Fly and bottom ash (FABA) produced primarily from coal combustion in a coal-fired power plant consists of fine particles of the organic and inorganic mixture and trace elements. Eight FABA samples from coal-fired power plants in Java, Indonesia, had been collected for composition and rare earth element and Yttrium (REY) mode of occurrence identification. The geochemical composition of both major and trace elements was determined by inductively coupled plasma-mass spectrometry/atomic emission spectrometry (ICP-MS/AES). Furthermore, the composition of FABA was identified by petrography with reflected light microscopy and X-ray diffraction (XRD) analysis. Simultaneously, scanning electron microscope determines the mode of occurrence of REY with an energy-dispersive X-ray (SEM–EDX). The study finds that the inorganic component of FABA consists of glass, Fe–Mg spinel, mullite, quartz, Fe-oxide mineral, and K-feldspar. In contrast, the organic component is dominated by unburned coal. Glass is the most abundant component with cenospheres as major and pleiospheres as minor constituents. Trace elements analysis indicates REY concentration with heavy REY (HREY) distribution pattern. Moreover, SEM–EDX analysis results show that Yttrium (Y) occurs in glass and has a low concentration in spinel. From the mode occurrence of REY, in particular Yttrium, it can be predicted that alkaline fusion followed by acid leaching will be the most appropriate extraction method to extract REY from Indonesian FABA.

The study of geopolymers has become an interesting concern for many scientists, especially in the infrastructure sector, due to having inherently environmentally friendly properties and fewer energy requirements in production processes. Geopolymer attracts many scientists to develop practical synthesis methods, useful in industrial-scale applications as supplementary material for concrete. This study investigates the geopolymerization of fly ash and geothermal silica-based dry activator. The dry activator was synthesized between NaOH and silica geothermal sludge through the calcination process. Then, the geopolymer mortar was produced by mixing the fly ash and dry activator with a 4:1 (wt./wt.) ratio. After mixing homogeneously and forming a paste, the casted paste moved on to the drying process, with temperature variations of 30, 60, and 90 °C and curing times of 1, 3, 5, 7, 14, 21, 28 days. The compressive strength test was carried out at each curing time to determine the geopolymer’s strength evolution and simulate the reaction’s kinetics. In addition, ATR-FTIR spectroscopy was also used to observe aluminosilicate bonds’ formation. The higher the temperature, the higher the compressive strength value, reaching 22.7 MPa at 90 °C. A Third-order model was found to have the highest R² value of 0.92, with the collision frequency and activation energy values of 1.1171 day⁻¹ and 3.8336 kJ/mol, respectively. The utilization of coal fly ash and silica geothermal sludge as a dry activator is, indeed, an approach to realize the circular economy in electrical power generations.

There is a shift from internal combustion engines to electric vehicles (EVs), with the primary goal of reducing CO₂ emissions from road transport. Battery technology is at the heart of this transition as it is vital to hybrid and fully electric vehicles’ performance, affordability, and reliability. However, it is not abundant in nature. Lithium has many uses, one of which is heat transfer applications; synthesized as an alloying agent for batteries, glass, and ceramics, it therefore has a high demand on the global market. Lithium can be attained by extraction from other natural resources in igneous rocks, in the waters of mineral springs, and geothermal brine. During the research, geothermal brine was used because, from the technological point of view, geothermal brine contains higher lithium content than other resources such as seawater. The nanofiltration separation process was operated using various solutions of pH 5, 7, and 10 at high pressures. The varying pressures are 11, 13, and 15 bar. The nanofiltration method was used as the separation process. High pressure of inert nitrogen gas was used to supply the driving force to separate lithium from other ions and elements in the sample. The research results supported the selected parameters where higher pressure and pH provided more significant lithium recovery but were limited by concentration polarization. The optimal operating conditions for lithium recovery in this research were obtained at a pH of 10 under a pressure of 15 bar, with the highest lithium recovery reaching more than 75%.