Leaching of Metals from Metallurgical Wastes in pH-static System: an Experimental Approach

The leaching characteristics of slag and fly ash from copper-cobalt smelting in the Zambian Copperbelt were studied using pH-static leaching experiments (CEN/TS 14997). The release of metallic contaminants as a function of pH and the influence of fine dust particles and/or time on leaching were investigated. Three types of slag samples with decreasing portion of particles < 500 μm were prepared to assess the effect of sample preparation on the leachability of metals. Fly ash was subjected to 48-h and 168-h experiments. The highest concentrations of contaminants were generally released in the acidic pH region. The presence of fine dust particles increased the concentrations of metals in the slag leachates (e.g., 655 mg Cu kg to 1100 mg Cu kg at pH 4). Significant release of metals from the fly ash was observed at pH 5 and 12, exhibiting a typical U-shaped trend. Only slight differences occurred between 48-h and 168-h leaching of Co, Cu, Pb and Zn, indicating the near-equilibrium conditions in the system.