Attia, Y. A.; Zeky, M. El.; Lei, W. W.; Bavarian, F. & Yu, S. Removal of organic and inorganic sulfur from Ohio coal by combined physical and chemical process. Final report, report, April 28, 1989; (https://digital.library.unt.edu/ark:/67531/metadc1386690/m1/37/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, digital.library.unt.edu; .