The paper presents modes of a direct utilization of the fly ash by-product of the combustion of black power coal in the slag - bottom boilers of the Division Plant Power Engineering ( DP PE ) of the U. S. Steel Košice ( next USSK ). The properties of fly ash limit its use in metallurgy and foundry industry. The fly ash is directly utilizable in the metallurgical industry as a component of powder cover mixtures and insulation inserts, heat insulation parts and exothermical mixtures. The most important components in the mixtures are light micro spheres – cenospheres and heavy micro spheres – plerospheres. The micro spheres significantly improve properties of the powder cover mixtures
