Hydrothermal enhanced etching of Ni for direct recovery of gold flakes from electronic waste†

The content of precious Au in electronic waste (e-waste) is often tens to hundreds of times higher than that in natural ore deposits. Current technologies for recovering Au from e-waste mainly involve a two-step process of leaching and reduction, which are accompanied by high energy consumption, greenhouse gas emissions and toxic agents. In this article, we present an efficient, environmentally friendly and scalable hydrothermal catalysis technique for the one-step recovery of Au solid flakes from e-waste. The recovery process avoids the use of strong acids, alkalis, or toxic agents and operates under mild conditions (80–130 °C). During the hydrothermal reaction, Ni beneath the Au layer is selectively etched by hydroxyl radicals (˙OH), allowing the Au layer to be directly peeled off and recovered. Au solid flakes with a high recovery rate (up to 99.2%) and high purity (96.6%, without a further purification process) are obtained, eliminating the need for any additional reduction process. This research emphasizes the crucial role of both hydrothermal conditions and catalysts (e.g. TiO₂) in promoting the generation of ˙OH. The results of an techno-economic analysis and life cycle assessment indicate that this hydrothermal catalysis technique is a low-cost and environmentally friendly method for large-scale Au recovery from e-waste.