Coal Microstructure and Pyrite Distribution

Abstract

The microstructure of coal is of interest in understanding coal properties. Microstructural features may affect the selection of coal beneficiation methods for removing impurities. For example, in planning sulfur removal schemes it is useful to understand the proportionment of inorganic sulfur compared with that of organic sulfur. Details of size, shape, orientation, and distribution factors for pyrite, certain pyrite and maceral groupings or fields, or other coal constituents (macerals and other inorganic components) are of importance in supporting rational designs of sulfur removal processes. Recent scanning electron microscope (SEM) investigations help to show the interrelations between macerals and inorganic phases such as pyrite (FeS 2 , the primary inorganic source of sulfur in coal) (1,2,3,4). This form of characterization complements optical microscope studies (5,6,7,8) and conventional transmission electron microscope (TEM) studies (9-15) which have been used to classify and to study coal constituents. SEM offers a way to visualize features hundreds and thousands of Angstroms in diameter by direct observation in three dimensions which is not available by any other technique. Many significant coal features (such as cellular components) and impurity crystals occur in this size range. Important features of coal constitution discovered by SEM are discussed below. Experimental InvestigationApparatus. A JSM-U3 SEM with an EDAX energy dispersive x-ray analysis system is used for the microscale structural and chemical studies.The resolution capabilities of the instrument on a dayto-day basis are somewhat better than 200 Â for microstructural information and submicrometer in a chemical analysis mode for localized crystal description. The system provides size, shape, orientation, and distribution information for inorganic phases and coal constituents.

Roles of Inherent Fine Included Mineral Particles in the Emission of PM10 during Pulverized Coal Combustion

“…carbonates and phosphates). It is known that Na, Ca, Sr, Ba, Fe, and P may be organically bound in coal (particularly low-rank coals) and/or exist as carbonates , and phosphates …”

“…It is known that Na, Ca, Sr, Ba, Fe, and P may be organically bound in coal (particularly low-rank coals) and/or exist as carbonates 26,27 and phosphates. 28 Based on the data in Figures 1 and 2, it is clear that the raw coal contains abundant fine included mineral particles, plus possibly small proportions of organically bound ash-forming species. Therefore, acid-washing indeed removes the acid-soluble mineral matter and produces a unique coal sample that contains only discrete included mineral particles.…”

Desulfurization of coal model compounds and coal liquids. [M. S. Thesis; treatment with metallic sodium or sodium salts followed by distillation]

“…Sulfur appears in both organic and inorganic forms. The latter is composed of pyrite, pyrrhotite, sulfate, and elemental sulfur, in that order of abundance (11,12). Pyrite is usually the chief inorganic sulfur species (13), and sulfates are important only in weathered coals (11,14).…”

“…The latter is composed of pyrite, pyrrhotite, sulfate, and elemental sulfur, in that order of abundance (11,12). Pyrite is usually the chief inorganic sulfur species (13), and sulfates are important only in weathered coals (11,14). In addition, forms such as sphalerite (ZnS), chalcopyrite (CuFeS ), and galena (PbS) occur, leading to errors in pyritic sulfur x determination (14).…”