Abstract
sMining waste rocks containing sulfide minerals naturally provide the habitat for iron- and sulfur-oxidizing microbes, and they accelerate the generation of acid mine drainage (AMD) by promoting the oxidation of sulfide minerals. Sulfate-reducing bacteria (SRB) are sometimes employed to treat the AMD solution by microbial-induced metal sulfide precipitation. It was attempted for the first time to grow SRB directly in the pyritic heap bioleaching residue to compete with the local iron- and sulfur-oxidizing microbes. The acidic SRB and iron-reducing microbes were cultured at pH 2.0 and 3.0. After it was applied to the acidic heap bioleaching residue, it showed that the elevated pH and the organic matter was important for them to compete with the local bioleaching acidophiles. The incubation with the addition of organic matter promoted the growth of SRB and iron-reducing microbes to inhibit the iron- and sulfur-oxidizing microbes, especially organic matter together with some lime. Under the growth of the SRB and iron-reducing microbes, pH increased from acidic to nearly neutral, the Eh also decreased, and the metal, precipitated together with the microbial-generated sulfide, resulted in very low Cu in the residue pore solution. These results prove the inhibition of acid mine drainage directly in situ of the pyritic waste rocks by the promotion of the growth of SRB and iron-reducing microbes to compete with local iron and sulfur-oxidizing microbes, which can be used for the source control of AMD from the sulfidic waste rocks and the final remediation.
Highlights
Mining activities produce large volumes of waste, comprising mainly sub-economic waste rock and tailings
The microbial community in pH 2.0 bottle showed the dominant phylum of Archean Euryarchaeota and bacteria Proteobacteria (Figure 1), of which the Archean Ferroplasma species is most abundant (61.8%), and bacteria Acidophilium (23.0%), and about 5.5% of the sulfate-reducing bacteria Clostridiaceae, and very few Acidithiobacillus (
Ferroplasma and Acidophilium both grew in the acid condition, with the capacity to anaerobically degrade the organic matter and reduce Fe3+ to Fe2+
Summary
Mining activities produce large volumes of waste, comprising mainly sub-economic waste rock and tailings. SRB bacteria are usually employed to treat an AMD solution by growing SRB in the AMD solution, through the microbial process of metal- and sulfate-reducing, and producing alkalinity, and attenuating the movement of metals by the precipitation of sulfide minerals [11,12] These processes are exploited in ex situ treatment of AMD after it comes out from the rocks [13,14,15]. The heap bioleaching residue is used to study the bioremediation process of SRB and iron reducing microbes for competition with the local autotrophic bioleaching microbes under the acidic condition, the SRB community succession during the remediation, and the influencing factors, for implication to the source control of AMD from the acid-generating rocks in situ
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