A method for separating thorium from spallation elements

Abstract

The application relates to a thorium and spallation element separation method, which comprises the following steps: injecting a thorium-based solution into column 1 to obtain a first effluent, washing column 1 with a first inorganic acid solution and a second inorganic acid solution in sequence to obtain a first washing solution and a first thorium solution respectively; injecting the first thorium solution into column 2 to obtain a second effluent, washing column 2 with a third inorganic acid solution and a second inorganic acid solution in sequence to obtain a second washing solution and a second thorium solution; mixing the first thorium solution and the second thorium solution, injecting into column 3 to obtain a third effluent, and washing column 3 with a fourth inorganic acid solution to obtain a third thorium solution. The method does not introduce other foreign reagents and is not polluted by foreign impurity ions, and the high ion potential of Th is utilized to preferentially adsorb on a cation column to achieve the purpose of separation from other spallation elements.

Description

Technical Field

[0001] This invention relates to the field of medical radioisotope manufacturing technology, and in particular to a method for separating thorium from spallation elements. Background Technology

[0002] The production of medical isotopes mainly relies on three methods: reactor production, accelerator production, and separation of high-level radioactive waste. In reactors, isotopes are primarily produced through (n, γ) reactions, and the resulting isotopes are generally of the same element as the target material. In contrast, radioactive isotopes produced by accelerators are generally different from the target material, making them easier to chemically separate and allowing for the production of carrier-free isotopes, thus obtaining high-purity, high-specific-activity radioactive isotopes. Accelerators have a significant advantage in producing alpha radionuclides; proton accelerator irradiation of thorium targets can produce various medical isotopes such as Ac-225, Ra-224, Ra-223, Bi-213, Bi-212, and Pb-212. However, Th-232, which undergoes nuclear reactions with high-energy protons, constitutes less than 0.1 wt% of the thorium target, with the remaining 99.9 wt% being natural thorium. This makes the separation of the target isotope from the large amount of matrix thorium a primary challenge in the production process.

[0003] Irradiated thorium targets undergo shearing, dissolution, acid adjustment, separation, and purification to obtain isotopes that meet process specifications. Ac-225 (containing a few parts per thousand of Ac-227) needs to be produced directly from thorium solution or by Ra-225→Ac-225 decay. Ra-223 and Ra-224 require thorium to be separated from other spallation elements first, and then produced by Th-227→Ra-223 and Th-228→Ra-224 decay reactions after a period of time. Bi-213, Bi-212, and Pb-212 are respectively produced by the above-separated Ra and Ac isotopes through Ac-225→Bi-213, Ra-224→Bi-212, and Ra-224(Ra-228)→Pb-212 decay. The low recovery rate of direct extraction of trace Ra and Ac target isotopes from large amounts of thorium results in the loss of target isotopes. Therefore, the primary goal of producing alpha radionuclides by irradiating thorium targets is to separate thorium from other impurity elements (split elements) and maximize the recovery rate of target isotopes.

[0004] While solvent extraction is the most convenient method for separating thorium, it introduces organic solvent waste into medical isotope production lines, is complex to operate remotely, and yields thorium with a purity far lower than that obtained by column separation. For example, patent CN 103602810A discloses a method for preparing high-purity thorium using extraction resin. This involves passing an acid-containing thorium solution through an extraction resin column, loading thorium, eluting with washing acid, and then analyzing with an elution acid solution to obtain a thorium-containing acid solution. Patent CN 113066598A discloses a method for separating and purifying Ra-223 from an irradiated thorium target Th-232. The Th removal method described involves passing the solution through an anion exchange column, sequentially eluting the anion exchange resin column with 0.4–0.6 mol / L ammonium sulfate solution and 0.04–0.08 mol / L nitric acid solution. The sulfate ions chelate the tetravalent Th ions, converting them into anionic form that can be directly passed through the anion exchange resin column, achieving separation from other impurity elements. However, this method inevitably introduces sulfate and ammonium ions during the thorium removal process, which means that the removal of these two ions must be considered in the subsequent process. Summary of the Invention

[0005] Based on the above analysis, this invention provides a method for separating thorium from spallation elements, addressing the problems of existing methods easily introducing foreign impurities, failing to simultaneously recover spallation elements such as Ra and Ac, and exhibiting low Th recovery rates. The method of this invention, during thorium recovery, simultaneously ensures the decontamination coefficients of Ra and Ac within the thorium, recovering most of Ra and Ac for subsequent separation and purification steps. During thorium separation, the selective adsorption of tetravalent thorium under high acid conditions is utilized to separate it from other low-valence elements, without relying on external reagents, thus avoiding the introduction of impurity ions.

