Characterisation of workplace aerosols in the manganese alloy production industry by electron microscopy

Abstract

Workplace aerosols in a combined FeMn and SiMn alloy smelter were studied by scanning and transmission electron microscopy. Special emphasis was placed on the characterisation of individual particles with diameters below 500 nm and on identification of the different manganese phases present in the workroom air. In high-carbon FeMn production, the submicron size fraction is dominated by MnO particles forming chain-like or compact agglomerates. Minor amounts of MnO(2), Mn(3)O(4), Mn(2)O(3) and Fe(3)O(4) are also observed. During production of SiMn, the submicron size fraction consists predominantly of MnSi particles, but small amounts of Mn(3)Si, Mn(6)Si and Mn(5)Si(2) are also found. Workplace aerosols from the manganese oxide refinement (MOR) process consist mostly of Mn oxides. Minor amounts of carbonaceous particles occurring as sheets, ribbons and as hollow carbon structures are observed along the whole production line. Carbonaceous particles are either amorphous or consist of poorly crystallised graphite. Particles with fibre morphology were encountered at all sampling locations but most prominently during tapping of FeMn with fibre concentrations between 0.1 and 0.7 per cm(3). The pronounced differences in particle composition along the production line clearly show that workers are exposed to a variety of Mn-containing species. MnO particles have a higher solubility than MnSi particles and are thus more bioaccessible, suggesting a higher risk of adverse health effects in the FeMn production than in the SiMn production.