Stability of hydrotalcite (Mg-Al layered double hydroxide) in presence of different anions

MgO contained in cementitious materials is experimentally observed to precipitate as poorly crystalline hydrotalcite (Mg-Al LDH). However, the geochemical modelling of challenging due lack consistent thermodynamic dataset for this phase. Hydrotalcites with Mg/Al = 2 were synthesised presence NaHCO3, NaCl, Na2SO4, NaNO3, and NaOH. Mass balance, XRD FT-IR indicated incorporation anions interlayer together some carbonate. The crystallinity phase increased depending on anion: SO42? < Cl? NO3? OH? CO32?. An in-situ increase temperature monitored by TGA showed that stability structure also depended incorporated anion. solubility products calculated based solution analysis samples re-equilibrated at different temperatures, while entropy heat capacity obtained from additivity method or molar volume. A simple solid-solution model containing CO3, OH, SO4, Cl NO3 suggested.