Factors affecting humic-nickel complex mediated seduction 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) citr ate as the bulk reductant was examined under various environmental conditio ns (e.g., pH and ionic compositions). Using Ca2+ Zn2+, and Hg2+ ions to var y Aldrich humic acid (HA)-Ni complex concentrations, pseudo-first-order rat e constants for TCE reduction were observed to be proportional to HA-NI lev els (as calculated by speciation modeling), confirming HA-Ni complexes as t he 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 E-h With pH. Evidence is presented which suggests that qu inone moieties may not be crucial for the humic-Ni mediated reduction of TC E. 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.