REDUCTIVE DEHALOGENATION OF CHLORINATED METHANES BY IRON METAL

Reduction of chlorinated solvents by fine-grained iron metal was studi ed in well-mixed anaerobic batch systems in order to help assess the u tility of this reaction in remediation of contaminated groundwater. Ir on sequentially dehalogenates carbon tetrachloride via chloroform to m ethylene chloride. The initial rate of each reaction step was pseudo-f irst-order in substrate and became substantially slower with each deha logenation step. Thus, carbon tetrachloride degradation typically occu rred in several hours, but no significant reduction of methylene chlor ide was observed over 1 month. Trichloroethene (TCE) was also dechlori nated by iron, although more slowly than carbon tetrachloride. Increas ing the clean surface area of iron greatly increased the rate of carbo n tetrachloride dehalogenation, whereas increasing pH decreased the re duction rate slightly. The reduction of chlorinated methanes in batch model systems appears to be coupled with oxidative dissolution (corros ion) of the iron through a largely diffusion-limited surface reaction.