Mathematical model and factors of paste thickener rake torque

Abstract

In mining, cement paste backfill technology uses the high concentration tailings that remain after mineral processing to backfill underground stopes. These tailings are prepared by dewatering, mixed with a proportion of cement or other binder, then, after sufficient mixing, the saturated homogenized slurry is pumped or gravity-transported. Therefore, high concentration tailings are a prerequisite for cement paste backfill preparation and high quality backfill. The paste thickener is a key component that shows high efficiency dewatering, and rake shearing greatly affects tailings dewatering performance; therefore, appropriate rake torque design is crucial for efficient paste thickener operation. Rake torque is a key factor in determining the dewatering extent and the rate of flocculation in the networked structure bed in the thickener compression zone. In some industry processes, the problems of rake bogging, rat holing, swirl motion, and insufficient underflow concentration can affect production or seriously damage equipment. All these problems can be attributed to poor rake design or operation. Based on the non-Newtonian characteristics of a mud bed and the correlation of slurry initial shear stress with solids concentration, a torque mathematical model was proposed. The model predicted a rake torque increase with an increase in underflow concentration during thickener operation; the percentage of rake torque variation reached 4.67%. Regression analysis indicates that the percentage of rake torque presents as a polynomial function of the underflow concentration. At the same time, bed height affected rake torque slightly and the rake torque percentage varied within 0.27% when the bed height fluctuated. The predicted effects of underflow concentration and bed height on rake torque are confirmed and compared with 64 h of operational data on thickener operations in a lead-zinc mine.