Coal and the Moessbauer Effect
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171 COAL AND THE MOESSBAUER EFFECT*
PEDRO A. MONTANO Department of Physics,
West Virginia University, Morgantown,West Virginia 26506
ABSTRACT The presence of iron bearing minerals in coal makes the Moessbauer effect extremely useful as an analytical tool. In this paper we present a general review of the use of Moessbauer spectroscopy in coal research. We discuss a simple method to identify iron bearing minerals in coal. Several researchers have used the Moessbauer effect to study the transformations of iron minerals during coal processing. We have studied the stoichiometries of iron sulfides produced during coal liquefaction. We found drastic changes in the stoichiometry of the pyrrhotites as a function of the total sulfur content of the coal, and the reaction conditions. Some in situ experiments are reported in this paper. We have observed evidence of reactions between the coal components and the iron sulfides at high temperatures (400' C). The possibility of studying in situ reactions makes the Moessbauer effect a unique analytical tool.
INTRODUCTION The diminishing supplies of domestic oil and the high cost of imported fuels have created great interest in the use of coal. By comparison to other energy resources coal represents 85% of the total reserves in fossil fuels in the United States [1]. However, direct coal utilization is not always feasible due to strong environmental constraints. The use of coal for transportation requires its conversion to a liquid fuel. This conversion method was already known in pre-war Germany, but the high cost of this process hinders its use in the present economic structure. Considerable research is necessary to obtain a better understanding of the coal conversion process, as well as to improve existing technologies of coal conversion. In order to completely characterize a coal a careful study of the organic and inroganic components is necessary. From the materials science point of view coal is a composite material with a very complex organic matrix. The carbon structure of coal can be viewed as consisting of hydroaromatic structures with aromaticity increasing from low-rank to high-rank coals [2]. The organic part of coal contains also sulfur, oxygen, nitrogen in variable amounts depending on the coal. There is not a single type of coal but many coals which can differ considerably in both components, organic and inorganic. In order to characterize a coal completely a coordinated study with as many techniques as possible is necessary. In recent years resonance techniques have become very powerful in the study of the different organic components appearing in coal (3]. The components of coal are of central importance from the point of view of Moessbauer spectroscopy. The first study of coal using Moessbauer spectroscopy was carried out by Lefelhocz et al. [4] in 1967. After a research gap of about 10 years renewed interest started in the use of Moessbauer spectroscopy to coal research [5,6,7]. This resurgence in the use of Moessbauer spectroscopy is as-
172 sociated to the gr
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