title: Biphasic reduction model for predicting the impacts of dye-bath constituents on the reduction of tris-azo dye Direct Green-1 by zero valent iron (Fe0).
abstract: Influence of common dye-bath additives, namely sodium chloride, ammonium sulphate, urea, acetic acid and citric acid, on the reductive decolouration of Direct Green 1 dye in the presence of Fe0was investigated. Organic acids improved dye reduction by augmenting Fe0corrosion, with acetic acid performing better than citric acid. NaCl enhanced the reduction rate by its 'salting out' effect on the bulk solution and by Cl-anion-mediated pitting corrosion of iron surface. (NH4)2SO4induced 'salting out' effect accompanied by enhanced iron corrosion by SO42-anion and buffering effect of NH4+improved the reduction rates. However, at 2g/L (NH4)2SO4concentration, complexating of SO42-with iron oxides decreased Fe0reactivity. Urea severely compromised the reduction reaction, onus to its chaotropic and 'salting in' effect in solution, and due to it masking the Fe0surface. Decolouration obeyed biphasic reduction kinetics (R2>0.993 in all the cases) exhibiting an initial rapid phase, when more than 95% dye reduction was observed, preceding a tedious phase. Maximum rapid phase reduction rate of 0.955/min was observed at pH2 in the co-presence of all dye-bath constituents. The developed biphasic model reckoned the influence of each dye-bath additive on decolouration and simulated well with the experimental data obtained at pH2.
authors.affiliation: Department of Environmental Science & Engineering, Indian School of Mines, Dhanbad 826004, Jharkhand, India. Electronic address: raja.kumar1010@gmail.com.
authors.forename: Raja
authors.initials: R
authors.lastname: Kumar
authors.affiliation: Department of Environmental Science & Engineering, Indian School of Mines, Dhanbad 826004, Jharkhand, India. Electronic address: aloksinha11@yahoo.com.
authors.forename: Alok
authors.initials: A
authors.lastname: Sinha
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D004396:Coloring Agents / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008956:Models, Chemical; D010084:Oxidation-Reduction; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D001391:Azo Compounds; D004396:Coloring Agents; D014874:Water Pollutants, Chemical; D007501:Iron
keywords: Biphasic kinetics/model; Direct Green 1; Dye-bath additives; Fe(0)