The effect of widely used dye-bath additives, namely sodium chloride, ammonium sulfate, urea, acetic acid and citric acid, on the reductive removal of azo dye AR73 by zero valent iron was investigated. Na+ induced ‘salting out’ effect on the dye molecules complemented with Cl- induced pitting corrosion of ZVI surface led to improved dye removal rate with increasing NaCl concentration. ‘Salting out’ effect of (NH4)2SO4 together with enhanced iron corrosion by aggressive SO4 2- and reducing effect of ‘sulfate green rust’ benefitted the reaction rates. However, beyond 1,000mg/L (NH4)2SO4 concentration, complex formation of NH4_x000D_ + and SO4 2- with iron oxides compromised ZVI reactivity. Urea inhibited the reaction by its chaotropic effect on the dye solution and also by wrapping the ZVI surface. Enhanced iron corrosion by organic acids improved the reaction rates. The dye removal followed biphasic kinetics with initial rapid phase, when more than 95% dye removal was observed in all the studies, followed by a slow phase. The experimental data could be well evaluated using biphasic rate equation (R2>0.995 in all the cases). Highest dye removal rate of 0.900 min-1 was achieved at pH 2 with all the additives amended. AR73 removal could be modelled using biphasic model considering the individual effect of each additive. Rapid dye reduction capability at varied solution composition makes ZVI more advantageous and promising for wastewater treatment.

Acid Red 73(AR73) Biphasic Kinetics Dye-bath Additives Modelling Zero Valent Iron (ZVI)

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