Evaluation of the possible use of a Bulgarian clinoptilolite for removing strontium from water media

The sorption of Sr (super 2+) ions by natural clinoptilolite was investigated using the batch method. The effects of pH, contact time and strontium concentrations were tested and the optimal conditions for sorption were determined. The process was very fast initially and equilibrium was reached within 24 h. Kinetic sorption data were fitted to pseudo-first-order, pseudo-second-order and intra-particle diffusion models. The simple pseudo-second-order rate model provides good agreement with the experimental data for Sr (super 2+) uptake. The respective rate constants, k (sub 2) , calculated at different initial Sr (super 2+) concentrations, were obtained. The equilibrium data were analysed by applying the Langmuir, Freundlich and Dubinin-Raduchkevich isotherm models. The Langmuir model describes the observed Sr (super 2+) uptake most accurately and the value of the monolayer sorption capacity is 32.81 mg Sr (super 2+) /g. The effect of Na (super +) ions and the effectiveness of uptake from low saline groundwater simulated solutions were also studied and discussed.