| http://www.w3.org/ns/prov#value | - However, the practice has been mostly discontinued in recent years because it proved to be uneconomical or because of environmental constraints on spent shale disposal. (See T. F. Yen, and G. V. Chilingarian, ???Oil Shale,??? Amsterdam, Elsevier, p. 292.) Further, surface retorting requires mining of the oil shale, which limits that particular application to very shallow formations.In the United S
|