[0006] On one hand, the present invention provides a method for separating thorium from spallation elements, comprising the following steps:

[0007] (1) The thorium-based solution is injected into column 1 to obtain the first effluent. Column 1 is washed with the first inorganic acid solution and the second inorganic acid solution in sequence to obtain the first washing solution and the first thorium solution, respectively.

[0008] (2) The first thorium solution is injected into column 2 to obtain the second effluent. Column 2 is washed sequentially with the third inorganic acid solution and the second inorganic acid solution to obtain the second washing solution and the second thorium solution.

[0009] (3) Mix the first thorium solution and the second thorium solution and inject the mixture into column 3 to obtain the third effluent. Wash column 3 with the fourth inorganic acid solution to obtain the third thorium solution.

[0010] (4) Mix the first effluent and the first washing liquid in step (1) to obtain the first product liquid. Mix the second effluent and the second washing liquid in step (2) to obtain the second product liquid. Mix the first product liquid, the second product liquid and the third effluent in step (3) as the mother liquor for the subsequent purification steps of Ra and Ac.

[0011] Furthermore, in step (1), the acidity of the thorium-based solution is 5-5.5 mol / L, and the thorium concentration in the thorium-based solution is 12-20 g / L.

[0012] Furthermore, in step (1), the resin packed in column 1 is a divinylbenzene strong acid cation exchange resin, and the resin exchange group is -SO3H.

[0013] Furthermore, in step (1), the first inorganic acid solution is a nitric acid solution with a concentration of 5-5.5 mol / L.

[0014] Furthermore, in step (2), the acidity of the first thorium solution is first adjusted to 5.8-6.2 mol / L, and then injected into column 2.

[0015] Furthermore, in step (2), the resin used to fill column 2 is a divinylbenzene strong acid cation exchange resin with -SO3H as the resin exchange group.

[0016] Furthermore, in steps (1) and (2), the second inorganic acid solution is a nitric acid solution with a concentration of 7.8-8.0 mol / L;

[0017] In step (2), the third inorganic acid solution is a nitric acid solution with a concentration of 5.8-6.2 mol / L.

[0018] Furthermore, in step (3), the first thorium solution and the second thorium solution are mixed and diluted to an acidity of 3.5-4.5 mol / L, and then injected into column 3.

[0019] Furthermore, in step (3), the resin used in column 3 is UTEVA extraction resin, and the loading extractant is dipentyl phosphonate, or the resin used in column 3 is TRU extraction resin, and the loading extractant is phenyl-N,N-diisobutylamine carboxymethylphosphine oxide.

[0020] Furthermore, in step (3), the fourth inorganic acid solution is a nitric acid solution or hydrochloric acid solution with a concentration of 0.01-0.1 mol / L.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0022] (1) The method of the present invention does not introduce other external organic solvents and is free from external impurity ion contamination. The present invention utilizes the high ionic potential of Th to preferentially adsorb onto the cation column to achieve separation from other spallation elements.

[0023] (2) Since the contents of Ra and Ac in thorium are low, the present invention uses an eluent to elute, which can reduce the loss of Ra and Ac. The method of the present invention can separate thorium from other spallation elements and recover the mother liquor containing Ra and Ac for further purification of Ra and Ac. The total recovery rate of Th is greater than 99.996%, the total recovery rate of Ra is greater than 99.5%, and the total recovery rate of Ac is greater than 97.5%.

[0024] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objectives and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description. Detailed Implementation

[0025] A specific embodiment of the present invention discloses a method for separating thorium from spallation elements, comprising the following steps:

[0026] (1) The thorium-based solution is injected into column 1 to obtain the first effluent. Column 1 is washed with the first inorganic acid solution and the second inorganic acid solution in sequence to obtain the first washing solution and the first thorium solution, respectively.

[0027] (2) The first thorium solution is injected into column 2 to obtain the second effluent. Column 2 is washed sequentially with the third inorganic acid solution and the second inorganic acid solution to obtain the second washing solution and the second thorium solution.

[0028] (3) Mix the first thorium solution and the second thorium solution and inject the mixture into column 3 to obtain the third effluent. Wash column 3 with the fourth inorganic acid solution to obtain the third thorium solution.

[0029] (4) Mix the first effluent and the first washing liquid in step (1) to obtain the first product liquid. Mix the second effluent and the second washing liquid in step (2) to obtain the second product liquid. Mix the first product liquid, the second product liquid and the third effluent in step (3) as the mother liquor for the subsequent purification steps of Ra and Ac.

