An acidic o-phenanthroline amide, a preparation method thereof, and a method for improving the purity of thorium and separating thorium from uranium

Abstract

The present invention relates to the technical field of spent fuel reprocessing, and specifically discloses an acidic phenanthroline amide and its preparation method, as well as a method for improving the purity of thorium and separating thorium from uranium. The structure of the acidic phenanthroline amide is as follows: It includes the steps of using 1,10-phenanthroline-2,9-dicarboxylic acid as a raw material, undergoing esterification, single hydrolysis, acyl chlorination, and then amidation with R2NH, and finally undergoing hydrolysis and acidification to obtain. The present invention provides an acidic phenanthroline amide with a brand-new structure. As an extractant, it can selectively separate U(VI) from a large amount of Th(IV), and has the advantages of high extraction rate, fast extraction kinetics, and easy stripping. High-purity thorium and uranium products can be obtained, and it has good application prospects in the field of U(VI) / Th(IV) separation. #imgabs0#

Description

Technical Field

[0001] The present invention relates to the fields of spent fuel reprocessing and thorium purification, and particularly relates to an acidic o-phenanthroline amide and a preparation method thereof, and a method for improving the purity of thorium and separating thorium from uranium by using the acidic o-phenanthroline amide. Background Art

[0002] In recent years, due to factors such as nuclear non-proliferation and the continuous increase in the demand for uranium resources, the thorium-based fuel cycle has attracted wide attention again. The content of thorium (Th) in the earth's crust is about 3-4 times that of uranium. Compared with the traditional uranium (U)-based fuel cycle, the thorium-based fuel cycle has advantages such as high conversion rate, low production of plutonium and minor actinides, and high inherent safety. 232 Th itself is a non-fissionable material and needs to be converted into a fissionable nuclide 233 U through a series of nuclear reactions such as neutron capture in a reactor. Therefore, high requirements are imposed on impurities with a large neutron absorption cross-section for thorium used as a nuclear fuel. The purification of thorium and the preparation of nuclear pure grade thorium are important prerequisites for the development of the thorium-based fuel cycle. 232 The 233 U generated during the Th conversion process fissions directly in the reactor in part, and is discharged as spent fuel in part. Separating uranium from irradiated thorium is also of great significance for improving fuel utilization and realizing the safety of nuclear energy utilization.

[0003] In addition, with the approval of Xofigo ( 223 RaCl2, Bayer) for the clinical treatment of bone metastases, targeted alpha therapy (TAT) has shown great application potential. Due to the high linear energy transfer and ray energy of alpha particles, TAT radiopharmaceuticals can show stronger killing effects on tumor cells within a shorter range, while minimizing the off-target effects on healthy cells. 227 As a medical isotope, Th 227 Th immunoconjugates obtained by connecting with multiple mAbs have also shown good clinical results. 227 Th can also be used as an in vivo generator of 223 Ra to further improve the treatment effect of sclerotic bone metastases. To ensure the radioactive purity and stability of therapeutic agents, the purity requirements for thorium used as a medical isotope are also correspondingly high.

[0004] Currently, commercially available thorium usually contains a small amount of uranium. Different from the separation of uranium and plutonium, it is more difficult because the chemical valence of thorium is relatively stable. Thorex is the only possible industrial process for uranium-thorium separation. This process uses TBP as an extractant to co-extract uranium and thorium and then purify uranium and thorium. However, TBP has strong water solubility and forms a third phase during use, and the presence of P element will inevitably bring the problem of secondary pollution caused by incomplete combustion.

[0005] Amide extractants such as DEHIBA (Pathak, P.N.; Kumbhare, L.B.; Manchanda, V.K. Solvent Extr. Ion Exch. 2001, 19, 105 - 126.) and DHDOGA (Mowafy, E.A.; Al Shammari, A.M.; Mohamed, D. Radiochemistry 2019, 61, 681 - 688.) have also received extensive attention due to advantages such as complete combustion and high extraction selectivity. However, their extraction distribution ratios are relatively low and further improvement is still needed.

