Mechanistic Insights into Copper Removal by Pyrolytic Tire Char through Equilibrium Studies

Abstract

This study showed that copper(II) can be removed from aqueous solution by activated pyrolytic tire char in three mechanistically distinct ways. On the basis of equilibrium studies, the mechanisms involved in the adsorptive removal of copper(II), namely, precipitation, surface adsorption, and pore diffusion, were elucidated. Precipitation of copper(II) resulted from changes in the solution pH to neutral levels. This was attributed to amphoteric zinc oxide on the char surface, formed during production of the pyrolytic char. Surface adsorption was revealed by X-ray photoelectron spectroscopy data, which showed a significant increase in copper(II) on the char surface after shaking in the copper solution. This surface adsorption took place despite the relatively low surface area and porosity of the char. However, some cracks and fissures were found to exist in the char that can trap small species such as copper ions. These trapped copper species were partially recovered by microwave-assisted acid digestion of the char.