Paper No. 228-9
Presentation Time: 10:55 AM
TARGETED RARE EARTH ELEMENT EXTRACTION FROM MINE DRAINAGE TREATMENT SOLIDS INFORMED BY ADVANCED CHARACTERIZATION
STUCKMAN, Mengling1, LOPANO, Christina2, HOFFMAN, Colleen3, SCHAFFER, Camille4, HEDIN, Benjamin5, CRAVOTTA III, Charles, B.A. Environmental Sciences, Ph.D. Geochemistry and Mineralogy6, CAPO, Rosemary C.7, STEWART, Brian7 and CHENG, Chin-Min8, (1)Department of Energy, National Energy Technology Laboratory, Pittsburgh, PA 15236, (2)U.S. Department of Energy, National Energy Technology Laboratory, 626 Cochran Mill Road, Pittsburgh, PA 15236, (3)NETL Support Contractor, 626 Cochran Mill Road, Pittsburgh, PA 15236, (4)Department of Geology & Environmental Science, University of Pittsburgh, 4107 O'Hara St, Pittsburgh, PA 15260; NETL Support Contractor, 626 Cochran Mill Road, Pittsburgh, PA 15236, (5)Hedin Environmental, 195 Castle Shannon Blvd, Pittsburgh, PA 15228, (6)U.S. Geological Survey, Pennsylvania Water Science Center, 215 Limekiln Road, New Cumberland, PA 17070; Cravotta Geochemical Consulting, 859 Bloody Spring Rd, Bethel, PA 19507, (7)Department of Geology and Environmental Science, University of Pittsburgh, Pittsburgh, PA 15260, (8)NETL Support Contractor, 626 Cochran Mill Road, Pittsburgh, PA 15236; U.S. Department of Energy, National Energy Technology Laboratory, 626 Cochran Mill Road, Pittsburgh, PA 15236
In support of a clean energy transition in the U.S., National Energy Technology Laboratory (NETL) has collaborated with staff at Hedin Environmental and students at the University of Pittsburgh to characterize critical mineral content and recovery potential from acid mine drainage treatment solids (AMD solids). AMD solids in Appalachia are an unconventional feedstock of rare earth elements (REEs), with potential of suppling 1,102 tons REE/year. To inform recovery efforts, select AMD solids were examined using synchrotron microprobe analysis in conjunction with USGS-developed geochemical modeling to indicate likely phases hosting critical minerals (REE, Co, Ni, etc.) and associated metals.
More than 100 AMD solids were collected from 94 passive AMD treatment systems in Pennsylvania, where limestone aggregates are used for acidity neutralization. As pH increases, dissolved metals and critical minerals in AMD are attenuated as surface coatings on limestone. The collected AMD solids contained up to 2000 mg/kg REE, up to 13,000 mg/kg transition metals (Co, Ni, Zn) and up to 440 mg/kg Li. Regardless of the diverse chemical compositions from AMD solids (Al-rich, Mn-rich, or Al,Fe,Mn-rich), REEs were mostly associated with Al and Mn (hydr)oxides, while select heavy REEs (e.g., Gd, Dy) were co-localized with Fe (hydr)oxides. Co and Ni have different distribution zones, while both co-localized with Mn (hydr)oxides.
Based on this characterization, NETL developed a patent-pending innovative step-leaching protocol, “Targeted Rare Earth Extraction (TREE)” to effectively recover up to 90% REE and 60% Co in separate steps. In addition, select post-TREE solid residuals (purified Al oxides, or Mn oxides) can be further developed into functional materials (e.g., lithium and CO2 sorbents) needed for green energy transition and carbon management. This characterization-informed approach as well as TREE processing from AMD solids can be used for other legacy wastes (e.g., coal ash, oil and gas drill cutting, mine tailings), and offers an opportunity to transform waste streams into environmental and economic assets that meet U.S. Department of Energy and U.S. Environmental Protection Agency goals.
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