Abinash Agrawal (Advisor), Hailiang Dong (Committee Member), David Kempisty (Committee Member)
Master of Science (MS)
A previous work demonstrated that sulfide-treated iron oxides (goethite, hematite, and magnetite) may not show reductive pathways with carbon tetrachloride (CT) as observed with lab-precipitated iron sulfide. We examined the kinetics and products of reaction of sulfide-treated hydrous ferric oxide (HFO) towards select chlorinated hydrocarbons in batch reactors with HFO: HS- molar ratio of 1:1.5 at pH 7. CT, 1,1,2-trichlroethane (1,1,2-TeCA), 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA) and 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA) showed faster kinetics whereas chloroform (CF) showed slower kinetics. Trichloroethene (TCE) degradation was observed at three pHs: 7, 8 and 10; the loss in the reactors were not much different from controls at pH 7, 8 and 10. The degradation products of 1,1,2-TCA (1,1-DCE, 33%), 1,1,1,2-TeCA (TCE, 29%), and 1,1,2,2-TeCA (TCE~100%) suggest dehydrohalogenation to be the major pathway. The degradation product of CT (4% CF; hydrogenolysis) and 1,1,1,2-TeCA (4% 1,1 DCE; ß elimination) shows reduction to be a minor pathway. This suggests that unlike the lab-precipitated FeS, formed by reaction of Fe (II) and HS-, reduction may not be a major pathway for sulfide-treated HFO. Recent studies identified a light independent pathway for generation of hydroxyl radicals in which hydroxyl radicals are produced during O2 reduction by electron donors such as Fe (II) and DOC. Most studies have focused on hydroxyl radical production from reduced structural Fe (II) in clays and sediments. Study of reduced iron oxide in this respect remains largely uninvestigated. In this part of the research, hydrous ferric oxide (HFO) was reduced by sodium dithionite (SD) and the resulting phase was oxygenated in the dark. This bench scale study shows the age of the phase formed by SD reduced HFO did not affect the rates of cis-1,2-DCE degradation. kobs1 of cis-1,2-DCE degradation did not depend on the initial amount of cis-1,2-DCE. kobs1 of cis-1,2-DCE degradation increased non-proportionately with increase in the concentration of dithionite. Effect on cis-1,2-DCE degradation rates were investigated at three HFO:SD molar ratios: 9.4:1, 4.7:1 and 2.4:1 (SD concentration is increasing by a factor of ~2 successively); The ratios of kobs1 were 1:10.8:13.8 (normalized to kobs1 of 9.4:1) for these three ratios respectively indicating a magnitude of order increase between 9.4:1 to 4.7:1 while it increased by 1.27 times between two higher ratios 4.7:1 to 2.4:1. Observed order of kobs1 was :1,1-DCE>TCE>PCE>cis-1,2-DCE>trans-1,2-DCE and ethene. The reactivity increased with decreasing number of chlorine substituents for 1,1-DCE>TCE>PCE and may be explained based on strong inductive effect exerted by chlorine atoms. Surprisingly, ethene with no chlorine substituents showed the least reactivity. The ratio of rate constants observed are consistent to that observed with hydroxyl radicals generated from other methods. The order for DCE isomers 1,1-DCE>cis-1,2-DCE>trans-1,2-DCE may be explained based on position of the chlorine substituents.
Department or Program
Department of Earth and Environmental Sciences
Year Degree Awarded
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