Adsorption of Cd(II), Cr(III) and Mn(II) on natural sepiolite

Heavy metals such as cadmium, chromium and manganese are toxic priority pollutants that commonly interfere with the beneficial use of wastewater for irrigation and industrial applications. The sorption of cadmium, chromium and manganese from aqueous solutions onto natural sepiolite has been studied. The efficiency of sepiolite as an adsorbent for the removal of these heavy metals from aqueous solutions has been determined. The adsorption was carried out using a batch method. Adsorption data have been interpreted in terms of Langmuir and Freundlich equations. The results were provided strong support for the adsorption of heavy metals into sepiolite. For investigation of exchange equilibria different amounts of sepiolite were contacted with a fixed volume of a heavy metal bearing solutions. Because the uptake of these heavy metals is mainly dominated by the pH of the liquid phase the pH value was varied between pH 0–3 and 0.5–5 g in each series of samples. The initial and final concentrations of heavy metals were determined by means of atomic absorption spectrophotometry. All the operations were conducted at room temperature (20±1°C). Exchange equilibria have been evaluated for sepiolite by means of the surface complex formation theory. For evaluation of equilibrium parameters the generalized separation factors were calculated from experimental data and plotted vs. the respective dimensionless sepiolite loadings. The experiments demonstrated that Cr3+ and Cd2+ ions were more efficiently adsorbed than Mn2+ ions by sepiolite.