Sustainable bio-extraction of rare earth elements from discarded LED lamps

Rare earth elements (REEs), known for their brightness, ferromagnetism, and superconductivity, are essential in technologies like lamps, batteries, wind turbines, and hybrid vehicles. This research developed a method for extracting rare earth elements (REEs), including praseodymium (Pr) and neodymium (Nd) from discarded LED (DLED) lamps using Acidithiobacillus thiooxidans. Optimization of biological sulfuric acid production was investigated by varying inoculum volumes in a 9 K culture medium with elemental sulfur. Three inoculum percentages (2%, 5%, and 10% v/v) were tested, with 5% yielding the highest production (10,500 mg/L, H⁺ 160 mM). Inhibition at lower and higher inoculum volumes was attributed to nutrient excess and deficiency, respectively. The effects of time and pulp density on Nd and Pr recovery via bio-generated acid were explored. Increasing pulp density from 10 to 50 g/L reduced extraction efficiency due to insufficient mixing and hydrogen ion consumption by other elements. Conversely, time had little impact, likely due to passive layer formation hindering proton penetration, confirmed by XRD, FTIR, and SEM analyses. The optimal conditions for bioleaching were identified as a pulp density of 10 g/L and a leaching time of 3 days, resulting in recovery rates of 43% for Pr and 28% for Nd. These findings emphasize the importance of optimizing process parameters to achieve efficient recovery of rare earth elements (REE) using biological acid.