Biosorption of Cadmium, Cobalt and Zinc by Moss Rhytidiadelphus squarrosus in the Single and Binary Component Systems

Biomass of moss Rhytidiadelphus squarrosus was studied as a potential biosorbent for cadmium, cobalt and zinc removal from single and binary solutions. It was shown that solution pH significantly influenced Cd, Co and Zn biosorption. Maximum uptake was reached at pH 5.0-6.0 and negligible biosorption was observed at pH 2.0. Experimental equilibrium biosorption data for cadmium, cobalt and zinc were analysed by the Langmuir and Freundlich isotherm models. The Langmuir isotherm was found to well represent the measured sorption data in single metal systems. The maximum sorption capacities Q(max) onto moss biomass were 186 mu mol/g for Zn, 173 mu mol/g for Cd and 123 mu mol/g for Co. Results revealed that the presence of Cd more significantly decreased the sorption of Co in binary Cd-Co mixtures than vice versa. In Cd-Zn binary system, both cadmium and zinc were sorbed with equal efficiency. The competitive Langmuir equations were used to fit the experimental data from the Zn-Cd and Cd-Co binary systems and simple two-dimensional isotherm curves were replaced by three-dimensional sorption isotherm surfaces.