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Knowledge of the residence time distributions (RTD) of solid particles through gravity settlers of the Bayer
process is essential to verify that they are operated effectively. Moreover, the RTD may be used to diagnose
some common problems occurring in settlers, like channelling and dead zone or to evaluate the effectiveness
of certain operational parameters, such as rake configuration. Because of the aggressive chemical
environment of the Bayer process it is difficult to realise RTD measurements. To monitor the mud
displacement, a ferromagnetic iron tracer was used with a new on line electromagnetic inductance
measurement method that has been described previously. Sedimentation tests performed in a laboratory
settler confirmed the effectiveness of this approach. In addition, a new method of RTD curves’ decomposition
has been used in order to facilitate the analysis of the data. This paper describes briefly the experimental
apparatus and presents an analysis of the RTD data obtained with our laboratory settler based on this novel
curve decomposition technique.
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