Preparation method for preparing amino methyl hypophosphorous acid extraction agent and application of amino methyl hypophosphorous acid extraction agent

Abstract

The invention relates to the technical field of metal separation application, and discloses a preparation method for preparing an aminomethyl hypophosphorous acid extractant, which comprises the following steps: S1, synthesizing monoalkyl hypophosphorous acid intermediates with different carbon chains; and S2, synthesizing amino methyl hypophosphorous acid extraction agents with different structures. The preparation of the monoalkyl hypophosphorous acid intermediate in the step S1 comprises the following steps: S11, sequentially adding sodium hypophosphite, glacial acetic acid, different carbon chain olefins, di-tert-butyl peroxide and tetrahydrofuran into a reaction kettle, then putting the mixture into the reaction kettle with a stirring device, and then reacting for 8 hours at 120 DEG C and 1200 rpm. According to the N, N-di-n-octyl amino methyl phenyl hypophosphorous acid developed by the invention, high-efficiency separation of heavy rare earth can be realized in the pH range of 4.00-1.25 and the acidity range of 0.1-2 mol / L, and the Lu / Y separation coefficient can reach 53.55; the Lu / Yb separation coefficient can reach 1.87, and compared with traditional extraction agents such as P507, P204 and Cyanex 272, the extraction agent has absolute advantages in separation coefficient and operation window.

Description

Technical Field

[0001] The invention relates to the technical field of metal separation application, and in particular to a method for preparing an aminomethylphosphorous acid extractant and application thereof. Background Art

[0002] Rare earth, zirconium, hafnium and other elements have been listed as strategic metal elements by the United States, Japan, Australia, China and other countries. Solvent extraction is one of the most important methods for separating and purifying metal elements, and the extractant is the most critical factor affecting its separation effect. Currently, the main extractants used for the extraction and separation of strategic mineral resources such as rare earth, zirconium, and hafnium are: 2-ethylhexyl phosphate-2-ethylhexyl ester (P507 or HEH [EHP] or PC88A), di (2-ethylhexyl) phosphoric acid (P204 or D2EHPA or HDEHP), di (2,4,4'-trimethylpentyl) phosphinic acid (Cyanex 272), tributyl phosphate (TBP), trioctylphosphine oxide (TOPO), sec-octylphenoxyacetic acid (CA-12), methyl isobutyl ketone (MIBK), tri-n-octylamine (TOA), methyl trioctyl ammonium chloride (Aliquat 336), etc. However, they all have problems such as small separation coefficient, low operating tolerance, small saturation capacity, and large environmental pollution. Therefore, the development of new extractants with high separation coefficient, large operating tolerance, large saturation capacity, and less environmental pollution has always been a research hotspot for achieving efficient and green separation of rare earth and other strategic metals.

[0003] Therefore, it is necessary to design a practical preparation method and application of aminomethyl hypophosphite extractant. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing an aminomethylphosphinoic acid extractant and its application, so as to solve the problems raised in the above background technology.

[0005] In order to solve the above technical problems, the present invention provides the following technical solution: a method for preparing an aminomethylphosphinoic acid extractant, comprising:

[0006] S1: Synthesis of monoalkyl hypophosphorous acid intermediates with different carbon chains, as shown in formula a:

[0007]

[0008] S2: Synthesize aminomethyl hypophosphite extractants of different structures, as shown in formula b:

[0009]

[0010] According to the above technical scheme, the preparation of the monoalkyl hypophosphorous acid intermediate in step S1 is as follows:

[0011] S11: Sodium hypophosphite, glacial acetic acid, olefins of different carbon chains, di-tert-butyl peroxide and tetrahydrofuran were added into a reaction kettle in sequence, and then placed into a reaction kettle with a stirring device, and then reacted at 120° C. and 1200 rpm for 8 hours.

