Rheological properties of bauxite residue: the role of tailings gradation and solids concentration

Debris flow ensued as a result of tailings dam failure depends greatly on the fluidity of slurry created and is better described by measuring the rheological properties. In the present study, rheological properties (i.e. viscosity and yield stress) of bauxite residue are measured using dynamic shear rheometer with parallel plate configuration to understand the role of tailings gradation, solids concentration, and moisture content. Rheology measurements are taken on three variety of tailings gradations (coarse: < 0.425 mm), medium: < 0.3 and > 0.15 mm), and fine: < 0.075 mm) by varying solids concentration from 67.57 to 72.46% and moisture content from 38 to 48%. Additionally, stress growth tests with resting time are performed to determine the static yield stress, the measurement of which is important to get insight into debris flow initiation. Herschel-Bulkley model is used to infer the information of viscosity and yield stress parameters. The viscosity is measured as 2033 Pa-s and 930 Pa-s with shear rate of 0.1 s(-1) at 38 and 48% moisture content, respectively. It is found that static yield stress is 15-20 times higher than the dynamic yield stress for bauxite residue, attributed to thixotropy behaviour. Besides measurements by rheometer, yield stress is also measured by slump tests using cylindrical mould set-up. It is noticed that bauxite tailings prevalently show non-Newtonian fluid characteristics and shear-thinning behaviour at different solids concentrations. The results are vital to assess the impacted area, run-out length, front velocity, distribution, and pumping energy of tailings if released instantaneously in colossal amount.