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.
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?
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Ore sorting either as method of pre-concentration or as a direct method of upgrading has always been an important tool. The opportunity is highly dependent, not unsurprisingly, on the mineralogy - namely the actual mineral, mineral properties (e.g. not all diamonds fluoresce under X-rays), size ranges and associations. Radiometric, UV and colour are the main characteristics and of course, coarser size ranges are better.
ReplyDeletehttp://www.appliedsorting.com.au/
ReplyDeleteApplied Sorting Technologies have been applying sorting to diamonds and tungsten ore bodies for many years ... optical sorting in the 70's and 80's and now x-ray sorting ... for tungsten it is used straight after crushing with 94% recoveries of tungsten minerals (woframite and scheelite)with a 50% plus mass reduction. These results are, of course, due to the amenability of the ore body
The catch in sorting is the relationship between particle size and liberation and the fact that particle mass is roughly a function of the third power of the characteristic size.
ReplyDeleteThe last fact limits quite effectively the applicability in both ends of the size distribution. In the fine end the capacity gets too low and in the coarse end the force needed to remove a large piece from the stream becomes too large to be created by a air jet. It needs mechanical means.
Another catch in the technology comes from the time needed to identify the particle property used for sorting. The identification time at any given time unit is a function of the number distribution of the particles flowing past the sensors. The capacity at the same time is a function of the mass distribution of the same particles. Thus the identification time will make the poor capacity for fines even more challenged. For the coarse particles the identification issue is different. Simply, how to get from surface distribution to a volume distribution for the property used in separation.
To me these fundamental issues makes the technology applicable to special circumstances but not a technology that can be universally used as the sales pitches go.
Kari Heiskanen, Aolto University, Finland
Sensor-based sorting can also bring added value in other parts of the mining process. The waste may now turn into treasure using TOMRA Sorting technologyTOMRA Sorting technology.can be seamlessly integrated with, and individually tailored to, existing mining
ReplyDeleteprocesses. This increases efficiency within tried and tested procedures and installations.
Great post.
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