the raffinate all decreased to below 1%. In the corresponding P507-N235 back-extraction solution, the total proportion of medium and heavy rare earth elements (Sm~Y) reached 73.02% (see Table 7), while light rare earth elements accounted for only 2.18%, and heavy rare earth elements (Tm+Yb+Lu) accounted for 24.80%, indicating that this stage of extraction is mainly enriched with medium and heavy rare earth elements.

[0043] Subsequently, the raffinate from P507-N235 (rich in light rare earth elements and a small amount of medium rare earth elements) was fed into the N1923 system for a second-stage extraction. As shown in Table 6, the extraction rates of light rare earth elements La, Ce, Pr, and Nd by N1923 were 5.59%, 3.83%, 7.38%, and 11.94%, respectively, with a total fraction of 63.44% after back-extraction (Table 7). Aluminum in the N1923 back-extraction solution was only 0.06 g / L, almost unextracted. Both stages of back-extraction achieved aluminum content below 0.06 g / L, with an aluminum removal rate exceeding 99%.

[0044] Table 7 further clarifies the grouping results: the P507-N235 back-extraction solution is mainly composed of medium and heavy rare earth elements (73.02%), while the N1923 back-extraction solution is mainly composed of light rare earth elements (63.44%). The two complement each other, achieving the separation of light rare earth elements from medium and heavy rare earth elements.

[0045] Table 6. Rare earth element composition of simulated rare earth chloride leachate two-stage extraction and back-extraction solutions

[0046] Table 7. Rare earth grouping and distribution of two-stage back-extraction liquids in the P507-N235 and N1923 systems.

[0047] Furthermore, a simulated rare earth sulfate leaching solution was prepared, which contained 15 rare earth elements and aluminum; the concentration of each rare earth element was controlled at about 1.0 g / L, of which the total concentration of rare earth elements was 13.2 g / L, the concentration of aluminum was 3.2 g / L, and the pH was adjusted to 2.0. The feed solution was subjected to single-stage extraction with the P507-N235 organic phase, and the raffinate was subjected to single-stage extraction with the N1923-isooctanol-kerosene system. Then, the two organic phases were back-extracted with 2 mol / L HCl to obtain pure rare earth feed solution. The rare earth element distribution and aluminum ion concentration of each solution were calculated, and the results are shown in Table 8. The extraction rates of the two stages are listed in Table 9. As can be seen from Table 8, the total rare earth element content of the original sulfuric acid solution was 13.2 g / L, and the rare earth elements were evenly distributed. After single-stage extraction with P507-N235, the extraction rates of light rare earth elements La, Ce, Pr, and Nd were extremely low (0.04%, 0.12%, 0.10%, and 0.01%, respectively), and their distribution in the raffinate increased from 8.05%, 7.02%, 7.01%, and 6.12% to 17.72%, 8.95%, 11.60%, and 11.58%, respectively. Meanwhile, the extraction rates of heavy rare earth elements Tm, Yb, Lu, and Y were as high as 97.66%, 98.62%, 99.02%, and 87.98%, respectively, and the raffinate contained almost no heavy rare earth elements. This trend is consistent with that of the chlorination system (Table 6), but the extraction rates of medium rare earth elements Sm to Gd by P507-N235 in the sulfuric acid system (1.24%–7.79%) are significantly lower than those in the chlorination system (41.71%–62.98%). The P507-N235 raffinate was subjected to a second-stage extraction with N1923. The results showed that N1923 significantly enhanced the extraction capacity of light rare earth elements (LREEs) in sulfuric acid medium: the extraction rates of La, Ce, Pr, and Nd reached 90.95%, 87.45%, 93.94%, and 91.83%, respectively, far exceeding the 5%–12% in the chlorination system (see Table 6). The N1923 back-extraction solution contained a total of 50.14% LREEs (see Table 9), 49.45% medium and heavy rare earth elements (Tm+Yb+Lu), and only 0.4% Tm+Yb+Lu, with an aluminum content of only 0.04 g / L. Meanwhile, in the P507-N235 back-extraction solution, Tm+Yb+Lu accounted for 39.22%, medium and heavy rare earth elements for 57.77%, and LREEs for only 3.01%.

[0048] Tables 8 and 9 together demonstrate that in the sulfate system, the extraction advantage of N1923 for light rare earth elements is amplified, forming a clearer division of labor with P507-N235. P507-N235 primarily extracts heavy rare earth elements, while N1923 primarily extracts light rare earth elements, and both back-extraction solutions achieve aluminum content below 0.08 g / L. This result verifies the design concept of the present invention, which allows for flexible adjustment of the extraction sequence based on the sulfate / chloride ratio of the feed solution.

