Fast Decolorization of Azo-Dye Congo Red with Zerovalent Iron Nanoparticles and Sequential Mineralization with a Fenton Reaction

Azo-dye compounds are widely used in the textile industry and are mostly discharged in industrial wastewater. In this study, we performed a chemical reduction of azo-dye Congo red (CR) using laboratory-synthesized nanoscale zerovalent iron (NZVI) particles to examine the effects of temperature and pH on decolorization kinetics and decomposition products. Decolorization of CR with NZVI undergoes a much faster reaction than that with microscale ZVI (MZVI). Decolorization behaviors of CR with NZVI follow pseudo-first-order kinetics. An increase in the dose of NZVI enhanced the decolorization rate of CR. Reaction rate constants did not decrease significantly with an increase in pH for CR. It was also found that the reaction rate increased slightly with an increase in temperature. Activated energy needed for the removal of CR with NZVI is smaller than that using MZVI (4.8 and 13.9 kJ/mol, respectively), suggesting an insignificant effect of temperature on the decolorization reaction. Intermediate analysis suggests the presence of broken azo bonds in CR with the NZVI surface. However, the mineralization of CR with NZVI is very low. Sequential NZVI/H sub(2)O sub(2) processes can effectively decompose CR due to the Fenton reaction. Combination of the reduction power of NZVI and its oxidized ions with H sub(2)O sub(2) can be considered an alternative for treating azo-dye wastewater.