Individual extraction constants of some divalent metal cations in the two-phase water–nitrobenzene system

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M2+(aq) + Sr2+(nb) ⇄ M2+(nb) + Sr2+(aq) taking part in the two-phase water–nitrobenzene system (M2+ = Mg2+, Ca2+, Ba2+, Cu2+, Zn2+, Cd2+, Pb2+, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{UO}}_{2}^{2 +} $$\end{document}, Mn2+, Fe2+, Co2+, Ni2+; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the individual extraction constants of the M2+ cations in the mentioned two-phase system were calculated; they were found to increase in the following cation order: \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{UO}}_{2}^{2 + } $$\end{document} < Zn2+, Ni2+ < Cu2+, Cd2+ < Co2+ < Mg2+ < Ca2+ < Mn2+, Fe2+ < Sr2+ < Pb2+ < Ba2+.