Centrifugal Gold Concentration

Falcon concentrator: The recovery mechanisms of the Falcon concentrator are quite different from those of Knelson. The Falcon rotates at higher "g" than Knelson (300 vs. 60) without fluidizing water. Operation of the batch unit is quite distinct from the continuous one. Upon starting and first feeding the Falcon, a bed material of quickly accumulates non-selectivity (generally after few seconds); once this bed is formed, selective recovery begins, and a second bed of denser particles progressively forms above and at the leading edge of the first. When this second bed saturates, recovery stops, or drops dramatically. This is partly because capture sites are no longer available, and partly because segments of the bed are periodically eroded by the flowing slurry. This occurs in part progressively, and in part catastrophically, yielding erratic performance. A third stratum is generally visible above the concentrate, made mostly of gangue particles that can readily eroded away. This third stratum is loosely held in place, as the underlying concentrate layer still grows and erodes. In the continuous Falcon, a recovery slot circles the bowl; the material is removed via the slot into 24 inner hoppers where concentrate flow rate and percent solids are carefully maintained.

Falcon's cone that is called the migration zone contains a flowing bed with a large amount of interlayer shear. Particle settling velocity is enhanced by the excess gravity, so heavy fines arrive at the wall before coarse light ones. Further up where particles begin to compact, they are still moving in layer and spaces open between them into which small denser minerals can move. These particles can work their way into the wall layer and may push coarser light ones out of it. The Falcon mechanism is called flowing film separation. Segregation should be completed when the stream arrives to the retention zone

Fig. 4.11 Falcon Concentrator