[0012] S12: removing tetrahydrofuran and unreacted olefins from step S11 by vacuum distillation;

[0013] S13: dissolving the product of step S12 with water and an organic solvent such as ether or dichloromethane, and then washing the ether phase with a 2-6% NaOH aqueous solution for multiple times, and collecting the aqueous phase product;

[0014] S14: adding 5-20% H2SO4 solution to the aqueous phase product in step S13 to make the pH <2, and then adding an organic solvent such as ether or dichloromethane;

[0015] S15: After removing the aqueous phase from step S14, the ether phase is washed with ultrapure water for multiple times until the pH of the aqueous phase is greater than 3;

[0016] S16: The solvent such as ether is removed by vacuum distillation to obtain a monoalkyl hypophosphorous acid intermediate. The preferred intermediate structure is shown below:

[0017]

[0018]

[0019] According to the above technical scheme, the molar ratio of sodium hypophosphite to olefin is 2:1-6:1, such as the masses of various materials are 0.3 mol, 16 g, 0.1 mol, 0.3 g, 25 g respectively, and the olefins are: 2,3-dimethyl-1-butene, diisobutylene, 2-ethyl-1-hexene, etc.

[0020] According to the above technical solution, the NaOH aqueous solution is a 4% NaOH aqueous solution.

[0021] According to the above technical solution, the H2SO4 solution is a 10% H2SO4 solution.

[0022] According to the above technical scheme, the aminomethylphosphorous acid in step S2 is prepared as follows:

[0023] S21: Add primary amine or secondary amine, monoalkyl hypophosphorous acid, and hydrochloric acid aqueous solution into a flask in sequence, heat to 30-100° C., add 37% formaldehyde solution, and react under reflux at this temperature for 8-24 hours;

[0024] S22: The product in step S21 is transferred to a separatory funnel using an organic solvent such as ether, and after removing the aqueous phase, the organic phase is washed several times with a 2-6% NaOH aqueous solution until the pH of the aqueous phase is greater than 10;

[0025] S23: Wash the organic phase of step S22 with 10% H2SO4 until the pH of the aqueous phase is less than 2;

[0026] S24: Wash the organic phase with pure water until the pH of the aqueous phase is greater than 3;

[0027] S25: Using reduced pressure distillation to remove solvents such as ether, the aminomethyl hypophosphorous acid product can be obtained. Preferably, the structure of the aminomethyl hypophosphorous acid is as follows:

[0028]

[0029]

[0030] According to the above technical scheme, the ratio of the primary amine or secondary amine to monoalkyl hypophosphorous acid is 1:(0.8-1.5), the concentration of hydrochloric acid is 2-6 mol / L, the molar ratio of formaldehyde to amines is (3-20):1, and the primary amine and secondary amine are: di-n-octylamine, di-iso-octylamine, isooctylamine, n-octylamine, n-hexylamine, di-n-hexylamine, etc.

[0031] On the other hand, the present application also provides a method for preparing an aminomethylphosphorous acid extractant and its application in the separation of strategic metals such as rare earth, zirconium, and hafnium.

[0032] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0033] 1. The present invention designs and synthesizes a type of bifunctional extractant containing both nitrogen and phosphorus - aminomethyl hypophosphorous acid. According to this synthetic route, the conversion and replacement of the carbon chain on the amine group and the different carbon chains on the phosphate functional group can be achieved, thereby synthesizing aminomethyl hypophosphorous acid with different structures.

[0034] 2. The extractant of the present invention can be widely used in the separation of rare earths, zirconium, hafnium, cobalt, nickel and other rare earths and other strategic metals.

[0035] 3. The N,N-di-n-octylaminomethylphenylphosphonic acid developed by the present invention can achieve efficient separation of heavy rare earths in the range of pH = 4.00 to 1.25 and the range of acidity of 0.1 to 2 mol / L. The Lu / Y separation coefficient can reach 53.55; the Lu / Yb separation coefficient can reach 1.87. Compared with traditional extractants such as P507, P204 and Cyanex272, it has absolute advantages in separation coefficient and operation window.

