Extracting agent as well as preparation method and application thereof in rare earth element separation

Abstract

The invention discloses an extraction agent, a preparation method thereof and application of the extraction agent in rare earth element separation. The extraction agent provided by the invention comprises dialkyl phosphite, a modifier and a diluent, the structural general formula of the dialkyl phosphite is shown in the specification, and R1 and R2 are the same or different and are independently selected from substituted or unsubstituted alkyl and substituted or unsubstituted aryl. The extraction agent disclosed by the invention has the advantages of low cost, stable chemical property, excellent extraction performance on heavy rare earth elements, high separation coefficient of any two heavy rare earth elements, stable extraction phase separation and easiness in reverse extraction; the method can effectively solve the problems of low rare earth extraction separation coefficient, long process flow, insufficient purity, difficulty in reverse extraction regeneration, high acid and alkali consumption, easiness in emulsification and the like in the prior art, and has obvious industrial application value. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the separation and purification technology of rare earth elements, and particularly to an extractant, its preparation method and application in the separation of rare earth elements, especially for the separation of heavy rare earth elements. Background Art

[0002] Due to their unique and excellent physical and chemical properties such as magnetism, optics and electricity, rare earth elements are widely used in high-tech fields such as new energy, electronic information, and catalytic materials. The separation and purification of single rare earth elements are the premise for their application. However, due to the similar chemical properties among rare earth elements, it is extremely difficult to separate them from each other. The solvent extraction method is currently the most commonly used method for rare earth separation and purification in industry, which has the advantages of large processing capacity, continuous and automated production, good rare earth separation effect, high recovery rate, etc. In the prior art, rare earth separation extractants are mostly acidic phosphorus compounds, neutral phosphorus compounds, organic carboxylic acid compounds and amine compounds. Among them, the acidic phosphorus compounds P507 and P204 are currently the two most commonly used extractants in the rare earth industry at home and abroad, but there are still problems such as low separation coefficient of medium and heavy rare earth elements, difficult stripping, large consumption of acid and alkali, long process flow, and unstable extraction phase separation.

[0003] Chinese Patent Application CN201510564337.X discloses a new rare earth separation extractant, bis-(2-ethylhexyl) phosphinic acid (P227), which has a higher separation ability for heavy rare earth elements than P507 and P204, and both extraction and stripping are carried out at a lower acidity, which can reduce the consumption of acid and alkali; Chinese Patent Application CN201410481761.3 discloses a method for extracting and separating heavy rare earth elements, using a mixture of alkyl phosphoric acid monoalkyl ester and dialkyl phosphinic acid as an extractant, which improves the separation coefficient among rare earth elements to a certain extent; Chinese Patent Application CN202110825206.8 discloses a carboxylic acid type extractant for the separation of rare earth elements, which can achieve efficient separation of lanthanide elements and yttrium elements, and is easy to strip and regenerate. Although a variety of new extractants have been disclosed for the separation of rare earth elements, the separation coefficient for adjacent heavy rare earth elements is still low, and it is difficult to achieve efficient separation of heavy rare earth elements. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] An extractant, the extractant comprising dialkyl phosphite, a modifier and a diluent;

[0006] The general structural formula of the dialkyl phosphite is as follows:

[0007]

[0008] Wherein, R1 and R 2 are the same as or different from each other, and are independently selected from substituted or unsubstituted alkyl groups (preferably C6-C12 alkyl groups), substituted or unsubstituted aryl groups (preferably C6-C18 aryl groups).

[0009] According to an embodiment of the present invention, the dialkyl phosphite includes but is not limited to at least one of dibutyl phosphite, diisobutyl phosphite, ditert-butyl phosphite, diphenyl phosphite, dibenzyl phosphite, di-n-octyl phosphite, diisooctyl phosphate, di-sec-octyl phosphite, 2-ethylhexyl octyl phosphite, dihexyl phosphite, etc., and preferably at least one of diisooctyl phosphate, di-n-octyl phosphite, di-sec-octyl phosphite, 2-ethylhexyl octyl phosphite.

[0010] According to an embodiment of the present invention, in the extractant, the concentration of the dialkyl phosphite is 0.01 mol / L - 2 mol / L, preferably 0.5 - 2 mol / L.

