MEASUREMENT OF RESIDENCE TIME DISTRIBUTION OF THE GAS-PHASE IN FLOTATION COLUMNS

The gas phase residence time distribution in flotation columns was inv estigated experimentally by the impulse response method using a radioa ctive tracer gas (Krypton-85). The experimental methodology consisted of introducing an impulse of radioactive gas inside the air sparger us ing a specially designed device, and on-line measurement of the transi ent response at various levels in the column. This technique was first tested in a pilot column of 10(cm) diameter and 8(m) height. Tests we re made at 0.8-0.9-1.0-1.5 (cm/s) superficial gas rates and 0-10-20 (p pm) frother dosage. Afterwards, the gas phase of an industrial column of 0.91(m) diameter and 15(m) height, operating in a molybdenite clean ing circuit, was studied. Tests were made at 1.3-1.7-2.1 (cm/s) superf icial gas rates and 0.7 (cm/s) superficial tailing rate. The transient response curves from pilot and industrial columns showed a typical ga s residence time of about 2-4(min), and the gas dispersion number was about 0.1 and 0.4, respectively. The gas phase in the froth zone behav ed closer to a plug flow while operating at superficial gas rates lowe r than 1.5(cm/s) and superficial wash water rates of 0.2-0.4(cm/s). A significant gas short-circuiting into the tailing flowrate was clearly observed in the industrial column.