Column Froths

Abstract

Abstract Column froths are discussed in terms of structure, effect of variables on gas holdup profiles, cleaning (rejection of entrained particles), selectivity (between hydrophobic species), carrying capacity and froth stability The froth is shown to be stabilized by wash water and to have two sections, one near the interface where gas holdup increases rapidly to about 74% and an upper one where change is less rapid. The upper section is subject to mixing by the wash water In cleaning an important factor is gas rate. Pulp water recovery, and hence entrainment, increases with gas rate: a superficial gas rate (volumetric gas rate per unit time per column cross-sectional area) less about 2 cm/s is recommended. Deep froths (>100 cm) do compensate for high gas rates to some extent. Increasing bias water rates (e.g., >0.3 cm/s) does not compensate for the effect of high gas rates but rather introduces excessive turbulence in the upper section of the froth and loss of cleaning action Carrying capacity is revealed as a major limiting factor for processing fine particles (<30 μm). Carrying capacity (as mass solids/unit time/unit column cross-sectional area) appears to depend linearly on particle size. Some design and operating consequences of carrying capacity are outlined Brief reference is given to reports of froth instability. No clear conclusion regarding the effect of solids is reached.