[0030] Compared with existing technologies, the method of this invention employs column separation, which avoids the introduction of external organic solvents and the generation of foreign impurities. This method utilizes the high ionic potential of Th to preferentially adsorb onto the cation column, achieving separation from other spallation elements. Simultaneously purifying thorium, this invention can also recover solutions containing Ra and Ac for further purification of Ra and Ac.

[0031] It should be noted that the thorium-based solution of this invention uses the calculated simulated source term elements obtained after irradiating a thorium target at 120 MeV and 500 μA for 10 days and then cooling for 10 days as an example to separate thorium from other spallation elements. After proton irradiation, thorium remains the main component of the natural thorium target, accounting for more than 99.9% by mass, with the remainder being spallation elements. These spallation elements mainly include monovalent alkali metal elements (Rb). + Cs + ), divalent alkaline earth metals and transition metals (Ca) 2+ 、Sr 2+ Ba 2+ Ra 2+ Mn 2+ Cd 2+ ), trivalent lanthanide actinides (Ac 3+ La 3+ Ce 3+ 、Sm 3+ Eu 3+ (etc.) and transition metals in different valence states (Ag, etc.) + Co 2 + Ru 3+ Cr 3+ SP-block metallic elements ([WO4]) 2- Po 4+ Pb 2+ ) and halogens (Br - I - At - The total mass of spallation elements is less than 0.1 Wt%.

[0032] It should be noted that the first product solution contains trace amounts of thorium, which accounts for approximately 0.01-0.03% of the thorium in the thorium-based solution. The leakage concentration of thorium in the first product solution is 0.01-0.03 g / L, of which Ac accounts for more than 55% of the total and Ra accounts for more than 98% of the total.

[0033] The second product solution contains a small amount of thorium, which accounts for about 1%-3% of the thorium in the thorium-based solution. The leakage concentration of thorium in the second product solution is 0.1-0.8 g / L, of which Ac accounts for more than 43% of the total and Ra accounts for more than 0.5% of the total.

[0034] In one specific embodiment, in step (1), the acidity of the thorium-based solution is 5-5.5 mol / L, for example, 5 mol / L, 5.1 mol / L, 5.2 mol / L, 5.3 mol / L, 5.4 mol / L, or 5.5 mol / L, and the thorium concentration in the thorium-based solution is 12-20 g / L, for example, 12 g / L, 14 g / L, 16 g / L, 18 g / L, or 20 g / L.

[0035] It should be noted that the acidity of the thorium-based solution can be adjusted by adding deionized water to dilute the thorium-based solution to an acidity of 5-5.5 mol / L, and the solution system is nitric acid.

[0036] In one specific embodiment, in step (1), the resin packed in column 1 is a divinylbenzene strong acid cation exchange resin with -SO3H as the resin exchange group.

[0037] In a preferred embodiment, the column 1 is filled with AG50W-X8 resin with a particle size of 50-400 mesh, preferably 200-400 mesh.

[0038] Specifically, the exchange capacity of the resin in column 1 is 0.5-4.5 meq / mL, preferably 1.5-2 meq / mL. For example, 0.5 meq / mL, 1.0 meq / mL, 1.5 meq / mL, 2.0 meq / mL, 2.5 meq / mL, 3.0 meq / mL, 3.5 meq / mL, 4.0 meq / mL, and 4.5 meq / mL.

[0039] Specifically, the resin-to-thorium ratio in column 1 is 15-25 g resin / g thorium, preferably 19-21 g resin / g thorium. For example, 15 g resin / g thorium, 16 g resin / g thorium, 17 g resin / g thorium, 18 g resin / g thorium, 19 g resin / g thorium, 20 g resin / g thorium, 21 g resin / g thorium, 22 g resin / g thorium, 23 g resin / g thorium, 24 g resin / g thorium, and 25 g resin / g thorium.

[0040] The thorium-based flow rate is controlled by a peristaltic pump at 0.5-1.0 mL / min, preferably 0.5-0.75 mL / min. For example, flow rates of 0.5 mL / min, 0.6 mL / min, 0.7 mL / min, 0.75 mL / min, 0.8 mL / min, 0.9 mL / min, and 1.0 mL / min are used.

[0041] It should be noted that in this invention, the flow rate of the thorium-based solution injected into column 1 is controlled. If the flow rate is too high, the adsorption process will not be completed and the separation degree will be insufficient. If the flow rate is too low, the time will be too long and the element will decay and be lost.

[0042] In one specific embodiment, in step (1), the first inorganic acid solution is a nitric acid solution with a concentration of 5-5.5 mol / L, preferably 5.3-5.5 mol / L. For example, 5 mol / L, 5.1 mol / L, 5.2 mol / L, 5.3 mol / L, 5.4 mol / L, and 5.5 mol / L.

