Modelling evaporation of paste tailings from the Bulyanhulu mine

Accurate predictions of drying rates are desirable to optimize surface deposition of thickened or paste tailings. A series of laboratory and field trials were implemented to study evaporation from tailings at the Bulyanhulu gold mine and were compared with numerical simulations using the unsaturated flow model SoilCover. The laboratory tests included two “large-scale” experiments on 10 cm thick layers of tailings 2 m by 1 m in plan, and a smaller column test on a 20 cm thick and 20 cm diameter sample. Data monitored during these tests included albedo, volume change, degree of cracking, matric suction, water content, and drying rate. Field data included gravimetric water contents and albedo values. The model could reasonably simulate the laboratory experiments when adjustments were made to account for self-weight consolidation and the effect of volume change on the relative permeability function. The model could simulate drying in the field for up to 3 weeks after deposition before the accumulation of gypsum and magnesium sulphate salts began to affect evaporation. Cracking and salt accumulation were observed both in the laboratory and in the field. A general model for simulating drying from paste tailings should incorporate the effects of cracking and salts.