Bauxite from Pará is constituted by the following layers: nodular (BN), nodular crystallized (BNC), crystallized (BC), crystallized - amorphous (BCBA) and amorphous (BA). From this geological profile only the BC layer is mined, dressed, transported through pipelines and purified in the Bayer process. The BCBA and BA layers have a high content of reactive SiO2 (6-7%) which makes its use unfeasible to the process. A proposal to double bauxite reserves, in accordance with the commercial parameter, depends on a study of characterization and beneficiation to identify the main difficulties for BCBA utilization in the Bayer process. Thus, the goals of this work were the characterization of BCBA bauxite as well as the rheological study to verify the feasibility of this bauxite for alumina production and its transport through pipeline. The characterization of BCBA bauxite used the following techniques: XRF, XRD, IR, SEM/EDS, particle size distribution through wet screening, zeta potential as well as chemical analysis by atomic absorption and potentiometric titration. To study the influence of solids concentration, particle size distribution produced by different grinding times, temperature and pH on the viscosity of bauxite pulp, a matrix experiment 24-1 around mean values was performed. The BCBA bauxite is essentially gibbsitic and is associated with kaolinite and hematite. After the steps of crushing, grinding, and screening this bauxite contains 41.7% of available Al2O3 and 7.1% of reactive SiO2. The XRD and IR identified kaolinite as the phase responsible for the high level of reactive silica in this bauxite. The statistical evaluation of the variables of the pulp preparation indicated that the solid concentration is the most influential variable on viscosity, followed by the influence of particle size and pH.
Bauxite; Reactive Silica; Characterization; Rheology
