Thermodynamic Model for Uranium Release from Hanford Site Tank Residual Waste

Abstract

A thermodynamic model of U solid-phase solubility and paragenesis was developed for Hanford Site tank residual waste that will remain in place after tank closure. The model was developed using a combination of waste composition data, waste leach test data, and thermodynamic modeling of the leach test data. The testing and analyses were conducted using actual Hanford Site tank residual waste. Positive identification of U phases by X-ray diffraction was generally not possible either because solids in the waste were amorphous or their concentrations were not detectable by XRD for both as-received and leached residual waste. Three leachant solutions were used in the studies: deionized water, CaCO3 saturated solution, and Ca(OH)2 saturated solution. Analysis of calculated saturation indices indicate that NaUO2PO4·xH2O and Na2U2O7(am) are present in the residual wastes initially. Leaching of the residual wastes with deionized water or CaCO3 saturated solution results in preferential dissolution Na2U2O7(am) and formation of schoepite. Leaching of the residual wastes with Ca(OH)2 saturated solution appears to result in transformation of both NaUO2PO4·xH2O and Na2U2O7(am) to CaUO4. Upon the basis of these results, the paragenetic sequence of secondary phases expected to occur as leaching of residual waste progresses for two tank closure scenarios was identified.

3D Electron Diffraction as a Powerful Tool to Study the Earliest Nanocrystalline Weathering Products: A Case Study of Uraninite Weathering

“…Uranyl in the aqueous solutions may be trapped in secondary minerals common in such systems . The thermodynamic stability of these minerals may impart control over the total concentration of dissolved U 6+ in the aqueous phase and thus affects the migration of U 6+ in the environment on a large scale. − Recent or subrecent weathering of uraninite is often connected with low-pH aqueous solutions in acid mine drainage (AMD). − Such processes can lead to the formation of a large suite of uranyl sulfate minerals. ,− From the mineralogical point of view, these minerals are being intensively studied. However, our understanding of their formation and gradual transformation is still insufficient.…”

Hydrogen bonding in the crystal structure of phurcalite, Ca2[(UO2)3O2(PO4)2]·7H2O: single-crystal X-ray study and TORQUE calculations

“…Generally, due to their low solubility products (see e.g. Ilton et al, 2010;Astilleros et al, 2013;Gö b et al, 2013), they can occur both in the vadose zone of the uranium deposits (Murakami et al, 1997;Finch & Murakami, 1999;Plá šil et al, 2006Plá šil et al, , 2009Gö b et al, 2013) and in mine dumps, wastes and tailings (Buck et al, 1996;Roh et al, 2000;Fuller et al, 2002;Catalano et al, 2006;Cantrell et al, 2011;Maher et al, 2013). This makes uranyl phosphate and arsenate minerals essential for controlling U mobility in the environment.…”

Horákite, a new hydrated bismuth uranyl-arsenate-phosphate mineral from Jáchymov (Czech Republic) with a unique uranyl-anion topology

“…Uranyl phosphate and arsenate minerals are environmentally important phases that result from hydration-oxidation weathering of primary U minerals, mainly uraninite (Finch and Murakami 1999;Krivovichev and Plášil 2013;Plášil 2014). Generally, due to their low solubility products (see e.g., Ilton et al 2010;Astilleros et al 2013;Göb et al 2013), they can occur both in the very leached parts of the uranium deposits (Finch and Murakami 1999;Plášil et al 2006Plášil et al , 2009Göb et al 2013) and in mine dumps, wastes and tailings (Buck et al 1995;Roh et al 2000;Catalano et al 2006;Cantrell et al 2011;Maher et al 2013). This makes uranyl phosphate and arsenate minerals essential in controlling U mobility in the environment.…”