[0011] According to an embodiment of the present invention, the modifier includes but is not limited to at least one of isooctanol, n-octanol, trioctyl phosphate, tributyl phosphate, N,N-bis(1-methylheptyl)acetamide (N503), N,N-diethyllauramide, trioctylamine, diisooctylamine, etc., and preferably at least one of trioctyl phosphate, tributyl phosphate, trioctylamine, diisooctylamine, etc.

[0012] According to an embodiment of the present invention, in the extractant, the concentration of the modifier is 0 mol / L - 1 mol / L, preferably 0 - 0.5 mol / L.

[0013] According to an embodiment of the present invention, the diluent is selected from diluents known in solvent extraction, including but not limited to at least one of sulfonated kerosene, n-dodecane, toluene, p-cymene, n-heptane, cyclohexane, dichloromethane, chloroform, m-nitrobenzotrifluoride, petroleum ether, methyl isobutyl ketone (MIBK), etc.

[0014] According to an embodiment of the present invention, the extractant is an organic phase.

[0015] According to an embodiment of the present invention, the extractant is used to extract rare earth elements from a solution containing rare earth elements.

[0016] According to an embodiment of the present invention, when the extractant is used to extract rare earth elements from a solution containing rare earth elements, it can be reused, for example, reused at least 2 times or more, preferably 5 times or more.

[0017] According to an embodiment of the present invention, in the rare earth element-containing solution, the rare earth elements are selected from the rare earth elements known in the art, preferably including heavy rare earth elements and / or light rare earth elements. Preferably, the heavy rare earth elements are selected from at least one of Ho, Er, Tm, Yb, and Lu. Preferably, the light rare earth elements are selected from at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy.

[0018] According to an embodiment of the present invention, the extraction rate of the extractant for rare earth elements is above 5%, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%.

[0019] According to an embodiment of the present invention, in the extractant, the separation factor between any two rare earth elements is at least 1 or more, for example, 1 - 100000.

[0020] According to an embodiment of the present invention, in the extractant, the separation factor between any two heavy rare earth elements is 2 or more, for example, 2 - 100000. In the present invention, the separation factor between any two heavy rare earth elements represents the degree of separation of two different rare earth elements during the extraction process.

[0021] The present invention also provides a preparation method of the above extractant. The preparation method includes: dissolving dialkyl phosphite and a modifier together in a diluent to obtain the extractant, wherein the dialkyl phosphite, the modifier, and the diluent have the meanings as described above.

[0022] The present invention also provides an application of the above extractant in separating rare earth elements, preferably for separating heavy rare earth elements.

[0023] The present invention also provides a method for separating rare earth elements. The separation method includes: extracting and separating the rare earth elements in the rare earth solution to be separated by using the above extractant.

[0024] According to a preferred embodiment of the present invention, the rare earth solution to be separated includes light rare earth elements and / or heavy rare earth elements, preferably heavy rare earth elements.

[0025] According to a preferred embodiment of the present invention, the rare earth solution to be separated includes at least one or two or more of heavy rare earth elements, preferably any two different heavy rare earth elements, for example, at least two of Ho, Er, Tm, Yb, and Lu.

[0026] According to an embodiment of the present invention, the rare earth solution to be separated refers to an acidic solution containing the rare earth elements, such as a hydrochloric acid solution or a nitric acid solution containing the rare earth elements. Exemplarily, the rare earth solution to be separated includes, but is not limited to, a hydrochloric acid solution or a nitric acid solution containing all rare earth elements, a hydrochloric acid solution or a nitric acid solution containing heavy rare earth elements; for example, at least one selected from leaching solutions of ionic rare earth ores, leaching solutions of ionic rare earth concentrates, leaching solutions of Baotou rare earth ores, leaching solutions of bastnasite ores, leaching solutions of waste NdFeB, leaching solutions of various rare earth secondary resources, etc. known in the art.

[0027] According to an embodiment of the present invention, the extraction and separation specifically includes: mixing the extractant with the rare earth solution to be separated, completing the extraction process after phase separation to obtain an organic phase extraction layer loaded with rare earth elements, and after performing a stripping process on the organic phase extraction layer, obtaining an aqueous phase enriched with rare earth elements and the stripped organic phase, wherein the stripped organic phase includes the extractant, and the extraction and separation is completed.

