Characterization of Bed Densification in a Laboratory Scale Thickener, by Novel Application of an Acoustic Backscatter System

The measurement of the local concentration of suspended particles within settling multiphase systems is important to many engineering applications; particularly for example in gravitational thickeners used extensively in minerals processing and water treatment. The ability to monitor concentration and stratification in situ may greatly aid in developing efficient separators and allow more accurate modeling of these processes. Acoustic backscatter systems (ABS) are a practical and relatively inexpensive characterization technique, with the ability to profile particle concentration as a function of depth in operational environments. Currently, such instruments are only used for sedimentology studies in dilute estuarine flows as their application in concentrated industrial suspensions is significantly more complicated and largely unstudied. A novel application is reported herein investigating the use of an ABS to characterize a model mineral separation system, utilizing a bespoke continuous flow laboratory scale thickener with inline pipe flocculator. A 1 MHz probe mounted in the near-bed region of the thickener was used to measure consolidated bed build-up and segmented density changes from the signal decay. Importantly, the influence of a scraper-rake on solids densification was observed by analyzing systems at two different scraper rotation speeds (0.1 and 1.1 rpm). An optimal rotation speed was observed that led to enhanced underflow solids fractions. Higher speeds led to an assumed fluidization of the bed from secondary flows, which reduced bed densities in the vicinity of the scraper.