[0049] Table 8. Distribution of rare earth elements in simulated rare earth sulfate leachate two-stage extraction and back-extraction solutions

[0050] Table 9. Rare earth grouping and distribution results of the two-stage back-extraction solution in the P507-N235 and N1923 systems.

[0051] Furthermore, the leachate from the rare earth concentrate H2SO4-HCl-Al2(SO4)3 system was used. The main components of the leachate were light rare earth and aluminum. The total rare earth concentration was about 29.41 g / L and the aluminum concentration was about 11.87 g / L. The feed solution was a polyaluminate strong acid feed solution. The feed solution was extracted in a single stage with the N1923-isooctanol-kerosene organic phase at a ratio of O:A=3:1. The raffinate was further extracted in a single stage with the P507-N235 organic phase. The two organic phases were back-extracted with 2 mol / L HCl to obtain two pure rare earth feed solutions with almost no aluminum, mainly composed of light rare earth and medium and heavy rare earth. The rare earth element composition and aluminum ion concentration in each solution are calculated and listed in Table 10. The extraction rates of the two stages are listed in Table 11. From Table 10, light rare earth elements (La+Ce+Pr+Nd total 90.66%) are the main components in the original feed solution, with an aluminum concentration as high as 11.87 g / L and a total rare earth element concentration of 29.41 g / L. After the first stage extraction using N1923-isooctanol-kerosene at a ratio O:A = 3:1, the extraction rates of La, Ce, Pr, and Nd reached 97.82%, 99.19%, 99.05%, and 99.34%, respectively. The total rare earth element concentration in the raffinate decreased to 0.38 g / L, indicating that most of the light rare earth elements had been extracted to the organic phase. Meanwhile, the aluminum concentration in the raffinate remained at 11.32 g / L, almost identical to the original 11.87 g / L, indicating that aluminum was hardly extracted by N1923. The total light rare earth content in the N1923 back-extraction solution reached 92.54% (see Table 11), while aluminum was only 0.19 g / L, with an aluminum removal rate of 98.4%.

[0052] The N1923 raffinate (mainly containing aluminum and a small amount of rare earth) was then subjected to a second-stage extraction using P507-N235. As shown in Table 10, this stage had a high extraction rate for the residual medium and heavy rare earths, such as Er, Tm, Yb, and Lu, with extraction rates of 82.62%, 92.12%, 99.82%, and 99.24%, respectively. In the back-extraction solution, Tm+Yb+Lu accounted for 45.43%, medium and heavy rare earths accounted for 52.45%, light rare earths accounted for only 2.12% (see Table 11), and aluminum accounted for only 0.08 g / L.

[0053] The synergistic results in Tables 10 and 11 show that when the concentration of rare earth sulfate in the feed solution is higher than that of rare earth chloride (i.e., high sulfate, high aluminum, and enrichment of light rare earth), the light rare earth is first extracted with N1923 and aluminum is removed simultaneously, and then the residual medium and heavy rare earth is recovered with P507-N235. This pre-coupling sequence can maximize the recovery rate of light rare earth while ensuring that the aluminum content of both stages of back-extraction solution is lower than 0.20 g / L. This verifies the rationality of the N1923 followed by synergistic extraction method in this invention when the rare earth sulfate concentration is high.

[0054] Table 10. Results of rare earth fractionation in the two-stage extraction and back-extraction solution of rare earth concentrate H2SO4-HCl-Al2(SO4)3 leachate.

[0055] Table 11. Rare earth grouping and distribution results of the two-stage back-extraction solution in the P507-N235 and N1923 systems.

