A Three-dimensional Finite Element Model to Predict Airflow and Pit Retention for an Open-Pit Mine

Abstract

Surface mining operations (e.g., blasting, loading, hauling, and crushing) are sources of airborne particles. The estimation of concentrations of fugitive dust for an open-pit mining situation has traditionally been done using United States Environmental Protection Agency (EPA) models such as the Industrial Source Complex (ISC) model. Since the dust-producing operations at open-pit mines may occur at depths up to several hundred meters below grade, only a fraction of fugitive dust generated inside the pit escapes to the surface, where it may then be transported to mine boundaries. This tendency for particulate matter (PM) to remain inside the pit has been called “pit retention” (TRC 1985). The magnitude of pit retention is expressed as “escape fraction”, defined as the mass fraction of emissions that escapes from the mine pit to the surface. The two mechanisms occurring simultaneously that contribute to the pit retention phenomenon are: the decoupling of the wind field in the pit from the wind field at the surface, and the deposition and settling of particulate on the mine pit surface and along the pit walls. A dispersion model ignoring the influence of pit retention will overpredict the downwind concentrations. The presence of a mine pit disturbs the airflow above and inside the pit, so that the plume of dust may not have the Gaussian distribution imposed by many dispersion models.