Improving the Bayer Process productivity – An industrial case study

Alumina production through Bayer Process is limited by the instability of soluble sodium aluminate in the supersaturated solutions used by the alumina refineries. The precipitation of aluminum hydrate can occur in equipment not designed for this purpose, causing significant loss of production. The stabilization of sodium aluminate in solution results in a decrease of the supersaturation, reducing the driving force for precipitation of aluminum hydrate. The reduction of supersaturation can be achieved by the application of stabilizing substances, known as nucleation inhibitors. This study has the objective of evaluating the effect of the concentration of a polymeric type nucleation inhibitor on the productivity of the Bayer Process. A set of experiments was executed in the laboratory, for the evaluation of the influence of the quantity of inhibitor and of the concentration of solids on the stability of the green liquor that feeds the filtration step. It was generally observed that supersaturation was significantly reduced. The amount of inhibitor used made little difference to the stability, whereas the concentration of solids was shown to have a strong influence. The implementation of the results of this work in an industrial plant resulted in an increase of alumina production of 100,000 ton/year.