23Na and 27Al NMR study of the products from carbonation of a bayer liquor

Abstract

A multinuclear magnetic resonance methodology combining magic angle spinning, cross-polarisation and double angle rotation has been used to characterise the product from the carbonation of a Bayer liquor as predominantly well ordered NaAlCO₃(OH)₂(dawsonite). The NMR spectra are dominated by resonances from this phase, but accurate simulation requires additional minor components, most likely a mixture of a poorly ordered aluminium hydroxide gel and an amorphous phase related to NaHCO₃, which is not observed by X-ray diffraction. Thermal decomposition of dawsonite at 350 °C proceeds through partial loss of CO₂ and OH with concomitant formation of disordered materials containing sodium species, four-, five- and six-fold coordinate Al sites, and two types of residual carbonate.