Monitoring the transformation of mackinawite to greigite and pyrite on polymer supports

作者：Lan Ying; Butler Elizabeth C^*

来源：Applied Geochemistry, 2014, 50: 1-6.

DOI：10.1016/j.apgeochem.2014.07.020

The objective of this study was to study the transformation of powdered mackinawite (FeS) to greigite (Fe3S4) and pyrite (FeS2) under geochemical conditions similar to those in pristine or contaminated aquifers. To observe the transformation without altering or damaging the crystal structures, mackinawite particles were immobilized on poly(methyl methacrylate) (PMMA) supports, and mineralogical changes monitored by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). Powders of mackinawite immobilized on PMMA supports were placed in aqueous solutions containing polysulfides and mildly elevated temperatures (75-78 degrees C) to promote the transformation to greigite and pyrite. SEM-EDS results were consistent with previously reported X-ray diffraction analysis that showed the transformation of mackinawite to greigite and pyrite. The similarities in sizes between most crystals over the course of the transformation from mackinawite to pyrite, as well as the coexistence of solids with morphologies and elemental compositions characteristic of mackinawite, greigite, and pyrite, are consistent with a solid state transformation. In some cases, however, much smaller pyrite crystals were formed, which may have resulted from direct nucleation from solution. The results reported here extend the applicability PMMA supports for studying mineralogical transformations (Birkefeld et al., 2005) to particles with dimensions from 100 nm to 2 mu m, and to elevated temperatures. Such supports can be used to monitor iron-sulfur mineralogical changes in pristine and contaminated environments.

• 出版日期2014-11