Avaliação da velocidade de queda e do processo de sedimentação de rejeito de minério de ferro

Abstract

In mining, sediment transport studies aid the design of sediment containment structures and hypothetical dam break studies. Uncertainties in mining studies arise from the predominant focus of sediment transport research, which is concentrated on the analysis of natural river sediments. Therefore, It is necessary to understand the characteristics of iron ore tailings, according to their mineralogical composition and the beneficiation processes to which they were subjected, that may alter their behavior in sediment transport, mainly concerning the deposition process. Among the parameters necessary for evaluating sedimentation, the particle settling velocity (ωs) and the velocity variation for different concentrations (ωc) stand out. In addition, it is also essential to evaluate how the sediment is transported in a flow and how diffusion occurs. Therefore, this dissertation characterized filtered iron ore tailings from a mine in Minas Gerais and natural sediment from the Salto do Paraopeba PCH reservoir. It estimated the particle settling velocity from the analysis of images of a settling column and the variation of velocity for different concentrations for the fine fraction (silt and clay) of the tailings with the graduated cylinder test. The research also evaluated the tailings sedimentation process in a channel under constant flow and concentration conditions. The tailings sample consists of fine silty sand with a sandy fraction composed mainly of silica, with a specific mass of 2,70 g/cm³, and a fine fraction of iron oxides and silica, with 4,00 g/cm³. The natural sediment comprises silica, aluminum, and iron, with 2,90 g/cm³ obtained by EDS-MEV analysis. In addition, the shape and roundness of the particles were estimated through images from the microscopy test, which resulted in an Sf close to 0.4 and 0.6 and a P close to 2.2 and 2.1 for the tailings and the natural sediment, respectively. The results of the particle settling velocity of the natural sediment were higher than those of the tailings for the sandy fraction, related to the lower specific mass of the tailings and their more angular shape. The equation that indicated the best fit was developed by Cheng (1997) for both materials. Other equations indicated satisfactory results regarding the Nash- Sutcliffe efficiency coefficient and RMSE. The graduated cylinder test indicated a behavior of decreasing settling velocity with increasing concentration, with the Hwang (1989) equation being the one that best described the behavior. In an experimental channel, the formation of a density current and the deposition of tailings along the channel were observed, identifying the formation of the current's vortices, head, and body. Chen's equation (1975) best estimated the channel retention efficiency. It was concluded that sediment characterization, including grain size distribution, specific mass, and origin, is fundamental for applying sediment transport equations and factors such as water temperature, concentration, and flow conditions.