Metodologia de avaliação de contaminação ambiental em área de mineração exaurida

Abstract

Mining activity is part of human exploratory activities, from prehistory to the present day, and its importance has been evident over the centuries. With the growth of world mining, the exploration of mineral resources in Brazil also developed, contributing to the formation and development of numerous locations. One of these examples was Minas do Camaquã, in the city of Caçapava do Sul, located in the interior of the state of Rio Grande do Sul. In this place, copper ore was explored, and after decades of exploration, the mine was deactivated and a good part of the tailings and effluents resulting from mining activities were released into the region's streams and/or deposited in the tailings dam. The tailings were stored very close to Arroio João Dias, with only the landfill as a separation between the dam and the beginning of the flooded area. Due to this, the importance of verifying the possibility of contamination and monitoring surface and underground water sources close to these regions was highlighted. With the objective of enabling the environmental monitoring of the area in question, samples were collected and analyzed in six different locations in order to investigate the quality of surface water. Furthermore, one sediment sample and four soil sample were also investigated through chemical analysis. The reading was performed using the X-ray fluorescence spectrometer, for soil and water samples, and the atomic absorption spectrometer, for reading water samples for the element iron (Fe). As a way of investigating the possibility of contamination by metals in the subsurface, the geophysical method of electroresistivity was applied, with the electric path technique, dipole-dipole arrangement in two different locations, one line over the tailings dam and one line over the landfill near Arroio João Dias, both lines are 360 meters long with electrode spacing of 5 meters. Based on geophysics, two 2D profiles of real resistivities were generated, in which the average thickness of the deposited tailings was evaluated, identifying areas of weathered rocks and places of probable percolation of water and/or dissolved metals. In relation to the water, sediment and soil samples, it was possible to qualify 8 (eight) chemical elements in the water samples and 14 (fourteen) chemical elements in the sediment and soil samples, it was also possible to quantify the element Fe (mg/L) in the collected water samples, in order to correlate them with the environment in which they are inserted. From the qualitative results, some elements stood out due to their relationship with the toxicity and contamination of the environment, the main one being cadmium (Cd) which presents an acute toxicity, even at low concentrations. Even without the quantification of all qualified elements in the samples, it was possible to propose a correlation between the elements found and the delimitations of important monitoring zones, mainly in the tailings dam. Finally, the results obtained by the geophysical method and the chemical analyzes were interpolated, thus proposing a geological-geophysical model for evaluating both lines, in addition to proposing an environmental monitoring method for active and inactive mining dams.