Comparative Study of Bioleaching Efficiency of Rare Earth Element from Different Carbonatite Ores in Mongolia

The increasing demand for rare earth elements necessitates the development of environmentally friendly and energy-efficient extraction methods. This study investigates the bioleaching efficiency of rare earth elements from carbonatite ores using both pure and mixed bacterial cultures under ambient conditions. Ores from the Lugiin Gol and Mushgia Khudag deposits underwent a 7-day bioleaching with a bacterial mixture and pure cultures origin from copper ore. The progress of bioleaching was monitored by measuring dissolved metal concentrations, pH, and oxidation-reduction potential. X-ray diffraction analysis revealed that rare earth elements predominantly exist as minerals synchysite and bastnasite in the Lugiin Gol ore, monazite and parasite in the Mushgia Khudag ore. Chemical analysis determined the total REE content to be 3.99% in Lugiin Gol ore and 7.66% in Mushgia Khudag ore. The bioleaching, conducted with a solid-to-liquid ratio of 1:6 at room temperature and utilizing six different ore particle sizes, demonstrated that mixed bacterial cultures were significantly more effective than pure cultures. The highest metal recovery rates achieved were 15.85% and 6.23% (wt.%) for Lugiin Gol and Mushgia Khudag ores, respectively. Furthermore, particle size was identified as a crucial factor influencing bioleaching efficiency, with optimal results observed at 4.0–5.0 mm particle sizes, likely due to the weakening of the rare earth element bearing ore matrix.