Energetics of cancrinite: Effect of salt inclusion

With its large 12-membered ring channel structure and the periodic arrangement of its ε-cage, cancrinite can host molecular water and a variety of guest anions such as nitrate, carbonate, chloride, and hydroxide. A series of cancrinite samples containing varying amounts of nitrate, carbonate, and water were investigated using high temperature oxide melt drop solution calorimetry. The enthalpies of formation from constituent oxides and from elements at room temperature were obtained. The enthalpy of formation from oxides becomes less exothermic and the water content decreases with increasing salt inclusion (NaNO3 and Na2CO3). This indicates a destabilizing effect of salt hosting on the cancrinite structure. The negative correlation between the amounts of salt and water inclusion suggests competition between water molecules, guest anions and possibly Na cations for the occupancy of the cancrinite channel and cage sites.