THE THERMODYNAMIC APPROACH TO PREDICTING SILICATE SOLUBILITY

Reactive silica leached in the digestion stage of the Bayer process is removed from the liquor phase by precipitation of sodium and calcium aluminium silicate desilication products (DSPs). Silicate management by conventional DSP precipitation has the disadvantages of incurring significant loss of sodium and aluminium oxy-hydroxides and the material requires neutralisation and long term storage. Finding an alternative to DSP has been a long standing challenge and the subject of a great deal of previous research. Despite the efforts, a cost effective solution remains elusive. With advances in Bayer liquor species activity coefficient models, taking a thermodynamic approach may provide clues to an innovative technological solution. This paper reviews relevant aqueous and solid phase thermodynamic data for the sodium-aluminium-silicon-water system. Information gaps and inconsistencies in the data are highlighted and discussed.