A Preliminary Economic Evaluation of Rare Earth Element and Yttrium (REY) in Indonesian Coal: Progress and Future Prospect

Abstract

Coal deposits have fascinated much attention in recent years due to its by-product waste as promising alternative sources for rare earth metals. Rare earth metals concentration in many coals and coal ashes are known have equal to or higher than those found in conventional ore. Indonesia is one of the most extensive coal-bearing sedimentary basins in SE Asia with unique tectonic and geological control that might be significance as prospective country of rare metals recovery from coal. This study shows recent progress from several Indonesian coal-bearing sedimentary basins: Ombilin, South Sumatra and Pasir basin. Surprisingly, the REY concentration in Ombilin, South Sumatera and Pasir basin has higher than the average world-coal with 126.15 ppm, 203.72 and 285.53 ppm, respectively. Based on the relationship market demand and supply of individual REY in recent years proposed by Seredin and Dai (2012), all of coal samples were clustered into Promising (II) type with base of critical outlook is 0.7 and cut-off grade is 1000 ppm in coal ashes. It comprises the various REY distribution types and can be regarded as promising REY raw metrials for economic development. REY-enrichment processes in Indonesian coal are different due its tectonic and geological processes that control the basin formation, both of pre-, syn- and post-forming. Genetically, major REY-enrichment processes in Indonesian coal are controlled by tuffaceous; infiltrational; and terrigenous process. Tuffaceous process is related to volcanism that produce tonstein layer during coal peatification, this type is determined in South Sumatera and Pasir basin. Terrigenous process is controlled by provenance sediment-source during coal-bearing formation is formed; basaltic-igneous basement is major controlled REY-enrichment in Ombilin and Pasir basin. Injections of marine water during coal peatification also known that lead REY-enrichment, this type called infiltrational type and its presence in all three basins. Recent study about REY-rich in Indonesian coal shows significance prospect for future rare earth metals recovery. Further study is needed in unexplored coal-bearing sedimentary basin such as Tarakan, Asem-asem, Barito, Ketungau, Melawi, Salawati and Bintuni basin.