[0006] There have been many literature reports on new extractants that may be used for uranium - thorium separation. Et - Tol - DAPhen with a pre - organized structure (Xiao, C.; Wang, C; Yuan, L.; Li, B.; He, H.; Wang, S.; Zhao, Y.; Chai, Z.; Shi, W. Inorg. Chem. 2014, 53, 1712 - 1720.) has strong extraction ability for actinides in various oxidation states, and acidic pyridine amide DEHAPA (Xu, C.; Zhu, L.; Liu, Q.; Yang, S.; Xue, Y.; Tian, G. A. J. Radioanal. Nucl. Chem. 2023, 332, 859 - 865.) also shows certain uranium - thorium separation ability, but the extraction effect is still not ideal enough. Summary of the Invention

[0007] Aiming at the problems of difficult uranium - thorium separation, strong secondary pollution of traditional extraction methods, and low extraction efficiency of existing extractants, the present invention provides an acidic o - phenanthroline amide extractant. This extractant can selectively separate U(VI) from an environment containing a large amount of Th(IV) with high separation efficiency, and also shows excellent performance in extraction kinetics and stripping.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] An acidic o - phenanthroline amide, the structure of the acidic o - phenanthroline amide is as follows:

[0010]

[0011] Among them, R is a straight - chain alkyl or branched - chain alkyl of C2 - C 10 10.

[0012] The present invention synthesizes an acidic phenanthroline amide with a novel structure. This compound can be used as an extractant to selectively separate U(VI) from a large amount of Th(IV), and relatively pure uranium and thorium products can be obtained respectively through the process of "extraction at high acid concentration and stripping at low acid concentration". Compared with the acidic pyridine amide ligand CPCA reported in the existing literature, a novel acidic phenanthroline amide extractant is constructed by introducing a phenanthroline skeleton in this patent. Due to the highly pre-organized characteristics of the phenanthroline skeleton, it is found that this type of extractant has extremely fast kinetics and can be applied to the reprocessing of thorium-based spent fuel and the preparation of high-purity thorium.

[0013] Preferably, R is one or more of ethyl, n-butyl, n-hexyl, n-octyl, and 2-ethylhexyl. This extractant has a high preparation yield, good solubility, and relatively good extraction effect.

[0014] The present invention also provides a preparation method of the acidic phenanthroline amide, including the steps of using 1,10-phenanthroline-2,9-dicarboxylic acid as a raw material, undergoing esterification and single hydrolysis to obtain 9-methoxycarbonyl-1,10-phenanthroline-2-carboxylic acid, then subjecting 9-methoxycarbonyl-1,10-phenanthroline-2-carboxylic acid to acyl chlorination and reacting with R2NH through amidation reaction to obtain an amidation product A, and after hydrolysis and acidification of product A, the acidic phenanthroline amide is obtained;

[0015] wherein R is as described in claim 1, and the structure of product A is as follows:

[0016]

[0017] Preferably, the preparation method of the acidic phenanthroline amide includes the steps:

[0018] Step 1, 1,10-phenanthroline-2,9-dicarboxylic acid undergoes an esterification reaction with methanol to obtain 2,9-dimethoxycarbonyl-1,10-phenanthroline. The reaction formula is as follows:

[0019]

[0020] Step 2, 2,9-dimethoxycarbonyl-1,10-phenanthroline undergoes a single hydrolysis reaction under the action of a strong base, and after acidification, 9-methoxycarbonyl-1,10-phenanthroline-2-carboxylic acid is obtained; the reaction formula is as follows:

[0021]

[0022] Step 3, 9-methoxycarbonyl-1,10-phenanthroline-2-carboxylic acid undergoes a reflux reaction with thionyl chloride, and after the solvent is evaporated to dryness, an acyl chlorination product is obtained; the acyl chlorination product is dissolved in a solvent, a deacidifying agent and R2NH are added, and a reflux amidation reaction is carried out. The product is washed and purified by column chromatography to obtain product A; the reaction formula is as follows:

[0023]

[0024] Step 4: The product A is hydrolyzed and acidified to obtain the acidic o-phenanthroline amide; the reaction formula is as follows:

[0025]

[0026] In Step 1, methanol is both a reactant and can also be used as a solvent; further preferably, a chlorinating agent and a dehydrating agent such as thionyl chloride, sulfuric acid, etc. are also included in Step 1. The dropping method is adopted, and an ice bath is used during the dropping process. After the dropping is completed, reflux reaction is carried out.

[0027] The reaction time of Step 1 is 3 - 7 h.

