The solids concentration distribution in the deep cone thickener: A pilot scale test

Cemented backfill or surface deposition of paste tailings is increasingly being considered as a simple and effective means of reducing the hazards of conventional slurry deposition and recovering water for recycle. Although gravity thickening has been widely used in the mineral industry to increase the solids concentration of tailings, the accurate prediction of the concentration distribution in three-dimensions and discontinuous operational state has proven to be difficult. We investigated the axial and radial solids concentration distribution at discontinuous state in a pilot deep cone thickener as a function of bed height and residence time. The feed flux of lead/zinc tailings was 0.254 t·h−1· m−2 with a flocculant (high molecular weight anionic polyacrylamide) dose of 20 g/t. The thickened solids bed was sheared by a rotating rake at a rate of 0.2 rpm. The underflow was recirculated at a flux of 0.5 t·h−1·m−2, which can introduce additional shear stresses into the bed. The results of the bed density profile showed that, beside the clarification zone, the area below the feedwell could be divided into four zones: the dilution zone caused by free settling and diffusing action, the hindered settling zone in which the concentration was lower than the gel point, the unraked bed zone with a large concentration gradient and, finally, the raking zone with the highest slurry concentration and lower concentration gradient.