The potential environmental risk implications of heavy metals based on their geochemical and mineralogical characteristics in the size-segregated zinc smelting slags

Abstract

Smelting slags must be classified as a typical hazardous solid, which represents the most important point sources of potentially harmful elements. In addition, it can be known that particle sizes have been considered as an important indicator of human exposure risks. In this context, the present work mainly concerned about the potential leachability, bioavailability, bioaccessibility and mobility of toxic heavy metals in four zinc smelting slag fractions under the strong influences of mineralogical and morphological factors. The results indicated that heavy metals were mostly enriched in the smallest particles, with the higher metal concentrations of 3558.19 g/t for As, 123.49 g/t for Cd, 6757.57 g/t for Cu, 1.76% for Pb and 1.78% for Zn. Geochemical evaluation revealed that Cd, Cu, Mn, Pb and Zn was the most worrying elements, due to their unstable geochemical properties. Moreover, XRD and SEM-EDS results confirmed the formation of gypsum (CaSO4.2H2O) phase in 0.075–0.15 mm (SS3) and <0.075 mm (SS4) of the zinc smelting slags. The combined results of various characterization clearly showed the particle size distribution, surface morphological structure and mineral weathered state had a profound impact on the geochemical stability of heavy metals in the zinc smelting slags. These combined results of geochemical analysis and technical characterization could update our fundamental knowledge to better understand the mineralogical and morphological controls influencing the geochemical behaviors of heavy metals. Meanwhile, these study results would be of great scientific and realistic significance to develop effective targeted strategies for the subsequent pollution control and risk reduction of smelting wastes.