[0028] The purification process of the esterification product in Step 1 includes: the reaction product is dissolved in dichloromethane, then washed successively with sodium bicarbonate solution and saturated brine, and dried with anhydrous sodium sulfate. After removing the dichloromethane solvent, 2,9-dimethoxycarbonyl-1,10-phenanthroline is obtained.

[0029] In Step 2, the single hydrolysis reaction solvent is any one or more of methanol, ethanol, tetrahydrofuran, 1,4-dioxane; the reaction raw materials are added dropwise, and an ice bath is used during the dropping process. After the dropping is completed, the reaction is carried out at room temperature for 3 - 7 h.

[0030] The strong base in Step 2 includes any one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide.

[0031] The acidifying reagent used in the acidification process includes any one or more of hydrochloric acid, acetic acid, etc.

[0032] After removing the solvent from the product of the single hydrolysis reaction in Step 2, water and an acidifying reagent are added to acidify to pH 1.5 - 3, and the precipitate is collected by filtration and dried to obtain 9-methoxycarbonyl-1,10-phenanthroline-2-carboxylic acid.

[0033] In Step 3, the acyl chlorination reaction is carried out for 2 - 5 h, and the acid-binding agent includes common acid-binding agents such as triethylamine, N,N-diisopropylethylamine, pyridine, sodium carbonate, etc. The amidation reaction is carried out for 2 - 5 h, and the product A is washed with saturated brine and dried with anhydrous sodium sulfate, or washed and dried by other conventional methods in the art.

[0034] In Step 4, the hydrolysis reaction solvent is any one or more of methanol, ethanol, tetrahydrofuran, 1,4-dioxane; the reaction raw materials are added dropwise, and an ice bath is used during the dropping process. After the dropping is completed, the reaction is carried out at room temperature for 3 - 7 h.

[0035] After removing the solvent from the product of the single hydrolysis reaction in Step 2, water and hydrochloric acid are added to acidify to pH 1.5 - 3, and the precipitate is collected by filtration and dried to obtain the acidic o-phenanthroline amide.

[0036] In the preparation process of the acidic phenanthroline amide, all raw materials are used in corresponding molar ratios, or appropriately some raw materials are in excess. During the reaction process, solvents, acid-binding agents, acidifying reagents, etc. are all used in conventional dosages in the art, and the solvents are all conventional organic solvents.

[0037] The present invention also provides a method for improving the purity of thorium. Using the acidic phenanthroline amide as an extractant, it is dissolved in an organic solvent to obtain an organic phase, which is mixed with an acidic aqueous phase containing thorium and uranium, and an organic phase containing uranium and an aqueous phase containing high-purity thorium are obtained by extraction.

[0038] The acidic phenanthroline amide of the present invention has a rigid phenanthroline ring and an asymmetric functional group, endowing it with highly pre-organized characteristics and strong complexing ability. It can selectively separate U(VI) from a large amount of Th(IV). This novel extractant has a very high distribution ratio for U(VI). When the nitric acid concentration in the aqueous phase is 4 mol / L, D U(VI) can reach 1566. At this time, the uranium-thorium separation factor SF U(VI) / Th(IV) is 1582. When continuously increasing the Th(IV) concentration in the aqueous phase until the U(VI) / Th(IV) ratio reaches 1 / 500, this extractant still has a very high selectivity for U(VI) (SF U(VI) / Th(IV) = 282), and can be used for the preparation or purification of thorium to obtain a high-purity thorium element product.

[0039] The uranium is hexavalent U(VI), and the thorium is tetravalent Th(IV);

[0040] The organic solvent includes at least one of n-octanol, 3-nitrobenzotrifluoride, cyclohexanone, toluene, or kerosene;

[0041] The molar concentration of the acidic phenanthroline amide in the organic phase is 0.001 - 0.01 mol / L; preferably, the molar concentration of the acidic phenanthroline amide in the organic phase is 0.005 - 0.01 mol / L;

[0042] The acidic aqueous phase is a nitric acid solution, and the nitric acid concentration is 0.5 - 4 mol / L. Preferably, the nitric acid concentration is 1 - 4 mol / L.

[0043] The volume ratio of the organic phase to the aqueous phase is 0.2 - 5:1;

[0044] The mixing time is more than 1 minute; the acidic phenanthroline amide of the present invention has extremely fast kinetics and can reach the extraction equilibrium in an ultra-short time. Experimental studies have found that this extractant can reach the extraction equilibrium in 4 minutes. Preferably, the mixing time is more than 4 minutes, and more preferably 4 - 30 min.

