Tailings desiccation process studied in environmental chamber experiment

Abstract

Case studies and numerical simulations show that the long-term stability of tailings dams largely depends on the evolution of their water content. Therefore, desiccation is one of the critical processes influencing the tailing dam's safety. In this work, the air-drying of tailings, starting from a sludge condition, is studied using a fully instrumented column experiment, performed in an environmental chamber with temperature and relative humidity control. Based on the experimental observations, a conceptual model for the desiccation process is proposed. The model consists of the combination of two mechanisms driven by evaporation: shrinkage and capillary rise. The latter is only activated after a granular structure develops (shielding skeleton), capable of sustaining the suction-induced intergranular forces. This evidence explains the tendency of real deposits to develop an unsaturated, dry tailings crust enclosing a body of mud-consistency tailings. In addition, the role of dissolved salts in the desiccation process was observed. Solutes in pore water limit the evaporation rate throughout the test by increasing osmotic suction. Moreover, salt precipitation was observed to cause an interruption of the desiccation process on two occasions during the experiment: first, by the formation of a superficial precipitation crust and later by pore clogging within a shallow layer.