Ion-exchange equilibria of Pb2+, Ni2+, and Cr3+ ions for H+ on Amberlite IR-120

A study of the binary cation-exchange equilibria between H+-form Amberlite IR-120 resin and aqueous solutions of lead, nickel, and chromium nitrates at pH < 3 has been made. Experiments were carried out at (283, 303, and 323) K with solutions having total cation concentrations of 0.1 eq center dot L-1. The experimental equilibrium data have been satisfactorily correlated using the homogeneous mass action law model (LAM). This model assumes nonideal behavior for both the solution and the solid phase. Wilson and Pitzer equations have been used to calculate activity coefficients in the solid and liquid phases, respectively. The standard enthalpy Delta H degrees(AB) and the standard entropy Delta S degrees(AB) Were determined. The values of both the thermodynamic constant and standard Gibbs free energy Delta G degrees(AB) demonstrate temperature dependence. The rise in temperature caused a slight increase in the value of the equilibrium constant (K-AB) for the ion exchange of all heavy metal ions tested in this study. According to e librium constants obtained, the Amberlite IR-120 exhibits the following order of selectivity, Cr3+ > Pb2+ > Ni2+, in all the ranges of the temperatures studied in agreement with the rule of higher selectivity at higher counterion charge.