Mechanism and kinetics of halogenated compound removal by metallic iron: Transport in solution, diffusion and reduction within corrosion films.
A detailed kinetic model comprised of mass transport (ktra), pore diffusion (kdif), adsorption and reduction reaction (krea), was developed to quantitatively evaluate the effect of corrosion films on the removal rate (kobs) 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 kobsvalues 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 ktravalues at 13.32, 12.12, 11.04 and 10.20 h-1, kdifvalues at 0.42-5.82, 0.36-5.04, 0.30-4.50, 0.30-3.90 h-1, and kreavalues at 14.94-421.18, 0-0.19, 0.01-1.30, 0.10-3.98 h-1, respectively. The variation of kobsvalue with reaction conditions depended on the reactant species, while those of ktra, kdifand kreavalues were irrelevant to the species. The effects of corrosion films on kdifand kreavalues were responsible for the variation of kobsvalue for halogenated compounds. For a mass-transfer-limited halogenated compound such as BrO3-, an often-neglected kdifvalue primarily determined its kobsvalue when pore diffusion was the rate-limiting step of its removal. In addition, the value of kdifmight influence product composition during a consecutive dechlorination, such as for TCAA and DCAA. For a reaction-controlled compound such as MCAA, an increased kreavalue was achieved under low oxic conditions, which was favorable to improve its kobsvalue. The proposed model has a potential in predicting the removal rate of halogenated compounds by metallic iron under various conditions.
State Key Joint Laboratory of Environmental Simulation and Pollution Control, Beijing Key Laboratory for Emerging Organic Contaminants Control, School of Environment, Tsinghua University, Beijing, 100084, PR China; Energy and Environment International Centre, School of Energy and Power Engineering, Beihang University, Beijing, 100191, PR China.
Shun
S
Tang
State Key Joint Laboratory of Environmental Simulation and Pollution Control, Beijing Key Laboratory for Emerging Organic Contaminants Control, School of Environment, Tsinghua University, Beijing, 100084, PR China.
Xiao-Mao
XM
Wang
State Key Joint Laboratory of Environmental Simulation and Pollution Control, Beijing Key Laboratory for Emerging Organic Contaminants Control, School of Environment, Tsinghua University, Beijing, 100084, PR China.
Shi-Ting
ST
Liu
State Key Joint Laboratory of Environmental Simulation and Pollution Control, Beijing Key Laboratory for Emerging Organic Contaminants Control, School of Environment, Tsinghua University, Beijing, 100084, PR China. Electronic address: yanghw@tsinghua.edu.cn.
Hong-Wei
HW
Yang
State Key Joint Laboratory of Environmental Simulation and Pollution Control, Beijing Key Laboratory for Emerging Organic Contaminants Control, School of Environment, Tsinghua University, Beijing, 100084, PR China; Environmental Programs, The Pennsylvania State University, 777 West Harrisburg Pike, Middletown, PA17057, USA.
Yuefeng F
YF
Xie
Energy and Environment International Centre, School of Energy and Power Engineering, Beihang University, Beijing, 100191, PR China.
Xiao-Yi
XY
Yang
D001959:Bromates / Q000737:chemistry / Q000302:isolation & purification*; D062845:Chloroacetates / Q000737:chemistry / Q000302:isolation & purification*; D003343:Corrosion; D004058:Diffusion; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
D001959:Bromates; D062845:Chloroacetates; D014874:Water Pollutants, Chemical; D007501:Iron
Corrosion films; Kinetic model; Mass diffusion; Removal mechanism; Zero-valent iron (Fe(0))