Cenospheres: From waste to profits

A cenosphere is a lightweight, inert, hollow sphere composed largely of silica and alumina that is filled with air or other gases. Cenospheres are a naturally occurring byproduct of the burning process at coal-fired power plants. They have properties similar to manufactured hollow-sphere products. Fly-ash, bottom ash and boiler slag are sluiced out of the power plant in the form of a slurry that is pumped into settling ponds. Once in the ponds, the cenospheres rise to the top of the pond because their specific gravity is less than that of water. Because an estimated 800 million ton/year of coal are burned, coal-combustion byproducts (CCBs) have become the nation`s third most-abundant mineral resource. Fabricated spherical products first appeared in the marketplace in the 1970s. Only in recent years have inorganic cenospheres harvested from power plants become important. Before they can be marketed, cenospheres must be reclaimed from the power plant settling pond and transported to a processing facility. The harvested cenospheres are dried, screened, sized and packaged. The paper discusses some of the use of cenospheres.