Effect of different composition in cement/Fe(II) system for dechlorination of Trichloroethylene

Abstract

Iron-based degradative Solidification/Stabilization, as a potential new technology for chlorinated organics and metals, is already widely studied by several researches. However, due to the complexity of the cement hydration products there is no clear evidence about the component solely responsible in cement for trichloroethylene (TCE) dechlorination. The goal of this research was to evaluate the dechlorination ability of different composition in cement/Fe(II) system. This work could lead to identify the active agent responsible for dechlorination of TCE. To achieve this goal, a variety of systems were conducted that contained different binders in the presence of Fe(II). First, special cements, high-alumina cement (CAC) and Calcium Sulfoaluminate (CSA) cement were respectively used as binder in DS/S system to check the reactivity for TCE degradation. CSA cement shown the TCE reduction capacity, while CAC did not show significant reduction in TCE concentration. In the XRD, SEM, and EDX analysis, Fe-ettringite associated with Fe(II) was generated only in the cement samples that showed TCE reduction capacity. Seconds, different of ettringite associated with Al3+ and Fe3+ were synthesized separately in laboratory, and these also used respectively to check dechlorination capacity in presence of Fe(II). to check the reactivity for degradation of TCE in cement/Fe(II) system. Al-ettringite and Fe-ettringite were successfully synthesized associated with Al3+ and Fe3+. However, only Fe-ettringite contained impure calcium ferrite shows reduction capacity for TCE. Finally, CSA and Gypsum were mixed with OPC and CAC to increase ettringite formation and batch experiment were conducted in the presence of Fe(II). When CSA mixed with OPC or CAC, both OPC+CSA and CAC+CSA sample show the enhanced reactivity for TCE degradation and the formation of ettringite was clearly founded in XRD and SEM analysis. Further, the addition of gypsum in cement shows that the reactivity for TCE reduction were observed to be dependent on the content of gypsum. The combination of OPC and gypsum improved reduction kinetics compared to OPC alone. There is possibility that the formation of ettringite could be related with TCE reduction, but these still require further investigations such as XRD, SEM, and EDX.