Analysis of Uranium Speciation in Phosphorites: Insights from Sequential Chemical Extraction & Mineral Synthesis Experimentation, Poster 48

Research carried out by the Vermont Geological Survey in the areas of Milton and Colchester revealed that groundwater produced from the Clarendon Springs Formation contains elevated levels of uranium and alpha radiation.... [ view full abstract ]

Research carried out by the Vermont Geological Survey in the areas of Milton and Colchester revealed that groundwater produced from the Clarendon Springs Formation contains elevated levels of uranium and alpha radiation. Geochemical investigations at Middlebury College indicate that uranium occurs in black phosphorite clasts and layers (within dolostone). The phosphorites contain 50-400 ppm U and the main mineral is fluoroapatite (XRD identification), which is capable of incorporating U+4 in a Ca+2 site. Stoichiometries from SEM-EDS indicate possible occurrence of autunite, coffinite and brannerite. The purpose of this study is to do sequential chemical extraction and slow-scan XRD of six representative U-bearing phosphorites to determine speciation of U. XRD of powdered phosphorite identifies presence of metaautunite (5-10% of phosphorites) as well as fluoroapatite. XRD and ICPMS analysis following each stage of the extraction thus far reveals that 0.5-1% of U (0.5-3.8 mg/kg) is available enough to be leached by weak (0.11 M) acetic acid and that it is likely derived from fluoroapatite, perhaps driven by oxidation of U+4 to U+6. A mineral alteration reaction with H2SO4 is also being carried out to test the hypothesis that pyrite weathering (which locally produces H2SO4) triggers alteration of flouroapatite to autunite.