[0036] 4. The aminomethyl hypophosphorous acid developed by the present invention can achieve good zirconium and hafnium separation effects in a nitric acid system, and the Zr / Hf separation coefficient can reach 8 to 10. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0038] Figure 1 Characterization of N,N-di-n-octylaminomethyl (2,3-dimethyl-1-butyl) hypophosphorous acid (DOAM-DMBPA), N,N-di-n-octylaminomethyl (2,4,4-trimethyl-pentyl) hypophosphorous acid (DOAM-TMPPA) and N,N-di-n-octylaminomethylphenyl hypophosphorous acid (DOAM-PPA) of the present invention (a) FT-IR; (b) 31P NMR; (c) 1H NMR, (d) ESI-MS schematic diagram;

[0039] Figure 2 It is a schematic diagram showing the effect of hydrochloric acid concentration and pH on the extraction and separation of heavy rare earth by DOAM-PPA, P507, Cyanex 272, and P204 of the present invention;

[0040] Figure 3 It is a schematic diagram of the effect of hydrochloric acid concentration and pH on the heavy rare earth separation coefficient of DOAM-PPA, P507, Cyanex 272, and P204 of the present invention;

[0041] Figure 4 Schematic diagram of the effect of sodium chloride concentration on DOAM-PPA extraction and separation of heavy rare earths in the present invention;

[0042] Figure 5 It is a schematic diagram of the effect of nitric acid concentration on zirconium and hafnium separation in the present invention. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] Example 1: Synthesis of N,N-di-n-octylaminomethyl (2,3-dimethyl-1-butyl) hypophosphorous acid:

[0045] After adding a magnetic particle into the reactor, 0.3 mol of sodium hypophosphite, 16.00 g of glacial acetic acid, 0.1 mol of 2,3-dimethyl-1-butene, 0.3 g of di-tert-butyl peroxide (DTBP), and 25 g of tetrahydrofuran were added in sequence, and then the mixture was heated in an oil bath at 120° C. and 1200 rpm on a magnetic stirrer for 8 h.

[0046] The tetrahydrofuran and unreacted olefins are removed by vacuum distillation;

[0047] Dissolve the above product in water and ether into a separatory funnel, then wash the ether phase 3 times with 4% NaOH aqueous solution (100 ml in total), and collect the aqueous phase product;

[0048] Add 10% H2SO4 solution to the aqueous phase product to make the pH <2, and add ether extractant solvent;

[0049] After removing the aqueous phase, wash the ether phase several times with saturated sodium chloride aqueous solution until the pH of the aqueous phase is >3;

[0050] Anhydrous magnesium sulfate is added to the organic phase and dried for 30 minutes, and then the ether and other solvents are removed by reduced pressure distillation to obtain 2,3-dimethylphosphorous acid.

[0051] Add 0.04mol dioctylamine, 0.048mol 2,3-dimethylphosphorous acid, 50ml water, 30ml concentrated hydrochloric acid to a round-bottom flask in sequence, heat to 85°C, add 15ml 37% formaldehyde aqueous solution, and react at this temperature under reflux conditions for 24h. After cooling, transfer the product to a separatory funnel with ether, remove the aqueous phase, and wash the organic phase with 4% NaOH aqueous solution several times until the pH of the aqueous phase is greater than 10. Wash the ether phase with 10% H2SO4 until the pH is less than 2. Wash the ether phase with saturated sodium chloride until the pH is greater than 3. Remove the ether by vacuum distillation to obtain light yellow viscous N,N-dioctylaminomethyl (2,3-dimethyl-1-butyl) hypophosphorous acid. The characterization of N,N-di-n-octylaminomethyl (2,3-dimethyl-1-butyl) hypophosphorous acid (abbreviated as DOAM-DMBPA) is as follows: FT-IR (v / cm-1), 3410.98 (OH), 1377.89 (CN), 1164.31 (P=O), 1005.70 (PC(N)), 946.88 (PO(H)). 31P NMR (202MHz, CDCl3) δ 34.73ppm. 1H NMR ( 500MHz,CDCl3)δ3.18(m,2H),3.16(m,4H),1.80(m,2H),1.70(m,4H),1.57(m,2H),1.41(m,1H),1.24-1.17(m,20H),0.93(d,3H),0.81-0.74(m,12H).ESI-MSm / z:[M+1]+404.37,[2M+1]+807.73, as shown in the figure Figure 1 shown.

