Nanomaterials-based solidification/stabilization of metal-contaminated soils

Abstract The effectiveness of multiple doses of nanocalcium silicate (NCS) on soils for desorption of heavy metals in polluted soils, subjected to a harsh environment of chemical extractants, specifically acetic acid, nitric acid, ethylene diamine tetra acetic acid (EDTA), and diethylenetriamine pentaacetic acid (DTPA), were evaluated. Four heavy metals—As, Cr, Hg, and Pb—were spiked on two semiarid soils and later amended with NCS in three percentages of 0.5%, 1.0%, and 1.5%. Extensive desorption tests were performed on these mixtures. It was found that for all the mixtures the removal efficiency for soils was more than 70% and EDTA with 1 M concentration gave the maximum removal efficiency. It was found that cationic metal ions were desorbed effectively by EDTA, whereas As anion was desorbed by nitric acid and Cr was desorbed by DTPA. The order of desorption for metal ions was As>Cr>Hg>Pb. Soils amended with NCS decreased the removal efficiency and encapsulated the metal ions in the interstices of soil NCS mixture and made them immobile and inert. It was found that there was an improvement of 52% in the retention of heavy metals for soils amended with NCS. Thus the diligence of NCS can be a utilitarian scheme to freeze heavy metals in soils.