1. Falcon, R.M.S., Snyman, C.P.: An introduction to coal petrography: atlas of petrographic constituents in the bituminous coals of Southern Africa, pp. 27. Geological Society of South Africa, Johannesburg (1986)
2. Clarke, T.M., Evans, B.J., Wynter, C., Pollak, H., Taole, S., Ratcliffe, D.: Investigation of virgin coals subjected to a mild acid treatment. Hyperfine Interact. 112, 227–230 (1998)
3. Ward, C.R.: Analysis and significance of mineral matter in coal seams. Int. J. Coal Geol. 50(1/4), 135–168 (2002)
4. Mangena, S.J., Bunt, J.R., Waanders, F.B., Baker, G.: Identification of reaction zones in a commercial Sasol-Lurgi FBDB Gasifier operating on North Dakota lignite. Fuel 90, 167–173 (2011)
5. Higman, C., van der Burgt, M.: Gasification, p. 391. Elsevier, Amsterdam (2003)