Abstract

The middle trough of spirals serves simultaneously as a buffer zone for variations in hydrodynamic parameters and as a region where mineral particles of different densities are prone to mixing, exerting a profound influence on particle-separation effect. This study employed a multi-fluid volume of fluid (VOF) model incorporating the Bagnold effect to simulate the ilmenite–chlorite slurry flow in a custom-designed Φ400 mm short-travel spiral concentrator with three turns. This study systematically investigated the influence of the transverse inclination angle of the middle trough (ranging from 3.5° to 9.5°) on separation indicators, flow film morphology, secondary circulation characteristics, and particle force dynamics. The results indicate that employing a lower transverse inclination angle is more conducive to improving the technical separation indicators for ilmenite and chlorite. When using enrichment ratio and separation efficiency as criteria, the optimal inclination angles range from 3.5° to 5° and 3.5° to 6.5°, respectively. Meanwhile the separation efficiency and its sensitivity to the middle trough transverse inclination angle vary remarkably with different feeding sizes. Feeding of 112 μm ilmenite and 19 μm chlorite yields the premium separation performance and is minimally affected by the middle trough transverse inclination angle. Conversely, as the ilmenite particle size decreases or the chlorite particle size increases, the separation indicators decline but become significantly regulated by the middle trough transverse inclination angle, exhibiting a desirable angle range of 3.5–6.5°. Hydrodynamic parameter analyses indicate that a moderate flow film depth, continuous secondary circulation morphology and stabilizing inner circulation in the middle trough can be obtained at a middle trough transverse inclination angle scope of 3.5–6.5°. Once the inclination angle exceeds 6.5°, a distinct ridge forms in the flow film of the middle trough, and extensive disruptions occur in the outward circulation, which subsequently impedes the outward transport of low-density particles along with the fluid. At a middle trough transverse inclination angle scope of 3.5–6.5°, the Bagnold force exerted on the ilmenite particles in the middle trough remains low during the initial stage of flow field evolution, which favors their retention in the lower fluid layer to become the concentrate product. Concurrently, the chlorite particles near the inner region experience a higher Bagnold force, which facilitates their suspension into the upper outer circulation, thereby amplifying the kinematic differences between the chlorite and ilmenite particles. This study demonstrates that fluid dynamic parameters and the force characteristics of mineral particles can effectively characterize the separation process of mineral particles in spirals.

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