Identification of pyrite using ⁵⁷Fe Mössbauer spectroscopy in core sediments from Erhai Lake, SW China combined with a series of acidic pre-treatments

Summary

A method has been developed for analyzing pyrite quantitatively in the sediments of Erhai Lake in southwest China using ⁵⁷Fe Mössbauer spectroscopy combined with a series of acidic pre-treatments. Following a washing with an alkaline solution (0.1N NaOH), the sediment samples were successively treated using HCl, HF, and then HCl (65 °C). The residues thus prepared were analyzed for pyrite using ⁵⁷Fe Mössbauer spectrometry. The presence of pyrite was also confirmed in the acidic residues of the sediments using sulfur K-edge X-ray absorption near edge structure. This method can be used to measure pyrite in aquatic sediments, especially when the concentration of pyrite is very low and the particles of pyrite are small or the crystallinity is low, and even in amorphous status. In addition, vertical variations of pyrite contents are positively correlated with organic matter and negatively correlated with hematite, superfine paramagnetic ferric iron and sedimentation rate in the cored sediment from the Erhai Lake. All these geochemical indicators may also reflect environmental changes in sedimentation conditions and diagenesis.