Comparison of Extraction Ability of Me-TODGA and TODGA for Sr

The extraction of Sr²⁺ from aqueous nitric acid solutions with Me-TODGA (N,N,N′,N′-tetraoctyl-2-methyl-3-oxapentanediamide) was studied to compare with that of TODGA (N,N,N′,N′-tetraoctyl-3-oxapentanediamide). The effect of acidity of aqueous phase, extractant concentration, Sr²⁺ concentration and temperature on distribution ratio was investigated. In order to prevent the formation of third phase, TBP was added as phase modifier and kerosene was used as diluent. A slope method was used to determine the compositions of the extracted species. The results show that the distribution ratio of Sr²⁺ (D_Sr) increases with nitric acid or the extractant concentration (c(HNO₃)=0.1-2.7 mol/L, c(extractant)=0.05-0.3 mol/L), and decreases with the increase of the concentration of Sr²⁺ or temperature. The extracted species are Sr(NO₃)₂•3Me-TODGA and Sr(NO₃)2•2TODGA. The ΔH is -69.46 kJ/mol and -51.39 kJ/mol, ΔS is -190.5 J/(mol•K) and -128.4 J/(mol•K), and ΔG is -12.68 kJ/mol and -13.12 kJ/mol for Me-TODGA and TODGA respectively. The D_Sr in MeTODGA is only one-fifth of that in TODGA.