Effects of process variables on the residence time distribution of a solid in a continuously operated flotation cell

Abstract

Effects of aeration rate, slurry flow rate, stirring rate, pulp density, and particle size on the residence time distribution of a solid in a continuously operated flotation cell under non-flotation conditions (no frother, no concentrate removal) have been examined. The mixing behaviour of the solid in the cell has been quantitatively analysed using a multiple parameter approach. The results indicate that only a part of the cell volume behaves as a perfect mixer, the remaining being dead. The exit residence time distribution E( t) and the mean residence time ( t ) of solid are described by: E(t)= Q V eff exp − Q V eff t and t= V eff Q where Q is the volumetric slurry flow rate. For the variables ranges examined, it is observed that the aeration does not have any significant effect on the mixing behaviour, V eff increases with increasing slurry flow rate and stirring rate but decreases with increasing pulp density. The mean residence time, on the other hand, increases with increasing stirring rate, decreases with increasing slurry flow rate and pulp density, and exhibits a maximum with respect to particle size. Following empirical equation correlating the effective volume of the cell with the operating variables for a unisize feed is obtained: V eff V =0.249 D i ρ N μ 1.962 Q ρ D i μ −1.472 Q VN 1.711 B −0.32 where B is the weight fraction of solid in the pulp.