DIBK-含磷萃取剂体系对锆铪的协同萃取机理研究

Separation of zirconium (Zr) and hafnium (Hf) is the key technology to prepare nuclear-grade products of Zr and Hf. The traditional MIBK process separating Hf from Zr is limited in industrial application due to the large water-solubility, easy volatility and inflammability of the extractant. The solvent extraction of metals is a process in which metal ions combine with the organic extractant to form the extracted complex and transfer into the organic phase. The research insufficiency of relationship between the structure of the extracted complex and its extraction performance is the key restrictive factor regarding the technology of separating Hf from Zr. Based on the previous DIBK technology, a novel synergistic extractants combining DIBk with P350 or TOPO (extractant containing phosphrus) are proposed to extract and separate of Zr and Hf. The extracting machanism of DIBK-P350 and DIBK-TOPO are investigated through discussing the composition and structure of extracted complex formed in the separation process. The thermodynamics and the kinetics of extracting Hf from Zr are analyzed by using a logarithmic extrapolation and a constant interfacial cell with laminar flow, respectively. Through comparing the structures of etxracted complex in DIBK-TBP synergistic system and DIBK-P204 synergistic system, the relationship between the structures of extracted complex and the extraction capacities of Zr and Hf can be established. It provides not only theoretical basises for screening and exploiting a synergistic extractant, but also ideas for developing environmentally friendly Zr and Hf separation process.

锆铪分离是生产核级锆和核级铪的核心技术。传统的MIBK分离锆铪工艺存在着萃取剂水溶性大、易挥发、易发生火灾等不利因素,工业应用受到限制。溶剂萃取的实质是金属离子与有机萃取剂形成的萃合物进入有机相的过程，目前萃合物结构与萃取性能之间的关系还不明确，导致了锆铪分离关键技术难以突破。课题在前期开发的DIBK法分离锆铪的基础上，提出将DIBK和含磷萃取剂P350或TOPO组成协萃体系对锆铪进行分离。通过确定协萃体系在萃取分离锆铪过程中所形成萃合物的组成和结构来研究DIBK-P350体系和DIBK-TOPO体系萃取锆铪的机理，利用对数函数外推法研究萃取锆铪的热力学，采用层流恒界面池法研究萃取锆铪的动力学，与DIBK-TBP协萃体系和DIBK-P204协萃体系进行对比，建立萃合物结构与萃取锆铪性能之间的关系，为筛选和开发出优先萃取铪的协萃剂提供理论依据，为开发新的、环境友好型的锆铪分离工艺提供思路。

锆铪分离是生产核级锆和核级铪的技术关键。我国核电所需的核级锆铪完全依赖从国外进口，其分离技术仍被国外所封锁。因萃合物结构与萃取性能之间的关系不明，限制了锆铪分离关键技术的突破。以DIBK和含磷萃取剂P350或TOPO组成协萃体系对锆铪进行分离，研究其萃取工艺、机理、热力学和动力学，建立萃合物结构与萃取锆铪性能之间的关系，为筛选和开发出优先萃取铪的协萃剂提供理论依据和技术支撑。.研究DIBK-P350体系和DIBK-TOPO体系分离锆铪的工艺，发现DIBK-P350体系优先萃取铪，其优化工艺参数为：萃取时间为10 min， P350浓度为45 v/v %，酸度为1.2 mol/L，硫氰酸铵浓度为3.5 mol/L，硫酸铵浓度为0.8 mol/L，分离系数达20.5。DIBK-TOPO体系优先萃取铪，其优化工艺参数为：萃取15 min，TOPO浓度 2.5 wt %，酸度为0.9~1.0 mol/L，硫氰酸铵浓度3.0 mol/L，硫酸铵浓度0.8 mol/L，分离系数达33.45。.采用斜率法和饱和容量法研究萃取锆铪的机理和热力学，发现两体系对锆和铪的萃取反应均属溶剂化作用机理。DIBK-P350体系萃合物组成分别为Zr(SCN)3.648•(HA2)0.3520•(DIBK)0.0.1043和Hf(SCN)2.6843•(HA2)1.4157•(DIBK)0.6894，对锆和铪萃取的焓变分别为 -8.42 kJ/mol和 -7.08 kJ/mol。DIBK-TOPO体系萃合物组成分别为Zr4(OH)8(H2O)10SCN4Cl4•4S•2B和Hf4(OH)8(H2O)8SCN8 4S•4B （其中，B为DIBK，S为TOPO)，对锆和铪萃取的焓变分别为-14.560 kJ/mol和-24.992 kJ/mol。.采用恒界面池法研究萃取锆铪的动力学，发现两体系萃取反应均符合准一级动力学，对锆的萃取属于相内反应控制，对铪的萃取属于混合控制，并分别求出其萃取动力学方程。.铪的路易斯酸性比锆大，而含磷萃取剂的路易斯碱性按下列顺序越来越强：R2C=O<(RO)3P=O<R3P=O，其对铪的萃取率越来越高，对锆铪的分离能力也越来越强，说明膦酸类协萃剂（含C-P键）比磷酸类协萃剂（含C-O-P键）更易萃取铪。