This paper discusses the toxicity and mobility of chromium species. And it presents the extent and kinetics of reductive remediation of hexavalent chromium, Cr+ using ferrous ion, Fe2+. Molar ratios of 1:3 and 1:6 of ...This paper discusses the toxicity and mobility of chromium species. And it presents the extent and kinetics of reductive remediation of hexavalent chromium, Cr+ using ferrous ion, Fe2+. Molar ratios of 1:3 and 1:6 of Cr (VI) to Fe (II) were used. Integral method of data analysis showed reaction followed second-order kinetics with R square values near unity. Reaction was initially fast but with a rapid precipitation attributed to Cr (III)-Fe (III) in previous studies. This colloidal precipitate ultimately stops the reaction, which explains while conversion efficiency increases with increased molar ratio of Cr (VI) to Fe (II). The impact of pH was investigated by adjusting the Cr (VI)-Fe (II) medium to pH 2.78, 5.24, 7.00, 9.00 and 11.96 using predetermined drops of acid or base. Reaction was more rapid under alkaline conditions with higher extent of degradation consistent with previous research. In soil system, mass transfer limitation was hardly noticed as high extent of reduction was recorded relative to aqueous phase. The high solubility of Cr (VI) aided the release into the aqueous media for reduction by ferrous sulfate.展开更多
The scope of this study was to determine techniques to remediate trichloroethylene contamination under different environmental conditions, media and in co-existence with chromium. The specific objectives were focused ...The scope of this study was to determine techniques to remediate trichloroethylene contamination under different environmental conditions, media and in co-existence with chromium. The specific objectives were focused on the oxidation of trichloroethylene (TCE) in soil and aqueous media using both unmodified KMnO4 particles and poly (methyl methacrylate), PMMA encapsulated KMnO4 in the presence and absence of hexavalent chromium, Cr(VI). Molar ratios (p-values) of KMnO4 to TCE were used as a determining factor in the TCE oxidation process. p-values of 2, 5 and 10 were investigated in aqueous media and an approximately 0.5 M-1·s-1 rate constant was obtained using unmodified KMnO4 in aqueous system. The extent of oxidation did not change with TCE concentration. In soil system, TCE oxidation requires a large amount of KMnO4 to produce similar results as in aqueous system. pH experiments indicate that except at high alkaline condition, pH does not impact the extent of TCE oxidation. Also, the presence of Cr(VI) did not hinder TCE oxidation by KMnO4. Using controlled release application, the rate of TCE oxidation was reduced by PMMA encapsulated KMnO4. Comparative study indicated an expectedly slow rate of TCE degradation using modified KMnO4 but similar overall extent of oxidation for both modified and unmodified KMnO4. The application of the encapsulated matrix yielded 88% ± 3% TCE oxidation and a simultaneous 81% ± 2.1% Cr(VI) reduction by ferrous ion in the same system.展开更多
文摘This paper discusses the toxicity and mobility of chromium species. And it presents the extent and kinetics of reductive remediation of hexavalent chromium, Cr+ using ferrous ion, Fe2+. Molar ratios of 1:3 and 1:6 of Cr (VI) to Fe (II) were used. Integral method of data analysis showed reaction followed second-order kinetics with R square values near unity. Reaction was initially fast but with a rapid precipitation attributed to Cr (III)-Fe (III) in previous studies. This colloidal precipitate ultimately stops the reaction, which explains while conversion efficiency increases with increased molar ratio of Cr (VI) to Fe (II). The impact of pH was investigated by adjusting the Cr (VI)-Fe (II) medium to pH 2.78, 5.24, 7.00, 9.00 and 11.96 using predetermined drops of acid or base. Reaction was more rapid under alkaline conditions with higher extent of degradation consistent with previous research. In soil system, mass transfer limitation was hardly noticed as high extent of reduction was recorded relative to aqueous phase. The high solubility of Cr (VI) aided the release into the aqueous media for reduction by ferrous sulfate.
文摘The scope of this study was to determine techniques to remediate trichloroethylene contamination under different environmental conditions, media and in co-existence with chromium. The specific objectives were focused on the oxidation of trichloroethylene (TCE) in soil and aqueous media using both unmodified KMnO4 particles and poly (methyl methacrylate), PMMA encapsulated KMnO4 in the presence and absence of hexavalent chromium, Cr(VI). Molar ratios (p-values) of KMnO4 to TCE were used as a determining factor in the TCE oxidation process. p-values of 2, 5 and 10 were investigated in aqueous media and an approximately 0.5 M-1·s-1 rate constant was obtained using unmodified KMnO4 in aqueous system. The extent of oxidation did not change with TCE concentration. In soil system, TCE oxidation requires a large amount of KMnO4 to produce similar results as in aqueous system. pH experiments indicate that except at high alkaline condition, pH does not impact the extent of TCE oxidation. Also, the presence of Cr(VI) did not hinder TCE oxidation by KMnO4. Using controlled release application, the rate of TCE oxidation was reduced by PMMA encapsulated KMnO4. Comparative study indicated an expectedly slow rate of TCE degradation using modified KMnO4 but similar overall extent of oxidation for both modified and unmodified KMnO4. The application of the encapsulated matrix yielded 88% ± 3% TCE oxidation and a simultaneous 81% ± 2.1% Cr(VI) reduction by ferrous ion in the same system.
