Abstract
The risk of generation of acid drainages in the tailings of the Pan de Azúcar mine that closed its activities more than three decades ago, was evaluated through biooxidation studies using iron- and sulfur-oxidizing extremophilic leaching consortia. Most of tailings showed a high potential for generating acid drainage, in agreement with the results from net acid generation (NAG) assays. In addition, molecular analysis of the microbial consortia obtained by enrichment of the samples, demonstrated that native leaching microorganisms are ubiquitous in the area and they seemed to be more efficient in the biooxidation of the tailings than the collection microorganisms. The acid drainages detected at the site and those formed by oxidation of the tailings, produced a significant ecotoxicological effect demonstrated by a bioassay. These drainages, even at high dilutions, could seriously affect a nearby Ramsar site (Laguna de Pozuelos) that is connected to the Pan de Azúcar mine through a hydrological route (Cincel River).
Highlights
Acid mine drainage (AMD) is a highly acidic wastewater rich in heavy metals and metalloids
The first step in the formation of AMD is the oxidation of metal sulfides such as pyrite that are capable of generating acidity
The acidophilic communities involved in AMD generation are very complex and include several microbial species; their composition and dynamics under different conditions have been widely documented [13,14,15,16,17,18,19,20]
Summary
Acid mine drainage (AMD) is a highly acidic wastewater rich in heavy metals and metalloids. The first step in the formation of AMD is the oxidation of metal sulfides such as pyrite that are capable of generating acidity. This reaction involves oxygen as the first oxidizing agent. Other metallic sulfides can be oxidized through similar processes by releasing the respective metals into solution In some of those cases, polysulfides and elemental sulfur can be the intermediates that are oxidized by the action of the same microorganisms [23,24]. The risks of acid drainage generation in the different zones of the stratified tailings dam (DC2) were analyzed through a biooxidation test using extremophilic acidophilic microorganisms. The ability of native and collection microorganisms to oxidize the tailings and the role of iron- or sulfur-oxidizing microorganisms were compared
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