Modeling of Gibbsite Solubility in Na+-K+-OH−-Al(OH)4−-SO42−-CO32− System Applied to Precipitation at Sintering Alumina Refineries

The quantitative prediction of the equilibrium gibbsite content in alkaline liquors of alumina production is a key parameter for controlling precipitation kinetics and ensuring product quality. Unlike Bayer alumina refineries, sintering alumina refineries use different alkali and impurity content ranges; moreover, they are characterized by the presence of significant amounts of potassium in aluminate liquors that are not considered in the existing gibbsite equilibrium models. This paper presents an extended mathematical model, which is based on the Rosenberg–Healey methodology and incorporates sodium (Na2O) and potassium (K2O) components into the total alkaline system. Model coefficients were optimized using 18 tests designed by the D-optimal method at temperatures of 50–85 °C and a total alkali content of [R2Ok] = 40–80 g/L, which contains up to 30% of potassium alkali K2O, as well as the impurities in the form of soda [Na2CO3] = 0–58 g/L and sodium sulfate [Na2SO4 ]= 0–25 g/L. The fine-tuned model was verified using the composition of actual refinery liquors and provides RMSE = 0.71 g/L Al2O3, thus demonstrating satisfactory solubility prediction accuracy. The presented model can be used to calculate aluminate liquor productivity at existing sintering refineries with a sodium–potassium system.