Sorption of As, Cd and T1 as influenced by industrial by-products applied to an acidic soil:: Equilibrium and kinetic experiments

In situ stabilization of toxic elements in contaminated soils by the addition of amendments is being considered as an effective technique for remediation. In this paper, we performed both kinetics and equilibrium-based sorption experiments of three toxic elements (As, Cd and T1) in soils amended with two by-products (hosphogypsum and sugar foam, rich in gypsum and calcium carbonate, respectively) to ascertain the feasibility of their application for improving the sorption capacity of As, Cd and T1 from the soil at 25, 35 and 50 degrees C. Kinetic studies indicated that the sorption follows a pseudo-second-order (PSO) kinetics and the sorption is a two-step diffusion process where both film and intraparticle diffusion played important roles in the sorption mechanisms of the elements. The Langmuir isotherms applied for sorption studies showed that the estimated maximum sorption capacity of the elements in control and amended soils decreased in the order of Cd > As > T1. Using the thermodynamic equilibrium parameters obtained at different temperatures, the thermodynamic constants of sorption (Delta G, Delta H and Delta S) were also evaluated, indicating spontaneous and endothermic nature of the process, except T1 which was exothermic. An optimal scaling procedure was undertaken to determine the relationships between the kinetic and equilibrium sorption parameters. By means of statistical analysis it was seen that these inter-parametric relationships are dependent on the element nature. (c) 2006 Elsevier Ltd. All rights reserved.