Influence of pH on the leaching behaviour of heavy metal(loid)s in copper smelting flue dust and mineralogical control mechanism

The release behavior of heavy metal(loid)s in Cu smelting flue dust, collected from a deserted Cu smelter, and its mineralogical control mechanism were studied using toxicity characteristic leaching procedure (TCLP) test and wide pH range (3–13) dependent leaching experiments. The concentrations of As, Cd, Cu, Pb and Zn in TCLP leachate were 704, 82.7, 2.08, 3.1 and 3.26 times threshold of corresponding elements listed in identification standards for hazardous wastes of China (GB 5085.3—2007), respectively. High release percentage of As ranged from 26.0% to 28.1% over the entire pH range. The leachability of Cd, Cu, and Zn was significantly high under acidic conditions, while that of Pb was highly released at pH 13.0. The geochemical analysis showed that As solubility was partly controlled by the new formation of Ca, Cu, Pb, and Zn arsenates under pH 5.5–11.5, and that of Cd, Cu, Pb, and Zn was mainly controlled by hydroxide precipitation under alkaline condition. BCR extraction and XRD analysis indicated that higher leachate Cd and Zn concentrations were consistent with their higher content of active forms in dust. The study provides scientific guidance for the treatment and disposal of the flue dust for heavy metal(loid)s pollution prevention.