Competitive Growth of Sulfate-Reducing Bacteria with Bioleaching Acidophiles for Bioremediation of Heap Bioleaching Residue

Abstract

Mining waste rocks containing sulfide minerals naturally provide the habitat for ironand 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 ironand 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. drainage (AMD) through oxidation [1][2][3]. Drainage from mining activities is often acidic and also frequently associated with high concentrations of heavy metals and metalloids. It is considered to be one of the most important sources for heavy metal contamination in the environment [4].When exposed to the atmosphere, sulfide minerals in the waste rocks are oxidized under water and oxygen, and then generate acid, make the environment of the waste rock acidified. The dissolution of sulfide minerals relies to a large extent on the chemical and microbiological processes caused by the reaction of the oxidant Fe 3+ and the activity of natural iron-and sulfur-oxidizing microorganisms [5]. The Fe 3+ is more aggressive and effective than O 2 for pyrite oxidation in acidic conditions [6][7][8][9]. Iron sulfide minerals such as pyrite usually provide the source of oxidant Fe 3+ . Pyrite usually acts as the most important source of AMD, since it is the most abundant sulfide minerals on earth [10].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]. However, a few researchers have used the SRB directly to treat the acid-generating waste rocks in situ to inhibit the ox...

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