[0028] According to an embodiment of the present invention, in the extraction and separation, the number of times of the extraction process and the stripping process is determined according to the specific components of the rare earth elements in the rare earth solution to be separated. In the present invention, the number of times of the extraction process and the stripping process are both expressed in stages.

[0029] Preferably, the number of stages of the extraction process is 1 - 50 stages, such as 5, 10, 15, 20, 25, 30, 35, 40, 45. Preferably, the number of stages of the stripping process is 1 - 10 stages, such as 5, 10, 15, 20, 25, 30, 35, 40, 45.

[0030] According to an embodiment of the present invention, the pH value of the rare earth solution to be separated is 1 - 7, preferably 3 - 6.

[0031] According to an embodiment of the present invention, during the mixing in the extraction and separation, the volume flow ratio of the extractant to the rare earth solution to be separated can be 0.1:1 - 20:1, preferably 0.5:1 - 10:1, such as 1:1. In the present invention, the change in the volume flow ratio mainly changes according to the change in the concentration of the rare earth elements in the rare earth solution to be separated. When the concentration of the rare earth elements in the rare earth solution to be separated is higher than the saturated loading concentration of the organic phase, the volume flow of the extractant can be increased to ensure a sufficient extraction rate.

[0032] According to an embodiment of the present invention, the rare earth elements loaded in the organic phase extraction layer are from the rare earth solution to be separated, preferably heavy rare earth elements.

[0033] According to an embodiment of the present invention, a washing process is performed on the loaded organic phase using hydrochloric acid or nitric acid solution.

[0034] According to an embodiment of the present invention, the washing process refers to: using a washing solution as the aqueous phase to selectively extract non-target rare earth elements in the oil phase extraction layer after extraction into the aqueous phase.

[0035] Preferably, the number of stages of the washing process is 1 - 50, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45.

[0036] According to an embodiment of the present invention, the hydrogen ion concentration in the washing solution is 0 - 3 mol / L, preferably 0.2 - 2 mol / L.

[0037] According to an embodiment of the present invention, the stripping process refers to: using a stripping solution as the aqueous phase to extract rare earth elements in the oil phase extraction layer after washing into the aqueous phase. Preferably, the stripping solution is selected from hydrochloric acid, oxalic acid or nitric acid solution.

[0038] According to an embodiment of the present invention, the hydrogen ion concentration in the stripping solution is 0 - 5 mol / L, preferably 2 - 4 mol / L.

[0039] According to an embodiment of the present invention, the flow rate ratio of the stripping solution to the extractant is 0.1:1 - 10:1, preferably 0.1:1 - 5:1.

[0040] According to an embodiment of the present invention, the oil phase after stripping can be further subjected to a second washing process.

[0041] According to an embodiment of the present invention, the second washing process includes: washing the oil phase after stripping with a washing solution to remove the entrained residual acid to obtain a regenerated extractant.

[0042] According to an embodiment of the present invention, the volume flow rate ratio of the washing solution to the oil phase after stripping is 0.1:1 - 10:1, preferably 0.1:1 - 5:1.

[0043] According to an embodiment of the present invention, the oil phase washed by the second washing process is a regenerated extractant and can be recycled, for example, recycled at least 2 times or more, preferably 5 times or more.

[0044] According to an embodiment of the present invention, the washing solution is selected from deionized water or an alkaline solution. Preferably, the alkaline solution is selected from at least one of ammonia water, sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0045] According to an embodiment of the present invention, the concentration of hydroxide ions in the alkaline solution is 0 - 5 mol / L, preferably 0 - 3 mol / L.

[0046] Beneficial effects

[0047] The extractant of the present invention has the advantages of low cost, stable chemical properties, excellent extraction performance for heavy rare earth elements, high separation factor between any two heavy rare earth elements, stable extraction phase separation, and easy stripping. It can effectively solve the problems of low rare earth extraction separation factor, long process flow, insufficient purity, difficult stripping and regeneration, large consumption of acids and alkalis, and easy emulsification at present, and has obvious industrial application value. Description of the Drawings

[0048] Figure 1 It is the experimental result of single-stage extraction and separation of rare earths by different dialkyl phosphites.

[0049] Figure 2 It is the experimental result of the influence of different dosages of diisooctyl phosphite on rare earth extraction and separation.

