Adsorption of Cd, Co, and Zn from multi-ionic solutions onto Iranian sepiolite isotherms

Nowadays, removal of heavy-metal contaminants from industrial waste waters is one of the most important environmental polemics which necessarily requires a solution. Clays, because of their low cost and unique chemical and structural properties have been widely used to remove heavy metals from aqueous solutions. In this investigation, sepiolite mineral was obtained from a mine near Fariman Township, Khorasan, Iran. The mineral samples used in this study were powdered with sizes less than 0.05 mm (<53 μm). Batch tests were conducted to investigate the adsorption behavior of Cd (II), Zn (II), and Co (II) by natural and heat pre-treated sepiolites at 150 and 250 °C in initial slurry concentrations of (60, 120, 180, 240, 360, 480, and 540 g/L). Langmuir and Freundlich isotherm models were investigated to illustrate the adsorption of heavy metals by natural and heat pre-treated sepiolites from aqueous solutions in two different pH values: 4 and 5. It was determined that the experimental data were more fitted to the Langmuir model (R2≈0.99) and it was observed that cobalt ions were more adsorbed than zinc and cadmium in the order of adsorbing regularity: Co>Zn>Cd. In this study, the quantities of released Mg2+ from the mineral structures were also investigated. In addition, changes in pH values in final solutions were investigated at the end of the experiments.