Spectroscopic investigations of mining residues drying kinetics to predict and prevent fugitive dust emission

Aluminum oxide extraction from bauxite generates over 3,000 tons of filtered bauxite residue daily at Rio Tinto’s Vaudreuil plant. Managing these mine tailings includes addressing the risks of fugitive dust scattering from their surfaces while they are momentarily stored in the open at the disposal site in Jonquière, Quebec. To mitigate these risks, continuous monitoring of the drying process is imperative. A real-time quantification of their surface moisture content (SMC) is necessary to predict and prevent fugitive dust scattering, thereby reducing managing and mitigating costs. Albedo measurements in the near infrared (λ = 1200–1550 nm) will be shown to be a precise, sensitive and selective optical method for characterizing the mine tailings’ SMC and monitoring their drying rate. A portable device has been designed for continuous in situ SMC measurement under adverse environmental and operational conditions. This device also facilitates laboratory investigations into the dependencies of the mine tailings’ drying rates on ambient air temperature and relative humidity, revealing how atmospheric boundary conditions influence water transport mechanisms within their interconnected porous network, namely capillary pumping and gaseous diffusion. Frozen tailings show reduced drying rates due to suppressed capillary transport, while increasing temperatures and decreasing relative humidity of the ambient air accelerate drying rates. A comprehensive and quantitative knowledge of the impact of these key parameters, along with that of meteorological conditions such as wind speed and solar irradiance, and their recent history, should improve our description of water transport mechanisms and kinetics within mine tailing. The quantification of their drying rates should also improve our prediction of the evolution of their SMC and promote the development and implementation of models and tools necessary for the forecasting and prevention of fugitive dust scattering events thereby contributing to the reduction of the environmental impact of mine tailings disposal site.