[0043] The volume of the first inorganic acid used is 4-6 times the volume of the resin bed.

[0044] Specifically, the first inorganic acid solution is a nitric acid solution with a concentration of 5-5.5 mol / L. This is because thorium exists in a tetravalent state, and can still be adsorbed onto column 1 compared to other lower valence elements, while the lower valence elements flow out with the solution.

[0045] It should be noted that in step (1), the thorium-based solution is injected into column 1, which is loaded with a large number of tetravalent thorium ions. Other low-valence elements flow out with the solution to obtain the first effluent. Column 1 is washed with a first inorganic acid solution, and the thorium loaded on column 1 is eluted with a second inorganic acid solution to obtain the first thorium solution.

[0046] In one specific embodiment, in step (2), the acidity of the first thorium solution is first adjusted to 5.8-6.2 mol / L, and then injected into column 2.

[0047] It should be noted that in step (1), the cation exchange resin does not adsorb low-valence elements or adsorbs less under high acid conditions, so Th is separated from Ra and Ac. At this time, more than 98% of Ra and more than 55% of Ac enter the first effluent, and a small amount of Ra and Ac are still mixed in the first thorium solution.

[0048] Step (2) aims to further recover Ac remaining in thorium by increasing the acidity to prevent Ac from being adsorbed by column 2 and separated from thorium. However, the acidity should not be too high, otherwise it will reduce the adsorption capacity of column 2 for thorium. This process will result in a significant amount of Th mixed in the second effluent in order to improve the recovery rate of Ac. However, considering that the production value of medical isotope Ac is far greater than that of Th, and that there will be a subsequent purification step for Ac isotopes, it is acceptable to reduce the recovery rate of Th to improve the recovery rate of Ac.

[0049] The acidity of the solutions loaded onto the column differs in steps (1) and (2). Step (1) aims to separate Th from other low-valence elements and prevent the loss of Ra (into the first thorium solution). However, at this point, the adsorption behavior of trivalent Ac and tetravalent Th is similar, with approximately 40-50% of Ac entering the first thorium solution. Step (2) primarily aims to recover the remaining Ac by increasing the acidity of the solution loaded onto the column, preventing Ac from being adsorbed by the cation column and entering the second effluent, thus ensuring the recovery rate of Ac. More than 40% of Ac enters the second effluent, but a small amount of Th also enters the second effluent at this time.

[0050] It should be noted that the specific method for adjusting the acidity of the first thorium solution is to add deionized water to dilute the thorium-based solution to an acidity of 5.8-6.2 mol / L, and the solution system is nitric acid.

[0051] In one specific embodiment, in step (2), the resin packed in column 2 is a divinylbenzene strong acid cation exchange resin with -SO3H as the resin exchange group.

[0052] Specifically, the resin used to fill column 2 is AGMP-50 with a particle size of 100-400 mesh, preferably 100-200 mesh.

[0053] Specifically, the resin exchange capacity in column 2 can be 0.2-2.5 meq / mL, preferably 1.0-2.0 meq / mL. For example, 0.2 meq / mL, 0.4 meq / mL, 0.6 meq / mL, 0.8 meq / mL, 1.0 meq / mL, 1.2 meq / mL, 1.4 meq / mL, 1.6 meq / mL, 1.8 meq / mL, 2.0 meq / mL, 2.2 meq / mL, 2.4 meq / mL, and 2.5 meq / mL.

[0054] Specifically, the resin-to-thorium ratio in column 2 is 13-22 g resin / g thorium, preferably 15-18 g resin / g thorium. For example, 13 g resin / g thorium, 14 g resin / g thorium, 15 g resin / g thorium, 16 g resin / g thorium, 17 g resin / g thorium, 18 g resin / g thorium, 19 g resin / g thorium, 20 g resin / g thorium, 21 g resin / g thorium, and 22 g resin / g thorium.

[0055] Specifically, the flow rate of the first thorium solution injected into column 2 is controlled by a peristaltic pump. The flow rate is 0.5-1.0 mL / min, preferably 0.5-0.75 mL / min, for example, 0.5 mL / min, 0.6 mL / min, 0.7 mL / min, 0.75 mL / min, 0.8 mL / min, 0.9 mL / min, and 1.0 mL / min.

[0056] It should be noted that in this invention, the flow rate of the first thorium-based solution injected into column 2 is controlled. If the flow rate is too high, the adsorption process will not be completed and the separation degree will be insufficient. If the flow rate is too low, the time will be too long and the element will decay and be lost.

