Análise de infiltração de canal de desvio e contribuição na geração de drenagem ácida de mina em pilha de rejeito de mineração de urânio
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Data
2022-04-13
Autores
Nascimento, Matheus Mistrinel Pacine Feitoza do
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Universidade Estadual Paulista (Unesp)
Resumo
A drenagem ácida de mina (DAM) é um problema comum a muitas minerações em cujos depósitos ocorrem sulfetos como minerais de minério ou associados. Este processo natural decorre da oxidação de sulfetos minerais como a pirita e posterior interação com água, com a geração de sulfato e ácido sulfúrico. Na indústria mineral este problema é agravado como consequência do acúmulo e da maior exposição desses minerais reativos aos agentes atmosféricos. É neste contexto que está inserida a Mina Osamu Utsumi (MOU), a primeira a lavrar e beneficiar minério de urânio no Brasil, administrada pelas Indústrias Nucleares do Brasil (INB). A mina está localizada no Maciço Alcalino de Poços de Caldas num contexto geológico caracterizado por rochas alcalinas como a nefelina-sienito, além de mineralizações uraníferas com altos teores de sulfetos. Durante sua operação foram movimentados milhões de toneladas de rejeitos que tiveram como destino final os bota-foras (BF) da mina, onde eram depositados o material proveniente do decapeamento e rochas com baixo teor de urânio. Atualmente a mina está num processo de descomissionamento, que compreende o período pós-encerramento das atividades no qual é preciso lidar com os passivos ambientais. A drenagem ácida de mina é o mais complexo dos passivos ambientais presentes na área. Os materiais foram lançados na área sob a forma de ponte de aterro, que promoveu o rearranjo das frações granulométricas em partículas mais grossas embaixo e as mais finas em cima. Este fato somado à heterogeneidade do material depositado permite que o BF-04 funcione como um sistema hidrogeológico permeável ao fluxo de água e oxigênio, ambos reativos aos sulfetos existentes. Um fator agravante é a presença do canal de desvio da antiga drenagem que fluía pelo vale (córrego da Consulta) e que foi posicionado na lateral NW do BF-04 em canal escavado diretamente em solo e rocha. Diante do exposto, esta pesquisa visa avaliar a influência da infiltração de águas do canal de desvio e a contribuição na geração de drenagem ácida de mina no interior do BF-04. Neste estudo são empregados os métodos geofísicos da Eletrorresistividade e da Polarização Induzida, obtidos de forma simultânea por meio de linhas de tomografia elétrica. Os modelos de inversão 2D realçam zonas de baixa resistividade (~50 Ω.m) em semelhança com resultados obtidos em estudos anteriores em áreas de fluxo de DAM. Também foi possível identificar zonas de alta cargabilidade (~10mV/V) em zonas de fluxo de água proveniente do canal de desvio e no interior do BF-04. Tais evidências indicam a efetiva contribuição do canal de desvio na geração de DAM no interior do BF-04 e a necessidade de sua impermeabilização para redução deste passível ambiental.
