Determination of the phase content of the aluminium industry raw materials by XRD.

What is it about?

In the last few decades, X-ray diffraction (XRD) systems have been paramount and irreplaceable in controlling bauxite exploration, as well as the Bayer and reduction processes. XRD quantitative phase analysis in the aluminum industry witnessed a steady deployment of the Rietveld method, which at present progressively replaces existing methodologies in research and plant laboratories. Rietveld analysis not only helped to surpass traditional XRD calibration methods, it also opened the door for new applications previously not possible. The use of the Rietveld method to characterize selected materials unique to the aluminum industry, such as bauxite, red mud and alumina is demonstrated and discussed. This paper also presents how synchrotron based diffractograms obtained for bauxite and red mud samples allowed a much better understanding of mineralogical representation, and made it possible to leverage their Rietveld quantification. Despite clear advantages, the Rietveld method also has limitations that are revealed. For alumina phase quantification, a dedicated Rietveld analytical program was built with structure data for 8 alumina mineralogical phases: alpha, beta (-Al2O3 = Na2O·11Al2O3), delta, gamma (2), kappa, sigma and theta. The paper gives unique examples of phase quantification in aluminas of various origins and phase composition.

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Why is it important?

Information about material's phase (mineralogical) composition is important because it determines material's properties and its commercial value. Application of the Rietveld-XRD method for determination of aluminium industry raw materials phase composition has been rarely encountered. One of the greatest advantages of the Rietveld-XRD method is that it only requires a quality diffractogram of the sample and gets away with standards.

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