Part I: REEs recovered from multiple AMDs via sorption to precipitated MnO2 with and without assistance of P-bearing ligands

Elevated concentrations of critical metals (CM) in acid mine drainage (AMD) has been the subject of many studies due to high demand that is only expected to grow. Some, like rare earth elements (REEs) and Co are an essential component to many modern technologies. Previously we developed a CM recovery technique wherein Mn2+ is oxidized and precipitated as MnO2 and functionalized with H2P2O72- or H2PO4, subsequently sorbing REEs to the surface. To probe the broad applicability of this approach, multiple AMDs of varying sources, concentrations of metals, and SO4 were used in this case study. Depending on the composition of the AMD, a staged precipitation process was used, where Fe2+ was oxidized and Fe and Al were subsequently removed by an initial pH adjustment to pH 4-4.5 to cause precipitation. We found that the composition of the AMD, specifically the concentration of SO4 and Al, impeded REE recovery. However, MnO2 precipitated in one volume of AMD could be used to remediate at least 16 volumes of additional AMD, in recycled batch experiments. We were able to achieve grades of 13.09 mg TREE/g of solid.