Abstract
Coal fly ash and bottom ash are by-products of lignite combustion in the thermal power plant REK Bitola in North Macedonia, representing a significant environmental challenge as well as a promising secondary resource. This study presents a comprehensive quantitative and qualitative analysis of these ashes, focusing on their physicochemical characteristics and potential for the recovery of critical and strategic raw materials, including rare earth elements. The chemical composition reveals that the ashes are silicate- rich (≈50 %) with lower alumina levels of about 19-20 %, and solid amounts of ferric oxide (12-15 %). Regarding qualitative and economic recovery potential, the biggest promise lies in gallium (30-35 mg kg−1), and side-streams of manganese (1100-5038 mg kg−1), cerium (147-153 mg kg−1) and an REE mixed concentrate. On the quantitative side, the in-place ash inventory at the REK Bitola landfill was estimated using a Digital Elevation Model-based screening workflow in Google Earth Engine. The geometric volume was estimated at 106.8 million m3 and should be considered a Tier-1 screening estimate. The resulting quantitative and qualitative properties are particularly relevant for key stakeholders, including the research community, industry actors, and potential investors, as they highlight the potential for sustainable recovery of valuable and rare metals from this secondary raw material.