[0045] The temperature during the mixing, separation, and extraction process is 0 - 50 °C;

[0046] The molar concentration of thorium in the acidic aqueous phase is more than 50 times that of uranium, such as 100 times, more than 200 times, more than 300 times, more than 400 times, more than 500 times, preferably 50 - 500 times. The extractant of the present invention can selectively separate trace uranium from a solution containing a large amount of thorium. Even when the U(VI) / Th(IV) in the aqueous phase reaches 1 / 500, the separation factor remains up to 282 at most.

[0047] The purity of thorium in the aqueous phase containing high-purity thorium is above 99.9%. The extractant of the present invention can basically remove uranium, and the thorium content in the obtained aqueous phase is significantly increased, preferably reaching above 99.5% in purity.

[0048] The present invention also provides a method for separating and extracting thorium and uranium, including the steps:

[0049] Step 1: Using the acidic phenanthroline amide as the extractant, dissolving it in an organic solvent to obtain an organic phase, mixing it with an acidic aqueous phase containing thorium and uranium, and extracting to obtain an organic phase containing uranium and an aqueous phase containing thorium;

[0050] Step 2: Mixing the organic phase containing uranium obtained by extraction in Step 1 with an aqueous nitric acid solution for back-extraction to obtain an aqueous phase containing thorium and an organic phase containing uranium, realizing the separation of thorium and uranium.

[0051] After the acidic phenanthroline amide of the present invention selectively separates U(VI) from a large amount of Th(IV), an aqueous phase containing high-purity thorium is obtained. In the organic phase containing uranium, low-concentration nitric acid is used for back-extraction, and part of the co-extracted thorium in the organic phase can be recovered with high selectivity and high back-extraction rate, realizing the truly effective and complete separation of the two elements.

[0052] In Step 2, the concentration of nitric acid in the aqueous nitric acid solution is 0.01 - 4 mol / L; preferably, the nitric acid concentration is 0.01 - 2 mol / L. In the present invention, 1 mol / L of nitric acid can selectively back-extract part of the co-extracted thorium with a high back-extraction rate, achieving the effect of "high-acid extraction and low-acid back-extraction".

[0053] Preferably, the back-extraction process in Step 2 is repeated 1 - 3 times. After multiple back-extractions, the purity of thorium and uranium can be further improved, which is of great significance for the reprocessing of thorium-based spent fuel. The three-stage back-extraction rate of Th(IV) is above 90%, preferably above 95%.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] The present invention provides an acidic o-phenanthroline amide with a brand-new structure. As an extractant, it can selectively separate U(VI) from a large amount of Th(IV), having the advantages of high extraction rate, fast extraction kinetics, and easy stripping, and can obtain high-purity thorium and uranium products, showing good application prospects in the field of U(VI) / Th(IV) separation. Brief Description of the Drawings

[0056] Figure 1 1H NMR spectrum of DOPAPA prepared in Example 1 1

[0057] Figure 2 Kinetic curves of DOAPA for extracting U(VI) and Th(IV) in Application Example 1

[0058] Figure 3 Effect of nitric acid concentration on the extraction effect of DOAPA in Application Example 2

[0059] Figure 4 Effect of Th(IV) concentration on the extraction effect of DOAPA in Application Example 3

[0060] Figure 5 Schematic diagram of the extraction process of "extracting with high acid and stripping with low acid" in Application Example 4 Detailed Description of the Invention

[0061] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Those skilled in the art who make modifications or equivalent replacements based on the understanding of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the protection scope of the present invention.

[0062] In the following embodiments, the raw materials used are all purchased from the market. Among them, the distribution ratio D is the ratio of the total concentration of the extracted substance in the organic phase to the total concentration in the aqueous phase, which is called the distribution ratio, that is:

[0063]

[0064] The separation factor SF is the ratio of the distribution ratios of two components to be separated under the same extraction experimental conditions, that is:

[0065]

[0066] In Formula ①, C org. represents the metal ion concentration in the equilibrium aqueous phase after one extraction, and C aq. represents the metal ion concentration in the aqueous phase before extraction.

