Cracking, salinity and evaporation in mesoscale experiments on three types of tailings

Evaporation is a phenomenon useful in assisting in the dewatering and stabilisation of various mineral wastes. This paper summarises findings on the influence of cracking and salinity on evaporation in mesoscale (1.0 m by 0.7 m in plan) deposition experiments on three different mineral slurries: thickened gold tailings, thickened oil sands tailings and oil sands tailings modified by in-line polymer flocculation. Each tailings exhibited substantially different evaporation related phenomena. In the two finer-grained oil sands tailings, crack development correlated with apparent actual evaporation rates larger than the potential rate, which ceased once crack volume stopped increasing. Total suction at the surface was dominated by osmotic suction in the thickened oil sands tailings, whereas total suction was largely matric in the other two tailings. In the gold tailings, no strong signal from cracks on evaporation could be detected. The gold tailings exhibited 'declining stage I' evaporation, which has been recently described from idealised drying experiments on sands. The relatively unique behaviour of each tailings type with respect to evaporation highlights the importance of considering larger scale effects when assessing tailing dewatering by evaporation.