[0050] Figure 3 It is the stripping experimental result of diisooctyl phosphite.

[0051] Figure 4 It is the recycling experimental result of diisooctyl phosphite.

[0052] Figure 5 It is the experimental result of the comparison of extraction performance between industrially common extractants and diisooctyl phosphite.

[0053] Figure 6 It is the experimental result of the comparison of separation performance between industrially common extractants and diisooctyl phosphite. Detailed Description of the Invention

[0054] 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 only for illustrative and explanatory purposes of the present invention, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection of the present invention.

[0055] Unless otherwise specified, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by known methods.

[0056] In the following embodiments, diphenyl phosphite, dibenzyl phosphite, di-tert-butyl phosphite, diisooctyl phosphite, diisobutyl phosphite, and dibutyl phosphite are all purchased from the exploration platform; the commonly used acidic phosphorus compounds P507, P204, and C272 in industry are purchased from Anychem Chemical Reagent Network and Aladdin Chemical Reagent Network respectively.

[0057] The extraction rate (E%) can intuitively show the extraction ability of the extractant. E% is the percentage change in the concentration of metal ions in the aqueous phase after extraction, that is, the extraction rate E% = (concentration of metal ions before extraction - concentration of metal ions after extraction) / concentration of metal ions before extraction) * 100%;

[0058] The distribution ratio refers to the ratio of the concentration of rare earth elements in the organic phase to the concentration in the aqueous phase after extraction, i.e., D = concentration of metal ions in the organic phase after extraction / concentration of metal ions in the aqueous phase after extraction. The higher the extraction rate, the larger the distribution ratio.

[0059] The separation factor (SF) is the ratio of the distribution ratios of two rare earth elements, and its magnitude reflects the ease of separation of the two components, i.e., SF = D2 / D1. When the separation factor is equal to 1, separation cannot be achieved; the greater the deviation of the separation factor from 1, the easier it is to be separated.

[0060] The stripping rate (S%) is the percentage of the amount of rare earth ions in the aqueous phase after stripping to the amount of rare earth ions loaded in the organic phase before stripping.

[0061] Preparation Example 1

[0062] Prepare a hydrochloric acid solution of mixed rare earth elements: Dissolve chlorides of different rare earth elements in deionized water and add hydrochloric acid to adjust the pH to 3 to obtain a hydrochloric acid solution of mixed rare earth elements, where the concentration of each rare earth element is 0.003 mol / L; the rare earth elements added include: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu.

[0063] Example 1

[0064] Prepare an extractant: Weigh different dialkyl phosphites, and dissolve them and the modifier trioctylamine in sulfonated kerosene to obtain different extractants as the organic phase, where the concentration of the dialkyl phosphite is 0.5 mol / L and the concentration of trioctylamine is 0.1 mol / L; the dialkyl phosphite is specifically selected from any one of the following: diphenyl phosphite, dibenzyl phosphite, di-tert-butyl phosphite, diisooctyl phosphite, diisobutyl phosphite, dibutyl phosphite.

[0065] The method for extracting rare earth elements is as follows:

[0066] Take the above different extractants and mix them with the hydrochloric acid solution of mixed rare earth elements in Preparation Example 1 under the condition of a volume flow ratio of 1:1, and then carry out the extraction process. The extraction process is single-stage extraction (i.e., one-time extraction); after extraction, phase separation is carried out, with the upper layer being the oil-phase extraction layer and the lower layer being the aqueous phase; use ICP-OES to measure the concentration of each rare earth element in the aqueous phase, and calculate the extraction rate results of different extractants, as Figure 1 shown.

[0067] Figure 1The results show that dialkyl phosphites have good extraction ability for heavy rare earth elements Ho, Er, Tm, Yb, and Lu. The order of extraction rates for heavy rare earth elements (Ho, Er, Tm, Yb, Lu) is: diphenyl phosphite > dibenzyl phosphite > di-tert-butyl phosphite > diisooctyl phosphite > diisobutyl phosphite > dibutyl phosphite;

[0068] The phase separation results after extraction of the above different extractants and the hydrochloric acid solution of mixed rare earths are as follows:

[0069] Using diisooctyl phosphite or diisobutyl phosphite as the extractant, the phase separation is stable after extracting rare earth elements from the hydrochloric acid solution of mixed rare earths, and there is no emulsification and third phase generation, and the phase separation phenomenon is better.

