Thermochemistry of Hydrotalcite-like Phases Intercalated with CO32-, NO3-, Cl-, I-, and ReO4-

Abstract

The enthalpies of formation of hydrotalcite-like phases containing Mg and Al and intercalated with NO3-, Cl-, I-, ReO4-, or CO32- were determined using high-temperature oxide melt and room-temperature acid solution calorimetry. The relative stability of phases bearing the various anions was gauged by comparing the enthalpy of formation from the single-cation components (ΔfHscc). Trends relating ΔfHscc to the nature of intercalating anions (halides, NO3-, and CO32-) show small stabilization from the mechanical mixtures of single-cation components. The aim of this study was to relate the enthalpy of formation to the nature of interlayer bonding in hydrotalcite-like compounds (HTLCs) bearing various anions, to uncover trends in the relative aqueous solubilities of these phases. The entropy of formation of these compounds was estimated using an approximation based on third-law entropy measurements for the compound Mg0.74Al0.26(OH)2(CO3)0.13·0.39H2O which were performed in a previous study. This approximation ...