Dual role of soil in dechlorination of soil-sorbed trichloroethene by CMC stabilized and sulfidated nanoscale zero-valent iron

Abstract

Carboxymethyl cellulose stabilized and sulfidated nano zero-valent iron (CMC-S-nZVI) can efficiently degrade trichloroethene (TCE) in water. However, little is known about the interaction between CMC-S-nZVI and TCE in soils. Here we studied the effects of two soils, a sandy (LY) and a sandy-loamy soil (DXAL), on TCE dechlorination by two types of CMC-S-nZVI particles. Continuous dechlorination of soil-sorbed TCE was observed for up to 96 h. LY and DXAL soil sorption suppressed 24-h dechlorination by 5–16 % and 25–51 %, respectively, although CMC significantly enhanced TCE release from the soils. Soil clay minerals, including Fe/Mn oxides and organic matter, promoted iron corrosion during the initial stage (< 8 h and < 2 h for the two particle types) through uptake of Fe2+ from the CMC-S-nZVI surface, but inhibited corrosion and TCE dechlorination at the later stage by blocking surface reaction sites, thereby hindering electron transfer. The dual effects of soil were more evident in DXAL, due to its higher content of clays and organic matter. Our findings show that CMC-S-nZVI can effectively dechlorinate soil-sorbed TCE, but reductant demand and the blocking effect from the soil should be considered to optimize engineering designs at TCE-contaminated sites.