[0070] It can be proved therefrom that when the extractant contains the dialkyl phosphite of the present invention, it is suitable for extracting a solution containing the following rare earth elements: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; moreover, when using diisooctyl phosphite or diisobutyl phosphite as the extractant, the phase separation is more stable.

[0071] Example 2

[0072] Refer to Example 1 to prepare an extractant containing diisooctyl phosphite. Specifically: Weigh different masses of diisooctyl phosphite and dissolve them in sulfonated kerosene with the modifier trioctylamine to obtain extractants with different concentrations of diisooctyl phosphite. Among them, the concentrations of diisooctyl phosphite are 0.25 mol / L, 0.5 mol / L, 0.75 mol / L, 1 mol / L, 1.25 mol / L, and 1.50 mol / L respectively; the concentration of trioctylamine is 0.1 mol / L.

[0073] The method for extracting rare earth elements is as follows:

[0074] After mixing the extractants with different concentrations prepared in this example and the hydrochloric acid solution of the mixed rare earth elements in Preparation Example 1 under the condition of a flow ratio of 1:1, an extraction process is carried out. The extraction process is single-stage extraction. After the extraction process, phase separation occurs. The upper layer is the oil-phase extraction layer, and the lower layer is the aqueous phase; Use ICP-OES to measure the ionic concentrations of various rare earth elements in the aqueous phase, and the extraction rate results of the extractant containing diisooctyl phosphite are as Figure 2 shown, where 0.25, 0.5, 0.75, 1, 1.25, and 1.50 represent extractants with diisooctyl phosphite concentrations of 0.25 mol / L, 0.5 mol / L, 0.75 mol / L, 1 mol / L, 1.25 mol / L, and 1.50 mol / L respectively.

[0075] From Figure 2It can be seen that as the concentration of diisooctyl phosphite increases, the extraction rate of the extractant for rare earth elements also gradually increases, and the extraction rate for heavy rare earth elements (such as Ho, Er, Tm, Yb, Lu) is higher than that for light rare earth elements (such as La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy).

[0076] Based on Figure 2 the results, the separation coefficients of diisooctyl phosphite for different rare earth elements were calculated, and the results are shown in Table 1. The separation coefficients of any two heavy rare earth elements Ho, Er, Tm, Yb, Lu are higher than those of currently known extractants. For example, the separation coefficients of Lu / Yb, Yb / Tm, Tm / Er, and Er / Ho are 2.14, 3.19, 3.78, and 2.90, respectively.

[0077] Table 1 Separation coefficients (SF) of diisooctyl phosphite between different rare earth elements

[0078]

[0079]

[0080] Example 3

[0081] The stripping performance of the extractant containing diisooctyl phosphite:

[0082] 1. Prepare a hydrochloric acid solution of lutetium chloride: Dissolve lutetium chloride in deionized water to obtain a hydrochloric acid solution containing lutetium ions, where the concentration of lutetium ions is 0.3 mol / L and the pH is 3.0.

[0083] 2. Prepare the extractant: Referring to Example 2, prepare an extractant with a concentration of 0.50 mol / L of diisooctyl phosphite and a concentration of 0.10 mol / L of trioctylamine.

[0084] 3. Extraction process: The extractant in step 2 and the hydrochloric acid solution of lutetium chloride in step 1 are subjected to single-stage extraction under the condition of a volume flow ratio of 1:1. After extraction, phase separation is carried out to obtain an aqueous phase and an oil-phase extraction layer respectively, where lutetium ions aggregate in the oil phase.

[0085] 4. Subsequently, the oil-phase extraction layer in step 3 is subjected to a stripping process with hydrochloric acid at different concentrations (concentrations are 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3.0 mol / L) respectively. Specifically: The oil-phase extraction layer in step 3 is mixed with hydrochloric acid at different concentrations and then further layered to obtain the stripped aqueous phase and oil phase; ICP-OES is used to measure the concentration of rare earth elements in the stripped aqueous phase, and thus the stripping rate results of the extractant in this example for hydrochloric acid at different concentrations are as Figure 3 shown. From Figure 3It can be seen that as the concentration of hydrochloric acid increases, the stripping rate of the extractant of the present invention gradually increases. When the hydrochloric acid concentration is higher than 2 mol / L, the stripping rate of the extractant of the present invention for lutetium approaches 100%.

