DETERMINATION OF GIBBSITE IN SMELTER-GRADE ALUMINA

Roach, G.I.D., Cornell, J., Dunn, J. and Kieppe, C.

Gibbsite is often present in smelter-grade alumina at low levels (typically <1.0%). Various techniques are currently used to quantify such gibbsite with x-ray diffraction (XRD) and differential scanning calorimetry (DSC) being the most common. Both techniques have associated errors. A study of the relative merits of these techniques and Fourier transform infra-red spectroscopy (FTIR) was undertaken on a series of smelter-grade aluminas and gibbsite. All techniques can readily detect gibbsite levels as low as 0.1% gibbsite in alumina. XRD and FTIR are prone to major bias and variability arising from sample preparation procedures related to preferred orientation problems. Also, there are major problems of acquiring a suitable standard - there is no single standard which is ideal. DSC is not sensitive to such problems and, provided correct sample preparation procedures are used, gives the best and most reliable analysis of gibbsite in smelter-grade alumina.