Reductive dechlorination of carbon tetrachloride using iron(II) iron(III) hydroxide sulfate (green rust)
- Royal Veterinary and Agricultural Univ., Frederiksberg C (Denmark). Chemistry Dept.
The reductive dechlorination of CCL{sub 4} and CHCl{sub 3} in the presence of the synthetic sulfate form of green rust (GR{sub SO{sub 4}}), Fe{sup II}{sub 4}Fe{sup III}{sub 2}(OH){sub 12}SO{sub 4}yH{sub 2}O at pH {approximately}8 and room temperature was investigated. Reduction of CCl{sub 4} produces CHCl{sub 3} and C{sub 2}Cl{sub 6} as main chloroaliphatic products, while GR{sub SO{sub 4}} is oxidized to magnetite (Fe{sub 3}O{sub 4}). The formation of C{sub 2}Cl{sub 6} indicates a coupling reaction between trichloromethyl radicals in the suspension. Chloroform was much less susceptible than CCl{sub 4} to reductive dechlorination by GR{sub SO{sub 4}} showing reduction rates approximately 100 times less than for reduction of CCl{sub 4}. The transformation of CCl{sub 4} by GR{sub SO{sub 4}} can be described by pseudo-first-order reaction kinetics with respect to formation of chloride. At room temperature the rate expression is given as: d[Cl{sup {minus}}]/dt {approx_equal} {minus}d[CCl{sub 4}]/dt = r{center_dot}k{sub obs}[Fe(II)]{sub GR}, where k{sub obs} is in the range (0.47 {times} 10{sup {minus}5})--(2.18 {times} 10{sup {minus}5}) s{sup {minus}1} for CCl{sub 4} concentrations above its aqueous solubility. This narrow range may be due to the constant CCl{sub 4}(aq) concentration owing to buffering of the CCl{sub 4}(aq) concentration by free phase CCl{sub 4}(l) thereby indicating that the reaction takes place in solution. Experiments with initial CCl{sub 4} concentrations below its aqueous solubility support this theory. The reaction kinetics are compared with similar reactions where iron(0) is used as reductant of CCl{sub 4}. The first-order rate constants for transformation of CCl{sub 4} with zerovalent iron and GR{sub SO{sub 4}}, respectively, are found to be in the same range. Thus, GRs formed during corrosion of iron(0) under nonacid conditions may considerably contribute to the total reduction of CCl{sub 4} measured in iron(0) systems.
- OSTI ID:
- 318752
- Journal Information:
- Environmental Science and Technology, Vol. 33, Issue 2; Other Information: PBD: 15 Jan 1999
- Country of Publication:
- United States
- Language:
- English
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