As flowing film gravity concentrators, spiral separators are extensively used in the processing of numerous minerals. Appropriate design of their cross-sectional geometries has been known as an effective method to improve the performance of spiral separators. However, limited work has been published on the impact of cross-sectional geometry on flow field characteristics in spiral separators. In this study, the effects of cross-sectional geometries with various parabolic profiles (|x|=m|y|ⁿ) of a spiral separator on the flow film thickness, flow pattern and flow regime were investigated by numerical simulation. The validity of the simulation approach was confirmed by the reasonably good agreement between the predicted and measured flow film thickness in the own laboratory spiral separator. Results have shown that the flow film thickness and the mean primary velocity in the inner and middle troughs are reduced by decreasing downward bevel angle or increasing parabolic index. The dominant region of the secondary flow can be expended inward by increasing the downward bevel angle and decreasing the parabolic index. As the radial position extends inward, a larger downward bevel angle is more conducive to improving the intensity of secondary flow. A wider laminar flow region can be obtained with a smaller downward bevel angle or a larger parabolic index. The flow film thickness has a significant positive correlation with the trough slope in the inner and middle troughs. It is recommended that the matching relationship between material properties and flow field characteristics should be fully considered when selecting the cross-sectional geometry. Thus, this study aids the structural design of the cross-sectional geometries of spiral separators.

One-dimensional Zn-doped α-Fe₂O₃ nanowires have been controllably synthesized by using the pure pyrite as the source of Fe element through a two-step synthesis route, including the preparation of Fe source solution by a leaching process and the thermal conversion of the precursor solution into α-Fe₂O₃ nanowires by the hydrothermal and calcination process. The microstructure, morphology, and surface composition of the obtained products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. It was found that the formation process of α-Fe₂O₃ is significantly influenced by the introduction of Zn²⁺. The gas sensing measurements indicated that the sensor based on 1% Zn-doped α-Fe₂O₃ nanowires showed excellent H₂S sensing properties at the optimum operating temperature of 175 °C. Notably, the sensor showed a low H₂S detection limit of 50 ppb with a sensor response of 1.5. Such high-performance sensing would be ascribed to the one-dimensional structure and high specific surface area of the prepared 1% Zn-doped α-Fe₂O₃ nanowires, which can not only provide a large number of surface active sites for the adsorption and reaction of the oxygen and H₂S molecules, but also facilitate the diffusion of the gas molecules towards the entire sensing materials.

Understanding the influence mechanism of the partial cross-sectional geometry of a spiral separator on the flow field characteristics and particle separation performance is conducive to the design of a combined cross-section profile. The impact of the trough slope in the inner and middle troughs on the flow field characteristics and particle separation performance was investigated by CFD methods. The results show that the average depth of the flow film, the average tangential velocity, and the average radial velocity in the partial radial region are linearly related to the trough slope. With the increase in the trough slope in the inner and middle troughs (r = 30–110 mm), the radial velocity reversal position will decline, resulting in an enlarged proportion of the outward flow. Adjusting the trough slopes of the two straight segments in the inner and middle troughs will have a positive effect on the precise segregation of particles. In comparison, changing the trough slope in the middle trough containing the miscible band had a more significant effect on particle separation. A maximum separation efficiency of 80.80% was obtained with a trough slope in the middle trough of 5°and a splitter position of 95 mm.