A eutectic extractant and its application in extracting and purifying yttrium element

Abstract

This invention relates to the field of rare earth element separation, and discloses a method for preparing a eutectic extractant and extracting and purifying yttrium. The eutectic extractant prepared by this invention has low water solubility and low viscosity. The extraction process does not require saponification treatment or dilution with organic solvents. It has strong extraction ability for rare earth elements, good selectivity, and is easy to prepare. It achieves efficient and green separation and purification of yttrium without saponification or solvents, without generating saponification wastewater, and with low separation cost.

Description

Technical Field

[0001] This invention relates to the field of rare earth element separation, specifically to a eutectic extractant and its application in the extraction and purification of yttrium. Background Technology

[0002] Currently, the primary process for purifying yttrium is saponification using naphthenic acid extraction. Naphthenic acids require saponification with alkalis, such as ammonia, during yttrium extraction. This process generates large amounts of saponification wastewater with high levels of ammonia nitrogen and salts, making it difficult to treat. Furthermore, naphthenic acids are byproducts of the petroleum industry, exhibiting complex compositions. Significant differences in composition exist between naphthenic acids produced by different manufacturers, leading to varying separation performance during yttrium extraction. This necessitates re-evaluating process conditions, increasing the complexity of the process. Moreover, saponified naphthenic acids are prone to emulsification after extraction, resulting in substantial losses due to their water solubility. Frequent replenishment of fresh naphthenic acids is required to maintain the extraction capacity of the organic phase. The water-soluble naphthenic acids not only pollute water bodies but also increase production costs. Therefore, some novel extractants and extraction processes have been used for the separation and purification of yttrium. For example, the patent document "A Method for Separating Rare Earth Elements" (CN113430373A) reports the use of N,N-dialkylaminocarboxylic acid compounds as extractants for the separation of rare earth elements. This extractant can separate and purify yttrium from mixed rare earth solutions. In addition, phenoxyacetic acid extractants such as CA12 and CA100 have also been used for the separation and purification of yttrium. However, the carboxylic acid extractants used above cannot avoid the problem of saponification. The separation coefficients of yttrium and heavy rare earth elements by phenoxycarboxylic acid extractants such as CA12 and CA100 are not high enough, and the use of volatile and toxic organic solvents as diluents for extraction is also unavoidable. Summary of the Invention

[0003] To improve the above-mentioned technical problems, the present invention provides a eutectic extractant, comprising a hydrogen bond donor, a hydrogen bond acceptor, and a co-extractant;

[0004] According to embodiments of the present invention, the hydrogen bond donor includes, but is not limited to, one, two, or more of long-chain fatty acids and their derivatives, drug derivatives such as ibuprofen and gemfibrozil, and long-chain dicarboxylic acids; for example, 2-hexyldecanoic acid, decanoic acid, oleic acid, lauryl iodide, and sebacic acid.

[0005] According to embodiments of the present invention, the hydrogen bond acceptor includes, but is not limited to, one, two, or more of the following: long-chain alcohols, long-chain phenols, sulfonic acids, diketones, pyridine carboxylates, hydroxyquinoline, aldoximes, ketooximes, long-chain fatty acids, amides, ibuprofen, gemfibrozil, lecithin, long-chain alkyl phosphates, long-chain alkyl hypophosphite, primary amines, tertiary amines, secondary amines, hydrophobic quaternary phosphine salts, hydrophobic quaternary ammonium salts, and tributyl phosphate (TBP); for example, decanol and dodecanol.

[0006] According to embodiments of the present invention, the co-extractant includes, but is not limited to, one, two, or more of the following: primary amines (such as primary amine N1923, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, etc.), secondary amines (di-n-hexylamine, di-n-octylamine, diisooctylamine, etc.), tertiary amines (N235, trioctylamine, tri(dodecyl)amine, etc.), lidocaine, 1,8-bis(dimethylaminonaphthalene, etc.).

[0007] According to an embodiment of the present invention, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:(0.1-20); for example, it is 1:(0.5-10); exemplary ratios are 1:1, 1:2, 1:3, 1:4, 1:5, and 1:9.

