Desilication Reactions at Digestion Conditions: An in Situ X-ray Diffraction Study

Abstract

The reactions of silica minerals at high temperature Bayer digestion conditions have been investigated using an in situ X-ray diffraction technique. Rapid precipitation of sodalite was observed following the addition of kaolin or quartz to Bayer liquor at 250 °C. The addition of calcium with kaolin/quartz resulted in the formation of calcium cancrinite. A reduction in the rate of both sodalite and calcium cancrinite formation was observed on decreasing the temperature in the range 180−250 °C. Seeding with sodalite/calcium cancrinite solids did not noticeably influence the reaction of quartz at 250 °C, but a slight increase in the formation of calcium cancrinite in the presence of calcium cancrinite seed was observed at 220 °C. The direct transformation of sodalite to calcium cancrinite was also investigated in the range 200−250 °C. The reaction proceeds quickly in the presence of calcium and hydrogarnet and is unaffected by the presence of titanium.