Azo-Dye Eriochrome Black T Degradation by Heterogeneous Fenton-Like Reaction Using Olive Stones Activated Carbon-Fe Catalyst

Chemically activated carbon K-AC was fabricated from a by-product of olive oil production (olive stones) after chemical treatment with KOH. The as-synthesized activated carbon was then used for; (1) adsorption of an azo dye, Eriochrome black T (EBT) and (2) to prepare a heterogeneous Fenton catalyst Fe-AC, for degradation of same dye using the Fenton-like process. Evaluation of the effect of pH (2-10), temperature (20-50 °C) and contact time required for adsorption was studied while effects of hydrogen peroxide concentration, EBT concentration and time on rate of degradation of EBT was also determined. Optimum conditions for both processes are reported while kinetics of EBT adsorption and degradation was also investigated. Results from the undertaken study showed that temperature and pH had a predominant impact on the adsorption of EBT by K-AC. Also, the Langmuir isotherm equation provided a better fit to experimental data than Freundlich equation implying monolayer adsorption on surface of K-AC. Maximum adsorption capacity of K-AC at 20 °C as determined using the Langmuir isotherm was 101.01 mg/g. RL (0.54-0.92) and n (1.04) values confirmed that the adsorption process is favorable while positive enthalpy (ΔH°; 32.7 KJmol-1) and negative free energy (ΔG°; -1.07 KJmol-1) referred to an endothermic and a spontaneous adsorption process. EBT degradation increased as time and peroxide concentration increased. However, it decreased as EBT concentration increased. Overall, degradation experiments were conducted at optimum conditions (6mM H2O2 and pH 4) to evaluate catalyst degradation efficiency. It was further observed that adsorption kinetics of EBT followed pseudo second order kinetic model based on R2 values. Further analysis on the regeneration of spent Fe-AC using water indicates that catalyst degradation efficiency can be maintained even after three cycles which makes it economical to use in EBT degradation. According to results obtained in this study, both K-AC and Fe-AC can act as adsorbent and catalyst for the efficient removal of EBT dye. Keywords: Olive stones, Fenton process, Adsorption, Eriochrome black T