Fe-containing sphalerite as a co-catalyst for degradation of Congo red dye

Abstract

Complex sulfide ores are associated with various sulfide minerals, characterized by their impurity content and physical defects. Sphalerite, a well known Zn-bearing mineral, consists of sulfides and inevitably contains various impurities. In this regard, minor metals in Zn concentrate complicate the flotation process or hydrometallurgical process. Nevertheless, the Fe-containing sphalerite is regarded as an efficient inorganic co-catalyst due to its surface properties with unsaturated S atoms and Fe atoms. Typically, the Fe(III) reduction determines the overall efficiency of the Fenton process, necessitating a stoichiometric excess of H2O2 and catalysts. To address the limitations of the Fenton process, this study proposes the use of Fe-containing sphalerite (ZnS) as co-catalysts to enhance the Fe(III)-H2O2 system. The redox reactions between ZnS and Fe(III) can efficiently decompose H2O2, which promotes the reaction between Fe(III) and Fe(II). Therefore, in this study, ZnS was evaluated as a co-catalyst to enhance the Fenton-like system for the degradation of Congo red (CR). The CR degradation was examined using different processes involving a single factor (ZnS, H2O2), dual factor (ZnS-H2O2, Fe(II)-H2O2, Fe(III)-H2O2), and triple factor (ZnS-Fe(III)-H2O2), to demonstrate co-catalyst effect. It was confirmed that both ZnS and Fe(III) were introduced into the system. Remarkably, 98.9% of ZnS-Fe(III)-H2O2 was degraded within 5 min, underscoring the effectiveness of ZnS as a co-catalyst in enhancing the activating of H2O2. When ZnS-Fe(III)-H2O2 system was used, CR degradation was affected by Fe(III) and H2O2 concentration, ZnS doses, and solution pH. During the reuse experiments, CR could be completely degraded, and Co-catalytic efficiency of ZnS was maintained for three reuse cycles.