[0056] Further, a simulated rare earth chloride leaching solution was prepared, containing 15 rare earth elements and aluminum. The concentration of each rare earth element was controlled at around 2.0 g / L, the total rare earth concentration was 32.47 g / L, the aluminum concentration was 5.50 g / L, and the pH was adjusted to 2.0. This solution was then subjected to single-stage extraction with the P507-N235 organic phase. The Cl- concentration in the raffinate was measured and calculated. The required sulfate (using magnesium sulfate) was calculated based on a sulfate to hydrochloride molar ratio of 1.2:1. The sulfate was added to the raffinate, and after uniform mixing, a protonated N1923-isooctanol-kerosene system was used for single-stage extraction. The two organic phases were back-extracted with 2 mol / L HCl to obtain two aluminum-free pure rare earth chloride solutions with light rare earth and medium-heavy rare earth as the main components. The rare earth element composition, aluminum ion concentration, and two-stage extraction rates of each solution are calculated and listed in Table 12. The rare earth element groupings are listed in Table 13. Table 12 shows that after the initial extraction with P507-N235, the extraction rates of light rare earth elements La, Ce, Pr, and Nd in the original chlorination solution (REO=32.47 g / L, Al=5.50 g / L) were extremely low, at 0.03%, 0.59%, 0.21%, and 1.40%, respectively. The extraction rates of heavy rare earth elements were all above 90%, consistent with the results in Table 6. The difference lies in the addition of magnesium sulfate (according to...) to the P507-N235 raffinate before the second-stage extraction. / A molar ratio of 1.2:1 was used to change the system from chloride-dominated to sulfate-dominated. Subsequent secondary extraction with N1923 showed that the extraction rates of light rare earth elements (La, Ce, Pr, and Nd) increased to 98.21%, 97.11%, 95.54%, and 93.21%, respectively, significantly higher than the extraction rates of light rare earth elements by N1923 (5.59%–11.94%) without sulfate addition, as shown in Table 6. This indicates that the introduction of sulfate significantly improved the extraction capability of N1923 for light rare earth elements.

[0057] In the N1923 back-extraction solution, the total light rare earth element content reached 76.49% (see Table 13), medium and heavy rare earth elements accounted for 23.30%, Tm+Yb+Lu accounted for only 0.21%, and aluminum was only 0.02 g / L; while in the P507-N235 back-extraction solution, medium and heavy rare earth elements accounted for 73.02%, Tm+Yb+Lu accounted for 24.8%, light rare earth elements accounted for only 2.18%, and aluminum was only 0.03 g / L. Both back-extraction solutions achieved an aluminum content of less than 0.03 g / L, with an aluminum removal rate exceeding 99.9%.

[0058] Tables 12 and 13 together demonstrate that by adding sulfate to the raffinate to change the medium composition, the extraction performance of N1923 for light rare earth elements can be improved. Thus, without changing the extractant formulation, the separation performance can be changed simply by adjusting the salt addition, allowing the same extraction system to handle both chlorination and sulfuric acid systems.

[0059] Table 12. Distribution of rare earth elements in simulated rare earth leachate after two-stage extraction with sulfate and back-extraction solution.

[0060] Table 13. Rare earth grouping and distribution results of the two-stage back-extraction solution in the P507-N235 and N1923 systems.

[0061] Comparative Example 1 This comparative study provides a method for processing rare earth materials that differs from the present invention, the method comprising the following steps: A mixed extractant was prepared according to a volume ratio of P204∶P507∶TBP∶2-octanol∶sulfonated kerosene = 15∶3∶2∶3∶77; 1+1 hydrochloric acid was added to the mixed extractant for pretreatment, with the amount of hydrochloric acid being 1 / 4 of the volume of the mixed extractant, and the acid washing time being 15 minutes. After that, it was repeatedly washed with pure water until there was no residual acidity. The pretreated mixed extractant was mixed with 6 mol / L ammonia water for saponification, and the degree of saponification was controlled to be 0.1. After saponification, it was left to stand for later use. Take the workshop's primary slag return liquid II (pH 2.5, rare earth concentration 0.55 mol / L, iron 0.12 g / L, aluminum 15.32 g / L, fluorine 397 μg / ml) with high fluorine, aluminum and low rare earth content as the high fluorine, aluminum and low rare earth content solution; then adjust the acidity of the high fluorine, aluminum and low rare earth content solution to 0.15 mol / L with 1+1 hydrochloric acid, then add 12.5% ​​N235 + 12.5% ​​isooctyl alcohol + kerosene extractant, stir for 5 min to 10 min, and then adjust the pH to 2.0 with 8 mol / L ammonia water to obtain the pretreated solution; The saponified synergistic extraction system and the pretreated feed solution were fed into the extraction tank. The extraction temperature was controlled at 45℃. The extraction was carried out by a three-stage cascade countercurrent extraction method with an organic phase to aqueous phase volume ratio of O / A = 10:1. After extraction, the raffinate containing high fluorine aluminum and low rare earth elements and the organic phase loaded with rare earth elements were separated. Countercurrent back-extraction was performed by introducing 8 mol / L hydrochloric acid into the organic phase loaded with rare earth elements. The back-extraction was performed 2 to 3 times, and the back-extraction solution was collected to obtain a high-concentration rare earth solution. Add solid oxalic acid at 2.5 times the theoretical amount according to the total amount of residual rare earth, stir at 40℃ for 30 min to form rare earth oxalate precipitate of residual rare earth, filter and recover the precipitate to complete the recovery of residual rare earth.

