Surface-mediated persulfate activation by steel swarf: Kinetics and stoichiometry

Steel swarf, an Fe-rich industrial byproduct, was investigated as an activator for persulfate (S 2 O 8 2– ) in the degradation of methyl orange, a representative dye pollutant. This study aimed evaluate the feasibility of using steel swarf as a persulfate activator and examined surface-mediated processes such as passive film depassivation, Fe 2+ release, and interfacial radical generation, which have not been systematically investigated before. Batch experiments demonstrated that the reaction followed pseudo-first-order kinetics after an initial lag phase associated with steel swarf depassivation. The lag duration decreased from 7 min to 2 min with increasing steel swarf and S 2 O 8 2– doses, and the apparent degradation rate increased linearly up to 0.18 min –1 as steel swarf and S 2 O 8 2– dose increased. Under limited agitation, mass transfer constraints markedly influenced persulfate activation kinetics at the steel swarf surface. Stoichiometric analysis confirmed a consistent relationship between pollutant degradation and persulfate consumption. These findings establish steel swarf as a cost-effective and mechanistically predictable S 2 O 8 2– activator suitable for advanced oxidation processes.