Adsorption of lead and cadmium ions from aqueous solution to the montmorillonite/water interface

In order to prevent contamination of subsoil and groundwater by leachates c ontaining heavy metals, montmorillonite linings are used on landfill bottom s. It is therefore important to understand ion uptake by this clay. The sor ption of Pb(II) and Cd(II) from aqueous solution to the montmorillonite/wat er interface has been studied as a function of pH, for three concentrations . Two montmorillonites have been used: an industrial bentonite and a refere nce clay. Clay acidity constants have been determined, indicating that both clays seem to have characteristics similiar to each other. Adsorption incr eases with pH. Whatever the clay or pH, lead is retained more than cadmium. A model that assumes two kinds of binding sites can describe metallic ion uptake: XNa groups, responsible of ion exchange, and ampholitic surface hyd roxyls SOH, responsible of surface complexation. (C) 2000 Elsevier Science B.V. All rights reserved.