Adsorption of Cd(II), Cu(II) and Pb(II) using recycled waste glass: equilibrium and kinetic studies

Recycled waste glass (RWG), from municipal solid wastes (MSW) sorting operations, may be used as a sorbent for cadmium, copper and lead ions removal from industrial wastewaters. To the purpose, the ability of RWG to adsorb Cd2+, Cu2+ and Pb2+ from aqueous solutions has been studied at different operating conditions: contact time, adsorbent amount and metal ion concentration. Batch adsorption kinetic experiments revealed that the sorption of Cd2+, Cu2+ and Pb2+ on RWG was very fast and the equilibrium was practically reached after only 60 min at constant temperature and pH (5.6 +/- 0.1). It was found that the adsorption mechanisms follow pseudo-second-order kinetics. The adsorption isotherm studies indicate that the adsorption of Cd2+, Cu2+ onto RWG follows Langmuir isotherms, while Pb2+ can follow Langmuir and Freundlich models. The maximum adsorption capacity (q(max)) for Cd2+, Cu2+ and Pb2+ were 6.29, 6.68 and 11.68 mg/g, respectively. From Dubinin-Kaganer-Radushkevich (DKR), the free energy E-value for Cd2+, Cu2+ and Pb2+ is 14.067, 18.467 and 19.724 kJ/mol, respectively. The positive values of E indicate that the sorption process is endothermic and the energy values for the studied metals sorption on RWG indicate that the sorption process is physisorption.