Friday, 27 November 2015

Diamonds are forever

During the last few days in South Africa I have been relaxing reading Ian Fleming's eponymous novel. Ironically neighbouring Botswana has been in the news in the last few days after the recovery of the biggest diamond in the last 110 years.

The 1,111 carat diamond, which is yet to be analysed and valued, is the second biggest stone ever to be mined. Around the size of a tennis ball it is beaten only by the 3,106-carat Cullinan diamond found in South Africa in 1905 which was cut into nine separate stones, many of which are in the British Crown Jewels.

I was particularly interested and pleased to read on MEI Online that the stone was recovered by an X-ray sorter manufactured by Physical Separation '15 sponsor TOMRA Sorting Solutions. The sorter was only installed in May of this year, replacing conventional heavy medium separation.  It is unlikely to be the last of big stones recovered by electronic sorting as the development of multiple sensors and rapid computing is making this technology an increasingly important feature particularly for reducing energy consumption in comminution circuits.

It must be remembered that although diamonds are the hardest minerals known they are also very brittle and many large stones must have been shattered in diamond crushing circuits. The Cullinan diamond might have suffered that fate if it had not been spotted in the wall of the mine itself and prised out by the mine manager using his pen-knife. It was part of a much larger stone which had been sheared off during mining. I remember visiting the mine in 1978 and seeing the new x-ray sorter, crude and low capacity by the standards of the modern TOMRA machine, but only a few months earlier it had recovered the Premier Rose, then the largest since the Cullinan, at 137 carats.

Expect to hear much more of the electronic sorting of many ore types in future.


  1. Yes, quite extraordinary Barry. Initial comments by William Lamb (CEO) after the "win" was, "that it had not really sunk in yet". The new diamond flowsheet is extraordinary as it uses an AG mill from which very large pebble/diamonds (-60+32 mm) are temporarily removed from the circuit and sent to the TOMRA "large diamond" x-ray sorter. After THE LARGE DIAMOND was recovered, the pebbles are sent back again to the crusher and/or the mill. The -32 mm fraction emerging from the mill discharge screen undersize is sent to conventional heavy medium separation. The TOMRA sorting unit does not replace the HMS as reported here. Never-the-less it is innovation inspired by Lucara Diamonds and has set a new path for diamond processing. Well done all.

    1. Thanks for the update Mike. Fascinating flowsheet- I look forward to hearing more from TOMRA at Physical Separation '17

  2. Good Afternoon Mike,

    I would like to clarify the above technically.

    At Karowe Tomra XRT/D Technology sorts a -60+32mm, -32+14mm & -14+8mm fraction respectively. Only the -8mm material is sent to traditional DMS technology.
    Please feel free to contact me should you have any additional questions you would like me to answer.



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