A novel step-wise indirect bioleaching using biogenic ferric agent for enhancement recovery of valuable metals from waste light emitting diode (WLED)

Highlights: • The novel step-wise indirect bioleaching using biogenic ferric was investigated for toxic LED waste recycling. • The leaching time was significantly decreased by step-wise indirect bioleaching using biogenic ferric. • Step-wise indirect bioleaching significantly improved gallium, copper and nickel leach yields. • Step-wise indirect bioleaching significantly reduced waste LED toxicity. -- Abstract: Waste light-emitting diodes (WLED) are of major interest as they are a considered secondary source of valuable metals with a high potential for polluting the environment. To recover the valuable metals from WLEDs, various methods have been applied such as direct and indirect bioleaching. A novel step-wise indirect bioleaching process has been developed in this study for recycling valuable metals from WLEDs using adapted Acidithiobacillus ferrooxidans. The ferric ion concentration was controlled at 4–5 g/L with step-wise addition of biogenic ferric for faster bioleaching rate. The results indicated the negative effect of bacterial attachment in bioleaching of WLEDs. A direct bioleaching offers low copper, nickel, and gallium leach yields, while all metals' recovery improved with step-wise indirect bioleaching. At a pulp density of 20 g/L, the copper, nickel, and gallium recovery efficiency was 83%, 97%, 84%, respectively. In addition, leaching time was reduced to 15 days from 30 days. From a technological perspective, the study proved that step-wise indirect bioleaching by biogenic ferric resulted in maximum valuable metal recovery from WLEDs at a low cost and via a short, simple and environmentally-friendly process.