[0062] Comparative Example 2 This comparative study provides a method for processing rare earth materials that differs from the present invention, the method comprising the following steps: Take the hydrochloric acid leaching solution of rare earth concentrate: aluminum content 0.944 g / L (calculated as Al2O3), rare earth content 84 g / L (calculated as REO), and solution pH=1.5.

[0063] 100 mL of the leachate was transferred to a 300 mL Erlenmeyer flask and then placed in a water bath with a magnetic stirrer. 0.712 g of cyclohexanecarboxylic acid was weighed, dissolved in 10 mL of ethanol, and slowly added to the Erlenmeyer flask with constant temperature stirring at 50 °C. After the addition was completed and the mixture was stirred evenly, 10% NaOH or other alkaline solution was added to slowly adjust the pH of the rare earth solution to 3.5. After stirring for 5 min, the mixture was vacuum filtered to obtain the precipitate and filtrate.

[0064] Comparative Example 3 This comparative study provides a method for processing rare earth materials that differs from the present invention, the method comprising the following steps: Take a rare earth hydrochloric acid leaching solution with an aluminum content of 3.036 g / L, a rare earth content of 5 g / L, and a solution pH of 0.5.

[0065] 50 mL of rare earth leachate was transferred to a 300 mL Erlenmeyer flask and placed in a magnetically stirred constant-temperature water bath. 2.482 g of glutamic acid was weighed and slowly added to the Erlenmeyer flask at a constant temperature of 40 °C with stirring. After the addition was completed and the mixture was stirred evenly, ammonia-ammonium chloride buffer solution was added to slowly adjust the pH of the rare earth solution to 4.5. After stirring for 20 min, 10 mL of Triton X-114 was added. The temperature was maintained at 40 °C and stirred for 10 min. After extraction and phase separation, the equilibrium time was 10 min. The extraction and phase separation yielded an aluminum-containing organic phase and a rare earth solution after aluminum removal.

[0066] Please refer to Table 14, which shows the comparison data of aluminum removal rates between the comparative examples and the embodiments of the present invention. As can be seen from Table 14, comparative examples 1 to 3 respectively cover three typical rare earth aluminum removal methods in the prior art, namely, five-component synergistic extraction method, cyclohexane carboxylic acid complex precipitation method and complexation-turbidity point extraction method. Among them, Comparative Example 1 uses a five-component synergistic extraction system, which can achieve a separation efficiency of more than 90% between rare earth and fluorine-aluminum. However, the composition of the extractant is relatively complex and it needs to be pretreated with hydrochloric acid and saponified with ammonia. The extraction ratio is 10:1. Back-extraction uses 8 mol / L hydrochloric acid. The residual rare earth in the raffinate needs to be precipitated and recovered with oxalic acid. Comparative Example 2 uses cyclohexane carboxylic acid complex precipitation, which can remove aluminum at a rate of over 90% and reduce rare earth loss to no more than 5%. However, this method is an intermittent operation and produces aluminum-containing precipitate waste residue. Comparative Example 3 uses the complexation-cloud point extraction method, which can achieve an aluminum extraction rate of over 70% and a rare earth extraction rate of no more than 6%, but requires the use of amino acid complexing agents and nonionic surfactants. All three methods mentioned above primarily aim at separating rare earth elements from aluminum, but they do not yet address the pre-grouping of light, medium, and heavy rare earth elements or the transition from sulfate systems to chloride systems. Based on the aforementioned prior art, this invention utilizes a combined process of P507-N235 synergistic extraction and N1923-isooctanol-kerosene coupled extraction to achieve highly efficient separation of rare earth elements and aluminum under mild conditions with a ratio of O / A of 1:1 and without the need for saponification (the separation coefficient between heavy rare earth elements and aluminum can reach up to 6000, and the aluminum in the back-extraction solution can be reduced to 0.01~0.12 g / L). Furthermore, the coupled extraction with N1923 achieves a comprehensive recovery rate of over 90% for light rare earth elements, uses a low concentration of back-extraction acid, and has a simple process. Simultaneously, it realizes the pre-grouping of light, medium, and heavy rare earth elements and the transformation from a sulfate system to a chloride system in the same process, providing a more integrated and efficient technical solution for the field of rare earth hydrometallurgy.

[0067] Table 14. Comparison of aluminum removal rates between comparative examples and embodiments of the present invention.

