This presentation outlines a process utilizing hardwood biochar-derived sorbents for the recovery of rare earth elements (REEs) from acid mine drainage (AMD) solutions. It also discusses relevant principles from membrane-based ion separations that apply to this scenario. AMD contamination is a significant environmental issue, affecting approximately 12,400 miles of streams. More than half of these impaired waterways are found in the Appalachian region. Research indicates that, if processed, AMD from Appalachia could produce at least 365 metric tons per year of rare earth oxides (REO).Rare earth elements in AMD streams exist at very low concentrations, typically in the parts per billion (ppb) range. Due to these dilute levels, sorbents offer a more suitable and sustainable approach for extracting REEs compared to membrane technologies. A hardwood-derived biochar has been engineered to serve as an efficient sorbent, demonstrating greater than 90% recovery rates for REEs from both simulated and field-collected AMD streams. The morphological characteristics of this biochar and the specific adsorption conditions that facilitate such high recovery rates will be described in detail. Beyond general REE extraction, the hardwood biochar is capable of selectively recovering particular REEs. This selectivity is achieved by exploiting differences in the adsorption kinetics, which are influenced by the hydrated radii of the ions. This approach is comparable to the exclusion mechanisms observed in nanofiltration membranes, where ion size plays a critical role in separation. The kinetic models and parameters relevant to the adsorption of selected REEs will be discussed. Additionally, a conceptual design for a column-based system will be introduced, which can facilitate high-throughput extraction of REEs from AMD.
