Enhanced Photocatalytic Degradation of Cyanide in Mining Wastewater Using a ZnO-BiOI Heterojunction Catalyst

The mining industry often relies on the natural degradation of tailings dams to break down cyanide in wastewater. However, this method has drawbacks, including high costs due to significant water demand and variable effectiveness dependent on environmental conditions, and it is a time-consuming process. To address this issue, this study focused on preparing, characterizing, and applying a ZnO-BiOI heterostructure for cyanide removal in water. The heterojunction was thoroughly characterized using techniques such as SEM-EDX, X-ray diffraction, nitrogen adsorption–desorption isotherms, photoluminescence, and XPS scans. The photocatalytic efficacy was evaluated by degrading CN−-containing solutions across varying photocatalyst masses, temperatures, and initial cyanide concentrations. The results showed that 5 mg of the heterostructure completely eliminated 40 ppm of cyanide in 35 min. Increasing the catalyst mass to 15 mg significantly reduced the time for the complete degradation of 40 ppm cyanide, while 25 mg of the photocatalyst achieved cyanide removal in 35 min. The optimal temperature was found to be 50 °C, with complete cyanide removal occurring in 20 min within the temperature range of 25 °C to 70 °C. Moreover, when the cyanide concentration ranged from 40 ppm to 100 ppm, 15 mg of heterojunction catalyst achieved a 97% destruction efficiency in removing a 100 ppm cyanide solution within 35 min. These results strongly indicate that the synthesized heterojunction has the potential to serve as an effective and efficient photocatalyst for cyanide degradation in process effluents and wastewater.