Bionanomining of copper-based nanoparticles using pre-processed mine tailings as the precursor

The bacterial synthesis of copper nanoparticles emerges as an eco-friendly alternative to conventional techniques since it comprises a single-step and bottom-up approach, which leads to stable metal nanoparticles. In this paper, we studied the biosynthesis of Cu-based nanoparticles by Rhodococcus erythropolis ATCC4277 using a pre-processed mining tailing as a precursor. The influence of pulp density and stirring rate on particle size was evaluated using a factor-at-time experimental design. The experiments were carried out in a stirred tank bioreactor for 24 h at 25 °C, wherein 5% (v/v) of bacterial inoculum was employed. The O₂ flow rate was maintained at 1.0 L min^-1 and the pH at 7.0. Copper nanoparticles (CuNPs), with an average hydrodynamic diameter of 21 ± 1 nm, were synthesized using 25 g.L^-1 of mining tailing and a stirring rate of 250 rpm. Aiming to visualize some possible biomedical applications of the as-synthesized CuNPs, their antibacterial activity was evaluated against Escherichia coli and their cytotoxicity was evaluated against Murine Embryonic Fibroblast (MEF) cells. The 7-day extract of CuNPs at 0.1 mg mL^-1 resulted in 75% of MEF cell viability. In the direct method, the suspension of CuNPs at 0.1 mg mL^-1 resulted in 70% of MEF cell viability. Moreover, the CuNPs at 0.1 mg mL^-1 inhibited 60% of E. coli growth. Furthermore, the NPs were evaluated regarding their photocatalytic activity by monitoring the oxidation of methylene blue (MB) dye. The CuNPs synthesized showed rapid oxidation of MB dye, with the degradation of approximately 65% of dye content in 4 h. These results show that the biosynthesis of CuNPs by R. erythropolis using pre-processed mine tailing can be a suitable method to obtain CuNPs from environmental and economical perspectives, resulting in NPs useful for biomedical and photocatalytic applications.