Potential of Soils Amended with a Nano Calcium Silicate Mixture for Lead Encapsulation in an Aqueous Medium

Lead (Pb2+) contamination in soils leads to its leaching and release which in turn, poses significant environmental and health risks. In lieu of this, a number of studies are available for solidification and stabilization as a remediation technique for brown fields typically contaminated with Pb2+. In this study, the performance of two soils in retaining Pb2+ has been evaluated. Two tropical soils were selected and amended with nano calcium silicate (potential stabilizing material) in small percentages to enhance the Pb2+ fixation. Batch adsorption studies, leaching tests and kinetic studies were conducted. The experimental data was then used to plot adsorption isotherms. Langmuir isotherm was found to be more suitable than Freundlich isotherm for both soil mixtures. Kinetic data was fitted on selected four models viz., pseudo first order, second order, Elovich and intra particle diffusion. Correlation coefficients obtained by all models fitted well with the following ranking: Elovich > Intraparticle diffusion > Pseudo second order > Pseudo first order. Qualitative measurements were also made using SEM and EDS. The leachable heavy metal concentrations were reduced following soil-nano calcium silicate treatment to concentrations lower than the TCLP standard regulatory threshold of < 5 mg L−1 for Pb2+ even after a curing period of more than 90 days. Results suggest that the soil nano-metallic Ca/CaO mixture is suitable for use in immobilization of Pb2+ contaminated soil under normal moisture conditions.