Thiosulfate-based leaching for eco-friendly urban mining: Recent developments and challenges

Thiosulfate-based leaching systems have been extensively investigated over several decades as potential alternatives to cyanidation for the extraction of precious metals from ores and concentrates. Currently, several literature reviews dedicated to thiosulfate-based leaching in conventional mining emphasize the importance of an extensive understanding of the mineralogical composition of ores and concentrates in metal extraction. Urban mining using thiosulfate-based leaching has also been explored as an environmentally friendly method for extracting precious metals, primarily from electronic waste (e-waste). However, e-waste contains various functional materials that do not resemble ores or concentrates. Furthermore, the relationship between the structure of e-waste and thiosulfate-based leaching systems and factors affecting metal recovery have not yet been established. Therefore, this paper presents a comprehensive review of thiosulfate-based leaching systems in urban mining, with a special emphasis on the factors that affect the leaching efficiency of e-waste. Some common factors, such as thiosulfate, ammonia and Cu ion concentration, dissolve oxygen are summarized and compared with ores and concentrates, where applicable. Additionally, important aspects unique to urban mining, such as the structural characteristics, types, metal composition, and pretreatment methods of e-waste, are thoroughly reviewed and highlighted. The early stage development of biogenic produced thiosulfate leaching in urban mining is also introduced.