Interfacial regulation of Al0's electron transfer for the recovery of gold from gold-cyanide complex wastewater

Gold-cyanide complex (Au(CN) 2 − ) prevalent in alkaline metallurgical/electroplating wastewater poses significant hazards, requiring environmentally friendly treatments. As a prominent amphoteric reductant, aluminum (Al 0 ) tends to react with water, regulating its electron transport process is crucial. Herein, a novel copper-modified aluminum composite (Cu@Al 0 ) was synthesized via one-step ball milling to tailor electron transport rate and direction, enabling rapid and efficient removal of Au(CN) 2 − (nearly 100% in 30 min) with simultaneous recovery of metallic gold. Specifically, over 92.13% of the gold was recovered as zero-valent gold (Au 0 ), whereas ∼100% total cyanide retained in the solution. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed that Au(I) was reduced to Au 0 and attached to Cu@Al 0 surface. The recovery of gold was primarily relied on the high electron utilization efficiency of Al 0 (94.51%), where electrons were preferentially allocated to the reduction of Au(CN) 2 − rather than to the side reaction of hydrogen production. It was observed that copper played a crucial role. During ball milling, interfacial interaction between Al 0 and CuSO 4 ·5H 2 O was induced, contributing to the in situ formation of zero-valent copper (Cu 0 ) through a solid-phase chemical reaction. During the decomplexation of Au(CN) 2 − , Cu 0 served as the affinity site for gold and an electron transport bridge, preventing the excessive corrosion of Al 0 under alkaline conditions, and controlling the transmission rate and direction of electrons and providing more electrons to Au(CN) 2 − . In conclusion, this study employs a novel approach to recover valuable resource from Au(CN) 2 − , offering a promising avenue for the treatment of metallurgical/electroplating wastewater.