A influência de algumas variáveis sobre a reologia de polpas minerais

Abstract

The study about slurrys rheology behavior has been showing a great importance due to the utilization of ores more and more slender. Nowadays, the slurry is present in several stages during processing due to the poor ore that has been processed. With the knowledge about the rheological characteristics, its possible to improve the performance of operations as: milling, cycloning and pipeline transport. When the topic is about slurrys transport from large distances, the determination of therheological characteristics becomes primordial to project pumps and pipelines. Currently, the utilization of pipeline as an alternative way for the railways transport has been studied a lot. Another similar application is the rejects pumping with high percentages of solids in mass (mineral paste) for the barrages, decreasing the necessary area to the rejects arrangement, avoiding the water recirculation and economizing energy.Rheology studies the fluids behavior when a tension is putting in practice. Fluids can be classified as Newtonians or Non-Newtonians. Besides this classification, Non- Newtonians fluids can be classified in: dilatant, pseudoplastic, pseudoplastic with yield stress e Binghams plastic.Another fluids classification is the function of dependence with time: It could be thixotropic or rheopectics. The thixotropics fluids are those that present a viscosity decrease with time, when subdue constant shear rate. Meantime, rheopectics fluids present a viscosity increase with time.This dissertation has the purpose of study the rheological behavior of a slurry that contain hematite, with a high degree of purity, through the determination of viscositys values, slump and yield stress for slurries with different solids concentration in weight. The mineral sampler was described with chemistry and mineralogy composition, density and size distribution. Tests was done to determine the zero charges point, and for rheological characteristics study. About the results obtained, can be concluded: the studied slurry has high purity (97% of hematite), owns 85% of pass in 44 m, the solids density is high (5 g/cm³), the zeropoints charge is in pH 6,8. About the rheological behavior, slurry showedcharacteristics of a rheopetic fluid. Besides, have knowledge of dependence between slurrys solids concentration and yield stress and this relation isnt linear. Just slurries with solids concentration in mass above 78% obtained yield stress results. For slurries with solids concentration above 78%, pH was changed to 11, using caustic soda. The addition of a base to increase pH causes a dispersion of the slurry and herewith tension necessary for shear (yield stress) is smaller. When pH of the slurry with solids concentration in 78% had been changed, it didnt obtained results for yield stress, but with natural slurry (pH 8,18) obtained result was close to 10,9 Pa.