Application of Clay Minerals to Decrease Hazard of Heavy Metals in Some Egyptian Soils

Abstract

The hazards of potential toxic elements are aggravated by their almost indefinite persistence in the environment. Heavy metals cannot be destroyed but can only be transformed from one oxidation stage or organic complex to another. In this study, the sorption behavior of Pb+2, Zn+2 and Ni+2 affected soils onto natural Zeolite and bentonite treated soils have been studied in order to evaluate these remediation materials as natural materials applied in different contaminated soil (calcareous and sand) ecosystems. Kinetic approach using electrical Stirred Flow Unit (ESFU) devise method was used to evaluate the minimizing hazards of pollutants released from the remediated soils. The rate constants of Hoerl's and Elovich kinetic models were determined in remediated soil which was drastically influenced by the concentrations of PTEs found in soils, amount of sand minerals and the type of soil used. The obtained results indicated that according to higher coefficient of determinations R2 and lower standard error SE, the rate of potential toxic elements PTE's in control or treated soils were mach fitted to Elovich and Horel's kinetic models compared to other tested. The numerical values of rate constants indicated that in natural materials, Zeolite has a sorption capacity to studied PTE's more than bentonite used. Also, results showed that sorption of pollutants on treated soils depend on pollutants charge density and hydrated ion diameter. According to the kinetic studies, the selectivity of pollutants to be sorbed on clay minerals take the order Zn+2>Ni2+>Pb2+. On the other hand the quantity of adsorbed heavy metals was in the sand soil more than calcareoussoils due to the charges on the surface sand particle and the big surface area. This study suggests that using of available natural materials could be an economic and promising alternative solution in contaminated soils to minimize hazards of such PTE's. Different mechanisms take place in removing of PTEs from the used soils were reported.