Chemical and Specialty Coal
Certain coals can be used to produce chemicals and specialty products. This is a small percentage of the overall coal market. Chemical and specialty coals must meet very specific requirements for the product or chemical process in which they will be used. Requirements (and relative grade terms) may be related to ash and sulfur contents, as with steam coals and metallurgical-grade coals, but also may be related to mechanical properties (e.g., Hardgrove grindability, free-swelling index), or to chemical composition (e.g., trace elements, amounts of reactive macerals).
The Blue Gem Coal and Silicon Metal
The Blue Gem coal is an exceptionally high-quality coal found in several areas of southeastern Kentucky. The coal can have sulfur contents below 1 percent and ash yields below 1.5 percent, which is less than the ash content of the living plants from which the coal formed! Because of its low sulfur and extremely low ash content (among other properties), this coal is one of only a few coals in the world that can be used to make silicon metal.Silicon metal is metallurgical-grade silicon, which is used to make aluminum-silicon alloy materials, in the chemical industry, and in the manufacture of electric semi-conductors.
Low ash-fusion temperature: The mineral fraction of the Blue Gem is dominated by siderite, rather than silicates. This gives the coal a low ash-fusion temperature that is favorable in the production of silicon metal (Gardner and others, 2007; Hower and others, 2007).
High silicon reactivity: The carbon in the Blue Gem exhibits high silicon reactivity, which is favorable in the production of silicon metal (Myrvagnes and Lindstad, 2007).