Acid mine drainage (AMD) is a problem common to many mines where sulfides occur in their deposits as ore or associated minerals. This natural process results from the oxidation of mineral sulfides such as pyrite and subsequent interaction with water, with the generation of sulfate and sulfuric acid. In the mineral industry this problem is aggravated as a consequence of the accumulation and greater exposure of these reactive minerals to atmospheric agents. This is where the Osamu Utsumi Mine (MOU), the first to mine and benefit uranium ore in Brazil, administered by the Indústrias Nucleares do Brasil (INB). The mine is located in the Alkaline Massif of Poços de Caldas in a geological context characterized by alkaline rocks such as nepheline-sienite in addition to uraniferous mineralizations with high sulfide contents. During its operation millions of tons of tailings were moved, which had as their final destination the waste rock piles (BF) of the mine where the material from the mine stripping and rocks with low uranium content were deposited. Currently the mine is in a process of decommissioning which comprises the post-closure period of activities in which environmental liabilities need to be dealt with. Acid mine drainage is the and the need for its waterproofing to reduce this environmental liability most complex of environmental liabilities present in the area. The materials were released in the area in the form of a landfill bridge, which promoted the rearrangement of the granulometric fractions in thicker particles underneath and the thinner ones on top. This fact added to the heterogeneity of the deposited material allows BF-04 to function as a hydrogeological system permeable to the flow of water and oxygen, both reactive to existing mineral sulfides. An aggravating factor is the presence of the bypass channel of the old drainage that flowed through the valley (Consulta stream) and that was positioned on the NW side of the BF-04 in a channel dug directly into soil and rock. In view of the above, this research aims to evaluate the influence of water infiltration of the diversion channel and the contribution to the generation of acid mine drainage inside the tailings. In this study, the geophysical methods of Electrical Resistivity (ER) and Induced Polarization (IP) are employed, obtained simultaneously by means of electrical tomography lines. The 2D inversion models highlight zones of low resistivity (~ 50 Ω.m) in similarity to results obtained in previous studies in areas of AMD flow. It was also possible to identify high chargeability zones (~10 mV/V) in water flow zones from the bypass channel and inside the waste rock pile (BF-04). Such evidence indicates the effective contribution of the diversion channel in the generation of AMD inside the BF-04 and the need for its waterproofing to reduce this environmental liability.
Acid mine drainage (AMD) is a problem common to many mines where sulfides occur in their deposits as ore or associated minerals. This natural process results from the oxidation of mineral sulfides such as pyrite and subsequent interaction with water, with the generation of sulfate and sulfuric acid. In the mineral industry this problem is aggravated as a consequence of the accumulation and greater exposure of these reactive minerals to atmospheric agents. This is where the Osamu Utsumi Mine (MOU), the first to mine and benefit uranium ore in Brazil, administered by the Indústrias Nucleares do Brasil (INB). The mine is located in the Alkaline Massif of Poços de Caldas in a geological context characterized by alkaline rocks such as nepheline-sienite in addition to uraniferous mineralizations with high sulfide contents. During its operation millions of tons of tailings were moved, which had as their final destination the waste rock piles (BF) of the mine where the material from the mine stripping and rocks with low uranium content were deposited. Currently the mine is in a process of decommissioning which comprises the post-closure period of activities in which environmental liabilities need to be dealt with. Acid mine drainage is the and the need for its waterproofing to reduce this environmental liability most complex of environmental liabilities present in the area. The materials were released in the area in the form of a landfill bridge, which promoted the rearrangement of the granulometric fractions in thicker particles underneath and the thinner ones on top. This fact added to the heterogeneity of the deposited material allows BF-04 to function as a hydrogeological system permeable to the flow of water and oxygen, both reactive to existing mineral sulfides. An aggravating factor is the presence of the bypass channel of the old drainage that flowed through the valley (Consulta stream) and that was positioned on the NW side of the BF-04 in a channel dug directly into soil and rock. In view of the above, this research aims to evaluate the influence of water infiltration of the diversion channel and the contribution to the generation of acid mine drainage inside the tailings. In this study, the geophysical methods of Electrical Resistivity (ER) and Induced Polarization (IP) are employed, obtained simultaneously by means of electrical tomography lines. The 2D inversion models highlight zones of low resistivity (~ 50 Ω.m) in similarity to results obtained in previous studies in areas of AMD flow. It was also possible to identify high chargeability zones (~10 mV/V) in water flow zones from the bypass channel and inside the waste rock pile (BF-04). Such evidence indicates the effective contribution of the diversion channel in the generation of AMD inside the BF-04 and the need for its waterproofing to reduce this environmental liability.
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Palavras-chave
Mineração, Drenagem ácida de mina, Pilha de rejeito, Eletrorresistividade, Polarização induzida, Mining, Acid mine drainage, Waste rock pile, DC resistivity, Induced polarization