DIBK-TBP萃取分离锆铪的热力学研究

Thermodynamics of Extraction and Separation of Zirconium and Hafnium Using Mixtures of DIBK and TBP

对二异丁基甲酮(DIBK)和TBP从HSCN介质中协同萃取锆铪的性能及热力学进行研究,采用对数函数外推法求得DIBK-TBP体系萃取反应的热力学平衡常数分别为log(K12,Zr)=4.73和log(K12,Hf)=-5.09,锆铪与SCN-形成配合物Zr(SCN)3+和Hf(SCN)3+的稳定性常数分别为1×109.86和1×10-0.80,而铪的分配比在硫氰酸盐存在时要大于锆的分配比,说明过渡金属离子锆和铪在硫氰酸盐存在时与一般金属离子与配位体形成的配合物的稳定性常数愈大,金属离子的分配比愈大的规律相矛盾,并计算出萃取反应的焓变分别为ΔHZr=-11.43 kJ.mol-1和ΔHHf=-7.80 kJ.mol-1,说明对锆铪的萃取反应为放热反应,升高温度不利于萃取反应的进行,常温下自由能变分别为ΔGZr=-26.54 kJ.mol-1和ΔGHf=28.57 kJ.mol-1,熵变分别为ΔSZr=51.54 J.(K.mol)-1和ΔSHf=-124.07 J.(K.mol)-1,说明铪离子比锆离子更易与SCN-形成配位键,从而生成中性分子Hf(SCN)4与有机相发生溶剂化作用而进入有机相中。

The thermodynamics and characteristics about synergistic extraction of zirconium and hafnium using the mixtures of DIBK and TBP from thiocyanic acid medium were studied.With the logarithmic extrapolation,the thermodynamic equilibrium constants of the extraction for zirconium and hafnium individually were imputed as log（K12,Zr）=4.73 and log（K12,Hf）=-5.09,and the two stability constants of Zr（SCN）3＋ and Hf（SCN）3＋ were 1×109.86 and 1×10-0.80,respectively.While the distribution ratio of the transition metal zirconium ion was larger than that of hafnium ion when the thiocyanic anion exist,this was in contradiction with the law that the distribution ratio increased with the complexes stability constants of the metal ions in general.The enthalpy changes of extraction for zirconium and hafnium were calculated as-4.93 and-68.32 kJ · mol-1,respectively.The results clearly showed that the extraction process of both zirconium and hafnium by the DIBK was exothermic and imposes a negative influence with temperature.The values of ΔG for zirconium and hafnium（ΔGZr and ΔGHf） were calculated and found to be-26.54 and 28.57 kJ · mol-1 at 298.15 K,respectively.The values of ΔS for zirconium and hafnium（ΔSZr and ΔSHf） were calculated and found to be 51.54 and-124.07 J ·（K · mol）-1 at 298.15 K,respectively.The results showed that the hafnium ion was easier to form coordinate bond with the thiocyanic anion and to go into organic phase with the form of neutral molecule Hf（SCN）4 than the zirconium ion.