O objetivo deste trabalho foi o de simular em escala de laboratório as zonas de oxidação e de redução do bota-fora 4 (bf-4), sendo os experimentos conduzidos em colunas de acrílico, onde o estéril permaneceu sob condições aeradas e inundadas, em experimentos paralelos. O controle dos parâmetros químicos (espécies químicas solubilizadas), físico-químicos (potencial redox, pH e condutividade) e biológicos (atividade bacteriana), foi realizado nas soluções ácidas geradas pelas reações químicas e biológicas ocorridas no estéril. Apesar dos resultados obtidos referenciarem-se a um período de quatro meses, alguns pontos de relevância puderam ser evidenciados e servirão de base para o necessário aprofundamento das pesquisas. A caracterização mineralógica identificou a existência de sulfetos de baixos potenciais de oxidação associados a pirita, o que explica as concentrações mais elevadas de zinco em solução do que de ferro. Por outro lado, a pirita ocorre em pequena quantidade (menos de 0,2%), apresentando grau de liberação em torno de 80 micrometros, o que lhe confere uma atividade química intermediária (a do tipo framboidal <5 micrometros, e a que apresenta maior reatividade).

Considering the planned closure of the first uranim mine and milling plat operating in Brazil, located in the Poços de Caldas Plateau, in the state of Minas Gerais, in the next two years, there is the need to obtain basic informations for its decommissioning. Special attention has been directed to the following critical áreas: open pit, taillings dam and waste rock piles, because these are the main sources of acid drainage generation. These Waters cannot be allowed to flow in the external environment because in addition to sulphuric acid, there is a number of elements in concentration above those allowed by regulations. Among the waste piles (bota-foras BF) two of them BF-4 and BF-8, are in a processo f acid generation, thus requiring more attention. The objective of this work was to simulate at the laboratory scale the oxidation and reduction zones of BF-4. The experiments were conducted in acrylic columns, where the waste sample was kept under aerated conditions and under saturated conditions, in different columns. The controlo f the chemical (solubilized chemical species), physico-chemical (redox potential, pH, conductibity) and biological (bacterial activity) parameters has been carried out solely on the acid solutions generated by the chemical and biological reactions that occur at the waste. Although the results refer to a four month period, some relevant points can be highlighted, which will serve as a basis for further research.Tineralogical characterization identified the existence of other sulphides associated to pyrite with lower oxidation potential than the later. This explains the higher concentration of zinc as compared to iron. On the other hand, the pyrite occurs in low quantity (less than 0.2%) with pyrite granules around 80µm in diameter which allow an intermediar chemical reactivity (the framboidal form with granules less than 0,5µm in diameter is the most reactive). Although the material is constituted of alcaline rock with moderated chemical reactivity (in comparison the carbonates presente high reactivity), the particle size analysis indicated that due to the natural weathering, this material has more than 20% in the silt and clay fractions, which confers a high chemical reactivity. The results obtained with the biological characterization for the two conditions studied revealed that the bacterial activity is more intense in the region in contact with air, than in the saturated region. It is thus concluded that the acid generation at the top of the pile is governed by a biological mechanism, while at the lower region the chemical mechanism prevails, mainly due the constant presence of a dumped watercourse. Once that acid is generated and consequently the reactions process is started, all the elements involved (except iron and calcium) are present in higher concentratio9ns at the aerated conditions. Iron could not be present in solution due to pH values in the range of 3.0 3.5.It is interesting to note that this pH range coincides with field monitoring for a long period of time. Although a more detailed research is needed, the results of this study indicate that, due the mineralogical characteristics of the material, the aluminosilicates presente in the waste pile act as a buffer. On the other hand, bacause the permanente infiltrations occuring in the pile, the problem of acid generation is not restricted to oxygen access. There is the necessity of hidrogeological studies to elucidate the role of the infiltration of underground water.