Valorization of steel slag towards a Fenton-like catalyst for the degradation of paraben by activated persulfate

Different iron-containing materials (named as S1-S5) obtained through an oxidative digestion in acid media of basic oxygen furnace (BOF) slag were studied for the activation of sodium persulfate (SPS) to generate active radicals for the oxidation of propylparaben (PP), a model endocrine disruptor, in water. It was found that the materials with magnetite in its composition (S1, S2 and S3) effectively catalyze SPS for the removal of PP, and the reaction followed a pseudo-first-order kinetic pattern (r(2) > 0.96). Within 90 min, a removal of approximately 90% of 0.4 mg/L of PP was accomplished by 1 g/L of SPS in presence of 50 mg/L of S1 catalyst with negligible iron leaching. Besides, the oxidation of PP was favored by higher dosages of S1 catalyst and SPS oxidant, lower initial PP concentration and neutral or alkaline pH. The generation of sulfate and hydroxyl radical was indirectly validated from the scavenging tests, using tert-butanol and methanol as scavenging agents. Based on the XPS analysis, it can be pointed out that the radical generation was due to the presence of Fe2+-Fe3+ on the surface of the catalysts. A degradation pathway based on the transformation products (TPs) resulting from PP degradation was also proposed.