The Use of S-XANES To Track Thermal Transformations of Metal Sulfides in Argonne Premium Coals

摘要

Argonne Premium Coal Samples are used by researchers world-wide as standards in coal research. They consist of a suite of eight samples of varying rank from the United States. The Sulfur X-ray Near-Edge Absorption Spectroscopy (S-XANES) third-derivative analysis method utilizes a well-defined library of model compounds to curve fit each sample spectrum and enables sulfur speciation to within about 10% for materials such as coals and kerogens. This direct non-destructive characterization technique, used in conjunction with other techniques such as X-ray photoelectron spectroscopy (XPS), can provide valuable information about chemical and thermal sulfur transformations. The S-XANES third-derivative analysis method provides quantitative results for organic sulfur species in coal but has not been used to quantify pyritic sulfur until recently. In general, the direct determination of the pyrite content, a metal sulfide, has been problematic. It is known through wet chemical methods that several of the Argonne premium coal samples exceed 50 mole% pyrite but only show a weak pyrite feature in the S-XANES absorbance and third-derivative spectrum. It has been shown that particle size effects are responsible for attenuating the pyrite signal for high-pyrite-containing Argonne Premium coals. In this study, iron sulfide transformations at two stages of pyrolysis for an Illinois # 6 Argonne Premium coal and an isolated pyrite sample are quantified using S-XANES.