Degradation of chlorofluorocarbons using granular iron and bimetallic irons.
Degradation of trichlorofluoromethane (CFC11) and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC113) by granular iron and bimetallic (nickel- or palladium-enhanced) irons was studied in flow-through column tests. Both compounds were rapidly degraded, following pseudo-first-order kinetics with respect to the parent compounds. The average pseudo-first-order rate constants for CFC11 were similar among different materials, except for palladium-enhanced iron (PdFe), in which the rate of degradation was about two times faster than for the other materials. In the case of CFC113, the rate constants for bimetallic irons were about two to three times greater than for the regular iron material. The smaller than expected differences in degradation rate constants of chlorofluorocarbons (CFCs) between regular iron and bimetallic irons suggested little, if any, catalytic effect of the bimetallic materials in the initial degradation step. Subsequent degradation steps involved catalytic hydrogenation, however, playing a significant role in further degradation of reaction intermediates. The degradation intermediates and final products of CFC11 and CFC113 suggested that degradation proceeded through hydrogenolysis and α/β-elimination in the presence of regular iron (Fe) and nickel-enhanced iron (NiFe). Even though there is only minor benefit in the use of bimetallic iron in terms of degradation kinetics of the parent CFCs, enhanced degradation rates of intermediates such as chlorotriflouroethene (CTFE) in subsequent reaction steps could be beneficial.
Department of Earth and Environmental Sciences, Chonbuk National University, Jeonju, Jeollabuk-do 561-756, Republic of Korea; The Earth and Environmental Science System Research Center, Chonbuk National University, Jeonju, Jeollabuk-do 561-756, Republic of Korea. Electronic address: sjeen@jbnu.ac.kr.
Sung-Wook
SW
Jeen
Remediation Consulting Group Inc., Calgary, Alberta T2C 5H3, Canada.
Snezana
S
Lazar
Pest Management Regulatory Agency, Health Canada, Ottawa, Ontario K1A 0K9, Canada.
Lai
L
Gui
Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
Robert W
RW
Gillham
D017402:Chlorofluorocarbons / Q000032:analysis / Q000737:chemistry*; D052918:Environmental Restoration and Remediation; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D018508:Water Purification / Q000379:methods*
D017402:Chlorofluorocarbons; D007501:Iron
CFC11; CFC113; Degradation pathway; Granular iron; Nickel–iron; Palladium–iron