Abstract:The application of acidophilic sulfate-reducing bacteria (SRB) for the treatment of acidic mine water has been recently developed to integrate mine water remediation and selective biomineralization. The use of biogenic hydrogen sulfide (H 2 S) produced from the dissimilatory reduction of sulfate to fabricate valuable products such as metallic sulfide nanoparticles has potential applications in green chemistry. Here we report on the operation of a low-pH sulfidogenic bioreactor, inoculated with an anaerobic sediment obtained from an acid river in northern Chile, to recover copper via the production of copper sulfide nanoparticles using biogenic H 2 S. The laboratory-scale system was operated as a continuous flow mode for up to 100 days and the bioreactor pH was maintained by the automatic addition of a pH 2.2 influent liquor to compensate for protons consumed by biosulfidogenesis. The "clean" copper sulfide nanoparticles, produced in a two-step process using bacterially generated sulfide, were examined using transmission electron microscopy, dynamic light scattering, energy dispersive (X-ray) spectroscopy and UV-Vis spectroscopy. The results demonstrated a uniform nanoparticle size distribution with an average diameter of less than 50 nm. Overall, we demonstrated the production of biogenic H 2 S using a system designed for the treatment of acid mine water that holds potential for large-scale abiotic synthesis of copper sulfide nanoparticles.

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Flotation tailings are hazardous due to physical and chemical instability and are currently considered one of the main pollution concerns of mining industry. Most of these tailings are fine-grained residues with low copper content (0.1-0.8%) and include toxic compounds, such as heavy metals, arsenic, and flotation reagents, among others. Another hazard is the generation of acid mine drainage (AMD) due to biological oxidation of tailings. On the other hand, low-grade ore is challenging the mining industry to commercially produce copper.The main objective of this work was to assess the use of flotation tailings and low-grade ore to produce a biologically-produced copper sulfide, as a product for further pyrometallurgical or fine chemistry processing. Low-grade ore and flotation tailings were first agglomerated at different proportions and leaching tests were performed in 1m columns, using either industrial or synthetic raffinate solution. Then, the PLS solution obtained from the column tests was subjected to selective precipitation of copper by using biogenic hydrogen sulfide (H2S) generated by a mixed culture of neutrophilic sulfate reducing bacteria (SRB), enriched from sediments of Caracarani river (located at 4,600 m over sea level in northern Chile).Over 91% of the copper soluble present in the PLS was recovered as copper sulfide in 28 days, while ferrous iron, other metals and arsenic remained in solution. Analysis performed by XRD confirmed the presence of copper in the precipitate (58% as covellite). This work demonstrates the possibility to apply bioleaching and bio-precipitation technologies to treat tailings and low-grade copper ore to produce a high quality copper sulfide.