Physical structure of brown coal
Brown coals have the advantage that they can be broken down by the comparatively gentle treatment of alkali digestion into fragments in the micron and submicron range. This results in a soluble fraction of humic acids and an insoluble residue, humins. With Victorian coals it has been found that maximum digestion occurs at pH 13 to give humic acid yields ranging from 15 to 40% of the dry coal mass. This paper reports on a study of digested coal fractions which were subjected to particle size analysis using sedimentation techniques. For the humins fractions a gravitational sedimentation technique was adopted, while the more finely divided humic acids required an ultracentrifuge to generate a sufficiently large force field. The nature of the fragments generated by this technique has resulted in a modified hypothesis of coal genesis. The revised model of coal structure which emerges from this study envisages a gel of humic acid molecules swollen by water and incorporating particulates. These include rods and detrital matter like pollen, cell remains, exinite material etc. which are held together by the humic acid glue. The bonds linking this mass together must be of a homopolar non-regenerable type as rheological studies of Victorian coals have shown that the bonds are broken by shear action during mechanical working and do not remake on standing. This excludes the hydrogen bond commmonly regarded as the major bond type for brown coal gels, as hydrogen bonds are known to remake after rupture. It appears that van der Walls type bonds may hold the structure together. On rupture the water which is liberated on shearing would be able to attach at the vacant sites and thus prevent the remaking of the original stronger bonds.
- Research Organization:
- Univ. of Melbourne, Parkville, Australia
- OSTI ID:
- 6176316
- Report Number(s):
- CONF-790415-P2
- Journal Information:
- Am. Chem. Soc., Div. Fuel Chem., Prepr.; (United States), Journal Name: Am. Chem. Soc., Div. Fuel Chem., Prepr.; (United States) Vol. 24:1; ISSN ACFPA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
010600* -- Coal
Lignite
& Peat-- Properties & Composition
ALKALI METAL COMPOUNDS
BROWN COAL
CARBONACEOUS MATERIALS
CHEMICAL BONDS
CHEMICAL PROPERTIES
COAL
ENERGY SOURCES
FOSSIL FUELS
FUELS
HUMIC ACIDS
HYDROGEN COMPOUNDS
HYDROXIDES
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PARTICLE SIZE
PHYSICAL PROPERTIES
SIZE
SODIUM COMPOUNDS
SODIUM HYDROXIDES
STRUCTURAL CHEMICAL ANALYSIS