[0067] ​Preparation of Example 1 DOAPA

[0068] Step 1: Add 4 g of 1,10-phenanthroline-2,9-dicarboxylic acid to 60 mL of methanol, and dropwise add 3 mL of thionyl chloride at 0 °C. After the addition is complete, heat under reflux for 5 h. After the reaction, remove methanol under reduced pressure. Dissolve the remaining yellow solid in dichloromethane, and then wash it successively with sodium bicarbonate solution and saturated brine, and dry it with anhydrous sodium sulfate. After removing the dichloromethane solvent, a grayish-white solid, 2,9-dimethyl ester-1,10-phenanthroline (3.96 g, 89%), is obtained and directly used for the next step. The reaction formula is as follows:

[0069]

[0070] Step 2: Dissolve 0.75 g of potassium hydroxide in methanol, and dropwise add it to a mixed solution of tetrahydrofuran / methanol containing 3.96 g of 2,9-dimethyl ester-1,10-phenanthroline cooled to 0 °C. After the addition is complete, remove the ice-water bath, stir the reaction at room temperature for 5 h, and then remove the solvent under reduced pressure. Add water to evenly disperse the remaining yellow solid, and acidify it with excessive hydrochloric acid to a pH of about 2. Filter and collect the obtained precipitate, and after drying, a grayish-white solid, 9-methyl ester-1,10-phenanthroline-2-carboxylic acid (3.20 g, 85%), is obtained. The reaction formula is as follows:

[0071]

[0072] Step 3: Add 2 g of 9-methyl ester-1,10-phenanthroline-2-carboxylic acid to the reaction flask. Use a double-tube to evacuate the system and fill it with argon. Add 50 mL of thionyl chloride, reflux the reaction for 3 h, then remove thionyl chloride with a cold trap. Add 50 mL of dichloromethane, and add 5.13 g of di-n-octylamine and 4.30 g of triethylamine under an ice-water bath condition, and reflux the reaction for 3 h. After the reaction is complete, wash it with saturated brine and dry it with anhydrous sodium sulfate. The crude product is separated by column chromatography (eluent: EA / PE = 5 / 1) to obtain a dark brown oily solid, 9-(N,N-dioctylamide)-1,10-phenanthroline-2-methyl ester (1.42 g, 44%). The reaction formula is as follows:

[0073]

[0074] Step 4: Dissolve 0.45 g of potassium hydroxide in methanol, and dropwise add it to a mixed solution of tetrahydrofuran / methanol containing 1.35 g of 9-(N,N-dioctylamide)-1,10-phenanthroline-2-methyl ester. Stir the reaction at room temperature for 5 h, and then remove the solvent under reduced pressure. Add water to evenly disperse the remaining yellow solid, and acidify it with excessive hydrochloric acid to a pH of about 2. Filter and collect the obtained precipitate, and after drying, a white solid, acidic phenanthroline amide DOAPA (1.23 g, 94%), is obtained.

[0075]

[0076] NMR characterization of DOAPA was carried out, and the results are as Figure 1 , and the attribution of each peak is as follows: 1 H NMR(500MHz,DMSO):δ8.67(dd,J=17.6,8.3Hz,2H),8.37(d,J=8.3Hz,1H),8.18 - 8.12(m,2H),7.92(d,J=8.2Hz,1H),3.52 - 3.47(m,2H),3.32 - 3.28(m,2H),1.79 - 1.65(m,4H),1.32(dt,J=33.8,14.4Hz,11H),0.98 - 0.92(m,2H),0.87(dt,J=10.7,6.6Hz,9H),0.80 - 0.73(m,2H),0.62(t,J=7.2Hz,3H).

[0077] Application Example 1

[0078] Dissolve the DOAPA prepared in Example 1 in n - octanol to prepare a solution with a ligand concentration of 10 mmol / L as the extraction organic phase. Prepare the aqueous phase as a nitric acid aqueous solution containing 1 mmol / L UO2(NO3)2 or Th(NO3)4, with a nitric acid concentration of 1 mol / L. Take 1 mL of the organic phase and the aqueous phase respectively and place them in a 10 mL centrifuge tube. Set different oscillation times in the range of 0.5 - 10 minutes, oscillate at room temperature, and then carry out centrifugal phase separation after completion. Use ICP - OES to measure the metal ion concentration in the aqueous phase before and after extraction. Figure 2 It is the extraction kinetic curve of DOAPA. The experimental results show that the extraction can reach equilibrium within 4 minutes, indicating that the kinetics of DOAPA is relatively fast.

