Assessment of the Effect of Organic Matter on the Retention of Lead in Perturbed Soils.

Abstract

Four types of soils were prepared with humified matter, bentonite, kaolin and inert matter, in order to control the organic matter (OM) content in the evaluation of retention of lead (II) by adsorption in disturbed soils with the possibility of being contaminated. The results indicated that retention capacity of Pb+2 increases as organic matter increases, however, this retention is not proportional to the organic matter increment. An increase of 10 units in the concentration of the background solution results in a decrease in the retention capacity of 50%. The outcomes also indicated that lead (II) adsorption is successfully explained by the Langmuir model and the adsorption kinetics fitted well to the Ho pseudo second order model. The thermodynamic values of the Gibbs free energy indicated that it was a spontaneous process and the energy of the process suggests a retention mechanism by ion exchange. A soil with high content of organic matter does not guarantee high retention of lead, even more so when the adsorption mechanism is given by ion exchange.