Sustainable Recovery of Silver and Copper Photovoltaic Metals from Waste-Conductive Silver Pastes Using Thiosulfate Extraction and Ultraviolet Photolysis

Abstract

Waste-conductive silver pastes are considered an important secondary resource. The recovery of metals from waste-conductive silver pastes have high economic value. The traditional cyanidation method has serious environmental pollution, while the thiosulfate method is green, environmentally friendly, and has become a viable alternative for metal extraction. The exposure of thiosulfate complexes to ultraviolet (UV) light has been found to generate metal sulfides, and this can be used to realize the recovery of valuable metals. In this study, the extraction of silver and copper from conductive silver pastes was systematically performed using sodium thiosulfate, and the effects of sodium thiosulfate concentration, solid-to-liquid ratio, and extraction and photolytic process temperatures were investigated. The photolytic products were characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. After 4 h of UV irradiation with a wavelength of 254 nm, 87% of silver and 49% of copper were recovered and transformed into silver and copper sulfide, respectively. This study demonstrates that thiosulfate can be applied in combination with UV photolysis technology to recover valuable metals in an environmentally friendly manner.