Adsorption kinetics and thermodynamics of rare earth on Montmorillonite modified by sulfuric acid

Montmorillonite (Mt), the major clay mineral in the tailings of weathered crust elution-deposited rare earth ores, was modified to improve its adsorption capacity of rare earth ions (RE3+). The effect of initial RE3+ concentration, temperature and solution pH on the adsorption capacity of Mt to La3+ and Y3+ were investigated in this study, and further the adsorption kinetics and adsorption thermodynamics were discussed to analyze the adsorbing behavior of modified Mt to RE3+. The adsorption capacity of RE3+ on modified Mt is related to the initial RE3+concentration and temperature. The pseudo-first-order, pseudo-second-order, intra-particle diffusion and Elovich models were applied to evaluate the adsorption kinetics. The results show that the adsorption process of RE3+ on modified Mt is more accurately represented by the pseudo-second-order model, and it is controlled by chemisorption rather than diffusion. The Arrhenius activation energy values of Y3+ and La3+ are 14.259 kJ/mol and 22.845 kJ/mol, respectively. The thermodynamics studies indicate that the adsorption process is a spontaneous endothermic process in the measured temperature range.