The solubility of sodalite and cancrinite in synthetic spent Bayer liquor

The equilibrium SiO2 solubility of sodalite and cancrinite crystals in sodium aluminate solutions containing low concentrations of aluminium (synthetic spent Bayer liquor) has been determined over a range of temperatures (90–220°C) and as a function of solution NaOH and Al(OH)3 concentration for cancrinite. The same SiO2 solubilities, within experimental error, were measured when equilibrium was approached from both above and below SiO2 solubility for spent Bayer liquors in contact with either sodalite or cancrinite crystals. The solubility of sodalite and cancrinite (expressed in terms of SiO2 concentration) increased linearly with increasing temperature. The equilibrium SiO2 solubility of sodalite was higher than that of cancrinite at all temperatures. The solubility of cancrinite increased with increasing concentration of NaOH (3.87–5.42 M) and Al(OH)3 (1.39–2.23 M) in solution. The SiO2 solubilities of four types of dimorphic sodalite/cancrinite mixed phase seed crystals synthesised from Bayer plant spent liquor and synthetic Na2CO3, Na2SO4 or NaNO3 rich NaOH solutions containing dissolved kaolinite were investigated. The solubility of the four types of mixed phase seed crystals was found to be substantially the same as the solubility for pure cancrinite