Variability behavior of yield stress for unclassified tailings pasted under measurement time‒velocity double factors

The rake torque of deep cone thickener, pipeline resistance, and paste accumulation slope were important technological parameters for the efficient paste backfill process, which are to be solved or optimized for the practical application in mines. The yield stress of paste was considered as an important rheological parameter for solving these technological parameters. In the past, the research of yield stress of the materials for unclassified tailings paste was limited to the concept and analysis of yield stress fluids used. For example, the fluids such as Bingham fluid, H–B fluid, and Casson fluid were commonly used. When the shear stress of the paste was less than yield stress, the slurry paste remained stationary, and the paste started to flow when shear stress was greater than yield stress. So it concluded that the yield stress was an important parameter in the transition from solid state to flow state. It was considered that yield stress of paste with a certain ratio of material had a unique value, which was regarded as inherent physical property of paste. At present, most rheological studies of concentrated suspensions had found that the evolution of particle structure in suspensions resulted in thixotropy, which increased the difficulty of measuring yield stress of suspensions. Considering the unclassified tailings as specific experimental sample, experiments with different mass fractions paste were carried out and yield stresses were measured. The influence of measuring velocity and measuring time on yield stress of paste was analyzed. It is found that the yield stress value is correlated with measuring protocol. By comparing and analyzing peak yield stress, dynamic yield stress, and static yield stress, the variations in yield stress of paste with measuring time and measuring velocity under certain conditions were obtained. It is observed that the peak yield stress and static yield stress are proportional to measuring velocity of paste, and the dynamic yield stress is inversely proportional to measuring time. The coefficients of variation of degree of yield stress with discreet features are evaluated. The dynamic yield stress of 74% mass fraction paste has the largest C_v, which is 27.07%, while the static yield stress of 66% mass fraction paste has the smallest C_v, which is 2.33%. Further, the variation of particle interaction force and particle network structure with measuring velocity and measuring time during paste yielding was analyzed from the mesoscopic level. The mechanism of variation in yield stress of paste was elucidated based upon the analysis and the results and the necessary values of parameters were obtained for the efficient backfill process.