Particle characterisation and bioaccessibility of manganese in particulate matter in silico- and ferromanganese smelters

Abstract

The aim of this study was to characterise particulate matter (PM) collected in the furnace area during SiMn and high carbon (HC)–FeMn production in terms of single particle analysis and to determine the bioaccessibility of Mn in the PM in a simulated lung fluid. Airborne PM was collected with Sioutas cascade impactors and respirable cyclones in the breathing zone of tappers and crane operators. Stationary samples were collected from the furnace area with a nanoMOUDI cascade impactor and an ESPnano electrostatic particle collector. Individual particles were characterised by scanning and transmission electron microscopy. Bioaccessibility of Mn was studied in terms of the dissolution of Mn in Gamble solution (24 hours leaching at 37 °C) relative to total Mn. Slag particles, alloy fragments, Mn and Fe oxides as well as carbonaceous particles were observed in the size fraction > 1 μm aerodynamic diameter (d_ae). Thermally generated condensation particles dominated the d_ae size range of 0.18–1 μm collected from the tapping fumes, while carbonaceous particles dominated the fraction below 0.18 μm. Condensation generated particles from the furnace area of HC–FeMn production were coated with an amorphous Si–O rich surface layer which seemed to hold primary particles together as aggregates. In the same size range, the particles from the furnace area of SiMn production were dominated by spherical condensation particles rich in Si, Mn and O, but without a Si–O rich surface layer. Instead, the Mn oxides were enclosed in an amorphous Si–O rich matrix. The bioaccessibility of Mn was low to moderate (<30%), but higher for SiMn furnace workers (highest median = 23%) than HC–FeMn furnace workers (highest median = 12%). This difference in bioaccessibility was significant for PM with d_ae up to 2.5 μm, and most pronounced in the d_ae size range between 0.25 and 1.0 μm. Also, a significantly higher bioaccessibility of Mn was found for PM larger than d_ae of 0.5 μm collected among crane operators compared to tappers in the HC–FeMn smelter.