MEASUREMENT OF SMELTER-GRADE ALUMINA PROPERTIES

Ledru, B. and Roach, G.I.D.

In assessing the quality of an alumina, customer and supplier must have confidence in the analytical methods used. A suite of smelter-grade alumina samples were analysed by both Pechiney and Alcoa of Australia using their standard methods. The properties selected for measurement were those that are considered important for aluminium smelting. The aluminas had a wide range of properties, and data for repeatability of the measurements were obtained. Excellent agreement was obtained for the chemical analyses data for sodium, iron, silicon, titanium and calcium even though different wet methods of chemical analysis were used. For phase analysis there was good agreement for alpha alumina values but for gibbsite, at the low levels of interest, large differences were obtained. Excellent agreements for sizing (both dry screen and laser diffraction), surface area, loose bulk density and L.O.I. were obtained. Differences were obtained for packed bulk density and attrition index because of differences in equipment and/or methods used. The comparison work highlighted the need for international reference standards and recognised international standard methods for properties such as attrition and bulk density. The size distribution data of sub-screen size material, which can now be reliably obtained using laser diffraction, could provide extra useful information on smelter-grade alumina, especially such sizing data for the attrition test.