[0079] Application Example 2

[0080] Dissolve the DOAPA prepared in Example 1 in n - octanol to prepare a solution with a ligand concentration of 10 mmol / L as the extraction organic phase. Prepare the aqueous phase as a nitric acid aqueous solution containing 1 mmol / L UO2(NO3)2 or Th(NO3)4, with nitric acid concentrations of 0.1 M, 0.5 M, 1 M, 2 M, 3 M, and 4 M respectively. Take 1 mL of the organic phase and the aqueous phase respectively and place them in a 10 mL centrifuge tube. Oscillate at room temperature for 10 minutes, and then carry out centrifugal phase separation after completion. Use ICP - OES to measure the metal ion concentration in the aqueous phase before and after extraction, and calculate the distribution ratio and separation factor.

[0081] The extraction effect of DOAPA on U(VI) or Th(IV) is as Figure 3As shown in the figure. It can be seen that as the acidity of the aqueous phase increases, the distribution ratio of DOAPA for U(VI) shows an upward trend. When the nitric acid concentration is 4 mol / L, the distribution ratio of DOAPA for U(VI) is 1566, and the distribution ratio for Th(IV) is 0.99. At this time, the uranium-thorium separation factor SF U(VI) / Th(IV) is as high as 1582, indicating that DOAPA has strong uranium-thorium separation ability.

[0082] Application Example 3

[0083] Considering that in thorium-based spent fuel, the content of Th(IV) is much higher than that of U(VI), the proportion of Th(IV) in the aqueous phase was increased, and the effect of the concentration of Th(IV) on the extraction effect was studied at a nitric acid concentration of 4 mol / L.

[0084] Dissolve the DOAPA prepared in Example 1 in n-octanol to prepare a solution with a ligand concentration of 10 mmol / L as the extraction organic phase, and configure the aqueous phase as a nitric acid aqueous solution containing UO2(NO3)2 and Th(NO3)4. Among them, the concentration of UO2(NO3)2 is 0.01 mmol / L, the concentration of Th(NO3)4 is 0.5, 1, 2, 5 mmol / L, and the U(VI) / Th(IV) molar ratios are 1 / 50, 1 / 100, 1 / 200, and 1 / 500 respectively. Take 1 mL of the organic phase and the aqueous phase and place them in a 10 mL centrifuge tube, shake at room temperature for 10 minutes, then centrifuge to separate the phases, and use ICP-OES to measure the metal ion concentrations in the aqueous phase before and after extraction, and calculate the distribution ratio and separation factor.

[0085] The results are as Figure 4 shown. When the U(VI) / Th(IV) ratio changes from 1 / 50 to 1 / 500, the distribution ratio of DOAPA for U(VI) increases slightly, and the distribution ratio for Th(IV) decreases slightly. Therefore, the SF U(VI) / Th(IV) value continuously increases. When the U(VI) / Th(IV) ratio is 1 / 500, its value is 282, indicating that in the presence of a large amount of Th(IV), DOAPA can still selectively separate U(VI) from it.

[0086] Application Example 4

[0087] The organic phase loaded with metal ions after extraction with a U(VI) / Th(IV) molar ratio of 1 / 500 in Application Example 3 was shaken with an equal volume of inorganic acid and sodium carbonate in a circulating oscillator for 10 minutes. After shaking, centrifuge to separate the phases and measure the metal ion concentrations in the aqueous phase before and after back-extraction by ICP-OES. 1 mol / L sulfuric acid, sodium carbonate, hydrochloric acid, and nitric acid were used as back-extraction agents respectively. The back-extraction rates of three back-extractions are shown in Table 1. The process flow diagrams of the extraction process and the back-extraction process are as Figure 5 shown.

[0088] As can be seen from Table 1, 1 mol / L nitric acid can selectively strip some of the co-extracted thorium, and the three-stage stripping rate of Th(IV) can reach 97.9%.

[0089] Table 1 Stripping rates of sulfuric acid, sodium carbonate, hydrochloric acid and nitric acid on the DOAPA-loaded organic phase

[0090]

Claims

1. An acidic o-phenanthroline amide, characterized in that, The structure of the acidic o-phenanthroline amide is as follows: Wherein, R is a straight-chain or branched-chain alkyl group with 2 to 10 carbon atoms.

