Aside from huge coal resources in Indonesia of about 140.47 × 109 tons (PSDMBP, 2020), studies on valuable elements in coal and coal ash are very limited, i.e. REY. Anggara et al. (2018) studied the effect of tonstein layer in enrichment process of REY in coal from South Sumatra Basin, Indonesia and showed that the coal is enriched beneath the tonstein layer.

According to Seredin and Dai (2012), there are four types of REY enrichment in coal basins; (1) terrigenous, (2) tuffaceous, (3) infiltration, and (4) hydrothermal. Referring to several coal basins that Indonesia possesses (see Figure 1) with different geological setting, we have proposed this study with objectives; (1) to study the REY concentration and enrichment processes as well as mode of occurrence in coal and coal-ash based on geological condition, and (2) to determine suitable extraction method of REY in coal-ash based on ash composition. Thus, instead of coal sampling from several coal basins, fly ash and bottom ash (FABA) from coal-fired power plants were also collected. Coal characteristics, major and trace elements were examined using petrography and geochemistry analysis, and similar comprehensive study was conducted for the fly ash and bottom ash (FABA).

The results showed some coal samples have REY concentration higher than the world coal average and there is no mineral bearing REY have been found. It is in conjunction with the SEM-EDX analysis of FABA showing Yttrium (Y) occurrence in glass and low concentration in spinel. Mode of REY occurrence in this study could be used as preliminary data to determine the extraction method as part of coal-as upcycling processes.

Keywords: Valuable elements, REY, coal and coal ash, mode of occurrence, extraction method.


Ferian Anggara has been an Associate Professor Department of Geological Engineering, UGM since 2019 and Head of Doctoral Program since 2021. Currently, he is in charge as the head of centre for unconventional geo-resources research group (https://ugrg.ft.ugm.ac.id/home/). His primary teaching and research interest include peat and coal geology, unconventional geo-resources, applied geochemistry as well as CO2-Enhanced Coal Bed Methane Recovery (ECBMR). For the past few years, he has developed strong research interests in the effect of CO2 injection in coal reservoir, spatial variability of tropical peatland, identification of valuable elements and rare earth elements and yttrium (REY) concentration in coal and coal-ash. Regarding to collaborations with industry, he has recently handled projects related to coal ash up-cycling (including cenosphere isolation, REY extraction, and geopolymer production), subsurface geophysical survey and modelling using seismic-resistivity method, surface geological mapping for coal exploration as well as oil and gas exploration.



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