Solubility of dicalcium silicate in the NaOH–NaAl(OH)4–Na2CO3 solutions: Determination and prediction

The utilization of low-grade aluminous materials to produce alumina by the sinter process has been attracted attention as high-grade bauxite ores are diminishing. The sinter process has strict desilication requirement for the precipitation of high quality Al(OH)3. The knowledge of the behavior and solubility of calcium silicates is highly significant for reducing the amount of silica entered into the liquor. For this reason, the solubility of dicalcium silicate (belite), a main silicon-bearing solids, in the NaOH, mixed NaOH–NaAl(OH)4 and NaOH–NaAl(OH)4–Na2CO3 solutions was determined at temperatures from 303.2 to 343.2 K. Co-precipitates from the reaction between calcium and silicate in the CaCl2–Na2SiO3–NaOH solution were calcined at 1200 °C for 4 h to obtain belite. It was found that solubility in 0.5–4 mol L− 1 NaOH solutions increases with increasing NaOH concentration and decreases with temperature increment. Solubility of belite in the NaOH–NaAl(OH)4 and NaOH–NaAl(OH)4–Na2CO3 solutions demonstrated to increase with the addition of Al(OH)3 and Na2CO3. The mixed-solvent electrolyte (MSE) model embedded in OLI software was employed to predict the solubility of belite based on the characterization of solid phases with reasonable agreement. This work provides a meaningful knowledge for the clinker dissolution and desilication operation in the sinter process.