2. The acidic o-phenanthroline amide according to claim 1, wherein The R is one or more of ethyl, n-butyl, n-hexyl, n-octyl, and 2-ethylhexyl.

3. A method for preparing the acidic phenanthroline amide according to claim 1, characterized in that, It includes the steps of: using 1,10-phenanthroline-2,9-dicarboxylic acid as a raw material, through esterification and single hydrolysis to obtain 9-methoxycarbonyl-1,10-phenanthroline-2-carboxylic acid, then acyl chlorinating 9-methoxycarbonyl-1,10-phenanthroline-2-carboxylic acid and carrying out an amidation reaction with R2NH to obtain an amidation product A, and after hydrolyzing and acidifying the product A, obtaining the acidic o-phenanthroline amide; Wherein R is as described in claim 1, and the structure of the product A is as follows:

4. The preparation method of the acidic o-phenanthroline amide according to claim 3, characterized in that, Specifically, it includes the steps of: Step 1, 1,10-phenanthroline-2,9-dicarboxylic acid reacts with methanol in an esterification reaction to obtain 2,9-dimethoxycarbonyl-1,10-phenanthroline; Step 2, 2,9-dimethoxycarbonyl-1,10-phenanthroline undergoes a single hydrolysis reaction under the action of potassium hydroxide, and after acidifying with hydrochloric acid, 9-methoxycarbonyl-1,10-phenanthroline-2-carboxylic acid is obtained; Step 3, 9-methoxycarbonyl-1,10-phenanthroline-2-carboxylic acid is refluxed with thionyl chloride, and after the solvent is evaporated to dryness, an acyl chlorination product is obtained; the acyl chlorination product is dissolved in a solvent, a deacidifying agent and R2NH are added, and the mixture is refluxed for an amidation reaction, and the product is washed and purified by column chromatography to obtain the product A; Step 4, the product A is hydrolyzed and acidified to obtain the acidic o-phenanthroline amide.

5. A method for improving the purity of thorium, characterized in that, Using the acidic o-phenanthroline amide described in claim 1 as an extractant, dissolving it in an organic solvent to obtain an organic phase, mixing it with an acidic aqueous phase containing thorium and uranium, and extracting to obtain an organic phase containing uranium and an aqueous phase containing high-purity thorium; The purity of thorium in the aqueous phase containing high-purity thorium is above 99.9%.

6. The method for improving the purity of thorium according to claim 5, characterized in that, The uranium is hexavalent U(VI), and the thorium is tetravalent Th(IV); And / or, the organic solvent includes at least one of n-octanol, 3-nitrobenzotrifluoride, cyclohexanone, toluene, or kerosene; And / or, the molar concentration of the acidic o-phenanthroline amide in the organic phase is 0.001 to 0.01 mol / L; And / or, the acidic aqueous phase is a nitric acid solution, and the nitric acid concentration is 0.5 - 4 mol / L.

7. The method for improving thorium purity according to claim 5, wherein The volume ratio of the organic phase to the aqueous phase is 0.2 - 5:1; And / or, the mixing time is more than 1 minute; And / or, the temperature during the mixing and separation extraction process is 0 - 50 °C; And / or, the molar concentrations of thorium and uranium in the acidic aqueous phase are each 0.01 - 1 mmol / L; And / or, the molar concentration of thorium in the acidic aqueous phase is more than 50 times that of uranium.

8. A method for separating and extracting thorium and uranium, characterized in that, It includes the steps of: Step 1, using the acidic o-phenanthroline amide described in claim 1 as an extractant, dissolving it in an organic solvent to obtain an organic phase, mixing it with an acidic aqueous phase containing thorium and uranium, and extracting to obtain an organic phase containing uranium and an aqueous phase containing thorium; Step 2, mixing the organic phase containing uranium extracted in Step 1 with an aqueous nitric acid solution for back-extraction to obtain an aqueous phase containing thorium and an organic phase containing uranium, realizing the separation of thorium and uranium.

9. The method for separating and extracting thorium and uranium according to claim 8, characterized in that, The nitric acid concentration in the aqueous nitric acid solution in Step 2 is 0.01 - 4 mol / L; And / or, the back-extraction process in Step 2 is repeated 1 - 3 times.

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