Concentrations and forms of heavy metals around two ore processing sites in Katanga, Democratic Republic of Congo

The concentration of heavy metals and the forms in which they occur were determined for tailings and derived deposits of two major processing sites of Cu–Co and Cu–Zn–(Pb) ores in the Katanga Copperbelt (Kipushi, Likasi). They were studied by a combination of methods, focussed on the nature of water- and EDTA-extractable compounds, the mineralogical composition of tailings and associated secondary minerals, and textural features of metal-bearing efflorescences. For the Kipushi area, sulfide minerals in tailings of decantation basins are identified as the source of extractable metals they contain, but input from an external source rather than local oxidation of substrate components is responsible for high levels of contamination in the Likasi area. Contaminated areas around Likasi are characterized by an abundance of Mg-sulfate efflorescences with high concentrations of cobalt and other metals, acting as an important vector for further dispersion of contaminants by wind and water.