[0008] According to an embodiment of the present invention, the co-extractant accounts for 1%-100% of the total volume of the hydrogen bond donor and hydrogen bond acceptor, for example 5%-50%, 10%-30%, and exemplarily 20%.

[0009] The present invention also provides a method for preparing the eutectic extractant, comprising the following steps: mixing the hydrogen bond donor, the hydrogen bond acceptor and the co-extractor to obtain the eutectic extractant; preferably, mixing the hydrogen bond donor and the hydrogen bond acceptor to obtain a eutectic mixture, and then mixing it with the co-extractor for activation to obtain the eutectic extractant;

[0010] According to an embodiment of the present invention, the activation method includes, but is not limited to, one, two or more of the following: direct mixing, heating, mechanical stirring, mechanical grinding, ultrasonication, microwave, ultraviolet irradiation.

[0011] The present invention also provides the application of the eutectic extractant in the extraction and purification of rare earth elements, such as yttrium.

[0012] The present invention also provides a method for extracting and purifying rare earth elements, comprising mixing the eutectic extractant with a rare earth solution for extraction.

[0013] The present invention also provides a method for extracting and purifying yttrium, comprising mixing the eutectic extractant with a rare earth solution containing yttrium for extraction.

[0014] According to an embodiment of the present invention, the extraction includes mixing the eutectic extractant with a rare earth solution and performing multi-stage extraction, washing, and / or back-extraction; after extraction, an aqueous raffinate phase and a loaded eutectic extractant organic phase are obtained; the aqueous raffinate phase is a difficult-to-extract rare earth element and / or a high-purity yttrium element, and the loaded eutectic extractant organic phase is washed and back-extracted to obtain an easily extractable rare earth element solution and / or a rare earth precipitate.

[0015] According to an embodiment of the present invention, the rare earth solution is a leaching solution or enrichment solution of ionic rare earth ore, a leaching solution of mineral rare earth ore, or a leaching solution of secondary resources containing rare earth elements.

[0016] According to an embodiment of the present invention, the pH value of the rare earth solution is 1 to 6, preferably 2 to 6, for example, pH value 3;

[0017] According to an embodiment of the present invention, the washing liquid used in the washing process is one or more of deionized water, hydrochloric acid, sulfuric acid, nitric acid, short-chain organic acids (such as formic acid, acetic acid, citric acid, lactic acid, malic acid, etc.) and organic acid salts, EDTA, etc. Preferably, the concentration of hydrochloric acid, sulfuric acid, nitric acid, short-chain organic acids (such as formic acid, acetic acid, citric acid, lactic acid, malic acid, etc.) and organic acid salts, EDTA is 0.01 mol / L to 2 mol / L.

[0018] According to an embodiment of the present invention, the stripping agent used in the stripping process is one or more of the following: deionized water, ammonium fluoride, ammonium bifluoride, sodium fluoride, sodium oxalate, oxalic acid, hydrochloric acid, sulfuric acid, nitric acid, short-chain organic acids (such as formic acid, acetic acid, citric acid, lactic acid, malic acid, etc.) and organic acid salts, EDTA, etc. Preferably, the concentration of ammonium fluoride, ammonium bifluoride, sodium fluoride, sodium oxalate, oxalic acid, hydrochloric acid, sulfuric acid, nitric acid, short-chain organic acids (such as formic acid, acetic acid, citric acid, lactic acid, malic acid, etc.) and organic acid salts, EDTA is 0.01 mol / L to 6 mol / L.

[0019] According to an embodiment of the present invention, the volume ratio of the eutectic extractant to the rare earth solution is 1:10 to 10:1, for example, 1:1; the volume ratio of the washing liquid or back-extraction liquid to the eutectic extractant is 1:10 to 10:1.

[0020] In addition, the reagents used in this invention are all commercially available products or can be prepared according to known corresponding methods. The preparation method of the eutectic extractant is simple, does not require additional saponification treatment, avoids the additional costs and post-processing steps caused by the use of alkali, and does not require the use of flammable, volatile and toxic organic solvents as diluents, thus combining economy, environmental protection and safety.

