Thermochemistry of hydrotalcite-like phases in the MgO-Al2O3-CO2-H2O system: A determination of enthalpy, entropy, and free energy

Enthalpy of formation of sulfate green rusts

“…2 and Table 8). A similar minor thermodynamic dependence as a function of Al content was observed for different hydrotalcites (Allada et al, 2005). It was argued that these differences were not substantial enough to promote significant thermodynamic preference for any given metal ratio (Allada et al, 2006).…”

Hydrotalcite Formation for Contaminant Removal from Ranger Mine Process Water

“…Substitution by Mn is common in synthetic hydrotalcites (e.g. Allada et al 2002;Obalova and Fila 2005), and is likely here, given the abundance of Mn in the Ranger process water. Although Mn-precipitates were also noted as a discrete phase forming late in the titration at high pH, the partial incorporation of Mn into hydrotalcite is a reasonable scenario for the fate of at least part of the Mn in the original solution.…”

Energetic and structural studies of amorphous Ca1−Mg CO3·nH2O (0 ⩽x⩽ 1)

“…The crystallization enthalpies approximate the relative stabilities because the TDS term contribution to free energy is expected to be small at room temperature for these phases. Our earlier entropy calculations from heat capacity measurements on layered hydroxycarbonates (hydrotalcites) indicate that the maximum entropy contribution (TDS term) to free energy is less than 2 kJ/mol (Allada et al, 2005). The total entropy of a system includes both configurational and vibrational components.…”

“…The total entropy of a system includes both configurational and vibrational components. For hydrotalcite, Mg 0.74 Al 0.26 (OH) 2 (CO 3 ) 0.13 Á0.39H 2 O, the total TDS contribution to the free energy is near zero due to the negative vibrational contribution (Allada et al, 2005). Because the detailed structure and disorder (including the contribution of H 2 O) are not known for these amorphous carbonates, an estimate of configurational entropy can not be made.…”