This is a question that I asked two and a half years ago, but things have moved on since!
Ore sorting is the original concentration process, having probably been used by the earliest metal workers several thousand years ago. It involves the appraisal of individual ore particles and the rejection of those particles that do not warrant further treatment. Hand sorting was used on the Cornish copper mines, women being employed to separate the high grade copper ore from the waste rock, and I remember seeing it being used in Greece in the late 1970s to separate high grade magnesite rock from waste.
Electronic sorting was first introduced in the late 1940s, and became an important technique for the pre-concentration of certain types of ore, such as diamond ores, but its application was fairly limited, due to simple sensors and low-power computers.
In recent years, however, the potential of dry ore beneficiation has become increasingly apparent, particularly where water conservation and other environmental issues are involved. Sensor based sorting technology, particularly using X-Ray-Transmission (XRT), has proved to be viable in industrial scale applications. High efficiencies and recovery rates can be achieved using the latest technologies. Increasingly powerful computers and sensitive X-ray scintillation counters have enabled the development of high-performance units. The machines have reached a status of rigid and reliable field stability and can be operated at grain sizes of 8 mm up to 70 mm, depending on the individual ore.
TOMRA Sorting Mining. Recognising the future importance of sorting in the physical beneficiation of ores, TOMRA are one of the major sponsors of Physical Separation ’13 in Falmouth in June.
Jens-Michael Bergmann of TOMRA will describe the basics of XRT-sorting technology, followed by an example of how a chromite processing plant in South Africa is using a state-of-the-art XRT sorting machine, together with spiral concentrators. The sorter is pre-concentrating the ROM chromite ore by removing barren waste and low grade rocks while after comminution the spirals are concentrating the ore to a market grade of above 46% Cr2O3. This paper will supplement papers from Australia on the potential of ore sorting and the next generation machines.
What are the limits to this technology?