THE DEVELOPMENT OF AN ON-LINE ULTRASONIC PARTICLE SIZE ANALYSER FOR BAYER LIQUORS

CSIRO Minerals has developed an ultrasonic particle size analyser (UltraPS) for use in minerals grinding applications. Over the past four years this technology has been further developed for use in Bayer Liquors, in particular for the conditions found in the precipitation circuits of alumina refineries. A number of scientific and technical challenges had to be addressed before the analyser could be deployed in Bayer liquor. Scientific challenges related to the supersaturated nature of the liquor, the presence of minute gas bubbles in the liquor and scaling. Variation in dissolved solids, bubbles and scale can affect the accuracy of the ultrasonic technique. Engineering challenges relate to the high caustic concentration and high temperature of the liquor. An analyser used on plant must be able to withstand the environment, especially any sensors which come into contact with liquor.

This paper discusses the methodologies developed to overcome each challenge. An early prototype of the analyser has been tested on batch Bayer liquor samples at the Worsley Alumina refinery. The correlation coefficient and standard error for the percentage of particles less than 44 microns was 0.95 and 0.19% (2.7% relative) respectively when comparing the analyser and the Worsley laboratory size analyser. Installation of a modified UltraPS system is planned for early 2008 for extended testing at the refinery. The system will monitor a continuous stream of slurry on a byline.