Acceleration and mechanistic studies of the mechanochemical dechlorination of HCB with iron powder and quartz sand

• The Mechanochemical method could destruct HCB powder by the fasted system of Fe/SiO2.
• Graphite and amorphous carbon were confirmed by Raman spectrum with the SiO2 addition’s role of accelerating carbonization.
• Peroxy radicals and E′ center radicals generated during the grinding of SiO2 were identified by the ESR spectrum.

Hexachlorobenzene (HCB) is considered as a probable human carcinogen and is toxic (LD50 3500 mg/kg) by all routes of exposure as a persistent organic pollutant. The mechanochemical destruction(MCD) of HCB via planetary ball milling was examined under different reaction conditions, with the intent of developing a method that is more effective than the traditionally used method involving the use of the CaO reagent. Comparing the different reagents’ efficiencies, the highest MCD efficiency was obtained with a combination of iron powder and quartz sand (Fe/SiO2); after 8 h ball milling, the HCB destruction yield was nearly 99.9%, in contrast to 84.9% using CaO. The HCB destruction yields using different reagents followed the sequence: Fe/SiO2 > CaO > CaO/SiO2 > SiO2 > Fe. Raman spectral analysis demonstrated that the addition of SiO2 could accelerate the carbonization process. Electron spin resonance (ESR) analyses confirmed the radical formation of unpaired electrons in samples with added SiO2 including peroxy radicals (SiOO) and E′ center radicals (Si). A mechanism for the mechanochemical destruction promoted by Fe/SiO2 was proposed, in which radical species facilitate the dechlorination of HCB.