A cascade impactor for mineral particle analysis

A cascade impactor (NCI) made of stainless steel with six stages was developed to collect particles using 50% cutpoints in the range of 0.64 to 19.4 mm. The sixth stage of the NCI was calibrated using monodisperse aerosols. The experimental MMAD (mass median aerodynamic diameter) was 0.634 mm, which agreed with the calculated MMAD. The NCI, stacked filter unit (SFU) and personal air samplers with the cyclone were used to characterize the workers exposure in two Brazilian plants where niobium minerals with thorium associated to the crystal lattice are processed. The Th, U, Nb, Zr, Pb, Fe, Sr, and Y air concentrations were determined. The MMAD of the particles containing these elements have shown the availability of mineral particles in the fine particles of aerosols. The Th concentration in the samples collected using SFU were in the same order of magnitude of those collected with the cascade impactor and are correlated.