Adsorption of nickel from aqueous solutions by natural and acid-activated nano-structured bentonite

Abstract

Heavy metals, such as nickel, due to their toxicity and stability, are harmful to human health. Natural bentonite and its acid-activated forms have been employed as adsorbents for the adsorption of Ni2+ ions from wastewater. In this process, natural bentonite was first activated with sulfuric acid so that its adsorption properties, such as specific surface area, cation exchange capacity, and adsorption capacity could be increased. The samples were then characterized through XRD, XRF, FTIR, and BET Analyses. The adsorption of Ni2+ was studied by pH, reaction temperature, and shaking rate experiments. BET studies showed that the activated samples had multimodal pore size distributions in micro and mesopores and the average pore diameters were around 4 nm. The XRD patterns of the acid-activated samples showed the intensity of Opal-A peaks was not significantly affected but the peaks corresponding to the calcite mineral decreased and even disappeared after the acid-activation. The result of the pH effect on the adsorption showed the low nickel adsorption in the acidic region due to the high amount of H3O+. The results showed that the concentration of acid and time were very important factors in acid activation and the uptake of Ni2+ could be successful through acid activation.