[0086] From the results of the stripping experiment, it can be seen that the acidic solution has excellent stripping performance for the extractant containing dialkyl phosphite of the present invention.

[0087] Example 4

[0088] Recycling stability of the extractant containing diisooctyl phosphite:

[0089] Steps 1-3 of this example were carried out with reference to steps 1-3 of Example 3. The water phase and oil phase obtained after single-stage extraction and phase separation were specifically as follows: 1. Preparation of a hydrochloric acid solution of lutetium chloride: Lutetium chloride was dissolved in deionized water to obtain a hydrochloric acid solution containing lutetium ions, wherein the concentration of lutetium ions was 0.3 mol / L and the pH was 3.0.

[0090] 2. Preparation of the extractant: With reference to Example 2, an extractant with a concentration of 0.50 mol / L of diisooctyl phosphite and a concentration of 0.10 mol / L of trioctylamine was prepared.

[0091] 3. Extraction process: The extractant in step 2 was subjected to single-stage extraction with the hydrochloric acid solution of lutetium chloride in step 1 under a volume flow ratio of 1:1. After extraction, phase separation was carried out to obtain a water phase and an oil phase extraction layer respectively, and the lutetium ions were concentrated in the oil phase extraction layer.

[0092] 4. The oil phase extraction layer obtained in step 3 above was stripped with 2.0 mol / L hydrochloric acid to obtain a stripped oil phase and a water phase; then the stripped oil phase was washed with deionized water multiple times until the pH value of the washed deionized water was close to neutral, and the washing of the oil phase was completed.

[0093] 5. The washed oil phase in step 4 above was used as the extractant and recycled again. Steps 1-4 above were repeated, and the extractant of this example was stopped after being recycled 5 times.

[0094] The experimental results of the above recycling are as Figure 4 shown. It can be seen from this that the recycling stability of the extractant of the present invention is good. After being recycled 5 times, the extraction rate of the extractant of the present invention for lutetium only decreases by about 3%.

[0095] Comparative Example 1

[0096] Acidic phosphorus compounds P507, P204 and C272 commonly used in industry were used to prepare extractants respectively, and the hydrochloric acid solutions of the mixed rare earth elements in Preparation Example 1 were extracted and separated respectively:

[0097] 1. Preparation of comparative extractants: Weigh P507, P204, and C272, and dissolve them separately with the modifier tributyl phosphate in sulfonated kerosene to obtain different comparative extractants. Among them, the concentrations of P507 and P204 are both 0.02 mol / L, the concentration of C272 is 0.1 mol / L, and the concentration of the modifier tributyl phosphate is 0.1 mol / L.

[0098] 2. The method for extracting rare earth elements is as follows: Perform a single-stage extraction process on the above comparative extractants and the hydrochloric acid solution of the mixed rare earth elements in Preparation Example 1 under the condition of a flow ratio of 1:1. After extraction, phase separation is carried out. The upper layer is the oil-phase extraction layer, and the lower layer is the aqueous phase; Use ICP-OES to measure the concentration of rare earth ions in the aqueous phase, and the extraction rate results calculated are as Figure 5 shown, Figure 5 The extraction rate of diisooctyl phosphite is the same as that in Example 2.

[0099] Based on Figure 5 the results, the separation coefficients between heavy rare earth elements calculated by referring to the method in Example 2 are as Figure 6 shown.

[0100] Figure 5 The results show that when the extraction abilities of P204, P507, and C272 for rare earth elements are roughly the same as that of diisooctyl phosphite, the concentration of the extractant used is lower, that is, the extraction ability is higher than that of diisooctyl phosphite, which also indicates that diisooctyl phosphite is more easily stripped.

[0101] Figure 6 The results show that the separation coefficients of the extractant using diisooctyl phosphite for heavy rare earth elements are significantly higher than those of the extractants using P204, P507, or C272, fully demonstrating the excellent separation performance of dialkyl phosphite for rare earth elements.

[0102] The above has described the exemplary embodiments of the present invention. However, the protection scope of this application is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An extractant, characterized in that The extractant comprises a dialkyl phosphite, a modifier and a diluent; The general structural formula of the dialkyl phosphite is as follows: Wherein, R1 and R2 are the same or different and are independently selected from substituted or unsubstituted alkyl, substituted or unsubstituted aryl.

