Wildfires in polluted areas: mineralogical transformations and remobilization of metal(loid)s

Abstract

Wildfires contribute to the global emissions of trace elements. This Ph.D. thesis focuses on highly polluted areas near smelting/mining polluted sites in Africa, where wildfires are frequent. Experimental samples corresponding to both representative biomass-rich topsoils and grass were investigated using a combination of mineralogical and geochemical methods. Wildfires were simulated using a thermodesorption (TD) technique (75-670 řC; Hg) and newly introduced experimental set-ups (250-850 řC), enabling the online detection of the released contaminants and the sampling the aerosols and ashes. The subsequent investigation revealed the mineralogical and chemical transformations necessary for understanding the temperature- dependent releases of the metal(loid) contaminants during the simulated wildfire. The thermodesorption experiments indicated that >90 % of Hg was released at ~340 řC. A comparison with the Hg reference compounds' TD curves confirmed that the Hg in the biomass- rich topsoils occurs as a mixture of the Hg bound to the organic matter and nanocrystalline black HgS, which exhibited similarities with the TD pattern of smelter flue dust residue. The release of the other metal(loid)s from the topsoils (As, Cd, Cu, Pb, Zn) is dependent on their solid-state speciation, which was determined by..