[0057] Both steps (1) and (2) use cation exchange resin as the material, and their purpose is to separate Th from Ra and Ac. However, if step (2) is performed directly, the Ra and Ac mixed solution will contain more than 100 times the amount of Th, which will increase the burden on subsequent Ra and Ac purification. Therefore, the two-step separation method can not only improve the recovery rate of Th, but also avoid the loss of Ra and Ac.

[0058] In one specific embodiment, in steps (1) and (2), the second inorganic acid solution is a nitric acid solution with a concentration of 7.8-8.0 mol / L, for example, a concentration of 7.8 mol / L, 7.9 mol / L, or 8.0 mol / L. The volume of the second inorganic acid solution used in steps (1) and (2) is 15-20 times the volume of the resin bed.

[0059] Specifically, in step (2), the third inorganic acid solution is a nitric acid solution with a concentration of 5.8-6.2 mol / L, for example, 5.8 mol / L, 5.9 mol / L, 6.0 mol / L, 6.1 mol / L, or 6.2 mol / L. The volume of the third inorganic acid solution used is 15-20 times the volume of the resin bed.

[0060] It should be noted that in step (2), the first thorium solution passes through column 2 to obtain a second effluent containing a small amount of Ra and a large amount of Ac. Thorium is still adsorbed on column 2. The third inorganic acid solution is used to wash column 2, and the second inorganic acid solution elutes the thorium loaded on column 2 to obtain the second thorium solution.

[0061] In one specific embodiment, in step (3), the first thorium solution and the second thorium solution are mixed and diluted to an acidity of 3.5-4.5 mol / L, and then injected into column 3. The resin used in column 3 is UTEVA extraction resin, and the loading extractant is dipentyl pentylphosphonate, or the resin used in column 3 is TRU extraction resin, and the loading extractant is phenyl-N,N-diisobutylaminoformylmethylphosphine oxide.

[0062] Specifically, the resin in column 3 has a particle size of 100-150 μm.

[0063] In one specific embodiment, in step (3), the fourth inorganic acid solution is a nitric acid solution or hydrochloric acid solution with a concentration of 0.01-0.1 mol / L, for example, with concentrations of 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, or 0.1 mol / L. The volume of the fourth inorganic acid solution used is 15-20 times the volume of the resin bed.

[0064] It should be noted that in step (3), after the first thorium solution and the second thorium solution are mixed, they are passed through column 3, where thorium is loaded onto column 3. The fourth inorganic acid solution elutes the thorium on column 3 to obtain the third thorium solution.

[0065] Specifically, a peristaltic pump is used to control the flow rate of the first and second thorium solutions entering column 3, with a flow rate of 1.0-5.0 mL / min, preferably 2.5 mL / min-2.85 mL / min. For example, 1.0 mL / min, 1.5 mL / min, 2.0 mL / min, 2.5 mL / min, 2.85 mL / min, 3.0 mL / min, 3.5 mL / min, 4.0 mL / min, 4.5 mL / min, and 5.0 mL / min.

[0066] It should be noted that in this invention, the flow rates of the first and second thorium solutions entering column 3 are controlled. Excessive flow rates will result in incomplete adsorption and insufficient separation, while excessively low flow rates will lead to prolonged decay and elemental loss. The final third thorium solution obtained in this invention is a purified thorium solution, which can be used as a raw material for the Th-Ra decay production of Ra-223 / 224.

[0067] This method, besides separating thorium from thorium target solutions, can also separate and purify Th from Ra during the Th-227→Ra-223 process for use in the next round of Ra-223 production. A 600g thorium target was irradiated for 10 days using a 120MeV, 500μA high-energy proton accelerator. After cooling for 10 days, the thorium target contained approximately 25Ci of Th-227. Th-227 and Ra-223 reached decay equilibrium at 21 days, at which point the target contained not only the target daughter Ra but also impurities such as Pa, At, Po, Bi, and Pb. Using the method of this invention, the daughter radium element in thorium is recovered every 21 days. After Ra separation, thorium is purified using this method. In fact, Ra is recovered during the thorium purification process, with a single recovery rate >98%.

[0068] The technical solution of the present invention will be explained below with reference to specific embodiments.

[0069] Example 1

[0070] This embodiment of a method for separating thorium from spallation elements includes the following steps:

[0071] (1) A thorium-based nitric acid solution with an acidity of 5 mol / L and a thorium concentration of 12 g / L is injected into column 1 to obtain the first effluent. Column 1 is packed with AG50W-X8 resin with a particle size of 50-400 mesh. The exchange capacity of the resin in column 1 is 0.5 meq / mL, and the ratio of resin to thorium in column 1 is 15 g resin / g thorium. The flow rate of the thorium-based solution injected into column 1 is controlled by a peristaltic pump at a flow rate of 0.5 mL / min. Column 1 is washed sequentially with a first inorganic acid solution and a second inorganic acid solution to obtain the first washing solution and the first thorium solution, respectively. The first inorganic acid solution is a nitric acid solution with a concentration of 5 mol / L, and the volume of the first inorganic acid solution used is 4-6 resin bed volumes. The second inorganic acid solution is a nitric acid solution with a concentration of 7.8 mol / L, and the volume of the second inorganic acid solution used is 15-20 resin bed volumes.

