Degradation of 1,2,3,4,5,6-hexachlorocyclohexane, γ-isomer (lindane) and hexachlorobenzene (HCB), a highly persistent and potentially carcinogenic pesticides, by ball-milled zero-valent magnesium (ZVMg) powder was investigated. The aim of this work is to demonstrate the use of ZVMg in ethanol solvent and acetic acid to enhance the reductive dechlorination of both lindane and HCB at room temperature. The results are compared for both target analytes in order to understand the degradation of both aliphatic and aromatic organo-chlorinated pesticides. Complete loss of the parent compounds was achieved within 15 minutes for lindane and HCB, respectively; however, HCB degraded at a much faster rate with no detection at three minutes. Complete dechlorination/dehydrohalogenation of lindane was achieved, resulting in formation of benzene as the major final non-chlorinated byproduct and γ-3,4,5,6-tetrachlorocyclohexene (γ-TeCCH) as the minor dehydrohalogenation byproduct. Trace level of additional degradation product including chlorobenzene was also detected. However, seven lower chlorinated benzene were detected by GC/MS for the dechlorination of HCB. The more heavily-chlorinated benzene byproducts showed faster degradation rates for HCB, resulting in 1,2,4-trichlorinated benzene as major byproducts of HCB degradation. The mole balances of lindane and HCB were 90.6% and 81.7%, respectively. Further studies were done to enhance degradation kinetics for HCB by re-spiking with acetic acid after two weeks of degradation. Although complete dechlorination was still not achieved, a slight improvement was observed for HCB. Degradation process for both substrates followed Pseudo first-order kinetics while the observed pseudo first-order rate constant was greater for the HCB than the lindane with around three times. The results indicate that ball-milled ZVMg represents a highly promising emerging technology for the degradation of aliphatic and aromatic organochlorines without the need for catalysts. It is anticipated that an understanding of these fundamental chemical processes will allow this system to be effective to a variety of complex ecological media.

Destruction of γ-hexachlorocyclohexane versus hexachlorobenzene in an acidified ethanol using ball-milled ZVMg

2019 Spring National Meeting

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