A Standard Characterization Methodology for Respirable Coal Mine Dust Using SEM-EDX

Abstract

A key consideration for responsible development of mineral and energy resources is the well-being of workers. Respirable dust in mining environments represents a serious concern for occupational health. In particular, coal miners can be exposed to a variety of dust characteristics depending on their work activities, and some exposures may pose risk for lung diseases like CWP and silicosis. As underscored by common regulatory frameworks, respirable dust exposures are generally characterized on the basis of total mass concentration, and also the silica mass fraction. However, relatively little emphasis has been placed on other dust characteristics that may be important in terms of identifying health risks. Comprehensive particle-level analysis to estimate chemistry, size, and shape distributions of particles is possible. This paper describes a standard methodology for characterization of respirable coal mine dust using scanning electron microscopy (SEM) with energy dispersive X-ray (EDX). Preliminary verification of the method is shown based several dust samples collected from an underground mine in Central Appalachia.

A Computer-Controlled SEM-EDX Routine for Characterizing Respirable Coal Mine Dust

“…To account for these differences, the atomic percentage limits for the CCSEM routine were gradually refined until automated and manual results agreed across a wide range of individual particles (i.e., between about 1-10 µm, and representing all defined chemical composition categories shown in Table 2). It should also be noted that observations during this process, along with previous observations [27,28], indicated that particles classified in the "mixed carbonaceous" category are most often small and/or thin alumino-silicate particles [27,28]. Therefore, the mixed carbonaceous and alumino-silicate categories have been combined (i.e., to a total alumino-silicate, TAS, category) for reporting CCSEM-EDX results in this paper.…”

“…Regarding particle chemistry, the classification criteria for the CCSEM-EDX routine were adapted from those previously reported for the manual routine [28]. In that earlier work, detailed manual SEM-EDX analysis of respirable dust samples representative of Appalachian coal mines was used to define six distinct classification categories: carbonaceous, mixed carbonaceous, alumino-silicate, quartz, carbonate, and heavy mineral.…”

“…Table 2. Classification criteria for dust particle chemical composition categories (modified from [28]). Categories are abbreviated as C: Carbonaceous (i.e., coal), MC: Mixed Carbonaceous (i.e., very small or thin alumino-silicates), AS: Alumino-Silicates (e.g., clays and feldspars), Q: Quartz (i.e., crystalline silica), CB: Carbonate (e.g., calcite, dolomite), HM: Heavy Minerals (e.g., pyrite, titanium dioxide).…”

“…Based on the manual method previously described by Sellaro et al (2015) [28], a CCSEM-EDX routine was developed to estimate particle size, aspect ratio, and chemistry classification distributions. It analyzes approximately 500 particles per sample, scanning multiple frames of view to cover a relatively wide sample area.…”

“…It involves manual analysis with a scanning electron microscope equipped with energy dispersive X-ray (SEM-EDX), and has been described in detail elsewhere [25][26][27][28]. SEM-EDX is a very powerful tool for particulate characterization, and is well established for chemical identification of particles (e.g., see [29][30][31][32][33][34][35]) and determination of size and shape parameters (e.g., see [33,36]).…”