Innovative bio-acid leaching method for high recovery of critical metals from end-of-life light emitting diodes

The main objective of this work is to introduce a new green recycling process for recovering valuable metals from electronic waste. One of the fastest-growing electronic waste streams is end-of-life light emitting diodes (LEDs). Due to environmental risk and a worldwide shortage of metals, recycling and recovering their valuable metal is an urgent task. In this study, an innovative bio-hydrometallurgical method for the extraction of valuable metals from end-of-life LED lamps is proposed. The present study evaluated a direct multi-step regulation strategy of waste content to enhance the bio-acid leaching of LED at a high pulp density (40 g/L) using a culture of sulfur-oxidizing bacteria Acidithiobacillus thiooxidans (A. thiooxidans). Through a step-wise feeding strategy (10 g/d), the extraction of the metal was further improved due to balancing of A. thiooxidans population and stabilization of pH, ORP, and sulfuric acid concentration in the bioleaching solution. By comparing the results of multi-step and one-stage contact bioleaching, with multi-step contact bioleaching, Cu, Ni, and Ga extraction yields increased from 67%, 92%, and 39% to 100%, 100%, and 75%. Furthermore, this study demonstrates that the presence/addition of EPS did not only adsorb metal ions but also increased diffusion barriers, thus diminishing metal ion transfer from LED into bioleaching solution for an extended period of time. The multi-step non-contact bio-acid leaching method enhanced strategic critical element leaching yields to 100% from end-of-life LEDs. The final product, enriched in Au and Ag, could be used as a secondary source of precious metals.