Solubility and Modeling of Sodium Aluminosilicate in NaOH–NaAl(OH)4 Solutions and Its Application to Desilication

The solubility of sodium aluminosilicate (sodalite), a major desilication product (DSP) in the Bayer process, in NaOH and NaOH–NaAl(OH) 4 solutions was determined and modeled at temperatures from 303.2 to 348.2 K. Sodium aluminosilicate was synthesized in a batch crystallizer and the effect of temperature, solution concentrations, and aging time was investigated. Solubility was found to increase with increasing NaOH concentration while the solubility sharply decreases with the addition of Al(OH) 3, reaches a minimum at about 0.8 mol·L –1, and then increases. A mixed-solvent electrolyte (MSE) model for the solubility of sodalite was developed with the help of the OLI platform via regression to obtain the model parameters. In addition, the desilication kinetics of NaOH–NaAl(OH) 4 solutions by using sodalite as seeds was studied experimentally and modeled with the aid of a second order kinetic model. The activation energy of desilication over the temperature range 323.2–363.2 K was found to be 92 ± 14 kJ·mol –1 . Under the optimal operation conditions, 80% silica was removed after 2 h.