Determination of quartz in bauxite by a combined X-ray diffraction and X-ray fluorescence method

Quartz is one of the important phase constituents of any bauxite and may vary from a small fraction to over 50% of the total SiO2 concentration. At present, the most practical method of estimating quartz is by wet chemistry or by using conventional X-ray diffraction (XRD) methods. Whether employing a direct or Rietveld approach, the XRD method is difficult and not possible for small quartz concentrations because of severe line overlaps. A new method uses bauxite material calcined at 1000 °C. Major bauxite phases, such as gibbsite, boehmite, kaolinite and goethite are entirely decomposed in the calcination process. The calcination procedure converts SiO2 containing kaolinite into XRD amorphous material. In addition to the amorphous portion, there are just four major crystalline phases present: corundum, hematite, rutile and quartz. Quartz in the calcined bauxite corresponds to the primary quartz occurring in the initial sample. Rutile is employed as the internal standard. First attempts to quantify quartz in calcined bauxite using XRD based Rietveld analysis will be described. Results are presented for the Sangaredi (Guinea) bauxite deposit.