[0072] (2) First, adjust the acidity of the first thorium solution to 5.8 mol / L and inject it into column 2 to obtain the second effluent. Specifically, the resin packed in column 2 is AGMP-50 with a particle size of 100-400 mesh. The resin exchange capacity in column 2 can be 0.2 meq / mL. The ratio of resin to thorium in column 2 is 13 g resin / g thorium. The flow rate of the first thorium solution injected into column 2 is controlled by a peristaltic pump at a flow rate of 0.5 mL / min. Column 2 is washed sequentially with a third inorganic acid solution and a second inorganic acid solution to obtain the second washing solution and the second thorium solution. The third inorganic acid solution is a nitric acid solution with a concentration of 5.8 mol / L and the volume of the third inorganic acid solution used is 15-20 resin bed volumes. The second inorganic acid solution is a nitric acid solution with a concentration of 7.8 mol / L and the volume of the second inorganic acid solution used is 15-20 resin bed volumes.

[0073] (3) The first thorium solution and the second thorium solution are mixed and diluted to an acidity of 3.5 mol / L, and then injected into column 3 to obtain the third effluent. The resin used in column 3 is UTEVA extraction resin, the particle size of the resin in column 3 is 100-150 μm, and the loading extractant is dipentyl pentylphosphonate. The flow rate of the first thorium solution and the second thorium solution into column 3 is controlled by a peristaltic pump, and the flow rate is 1.0 mL / min. Column 3 is washed with a fourth inorganic acid solution to obtain the third thorium solution. The fourth inorganic acid solution is a 0.01 mol / L nitric acid solution, and the volume of the fourth inorganic acid solution used is 15-20 resin bed volumes.

[0074] (4) Mix the first effluent and the first washing liquid in step (1) to obtain the first product liquid. Mix the second effluent and the second washing liquid in step (2) to obtain the second product liquid. Mix the first product liquid, the second product liquid and the third effluent in step (3) as the mother liquor for the subsequent purification steps of Ra and Ac.

[0075] Example 2

[0076] This embodiment of a method for separating thorium from spallation elements includes the following steps:

[0077] (1) A thorium-based nitric acid solution with an acidity of 5.3 mol / L and a thorium concentration of 16 g / L was injected into column 1 to obtain the first effluent. Column 1 was packed with AG50W-X8 resin with a particle size of 200-400 mesh. The exchange capacity of the resin in column 1 was 2.5 meq / mL, and the ratio of resin to thorium in column 1 was 1.75 g resin / g thorium. The flow rate of the thorium-based solution injected into column 1 was controlled by a peristaltic pump at 0.75 mL / min. Column 1 was washed sequentially with a first inorganic acid solution and a second inorganic acid solution to obtain the first washing solution and the first thorium solution, respectively. The first inorganic acid solution was a nitric acid solution with a concentration of 5.25 mol / L, and the volume of the first inorganic acid solution used was 4-6 resin bed volumes. The second inorganic acid solution was a nitric acid solution with a concentration of 7.9 mol / L, and the volume of the second inorganic acid solution used was 15-20 resin bed volumes.

[0078] (2) First, adjust the acidity of the first thorium solution to 6.0 mol / L and inject it into column 2 to obtain the second effluent. Specifically, column 2 is packed with AGMP-50 resin with a particle size of 100-200 mesh. The resin exchange capacity in column 2 can be 1.1 meq / mL. The ratio of resin to thorium in column 2 is 17 g resin / g thorium. The flow rate of the first thorium solution injected into column 2 is controlled by a peristaltic pump at 0.75 mL / min. Column 2 is washed sequentially with a third inorganic acid solution and a second inorganic acid solution to obtain the second washing solution and the second thorium solution. The third inorganic acid solution is a 6.0 mol / L nitric acid solution, and the volume of the third inorganic acid solution used is 15-20 resin bed volumes. The second inorganic acid solution is a 7.9 mol / L nitric acid solution, and the volume of the second inorganic acid solution used is 15-20 resin bed volumes.

