Estimating effective volumes in industrial forced-air flotation cells

Mean residence time (MRT) in industrial flotation cells is one of the key parameters for kinetic modelling and identification of effective volumes. However, not all plants have access to robust tracer techniques to reliably measure this parameter with reasonable accuracy. For this reason, flotation practitioners estimate the mean residence time from the volumetric pulp flowrate and the effective cell volume. The latter requires assumptions on the air and froth volumes inside the machines, which has led to inaccuracies in MRT estimations. To overcome this challenge, the present communication correlated the measured (τ_m) and calculated MRTs from the rougher circuits of four copper flotation plants (twenty-eight surveys). The rougher stages of these plants consisted of forced-air mechanical cells of 100, 160 and 200 m³. The correlation between the measured and calculated MRTs showed that the following equation can be used as an approach to predict the MRT in industrial forced-air flotation cells: τ_m = αV_T/Q, with α=0.872 representing the relative effective volume (95% confidence interval of 0.839–0.905), V_T the total cell volume, and Q the volumetric feed flowrate of pulp. This interval for the relative effective volume is proposed as a reference range to consolidate current assumptions for cell sizing, or to revisit these assumptions in case of significant deviations regarding the observed interval.