Influence of lead and chromium ions as toxic heavy metals between AFt and AFm phases based on C3A and C4A3 S
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Three calcium aluminate (C3A) and calcium sulphoaluminate (C4A3 ) as clinker minerals were synthesized to investigate the solidification/stabilization (S/S) mechanism of lead and chromium ions on cement matrix. Effects of AFt phases on S/S mechanism were analyzed using FT-IR, SEM-EDS and heat evolution. Lead and chromium leachability from solidified AFt phases was also investigated using the toxicity characteristic leaching procedure (TCLP) recommended by the U.S. Environmental Protection Agency (EPA). The results showed that clinker mineral types considerably affected the S/S mechanism of AFt and AFm phases incorporating chromium and lead ions. In the case of adding chromium, both AFt and AFm phases based C3A and C4A3 allowed ionic substitution Cr3+ for the trivalent ion as Al3+ and CrO4 2− for SO4 2− . Moreover, chromate hydrocalumite [3CaO • Al2O3 • CaCrO4 • nH2O] was also observed. However, in the case of adding lead, it was found that when C3A and C4A3 were hydrated, the formation of AFt and AFm phase based C4A3 was faster than C3A. Especially, AFt phases and the calcium lead hydroxides (Ca[Pb(OH)3 • H2O]2) incorporating lead ions were formed during hydration of C4A3 in the early stage compared to the C3A case. This showed that AFt and AFm phase based C4A3 for S/S of lead were more effective than that of C3A.
Abstract
Three calcium aluminate (C3A) and calcium sulphoaluminate (C4A3 ) as clinker minerals were synthesized to investigate the solidification/stabilization (S/S) mechanism of lead and chromium ions on cement matrix. Effects of AFt phases on S/S mechanism were analyzed using FT-IR, SEM-EDS and heat evolution. Lead and chromium leachability from solidified AFt phases was also investigated using the toxicity characteristic leaching procedure (TCLP) recommended by the U.S. Environmental Protection Agency (EPA). The results showed that clinker mineral types considerably affected the S/S mechanism of AFt and AFm phases incorporating chromium and lead ions. In the case of adding chromium, both AFt and AFm phases based C3A and C4A3 allowed ionic substitution Cr3+ for the trivalent ion as Al3+ and CrO4 2− for SO4 2− . Moreover, chromate hydrocalumite [3CaO • Al2O3 • CaCrO4 • nH2O] was also observed. However, in the case of adding lead, it was found that when C3A and C4A3 were hydrated, the formation of AFt and AFm phase based C4A3 was faster than C3A. Especially, AFt phases and the calcium lead hydroxides (Ca[Pb(OH)3 • H2O]2) incorporating lead ions were formed during hydration of C4A3 in the early stage compared to the C3A case. This showed that AFt and AFm phase based C4A3 for S/S of lead were more effective than that of C3A.
참고문헌 (9)
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