Azo dye decolorization by ZVI under circum-neutral pH conditions and the characterization of ZVI corrosion products

This study examined the effects of initial solution pH (Oh), ZVI dosage, initial Trypan Blue (TB) concentration ([TB](o)), and background electrolytes (NaCl and NaNO3) on the rate and extent of dye decolorization. TB azo dye ([TB](0)=90 mu M) was almost completely removed in 1320 min at pH(i) 4, while only 54% at pH(i) 10. The effects of Cl- and NO3- as a common major anion (10 mM) were contrasting on the efficiency of ZVI decolorization. The former accelerated the decolorization presumably due to impeding surface passivation of secondary Fe (oxyhydr)oxides by forming dissolved Fe-Cl complexes. On the contrary, the latter promoted the formation of secondary oxide layers resulting in the declining the ZVI reactivity. The XRD spectra of reacted ZVI particles suggested that lepidocrocite was initially formed as the ZVI corrosion products, which gradually transformed to magnetite. FT-IR spectroscopy revealed the decolorization processes as the destruction of N=N bond in TB dye structure, followed by the formation of free aromatic amine groups (-NH2) after 1320 min of reaction with ZVI. The experimental results demonstrated that the novel ZVI treatment system could be a potential and promising alternative technique to remove TB dye by reductive decolorization treatment processes. (C) 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.