Process Simulation with Tertiary Cyclone for Kaolinite Removal from Amazonian Bauxite

Bauxite is the main ore for metallic aluminum production, consisting of aluminum and iron oxides and kaolinite, a clay mineral commonly found in Amazonian bauxites, as the main carrier of reactive silica. In the process, due to the small particle size, kaolinite is usually removed by attrition and washing of coarse material followed by desliming using hydrocyclones. In the Bayer process, kaolinite reacts with sodium hydroxide, increasing reagent consumption in the process. The beneficiation process at Mineração Paragominas is based on the separation of coarser fractions with higher gibbsite content from the clay minerals, where kaolinite is more concentrated. The separation takes place in hydrocyclones, equipment that inherently presents a by-pass of fine particles for the underflow, consequently, contaminating the concentrate with kaolinite, and increasing the operating cost in the Bayer process. Additional desliming stages were evaluated for a potential increase in kaolinite removal. Industrial surveying campaigns were carried out and mass balances obtained after laboratory characterization and statistical analysis of operational databases. Nageswararao model for hydrocyclones was calibrated and used in tertiary stage simulation. A black-box model was developed for predicting the benefits of bauxite chemical composition. Five routes for bauxite silica reduction were analyzed considering the inclusion of tertiary stages of desliming in cyclones. Process simulations pointed to a potential solution for the reduction of reactive silica in Paragominas’ bauxite, setting tertiary cyclone in fine classification circuit (26″ cyclones) as the most attractive solution, with a potential silica reduction of 4.9%, with 0.4% loss in metallurgical recovery of alumina.