Tricalcium silicate (C3S) as clinker minerals was synthesized to investigate the solidification/stabilization (S/S) mechanism of lead, chromium and zinc ions on cement matrix. Effects of various hydration phases on the S/S mechanism were analyzed using XRD, SEM-EDS and heat evolution. Lead, chromium and zinc leachability from solidified hydration phases were also investigated using the toxicity characteristic leaching procedure (TCLP) recommended by the U.S. Environmental Protection Agency (EPA). The results showed that heavy metal ions considerably affected the S/S mechanism of C-S-H phases. The presence of lead appears to induce considerable retardation in the curing process during hydration of C3S until 28 days. Moreover, in case of adding chromium, retardation of C3S hydration due to the formation of CaCrO4 • H2O phases also appeared in the early stages. Especially, in case of adding zinc, it was founded that the leaching of zinc ions from specimens at 10,000 ppm was lower than that of specimens with lead at the same dosage.

Keywords: C3S, C-S-H phases, Lead, Chromium (III), Zinc.