Nanosize-effect on the distribution of heavy metals in copper smelting dust: Based on sophisticated dust sorting approach

Dust particles emitted from smelters can be hazardous to ecosystems and humans, as they are often enriched in metallic compounds. Here, we combined multi-method mineralogical analysis with a sophisticated size sorting approach for copper smelting dust to study the nanosize-effect on heavy metal distribution, which has hitherto been underestimated. Three types of dust were collected from a copper flash smelter and then size-sorted using a Dekati low-pressure impactor. Results showed that all three samples could easily sort out nanoscale dust particles (< 1 μm, grades 10–2) and even those smaller than 100 nm (grades 5–2). Especially for electrostatic precipitators dust, the mass fraction of nanoscale dust (< 1 μm) could reach 10.71%. The presence of heavy metals (Pb, Zn, Cu, and As) and their mineral species in dust was examined at various particle sizes. It was discovered that different heavy metals are enriched on nanoparticles in specific sizes. In micron-sized particles, heavy metals are generally found in discrete phases (e.g., CuSO₄, PbSO₄, and As₂O₃). In nanoscale particles, the dominant phase is Fe₃O₄, while heavy metals are mostly found in lattice substitution (e.g., CuFe₂O₄ and ZnFe₂O₄). Two distinct nano-dust morphologies were found: One with irregular mesh or chain structures consisting of particles of a few nanometers, and the other with polygonal crystals in larger sizes of hundreds of nanometers. The enrichment of heavy metals in the latter morphology is more pronounced, possibly because lattice substitution of heavy metals is more likely to occur when polycrystalline particles are formed.