Trichloroethylene dechlorination rates, pathways, and efficiencies of ZVMg/C in aqueous solution

Highlights: • TCE was dechlorinated completely within 2 h under uncontrolled pH conditions. • Cl^- evolution was likely to participate in pitting corrosion of Mg surfaces. • TCE as an excellent electron scavenger could induce more electrons from Mg⁰. • ZVMg/C aging effects in air or water on TCE dechlorination was insignificant. • Ball-milled ZVMg/C was firstly used to remove chlorinated hydrocarbons in groundwater. The removal mechanism from the reductive dechlorination of trichloroethylene (TCE) by zero valent magnesium (ZVMg) in aqueous solution is systematically studied. Following the preparation and characterization of ball-milled micro ZVMg with graphite (ZVMg/C) particles, this paper evaluated the TCE reaction rates, pathways, utilization rates and aging effects of ZVMg/C particles in aqueous solution under uncontrolled pH conditions. Overall, 38 μM of TCE was transformed by 10 g/L of ZVMg/C to methane (62.51%) and n-hexane (11.86%) and ethane (7.40%) and other alkene and alkyne products through the catalytic hydrogenation pathway. The measured surface area normalized pseudo-first order rate constants (K_SA) were up to 9.31 × 10⁻² L/m²/h and the utilization rate of Mg⁰ accounted for around 60%. The K_SA were decreased to 1.90 × 10⁻² L/m²/h in case of ZVMg/C being exposed in the atmosphere for 6 days due to 7.3% reduction in the utilization rate of Mg⁰ from the initial 85.2%, and 5.11 × 10⁻² L/m² h in case of ZVMg/C aged in water for one day. The removal efficiencies of approximately 56%, 58% and 87% by 10 g/L of ZVMg/C were achieved in the contaminated groundwater comprising 38 μM of TCE, 43 μM of 1,2-dichlorobenzene and 8.12 μM of trichlormethane. Therefore, it is concluded that ZVMg/C is viewed as a potential and effective remediation reagent for the groundwater remediation.