Application of Steel Waste as a Heterogenous Catalyst in Advanced Oxidation Processes—Preliminary Study

The suitability of steel shavings (SS) as a low-cost waste catalyst in catalytic ozonation and the heterogeneous Fenton process was evaluated. Three dyes were selected for the research: Indigo Carmine, Tartrazine, and Allura Red AC. Single processes (oxidation by H2O2, O3, and heterogeneous Fenton process) and hybrid processes (O3 + Fenton) were applied. The Fenton process had the highest efficiency at pH = 3 and with the highest dose of catalyst (5 mg of SS) and hydrogen peroxide (30 µL). More than 98% discoloration of the solution was observed in 10 min. Analyzing ozone-based processes, they can be ranked with the highest efficiency as follows: (O3 + H2O2 + SS) > (O3 + H2O2) > O3 > (O3 + SS). The combination of the Fenton process (5 mg of SS + 15 µL of H2O2) with ozonation accelerated the reaction rate in the case of Indigo Carmine. In the hybrid process, only 5 min were enough for complete decolorization, while more than 98% in the Fenton process was reached after 30 min. Kinetic studies revealed that the degradation of dyes in an aqueous solution through advanced oxidation processes followed first- and second-order reaction kinetics. The calculation of the energy requirement confirmed that the most economic process for removing Indigo Carmine was the O3+Fenton process (SS dose = 5 mg, H2O2 dose = 15 µL, pH = 3).