Leaching of metals from copper smelter flue dust (Mufulira, Zambian Copperbelt)

The leaching behaviour of electrostatic precipitator dust from the Mufulira Cu smelter (Copperbelt, Zambia) was studied using a 48-h pH-static leaching experiment (CEN/TS 14997). The release of metals (Cd, Co, Cu, Ni, Pb and Zn) and changes in mineralogical composition using X-ray diffraction and PHREEQC-2 modelling were investigated in the pH range of 3–7.

The highest concentrations of metals were released at pH 3–4.5, which encompasses the natural pH of the dust suspension (∼4.3). About 40% of the total Cu was leached at pH3, yielding 107g/kg. Chalcanthite (CuSO4·5H2O), magnetite (Fe3O4) and delafossite (CuFeO2) represented the principal phases of the studied dust.

In contact with water, chalcanthite was dissolved and hydrated Cu sulphates precipitated at pH4–7. Gypsum (CaSO4·2H2O) and secondary Fe or Al phases were observed in the leached residues. Serious environmental impact due to leaching may occur in dust-contaminated soil systems in the vicinity of the smelting plants.