Silicon saturation coefficient changes in hydrogarnets during the Bayer process with lime addition

Abstract

The relationship between the silicon saturation coefficient of hydrogarnets and Bayer reaction parameters was studied. The peak position, crystal plane spacing, and cell edge length of typical hydrogarnet patterns were calculated to find the key factors influencing the relationship. The results showed that the crystal face (420) is the optimal garnet growth direction during hydration and crystal growth along the faces (521) and (611) were not affected significantly by the varying experimental conditions. The reaction temperature significantly influenced the silicon saturation coefficient of hydrogarnets. The silicon saturation coefficient of hydrogarnets increased from 0.2 to about 1.0 in the temperature range of 30–270 °C and a rapid expansion process was observed in the temperature range of 120–150 °C. Moreover, the reaction time, alumina concentration, and C / S were shown to be less important factors. Averaging the results obtained by the 3 methods was shown suitable for calculating the SiO 2 saturation coefficient of hydrogarnets. The calculated results of the Al 2 O 3 and SiO 2 contents matched the actual ones. However, the actual SiO 2 content was about 10 % less than the calculated one for SiO 2 saturation coefficients higher than 1. The average calculation results of “Peak position method”, “Crystal plane spacing method” and “Cell edge length method” match the actual contents well, but the actual SiO 2 content is about 10% lesser than the calculation contents when the SiO 2 saturation coefficient is higher than 1. The residue composition can be predicted by this method.