Coal related fires in Portugal: New occurrences and new insights on the characterization of thermally affected and non-affected coal waste piles

This study presents a comprehensive investigation on the petrographic and geochemical characterization of new occurrences self-burning coal waste piles in Douro Coalfield (Portugal). It also includes reappraisal data about resulting from past mining, aiming to assess their environmental economic potential. Burned unburned material two that ignited 2017 were studied for petrographic, mineralogical characterization, identification thermally induced changes caused by combustion. Geochemical relative more than 20 integrated enrichment elements was investigated comparison with reference values. The results show organic fraction affected samples dark reaction rims, cracks, devolatilization vacuoles, plasticized edges, pyrolytic carbon lower vitrinite reflectance, despite presence unaltered particles. formation iron oxides is attributed burning process. observations allow less intense materials which indicates heterogeneity process within piles, gives information newly formed minerals attained combustion temperatures. composition generally range expected coaly materials. More noticiable differences are reported most sample. When considering all it noticed majority concentration increase burned due C consumption loss other volatilization. decrease As, Cd, Co, Mn, Pb, Sb, Sn, Zn partial volatilization these at high Considering slightly significantly enriched materials, Ba, Ga, Hf, Li, Nb, Sc, Ta, V, W, REE considered critical raw European Commission, while Cr, Cu, Mo, Ni, U represent concerns. Therefore reutilization as secondary source could be economically relevant will mitigation impacts deposition.