Micro-scale mechanism of sealed water seepage and thickening from tailings bed in rake shearing thickener

Paste and Thickened Tailings (PTT) technology has the advantages of water-saving, dam safety, and environmentally friendly, which can improve tailings disposal and backfill operation. In the process of thickening preparation, the ultra-fine tailings particles are prone to form suspended water-locking flocs, which are severely detrimental to the underflow concentration improvement in the thickener. This study focuses on the deep cone thickener underflow density improvement. The high-precision CT scanning and three-dimensional reconstruction technology were used to explore the pore structure shear evolution to enhance underflow slurry dewatering behavior and reveal the thickening mechanism. Results show that when the shearing rate of the rake is two revolutions per minute (rpm), the concentration of tailings underflow rises from 59.2% wt to 68.5% wt, increases by 15.71%. The rake shearing breaks the pore structure of the flocs network, the pores quantity increases and the porosity decreases by 21.74%. After shearing, suspended particles fill the pores, the pore connectivity decreases by 26.74%, the absolute permeability decreases by 31.35%, the sealed pore water is discharged, and the bed slurry can be thickened. The study can improve the utilization rate of tailings (from classified tailings to whole tailings), make the thickening process going deep(raising high concentration slurry to paste slurry), and increase the backfill capacity (backfill underground goaf in time), so as to effectively reduce the tailing pond and goaf quantity.