Fly ash waste is a by-product of coal burning at PLTU Nagan Raya, Aceh Province, Indonesia. Since 2017, the coal used is a mixture of 90% Kalimantan coal (sub-bituminous) and 10% local Nagan Raya coal (lignite) which is still young so that the mineral ash content is still high. Silica is among the interesting minerals to be extracted from fly ash, given its wide range of benefits. This paper describes the process of extracting silica from fly ash at the Aceh power plant through the leaching method using a chemical solution and heating for 2 and 4 hours at a temperature of 100˚C. The difference in heat treatment aimed to study the changes in properties and obtain the best method in the silica extraction process. The effect of heat treatment on silica characteristics was studied based on XRD (X Ray Diffraction) test for phase identification, SEM (Scanning Electron Microscopy) test for morphological identification, EDS (Energy Dispersive X-Ray Spectroscopy) test for mineralogy element identification, FTIR (Fourier Transform Infra-Red) test for identification of functional groups and surface chemistry, and DSC/TGA (differential calorimetric analysis/ thermogravimetric) test for identification of thermal properties. As a result, it was found that fly ash still contains unburned carbon, which significantly affects its color, and has the potential for application as a hydrogen storage material because its pore diameter structure is larger than 0.7 nm. The silica extracted from fly ash is capable of achieving a purity of up to 87% and exhibits excellent thermal stability, especially at temperatures between 120˚C-300˚C; thus, it has the potential to be a catalyst material in the adsorption-desorption reaction of hydrogen by magnesium, although further research is still needed.