Bioweathering Using Shewanella oneidensis MR-1 Enhances Recovery of Rare Earth Elements from Alaskan Coal Mines

Alaskan coal mines with high rare earth element (REE) levels (286–524 mg/kg) serve as an alternative domestic REE source. Existing leaching/separation technologies require hazardous chemicals to recover REEs from the feedstock with multiple downstream purification stages, increasing the overall operational cost. This study aims at bioweathering coal from two Alaskan coal mines (Wishbone Hill and Healy) at three specific gravity fractions (1.3 float and 1.3 and 1.5 sink) using Shewanella oneidensis MR-1 for achieving REE recovery. Optimizing the bioweathering process by varying the solids percentages (5.7 to 14.3% w/v), particle size (74 to 1180 μm), incubation temperatures (30 to 34 °C), and inoculum dosing (0.2 to 1% v/v) resulted in the highest recovery of neodymium (75.3%) and total REEs (98.4%) from 1.3 float Wishbone Hill and 1.3 sink Healy coal, respectively. Chemical leaching had higher recovery of REEs in most fractions; however, bioweathering had enhanced recovery of the individual REEs, especially scandium, yttrium, ytterbium, terbium, erbium, and lutetium from Healy coal at low specific gravity samples and yttrium from Wishbone Hill coal at high specific gravity samples. The results highlight the potential for developing cost-effective and selective REE biorecovery processes that can help address the global critical mineral supply chain risk.