The potential of a natural iron ore residue application in the efficient removal of tetracycline hydrochloride from an aqueous solution: insight into the degradation mechanism.

In the existing research, most of the heterogeneous catalysts applied in the activation of persulfate to degrade organic pollutants were synthesized from chemical reagents in the laboratory. In this paper, we have obtained a spent iron ore (IO) residue directly collecting from the iron ore plants, and efficiently activating peroxydisulfate (PS) to produce reactive free radicals. The experimental results demonstrated that the IO could effectively activate PS to degrade tetracycline hydrochloride (TCH), with TCH removal rate reaching up to 85.6% within 2 h at room temperature. The TCH removal rate was increased with increasing iron ore dosage, while the more acidic pH condition would be favorable to TCH removal process. The material characterization results demonstrated that the dominant components of IO were Fe3O4 and FeOOH. The transformation from Fe(II) to Fe(III) at the surface IO was observed after TCH degradation. What's more, the quenching experiment and EPR detection results confirmed that the sulfate radical (SO4•-) and hydroxyl radicals (•OH) would be acting as the main free radicals for TCH degradation. This study could not only explore a novel way to recycle the discarded iron ore, but also further expand its application in an effective activation of PS in an aqueous solution.