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QUANTIFYING THE BREAKAGE BEHAVIOUR OF ALUMINA SAMPLES

Ilievski, D., Schibeci, M. and Livk, I.

To control the breakdown of alumina it is first necessary to understand how an alumina sample breaks, which requires an ability to reproducibly and meaningfully quantify the breakdown behaviour. During the AMIRA P575 project on Alumina Quality, which was sponsored by nine alumina companies and one engineering company, alumina samples from an extensive plant sampling and laboratory program were tested for toughness. To date, the toughness of nearly 50 refinery and laboratory alumina samples has been measured and the samples ranked as being tough or weak. Two interesting observations emerged upon inspecting the raw attrition data and corresponding scanning electron microscopy images of the attrited aluminas:

  1. tough and weak aluminas appear to break differently, and
  2. certain aluminas classified as tough showed very different breakdown characteristics.

This paper reports on a novel technique, developed at the Parker Centre, for quantifying the breakage behaviour of an alumina sample in terms of the breakdown behaviour of the parent particles (i.e. prior to being subjected to attrition processes) and the daughter particles. The method quantifies the breakage of alumina particles in terms of a breakage rate, daughter particle size distribution after a breakage event, and ‘breakage activity’ parameter. A key unique feature of the method is that it captures the time-dependent behaviours observed in breakage processes, e.g. the situation where the easier to break structures are broken initially leaving behind progressively stronger particles. A particularly useful feature of the model-based breakage characterization method is its ability to visualise the complex, multi-dimensional information needed to characterise alumina breakage through visualization tools such as ‘breakage maps’ and ‘breakage activity’ plots.

The quantitative breakage behaviours of four aluminas, prepared from refinery hydrates, are presented and the results interpreted. Two of the aluminas investigated were classified as tough, one as weak, and the other one as intermediate. The two ‘tough’ aluminas had very different morphologies and their breakage behaviours were significantly different: one had tougher parent particles but produced weaker daughter particles; one breaks predominantly by a cleavage mechanism whereas the other by a combination of cleavage, chipping and attrition mechanisms. The sample classified as being of ‘intermediate’ toughness was found to have tough parent particles but weak daughter particles. The sample classified as ‘weak’ was shown to have weak parent and daughter particles. Attrition is the predominant breakage mechanism for these two samples.

The challenge for the future is to predict breakage behaviour based on the properties of the alumina or pre-cursor hydrate.