Modified tailings of weathered crust elution-deposited rare earth ores as adsorbents for recovery of rare earth ions from solutions: Kinetics and thermodynamics studies

Abstract

Weathered crust elution-deposited rare earth ores tailings are mainly composed of clay minerals, which can be used as efficient adsorption materials. In order to explore the possibility of recovering rare earth ions using tailings from mine waste liquid, the weathered crust elution-deposited rare earth ores tailings were modified to adsorb La3+ and Y3+ with respect to initial concentrations of La3+ and Y3+, temperatures and impurity ions, and the adsorption kinetics and thermodynamics were further discussed to analyze the adsorption behavior. The results show a higher adsorption capacity of heavy rare earth Y3+ than that of light rare earth La3+. The presence of impurity ions does not adversely affect adsorption of rare earth ions by the modified tailings. The adsorption performance is well fitted with the Langmuir adsorption isotherm model rather than the Freundlich adsorption isotherm model, and the maximum adsorption capacity is 0.0226 mmol/g and 0.0197 mmol/g for Y3+ and La3+, respectively. Pseudo-first-order, pseudo-second-order, intraparticle diffusion and Elovich model were applied to fit the adsorption results. The results show that the adsorption process of modified tailings for La3+ and Y3+ is more in line with the pseudo-second-order kinetic model, suggesting the dominated chemical adsorption. The adsorption activation energies of La3+ and Y3+ on modified tailings are 11.60 KJ/mol and 7.60 KJ/mol, respectively. Thermodynamic studies show that the adsorption process of modified tailings for La3+ and Y3+ is a spontaneous endothermic reaction in the experimental temperature range. The recovery of rare earth ions form the modified tailings can be carried out by the leaching solution of weathered crust elution-deposited rare earth ores, 0.2 mol/L (NH4)2SO4 solution. In addition, the modified tailings are reversible and keep functionality to reuse in several cycles after elution process.