In this research, geochemistry effect and competitive effect of TCE on the reactivity of zero-valent iron for hexavalent chromium removal (Cr[VI] removal) were investigated. Column study was set up under different hardness and carbonate combinations. The Cr(VI) removal capacity of Fe⁰ was found to be about 4 mg Cr/g Fe⁰ without presence of hardness and carbonate present. A slight decrease in Cr(VI) removal capacity was found in the presence of calcium or magnesium hardness at low to moderately hard level. Results also revealed that carbonate changed the morphology of Fe⁰ with formation of pale green precipitates on the iron filings but without reduction in removal capacity. However, the presence of hardness and carbonate in groundwater have great impact on Fe⁰. The formation of passivat...[ Read more ]

In this research, geochemistry effect and competitive effect of TCE on the reactivity of zero-valent iron for hexavalent chromium removal (Cr[VI] removal) were investigated. Column study was set up under different hardness and carbonate combinations. The Cr(VI) removal capacity of Fe⁰ was found to be about 4 mg Cr/g Fe⁰ without presence of hardness and carbonate present. A slight decrease in Cr(VI) removal capacity was found in the presence of calcium or magnesium hardness at low to moderately hard level. Results also revealed that carbonate changed the morphology of Fe⁰ with formation of pale green precipitates on the iron filings but without reduction in removal capacity. However, the presence of hardness and carbonate in groundwater have great impact on Fe⁰. The formation of passivated precipitates on Fe⁰ reduced one-third of the removal capacity. Another column study was set up with TCE added. Cr(VI) and TCE were found to be electron competitors in the reduction-oxidation reactions. The degradation rate of Cr(VI) decreased when TCE was added and vice versa. However, there was no apparent effect on the specific reaction rate, k_SA, of TCE when Cr(VI), hardness and carbonate were all present. It revealed that TCE was a stronger electron competitor of Cr(VI) and the degradation of TCE became more favorable when both hardness and carbonate were present. This suggests that the passivated precipitates formed on the Fe⁰ surface in the presence of both hardness and carbonate may significantly affect Cr(VI) removal but has insignificant effect on TCE removal.