A MATHEMATICAL APPROACH FOR ESTIMATING SILICA REDUCTION IN BAUXITE DESLIMING WITH HYDROCYCLONES

Bauxite is the main ore for metallic aluminum production, consisting of aluminum and iron oxides/hydroxides 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 hydro-cyclones. In the Bayer process, kaolinite reacts with sodium hydroxide, increasing reagent consumption in the process. The beneficiation process at Hydro Mineração Paragominas is based on the separation of coarser fractions with higher gibbsite content from the clay minerals, where kaolinite is also more concentrated. Test trials were carried out in a pilot plant using a 254 mm diameter cyclone, aiming at a reduction on clay particles bypass and, consequently, a bauxite product with lower levels of kaolinite. In this context, an approach based on mathematical modelling and process simulations for a tertiary desliming stage, combined with granulochemical vectors analysis, was developed, and validated through pilot tests, allowing the calculation of mass and metallurgical recoveries of the elements of interest for different tertiary circuits and cyclones configurations, enabling the scale-up of the potential for reducing reactive silica for the industrial plant. Overall, the integration of model fitting, process simulations and granulochemical analysis demonstrated a comprehensive and systematic approach toward improving the efficiency and quality of the bauxite desliming process. The simulation approach showed an average potential reduction of 2.4 percentual points (absolute) in reactive silica while actual reduction on pilot tests was 2.6 percentual point, with no significative statistical difference observed between simulation and actual results.