EXPLORING FEOOH BREAKDOWN AS THE GEOCHEMICAL TRIGGER FOR LANTHANIDE ENRICHMENT IN PHOSPHORITE DEPOSITS

The increasing demand for Lanthanides (YREE) in technological and medical applications necessitates a reliable and sustainable supply chain. In our study, we investigate the breakdown of FeOOH (ferrihydrite and goethite) to understand the source of YREE enrichment in sedimentary phosphorite deposits within the Western Canadian Sedimentary Basin. We conducted both short-term (1 week) and long-term (3-6 weeks) batch experiments under varying pH conditions to simulate natural environments: seawater (pH 8.2), acidic (pH ~2-3), neutral (pH ~7), and basic (pH ~11-12). Initial experimental conditions included an Fe concentration of 14.5 mM and YREE concentrations of 0.662, 6.62, and 66.2 µM, with 0.125 g of synthesized FeOOH sediment in a 120 mL solution at 25°C, 50°C, and 80°C. Daily sampling over 24-hour intervals and subsequent analyses using LA-ICP-MS, Raman, and SEM provided insights into concentration dynamics, characterization, and morphological changes.

In addition to the FeOOH breakdown experiments, we conducted phosphorite growth experiments under similar pH conditions to study the kinetics of YREE adsorption and incorporation into phosphorite. We expect data to indicate a rapid initial adsorption phase followed by slower incorporation rates, with the highest YREE uptake at acidic and neutral pH levels. The kinetic analysis yielded a rate constant of approximately 0.004 hr⁻¹ for YREE adsorption at 25°C. Arrhenius analysis provided an activation energy of 30.37 kJ/mol, with rate constants increasing to 0.001 hr⁻¹ at 50°C and 0.027 hr⁻¹ at 80°C, revealing the sensitivity of the reaction rate to temperature changes and helping predict YREE mobilization under different thermal conditions in sedimentary environments.

Our predictions, based on preliminary pH data and extrapolated rates, suggest notable trends in YREE and Fe concentrations, with potential implications for understanding YREE mobilization and enrichment mechanisms. This research contributes to geochemical modeling of sedimentary deposits and FeOOH behavior under varied conditions. It enhances understanding of pH impacts on FeOOH stability and YREE behavior in marine and diagenetic environments. These findings inform predictions of mineral stability and element cycling, aiding both academic research and practical applications in resource exploration and environmental management.