2. The extractant according to claim 1, characterized in that The dialkyl phosphite includes at least one of dibutyl phosphite, diisobutyl phosphite, di-tert-butyl phosphite, diphenyl phosphite, dibenzyl phosphite, di-n-octyl phosphite, diisooctyl phosphate, di-sec-octyl phosphite, 2-ethylhexyl octyl phosphite, and dihexyl phosphite. Preferably, in the extractant, the concentration of the dialkyl phosphite is 0.01 mol / L-2 mol / L. Preferably, the modifier includes but is not limited to at least one of isooctyl alcohol, n-octanol, trioctyl phosphate, tributyl phosphate, N,N-bis(1-methylheptyl)acetamide (N503), N,N-diethyllauramide, trioctylamine, diisooctylamine, etc. Preferably, in the extractant, the concentration of the modifier is 0 mol / L-1 mol / L.

3. The extractant according to claim 1 or 2, characterized in that The diluent is selected from at least one of sulfonated kerosene, n-dodecane, toluene, p-cymene, n-heptane, cyclohexane, dichloromethane, chloroform, m-nitrotrifluorotoluene, petroleum ether and methyl isobutyl ketone. Preferably, the extractant is an organic phase. Preferably, the extractant is used to extract rare earth elements from a solution containing rare earth elements.

4. The extractant according to any one of claims 1 to 3, characterized in that In the rare earth element-containing solution, the rare earth elements include heavy rare earth elements and / or light rare earth elements. Preferably, the heavy rare earth element is selected from at least one of Ho, Er, Tm, Yb, and Lu. Preferably, the light rare earth element is selected from at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy. Preferably, the extraction rate of the extractant for rare earth elements is above 5%. Preferably, in the extractant, the separation coefficient of any two rare earth elements is at least 1. Preferably, in the extractant, the separation coefficient of any two heavy rare earth elements is greater than 2.

5. The method for preparing the extractant according to any one of claims 1 to 4, characterized in that: The preparation method comprises: dissolving a dialkyl phosphite and a modifier in a diluent to obtain an extractant.

6. Use of the extractant described in any one of claims 1 to 4 in separating rare earth elements.

7. A method for separating rare earth elements, characterized in that: The separation method comprises: extracting and separating the rare earth elements in the rare earth solution to be separated using the extractant described in any one of claims 1 to 4. Preferably, the rare earth solution to be separated comprises light rare earth elements and / or heavy rare earth elements.

8. The separation method according to claim 7, characterized in that The rare earth solution to be separated includes at least one or two or more heavy rare earth elements. Preferably, the rare earth solution to be separated is an acidic solution containing the rare earth element. Preferably, the extraction separation specifically includes: mixing the extractant with the rare earth solution to be separated, completing the extraction process after phase separation to obtain an oil phase extraction layer loaded with rare earth elements, and performing a back extraction process on the oil phase extraction layer to obtain a water phase enriched in rare earth elements and an oil phase after back extraction, wherein the oil phase after back extraction includes the extractant, thereby completing the extraction separation. Preferably, the pH value of the rare earth solution to be separated is 1-7. Preferably, during the mixing for extraction separation, the volume flow ratio of the extractant to the rare earth solution to be separated is 0.1:1-20:

1. Preferably, the rare earth elements loaded in the oil phase extraction layer come from the rare earth solution to be separated.

9. The separation method according to claim 7 or 8, characterized in that The loaded organic phase is washed with hydrochloric acid and nitric acid solutions. Preferably, the washing step refers to: using the washing liquid as the aqueous phase to selectively extract the non-target rare earth elements in the extracted oil phase extraction layer into the aqueous phase. Preferably, the hydrogen ion concentration in the washing liquid is 0-3 mol / L.

10. The separation method according to any one of claims 7 to 9, characterized in that: The stripping step refers to: using the stripping liquid as the water phase to extract the rare earth elements in the washed oil phase extraction layer into the water phase. Preferably, the hydrogen ion concentration in the stripping solution is 0-5 mol / L. Preferably, the flow ratio of the stripping solution to the extractant is 0.1:1-10:1.

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