[0052] Example 2: Synthesis of N,N-di-n-octylaminomethylphenylphosphite:

[0053] Add 0.04 mol of di-n-octylamine, 0.048 mol of phenylphosphite, 50 ml of water, and 30 ml of concentrated hydrochloric acid to a round-bottom flask in sequence, heat to 85°C, add 15 ml of 37% formaldehyde aqueous solution, and react at this temperature under reflux conditions for 24 hours;

[0054] After cooling, the product was transferred to a separatory funnel with ether, the aqueous phase was removed, and the organic phase was washed several times with 4% aqueous NaOH solution until the pH of the aqueous phase was >10;

[0055] Wash the ether phase with 10% H2SO4 until the pH is less than 2;

[0056] Wash the ether phase with pure water until pH>3;

[0057] The ether is removed by vacuum distillation to obtain a light yellow to white solid N,N-di-n-octylaminomethylphenylphosphite;

[0058] The characterization of N,N-di-n-octylaminomethylphenylphosphorous acid (abbreviated as DOAM-PPA) is as follows: FT-IR (v / cm-1), 3417.73 (OH), 1377.41 (CN), 1183.60 (P=O), 1038.48 (PC (N)), 957.97 (PO (H)). 31P NMR (202MHz, CDCl3) δ12.47ppm. 1H NMR (500MHz, CDCl3) δ7.90 (m, 2H), 7.42 (m, 3H), 3.17 (d, 2H), 3.12 (s, 4H), 1.58 (s, 4H), 1.23-1.17 (m, 21H), 0.85 (t, 6H). ESI-MS m / z: [M+1]+396.30, [2M+1]+791.60, as shown in the specific figure Figure 1 shown.

[0059] Example 3: Synthesis of N,N-di-n-octylaminomethyl (2,4,4-trimethyl-pentyl) hypophosphorous acid:

[0060] After adding a magnetic particle into the reactor, 0.3 mol of sodium hypophosphite, 16.00 g of glacial acetic acid, 0.1 mol of diisobutylene, 0.3 g of di-tert-butyl peroxide (DTBP), and 25 g of tetrahydrofuran were added in sequence, and then the mixture was heated in an oil bath on a magnetic stirrer at 120° C. and 1200 rpm for 8 h.

[0061] The tetrahydrofuran and unreacted olefins are removed by vacuum distillation;

[0062] Dissolve the above product in water and ether into a separatory funnel, then wash the ether phase 3 times with 4% NaOH aqueous solution (100 ml in total), and collect the aqueous phase product;

[0063] Add 10% H2SO4 solution to the aqueous phase product to make the pH <2, and add ether extractant solvent;

[0064] After removing the aqueous phase, wash the ether phase several times with saturated sodium chloride aqueous solution until the pH of the aqueous phase is >3;

[0065] Anhydrous magnesium sulfate is added to the organic phase and dried for 30 minutes, and then the ether and other solvents are removed by reduced pressure distillation to obtain 2,4,4-trimethylpentyl hypophosphorous acid.

