Nitrate cancrinite: Synthesis, characterization, and determination of the enthalpy of formation

Nitrate cancrinite, with an ideal formula of Na8[Al6Si6O24](NO3)2 · 4H2O, is an important constituent of high-level nuclear wastes at several US Department of Energy (DOE) storage sites. A simple synthesis route for this material is described. Pure nitrate cancrinite has been prepared using a mixed solution of sodium silicate, sodium aluminate, sodium nitrate, and sodium hydroxide. Crystallization took place rapidly at 90 °C and the cancrinite phase emerged within a few hours of aging. Both X-ray diffraction and composition analyses indicated the formation of pure nitrate cancrinite. Solution calorimetric measurements of this material were performed with a Calvet-type calorimeter operated at 701 °C using molten lead borate (2PbO · B2O3) as the solvent. Enthalpies of formation from the constituent oxides and from the elements are −903.3 ± 15.7 kJ/mol and −14,258.3 ± 17.3 kJ/mol, respectively, for a sample with the analyzed formula of Na7.282[Al5.854Si6.146O24](NO3)1.336(CO3)0.046 · 3.365H2O.