Rare earth elements have properties that make them useful in many applications. However, they are difficult to isolate from their constituent elements which results in environmentally costly refinement. This project analyzed the application of biooxidation to the extraction of REEs from coal waste as a means of economically separating REEs from their constituents. To this end, 60% pure pyrite (FeS2) ores, collected from coal waste which would have ended up as tailings and caused acid rock drainage, were used as the food source for the bacteria, resulting in sulfuric acid production within the reactor. They were fed into a bioreactor containing <i>acidithiobacillus ferrooxidans</i>, an iron consuming bacterium that was used to oxidize Fe2+ to Fe3+. The rate of biooxidation was tracked by monitoring the Eh of the system. Bacterial vitality was monitored by periodic ferrous oxidation tests which quantified the bacterial population by adding a predetermined quantity of ferrous sulfate and subsequent ferrous ion oxidation monitoring. The ferrous biooxidation rate was determined using Michaelis-Menten kinetics. Precipitation tests with magnesium and sodium carbonate were performed. The initial precipitate was redissolved and a secondary test with oxalic acid was performed. Once precipitation tests finished, the filter cake was dried for further analysis. REE recoveries were analyzed using Energy-Dispersive X-Ray Spectroscopy (EDS) and Scanning Electron Microscope (SEM) analysis. Various precipitates began forming in iron-rich solutions above pH 2. Precipitation events are helpful in selectively removing iron compounds. X-Ray Diffraction (XRD) analysis of the precipitate, indicates the main precipitate is a jarosite compound. Analysis of the recoveries showed that the primary element in the recovery was Yttrium (Y) at 22%, followed closely by Cerium (Ce) at 21% of total recovery. Future work will use the information gathered from this project to facilitate commercial implementation of biooxidation REE extraction in industry.

Economic extraction, recovery, and upgrading of rare earth elements from coal-based resources

ACS Spring Meeting 2021

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