Abstract
Rare earth elements (including fifteen lanthanides, yttrium, and scandium) are critical materials due to their unique properties. They are necessary components of various advanced technologies, such as batteries, catalysts, and magnets, and play a crucial role in energy security, economic growth, and environmental sustainability. The growing demand for advancing technologies made from rare earth elements is predicted to reach $2.5 trillion worldwide by 2030. Although the need for rare earth minerals is only expected to rise, the United States is heavily reliant on rare earth imports, mainly from China. Traditional extraction of rare earth elements involves the use of harsh chemicals and leaves behind hazardous waste. Biological methods of extraction, such as bioleaching, are a promising alternative to mitigate these wastes. Organic acid bioleaching is often performed under milder conditions than traditional extraction. In addition, organic acids can be produced from renewable sources, such as agricultural waste or by-products. Previous bioleaching studies, using the bacterium Gluconobacter oxydans to produce gluconic acid have shown promising performance. We investigated the sustainability of a gluconic acid bioleaching and molten salt electrolysis production process of mixed rare earth metals from surface soil sourced in Idaho. Life cycle analysis revealed that most process emissions are due to high energy usage during bioleaching. We found that utilizing a novel ultrasound leaching technique can improve the REE leaching rate and can significantly decrease process emissions and energy. Our work demonstrates that higher solids loading in the bioleaching reaction can promote economic feasibility and reduce chemical wastes.