Investigation of flocculation behavior of tailings during settling-concentration: influence of true density, particle size, and mud layer height

Abstract

The rapid concentration of tailings is a crucial initial step in the cemented paste backfill (CPB) process, as it ensures the stability of the backfilling slurry concentration and the continuity of the backfilling process. The structure of flocs plays a pivotal role in tailings concentration, directly contributing to such critical technical parameters as settling speed and bottom flow concentration. However, most of the current studies focus on flocculant addition rather than the tailings slurry itself. Also, there is a lack of uniform characterization of the flocculant structure in the flocculation and settling system. This study establishes a semi-quantitative assessment system for evaluating the fine structure of tailings flocs based on indicators such as the exposure state of coarse particles, floc size, and floc compactness (porosity). The findings reveal that, during the settling process, the higher true density of tailings (3.156 g/cm3) and intermediate particles (40 wt% of 38 μm–74 μm particles) attenuates the clamping effect of turbulence on settling, leading to a faster settling rate to 0.65 cm/s and 0.29 cm/s respectively. Moreover, in the thickening process, tailings located at the bottom of the mud layer expedite the precipitation of interstitial water within the floc structure through the combined influence of gravity and rake frame shear. Consequently, a denser floc structure forms, as evidenced by a higher concentration of bottom flow at a macroscopic level. This conclusion provides a theoretical basis for faster preparation of highly concentrated tailings slurry in CPB.