Abstract
Gibbsite scaling on surfaces such as tanks, pipe-work or measuring equipment is the source of many difficulties in the Bayer process. The study presented here investigates the role of surface roughness of steel in aiding gibbsite scale build-up. Steel surfaces of different temperature roughnesses (ra = 0.01–1.44 µm) were prepared and tested for gibbsite scaling rates in real Bayer process conditions in pregnant liquor in a filtrate tank. The roughness of the steel samples influenced the scale nucleation time and the strength of adhesion of the scale. The smoother the steel sample, the longer it took to form a complete layer of scale and the lower the adhesion strength. Once a complete layer of scale had formed then the rate of scale-on-scale growth was similar for all samples, as expected. The scale growth rate under the conditions tested was found to be an average of 22.63 mm/year.
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