Studies on the Equivalence of Air and Water Elutriation of Amphibole Elongate Mineral Particles

Abstract

There appear to be few, if any, published data on the size distributions of the respirable fractions of airborne elongate mineral particles (EMPs) that can arise from dispersion of dust generated by comminution of known nonasbestiform amphiboles. Some air sample information is available from mining activities thought to contain only nonasbestiform amphibole, but these data can be criticized on the basis that mines are inhomogeneous and may contain minor occurrences of asbestiform material. Selected crystals of five nonasbestiform amphiboles were used in a laboratory study to compare the size distributions of the respirable fractions separated by water and air elutriation. Water elutriation was carried out using the fractional extraction procedure. For the air elutriation measurements, emissions of EMPs from a dual-component vibrating bed aerosol generator were sampled on to polycarbonate filters at the top of a vertical elutriator. For the water elutriation measurements, TEM specimens were prepared from the aqueous suspensions using the filtration and preparation procedures of ISO 13794. For the air elutriation measurements, TEM specimens were prepared from the polycarbonate filters using ISO 10312. For each of the measurements, the dimensions of approximately 200 EMPs longer than 5 μm were determined. The size distributions of the respirable fractions derived from each of the elutriation procedures were compared. It was determined that separation of the respirable fractions of comminuted nonasbestiform amphiboles by water elutriation is a reproducible procedure, both with respect to the size distributions and the number of respirable EMPs per gram of respirable dust. Air elutriation gave similar results for the five nonasbestiform samples, but differences were observed in some of the EMP size distributions. It appears that, in TEM analyses, the mean widths of a proportion of the nonasbestiform amphibole EMP population are overestimated for water deposition on filters, and are underestimated for air deposition on filters.