Factors affecting humic-nickel complex mediated reduction of trichloroethene in homogeneous aqueous solution.
The kinetics of trichloroethene (TCE) reductive dechlorination mediated by humic-Ni complexes in homogeneous aqueous solution using titanium(III) citrate as the bulk reductant was examined under various environmental conditions (e.g., pH and ionic compositions). Using Ca2+, Zn2+, and Hg2+ ions to vary Aldrich humic acid (HA)-Ni complex concentrations, pseudo-first-order rate constants for TCE reduction were observed to be proportional to HA-Ni levels (as calculated by speciation modeling), confirming HA-Ni complexes as the probable active mediator species. TCE reduction by HA-Ni was observed to be strongly pH dependent and could be due to both the variations of HA-Ni concentration and Eh with pH. Evidence is presented which suggests that quinone moieties may not be crucial for the humic-Ni mediated reduction of TCE. A variety of natural soil and aqueous humic material and Ni systems were examined, and some showed reactivity toward TCE. Humic-metal complexes may be important electron-transfer mediators in natural systems.
Ma
H A
HA
Air Force Research Laboratory, AFRL/MLQL, 139 Barnes Drive, Suite 2, Tyndall Air Force Base, Florida 32403-5323, USA.
O'Loughlin
E J
EJ
Burris
D R
DR
D016227:Benzoquinones / Q000737:chemistry; D006812:Humic Substances / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009532:Nickel / Q000737:chemistry*; D010084:Oxidation-Reduction; D012997:Solvents / Q000737:chemistry*; D014241:Trichloroethylene / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis*
D016227:Benzoquinones; D006812:Humic Substances; D012997:Solvents; D014874:Water Pollutants, Chemical; D014241:Trichloroethylene; C004532:quinone; D009532:Nickel