Rapid mechanochemical dechlorination of hexachlorobenzene with zero-valent silicon as a novel additive: The attempt of zero-valent nonmetallic

The used of different zero-valent metals as reducing agents for dechlorination of polychlorinated biphenyl (PCB) based on mechanochemical method have been studied intensively, while few studies have been conducted on zero-valent nonmetallic reducing agents. Therefore, in this study, zero-valent silicon (ZVS), easily obtainable from photovoltaic panel waste in near future, has been used to serve the purposes as additive to dechlorinate persistent organic pollutants i.e., hexachlorobenzene (HCB). High-energy ball milling rapidly removes the passivated layer from the ZVS surface, exposing its fresh surface to release free electrons for the dechlorination of HCB at shortened time with eventually condensed amorphous carbon and hydrated silica as final products, safe to the soil. The degradation efficiency could achieve at 96.12% and dechlorination rate at 83.91% within only 60 min milling and 10% additive amount even if the concentration of HCB in simulated contaminated samples was as high as 5%. Various characterizations have been performed to fully analyze the intermediate phases and to understand the decomposition mechanism. Cyclic voltammograms (CV) curve and Tafel polarization scanning test as electrochemical evaluation method were performed to explore the involvement of electron release in the HCB remediation, for explaining the superior performance of ZVS compared to other additives based on radical dechlorination pathway. Overall, this work is expected to introduce a brand-new alternative toward practical application of mechanochemical remediation for the polluted soils, not only from environmental remediation perspective, but also the waste disposal.

Automated summary

This study investigates the use of zero-valent silicon as an additive for mechanochemical dechlorination of hexachlorobenzene. The results show that zero-valent silicon can efficiently degrade hexachlorobenzene and produce safe byproducts for soil remediation. This research introduces a new alternative for practical application of mechanochemical remediation.