Compression and channelling in gravity sedimenting systems

In-situ solid concentration measurements and observations during the sedimentation of calcite, talc and aragonite suspensions showed that the top of the channel region coincided with a solid concentration characteristic propagating from the base of the column. The solid concentration of this characteristic represented the first significant increase in concentration over that of the original suspension, and not a unique characteristic value for each mineral. The region above the top of the channels diluted, and this increased the suspension/supernatant interface velocity. Further rapid acceleration occurred when the top of the channels reached the interface, prior to the consolidation period when the interface slowed and compression resulted. Stirring the suspensions could completely suppress the channels and, under these conditions, the maximum sediment concentration was substantially increased. The sedimentation velocity and, therefore, flux at the interface was greater in the presence of channels. However, for concentrations below the interface stirring improved the batch sedimentation flux as well as the sediment concentration. Hence, the settling flux limiting value during continuous thickening may be improved by more rapid stirring than is currently employed.