[0021] Beneficial effects

[0022] This invention prepares a novel eutectic extractant that effectively improves the extraction rate and separation coefficient of heavy rare earth elements and yttrium. Compared with traditional extractants such as naphthenic acids for rare earth element separation, it has advantages such as low water solubility, no need for saponification treatment, no need for diluents, saving raw materials, low cost, recyclability, good rare earth element separation effect, high rare earth extraction rate, low pollution, no emulsification during the extraction process, and wide availability of raw materials. It avoids the additional costs and post-processing steps caused by the use of alkali, and does not require the use of flammable, volatile, and toxic organic solvents as diluents, thus combining economy, environmental protection, and safety. Furthermore, the eutectic extractant described in this invention is designable and adjustable; its composition can be adjusted according to the solution composition and element concentration, thereby achieving efficient separation of rare earth elements.

[0023] Terminology Definitions and Explanations

[0024] The term "long chain" refers to a straight-chain or branched hydrocarbon group (such as alkyl, alkenyl or alkynyl) having 2-40 carbon atoms, preferably a straight-chain or branched hydrocarbon group having 5-20 carbon atoms; more preferably a straight-chain or branched hydrocarbon group having 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18 carbon atoms. Detailed Implementation

[0025] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0026] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0027] Example 1:

[0028] Preparation of eutectic extractants

[0029] First, hydrogen bond acceptor decanol and hydrogen bond donor 2-hexyldecanoic acid were weighed in a molar ratio of 1:1, heated to 40°C, and mixed and stirred for 30 minutes to obtain a eutectic mixture. Then, diisooctylamine, a co-extractant accounting for 20% of the volume fraction of the eutectic mixture, was added and ultrasonically activated at room temperature to obtain a eutectic extractant, which is a low-viscosity liquid at room temperature.

[0030] Extraction and separation of rare earth elements using eutectic extractants

[0031] The concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y in the rare earth solution were all 0.002 mol / L, and the initial pH value was 2.9.

[0032] The prepared eutectic extractant was mixed with a rare earth solution for single-stage extraction at a volume ratio of 1:1. The extraction rates of each rare earth element are shown in Table 1, and the separation coefficients are shown in Table 2. The eutectic extractant can effectively extract rare earth elements without saponification or solvents, and the separation effect is good. The separation coefficient for Ho / Y reaches 2.57, and the separation coefficient for Er / Y reaches 2.91. Through multi-stage extraction, the separation of heavy rare earth elements and yttrium can be achieved, thus purifying yttrium.

[0033] Table 1 Extraction rate of rare earth elements

[0034]

[0035] Table 2 Separation coefficients of heavy rare earth elements and yttrium

[0036]

[0037] Example 2:

[0038] Preparation of eutectic extractants

[0039] First, hydrogen bond acceptor decanol and hydrogen bond donor 2-hexyldecanoic acid were weighed at a molar ratio of 2:1, heated to 40°C, and mixed and stirred for 30 minutes to obtain a eutectic mixture. Then, diisooctylamine, a co-extractant accounting for 20% of the volume fraction of the eutectic mixture, was added and ultrasonically activated at room temperature to obtain a eutectic extractant, which is a low-viscosity liquid at room temperature.

[0040] Extraction and separation of rare earth elements using eutectic extractants

[0041] The concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y in the rare earth solution were all 0.002 mol / L, and the initial pH value was 2.9.

[0042] The prepared eutectic extractant was mixed with a rare earth solution for single-stage extraction at a ratio of 1:1. The extraction rates of each rare earth element are shown in Table 3, and the separation coefficients are shown in Table 4. The eutectic extractant does not require saponification treatment and has a high extraction rate of rare earth elements. The separation coefficient for Ho / Y reaches 2.06, and the separation coefficient for Er / Y reaches 2.39. Through multi-stage extraction, the separation of heavy rare earth elements and yttrium can be achieved, thus purifying yttrium.

