The role of EPS in the selective biosorption and desorption of REEs
Rare earth elements (REEs) are critical components of green technologies, but current mining and purification methods remain environmentally unsustainable due to their high energy consumption and intensive chemical requirements. Bio-hydrometallurgical processes have the potential to concentrate and recover REEs at a circumneutral pH. Work presented here uses bacteria at neutral pH to concentrate REEs from solution and subsequently recover those REEs using sodium citrate. Shewanella oneidensis MR-1 was incubated anaerobically in a culture media solution spiked with 14 REEs and yttrium for one to six days. REE concentrations remaining in solution were then compared to REE concentrations on cell pellets. For these same timepoints, the loosely bound extracellular polymeric substance (LB-EPS) was removed from cells prior to quantifying REEs on pellets to narrow down the location of REE binding. Moreover, cell pellets collected after 5 days in REE spiked solution were subjected to a time series desorption assay using sodium citrate. Shewanella oneidensis at a starting OD600 of 0.6 adsorbed 1.18mg/g of REE after 3 days. 80% of these REEs were located in the LB-EPS. In 10 minutes, 0.5 M sodium citrate desorbed about 75% of REEs from cells and over 95% after 24 hours. This method was also applied to Alaskan coal and showed that 68-86% of REEs were desorbed form S. oneidensis. This study elucidates the REE binding location and capacity of S. oneidensis, REE removal efficiency of sodium citrate overtime, and the application of this sustainable biotechnology for REE recovery at a circumneutral pH from Alaskan coal. ImportanceRare earth elements (REEs) are essential for technologies such as electric vehicles, wind turbines, batteries, and medical devices, but current methods for obtaining them are energy-intensive and can harm the environment with acidic waste. This study demonstrates a non-acidic sustainable approach using naturally occurring bacteria to capture REEs and then recover them with a biologically derived solution. The research also identifies where these elements attach to the bacteria, providing new insight into how the process works and how it can be improved. Importantly, the method successfully recovered REEs from Alaskan coal, highlighting its potential for real-world applications. By improving our understanding of microbial methods for rare earth element recovery, this work could help reduce the environmental impacts of mining and support more sustainable, secure supplies of the critical materials needed for clean energy and other advanced technologies.