Thursday, 3 June 2010

Modern Gravity Concentrators

Next year we will be running Physical Separation '11 in Falmouth, where one of the themes will be "Gravity concentration methods - single and multi-G separators and dense medium separation".

Gravity concentration is the oldest method of concentration, and gravity machines come and go- my blog of 28th May mentioned buddles, round frames, rag frames and Frue vanners, machines all consigned to history and museums. With the advent of froth flotation in the early 20th century, many people thought that gravity concentration would become obsolete, but it survived. New machines were developed, such as the shaking table, and spirals, which still survive today, but many remained on the scene for only a short time. Who remembers the Bartles-Mozley Frame, the Bartles Cross-Belt Separator, and Duplex Concentrators? Are they being used anywhere now?  And what about the Reichert Cone which was widely used in the 70s and 80s- is it still manufactured and used?

Gekko, Falcon and Knelson enhanced gravity concentrators now seem to dominate the industry - did the Mozley Multi-Gravity Separator ever become a major player in this area?

Let's have your views on the current status of gravity concentration in modern mineral processing plants.


  1. I remember seeing Bartles-Mozley Frames and Cross-belt separators at Geevor Tin Mine in Cornwall in the late 1970s, but not sure what their role was.

    Ian Soper, Atlanta, USA

  2. Ian, the B-M Frames were used to concentrate fine cassiterite, and the Cross-Belt separators upgraded the concentrates from the frames.

    I remember the B-M concentrators as very large, cumbersome, semi-continuous devices. They were developed by the late Ricard Mozley, in collaboration with the Redruth mining equipment company Bartles of Carn Brea.

    Incidentally, Richard Burt, who wrote the book 'Gravity Concentration Technology' was based at Bartles in the 70s. Geevor finally closed in 1990.

  3. I was looking at a flowsheet the other day of a lead concentrator in 1870’s that featured jigs, buddles and spitzcasten (I believe that is the plural) to concentrate galena. Reported recoveries were in the range of 70% lead. As we all know in 1900’s flotation replaced gravity due to finer liberation sizes and improved recoveries.

    The renewed focus on energy efficiency in processing I believe lead to increased use of gravity in mineral processing. Gravity processing has the potential to process ore at coarse sizes that can be achieved by crushing circuits rather than the fine grind required by flotation. Not to mention that gravity processing has the additional environmental / economic benefit of no reagents and low power requirements (at least for the InLinePressure Jig).

    Roles such as pre-concentration of coarse ore at the front of a plant by gravity aren’t new role for gravity. Going forward, rather than just using a stand alone pre-concentration plant there is significant untapped benefit in integrating these gravity steps into the comminution, classification and final separation processing circuits rather than relying on a single process to do all the work. For example in the gold industry plants using GFIL (gravity-float-intensive-leach) flowsheet as a high recovery, low energy usage options are becoming more prevalent for coarse gold and mixed (sulphide/oxide) ores.

    The really exciting trend we are seeing at Gekko at the moment is the interest of bulk commodity processers (coal and iron ore) and people from large base metal concentrators getting interested in the IPJ (InLine Pressure Jig). We’ve got units installed in both these groups at the moment looking at using gravity to complement their existing processing steps. These applications range from removing sulphides from a milling circulating load to taking the fine fractions of a dense medium plant to allow the feed size to the dense media cyclones to be increased. The present challenge is the development of a Super-IPJ to handle the high tonnages associated with these applications.

    Ben Murphy
    Gekko Systems

  4. Barry,

    The Reichert Cone (which was an elaborate arrangement of pinched sluice separators) was killed off in the early 1980s by the development of the wash-waterless, high capacity spiral. Plants using these were more efficient and lower cost than cone plants.

    The separation mechanism on a spiral separator is still not well understood by the industry at large. Too often it is seen as a two-product separator when in fact the middlings is a distinctly different product in terms of size/density of components. I refer you to a paper by Ncede & Pieterse from the MetPlant Conference 2008 which showed that a combination of spiral separators, with up-current classification of the middlings, gave superior separation performance.
    I would encourage your readers to use quantitative mineralogy such as MLA to better understand the nature of intermediate streams from gravity devices to enhance circuit design.

    Craig Brown - Lycopodium Minerals

  5. Understanding the outcomes of gravity concentration has come a long way with the work of Andre Laplante on the batch centrifugal concentrators (GRG) and Gekko on the continuous, higher mass pull devices (CGR). Mineral Technologies can give very accurate predictions of outcomes when treating mineral sands with spirals. I agree that the control of the units in the circuit and the installation appears to be the greatest area of need. Installation and control still lack engineering expertise and good general knowledge. Gravity separation is not very forgiving if not properly set up and the interactions between control inputs and recovery and operating outcomes are not well known. These can often be counterintuitive. Further attention and research in this area is required to support ongoing growth of this environmentally positive and low cost processing option.
    Elizabeth Lewis-Gray, Gekko Systems, Australia

  6. Kesley jigg is a fantastic equipment we tested diferent minerlas with a very high ratio of concentration and 7 to 15 times the enrichment ratio.

    1. Yes! I have had a good experience separating Monazite from a "middlings" reject type of stream that was stockpiled. It consisted of Garnet Zircon & a bit of rutile.


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