Mapeamento em subsuperfície com método de eletrorresistividade e ensaios geoquímicos para caracterização do perfil em profundidade da barragem de rejeito da antiga Minas do Camaquã, RS

Abstract

Mining tailings are associated with several environmental impacts. They are generated in large quantities, and therefore need large areas for their disposal. Tailings dams are a form of disposal and can cause major environmental disasters. Also, even after the activities are closed, the area remains an environmental liability, and there may be nutritive problems in the soil for revegetation and the emergence of serious erosive processes, which will imply in loss of soil and transport of sediments to the surrounding water bodies. Thus, the objective of this study was to analyze the profile of an old tailings dam in Minas do Camaquã, RS. For this, the geophysical method of electroresistivity was used to map the area in depth, using five lines covering different areas of the dam. After interpreting the results, points were selected for sampling in four of the five lines. The samples were prepared and analyzed in geochemical tests (pH in paste and NAG liquid acidity generation test) and elemental analysis (EDXRF). Regarding geophysics, significant differences were observed in at least three layers, where the most superficial and with lower resistivity characterizes the tailings itself, varying up to 10 meters in depth. The pH measured by pH in paste is not acidic, as well as the results obtained by the NAG test, where all samples are around pH 8 in both tests. The elemental analysis shows Si, Al, Fe, Mg and K as predominant components, indicating the presence of silicate minerals and Fe and Al oxides. From this and from the methodologies used in this study and for the samples tested, the material has no evidence of acidity generation and contamination risks regarding the investigated metals. However, it should be noted that the dam has large areas of exposed soil or with little vegetation cover and serious erosion problems, which can be a source of particulate matter as well as cause an increase in the contribution of sediments to nearby water bodies.