Centrifugal and Non-Centrifugal Gold Concentrators

 

Before the application of centrifugal concentrators at full scale, gold gravity recovery was performed using non-centrifugal concentrators. For example, the oldest form of gold recovery, the sluice uses centrifugal forces created by vortices downstream the riffles and the efficiency can be reduced if sluice geometry of flowrate are not within the appropriate range, as the centrifuge action of the vortices can completely disappear. Even when operating efficiently, its lower recovery limit is probably around 100 micron. Other units commonly used are the spiral, the Reichert Cone, jig, shaking table and packed hydrosizer.

Spirals and cones are very reliable gravity units, but the introduction of centrifugal units has improved the results obtained by both. The design of spirals has been improved over the past thirty years. Making them easy to operate and more capable of fines recovery. Spirals are in fact capable of recovering gold at a slightly finer size than jigs, presumable because spirals are not usually badly overloaded, severe spilling would ensue, whereas many jigs in gold gravity circuits are. Where there is staff willing to put in the efforts for house and operating adjustments, spirals will be effective. Spirals still have their place in alluvial gold recovery, because of their ruggedness, in many cases where centrifugal concentrators are counter indicated. Cones in many ways, receive a verdict similar to that of spirals. They undoubtedly require significant housekeeping of very tedious nature, as the concentrate slots, where blockage is most likely, are difficult to access. In fact their use is virtually impossible where copper blasting wire is used. Nevertheless, they offer advantages over spirals.

The use of the jigs has been curtailed by the advent of the Knelson, but it is still common. The recovery of gold in jigs tends to decrease with decreasing particle size and this is serious handicap as gold accumulates mostly in the fine fraction of the circulating load, where grinding kinetics are slowest. Next table shows a comparative table to illustrate the relative similitude between centrifugal and non-centrifugal gold concentrators.