Effects of iron surface pretreatment on sorption and reduction kinetics of trichloroethylene in a closed batch system
Resource
Water Research 39 (6): 1037-1046
Journal
Water Research
Journal Volume
39
Journal Issue
6
Pages
1037-1046
Date Issued
2005
Date
2005
Author(s)
Lin, Chin Jung
Abstract
The decline of trichloroethylene (TCE) in a metallic iron-water system results from the combination of reduction reaction and sorption onto iron surfaces. Sorption, particularly by highly impure iron, accelerates the removal of TCE from the aqueous phase, but delays the prevalence of steady-state conditions. In this case, an overly high value of reaction rate constant in the design of a treatment system would be used. In this work, the effects of an iron surface with 8.0% C, 6.1% O and 0.8% Si separately following HCl-washing and H2-reducing pretreatment on sorption and reduction rates were examined. The amounts of both aqueous and sorbed TCE were measured using a modified solvent-extraction method. TCE sorption onto an iron surface, as quantified by the Langmuir sorption maximum, followed the trend H 2-reduced Fe0>HCl-washed Fe0>untreated Fe0 (0.887, 0.365 and 0.311 mg/g, respectively). Measurements of the concentration of sorbed TCE revealed that about 34-37% of the initial mass of TCE in the aqueous phase was removed by sorption by H2-reduced Fe0, 16-19% was removed by HCl-washed Fe0 and 13-16% was removed by untreated Fe0. A combination of new and previously reported data on cast iron's capacity to sorb TCE revealed a linear relationship between this capacity and the C fraction in the surface of the iron, with the coefficient of determination (r2) exceeding 0.99. The first-order observed rate constants (kobs) of the reduction of TCE in contact with Fe 0 were obtained from the slope of a plot of total TCE loss rate (-dCT/dt) versus the amount of TCE in the aqueous phase (Cw) using linear least-squares analysis. The kobs values were 0.080, 0.148 and 0.191 h-1 for untreated, HCl-washed and H2-reduced Fe 0, respectively. Normalized to iron surface area concentration, the specific rate constants (kSA) were 2.37×10-3, 2.31×10-3 and 5.62×10-3 h-1 m -2 L, respectively. The results indicated that HCl-washing approximately doubled kobs, primarily because of the increase in the surface area of the iron, and it slightly decreased kSA due to rapid corrosion during the rinsing process. Both the number of reactive sites and the sorption capacity per unit iron surface area through the H2-reducing pretreatment were increased due to the reduction of iron oxide layer and the carbonization of carbon-containing subjects on the iron's surface. Hence, the H2 reduction of cast iron promotes the removal of TCE from contaminated water by the concurrent sorption and reduction. © 2005 Elsevier Ltd. All rights reserved.
Subjects
Acid-washing process; Iron surface pretreatment; Permeable reactive barriers; Zero valent metal
Other Subjects
Corrosion; Linear systems; Reaction kinetics; Reduction; Solvents; Sorption; Surface treatment; Iron surface pretreatment; Iron-water systems; Langmuir sorption; Trichloroethylene (TCE); Iron; carbon; hydrochloric acid; hydrogen; iron; iron oxide; silicon; trichloroethylene; Trichloroethylene; analytic method; aqueous solution; article; corrosion; detoxification; intermethod comparison; kinetics; Langmuir Blodgett film; linear system; priority journal; quantitative analysis; reduction; solvent extraction; surface property; water contamination; water sampling; water treatment
Type
journal article
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