Bioleaching experiments, electrochemical tests, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were conducted to investigate the intermediates transformation of bornite by Leptospirillum ferriphilum and Acidithiobacillus caldus. The bioleaching experimental results showed that the presence of L. ferriphilum and A. caldus significantly accelerated the bornite bioleaching. In addition, the intermediate species of bornite bioleaching with these two kinds of bacteria were similar. Electrochemical analysis indicated that the dissolution of bornite was an acid-consuming process. The results of XRD showed that intermediate species, namely covellite (CuS), mooihoekit (Cu9Fe9S16) and isocubanite (CuFe2S3), were formed during bornite bioleaching, and a mass of elemental sulfur was formed in the late stage of bioleaching. The Cu 2p photoelectron spectrum revealed that Cu was present in the form of Cu (I) during the bornite bioleaching. Additionally, the S 2p3/2 photoelectron spectrum suggested that S2− and S22− were gradually converted to Sn2−/S0, and the formation of elemental sulfur hindered the further dissolution of the bornite.

Effective biosynthesis of magnetite nanoparticles using current technology is challenging. We investigated the synthesis of nanoparticles by Acidithiobacillus ferrooxidans grown on ferrous iron, elemental sulphur, and mixtures of both substrates. A comparison of tests with different doping amounts of elemental sulphur in ferrous-containing medium showed that the addition of 0.25 and 0.5 M elemental sulphur to the medium resulted in an increased delay of microbial growth and ferrous iron oxidation. TEM suggested that the ferrous material was an essential energy source for the synthesis of nanoparticles in cells. TEM results indicated that the different ratios of ferrous and sulphur had no significant effect on the morphology of bacteria and the size of nanoparticles. High-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), and X-ray absorption near edge structure (XANES) showed that the nanoparticles were composed of magnetite. For the first time, HRTEM and XANES spectra in-situ characterization was conducted to investigate the nanoparticles that were synthesized by A. ferrooxidans. The findings from this study indicated that the different ratios of ferrous and sulphur had no significant effect on size and shape of nanoparticles synthesized by A. ferrooxidans.