Contribution to the Thermodynamics of Sc3+, Y3+, La3+ and Trivalent Lanthanide Cations in the Two-Phase Water-Nitrobenzene Extraction System

From the exchange extraction constants corresponding to the general equilibrium M3+(aq) + 3H+(nb) __M3+(nb) + 3H+(aq) occurring in the two–phase water–nitrobenzene system (M3+ = Sc3+, Y3+, La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+; aq = aqueous phase, nb = nitrobenzene phase), the individual extraction constants of 16 trivalent metal cations were calculated. It was found that these individual extraction constants in the mentioned two-phase system increase in the following cation order: Sc3+ < Yb3+< Ho3+ < Er3+ < Tm3+, Lu3+ < Y3+, Dy3+ < Tb3+ < Gd3+ < Eu3+ < Sm3+ < Nd3+ < Pr3+ < La3+, Ce3+.