[0068] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0069] 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 synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum, characterized in that, The method includes the following steps: Determine the relative concentrations of rare earth sulfate and rare earth chloride in the aqueous feed solution; When the concentration of rare earth sulfate is lower than that of rare earth chloride, the first extraction sequence is executed: first, the medium and heavy rare earths are extracted using the extractant, and then the light rare earths are extracted using N1923-isooctanol-kerosene. When the concentration of rare earth sulfate is higher than that of rare earth chloride, the second extraction sequence is performed: first, light rare earth is extracted using N1923-isooctanol-kerosene, and then medium and heavy rare earth is extracted using an extractant; the organic phase loaded with medium and heavy rare earth and the organic phase loaded with light rare earth are back-extracted with hydrochloric acid to obtain light rare earth, medium rare earth, medium and heavy rare earth and thulium-ytterbium-lutetium heavy rare earth products.

2. The method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum according to claim 1, characterized in that, The process involves first extracting the medium and heavy rare earth elements using an extractant, and then extracting the light rare earth elements using N1923-isooctanol-kerosene. The specific steps are as follows: Step 1: Extract the aqueous phase solution using an extractant to obtain an organic phase loaded with heavy rare earth ions, a first part of light rare earth, a first part of medium rare earth and aluminum raffinate aqueous phase. Step 2: The organic phases loaded with medium and heavy rare earth ions were backwashed and back-extracted using hydrochloric acid of different concentrations to obtain medium and heavy rare earth elements and thulium, ytterbium, and lutetium heavy rare earth elements, respectively. Step 3: Use N1923-isooctanol-kerosene to couple extract the raffinate aqueous phase of light and medium rare earth elements and aluminum to obtain the organic phases of light and medium rare earth elements; use hydrochloric acid to backwash and backextract the organic phases of light and medium rare earth elements to obtain the second part of light rare earth elements and the second part of medium rare earth elements, respectively.

3. The method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum according to claim 2, characterized in that, The process involves first extracting light rare earth elements using N1923-isooctanol-kerosene, followed by extracting medium and heavy rare earth elements using an extractant. The organic phases loaded with medium and heavy rare earth elements and those loaded with light rare earth elements are then back-extracted with hydrochloric acid to obtain light rare earth, medium rare earth, medium and heavy rare earth, and thulium-ytterbium-lutetium heavy rare earth products. The specific steps are as follows: Step 1: Extract the aqueous phase solution using N1923-isooctanol-kerosene to obtain the rare earth-loaded organic phase; Step 2: Use hydrochloric acid to back-extract the organic phase loaded with rare earth elements to obtain a mixed medium and heavy rare earth chloride solution and light rare earth elements. Step 3: Extract the mixed medium and heavy rare earth chloride solution with an extractant to obtain an extractable organic phase loaded with medium and heavy rare earths; Step 4: Use hydrochloric acid of different concentrations to backwash and back-extract the organic phases loaded with medium and heavy rare earth elements to obtain medium and heavy rare earth elements and thulium-ytterbium-lutetium heavy rare earth elements, respectively.

4. The method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum according to claim 3, characterized in that, The extractant is prepared from P507, N235 and sulfurized kerosene, wherein the volume fraction of P507 is 30%, the volume fraction of N235 ranges from 0 to 30%, the diluent is sulfonated kerosene, and the synergistic extraction ratio O / A ranges from 1:2 to 2:

1.

5. The method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum according to claim 4, characterized in that, The pH range of the aqueous phase feed solution is 0.5~2.5, the temperature range of the synergistic extraction is 0~55℃, and the shaking time is 10min.

6. The method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum according to claim 5, characterized in that, The organic phase loaded with medium and heavy rare earth ions was backwashed and back-extracted using hydrochloric acid of different concentrations. The concentration of hydrochloric acid used in the first backwash and back-extraction was 1.0-2.0 mol / L, and the back-extraction time was 10 min. The concentration of hydrochloric acid used in the second backwash and back-extraction was 4.0-5.0 mol / L, and the back-extraction time was 10 min.

7. The method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum according to claim 6, characterized in that, In the process of backwashing and back-extracting the organic phases of light and medium rare earth elements using hydrochloric acid, the concentration of hydrochloric acid ranges from 0.1 to 2 mol / L.

8. The method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum according to claim 7, characterized in that, In the N1923-isooctanol-kerosene mixture, the ratio of N1923, isooctanol, and kerosene is 2:1:

7.

9. The method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum according to claim 8, characterized in that, In the process of back-extracting the organic phase loaded with rare earth elements using hydrochloric acid, the concentration of hydrochloric acid ranges from 0.1 to 2 mol / L.

10. The method for synergistic-coupled extraction and separation of light, medium, and heavy rare earth elements and aluminum according to claim 9, characterized in that, The medium and heavy rare earth elements are enrichments of samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, or yttrium.

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