Kinetics of halogenated organic compound degradation by iron metal

A combination of new and previously reported data on the kinetics of dehalogenation by zero-valent iron (Fe⁰) has been subjected to an analysis of factors effecting contaminant degradation rates. First-order rate constants (k(obs)) from both batch and column studies vary widely and without meaningful correlation. However, normalization of these data to iron surface area concentration yields a specific rate constant (k(SA)) that varies by only 1 order of magnitude for individual halocarbons. Correlation analysis using k(SA) reveals that dechlorination is generally more rapid at saturated carbon centers than unsaturated carbons and that high degrees of halogenation favor rapid reduction. However, new data and additional analysis will be necessary to obtain reliable quantitative structure-activity relationships. Further generalization of our kinetic model has been obtained by accounting for the concentration and saturation of reactive surface sites, but k(SA) is still the most appropriate starting point for design calculations. Representative values of k(SA) have been provided for the common chlorinated solvents.