[0043] Table 3 Extraction rates of rare earth elements

[0044]

[0045] Table 4 Separation coefficients of heavy rare earth elements and yttrium

[0046]

[0047] Example 3:

[0048] Preparation of eutectic extractants

[0049] First, hydrogen acceptor decanol and hydrogen bond donor 2-hexyldecanoic acid were weighed at a molar ratio of 3:1, heated to 40°C, and mixed and stirred for 30 minutes to obtain a eutectic mixture. Then, diisooctylamine, a co-extractant accounting for 20% of the volume fraction of the eutectic mixture, was added and ultrasonically activated at room temperature to obtain a eutectic extractant, which is a low-viscosity liquid at room temperature.

[0050] Extraction and separation of rare earth elements using eutectic extractants

[0051] The concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y in the rare earth solution were all 0.002 mol / L, and the initial pH value was 2.9.

[0052] The prepared eutectic extractant was mixed with a rare earth solution for single-stage extraction at a ratio of 1:1. The extraction rates of each rare earth element are shown in Table 5, and the separation coefficients are shown in Table 6. The eutectic extractant does not require saponification or diluent and maintains a low viscosity after extraction of rare earth elements. The rare earth element extraction rate is high, with single-stage extraction rates of heavy rare earth elements exceeding 50%. The separation coefficients for Ho / Y reach 2.14, Er / Y reach 2.56, and Lu / Y reach 4.37, which are higher than those for naphthenic acid and CA12 extractants. Through multi-stage extraction, the separation of heavy rare earth elements and yttrium can be achieved, thus purifying yttrium.

[0053] Table 5 Extraction rates of rare earth elements

[0054]

[0055] Table 6 Separation coefficients of heavy rare earth elements and yttrium

[0056]

[0057] Example 4:

[0058] Preparation of eutectic extractants

[0059] First, hydrogen bond acceptor decyl alcohol and hydrogen bond donor 2-hexyldecanoic acid were weighed at a molar ratio of 4:1, heated to 40°C, and mixed and stirred for 30 minutes to obtain a eutectic mixture. Then, diisooctylamine, a co-extractant accounting for 20% of the volume fraction of the eutectic mixture, was added and ultrasonically activated at room temperature to obtain a eutectic extractant, which is a low-viscosity liquid at room temperature.

[0060] Extraction and separation of rare earth elements using eutectic extractants

[0061] The concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y in the rare earth solution were all 0.002 mol / L, and the initial pH value was 2.9.

[0062] The prepared eutectic extractant was mixed with a rare earth solution for single-stage extraction at a ratio of 1:1. The extraction rates of each rare earth element are shown in Table 7, and the separation coefficients are shown in Table 8. The eutectic extractant does not require saponification or diluent and maintains a low viscosity after extraction of rare earth elements. The rare earth element extraction rates are high, with single-stage extraction rates of heavy rare earth elements exceeding 60%, while the extraction rate of yttrium is 46.6%. The separation coefficients for Ho / Y reach 2.06, Er / Y reach 2.41, and Lu / Y reach 4.16. The separation coefficients for both heavy rare earth elements and yttrium are higher than those for naphthenic acid and CA12 extractants. Through multi-stage extraction, the separation of heavy rare earth elements and yttrium can be achieved, thus purifying yttrium.

[0063] Table 7 Extraction rates of rare earth elements

[0064]

[0065] Table 8 Separation coefficients of heavy rare earth elements and yttrium

[0066]

[0067] Example 5:

[0068] Preparation of eutectic extractants

[0069] First, hydrogen bond acceptor decyl alcohol and hydrogen bond donor decanoic acid are weighed at a molar ratio of 5:1, heated to 40°C, and mixed and stirred for 30 minutes to obtain a eutectic mixture. Then, diisooctylamine, a co-extractant accounting for 20% of the volume fraction of the eutectic mixture, is added and ultrasonically activated at room temperature to obtain a eutectic extractant, which is a low-viscosity liquid at room temperature.

[0070] Extraction and separation of rare earth elements using eutectic extractants

[0071] The concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y in the rare earth solution were all 0.002 mol / L, and the initial pH value was 2.9.

