Potential for Utilizing Coal Combustion Residues in Co-Utilization Products

Abstract

Approximately 90 millions tons of coal combustion by-products are produced annually in the United States, consisting of 54 million tons of fly ash (solid particles removed from smoke), 15 million tons of bottom ash, 3 million tons of boiler slag, and 20 million tons of flue gas desulfurization (FGD) material. Markets for boiler slag are well developed, but only 33\% of bottom ash, 25\% of fly ash and 8\% of FGD residues are beneficially used. Numerous opportunities for agricultural use of these materials have been identified. Fly ash (a very fine, relatively inert, dry powder consisting mostly of Fe, Al, Ca, Si, and O) provides a means of reducing water contents of wet mixtures, and can also provide B and other micronutrients to plants. Fly ash is currently being used to improve the texture and water-holding capacity of potting mixtures and artificial soils. Class C fly ash (produced from burning coal from Western US) can have a calcium carbonate equivalency of up to 50\% and may serve as a substitute for aglime. Mixtures of fly ash and sewage sludge produced an effective medium for growth of apple trees in northern West Virginia, and mixtures of fly ash and municipal compost produced an acceptable soil substitute for nurseries in Ohio. FGD materials contain mainly calcium sulfate or calcium sulfite, as well as some unreacted alkaline sorbent. These products can be used as substitutes for aglime, as an insolubilizer for phosphorous from animal manure in environmentally sensitive watersheds where excess P occurs in run-off, as a source of Ca and S in potting mixtures, as an antisodicity agent for displacing Na from certain degraded mine lands being treated with sawmill by-products, and to improve subsoil root growth enhancement properties of surface-applied amendments. Fluidized bed combustion materials, which contain both ash and FGD components, can be used for similar purposes.