[0066] Add 0.04 mol of di-n-octylamine, 0.048 mol of 2,4,4-trimethylphosphorous acid, 50 ml of water, and 30 ml of concentrated hydrochloric acid to a round-bottom flask in sequence, heat to 85°C, add 15 ml of 37% formaldehyde aqueous solution, and react at this temperature under reflux conditions for 24 hours;

[0067] After cooling, the product was transferred to a separatory funnel with ether, the aqueous phase was removed, and the organic phase was washed several times with 4% aqueous NaOH solution until the pH of the aqueous phase was >10;

[0068] Wash the ether phase with 10% H2SO4 until the pH is less than 2;

[0069] Wash the ether phase with pure water until pH>3;

[0070] The ether is removed by vacuum distillation to obtain N,N-di-n-octylaminomethyl (2,4,4-trimethylpentyl) hypophosphorous acid. The characterization of N,N-di-n-octylaminomethyl (2,4,4-trimethylpentyl) hypophosphorous acid (abbreviated as: DOAM-TMPPA) is as follows: FT-IR (v / cm-1), 3402.78 (OH), 1363.91 (CN), 1168.17 (P=O), 1054.39 (PC (N)), 943.98 (PO (H)). 31P NMR (202MHz, CDCl3) δ35.72ppm. 1H NMR (500MHz, CDCl3) δ3.25 (s, 2H), 3.23 (s, 4H), 2.01 (s, 1H), 1.74 (m, 6H), 1.61 (m, 1H), 1.29-1.21 (m, 22H), 1.09 (d, 3H), 0.87 (s, 9H), 0.83 (t, 6H). ESI-MS m / z:[M+1]+432.39,[2M+1]+863.78, as shown in the figure below Figure 1 shown.

[0071] Example 4: Using kerosene as diluent, Cyanex 272, P507 and P204 solutions with an extractant concentration of 10 mM were prepared as organic phase;

[0072] A mixed solution of six heavy rare earth ions (Y, Ho, Er, Tm, Yb, Lu) was prepared, the concentration of each rare earth ion was 20ppm, the Cl- concentration was 0.1mol / L, and the initial pH values ​​of the aqueous phase were: 4.00; 3.00; 2.50; 2.00; 1.75; 1.50; 1.25; aqueous phase 1;

[0073] Prepare a mixed solution containing six heavy rare earth ions (Y, Ho, Er, Tm, Yb, Lu), the concentration of each rare earth ion is 20ppm, and the concentration of hydrochloric acid is 0.1mol / L; 0.5mol / L; 1mol / L; 2mol / L; 4mol / L; 6mol / L of aqueous phase 2;

[0074] The organic phase and the aqueous phase 1 or the aqueous phase 2 were mixed in a volume ratio of 1:1, the extraction temperature was 25°C, the extraction time was 2h, and the shaking speed was 220rpm;

[0075] After the extraction is completed, the aqueous phase and the organic phase are separated in a centrifuge, and the concentration of each rare earth ion in the aqueous phase is determined using ICP-OES;

[0076] The extraction rate of each rare earth ion of N,N-dioctylaminomethylphenylphosphite changes with the concentration of hydrochloric acid and pH. Figure 2 The corresponding partial separation coefficient is shown as Figure 3 shown.

[0077] Comparative example:

[0078] The type of extractant was set as a variable test. Other extractants were P507, Cyanex 272, and P204. The test conditions were consistent with those in Example 4. The extraction rate of each rare earth ion varied with the concentration of hydrochloric acid and pH. Figure 2 As shown, the corresponding partial separation coefficients are Figure 3 shown.

[0079] The test results show that the N,N-di-n-octylaminomethylphenyl hypophosphorous acid developed by the present invention has a good heavy rare earth separation effect, and maintains a good rare earth extraction and separation effect in the range of hydrochloric acid concentration from 2 mol / L to pH=4. Compared with the traditional Cyanex 272 and P507, it has stronger industrial fault tolerance, is more suitable for industrial applications, and has a wider industrial range. In addition, for the Lu / Y and Lu / Yb separation coefficients, the N,N-di-n-octylaminomethylphenyl hypophosphorous acid developed by the present invention can reach 43.45 βLu / Y under 0.5 mol / L HCl conditions, which is higher than the separation coefficients of other extractants, and at this time βLu / Yb reaches 1.87. Therefore, the effect of N,N-di-n-octylaminomethylphenyl hypophosphorous acid on rare earth separation is significantly better than that of traditional P507, Cyanex 272 and P204. Therefore, compared with the traditional Cyanex 272 and P507 extractants, the N,N-di-n-octylaminomethylphenylphosphite developed by the present invention has higher industrial fault tolerance, higher extraction rate, and better separation coefficient, and therefore has greater industrial application prospects.

