Oxidative degradation of malachite green by Fenton generated hydroxyl radicals in aqueous acidic media.

Fenton-generated hydroxyl radicals removes the color of the malachite green, a basic dye with triphenylmethane group, almost (approximately 98%) completely in weakly acidic aqueous media possibly through oxidative degradation pathways as evidenced from a remarkable lowering in the COD value of the product mixture in comparison to the title dye under identical conditions and almost full quenching of the reaction in presence of hydroxyl radical scavengers. The dye can most effectively be degraded at dye:Fe2+:H2O2 molar ratio of 1:3.3:81.7 for 1.08 x 10(-5) mol dm(-3) dye at pH 2.5-2.8 and at 299K. The rate law of the dye degradation process appears to be: -a[dye]/dt = k[dye] [Fe2+]0.79 [H2O2]0.12, where k = (33 +/- 5) (dm3 mol(-1))0.91 s(-1) at 299K. Salts like NaCl or NaBr retard the degradation rate markedly whereas SO4(2-) or ClO4- are rather innocent. In presence of Cl-, the radical reaction: ClOH*- + Fe2+ --> Cl- + HO- + Fe3+ may account for the gross lowering of degradation rate. The results may be helpful for designing the treatment plants of wastewater containing dyes with triphenylmethane group.