A review study of the relationship between coal fly ash characteristics and the presence of rare earth metals from steam power plants in Indonesia

The establishment of a coal mining downstream ecosystem focused on a sustainable and environmentally friendly economy is an important goal for many countries. One strategic step in achieving this goal is the utilization of coal fly ash (CFA) waste as a secondary source of rare earth elements (REE). The use of CFA provides a solution to the environmental and health challenges resulting from mining primary sources. Prior to developing REE extraction technology, CFA characterization must be conducted. Therefore, this study addresses the relationship between CFA characteristics and the presence of REE. Based on the ASTM C618-12 standard, CFA in Indonesia is dominated by type F, with Ce being the most abundant REE element. Potential locations for REE sources in Indonesia include power plants in Sumatra, Kalimantan, and the western part of Java. There is a significant correlation between the oxide contents of SiO2, Al2O3, and Fe2O3 with the LREE and CREE groups in CFA in Indonesia. Correlation analysis shows a strong positive relationship between LREE and SiO2 (0.90) and Al2O3 (0.95), while Fe2O3 shows a negative relationship (-0.58). However, Fe2O3 also contributes positively to the presence of CREE (0.89).