[0072] The prepared eutectic extractant was mixed with a rare earth solution for single-stage extraction at a ratio of 1:1. The extraction rates of each rare earth element are shown in Table 9, and the separation coefficients are shown in Table 10. The eutectic extractant does not require saponification or diluent and maintains a low viscosity after extraction of rare earth elements. The extraction rates of rare earth elements are high, with single-stage extraction rates of heavy rare earth elements exceeding 60%, while the extraction rate of yttrium is 44.6%. The separation coefficients for Ho / Y reach 2.07, Er / Y reach 2.35, and Lu / Y reach 4.12. The separation coefficients for both heavy rare earth elements and yttrium are higher than those for naphthenic acid and CA12 extractants. Through multi-stage extraction, the separation of heavy rare earth elements and yttrium can be achieved, thus purifying yttrium.

[0073] Table 9 Extraction rates of rare earth elements

[0074]

[0075] Table 10 Separation coefficients of heavy rare earth elements and yttrium

[0076]

[0077] Example 6:

[0078] Preparation of eutectic extractants

[0079] First, hydrogen bond acceptor dodecanol and hydrogen bond donor 2-hexyldecanoic acid were weighed at a molar ratio of 4:1, heated to 40°C, and mixed and stirred for 30 minutes to obtain a eutectic mixture. Then, diisooctylamine, a co-extractant accounting for 20% of the volume fraction of the eutectic mixture, was added and ultrasonically activated at room temperature to obtain a eutectic extractant, which is a low-viscosity liquid at room temperature.

[0080] Extraction and separation of rare earth elements using eutectic extractants

[0081] The concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y in the rare earth solution were all 0.002 mol / L, and the initial pH value was 2.9.

[0082] The prepared eutectic extractant was mixed with a rare earth solution for single-stage extraction at a ratio of 1:1. The extraction rates of each rare earth element are shown in Table 11, and the separation coefficients are shown in Table 12. The eutectic extractant does not require saponification or diluent and maintains a low viscosity after extraction of rare earth elements. The rare earth element extraction rates are high, with single-stage extraction rates of heavy rare earth elements exceeding 50%, while the extraction rate of yttrium is 38.6%. The separation coefficients for Ho / Y reach 2.02, Er / Y reach 2.36, and Lu / Y reach 4.30. The separation coefficients for both heavy rare earth elements and yttrium are higher than those for naphthenic acid and CA12 extractants. Through multi-stage extraction, the separation of heavy rare earth elements and yttrium can be achieved, thus purifying yttrium.

[0083] Table 11 Extraction rates of rare earth elements

[0084]

[0085] Table 12 Separation coefficients of heavy rare earth elements and yttrium

[0086]

[0087] Example 7:

[0088] Preparation of eutectic extractants

[0089] First, dodecanol, the hydrogen bond acceptor, and oleic acid, the hydrogen bond donor, are weighed at a molar ratio of 4:1. The mixture is heated to 35°C and stirred for 30 minutes to obtain a eutectic mixture. Then, diisooctylamine, a co-extractant accounting for 20% of the volume fraction of the eutectic mixture, is added and ultrasonically activated at room temperature to obtain a eutectic extractant, which is a low-viscosity liquid at room temperature.

[0090] Extraction and separation of rare earth elements using eutectic extractants

[0091] The concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y in the rare earth solution were all 0.002 mol / L, and the initial pH value was 2.9.

[0092] The prepared eutectic extractant was mixed with a rare earth solution for single-stage extraction at a ratio of 1:1. The extraction rates of each rare earth element are shown in Table 13, and the separation coefficients are shown in Table 14. The eutectic extractant does not require saponification or diluent and maintains a low viscosity after extraction of rare earth elements. The rare earth element extraction rates are high, with single-stage extraction rates of heavy rare earth elements exceeding 80%, while the extraction rate of yttrium is 73.1%. The separation coefficients for Ho / Y reach 1.97, Er / Y reach 1.99, and Lu / Y reach 2.92. The separation coefficients for heavy rare earth elements and yttrium are comparable to those for naphthenic acid and CA12 extractants. Through multi-stage extraction, the separation of heavy rare earth elements and yttrium can be achieved, thus purifying yttrium.

