Parameters affecting the precipitation of Al-phases from aluminate solutions of the Pedersen process

A theoretical thermodynamic study of a sodium aluminate solution originating from the
Na2CO3 leaching of a calcium aluminate slag was conducted to specify the
thermodynamically favoured species that exist within. Using the HSC 9.0 software, a
carbonation process (neutralisation of the aluminate solution with CO2 gas) was simulated in
order to assess the thermodynamically favoured solid phases that precipitate. Laboratory
carbonation experiments were conducted to verify the theoretical predictions. According to
the theoretical study, at temperatures below 50 °C gibbsite precipitates in the first 20 minutes
of the process and then is transformed to dawsonite. Temperatures over 65 °C favour the
direct precipitation of dawsonite. The experimental work verified the latter observation but
not the former.