Mineral matter intrinsic

Ash particulates are formed from mineral matter due to three different mechanisms. First, part of the mineral matter is found in layers or bands separate from the organic matter. This is called adventitious mineral matter, and it can be partially separated from the coal after crushing and fine grinding. The adventitious mineral matter is transformed directly to ash in the combustor, and the shape is semirounded. Second, mineral matter in coal is contained within the organic matrix in the form of chemically bound molecules and submicron crystals. Grinding does not liberate this intrinsic mineral matter. Third, some of the mineral matter is vaporized during combustion and condenses on cooler surfaces such as turbine blades. 

Adventitious mineral matter is transformed directly to ash in the combustion zone. Depending on the temperature-time history, the ash particles will be spherical or semirounded. The size distribution of this ash depends on the size distribution of the adventitious mineral matter. Intrinsic mineral matter forms ash nodules in the pores of the char, and as char burnout proceeds, the ash nodules coalesce on the surface of the char. 

Large uncertainties exist in the apparent and intrinsic rate of char combustion. Estimates of the rate of char combustion within the range of uncertainties can result in over designed or under designed boilers. A review (2) has shown that one of the major uncertainties in the rate of char combustion is the catalytic influence of mineral matter. This paper reviews the available information on the catalytic effects of mineral matter and concludes that many coals contain sufficient sodium and calcium to increase the rate of char combustion by a factor of 100 at low temperatures. However, insufficient information is available to assess the influences of catalysis by mineral matter at combustion temperatures. 

The disposal of nuclear waste in ancient geologic salt formations compels systematic investigation of actinide chemistry in brines to predict their behavior in these natural, highly concentrated salt environments. Actinide release scenarios from the repository involve the dissolution and transport of actinide species in brine that has intruded into the waste emplacement area. To accurately predict the amounts of radionuclides that could be released to the surrounding environment we need to know the solubility, solution speciation, and the interactions with particulate matter and mineral surfaces under these conditions. Radiolysis produces oxidants in brines and the intrinsic high anion concentration are likely to stabilize actinides in their higher oxidation states (Biippelmann et al., 1988 Magirius et al., 1985). 

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