The problem:
A cenosphere is a lightweight, inert, hollow sphere made largely of silica and alumina and filled with air or inert gas, typically produced as a byproduct of coal combustion at thermal power plants. On average 0.5% of the fly ash generated in a coal fired power station boiler are Cenospheres.
When fly ash is wet discharged in to ash ponds/lagoons cenospheres float on the water surface, get finally air borne and cause dust pollution.
The solution:
The floaters are collected from the water surface, dried and graded by screening into particle sizes between 150 to 300 micron.
Picture of Cenospheres
The end-product is used as a filler in compounds and paints as well as a component in oilwell cement.