SEPFITRAH. ANALISIS PROXIMATE KUALITAS BATUBARA HASIL TAMBANG DI RIAU. SAINSTEK, [S. l.], v. 4, n. 1, p. 18–26, 2016. Disponível em: https://ejournal.sttp-yds.ac.id/index.php/js/article/view/106. Acesso em: 24 feb. 2026.