Photocatalytic application of defective WO<inf>3</inf> nanoparticles for precious metal recovery from plating effluent

Abstract

Background: Plating units of electronics industry generally release wastewater with various types of metal ions and sometimes precious metal ions such as gold. Discharging of gold-containing wastewater is an economic loss. Accordingly, the photocatalytic process has emerged as the effective process to recover gold ions. Methods: The defective WO3 NPs were synthesized by sequential process of acid precipitation and annealing method to recover gold from a cyanide-free plating bath solution. The impacts of annealing temperatures and operating conditions on the photocatalytic property and activity of WO3 NPs were explored. Significant findings: An annealing temperature in the range of 650 – 950 °C did not significantly affect the surface property of the WO3 samples, but remarkably impacted the optical property. A high temperature induced the generation of W5+ and oxygen vacancies in the WO3 structure, promoting the visible light response. Among all synthesized samples, the WO3 sample annealed at 850 °C (W85) exhibited the superior photocatalytic activity to recover gold up to 90.8 % at photocatalyst loading of 2 g/L, initial pH of effluent of 9.2, C2H5OH concentration of 10 vol.% in the presence of 6 mM Na2S2O3. In addition, the W85 sample possessed consistent stability to recover gold from the plating effluent even at the 5th cycle.