Evaluating the interference potential of minerals in infrared absorbance-based quantification of respirable crystalline silica in mine dusts

Miners face a variety of respiratory hazards on the job, including exposure to respirable crystalline silica (RCS), which can lead to adverse health outcomes such as silicosis and lung cancer-both potentially fatal lung diseases. Infrared spectrometry offers the possibility of portable end-of-shift quantification of RCS at mine sites. However, some mine dusts contain minerals that may interfere with this quantification method, as their infrared absorbance bands overlap with those of silica. To evaluate the impact of such interferences, potential mineral interferants were identified in the geologies of 27 metal mines using the United States Geological Survey and Mindat.org databases. These mines were selected based on historically high RCS levels, as evidenced in the Mine Safety and Health Administration (MSHA) field-sampling database, and on the number of employees potentially exposed. The significance of 44 potential interferants was evaluated using Fourier Transform Infrared spectroscopy (FT-IR), by measuring their absorbance per unit mass in the α-quartz doublet region of the spectrum (816-767 cm^-1). The extent to which each mineral interfered with this region was quantified as its integrated absorbance relative to RCS. This quantification of interference provides data critical for the timely and portable quantification of RCS in mine dusts. Of the 44 specimens analyzed, three (goethite, azurite and actinolite), which are not mentioned in the standard infrared methods for quantification of RCS, were found to interfere with a magnitude of 10% or more. Despite being commonly mentioned as interferants in the literature, the feldspars Albite and Anorthite did not interfere with a magnitude of 10% or more.