Effect of different types of calcium sulfate on the reactivity of cement/Fe(II) system in dechlorination of trichloroethylene

Abstract

Several studies have been carried out to find out the reactive species in cement/Fe(II) system for the treatment of ground water contaminated with a number of chlorinated organic pollutants such as trichloroethylene (TCE). The previous studies suggest that cement hydration minerals associated with sulfate (SO42-) could be one of the reactive species responsible for dechlorination reaction. Calcium sulfate which is a primary source of sulfate in cement has not been studied in detail. Present study deals with the effect of different types of calcium sulfate on the reactivity of cement/Fe(II) system in dechlorination of TCE. To evaluate the effect of different types of calcium sulfate on reactivity of cement/Fe(II) system, different types of calcium sulfate were mixed with clinker powder to get three different types of cements. TCE reduction experiments were carried out in the presence of Fe(II) using these cements. The results showed that cement with anhydrate and hemihydrate forms of calcium sulfate showed improved TCE reduction kinetics compared to cement with calcium sulfate dihydrate. Different analytical tools such as thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy were used to differentiate between the types of calcium sulfate and understand the minerals generated at the end of TCE reduction experiments. Further studies revealed that the dissolution behavior of calcium sulfate in individual cement was different and had an influence on the formation of ettringite, which was suspected as a reactive mineral.