Dispersion of particulate matter generated at higher depths in opencast mines

• Vertical concentration profile of particulate matter is measured.
• Size variability of particles in background air and mining emission is estimated.
• Particulate matter dispersion dependency on depth is estimated.
• Predictor equations for the upward movement of particles are developed.
• No significant relationship was found between particle concentration and wind speed.

Dispersion studies of particulate matter generated during opencast mining until now have mostly been confined to estimation of emissions from individual mining activity as well as total emission from an opencast mine. No study is available on particulate matter dispersion inside the mine since its generation until it escapes the mine. However, this is important particularly for deep mines where mine workings are confined to bottom benches and emission from it passes across all benches before it reaches surface, thus affecting the exposure level of workers at higher benches. This paper presents the results of a study on the dispersion of particulate matter in Malanjkhand Copper Project, one of the deepest opencast mines in India. The study was conducted for 4–5 h daily for 10 days during the month of October 2013. Mining activities at 168–180 m depth were the source of particulate matter. Particulate matter concentrations were measured by portable aerosol spectrometer. Meteorological data were collected using portable weather station. There was no direct correlation between wind speed and particulate matter concentration. Correlation between wind direction and particulate matter concentration was somewhat better. While coarse particle (PM2.5–10) constituted 6%–8% of the background concentration, it increased to 31%–61% during mining, primarily due to generation of more coarse particles during mining. At locations farther from and higher than the source location, continuous decrease of concentration of particles of all sizes was observed due to settling and dispersion of particles. From source locations to the surface, the average mining induced incremental concentration of PM2.5–10, PM1–2.5 and PM1 decreased from 127.02 to 3.98 μg m−3, 5.39 to 1.95 μg m−3 and 20.26 to 2.74 μg m−3 respectively. An empirical relationship has been established between particulate matter concentration and depth.

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