Slide Background
Slide Background

QUANTIFYING ALUMINA PHASES IN SMELTER-GRADE ALUMINA BY X-RAY DIFFRACTION

Roach, G.I.D, Cornell, J.B., Li, D.Y. and O'Connor, B.H.

X-ray diffraction (XRD) is routinely used to quantify alpha alumina in smelter-grade alumina. XRD also has the potential to quantify gibbsite and intermediate aluminas. However, there are many difficulties in achieving this because of problems such as preferred orientation, fine crystallite size of the intermediate phases, and the possible presence of amorphous alumina. The use of full profile analysis of the diffraction pattern (using both Rietveld and non-Rietveld methods) enables most of these difficulties to be overcome and new opportunities to be realised. The potential benefits of using such full profile analysis to provide information on hydrate morphology, and identifying and quantifying intermediate and alpha alumina in smelter-grade alumina have been investigated. Over ninety diffraction patterns reported in the literature for intermediate alumina phases were evaluated for their crystallographic information. The patterns chosen for the intermediate phases were those which were entirely consistent with the reported cell data. The full profile analysis procedure was then used to quantify the alumina phases identified. A simple personal computer version of the required programmes for quantifying alumina phases in smelter-grade alumina is being developed. Examination of Alcoa of Australia Limited smelter-grade alumina samples indicated that the major phases were approximately 65% theta, 15% gamma, 10% alpha; there was about 10% alumina unaccounted for, being possibly amorphous alumina. There is a need for industry wide standards of alumina phases and gibbsite for such quantitative XRD analysis.