Influence of Mineral and Organic Impurities on the Alumina Trihydrate Precipitation Yield in the Bayer Process

Precipitation yields of alamina trihydrate from different sodium aluminate solutions, synthetic or industrial, with variable content in mineral and organic impurities, have been determined at different soda concentrations. The conditions of precipitation were the same for all the solutions. A mathematical model of experimental results, taking into account possible interactions between impurities, has been established, allowing to predict specific effect of each mineral impurity and overall effet of organic content. With the kinetic equation of precipitations, the use of the mathematical model permits the calculation of equilibrium composition of the aluminate solution as a function of the content of impurities. Calculated and experimental values are in agreement. So, with equilibrium values and the kinetic equation, it is possible to predict the precipitation yield of any liquor knowing its chemical composition and condition of precipitation (temperature, seed charge, retention time).