Respirable coal mine dust (RCMD) has long been recognized as an occupational health hazard. In addition to coal, RCMD can contain minerals such as crystalline silica (i.e., most often present as quartz). There has been a resurgence of lung diseases among US coal miners since the late-1990s which has emphasized the need for better quartz monitoring, and better dust characterization in general. Quartz monitoring in coal mines has traditionally used infrared (IR) spectroscopy-based analytical methods such as the MSHA Method P7 that require significant sample preparation and must be performed in a centralized lab. There are generally thus days to weeks between dust sample collection and reporting of results, which can prevent the prompt mitigation efforts to better control dust and reduce exposures. Recently, a rapid analysis method for quartz has been developed by the US National Institute for Occupational Safety and Health (NIOSH) using direct-on-filter (DOF) Fourier Transform Infrared (FTIR) spectroscopy. The method has been demonstrated in a number of NIOSH-led studies using both laboratory and field samples, and the results show very good accuracy relative to the Method P7 reference. However, it has heretofore not been widely used by others or compared to results from other non-IR analytical methods. Moreover, while FTIR can allow the measurement of additional analytes, this has not yet been a focus of DOF FTIR for RCMD analysis. Analytes such as kaolinite and calcite could be of particular interest in the context of RCMD source apportionment.
In this thesis, the DOF FTIR method is used to estimate silica, kaolinite, and calcite mineral fraction in RCMD samples collected in 16 coal mines, and in the laboratory using dust source materials from those same mines. The results are compared to results from other dust characterization methods such as mass-based thermogravimetric analysis (TGA) and particle-based scanning electron microscopy with energy dispersive X-ray (SEM-EDX). Results indicate the usefulness of the DOF FTIR method, and comparison suggests the presence of significant non-carbonate minerals other than silica and kaolinite in the coal mine dust. The results also show that SEM-EDX frequently indicates more mineral content (primarily other aluminosilicates), than that is predicted by either FTIR or the TGA. Additionally, by focusing mainly on calcite (generally sourced from limestone-based rock dust used in coal mines to prevent coal dust explosion), the second part of this study explores basic source apportionment by analyzing mine samples and samples of major dust source materials (such as run-of-mine coal, rock strata, and rock dust products). Results show that calcite can serve as a suitable proxy for rock dust in coal mine dust, and the results are consistent with expectations surrounding the contribution of dust from different mine locations and sample sources. Additionally, the DOF FTIR also showed good agreement with the TGA and SEM-EDX. / Master of Science / Respirable dust generated in coal mines has long been recognized as an occupational health hazard. In addition to coal, coal mine dust can contain minerals such as crystalline silica, which is particularly hazardous. Since the mid-1990s, there has been an alarming and unexpected increase in lung diseases in coal miners. Respirable crystalline silica is assumed to be a likely causal factor for this resurgence of lung diseases, and this has emphasized the need for better respirable crystalline silica monitoring and to better understand coal mine dust composition. The standard method of measurement of silica (called the MSHA Method P7) generally takes days to weeks between dust sample collection and reporting of results, which can prevent the mine from taking prompt mitigative efforts to better control dust and reduce exposures. Recently, a rapid analysis method for silica has been developed by the US National Institute for Occupational Safety and Health (NIOSH) called the DOF FTIR (direct-on-filter Fourier Transform Infrared Spectroscopy). This method has been shown to have very good accuracy relative to the standard method (MSHA P7). However, it has heretofore not been widely used by others or compared to results from other analytical methods. Moreover, DOF FTIR can also be used to estimate other minerals of interest such as kaolinite and calcite, which can be important in the context of understanding coal mine dust sources.
In this thesis, the DOF FTIR method is used to estimate silica, kaolinite, and calcite mineral fraction in coal mine dust samples collected in 16 coal mines, and in the laboratory using dust source materials from those same mines. The results are compared to results from other dust analysis methods such as mass-based TGA (thermogravimetric analysis) and particle-based SEM-EDX (scanning electron microscopy with energy dispersive X-ray). Results indicate the usefulness of the DOF FTIR method, and comparison suggests the presence of significant non-carbonate minerals other than silica and kaolinite in the coal mine dust. The results also show that SEM-EDX frequently indicates more mineral content than that is predicted by either FTIR or the TGA. Additionally, by focusing mainly on calcite—which is generally sourced from limestone-based rock dust used in coal mines to prevent coal dust explosion—the second part of this study explores the sources of the dust by analysing samples collected in mines, and samples generated in lab from major dust source materials (such as the raw coal, rock strata, and rock dust products obtained from the mines). Results show that calcite can be representative of rock dust in coal mine dust, and the results are consistent with expectations surrounding the contribution of dust from different mine locations and sample sources. Additionally, the DOF FTIR also showed good agreement with the TGA and SEM-EDX.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/104971 |
| Date | 09 September 2021 |
| Creators | Pokhrel, Nishan |
| Contributors | Environmental Science and Engineering, Sarver, Emily A., Marr, Linsey C., Keles, Cigdem |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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