Process development and techno-economic feasibility of thiosulfate-based hydrometallurgical recycling for waste printed circuit boards

In this study, we developed a comprehensive process for metal recovery from waste printed circuit boards (WPCBs) using an environmentally friendly thiosulfate leaching method, followed by a detailed techno-economic analysis. The metal recovery process consisted of two leaching stages: the first stage used sulfuric acid in the presence of hydrogen peroxide for copper (Cu) recovery and the second stage used thiosulfate for gold (Au) leaching. After leaching, Cu was recovered via crystallization, and Au was recovered via reduction using sodium dithionite. To optimize Au recovery, the residual Cu ions in the WPCBs following the first leaching stage were carefully managed to stabilize the Au-thiosulfate complex and minimize water usage. The preliminary techno-economic analysis estimated the net present value (NPV) of the proposed recycling process at a small scale (1200 tons per year) to be 5.94 million USD, with an 18.04 % rate of return on investment over a 20-year project lifespan; the estimated payback period was approximately 3.9 years. Sensitivity analysis revealed that the NPV is highly sensitive to the WPCB market price and Au recovery efficiency. Overall, the results demonstrate that employing an environmentally friendly thiosulfate leaching process is profitable under optimized conditions, offering valuable insights into green technologies for e-waste processing.