Facile synthesis of Cr-doped ferrite catalyst from Cr-containing electroplating sludge with activated persulfate for efficient degradation of tetracycline

Electroplating sludge (ES) is a typical industrial hazardous waste, which contains multitudes of valuable transition metal resources. Hence, there is an urgent need for a method which can not only effectively detoxify, but also reasonably reuse ES resources. In this work, we synthesized Cr-doped ferrite catalyst (HT-ES) derived from Cr-containing ES via hydrothermal treatment, and applied it for the degradation of tetracycline (TCH). After hydrothermal treatment, the HT-ES with double metal oxide structure and large specific surface area (168.3 m2 g−1) was obtained. The removal percentage of TCH could reach 90.79%, under the optimum conditions derived by response surface methodology. Experimental results demonstrated that HT-ES also exhibited high resistance to water impurities (i.e., Cl-, HCO3-, NO3 and humic acid) and perfect reusability. The electron spin resonance and radical quenching experiments revealed that SO•-4, •OH and O•-2 radicals appeared in the TCH degradation reaction system. Finally, a probable degradation mechanism of TCH was proposed based on the experimental results. This work not only achieved the stabilization of Cr-containing ES, but also obtained an excellent catalyst for the removal of TCH, realizing the goal of treating waste with waste.