Cadmium soil sorption at low concentrations. IV. Effect of waste leachates on distribution coefficients

Abstract

Sorption onto two mineral soils of Cd present at low concentrations in unpolluted soil solution (10⁻³ M CaCl₂) and waste leachates (compost, incinerator slag, sewage sludge) was examined by laboratory batch experiments in terms of kinetics, equilibrium distributions isotherms and the effect of pH. From an environmental point of view, sorption of Cd from waste leachates is a fast process (equilibrium within 2 hr) although slightly slower than from unpolluted soil solution. Both soils (sand, sandy loam) exhibited approximately linear sorption isotherms for all solutes. The slope of the isotherms, the Cd distribution coefficient, was 30 to 250 times smaller from waste leachates than from unpolluted soil solution, indicating a much increased mobility of Cd in waste leachates. The effect of pH on the Cd distribution coefficients was less consistent in waste leachate than in unpolluted soil solution, varying from hardly any effect to a 7 fold increase for a pH increase of approximately one unit.