Photocatalytic Gold Recovery from Industrial Gold Plating Effluent by ZnO Nanoparticles: Optimum Condition and...

The comparative study of photocatalytic gold recovery from cyanide-based gold plating solution was explored via commercial and hydrothermally synthesized ZnO nanoparticles (NPs). The effects of hydrothermal temperatures on the properties and photocatalytic activities of synthesized ZnO NPs were investigated. In addition, the effects of operating parameters including types of hole scavenger, concentrations of the best hole scavenger, the initial pH of wastewater, and photocatalyst dosages were examined. The obtained results demonstrated that the commercial ZnO NPs exhibited a higher photocatalytic activity for gold recovery than that of the synthesized ones owing to their good crystal quality and the presence of non-lattice zinc ions and appropriate non-lattice oxygen ions. Via the commercial ZnO NPs, the gold ions were almost completely recovered from the cyanide-based gold plating effluent within 7 h at an initial pH of 11.0 in the presence of 10 vol % C₂H₅OH and 1.0 g/L of photocatalyst loading with a pseudo-first-order rate constant of 0.2637 h^-1. Finally, the resultant gold-decorated ZnO NPs exhibited a higher photocatalytic property for color reduction from industrial wastewater and antibacterial activity than that of fresh ZnO NPs. The results obtained in this study possess benefits and pave the way for waste remediation and management for the plating industries.