Abstract
Fluvial sediments, soils, and natural waters in northern Chile are characterized by high arsenic (As) content. Mining operations in this area are potential sources of As and other metal contaminants, due to acid mine drainage (AMD) generation. Sulfate Reducing Bacteria (SRB) has been used for the treatment of AMD, as they allow for the reduction of sulfate, the generation of alkalinity, and the removal of dissolved heavy metals and metalloids by precipitation as insoluble metal sulfides. Thus, SRB could be used to remove As and other heavy metals from AMD, however the tolerance of SRB to high metal concentrations and low pH is limited. The present study aimed to quantify the impact of SRB in As removal under acidic and As-Fe-rich conditions. Our results show that SRB tolerate low pH (up to 3.5) and high concentrations of As (~3.6 mg·L−1). Batch experiments showed As removal of up to 73%, Iron (Fe) removal higher than 78% and a neutralization of pH from acidic to circum-neutral conditions (pH 6–8). In addition, XRD analysis showed the dominance of amorphous minerals, while Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy (SEM-EDX) analysis showed associations between As, Fe, and sulfur, indicating the presence of Fe-S-As compounds or interaction of As species with amorphous and/or nanocrystalline phases by sorption processes. These results indicate that the As removal was mediated by acid/metal-tolerant SRB and open the potential for the application of new strains of acid/metal-tolerant SRB for the remediation of high-As acid mine waters.
Highlights
Arsenic (As) is a ubiquitous and toxic trace metalloid, which is widely distributed in natural environments [1]
These results suggest that Sulfate Reducing Bacteria (SRB) can tolerate high concentrations of As and Fe in solid and dissolved phases, and can develop metal resistance mechanisms to protect their cellular components
Our results indicate that acid/metal-tolerant SRB could be decisive for mechanism is relevant the As removal, as integration mediated of byboth acid/metal-tolerant
Summary
Arsenic (As) is a ubiquitous and toxic trace metalloid, which is widely distributed in natural environments [1]. In the Azufre River sub-basin, the release of contaminants from natural and anthropogenic sources negatively impact the quality of rivers and surface waters. In this area, hydrothermal waters emerge with high concentrations of dissolved As (>3 mg·L−1 ), iron (Fe) (>80 mg·L−1 ), and a pH lower than. The As occurrence in fluvial waters is linked to the presence of ferric Fe(III)-oxyhydroxide ores, because As is sorbed onto these minerals [6]. Arid and semiarid climates strongly contribute to the generation of As-rich waters, due to high evaporation rates that concentrate surface runoff [7]. Little is known about the microbial speciation, precipitation/dissolution, or sorption processes that are involved in the fate of As in these systems and how they could be optimized in treatment systems
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