百克量级花岗岩中痕量镎的分离纯化方法研究

镎的高生物毒性和长半衰期（t_1/2＝2.14×10⁶ a）以及在环境中易迁移的性质，使之成为环境放射性污染普查及核设施监测过程中主要关注的核素之一。本文利用酸式消解法实现了百克量级花岗岩的全溶解。以自制的DMDODGA/CMG20树脂作为分离材料，利用其对氢氟酸中镎的吸附特性，建立了大体积溶解液中痕量镎的富集-分离流程。同时采用Dowex 1×4阴离子交换树脂进一步实现了对镎的浓缩和纯化。在此基础上，提出了百克量级花岗岩的分离流程，并对流程进行了实验验证。结果表明，花岗岩溶解液澄清、无残渣，分离流程对镎的回收率为87.6%，对岩石基体元素和铀的去污因子均大于1.0×10⁵。

Separation and Purification of Trace Neptunium from Hundred-gram Granite

The study of the separation method of neptunium in environmental sample is of great significance in the context of radioactive survey and nuclear emergency monitoring. In China, the radioactive waste disposal site and the nuclear fuel cycle facility are located in northwest, and the main rock type is granite. To study the distribution of radionuclides in granite, it is necessary to study the dissolution of the granite and the separation of neptunium to facilitate the detection of trace neptunium. Commonly, HF and inorganic acids such as HNO₃ and HClO₄ were used as digestion. However, the addition of HF could form insoluble Mg-Ca-Al fluoride in the solution, so that trace neptunium will be mixed into the precipitation, resulting in the loss of neptunium. Ammonium bifluoride could effectively digest insoluble accessory minerals in rocks, avoiding the precipitation of insoluble fluoride and realizing the complete digestion of granite. Since the amount of ammonium bifluoride is 4-6 times that of rocks, the solution contains a certain amount of fluoride ions. However, Np⁴⁺ has strong complexation with F^-, so it is difficult to separate and purify neptunium by ion exchange resin, TTA extraction. In this paper, the acid digestion method was used to realize the complete dissolution of granite of the order of 100 grams. A new kind of absorbent was synthesized by impregnating DMDODGA into polymethyl methacrylate resin (CMG20). Under the conditions of different concentrations of nitric acid, hydrochloric acid, hydrofluoric acid and mixed acid, the adsorption performance of DMDODGA/CMG20 for Np(Ⅳ) was studied. The results show that the adsorbent is able to complex Np(Ⅳ) in the range of 0.5-4 mol/L nitric or hydrochloric acid, with the distribution coefficient up to 10⁵ mL/g. According to the characteristics of adsorption neptunium in hydrofluoric acid, the DMDODGA separation process was proposed, which realized the enrichment of neptunium from large volume rock solution. By using Dowex 1×4 anion exchange separation, the purpose of removing complexants in the stripping of DMDODGA separation process and concentration of neptunium is achieved. The method was verified by separating neptunium from 100 grams of granite. The results show that the granite solution is clear and free of residues. The yield of neptunium in the process is 87.6%, and decontamination factors of rock matrix elements and uranium are greater than 1.0×10⁵. Neptunium is concentrated 200 times in the process. This method realizes the complete dissolution of siliceous rocks on the order of 100 grams. It can enrich and purify the femtogram quantities of neptunium in a large amount of rock dissolution liquid without masking F^- and addition of carriers. This method provides a new technical support for environmental radioactive survey and monitoring.