Abstract
Acid Mine Drainage (AMD) is an environmental problem associated with mining activities, which resulted from the exposure of sulfur bearing materials to oxygen and water. AMD is a pollution source due to its extreme acidity, high concentration of sulfate, and soluble metals. Biological AMD treatment is one alternative to couple environmental amelioration for valuable dissolved metals recovery, as a new source of raw materials. Covellite (CuS) particles were synthetized from an AMD sample collected in a Brazilian copper mine, after 48 and 96 h of exposure to hydrogen sulfide (H2S) produced in a bioreactor containing acidophilic sulfate reducing bacteria (SRB). The time of exposure affected the morphology, nucleation, and size of CuS crystals. CuS crystals synthetized after 96 h of H2S exposure showed better ordination as indicated by sharp and intense diffractograms obtained by X-ray diffraction (XRD), and the predominance of placoid sheets with hexagonal habit structure as observed by scanning electrons microscopy (SEM). Energy dispersive X-ray fluorescence (EDXRF) spectrometry indicated a Cu:S molar ratio in agreement with CuS. Granulometric analysis demonstrated that 90% of CuS particles were less than 22 µm size. AMD biological treatment is a potential economical CuS recovery option for metallurgical process chain incorporation, or new industrial applications, since the alteration of synthesis conditions can produce different crystal forms with specific characteristics.
Highlights
Acid mine drainage (AMD) is an acidic and metal-rich effluent that occurs as a result of mineral sulfides exposure to water, oxygen, and iron/sulfur oxidizing bacteria, such as Acidithiobacillus ferrooxidans and A. thiooxidans, among others
The main advantage of Acid Mine Drainage (AMD) bioremediation by sulfate reducing bacteria (SRB) is the absence of sludge generation—excluding transport and storage costs—in addition to the selective soluble valuable metals recovery that can alleviate treatment costs
The aim of this work was to optimize the synthesis of covellite crystals by exposing real AMD, collected from a copper mine in the Amazon region, to hydrogen sulfide (H2 S) produced by a sulfidogenic bioreactor
Summary
Acid mine drainage (AMD) is an acidic and metal-rich effluent that occurs as a result of mineral sulfides (e.g., pyrite) exposure to water, oxygen, and iron/sulfur oxidizing bacteria, such as Acidithiobacillus ferrooxidans and A. thiooxidans, among others. AMD can reach extremely low pH (20.000 g/L) and soluble metals/metalloids concentrations [1], comprising an environmental thread and a pollution source for groundwater, rivers, and soils [2]. Chemical AMD remediation by the addition of alkaline substances is the most common approach adopted for pH neutralization and metals/metalloids precipitation. Metals 2019, 9, 206 toxic slurry composed by metal hydroxides and carbonate precipitates that must be safely removed and stored to avoid environmental contamination, thereby raising treatment costs [4]. The main advantage of AMD bioremediation by SRB is the absence of sludge generation—excluding transport and storage costs—in addition to the selective soluble valuable metals recovery that can alleviate treatment costs
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