Kinetic study of cis-dichloroethylene (cis-DCE) and vinyl chloride (VC) dechlorination using green rusts formed under varying conditions.

Abiotic degradation of cis-dichloroethylene (cis-DCE) and vinyl chloride (VC) was investigated using Fe hydroxides obtained by hydrolyzing Fe(II) salts over a pH range of 7.7-8.0. Within this narrow pH range, a green rust (GR) precipitated. The dechlorination reactivity of the resulting GR precipitates increased with the dissolved Fe(II) concentration remaining in solution after precipitation. Controls run using only the dissolved Fe(II) supernatant were not reactive, suggesting the relative amount of Fe(II) on the surface of precipitated GRs was the causative agent in the relative reactivity. To test this, a series of GR batches with varying dissolved Fe(II) concentrations were prepared by acid-base titration and examined for cis-DCE and VC dechlorination kinetics under reducing conditions. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses of these batches were performed to characterize the bulk mineralogy and the excess surface Fe(II), respectively. Cis-DCE and VC dechlorination results along with solid phase characterization show that different surface Fe(II)/Fe(III) compositions are responsible for the different reactivity of GRs formed within the GR precipitation zone.