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Kristiansen LT, Prytz AK, Tveten E

High level of fines in alumina is a well known problem in aluminium smelters, negatively affecting conveying, segregation, dusting, fume treatment, cell feeding stability and sludge formation. The ultimate effect can be poor pot line performance and increased emissions.

Fines are present in the dispatched alumina from the refinery, and also formed along the alumina supply chain from calcination to cell feeding. The standard test for analysing fines forming potential, the Forsythe-Hertwig Attrition Index, has a number of disadvantages. There is a wider consensus that a new definition for how attrition is defined and measured would be of advantage to the industry. A new method should improve the ability to predict fines generation, as well as giving a better characterisation of particle strength, to be used as feedback to the ongoing development work aiming at producing stronger hydrate and alumina particles at the refinery.

A rapid method for progressive attrition testing of alumina has been developed, which characterises particle breakage properties at progressively increased forces. Main advantages of the method are: i) it is less time consuming than the Forsythe-Hertwig Attrition Index test; ii) particle breakage can be measured at forces more relevant to each individual smelter; iii) the measurement data output gives the complete particle size distribution (PSD) before and after exposure to attrition testing, which gives a number of alternative possibilities to how attrition can be defined.