Experimental analysis of water and slurry flows in gravity-driven helical mineral separators

This paper aims to provide essential information of the water and slurry flow behaviour in a popular full-scale mineral separation spiral. Besides critical measurements of the free surfaces, the wall roughness and wall contact angle, novel measurements and assessment of the commonly encountered 'bubble line' are provided herein. The free surface shapes of three flows: water-only, chromite slurry and magnetite slurry are compared for the first time, which highlights operational spiral phenomena. The research provides insight into the mechanics behind the 'wetting-in' process by showing that this process affects the wall contact angle more than the surface roughness. The most representative roughness height of the spiral trough was found to be 138.4 mu m and the wall contact angle of the spiral surface was 88.14 degrees, measured in the water phase. The experiments showed that the free surface shape and the position and width of the bubble line in a water-only flow reached a steady state after 1.25 spiral turns. The results and findings are applicable to spirals of other makes and models and can validate future spiral fluid flow simulations.