Kinetic and thermodynamic study of Eu(III) sorption on natural red earth in South China

We did a kinetic and thermodynamic study of Eu(III) sorption on natural red earth (NRE) in South China as a function of contact time, pH values, ionic strength, humic acid (HA) and temperature under ambient conditions. Linear and nonlinear regression methods in selecting the optimum sorption isotherm were applied on the experimental data. The results suggest that sorption of Eu(III) on NRE can be described by a pseudo-second-order rate equation and strongly dependent on ionic strength at pH<7. Sorption of Eu(III) on NRE increased with increasing temperature, two-parameter and three-parameter isotherms were applied to analysis the equilibrium adsorption data, and a comparison of linear and nonlinear regression methods was done. The thermodynamic parameters (ΔH0, ΔS0 and ΔG0) of Eu(III) sorption on NRE at different temperatures were calculated from the temperature-dependent sorption isotherms, indicating that the sorption process of Eu(III) was spontaneous. The results showed that the nonlinear method is a better way to obtain the isotherm parameters and the data were in good agreement with the Freundlich isotherm model.