Clay adsorption of lead from landfill leachate

This paper examines clay adsorption of lead from leachates originating in controlled landfills for municipal solid wastes. Special attention has been given to determining the extent to which Freundlich and Langmuir-derived isotherms may represent the system in various experimental conditions (metal concentration and pH). Lead adsorption is satisfactory described at constant pH by using the Langmuir/Freundlich isotherm over the entire pH range examined (4.0-8.5). By using theoretical speciation, adsorption related to free Pb (Pb2+) in solution makes the results more generalizable than in terms of total Pb. Theoretical speciation also allows for interpreting the pH effect on adsorption: as pH increases, adsorption of free Pb increases but at the same time free Pb decreases. Depending on which effect is prevailing, adsorption at a fixed total Pb concentration can increase or decrease, as pH changes. As an environmental implication, an increase of pH does not always entail stronger attenuation of pollutants by soil adsorption.