Sepiolite as a feasible soil additive for the immobilization of cadmium and zinc.

The sorption behaviour of sepiolite has been studied with respect to cadmium and zinc in order to consider its application to remediate soils polluted with these metals. The Langmuir model was found to describe well the sorption processes offering maximum sorption capacities of 17.1 and 8.13 mg/g for cadmium and zinc, respectively, at pH 6. The sorption capacities are pH dependent undergoing a decrease with H(+) concentration increase. The effect of sepiolite amendment in a highly polluted mining soil has been studied by means of batch extractions and leaching column studies. The soluble amount of both metals as well as their readily-extractable fractions are substantially decreased at any concentration of sepiolite applied to soil (1, 2, 4%), although the highest decrease is obtained at the 4% dose. In this case the soluble fractions of both metals are decreased by 95%. The column studies also show a high reduction in the leaching of cadmium and zinc (69 and 52%, respectively) when a sepiolite dose of 4% is applied.