Rapid photocatalytic gold recovery from industrial cyanide-based gold plating wastewater via TiO<inf>2</inf>/WO<inf>3</inf> nanocomposites: Role of mixed hole scavengers and operating conditions

Abstract

A rapid photocatalytic gold recovery from the industrial cyanide-based gold plating wastewater was carried out via TiO2/WO3 nanocomposites synthesized by hydrothermal method. Effects of different weight ratios of TiO2 and WO3 in nanocomposites, types of hole scavenger (Na2S2O3, C2H5OH, Na2S2O3/C2H5OH), concentrations of Na2S2O3 (0–100 mM) and photocatalyst loading (1–4 g/L) were examined. The preliminary results demonstrated that the employed wet chemical process induced a well formation of TiO2/WO3 nanocomposites with better textural properties as well as a more negative band position than the pristine WO3. The presence of mixed hole scavengers of Na2S2O3 and C2H5OH played a crucial role on the photocatalytic gold recovery from the cyanide-based gold plating wastewater. A more stable form of gold cyanide ([Au(CN)2]-) was altered to a less stable form ([Au(S2O3)2]3-) by the addition of Na2S2O3. At the end, approximately 85.9 % and 98.2 % of gold were respectively recovered within 180 and 300 min via the T6/WO3 nanocomposite in the presence of 10 mM Na2S2O3 and 20 vol% C2H5OH at photocatalyst loading of 2 g/L and light intensity of 3.20 mW/cm2. The photocatalytic gold recovery was significantly improved via the 1st reused T6/WO3 nanocomposite, in which 99.9 % of gold was recovered within 180 min. The obtained results can pave the way for the design of novel TiO2/WO3 nanocomposites for gold recovery as well as the strategy of waste management for the practical operation.