Liquid-Liquid Extraction of Metals Using Environmentally Friendly Fluorinated Solvents

Solvent extraction is one of the most effective techniques to separate metal ions selectively from aqueous solutions. Conventional solvent extraction methods use low-polarity hydrocarbon organic solvents such as dodecane and cyclohexane. In this study, we proposed a new solvent extraction method using environmentally friendly fluorinated solvent HCFO-1233yd with low GWP. Because fluorinated solvents have low boiling points and are nonflammable, they can be reused by distillation. We selected Cs, Rb, Sr, Cu, and Ca as metal species. Cs, Rb, and Sr are often found in nuclear wastewater. Cu and Ca are often found in industrial wastewater and have been investigated frequently in solvent extraction. When bis(2-ethylhexyl) phosphoric acid (D2EHPA) was used, the extraction performance of HCFO-1233yd was comparable to those of HFE-347pc-f and cyclohexane used as control systems. Divalent metals were an extracted rate of over 90% under weakly acidic equilibrium conditions, and monovalent metals were an extracted rate of over 60% under more neutral equilibrium conditions. A monovalent metal extraction using a Ca-saponified extractant instead of pH adjustment showed an extraction rate of over 80%, even under neutral conditions. It was confirmed that HCFO-1233yd was a preferred extraction solvent for extracting various metals.