EFFECTS OF MORPHOLOGY ON ALUMINA STRENGTH AND DUSTINESS

Olsen D., Behrens, C.A., Hamberg, K., Prytz, A.K. and Tveten, E.

Hydro Aluminium’s recent research on alumina quality has confirmed that fines content and particle strength are the most important of the standard alumina quality parameters related to dustiness. We have also seen significant effects of moisture. However, there are differences in dustiness between alumina from different refineries that cannot be explained by our standard quality parameters. Particle shape and morphology have often been mentioned as candidates to explain these differences. In recent years several methods for quantifying particle morphology have become available. This paper describes breakage tests of alumina in a full size pneumatic transportation rig. Observed breakage is compared to the standard Attrition Index. Material from various stages of the tests has undergone a comprehensive program of Particle Size Distribution analysis, Perra dustiness test, flowability test and morphology analyses. Data on hydrate shows clear relationships between selected morphological characteristics as defined by the Zacknich method and particle strength, while the corresponding picture for calcined alumina is much more blurred. Morphology analyses from different stages of the breakage tests indicate that the degree of weak morphological characteristics is gradually reduced as the breakage proceeds. There are indications that certain morphological characteristics also affect the dustiness as expressed by the Perra index. The number based roundness parameter from the Malvern PharmaVision system also shows clear correlation with dustiness.