Application of X-ray diffraction with Rietveld refinement to quantify mineral composition including crystalline silica in respirable dust.

Abstract

This study aimed to test the use of Rietveld refinement on respirable aerosol samples to determine the phase of respirable crystalline silica (RCS) and other minerals. The results from the Rietveld refinement were compared to an external standard method and gravimetrical measurements. Laboratory samples consisting of α-quartz, feldspar, and calcite with variable proportions and total mass loadings were made and analyzed using the NIOSH 7500 Silica, Crystalline, by XRD (filter redeposition) method, followed by Rietveld refinement. Field samples of respirable dust, from construction sites working with concrete, brick, and other materials were included. To correct for amorphous content and unidentified phases, an internal standard was added to the field samples, which were treated like laboratory samples. Rietveld refinement was successfully used for quantification of RCS in laboratory and field samples. The method showed comparable results to the NIOSH 7500 method for quartz and remained linear for laboratory samples up to 20 mg. The lowest quantified amounts of quartz in the laboratory samples were 5 µg. The two methods yielded similar results for RCS in field samples with a total mass of up to 15 mg and a quartz content of 1.8 wt% to 11 wt%. A total sample mass of above 0.5 mg was required for optimal quantification of crystalline phases by Rietveld refinement. The method proved useful in determining RCS and other crystalline components in field samples and corrected for interferences even with a complex matrix and high mass loading.