Cyanex572硝酸体系萃取分离锆铪的机理研究

Nuclear power as an economic, efficient and clean energy can replace the thermal power to avoid the atmospheric pollution problem. Nuclear grade zirconium and hafnium are the key marteials for nuclear reactor, however, their preparation are restricted by extraction and separation technology. The slight hafnium can be extracted over zirconium by the MIBK separation technology, but the separation technology has some disadvantages of the high water solubility and volatility, especially thiocyanate easily decomposed into toxic substances. The development of green separation technology of hafnium being extracted over zirconium is imminent. During the former research of the relationships between the structure of extracted species and extraction performance in DIBK synergistic extraction system, it is found that hafnium can be extracted over zirconium by using Cyanex572 with nitric acid solution while without thiocyanate. The effects of diluents, synergetic agents, acidty, ion concentrations of zirconium and hafnium, salting out agents and temperature on the seperating between zirconium and hafnium should be further investigated, respectively. The synergistic extraction system will be sreened by the Synergistic Extraction Theory, the stability of the extrated species will be interpreted by the Hard and Soft Acid-base Theory, and the extractability of the extrated species will also be analyzed by the Electroneutrality Principle and the Hydrophilicity Loss Principle. The extraction mechanisms will be discussed by the extraction reaction research methods, the convective mass transfer coefficient will be calculated by the Dual-mode Model, and the extraction kinetics will be investigated by the Constant Interfacial Cell Method. These researchs also aim to determine the compositions of the extrated species, reveal the extraction mechanisms, build the dynamic models, and optimize the seperation technology between zirconium and hafnium in the Cyanex572 synergistic extraction system. An excellent resolution is provided to develop a environmental friendly separation technology of hafnium extracted over zirconium.

核电是替代火电解决空气污染问题的经济高效清洁能源，而核级锆和铪是核反应堆的关键材料，受锆铪分离技术的制约。MIBK分离工艺虽优先萃取锆铪含量中较少的铪，但存在萃取剂高水溶性、易挥发，硫氰酸易分解成有毒物质等缺点，使开发优先萃取铪的绿色分离工艺迫在眉捷。在前期研究DIBK协萃体系萃合物结构与萃取性能的关系时，发现Cyanex572不需硫氰酸盐也能在硝酸体系中优先萃取铪，需进一步探索不同体系中稀释剂、协萃剂、酸度、锆铪离子浓度、盐析剂和温度等因素对锆铪分离的影响，依据协萃效应原理筛选协萃体系、软硬酸碱理论解释萃合物稳定性、电中性和丧失亲水性等原则分析萃合物可萃性，采用萃合反应研究法探讨萃取机理、双模模型计算对流传质系数、恒界面池法研究萃取动力学，以确定Cyanex572协萃体系萃合物组成和萃取机理，构建动力学模型，优化锆铪分离工艺，为开发优先萃取铪的、环境友好型的锆铪分离技术提供新思路。

锆铪的物理化学性质相同，核性相异，使得锆铪分离是制备核级锆铪的技术关键。针对MIBK工艺的缺点，开发了优先萃取铪的Cyanex572体系和Cyanex923体系，探索稀释剂、水相酸度、锆铪离子浓度、萃取时间、萃取剂浓度、盐析剂种类及浓度等因素对萃取分离锆铪的影响规律，获得其优化分离的工艺参数，在优化条件下，Cyanex572体系对铪的萃取率为77%，分离系数达15.7。Cyanex923体系对铪的萃取率达87.1%，分离系数达37.1。.为提高硫氰酸盐的稳定性，利用阳离子型萃取剂N1923和N263与SCN-形成稳定的[N1923][SCN]和[N263][SCN]结构，开发出N1923体系和N263体系，探索了萃取剂浓度、料液硫氰酸浓度、预饱和硫氰酸浓度、水相酸度、盐析剂类型及浓度、萃取时间、相比等因素对锆铪分离的影响规律，获得其优化分离的工艺参数，在优化条件下，N1923体系对铪的萃取率为86%，分离系数为20.9，N263体系铪的萃取率为93.40%，分离系数为21.59，优于MIBK工艺。.对这萃取铪的机理进行了研究，结合斜率法、饱和容量法、红外光谱法、核磁共振波谱法等研究了四个体系萃取锆和铪的机理，推导出萃合物可能结构式。.利用不同酸性介质和碳酸盐对Cyanex923、N1923和N263体系负载有机相进行反萃取研究，结果表明是Cyanex923体系用2 mol/L的碳酸铵反萃，相比2:1，锆和铪的反萃率分别为61.87%和91.67%。N1923体系用2 mol/L的碳酸铵反萃，锆和铪的反萃率分别为90.7% 88.6%。N263体系先用3.0 mol/L H2SO4反萃，相比4:1时，锆和铪的反萃率分别为58.87%和4.60%，再用6.0 mol/L H2SO4对铪进行洗脱，铪的洗脱率为92.39%。.采用恒界面池法研究了N263体系萃取锆和铪的萃取动力学，结果表明萃取过程为相界面处化学反应控制过程，锆和铪萃取的焓变分别为39.59 KJ·mol-1和29.30 KJ·mol-1，熵变分别为147.53 J·mol-1·K-1和-174.38 J·mol-1·K-1，在298.15K时，吉布斯自由能变分别为83.57 KJ·mol-1和81.29 KJ·mol-1。