THE EFFECT OF ANATASE AND LIME ON THE TRANSFORMATION OF SODALITE TO CANCRINITE IN BAYER DIGESTION AT 250℃

摘要

Sodalite (SOD) and cancrinite (CAN) are important desilication products in the refining of high silica bauxites by the Bayer process. SOD, usually formed at predesilication or low temperature digestion, is transformed to CAN under high temperature digestion. CAN provides opportunities to minimize soda loss and reduce both silica contamination of product and silicate scaling. This paper reports the influence of anatase and types of lime on the transformation. It was found that the rate of transformation is greatly increased by lime, but when anatase is also present, the rate is suppressed by a coating of sodium titanate on SOD. Reducing sodium titanate by forming calcium-containing titanates was critical for the transformation. The efficiency of calcium titanate formation depended on lime charge and type. Calcite as calcium source was more efficient than CaO, enhancing the formation of CAN and promoting the formation of more stable perovskite. The underlying mechanisms are discussed.