Mechanism and kinetics of halogenated compound removal by metallic iron: Transport in solution, diffusion and reduction within corrosion films. (July 2017)

• Record Type: Journal Article
• Authors: Tang, Shun; Wang, Xiao-mao; Liu, Shi-ting; Yang, Hong-wei; Xie, Yuefeng F.; Yang, Xiao-yi
• Is Part Of: Chemosphere. Volume 178(2017)
• Page Start: 119
• Page End: 128
• Publication Date: 2017-07
• Subjects: Zero-valent iron (Fe0) -- Corrosion films -- Removal mechanism -- Kinetic model -- Mass diffusion; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2017.03.006
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: A detailed kinetic model comprised of mass transport ( k tra ), pore diffusion ( k dif ), adsorption and reduction reaction ( k rea ), was developed to quantitatively evaluate the effect of corrosion films on the removal rate ( k obs ) of halogenated compounds by metallic iron. Different corrosion conditions were controlled by adjusting the iron aging time (0 or 1 yr) and dissolved oxygen concentration (0–7.09 mg/L DO). The k obs values for bromate, mono-, di- and tri-chloroacetic acids (BrO3 −, MCAA, DCAA and TCAA) were 0.41–7.06, 0–0.16, 0.01–0.53, 0.10–0.73 h −1, with k tra values at 13.32, 12.12, 11.04 and 10.20 h −1, k dif values at 0.42–5.82, 0.36–5.04, 0.30–4.50, 0.30–3.90 h −1, and k rea values at 14.94–421.18, 0–0.19, 0.01–1.30, 0.10–3.98 h −1, respectively. The variation of k obs value with reaction conditions depended on the reactant species, while those of k tra, k dif and k rea values were irrelevant to the species. The effects of corrosion films on k dif and k rea values were responsible for the variation of k obs value for halogenated compounds. For a mass-transfer-limited halogenated compound such as BrO3 −, an often-neglected k dif value primarily determined its k obs value when pore diffusion was the rate-limiting step of its removal. In addition, the value of k dif might influence product composition during a consecutive dechlorination, such as for TCAA and DCAA. For a reaction-controlled compound such as MCAA, an increased k rea value was achieved under low oxic conditions, which was favorable to improve its k obs value. The proposed model has a potential in predicting the removal rate of halogenated compounds by metallic iron under various conditions. Graphical abstract: Highlights: A kinetic model including k obs, k tra, k dif and k rea was proposed to elucidate the role of corrosion films. The trends of k obs, k tra, k dif and k rea values varied with the reactant species, operation time and O2 content were explored. The effects of corrosion films on k dif and k rea values were responsible for the variation of k obs value. Various product compositions were probably attributed to mass diffusion.