Knelson: The Best Gravity Concentrators Ever

Anyone who is familiar with the history of GCA will know that GCA stands for Gravity Concentrators Africa, and that the company used to be called Knelson Concentrators Africa, with the name change being brought about by the FLSmidth acquisition of Knelson Concentrators. Since it’s inception in 1997, GCA has been the official agent of Knelson Concentrators, and more recently of FLSmidth Knelson Technologies. As such, some might suggest that this article in itself is inherently biased.

That said, it should be stated that the founders of GCA chose to be the official agents of Knelson Concentrators because they have always been, and will continue to be, the best gravity concentrators in the world. Byron Knelson redefined gravity concentration several decades ago with his fluidised concentration design, and Knelson Concentrators have remained industry leaders ever since. For convenience sake GCA has compiled a short list demonstrating why:


Anyone who has mined precious metals knows and accepts that Knelson Concentrators are unparalleled at recovery of “typical” free gold, i.e. medium to coarse particle sizes. However, for years a myth has perpetuated that they are unsuited to very fine free gold. This myth seems to have been started by somewhat limited research at a Belgian university over 20 years ago, and has been perpetuated by competitor equipment manufacturers ever since, as a means of attempting to prove that their products are better suited to the job. The simple fact is that they aren’t. The limited research, last millennium, was conducted at laboratory scale in less than optimal conditions, and since that time many Knelson installations worldwide have dispelled the myth by recovering extremely fine free gold, generally more efficiently than other devices.

 The myth:

Some competitor manufacturers claim that their equipment can reach higher g forces to better recover fine gold, but is it really an advantage? The same excessive g forces are applied to very fine gold as to relatively (very) coarse gangue, and the competition for recovery of fine gold becomes more difficult if anything. FLSmidth Knelsons can actually run at up to 200g (more reliably and with less vibration than other machines), but very seldom has FLSmidth Knelson been able to determine a benefit for very high g’s in a mill installation, where over 90% of centrifuge concentrators are installed. Yes, in fine feed applications without coarse gangue there is justification for very high g’s, and in this vein Knelson developed a concentrating cone specifically for these duties. Unlike other manufacturers, FLSmidth Knelson does not use the same cone for all feed situations, and only goes to very high g’s when justifiable and necessary.

 Dispelling the myth:

There are abundant documented cases of FLSmidth Knelson Concentrators recovering extremely fine gold – “paint” or “powder” gold that floats on water – and in some trials and installations in Africa, FLSmidth Knelsons have recovered this very fine gold downstream of competitor products that claimed to be better suited for the job.

There are also several fine gold sites where FLSmidth Knelsons have replaced competitor products, and in practically every side-by-side Knelson-competitor installation, Knelson comes out well in front, right across all free gold particle sizes.


Knelson Concentrators were the first fluidised centrifuges. Every similar product that followed simply copied Byron Knelson’s exceptional concept. As mentioned previously, Knelson started out in front and remains so due to numerous design advantages. These include:

  • Tangential fluidising (better fluidising coverage, no rat-holing, no spray bars and inching drives to flush concentrate)
  • Isolation of any rotor vibration from the machine frame and structure, disallowing frequent shutdowns due to excess vibration
  • A vast range of specific, custom-designed concentrating cones for different applications and duties
  • Fully-fluidised cones that reduce wear and eliminate particle packing (and resultant unbalanced rotors and vibration)
  • Conical water jackets designed to move silt to the top outer edges, ejecting it from the machine rotors
  • Continuous research and development


The robustness of FLSmidth Knelson Concentrators results in them having both a higher availability and a longer lifespan than competitor products. When spinning a heavily-engineered rotor between 60 and 200 g’s, it’s important to get things right, and that is something that the design team at Knelson has done from inception. As such, the machines offer the best availability in the industry and often last for the lifetime of a mine or plant. Furthermore, FLSmidth Knelson Concentrators do not regularly shut down on vibration alarms and in fact most Knelsons do not need to be fitted with vibration sensors. There are well over 100 machines in Africa alone that are over 15 years old, and still delivering concentrate as they have since commissioning.

In Zimbabwe, a 20-year-old Knelson was replaced by a competitor machine on the promise of better support from the competitor. Within three years, the mine purchased and installed a new FLSmidth Knelson instead. Similarly, there is a mine in Zambia that five years ago had 11 other machines, before trialling their first Knelson. There are now 17  Knelsons on site. The facts speak for themselves.


It is not solely durability and availability that brought about the examples above, but also lower operating costs. Any machine spinning at extremely high speeds in highly abrasive slurry is bound to wear, and of course Knelsons do too, primarily the concentrating cones. However, they don’t shake themselves to pieces or transmit vibration to bearings, shortening bearing life, and they don’t have un-fluidised (and thus un-lubricated) zones that inevitably wear quicker. There is a reason we have seen recent changes to competitor devices, such as additions of vibration isolators and changes to outer launder covers, to more closely resemble FLSmidth Knelsons. Again, FLSmidth Knelson Concentrators are leading whilst others follow.

In addition, continual development in refining design, user friendliness and reduced operating costs has resulted in continuous improvement to the concentrating cones, the primary wear part. With each generation FLSmidth Knelson cones become cheaper, easier to clean and lower on maintenance requirements. The cones are now disposable parts that don’t have to be shipped back to the factory for costly re-builds.


The first Knelson Concentrator was trialled in 1976, 40 years ago, and Knelsons have been at the forefront of the industry ever since. Through all those years, Knelson has been widely accepted as the gold standard of gravity recovery. Not long after the first Knelson was unveiled, other companies and would-be manufacturers picked up on the idea and tagged along. So they have also been around for some time, but 40 years on FLSmidth Knelson still has over 80% of world market share.

Again, the facts speak for themselves. In the words of the great Byron Knelson: “Unless you’re the lead dog, the view never changes”. And with the FLSmidth Knelson Concentrator, the constantly changing view is something to be admired.

Having definitively proved that FLSmidth Knelson Concentrators are not only superior at mineral recovery, but also last longer and have better after-sales service and R&D, the choice for any mining company considering gravity concentration should be simple.

If you would like to know more, or would like to know how to get your hands on a FLSmidth Knelson Concentrator, please feel free to get in touch.

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view of smelted gold being pouredKnelson Concentrator viewed through a pipe