Mineralogy of particles deposited on biomass and in soils from various smelter-polluted sites

<p>For this investigation, biomass and soil samples from several smelter areas in sub-Saharan Africa were used. Grass samples and topsoils were collected in the Tsumeb area in northern Namibia (Cu-smelter, former mine), Selebi-Phikwe in Botswana (Ni-Cu mine and smelter), Luanshya in the Zambian Copperbelt (Cu mine and smelter), and Kabwe in central Zambia (Pb-Zn mine and smelter). Metal(loid)s concentration in soils and grass were generally in the order of hundreds to thousands mg/kg.</p><p>The surfaces of all the grass biomass samples contained a variety of geogenic (quartz, carbonates, clay minerals, feldspars) and anthropogenic (usually metal-bearing) particles directly attached to the biomass tissues. These smelter-derived particles are predominantly slag fragments enriched in various contaminants, droplets of metals/sulfides, and, in the case of the biomass from Kabwe, newly formed aggregates of submicrometric anglesite (PbSO₄) crystals. Heavy mineral fractions were obtained from all biomass samples to better understand the solid-phase speciation of contaminants. In Tsumeb, the key metal-hosting minerals/phases on biomass were Cu-Fe sulfides, arsenolite (As₂O₃) and metal-bearing slag glass. In Selebi Phikwe pyrrhotite (Fe_1-xS), pyrite (FeS₂), pentlandite [(Fe,Ni)₉S₈] and chalcopyrite (CuFeS₂) were predominant. Samples from Kabwe were composed of galena (PbS), pyrite (FeS₂), sphalerite (ZnS), chalcopyrite (CuFeS₂) and anglesite (PbSO₄) and in Luanshya, the particulates were mainly formed by phases from the Cu-Fe-S ternary system. The mineralogy of particulates collected in the grass samples was similar to that in the corresponding topsoil samples. The knowledge of solid-phase speciation is of key importance for determining the fate of contamination in such environments.</p><p>This study was supported by the Czech Science Foundation (GA&#268;R project no. 1-23794J) and a grant from the Endowment Fund of the Faculty of Science, Charles University, attributed to M. Tuh&#253;. The Charles University team was partially supported by the institutional funding from the Center for Geosphere Dynamics (UNCE/SCI/006).</p>