Combined calcium sulfoaluminate and ordinary portland cement/Fe(II) system for enhanced dechlorination of trichloroethylene

Abstract

The trichloroethylene (TCE) reduction capacity of four different types of cements, ordinary Portland cement (OPC), two types of calcium aluminate cements (CAC) with higher Al2O3 (UAC-50), and higher Fe2O3 (ISTRA-40), and calcium sulfoaluminate cement (CSA), were evaluated in presence of Fe(II). The OPC and CSA cements individually showed dechlorination capacity for TCE, following pseudo-first-order kinetics, but both types of CAC cements did not show reduction capacity. Further combined systems of CSA and OPC were found to enhance the rate of dechlorination compared to OPC or CSA used alone. The cement mixtures were optimized to get fastest reduction kinetics. The iron oxide and sulfate originally present in cement during manufacturing were found to play a significant role together. The end products of the dechlorination reaction were acetylene, ethylene and ethane suggesting β-elimination as the major pathway. The X-ray diffraction (XRD), scanning electron microscope with energy dispersive spectroscopy (SEM–EDS), analyzes were used to identify the solids that were produced during TCE reduction experiments. Ettringite crystals were abundant in all the reactive cement samples. However the formation of ettringite was not seen in nonreactive cement samples. It is speculated that Fe–ettringite associated with Fe(II) could be one of the reactive species in TCE reduction.