LAUSR

Based on epidemiological records of workers at Ni operations, regulatory guidelines often target specific Ni compounds for setting exposure limits. Thus, reliable methods of Ni speciation in airborne dust samples are required for effective monitoring of workplace exposure. In this study, Ni speciation of dust collected from a stainless steel operation was performed using a variety of methods: Zatka sequential leaching (original and modified protocols), soluble and insoluble Ni as described in ISO 15202, and quantitative mineralogy (QEMSCAN). Mineral characterization was also performed on bulk material collected from selected work areas at the plant. The quantitative mineralogical analysis determined that the Ni dust is composed of oxidic Ni (Ni in chromite and trevorite, > 80 % of the Ni in most samples) and metallic Ni (Ni-Fe alloy), and the results were validated against chemical assays and alternate methods of mineral characterization (Electron Probe Microanalysis, EPMA). In contrast, the original Zatka method erroneously identified soluble Ni as a major Ni contributor, whereas the modified Zatka method identified sulfidic Ni. The mineralogy identified ambient dust and grain sizes and textures of individual Ni compounds as potential factors that can affect leaching selectivity. Improving methods of sequential leaching is important because the resolution of quantitative mineralogical techniques diminishes at < 3 µm (respirable dust fraction). We recommend that quantitative mineralogy be performed in parallel with methods of sequential leaching to provide a robust system of characterization.