Salt Mineralogy of Hanford High-Level Nuclear Waste Staged for Treatment

The Hanford site near Richland Washington, United States, is staging some of its 56 million gallons of high-level waste for treatment. Limited understanding of solids precipitated from the concentrated electrolyte solutions complicates the development of waste treatment options. The implications for the precipitation of these solids are that overlying liquids are saturated in these salts, which may cause unwanted precipitation during downstream processing. This study characterizes the salts in two of these Hanford staged feed tanks (Tanks AP-103 and AP-108) by ion chromatography (for anions), X-ray diffraction, polarized light microscopy, and scanning electron microscopy with energy dispersive X-ray spectroscopy. The results show that Na 2 CO 3 ·H 2 O (thermonatrite) was the most prevalent salt in one tank, whereas the double salt Na 7 F(PO 4 ) 2 ·19H 2 O (natrophosphate) was the dominant salt in the other. Natrophosphate occurred in both tanks as octahedrons in sizes ranging from 10 μm to a millimeter in diameter. Natroxalate (Na 2 C 2 O 4 ) and kogarkoite (NaFSO 4 ) were also common phases observed. Waste processing planners should recognize that these salts may have to be dissolved prior to treatment, and solutions saturated with these salts may complicate downstream processing.