In situ characterisation of a concentrated colloidal titanium dioxide settling suspension and associated bed development: Application of an acoustic backscatter system

Abstract

ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. eait.dean@uq.edu.au (S.Biggs). T.N.Hunter@leeds.ac.uk (T.N. Hunter).1 Present address: University of Queensland, Brisbane, Qld 4072, Australia 2 AbstractThe ability to accurately characterise the settling of particulate suspensions is imperative in numerous industries for improved processing, optimisation and control. Characterisation is typically a non-trivial process, and in situ measurements that remove the restriction of requiring particular sample sizes are preferred. Here for the first time, we explore the use of an acoustic backscatter system (ABS) to characterise key settling dynamics within a common colloidal mineral suspension, where backscatter attenuation is heightened due to the associated low scattering cross sections of the particles. Settling titanium dioxide dispersions with concentrations ranging 0.05 -3.00 vol% were successfully profiled using ABS transducers of 1, 2 and 4 MHz frequencies. This approach enabled the simultaneous visualisation of both the settling interface and sediment bed formation, generating sedimentation curves and eluding settling velocities. Furthermore, backscatter attenuation was empirically correlated with the attenuation-concentration relationship established for homogenous dispersions, to obtain concentration profiles of the settling suspensions. The data depicted concentration changes as a function of time in a hindered settling suspension, and allowed observation of the segregation of a size polydisperse suspension. Data were compared with sedimentation data obtained via two common ex situ bench-scale techniques. Critically, the acoustic backscatter method was validated as a powerful in situ characterisation tool for opaque concentrated heterogeneous dispersions, with the ability to provide concentration density information in conjunction with settling kinetics that is not easily attainable via other methods.

Measurement and density normalisation of acoustic attenuation and backscattering constants of arbitrary suspensions within the Rayleigh scattering regime

“…5). The intensity subsequently decreases monotonically with distance, consistent with attenuation-dominated systems [26][27][28][29], followed by an intense peak marking the column base at the furthermost measured transducer range.…”

“…The size range of barytes is larger than the pMMA (although still largely below 10 µm) and were notably more polydisperse than the latex particles, having a CV = 1.5. The titania had the highest level of polydispersity (CV = 5), and in fact, it is known they are highly aggregated structures in suspension, comprising a fraction of colloidal particles, intermediately sized aggregates and a fraction of larger clusters [27]. In addition to the high polydispersity, such structuring may suggest potential complexities in their acoustical scattering behaviour, due to the influence of the primary particles on the overall scattering of the aggregate [44][45][46].…”

“…The current authors have previously undertaken similar analysis alongside phenomenological approaches to characterise concentrated, settling and turbulent dispersions of large glass beads, plastic particles and colloidal minerals in pipe flows, as well as small and large industrial scale tanks [26][27][28][29][30][31][32]. Collectively, this research provides pathways to enable online characterisation of many concentrated dispersion systems in industries ranging from cosmetic, pharmaceutical, food and paint products, to water treatment, minerals and nuclear waste processing.…”

Numerical and experimental analysis of the sedimentation of spherical colloidal suspensions under centrifugal force

“…For each interface height obtained under centrifugal force, the corresponding time can be converted to an equivalent time in Earth gravity conditions using Eq. (24). Performing this conversion for each available data point, a times series of interface heights in Earth gravity conditions can be recovered from data collected under centrifugal force.…”

Large-scale trials of a real-time acoustic backscatter system for solids concentration measurement during nuclear waste cleanup

“…Previous research has highlighted the potential of ultrasonic backscatter and transmission systems as in situ techniques to measure batch-scale sediment settling [3][4][5][6] and pipe flow segregation [7,8]; although to date such systems have not generally been applied to industrial environments. This research however, seeks to investigate a large-scale application of an acoustic backscatter system as a solids concentration profiler.…”