Removal of metal ions from multi-component mixture using natural lignite

Removal of Pb2 +, Cu2 +, Cd2 +, and Zn2 + ions from their multi-component aqueous mixture by sorption on natural lignite was investigated. Sorption kinetics, dependence of sorbed amount on pH, initial concentration of metal ions, and on temperature, effect of electrolytes (KNO3 and NaCl) were tested as well as desorption of sorbed metals into water. Cadmium was displaced at high metal concentrations. The maximum sorption capacities were 39 mg/g for Pb, 26 mg/g for Cu, 15 mg/g for Zn, and 5 mg/g for Cd. Experimental data were analyzed using Langmuir and Freundlich adsorption models, the relevance of thermodynamics descriptors for the multicomponent sorption is discussed. Desorption test showed tight bonding of all metals. Lignite is suitable and cheap sorption material for mixtures of metal ions, that is effective also at low metal concentrations.