Biorecovery of rare earth elements and critical minerals via Gluconobacter oxydans

Abstract

The depletion of high-grade ore deposits, accumulation of electronic waste, and the geopolitical challenges in sourcing critical materials have emphasized the need for sustainable metal recovery methods and recycling efforts in the United States. Conventional metal recovery approaches, including pyrometallurgy and hydrometallurgy, are not only environmentally unsustainable but also inadequate for the retrieval of metals from low-grade deposits. Biorecovery, defined by microorganism-mediated metal recovery, provides an advantageous alternative to traditional recovery methods due to increased sustainability, lower operational costs, and high efficiencies observed for the recovery of low-grade feedstocks. This study investigates the potential of bioleaching as an eco-friendly alternative in the recycling of two distinct waste feedstocks: magnetic swarf and lithium-ion batteries (LIBs). Cultivation of Gluconobacter oxydans was investigated under varying growth medium compositions, wherein increased concentrations of yeast extract were substituted for KH 2PO 4, to determine the subsequent impact on the base metal and rare earth element recovery through the application of the cell-free biolixiviant. This substitution resulted in increased growth yields and enhanced recovery with respect to magnetic swarf, whereas negligible improvement was observed for LIBs. Biorecovery has also been demonstrated for the recovery of metals from ore, where yields are a function of comminution and concentration efficiencies. Typical compressive comminution practices account for the largest proportion of energy expenditures in a mining process. Transcritical CO 2 (tCO 2) comminution, wherein ore is fractured through overcoming a rock's tensile strength, was examined to determine whether physical differences in particle generation were present as compared to traditional fracture techniques. An ore deposit in British Columbia, rich in a nickel-iron alloy mineral phase called awaruite, was examined through scanning electron microscopy, backscatter electron imaging, and energy dispersive spectroscopy to determine the impact of comminution method on awaruite recovery. Image processing was used to investigate shape factors for the individual particles. Preliminary evidence indicates despite a lack of distinct particle differences, tCO 2 comminution resulted in increased liberation and recovery of awaruite ore. Abiotic leaching studies were conducted to determine whether the method of comminution impacted leaching efficiencies. Although samples could not be quantitatively measured, initial qualitative results indicate tCO 2 comminution provides increased yields.