Effect of collection zone height and operating variables on recovery of overload flotation columns

This paper presents results of column flotation of silica sand (d80=190 μm) that show typical column heights may adversely affect the performance of the flotation, when relatively dense flotation slurries of floatable mineral are processed. For slurry densities above 20% of solids (w/w), floated under typical conditions (Jg=1.46 cm/s, Jt=1 cm/s, Jww=0.16 cm/s, hf=0.3 m), the bubble–particle aggregate reaches density values close to one losing their buoyancy. Under these conditions, mineralized bubbles accumulate, coalesce (losing a fraction of the particles that transport) and may even be carried out to the tailings discharge, affecting both the recovery and the processing capacity of the column. By reducing the height of the collection zone of the column (hc) this abnormal operation may be substantially mitigated. In this work, recovery increased from 55% to 78% by decreasing hc from 4 to 1.5 m when processing a pulp with 30% of floatable minerals. The paper also discusses the effect of column height upon other important variables.