[0080] Example 5: Using kerosene as the diluent, preparing N,N-di-n-octylaminomethylphenylphosphite with an extractant concentration of 10 mM as the organic phase;

[0081] A mixed solution containing six heavy rare earth ions (Y, Ho, Er, Tm, Yb, Lu) was prepared, the concentration of each rare earth ion was 20ppm, the initial aqueous phase hydrochloric acid concentration was 0.5mol / L, and the concentrations of the salting-out agent NaCl were set to: 0mol / L; 0.1mol / L; 0.5mol / L; 1mol / L; 2mol / L;

[0082] The organic phase and the aqueous phase were mixed in a volume ratio of 1:1, the extraction temperature was 25 °C, the extraction time was 2 h, and the shaking speed was 220 rpm;

[0083] After the extraction is completed, the aqueous phase and the organic phase are separated in a centrifuge, and the concentration of each rare earth ion in the aqueous phase is determined by ICP-OES. The extraction rate of each rare earth ion in N,N-di-n-octylaminomethylphenyl hypophosphite changes with the concentration of NaCl as shown in the figure. Figure 4 shown.

[0084] The test results show that after adding 0.5 mol / L salting-out agent NaCl, the N,N-di-n-octylaminomethylphenylphosphite (DOAM-PPA) developed by the present invention can increase βLu / Y to 53.55, and its distribution coefficient is much higher than that of other extractants. Therefore, the N,N-di-n-octylaminomethylphenylphosphite (DOAM-PPA) developed by the present invention is a potential heavy rare earth separation extractant that can replace traditional P507, Cyanex 272 and P204 extractants.

[0085] Example 6: Using kerosene as a diluent, N,N-di-n-octylaminomethyl (2,3-dimethyl-1-butyl) hypophosphorous acid (DOAM-DMBPA), N,N-di-n-octylaminomethyl (2,4,4-trimethyl-pentyl) hypophosphorous acid (DOAM-TMPPA) and N,N-di-n-octylaminomethylphenyl hypophosphorous acid (DOAM-PPA) with an extractant concentration of 10 mM were prepared as an organic phase;

[0086] A mixed solution containing zirconium and hafnium ions was prepared, the concentration of each rare earth ion was 50 ppm, and the initial aqueous phase nitric acid concentrations were 0.1; 0.5; 1; 2; 4; 6 mol / L respectively;

[0087] The organic phase and the aqueous phase were mixed in a volume ratio of 1:1, the extraction temperature was 25 °C, the extraction time was 2 h, and the shaking speed was 220 rpm;

[0088] After extraction, the aqueous phase and the organic phase were separated in a centrifuge, and the concentrations of zirconium and hafnium ions in the aqueous phase were determined using ICP-OES. The changes in the extraction rates of zirconium and hafnium ions of DOAM-DMBPA, DOAM-TMPPA and DOAM-PPA with changes in nitric acid concentration are shown in Figure 2. Figure 5 shown.

[0089] The test results show that DOAM-DMBPA, DOAM-TMPPA and DOAM-PPA developed in the present invention have good zirconium and hafnium separation performance under the condition of 1-4 mol / L nitric acid concentration. When the nitric acid concentration is 2 mol / L, the zirconium and hafnium separation coefficients βZr / Hf can reach 9.70, 8.32 and 9.23 respectively.

