Cadmium Fixation Studies on Contaminated Soils Using Nano Calcium Silicate—Treatment Strategy

In this study soils were sampled from three different locations which were at high risk for contamination having different categories of hazardous wastes such as steel plant, automobile and batteries work unit and municipal dumpsite near Bangalore City, India. These soils were artificially spiked with high concentration of cadmium (Cd2+) to the tune of 3,000 mg/L. The leaching behaviour of cadmium (Cd2+) with these soils and soils amended with nano calcium silicate (NCS) were studied with four different leaching methods viz. ASTM D3987, toxicity characteristics leaching procedure (TCLP), extended TCLP, and caged TCLP. In order to understand the type of sorption taking place in the soil matrices, sequential extraction in five stages was performed on these Cd2+ spiked soils. It was found that soils treated with nano calcium silicate sorb cadmium effectively and as per ASTM D3987. The retention of Cd2+ was permanent over long term and TCLP tests proved sorption was 90% better with NCS treated soils and the leaching rate for treated soils was found to be less than 1cm/yr. Sequential extraction confirmed that encapsulation of Cd2+ as a dominant mechanism in immobilizing it in the matrices of soil and NCS.