Comparative Study on the Decolorization of Orange II by Zero-valence Tin in Citric and Hydrochloric Acids

Zero-valence tin reductively degraded a persistent azo dye, Orange II to produce colorless aromatic amines. The effects of acid concentrations and initial Orange II concentrations on the decolorization of Orange II by tin in citric and hydrochloric acids were investigated. The decolorization reaction in citric acid was faster than that in hydrochloric acid at 2.5 and 5 mM acid concentrations. The faster reaction would be related to the characteristic dissolution reaction of tin in citric acid. The first-order kinetic was applicable in citric acid over the examined range of 0.1 - 0.4 mM initial Orange II. However, at more than 0.2 mM initial Orange II the first-order kinetic was not applicable in hydrochloric acid and thus the relaxation first-order reaction kinetic was applied. The result that zero-valence-tin/citric acid system demonstrated successful decolorization in repeated use supports the possibility of its application for azo dye wastewater.