Dittmarite Nanosheets Capture Dissolved Iron Released by Anaerobic Corrosion of S-nZVI and Enhance Trichloroethene Degradation in Groundwater

Sulfidation of nanoscale zerovalent iron (nZVI) toward substantially enhancing electron selectivity to trichloroethene (TCE) and its degradation efficiency to benign end products has been a major breakthrough. However, the electron transfer from S-nZVI to TCE or water also results in leaching of Fe2+, and the mitigation of this reaction has not been addressed. Anaerobic corrosion of 1.2 g/L S-nZVI during TCE degradation led to high dissolved Fe, up to 353 ± 26 mg/L under electron-excess conditions and 427 ± 30.2 mg/L under electron-limited conditions, thus compromising treated water quality during (ground)water treatment. In this study, a dittmarite-S-nZVI (DS-nZVI) composite yielded efficient TCE degradation with the continuous sequestration of released Fe. S-nZVI was well-dispersed on the dittmarite (NH4MgPO4·H2O) nanosheets. DS-nZVI yielded faster and complete dechlorination and a ∼1000-fold decrease in Fe leaching (<0.3 mg/L) compared to S-nZVI (353 ± 26 mg/L) under electron excess conditions, and >90% iron removal under electron-limited conditions with TCE degradation capacity of 1.46 × 1023 molecules per mol of Fe0. Continuous exchange of Fe2+ with Mg2+ ions and complexation with phosphate ions was followed by structural transformation to crystalline baricite, (Fe, Mg)3(PO4)2·8H2O, leading to a more sustainable TCE degradation approach for groundwater remediation.