KHAN, M. Upgradation of coal by froth flotation method; A case study of Akkakhel, Akhorwal and Shekhan coal mines. Journal of Himalayan Earth Sciences, [S. l.], v. 54, n. 2, p. 61-69, 2021. Disponível em: http://ojs.uop.edu.pk/jhes/article/view/1694. Acesso em: 26 jul. 2025.