Separation of Rare Earth Elements (REEs) from Acid Mine Drainage using Hardwood Biochar

To reduce reliance on foreign nations, it is in the interest of the United States to identify domestic sources of rare earth elements (REE) production and develop sustainable technologies to effectively recover them. REEs are critical for energy, electronics, and defense technologies due to their unique physical and chemical properties. Acid mine drainage (AMD) is one such source that has attracted interest because of the presence of a wide range of REEs. The concentration of REEs in these sources is, however, dilute (at the ppb level), and while conventional processes, such as solvent extraction, effectively recover them, they are associated with high energy and chemical usage. In this work, a hardwood biochar-based adsorption process is described for REE recovery from AMD. A number of adsorption parameters were tuned to identify the optimum operating conditions, and the biochar was characterized using various morphological and transport-based techniques, using La3+ as a representative REE. The thermodynamic and kinetic interactions of the REEs with the biochar are evaluated based on equilibrium adsorption uptakes and adsorption kinetics, using selected ions with similar size and charge as probe ions. These results demonstrate that intra-REE separation is possible due to differences in the adsorption kinetics behavior of these ions, showing the synergistic role of ion size and charge on the overall performance. Beyond ideal single ion solutions, the biochar performance was also evaluated for synthetic multi-ion solutions and real AMD solutions. Finally, some preliminary results on the weak acid-induced desorption behavior and its effects on biochar reusability were included. Overall, this study shows that biochar adsorption offers an effective, sustainable method for REE recovery from AMD, supporting efforts in developing the domestic REE supply chain while addressing environmental challenges raised by AMD.