[0093] Table 13 Extraction rates of rare earth elements

[0094]

[0095] Table 14 Separation coefficients of heavy rare earth elements and yttrium

[0096]

[0097] Example 8:

[0098] Preparation of eutectic extractants

[0099] First, dodecanol, the hydrogen bond acceptor, and oleic acid, the hydrogen bond donor, are weighed at a molar ratio of 4:1. The mixture is heated to 35°C and stirred for 30 minutes to obtain a eutectic mixture. Then, co-extractant N1923, which accounts for 20% of the volume fraction of the eutectic mixture, is added and ultrasonically activated at room temperature to obtain a eutectic extractant, which is a low-viscosity liquid at room temperature.

[0100] Extraction and separation of rare earth elements using eutectic extractants

[0101] The concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y in the rare earth solution were all 0.002 mol / L, and the initial pH value was 2.9.

[0102] The prepared eutectic extractant was mixed with a rare earth solution for single-stage extraction at a ratio of 1:1. The extraction rates of each rare earth element are shown in Table 15, and the separation coefficients are shown in Table 16. The eutectic extractant does not require saponification or diluent and maintains a low viscosity after extraction of rare earth elements. The rare earth element extraction rates are high, with single-stage extraction rates of heavy rare earth elements exceeding 80%, while the extraction rate of yttrium is 72.2%. The separation coefficients for Ho / Y, Er / Y, and Lu / Y reach 1.97 and 2.83, respectively. The separation coefficients for heavy rare earth elements and yttrium are comparable to those for naphthenic acid and CA12 extractants. Through multi-stage extraction, the separation of heavy rare earth elements and yttrium can be achieved, thus purifying yttrium.

[0103] Table 15 Extraction rates of rare earth elements

[0104]

[0105] Table 16 Separation coefficients of heavy rare earth elements and yttrium

[0106]

[0107] Example 9:

[0108] The eutectic extractant prepared in Example 8 was used to purify yttrium from a yttrium-rich solution of a southern ionic rare earth ore deposit (Longnan, Ganzhou). The total rare earth concentration was 0.2 mol / L, with yttrium purity of 87.88% and heavy rare earth elements (Dy~Lu) mass fraction of 2.12%. The initial pH of the solution was 4.0, and the target purification level was 99.5%. The ratio of eutectic extractant to rare earth solution was 1.5:1; the washing solution was hydrochloric acid. After 15 stages of extraction and 12 stages of washing, the purity of yttrium in the raffinate aqueous phase was greater than 99%. The organic phase of the loaded eutectic extractant was back-extracted with 0.1 mol / L sodium oxalate to obtain a mixed heavy rare earth oxalic acid precipitate. After calcination, mixed heavy rare earth oxides were obtained. The eutectic extractant after back-extraction was washed with water and then directly recycled.

[0109] Example 10: Preparation of Eutectic Extractant

[0110] First, decanol, the hydrogen bond acceptor, and oleic acid, the hydrogen bond donor, are weighed at a molar ratio of 9:1. The mixture is heated to 35°C and stirred for 30 minutes to obtain a eutectic mixture. Then, diisooctylamine with a molar ratio of 5:1 to oleic acid is added, and the mixture is stirred at room temperature to obtain a eutectic extractant, which is a low-viscosity liquid at room temperature.

[0111] Extraction and separation of rare earth elements using eutectic extractants

[0112] The prepared eutectic extractant was used to purify yttrium from a yttrium-rich solution of a southern ionic rare earth ore deposit (Longnan, Ganzhou). The total rare earth concentration was 0.2 mol / L, with yttrium purity of 87.88% and heavy rare earth elements (Dy~Lu) mass fraction of 2.12%. The initial pH of the solution was 4.0, and the target purification level was 99.5%. The separation coefficients of the prepared eutectic solvent for heavy rare earth elements and yttrium are shown in Table 17. The separation coefficients for Ho / Y reached 3.19, Er / Y reached 4.47, and Lu / Y reached 13.25. These separation coefficients are significantly higher than those of reported carboxylic acid extractants.

