ALUMINA DUSTINESS RELATED TO PHYSICAL QUALITY PARAMETERS - USER EXPERIENCE AND R&D IN HYDRO ALUMINIUM

Dust emission during unloading, handling and pot operation is the main alumina related environmental problem experienced in Hydro Aluminium's smelters in Norway. Our system uses alumina from more than 10 different sources. The dustiness of each alumina is one of the main criteria for approving alumina sources. The dustiness of various alumina qualities has been investigated through sampling and measurements during unloading and pot operation at two of our smelters, as well as analyses and tests in the laboratory. Our data shows that fines content is the most important of the traditional alumina quality parameters, although no general correlation has been found. However, Perra Pulvimeter tests using test samples from one single source yield a strong correlation between dustiness and fines content. The effect of attrition index depends strongly on the handling system at each plant. According to our data the Perra Pulvimeter provides a better prediction of alumina dustiness than any of the traditional quality parameters, not only during handling, but also in Soederberg potlines. There are indications that alumina dustiness is more closely linked to properties of the dust fraction itself, than to bulk alumina properties. Data from refinery plant tests shows an almost perfect correlation between hydrate strength and fines content of the alumina. Our working hypothesis is that the strength and structure of the hydrate is the major key to alumina dustiness. A better understanding of the link between White Side conditions, hydrate properties and further on to alumina properties and dustiness is fundamental to achieve the ultimate goal; to produce a less dusty alumina at the refineries.