Reductive Dechlorination of Hexachlorobutadiene by a Pd/Fe Microparticle Suspension in Dissolved Lactic Acid Polymers: Degradation Mechanism and Kinetics

Reductive dechlorination of hexachlorobutadiene (HCBD) was performed by a suspension of scattered spots of palladium nanoparticles deposited on iron microparticles (nPd/μZVI) in a mixture of dissolved lactic acid polymers and oligomers (referred to as PLA). The effects of nPd/μZVI loading, temperature, HCBD initial concentration, and PLA content were investigated as to define the best conditions for the dechlorination. HCBD dechlorination by nPd/μZVI occurred in a two-step process: first, HCBD adsorbed onto the nPd surface, which resulted in a rapid initial disappearance of pollutant in solution, and, second, it degraded chemically by atomic hydrogen H*, which resulted from the dissociative adsorption of H2 on nPd. HCBD remained adsorbed on the surface until its complete degradation in nonchlorinated product, in agreement with the formation of an ordered activated complex on the nPd/μZVI surface as suggested by the negative entropy of activation calculated from the Eyring equation. Hence, a minimum amount...