[0113] Table 17 Separation coefficients of heavy rare earth elements and yttrium

[0114]

[0115] After multi-stage cascade extraction, the purity of yttrium in the raffinate aqueous phase outlet is greater than 99%. The organic phase of the loaded eutectic extractant is back-extracted with 0.1 mol / L sodium oxalate to obtain mixed heavy rare earth oxalic acid precipitate. After calcination, mixed heavy rare earth oxides can be obtained. The eutectic extractant after back-extraction is directly recycled after washing with water.

[0116] Comparative Example 1:

[0117] Naphthenic acid with a saponification degree of 60% was dissolved in 260# kerosene at a concentration of 0.1 mol / L, and 20% TBP was used as a phase modifier. The concentrations of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y in the rare earth solution were all 0.002 mol / L, with an initial pH of 2.9. The saponified naphthenic acid was mixed with the rare earth solution for single-stage extraction at a ratio of 1:1. The separation coefficients of the obtained rare earth elements are shown in Table 17. The separation coefficient of naphthenic acid for heavy rare earth elements and Y was greater than or equal to 2.0, but lower than the separation coefficient of the prepared eutectic extractant for heavy rare earth elements and yttrium. Without the addition of a phase modifier, naphthenic acid extraction resulted in emulsification, and without saponification, it had no extraction performance for rare earth elements.

[0118] Table 18 Separation coefficients of heavy rare earth elements and yttrium

[0119]

[0120] The embodiments of the technical solution of the present invention have been described above by way of example. It should be understood that the protection scope of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the protection scope of the claims of this application.

Claims

1. A method for extracting and purifying rare earth elements, comprising mixing a eutectic extractant with a rare earth solution containing yttrium, performing multi-stage extraction, washing, and back-extraction; obtaining an aqueous raffinate phase and a loaded eutectic extractant organic phase after extraction; wherein the aqueous raffinate phase is high-purity yttrium, and the loaded eutectic extractant organic phase is washed and back-extracted to obtain an easily extractable rare earth element solution and / or rare earth precipitate; The eutectic extractant includes a hydrogen bond donor, a hydrogen bond acceptor, and a co-extractant; The hydrogen bond donor is selected from one of 2-hexyldecanoic acid, decanoic acid, and oleic acid; The hydrogen bond acceptor is selected from one of decanol and dodecanol; The co-extractant is selected from one of the primary amine N1923 and diisooctylamine; The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:(1-9); The co-extractant accounts for 10%-30% of the total volume of the hydrogen bond donor and hydrogen bond acceptor.

2. The method according to claim 1, characterized in that, The yttrium-containing rare earth solution is a leaching solution or enrichment solution of ion-type rare earth ore, a leaching solution of mineral-type rare earth ore, or a leaching solution of secondary resources containing rare earth elements. And / or, the pH value of the rare earth solution is 1 to 6.

3. The method according to claim 1, characterized in that, The washing process uses one or more of the following: deionized water, hydrochloric acid, sulfuric acid, nitric acid, formic acid, acetic acid, citric acid, lactic acid, malic acid, and EDTA.

4. The method according to claim 3, characterized in that, The concentrations of hydrochloric acid, sulfuric acid, nitric acid, formic acid, acetic acid, citric acid, lactic acid, malic acid, and EDTA are 0.01 mol / L to 2 mol / L.

5. The method according to claim 1, characterized in that, The stripping agent used in the stripping process is one or more of the following: deionized water, ammonium fluoride, ammonium bifluoride, sodium fluoride, sodium oxalate, oxalic acid, hydrochloric acid, sulfuric acid, nitric acid, formic acid, acetic acid, citric acid, lactic acid, malic acid, and EDTA.

6. The method according to claim 5, characterized in that, The concentrations of ammonium fluoride, ammonium bifluoride, sodium fluoride, sodium oxalate, oxalic acid, hydrochloric acid, sulfuric acid, nitric acid, formic acid, acetic acid, citric acid, lactic acid, malic acid, and EDTA are 0.01 mol / L to 6 mol / L.

7. The method according to claim 1, characterized in that, The volume ratio of the eutectic extractant to the yttrium-containing rare earth solution is 1:10 to 10:1; the volume ratio of the washing liquid used for washing or the back-extraction liquid used for back-extraction to the eutectic extractant is 1:10 to 10:1.

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