Meguro Y, Iso S, Yoshida Z
Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-11, Japan.
Anal Chem. 1998 Apr 1;70(7):1262-7. doi: 10.1021/ac970818b.
The extraction equilibrium of U(VI) between a nitric acid solution and a supercritical CO(2) phase containing tributyl phosphate (TBP) is formulated taking into account that (i) a distribution ratio of a metal extracted is a function of a distribution constant of each component involved in the extraction reaction, (ii) the distribution constant is defined as a ratio of solubilities of the component in both phases, and (iii) the solubility in the CO(2) phase is correlated with density of CO(2). A simple linear relationship between the distribution ratio, D(U), of U(VI) and density, ρ, of CO(2) is derived; log D(U) = a log ρ + A + B, in which a is a proportional constant implying the solvation characteristic of the solute in supercritical CO(2), A is a pressure-independent constant, and B is a variable determined by the distribution equilibrium of HNO(3). The equation derived was verified experimentally by the measurement of the distribution ratio of U(VI) and HNO(3) under various conditions of pressure and temperature. A novel concept of selective supercritical fluid extraction of metals by means of pressure-tuning or CO(2) density-tuning was proposed.
考虑到以下几点，建立了硝酸溶液与含磷酸三丁酯（TBP）的超临界CO₂相之间U(VI)的萃取平衡：（i）被萃取金属的分配比是萃取反应中各相关组分分配常数的函数；（ii）分配常数定义为该组分在两相中溶解度之比；（iii）在CO₂相中的溶解度与CO₂密度相关。推导出了U(VI)的分配比D(U)与CO₂密度ρ之间的简单线性关系：log D(U) = a log ρ + A + B，其中a是一个比例常数，表明溶质在超临界CO₂中的溶剂化特性，A是一个与压力无关的常数，B是由HNO₃分配平衡决定的变量。通过在不同压力和温度条件下测量U(VI)和HNO₃的分配比，对所推导的方程进行了实验验证。提出了一种通过压力调节或CO₂密度调节选择性超临界流体萃取金属的新概念。
