Reactive Silica Reduction in Brazilian Bauxite via Selective Grinding: Mineralogical and Physicochemical Insights into Kaolinite Behavior

The use of bauxite ores with high silica content has emerged as a critical aspect in meeting the growing demands of the aluminum industry. However, the presence of reactive silica, predominantly occurring as kaolinite, presents major challenges in processing Brazilian bauxite ores, leading to increased red mud production during alumina refining. This study investigates the beneficiation of bauxite from Pará, Brazil, with emphasis on the selective removal of reactive silica through grinding and washing techniques. A thorough physicochemical characterization was conducted employing a suite of characterization techniques, including wet chemical analysis, XRD, FTIR, XRF, SEM-EDS, thermal analysis (TGA-DTG), and zeta potential measurements. The results revealed kaolinite as the dominant silicate phase, closely associated with gibbsite particles. The beneficiation process reduced reactive silica content from 10.4 wt% to 5.3 wt%, with granulometric analysis confirming its preferential concentration in finer fractions. Zeta potential measurements indicated positive surface charges across a wide pH range (2.0 to 10.5), suggesting favorable electrostatic interactions between kaolinite and gibbsite. These findings provide insights into the behavior of silicate minerals in bauxite and support the development of silica-targeted beneficiation strategies to improve alumina production efficiency and reduce environmental impact.