Effect of Wall Roughness in the Middle Zone of Spiral Concentrator on the Flow Field Evolution of Hematite–Quartz Slurry and Particle Separation Behaviour

The spiral concentrator is usually the first operation in the combined process of iron ore beneficiation. The industrial separation index decreases as the trough surface undergoes increased wear. A combination of surface roughness measurement and numerical experimental methods is utilized to systematically investigate the effect of wall roughness in the middle zone on the evolution of the flow field of a slurry consisting of hematite, quartz and water in a spiral concentrator. The radial migration and distribution characteristics of hematite and quartz particles are analysed, and the separation indexes are further evaluated. The results show that an increase in wall roughness (Ks value) in the middle zone has been shown to decrease the depth of slurry flow, the velocity and radial flux of secondary flow in the inner and middle zones of the trough, and to narrow the space of inward flow. The variation in hydrodynamic parameters is particularly pronounced as the Ks value increases from 0.1 mm to 0.2 mm, resulting in a significant reduction in the space available to the separation fluid and an observable interruption in the inward flow. The migration tendency of hematite and quartz particles to the inner trough is reduced depending on the flow field parameters, and their enrichment zones are both shifted outward. The migration amount and distance of particles show apparent differences in density and size. The separation indexes decrease slightly as the wall roughness (Ks value) in the middle zone increases in the 0.01 to 0.1 mm range, but the iron grade of concentrate decreases significantly, and the separation effect worsens as the Ks value increases from 0.1 mm to 0.2 mm. The separation effect of hematite and quartz particles in the spiral concentrator is influenced by the comprehensive interaction of feed size and wall roughness in the middle zone. The results of this study provide a theoretical basis for the selection of trough material, surface structure design and the production process control of the spiral concentrator.