The significance of internal recycle in froth flotation

Significant research effort in froth flotation modelling has been directed towards decoupling the pulp and froth zone contributions to overall recovery. This paper examines the material flows in and around a flotation cell when floatability was changed by varying collector addition rate. Highly controlled experiments were conducted in a continuously operated pilot scale flotation rig in which all stream flows could be measured with high precision. A Bubble Load analyser was used to measure the internal fl ows of material between the pulp and froth zones. The work was carried out in the lead circuit of a silver-lead-zinc mine, on a reagent-free stream to which collector could be added. Totally contrary to expectation, the fl ow of galena entering the froth phase attached to bubbles was found to decrease with increasing collector addition rate. This was a result of the froth becoming more stable with increasing collector addition rate. Higher froth stability meant that more galena exited in the concentrate, and less dropped back into the pulp to be re-attached to bubbles, resulting in a low Bubble Load. At low collector addition rates, the froth was less stable, and there was a large amount of galena recirculating between the pulp and froth, resulting in very high Bubble Loads. This has provided a valuable insight into the significance of the internal recirculating fl ow of hydrophobic material between the pulp and froth zones. In this system, the fl ow returning via dropback from the froth essentially dictates the observed Bubble Load in the pulp. This has important implications for flotation modelling, in that the pulp and froth zones – far from being decoupled – are highly interdependent via the fl ow of attached/detached material between them. Thus mechanistic models of the pulp and froth zones must be developed together in order to provide meaningful results. The current definition of floatability, as the response of mineral particles to pulp phase phenomena only, is insufficient to capture this interdependence