Reductive Degradation of Co-Contaminant Medium of TCE and Cr(VI) Using Atomized Iron Powder

Elemental Iron in the form of atomized iron powder (Zero Valent Iron, ZVI or Fe(0)) was used to individually and simultaneously degrade a co-contaminant medium of hexavalent chromium (Cr(VI)) and trichloroethylene (TCE). Under appropriate conditions of initial concentrations, the overall degradation reaction was modeled as a combination of two pseudo-first order reactions. The reaction kinetics, degradation efficiency and reductant demand of both Cr(VI) and TCE were determined. Over a 2-hour period, degradation of TCE and Cr(VI) yielded 85% and 25% reduction, respectively with excess amounts of Fe(0). Over a 5-hour period, TCE percent remained at 85% whilst Cr(VI) degradation increased rapidly to almost 100%. This observation is attributed to: (1) increased polarization and destabilization of the double bond in the TCE leading to cleavage of the Chloride and solubility equilibria; (2) the formation of a passive layer of chromic-ferric mixed oxides and oxyhydroxides on the surface of iron particles, which impeded degradation but dissolved due to increasing acidity to expose fresh reactive sites. The observed pseudo-first order degradation rate constants for individual and combined degradations of the co-contaminant were determined.