Comparação entre modelagem numérica e experimento de campo em escala real para um sistema de cobertura na Mina Fazenda Brasileiro (Bahia)

Abstract

The concern about the closure of mines after the end of their activities is recent in Brazil, where discussions about this subject began only some years ago. Here, in most cases, the mining wastes are disposed in mud form inside reservoirs formed by dams or dikes constructed using the mining tailings themselves. A well-designed cover system constructed over the tailings at the end of the reservoir life is essential to minimize environmental impacts. In this research, field experiments were performed simulating different cover systems for a mining waste reservoir. The experiment was installed at Mina Fazenda Brasileiro (MFB), located near the city of Teofilândia in the state of Bahia, Brazil. This company explores gold from both underground and open-pit mining operations. The tailings disposal system has been operating since 1988 and consists of a set of dams forming sequential lakes. Different cover systems were designed and placed over the lysimeters especially constructed for these experiments in real scale and filled with mining wastes. These lysimeters were instrumented and monitored during approximately a year. The experimental cover system was composed by one evapotranspirative layer placed over a capillary barrier layer. The thickness and position of these layers varied from lysimeter to lysimeter. The geotechnical properties of the materials used to construct the cover systems were measured in laboratory. Volumetric water content sensors were fixed inside the cover layers and tailings and the volume of fluid percolated through the lysimeter was also measured. The analysis of the water flow through the cover system and the lysimeter were performed by the software Vadose/W. The data measured from the field experiments were compared to those of the numerical modeling allowing the adjustment of the parameters used by the model. It was possible to compare different designs of cover systems to verify the most efficient one.