Physical, mineralogical and wetting characteristics of dusts from Interior Basin coal mines

Abstract

This paper presents physical, mineralogical and wetting characteristics for dust samples from the Interior Basin coal mines. The samples were from three sources: 1) Produced in the laboratory from bulk samples of coal and immediate roof and floor strata, 2) In-mine samples collected through gravimetric sampling of active mining areas, and 3) In-mine samples collected from wet-scrubbers on continuous miners. Particle size distribution analysis showed that about 30, 67, 68 and 60% of dust particles are in the respirable range (<10μm) for bulk samples of coal, and roof, and floor strata and for in-mine dust samples collected from scrubber, respectively. SEM image analysis of in-mine gravimetric dust samples showed most particles to be spherical and large number of particles to be of ≤1μm. Bulk samples of roof and floor strata were determined to have varying quartz content from 6.2 to 13.7% by weight. Quartz, kaolinite, calcite, pyrite and illite were the most prevalent minerals in bulk dust samples. XRD data showed presence of quartz in un-wetted dust particles indicating the co-existence of minerals and macerals. Coal petrography analysis showed vitrinite as the dominant maceral (68–86%) in bulk coal samples.Two approaches were used to assess dust wettability rates: 1) fixed-time wettability that attempts to simulate wetting around mining environments, and 2) absolute-time wettability that evaluates intrinsic wettability rates. Fixed-time wettability for coal dusts were in the range 57–99% (% wt.) with majority of mines having values above 90%. The middle portion of the coal seam was found to be least wettable. The contact time between dust particles and water droplets was an important factor for improving wetting of coal dust. An increase in contact time from 10 to 25s showed 3–27% improvement in fixed time wettability. Absolute-time wettability data showed that coarser particles required more time for complete wetting. The data above is being actively used to design engineering controls for improved dust control in mines.