Abstract:

C.I. Reactive Black 5 (RB5) is the most commonly used dye in the textile industry. Ozone is a strong oxidan that can decompose many barely degradable pollutants, including dyes. Although there are many literature reports devoted to the treatment of textile wastewater and dye solutions by ozone, the ozonation mechanism and modeling of the kinetics is still not well covered. In this work a kinetic model of the process of RB5 decolourisation by ozone has been proposed and validated on the basis of experimental data. The experiments were carried out in a liquid-liquid system to avoid mass transfer limitation. A model was established for acid reaction medium. The main RB5 reaction was direct oxidation of the dye with molecular ozone. The self-decomposition of ozone in liquid phase was taken into account and described by an empirical equation. The reaction rate constants of RB5 with ozone were estimated from the experimental data in the range of (1.88 ± 0.08) × 10⁴ – (2.53 ± 0.10) × 10⁵ M^-1s^-1 (invariant with initial dye concentration). An empirical equation k2′ = 1.06 × 10⁸(C_OH−)0.31 was built for the constant to make it dependent on the pH value. A solution of the non-linear inverse problem allowed for identification of the kinetic constants on the basis of the experimental data obtained. The model gave a good match between the prediction and experimental data for pH between 1.88 and 4.0.