[0090] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0091] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing an aminomethylphosphinate extractant, characterized in that: include: S1: Synthesis of monoalkyl hypophosphorous acid intermediates with different carbon chains, as shown in formula a: S2: Synthesize aminomethyl hypophosphite extractants of different structures, as shown in formula b:

2. A method for preparing an aminomethylphosphinothioic acid extractant according to claim 1, characterized in that: The preparation of the monoalkyl hypophosphorous acid intermediate in step S1 is as follows: S11: Sodium hypophosphite, glacial acetic acid, olefins of different carbon chains, di-tert-butyl peroxide and tetrahydrofuran were added into a reaction kettle in sequence, and then placed into a reaction kettle with a stirring device, and then reacted at 120° C. and 1200 rpm for 8 hours. S12: removing tetrahydrofuran and unreacted olefins from step S11 by vacuum distillation; S13: dissolving the product of step S12 with water and an organic solvent such as ether or dichloromethane, then washing the ether phase with a 2-6% NaOH aqueous solution for multiple times, and collecting the aqueous phase product; S14: adding 5-20% H2SO4 solution to the aqueous phase product in step S13 to make the pH <2, and then adding an organic solvent such as ether or dichloromethane; S15: After removing the aqueous phase from step S14, the ether phase is washed with ultrapure water for multiple times until the pH of the aqueous phase is greater than 3; S16: The solvent such as ether is removed by vacuum distillation to obtain a monoalkyl hypophosphorous acid intermediate. The preferred intermediate structure is shown below:

3. A method for preparing an aminomethylphosphinothioic acid extractant according to claim 2, characterized in that: The molar ratio of sodium hypophosphite to olefin is 2:1-6:

1. For example, the masses of various materials are 0.3 mol, 16 g, 0.1 mol, 0.3 g, and 25 g, respectively. The olefins are: 2,3-dimethyl-1-butene, diisobutylene, 2-ethyl-1-hexene, etc.

4. A method for preparing an aminomethylphosphinothioic acid extractant according to claim 3, characterized in that: The NaOH aqueous solution is a 4% NaOH aqueous solution.

5. The method for preparing an aminomethylphosphinothioic acid extractant according to claim 4, characterized in that: The H2SO4 solution is a 10% H2SO4 solution.

6. The method for preparing an aminomethylphosphinothioic acid extractant according to claim 5, characterized in that: The aminomethylphosphorous acid in step S2 is prepared as follows: S21: Add primary amine or secondary amine, monoalkyl hypophosphorous acid, and hydrochloric acid aqueous solution into a flask in sequence, heat to 30-100° C., add 37% formaldehyde solution, and react under reflux at this temperature for 8-24 hours; S22: The product in step S21 is transferred to a separatory funnel using an organic solvent such as ether, and after removing the aqueous phase, the organic phase is washed several times with a 2-6% NaOH aqueous solution until the pH of the aqueous phase is greater than 10; S23: Wash the organic phase of step S22 with 10% H2SO4 until the pH of the aqueous phase is less than 2; S24: Wash the organic phase with pure water until the pH of the aqueous phase is greater than 3; S25: Using reduced pressure distillation to remove solvents such as ether, the aminomethyl hypophosphorous acid product can be obtained. Preferably, the structure of the aminomethyl hypophosphorous acid is as follows:

7. The method for preparing an aminomethylphosphinothioic acid extractant according to claim 6, characterized in that: The ratio of primary amine or secondary amine to monoalkyl hypophosphorous acid is 1:(0.8-1.5), the concentration of hydrochloric acid is 2-6 mol / L, the molar ratio of formaldehyde to amines is (3-20):1, and the primary amine and secondary amine are: di-n-octylamine, di-iso-octylamine, isooctylamine, n-octylamine, n-hexylamine, di-n-hexylamine, etc.

8. A preparation of an aminomethylphosphorous acid extractant as described in Claims 1 to 7 and its application in the separation of strategic metals such as rare earth, zirconium, and hafnium.

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