Identification of Active Agents for Tetrachloroethylene Degradation in Portland Cement Slurry Containing Ferrous Iron

Abstract

Experimental studies were designed to identify the active agents in Fe(II)-based degradative solidification/stabilization (Fe(II)-DS/S) that are responsible for the degradation of tetrachloroethylene (PCE) as well as the conditions that enhance the formation of these active agents. First, the conditions that lead to maximizing production of the active agents were identified by measuring the ability of various chemical mixtures to degrade PCE. Results showed that Fe(II), Fe(III), and Cl were the elements most closely associated with high degradation rates. In addition to elemental composition, unknown factors associated with the formation of solid phases could also be important in determining the extent of formation of active reducing agents. Second, instrumental analysis techniques (XRD, SEM, SEM-EDS) were used to identify compounds in chemical mixtures that were observed to have high activities for PCE degradation. SEM-EDS analysis indicated that Fe was associated with hexagonal particles, which is the typical shape of several AFm phases in hydrated Portland cement that are composed of calcium, aluminum/iron, hydroxide, and possibly other anions. No Fe-containing solid phases could be identified. Therefore, it appears that AFm phases are the most likely active agents for PCE degradation in mixtures containing Portland cement or its acid extract. Mixtures without cement did not form the same solid phases but were observed to form ferrous hydroxide as a major solid phase.