1. Schweinfurth SP. Coal – a complex natural resource. US Geol Survey Circ 2005;39:1143.
2. Kalyoncu RS. Coal combustion production. In: US geological survey minerals yearbook 1999. p. 19.1–19.4.
3. Clean and efficient coal-fired power plants;Termuehlen,2003
4. Basic properties of flue-gas desulfurization gypsum;Kovacs;Acta Montanistica Slovaca,2003
5. American Coal Ash Association. CCP Survey. ; 2006 [site verified on June 28, 2007].