RESUMO
Brazilian coal area (South Brazil) impacted the environment by means of a large number of coal waste piles emplaced over the old mine sites and the adjacent areas of the Criciúma, Urussanga, and Siderópolis cities. The area studied here was abandoned and after almost 30 years (smokeless visual) some companies use the actual minerals derived from burning coal cleaning rejects (BCCRs) complied in the mentioned area for industry tiles or refractory bricks. Mineralogical and geochemical similarities between the BCCRs and non-anthropogenic geological environments are outlined here. Although no visible flames were observed, this study revealed that auto-combustion existed in the studied area for many years. The presence of amorphous phases, mullite, hematite and other Fe-minerals formed by high temperature was found. There is also pyrite, Fe-sulphates (eg. jarosite) and unburnt coal present, which are useful for comparison purposes. Bad disposal of coal-dump wastes represents significant environmental concerns due to their potential influence on atmosphere, river sediments, soils and as well as on the surface and groundwater in the surroundings of these areas. The present study using advanced analytical techniques were performed to provide an improved understanding of the complex processes related with sulphide-rich coal waste oxidation, spontaneous combustion and mineral formation. It is reporting huge numbers of rare minerals with alunite, montmorillonite, szomolnokite, halotrichite, coquimbite and copiapite at the BCCRs. The data showed the presence of abundant amorphous Si-Al-Fe-Ti as (oxy-)hydroxides and Fe-hydro/oxides with goethite and hematite with various degrees of crystallinity, containing hazardous elements, such as Cu, Cr, Hf, Hg, Mo, Ni, Se, Pb, Th, U, Zr, and others. By Principal Component Analysis (PCA), the mineralogical composition was related with the range of elemental concentration of each sample. Most of the nano-minerals and ultra-fine particles found in the burned coal-dump wastes are the same as those commonly associated with coal cleaning rejects, in which oxidation of sulphides plays an important role to environment and human health.