Kinetics of the oxidative decolorization of some organic dyes utilizing Fenton-like reaction in water

The decolorization kinetics of some organic pollutants in water such as commercial dyes, namely, Malachite green (MG), Rhodamine B (RB), Methylene blue (MB) and Crystal violet (CV) were studied using a Fenton-like reagent. The effects of different parameters like the initial dye concentration, Fe^3+, concentration of H2O2, pH of the solution, reaction temperature, and added electrolytes on the kinetics were determined. The results indicate that the optimum pH for the decolorization of all dyes examined is in the range between 3 and 4. The rate of decolorization showed remarkable dependence on the initial Fe^3+ concentration. Using dilute dye solutions in the range of (0.30–1.50×10^-5 mol dm^-3) the rate increased as the Fe^3+ concentration was increased from 1.5× 10^-4 to 6.0×10^-4 mol dm^-3, and becomes practically constant when it exceeds 6.0× 10^-4 mol dm^-3. Below 1.5× 10^-4 mol dm^-3 of Fe^3+, the decolorization reaction is too sluggish to account for any practical significance. But the decolorization rate of all examined dyes decreased at high Fe^3+ concentrations (≥1.0 × 10^-3 mol dm^-3). There is an optimum H2O2 concentration in the range of 0.01–0.04 mol dm^-3 that is effective for decolorization of the dyes. It was observed that the presence of halide salts at the same concentration level substantially decreased the rate and the extent of decolorization, whereas for nitrate salt, there is an increase in the extent of dye decolorization. An increase in the extent of decolorization of the dye was observed when the reaction temperature was raised. The results will be useful for designing the treatment systems of various dye-containing wastewaters. It was also found that the decolorization of the dyes undergoes a fast reaction than the mineralization.