Prediction of Water Vapor Movement through Waste Rock

Evaporative losses from the surface of barren waste rock piles in arid environments occur as a result of water vapor diffusion. Water vapor diffusion is accompanied by adsorption of water vapor. A review of the literature found that adsorption of water vapor is commonly described as a sigmoidal function of suction with a predominant linear portion when plotted against the log of suction. Laboratory column tests were conducted with glass beads and waste rock to study water vapor diffusion. A monitoring system was developed for measuring relative humidity and temperature through the column. Water vapor fluxes and relative humidity profiles through the column were measured under steady-state conditions to establish the method of estimating the water vapor diffusion coefficient. Transient water vapor fluxes and relative humidity profiles were measured and a numerical model was developed to simulate the laboratory observations. The numerical model demonstrated the importance of water sorption in controlling the transient water vapor flux. Sorption described as a log–linear function of suction gave reasonable results for the numerical modeling of the glass beads and waste rock.