[0079] (3) The first thorium solution and the second thorium solution are mixed and diluted to an acidity of 4.0 mol / L, and then injected into column 3 to obtain the third effluent. The resin used in column 3 is TRU extraction resin, the particle size of the resin in column 3 is 100-150 μm, the loaded extractant is phenyl-N,N-diisobutylamine formyl methylphosphine oxide, the flow rate of the first thorium solution and the second thorium solution into column 3 is controlled by a peristaltic pump, the flow rate is 3.0 mL / min, and column 3 is washed with a fourth inorganic acid solution to obtain the third thorium solution. The fourth inorganic acid solution is a 0.05 mol / L nitric acid solution, and the volume of the fourth inorganic acid solution used is 15-20 resin bed volumes.

[0080] (4) Mix the first effluent and the first washing liquid in step (1) to obtain the first product liquid. Mix the second effluent and the second washing liquid in step (2) to obtain the second product liquid. Mix the first product liquid, the second product liquid and the third effluent in step (3) as the mother liquor for the subsequent purification steps of Ra and Ac.

[0081] Example 3

[0082] This embodiment of a method for separating thorium from spallation elements includes the following steps:

[0083] (1) A thorium-based nitric acid solution with an acidity of 5.5 mol / L and a thorium concentration of 20 g / L was injected into column 1 to obtain the first effluent. Column 1 was packed with AG50W-X8 resin with a particle size of 100-300 mesh. The exchange capacity of the resin in column 1 was 4.5 meq / mL, and the ratio of resin to thorium in column 1 was 25 g resin / g thorium. The flow rate of the thorium-based solution injected into column 1 was controlled by a peristaltic pump at a flow rate of 1.0 mL / min. Column 1 was washed sequentially with a first inorganic acid solution and a second inorganic acid solution to obtain the first washing solution and the first thorium solution, respectively. The first inorganic acid solution was a nitric acid solution with a concentration of 5.5 mol / L, and the volume of the first inorganic acid solution used was 4-6 resin bed volumes. The second inorganic acid solution was a nitric acid solution with a concentration of 8.0 mol / L, and the volume of the second inorganic acid solution used was 15-20 resin bed volumes.

[0084] (2) First, the acidity of the first thorium solution is adjusted to 6.2 mol / L and then injected into column 2 to obtain the second effluent. Specifically, the resin packed in column 2 is AGMP-50 with a particle size of 200-300 mesh. The resin exchange capacity in column 2 can be 2.5 meq / mL. The ratio of resin to thorium in column 2 is 22 g resin / g thorium. The flow rate of the first thorium solution injected into column 2 is controlled by a peristaltic pump at a flow rate of 1.0 mL / min. Column 2 is washed sequentially with a third inorganic acid solution and a second inorganic acid solution to obtain the second washing solution and the second thorium solution. The third inorganic acid solution is a nitric acid solution with a concentration of 6.2 mol / L and the volume of the third inorganic acid solution used is 15-20 resin bed volumes. The second inorganic acid solution is a nitric acid solution with a concentration of 8.0 mol / L and the volume of the second inorganic acid solution used is 15-20 resin bed volumes.

[0085] (3) The first thorium solution and the second thorium solution are mixed and diluted to an acidity of 4.5 mol / L, and then injected into column 3 to obtain the third effluent. The resin used in column 3 is UTEVA extraction resin, the particle size of the resin in column 3 is 100-150 μm, and the loading extractant is dipentyl pentylphosphonate. The flow rate of the first thorium solution and the second thorium solution into column 3 is controlled by a peristaltic pump, and the flow rate is 5.0 mL / min. Column 3 is washed with a fourth inorganic acid solution to obtain the third thorium solution. The fourth inorganic acid solution is a 0.1 mol / L hydrochloric acid solution, and the volume of the fourth inorganic acid solution used is 15-20 times the resin bed volume.

[0086] (4) Mix the first effluent and the first washing liquid in step (1) to obtain the first product liquid. Mix the second effluent and the second washing liquid in step (2) to obtain the second product liquid. Mix the first product liquid, the second product liquid and the third effluent in step (3) as the mother liquor for the subsequent purification steps of Ra and Ac.

[0087] Comparative Example 1

[0088] The method of this comparative example is the same as that of Example 1, except that step (2) is omitted and the first thorium solution is directly injected into column 3.

[0089] Comparative Example 2

[0090] The method of this comparative example is the same as that of Example 1, except that in step (3), the resin filled in column 3 is the same as that in column 1.

[0091] Experimental Example 1

[0092] The total recoveries of Th, Ra, and Ac in the methods of Example 1 and Comparative Examples 1-2 were tested respectively, and the results are shown in Table 1.

