On the thixotropy of mature fine tailings

Abstract

The rheological behavior of mature fine tailings (MFTs) is investigated using transient and steady shear flow fields. The structure breakdown of intact MFT samples is examined by a startup flow experiment at various shear rates. The yield stress of MFTs is estimated by the steady shear stress values at low shear rates. Oscillatory shear (strain amplitude sweep) is also used to verify the obtained yield stress value. MFT samples exhibit thixotropy and a positive hysteresis loop at short shearing time intervals in increasing and decreasing stepwise shear rate tests. The observed hysteresis loops and thixotropy disappear by increasing the shearing time intervals, as the system reaches its equilibrium steady-state structure. The time-dependent rheological behavior of MFTs is quantified by a structural kinetics model through the dimensionless structure parameter, λ. [Toorman, “Modelling the thixotropic behaviour of dense cohesive sediment suspensions,” Rheol. Acta 36, 56–65 (1997).] The kinetic parameters are estimated based on steady-state stresses, elucidating the relative effects of shear rate and Brownian motion on buildup and breakdown of the structure. The flow behavior of MFTs predicted by the structural kinetics model is in agreement with the experimental data.