Chemical decolorization of the azo dye CI Reactive Orange 96 by various organic/inorganic compounds

Abstract

Batch experiments were performed to investigate the possibility and kinetics of chemical decolorization of the reactive mono-azo dye CI Reactive Orange 96 (RO 96) with various compounds such as cysteine, ascorbate, Ti(III)-citrate, Fe(II)-sulfate, and yeast extract. Cysteine and ascorbate (10 mmol dm−3 respectively) decolorized RO 96 (0.19 mmol dm−3) in the absence of oxygen. Increasing the concentration of either reductant (to 20 or 38 mmol dm−3) enhanced the decolorization rate, showing first-order kinetics with respect to both the concentration of the dye and of cysteine or ascorbate. The rate constants, k, for cysteine and ascorbate were 0.0003 and 0.0010 dm3mmol−1 h−1 respectively at pH 7.1 and 33 °C. Ti(III)-citrate (10 mmol dm−3) decolorized RO 96 (0.20 mmol dm−3) within 5 min, independent of the presence of oxygen. Fe(II)-sulfate was not effective in the decolorization of RO 96 at pH 8, whereas a rapid decolorization occurred at pH 12. This study suggests that a variety of abiotic processes may be involved in decolorization under anaerobic conditions. © 2002 Society of Chemical Industry