Direct Detection of Fe(II) in Extracellular Polymeric Substances (EPS) at the Mineral-Microbe Interface in Bacterial Pyrite Leaching.

We herein investigated the mechanisms underlying the contact leaching process in pyrite bioleaching by Acidithiobacillus ferrooxidans using scanning transmission X-ray microscopy (STXM)-based C and Fe near edge X-ray absorption fine structure (NEXAFS) analyses. The C NEXAFS analysis directly showed that attached A. ferrooxidans produces polysaccharide-abundant extracellular polymeric substances (EPS) at the cell-pyrite interface. Furthermore, by combining the C and Fe NEXAFS results, we detected significant amounts of Fe(II), in addition to Fe(III), in the interfacial EPS at the cell-pyrite interface. A probable explanation for the Fe(II) in detected EPS is the leaching of Fe(II) from the pyrite. The detection of Fe(II) also indicates that Fe(III) resulting from pyrite oxidation may effectively function as an oxidizing agent for pyrite at the cell-pyrite interface. Thus, our results imply that a key role of Fe(III) in EPS, in addition to its previously described role in the electrostatic attachment of the cell to pyrite, is enhancing pyrite dissolution.

Speciation of antimony in PET bottles produced in Japan and China by X-ray absorption fine structure spectroscopy.

The oxidation state and coordination environment of antimony (Sb) incorporated into polyethylene terephthalate (PET) bottles were estimated based on X-ray absorption fine structure (XAFS) at Sb K-edge. Prior to XAFS analyses, Sb concentrations in 177 PET bottles collected in Japan and China were determined, showing that 30.5% and 100% of Japanese and Chinese PET bottles, respectively, contained more than 10 mg/kg of Sb. Most of the bottles used for aseptic cold filling and carbonated drinks contained a larger amount of Sb. Extended X-ray absorption fine structure (EXAFS) showed that the first neighboring atom of Sb in PET was estimated to be oxygen with a coordination number of about three. In addition, the contribution of Sb to Sb shell was discounted in the EXAFS, showing that Sb was not present as Sb2O3 in PET, although Sb was initially added as Sb2O3 in the production of PET. This information is consistent with the coordination environment estimated from the polycondensation reaction catalyzed by Sb, where Sb can be present as either Sb glycolate or Sb glycolate binding to the end group of the PET polymer. X-ray absorption near-edge structure (XANES) showed that Sb(III) initially added as Sb2O3 into PET was partially oxidized and the Sb(V) fractions reached approximately 50% in some samples. However, the oxidation state and coordination environment of Sb in PET had no relationship with the concentrations of Sb that leached into water from PET. Based on the present XAFS results and previous studies on the effects of temperature and others, it was concluded that the leaching behavior of Sb into water is primarily due to the degradation of PET itself, but is not related to the Sb species in the PET bottles.