Elucidating the dechlorination mechanism of hexachloroethane by Pd-doped zerovalent iron microparticles in dissolved lactic acid polymers using chromatography and indirect monitoring of iron corrosion

• Published in: Environmental science and pollution research international Vol. 26; no. 7; pp. 7177 - 7194
• Main Authors: Rodrigues, Romain, Betelu, Stéphanie, Colombano, Stéfan, Masselot, Guillaume, Tzedakis, Theodore, Ignatiadis, Ioannis
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.03.2019; Springer Nature B.V; Springer Verlag
• Subjects: Applied geology; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Chromatography; Conductivity; Corrosion; Corrosion mechanisms; Dechlorination; Dispersed gas phase hold up; Dosage; Earth and Environmental Science; Earth Sciences; Ecotoxicology; Environment; Environmental Chemistry; Environmental Health; Environmental science; Evolution; Gas chromatography; Hexachloroethane; Hydrogen; Iron; Lactic acid; Linear equations; Mass transfer; Mass transport; Microparticles; Oligomers; Organic chemistry; Oxidation; Oxidation-reduction potential; pH effects; Pollution monitoring; Polymers; Redox potential; Reduction; Research Article; Sciences of the Universe; Stoichiometry; Tetrachloroethylene; Waste Water Technology; Water Management; Water Pollution Control; Pd/Fe microparticles; Iron corrosion; Physical and chemical monitoring; Dechlorination mechanism; Hexachloroethane; Lactic acid polymers
• ISSN: 0944-1344; 1614-7499
• DOI: 10.1007/s11356-019-04128-y

The degradation mechanism of the pollutant hexachloroethane (HCA) by a suspension of Pd-doped zerovalent iron microparticles (Pd-mZVI) in dissolved lactic acid polymers and oligomers (referred to as PLA) was investigated using gas chromatography and the indirect monitoring of iron corrosion by continuous measurements of pH, oxidation-reduction potential (ORP), and conductivity. The first experiments took place in the absence of HCA, to understand the evolution of the Pd-mZVI/PLA/H 2 O system. This showed that the evolution of pH, ORP, and conductivity is related to changes in solution chemistry due to iron corrosion and that the system is initially cathodically controlled by H + mass transport to Pd surfaces because of the presence of an extensive PLA layer. We then investigated the effects of Pd-mZVI particles, temperature, initial HCA concentration, and PLA content on the Pd-mZVI/PLA/HCA/H 2 O system, to obtain a better understanding of the degradation mechanism. In all cases, HCA dechlorination first requires the production of atomic hydrogen H * —involving the accumulation of tetrachloroethylene (PCE) as an intermediate—before its subsequent reduction to non-chlorinated C 2 and C 4 compounds. The ratio between Pd-mZVI dosage, initial HCA concentration, and PLA content affects the rate of H * generation as well as the rate-determining step of the process. A pseudo-first-order equation can be applied when Pd-mZVI dosage is much higher than the theoretical stoichiometry (600 mg for [HCA] 0  = 5–20 mg L −1 ). Our results indicate that the HCA degradation mechanism includes mass transfer, sorption, surface reaction with H * , and desorption of the product.