Solubility of sodium aluminosilicates in synthetic Bayer liquor

The solubility of two major sodium aluminosilicate Bayer refinery scale phases, sodalite and cancrinite, has been measured in sodium aluminate liquor as a function of time, sodium carbonate concentration, initial seeding phase, and temperature. Solubility is assessed by the measurement of SiO2 concentration in solution for at least 13 days. At both 90 degrees C and 160 degrees C, sodalite seed partially transforms to cancrinite over 13 days. As this transformation is partial, the use of the term "equilibrium solubility" is not justified. The kinetics of this process are faster at the higher temperature; hence, the proportion of cancrinite in the final crystalline products is greater at 160 degrees C. As expected, the more thermodynamically stable product, cancrinite, was found to be less soluble. Hence, SiO2 solubility in sodalite-seeded solutions was not greater at 160 degrees C than at 90 degrees C. In cancrinite seeded solutions, where no further phase transformation occurs, the equilibrium SiO2 concentration in solution increases with increasing temperature. Increasing Na2CO3 concentration does not appear to affect the sodalite-to-cancrinite transformation kinetics. In all sodalite or cancrinite-seeded solutions, SiO2 solubility decreases with increasing Na2CO3 concentration.