CFD-PBM Simulation of Flocculation-Settling in Deep-Cone Thickener: Effects of Fine Tailings Content and Rake Rotational Speed

High-concentration slurry preparation via deep-cone thickeners (DCTs) is crucial for tailings recycling in cemented paste backfill (CPB), where fine tailings content (FTC) and rake rotational speed (RRS) are key regulators of thickening efficiency. Based on a coupled computational fluid dynamics–population balance model (CFD-PBM), laboratory-scale numerical simulations were conducted to reveal the effects of three FTC levels and four RRS levels on tailings flocculation-settling and thickening behavior. Results indicate that the median floc size D50 presents an inverted U-shaped trend with increasing FTC and peaks at 60% FTC, corresponding to a mud layer height of 739 mm, optimal solid-phase uniformity, and superior settling performance. A low RRS of 0.1 r/min facilitates particle agglomeration and removes bottom eddy-stagnant zones; 1 r/min achieves the most uniform global velocity distribution, whereas intense shear at 10 r/min destroys floc structures and markedly impairs solid–liquid separation. The 37 μm fine tailings fraction is recommended to be controlled at 50–70%, paired with an RRS range of 0.1–1 r/min. This study not only advances the fundamental understanding of tailings flocculation-settling but also offers actionable theoretical guidance on parameter optimization and enhancing robust DCT performance.