Analisis Proksimat, Kandungan Sulfur dan Nilai Kalor dalam Penentuan Kualitas Batubara. Indonesian Journal of Engineering (IJE), [S. l.], v. 1, n. 2, p. 85–94, 2021. Disponível em: https://ejournal.ununtb.ac.id/index.php/ije/article/view/28.. Acesso em: 20 mar. 2026.