Characterization of workplace aerosols in the manganese alloy production industry by X-ray diffraction, inductively coupled plasma optical emission spectrometry, and anion chromatography

Abstract

Workers in the manganese (Mn) alloy industry are exposed to a variety of Mn com- pounds, which may lead to a neurological condition called manganism. To better assess health effects due to Mn exposore, it is important to know to which Mn species workers are exposed. In this thesis, three different aerosols types from ferromanganese (FeMn) and silicomanganese (SiMn) production were characterized: a) furnace fumes generated inside the FeMn and SiMn furnaces; b) workplace aerosols collected in the FeMn and SiMn tapping areas; and c) workplace aerosols collected using personal respirable cyclones worn by FeMn and SiMn tappers. Furnace fumes were studied by X-ray diffraction (XRD), aided by inductively cou- pled plasma optical emission spectrometry (ICP-OES) for elemental analyses, ion chromatography (IC) for determination of water-soluble anions, and pH measurements to assess acidity and alkalinity. Workplace aerosols were studied by XRD and ICP-OES, and personal exposure filters were studied by XRD only. Here it is shown that the crys- talline phases are predominantly manganese(II) dimanganese (III) tetraoxide (Mn3O4), β-quartz, and dipotassium sulfate (K2SO4); however, the source of detected β-quartz is not known. Minor amounts of several other phases were detected, e.g. magnesium(II) carbonate (MgCO3), magnesium(II) oxide (MgO), diiron(III) magnesium(II) tetraoxide (MgFe2O4), and zinc(II) oxide (ZnO). Elemental analysis revealed the major compo- nents of the samples to be potassium (K), Mn, and silicon (Si). Anion chromatography revealed that water-soluble anions were present as sulfate (SO42 – ), chloride (Cl – ), and fluoride (F – ), which agree well with XRD results. The FeMn and SiMn furnace-fume water-extracts were slightly alkaline. The findings of this thesis show that workers are exposed to a variety of different compunds, which agree well with previous studies. In addition to sample characterization, XRD background levels of polyvinyl ethylene (PVC), polycarbonate (PC), and polytetrafluoroethylene (PTFE) membrane filters were checked. Further, XRD background signals of various sample plates were checked: aluminium (Al) plate, cellullose membrane filter, single-crystal Si plate manufactured by PANalytical, and a single-crystal Si plate manufactured by MTI corporation. PVC background levels were significantly lower than PC and PTFE filters, and the two single- crystal Si plates were, as expected, of superior quality with respect to XRD background levels. Phase identification of aerosol filters and personal exposure filters was limited by low signal-to-noise ratio, due to the low amount of sample mass on the filters. Stacking of filters resulted in a large increase of diffracted signals, but also a large increase in noise. The use of a monochromator in the XRD instrument may improve spectral purity and reduce background signals. Future investigations should focus on increasing sample material for XRD characterization of aerosol samples. One way to achieve this may be by adapting NIOSH Method 7500 to manganese-holding aerosol samples. The possible exposure to α-quartz should also be investigated further.