Flowability of various dusts collected from secondary copper smelter off-gas

Stable flow of off-gas dust from dust collector hoppers and storage silos is important for smooth operation. Flow properties of the collected off-gas dust are critical to achieve suitable flow. Various dust samples collected from secondary copper smelter off-gases were studied. The median diameter of the fine-grained dusts varied from 0.8 to 1.4 μm and the flowability ranged from "cohesive" to "very cohesive". The flowability of shaft and anode furnace dust improved slightly with increasing consolidation stress and their wall friction angles decreased, which is a typical behavior. In contrast, the flowability of converter dust decreased with increasing consolidation stress and its wall friction angles increased. Pre-shear treatment of converter dust worsened its flowability, increased the wall friction angle, and improved the flowability with increasing consolidation stress. This is believed to occur because pre-shear treatment fragments small agglomerates in the dust that improve flowability. The presence of such agglomerates was confirmed by sieving tests. A diagrammatic representation of the flowability showing that the unconfined yield strength is dependent on consolidation stress can be improved by using logarithmically scaled axes.