Thursday, 16 August 2012

Advances in X-ray computed tomography for analysis of heap leaching systems

One of the two keynote lectures at Process Mineralogy ’12 in November will be given by Prof. Jan Miller of the University of Utah. He will show how X-ray micro- and nano-CT provide for quantitative mineral exposure/liberation analysis of multiphase particle populations in 3D. In the case of micro-CT, analysis of more than 30,000 particles, 100 microns in size, can now be accomplished non-destructively in less than 5 hours at 2 micron voxel resolution with little sample preparation.

In a recent review article in Volume 35 of Minerals Engineering, Prof. Miller and co-workers at Utah highlight the recent advances that have been made in the application of X-ray CT in the analysis of heap leaching systems.

Heap leaching technology is moving forward rapidly as it satisfies most techno-economic considerations and provides several benefits such as low cost, cleaner environment and product, flexibility, and diversified process conditions. In view of the important role of comminution and agglomeration in heap leaching systems, both of which have to do with particle size distribution (PSD), improved characterization methods have become of significance in the design and operation of heap leaching systems.

X-ray CT characterization has introduced a new prediction tool for 3D analysis of multiphase particles and packed particle beds, an analytical capability not realized until recently. For example, establishing a correlation between mineral leaching against time from column leaching results and the information obtained from X-ray CT images is now possible. The paper presents some potential capabilities of the technique to illustrate the improvement in traditional metallurgical test work. The authors conclude that X-ray CT as an analytical technique can improve our understanding of heap leaching operations and make heap leach technology even more adaptable to ever-increasing complex ores in the foreseeable future.


  1. Why is there apparently so little interest in this technology for other applications? Is it ignorance, poor understanding of scale-up, lack of belief in resolution or what? Back in the 1980's, the Utah Comminution Centre was at the forefront of fundamental research and though they are still at that edge, it is surely time for a greater interest/impetus? One area that has hugely lagged (likely due to resolution effects, admittedly) is testing liberation bias between 2-D and 3-D measurements.Any comments to get X-ray CT discussion going? Barry, I'm with you...
    Chris Hamilton, Consulting Process Mineralogist, Canada

    1. Resolution in dense ores is still an issue for X-ray CT from my limited experience. This is limitating if you intend to detect cracks generated by different grinding modes. But, I fully agree that fundamental research must go on on that topic.
      Concerning 2D vs 3D liberation it is only realistic to achieve results on (very) simple ores. My personal experience is linked to 2D vs 3D size and shape analysis. This is up to now the most feasible application for a better understanding of analytical biases (in conventional particle analysis).
      Eric Pirard, University of Liege, Belgium

    2. X ray CT: Can it be useful in generating 2D or 3D images of multiple locked complex sulphide mineral particles of <5microns. How it will be applicable for measurement of liberation of desired mineral? If possible than it is a strong supportive tool.
      Dr Navin K Sharma: A consulting Mineral Advisor @vedanta, Hindustan Zinc, CRDL,Udaipur, India

    3. With regard to Chris' comment, our lab has largely ignored X-ray CT scanning and 3-d liberation data because we have a huge comparative database of 2-d liberation data from SEM-based sources. For mineral concentration circuits, one of the most frequent questions is why has the recovery changed? This can be due to ore source, or operational drift. To help decide, one of the things we most commonly look at is comparative liberation data between recent lower recovery days and historical data with higher recovery. I prefer to compare my apples to apples - so I stick with what works and what I have which is 2-d data. So I suppose there is a certain amount of data inertia for these systems to overcome. Note that it was easy for us to make the change to SEM-based systems from optical based, because we still had the same 2-d polished blocks. And there was the added bonus of not having to do all that dreaded point counting.

      There will have to be a step-changing advantage for these systems to take hold - either drastically reduced price or increased speed or resolution that you just can't do without. Simply saying that your sample is 89% liberated in 3-d vs. 96% liberated in 2-d will not be enough.
      Frederick Ford, Vale, Canada


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