[0093] Table 1

[0094]

[0095] As shown in Table 1, the two-step separation of Th using ion exchange resin and purification of Th using extraction resin is a method for separating Th from other spallation elements. During the separation process, it achieves the separation of large amounts of Th from trace spallation elements in the matrix solution while avoiding the problem of medical isotopes contaminating Th. The final Th recovery rate was 98.1%, with a purity of over 99.99% and low impurity element content. Simultaneously, the recovery rate of medical isotope Ra was 98.8%, and the Ac recovery rate was 97.4%. The purified Th can be recovered for retargeting or used to produce Ra-223 from the decay of Th-227, yielding Ra with high radioactive purity. It is worth noting that step (2) cannot be omitted, otherwise a large amount of Ac will enter Th and cannot be recovered. Furthermore, the presence of the extraction resin column is essential. Ion exchange resin columns cannot purify Th, while UTEVA or TRU resin columns can specifically adsorb Th and desorb it under low-acid conditions, making Th purification indispensable.

[0096] The inventors also conducted the above-mentioned experiments on other embodiments, and the results were basically the same. Due to space limitations, they will not be listed one by one.

[0097] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for separating thorium from spallation elements, characterized in that, Includes the following steps: (1) The thorium-based solution is injected into column 1 to obtain the first effluent. Column 1 is washed with the first inorganic acid solution and the second inorganic acid solution in sequence. The resin packed in column 1 is a divinylbenzene strong acid cation exchange resin with -SO3H as the resin exchange group. The first washing solution and the first thorium solution are obtained respectively. (2) The first thorium solution is injected into column 2 to obtain the second effluent. Column 2 is washed sequentially with the third inorganic acid solution and the second inorganic acid solution to obtain the second washing solution and the second thorium solution. (3) The first thorium solution and the second thorium solution are mixed and injected into column 3 to obtain the third effluent. Column 3 is washed with the fourth inorganic acid solution to obtain the third thorium solution. The resin used in column 3 is UTEVA extraction resin and the loading extractant is dipentyl pentylphosphonate. Alternatively, the resin used in column 3 is TRU extraction resin and the loading extractant is phenyl-N,N-diisobutylaminoformylmethylphosphine oxide. (4) Mix the first effluent and the first washing liquid in step (1) to obtain the first product liquid. Mix the second effluent and the second washing liquid in step (2) to obtain the second product liquid. Mix the first product liquid, the second product liquid and the third effluent in step (3) as the mother liquor for the subsequent purification steps of Ra and Ac. The first inorganic acid solution is a nitric acid solution with a concentration of 5-5.5 mol / L; The second inorganic acid solution is a nitric acid solution with a concentration of 7.8-7.9 mol / L; The third inorganic acid solution is a nitric acid solution with a concentration of 5.8-6.2 mol / L; The first product solution contains trace amounts of thorium, accounting for 0.01-0.03% of the thorium in the thorium-based solution. The leakage concentration of thorium in the first product solution is 0.01-0.03 g / L, of which Ac accounts for more than 55% of the total and Ra accounts for more than 98% of the total. The second product solution contains a small amount of thorium, which accounts for about 1%-3% of the thorium in the thorium-based solution. The leakage concentration of thorium in the second product solution is 0.1-0.8 g / L, of which Ac accounts for more than 43% of the total and Ra accounts for more than 0.5% of the total.

2. The method for separating thorium from spallation elements according to claim 1, characterized in that, In step (1), the acidity of the thorium-based solution is 5-5.5 mol / L, and the thorium concentration in the thorium-based solution is 12-20 g / L.

3. A method for separating thorium from spallation elements according to claim 1 or 2, characterized in that, In step (1), the first inorganic acid solution is a nitric acid solution with a concentration of 5.1-5.4 mol / L.

4. The method for separating thorium from spallation elements according to claim 1, characterized in that, In step (2), the acidity of the first thorium solution is first adjusted to 5.8-6.2 mol / L, and then injected into column 2.

5. A method for separating thorium from spallation elements according to claim 1 or 4, characterized in that, In step (2), the resin packed in column 2 is a divinylbenzene strong acid cation exchange resin with -SO3H as the resin exchange group.

6. A method for separating thorium from spallation elements according to claim 1 or 4, characterized in that, In step (2), the third inorganic acid solution is a nitric acid solution with a concentration of 5.9-6.1 mol / L.

7. The method for separating thorium from spallation elements according to claim 1, characterized in that, In step (3), the first thorium solution and the second thorium solution are mixed and diluted to an acidity of 3.5-4.5 mol / L, and then injected into column 3.

8. The method for separating thorium from spallation elements according to claim 1, characterized in that, In step (3), the fourth inorganic acid solution is a nitric acid solution or hydrochloric acid solution with a concentration of 0.01-0.1 mol / L.

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