Sedimentation and consolidation of different density aggregates formed by polymer-bridging flocculation

Benn, F, Fawell, P, Halewood, J, Austin, P, Costine, A, Jones, W, Francis, N, Druett, D and Lester, D 2018, 'Sedimentation and consolidation of different density aggregates formed by polymer-bridging flocculation', Chemical Engineering Science, vol. 184, pp. 111-125.


Document type: Journal Article
Collection: Journal Articles

Title Sedimentation and consolidation of different density aggregates formed by polymer-bridging flocculation
Author(s) Benn, F
Fawell, P
Halewood, J
Austin, P
Costine, A
Jones, W
Francis, N
Druett, D
Lester, D
Year 2018
Journal name Chemical Engineering Science
Volume number 184
Start page 111
End page 125
Total pages 15
Publisher Elsevier
Abstract There are numerous models of sedimentation in fine particle suspensions, derived from or validated withphysical measurements. Such models could be applied to optimise and control gravity thickeners used forsolid-liquid separation in mineral processing. However, these applications rely upon particle bridging byhigh molecular weight polymers to form large, low density and fragile aggregates. The evolution andrefinement of sedimentation modelling for flocculated systems is restricted by a lack of meaningful con-trol of flocculation conditions and inadequate detail in the experimental sedimentation data used forvalidation.To address this problem, an experimental system was built to give high fidelity sedimentation data, itsuse demonstrated for flocculated calcium carbonate suspensions. Turbulent pipe flow flocculation offerstight control of dosage, mean shear rate and reaction time, with aggregate size monitored in-line. Thepipe discharges into the base of a wide (190 mm ID) transparent column for which the contents canbe isolated, with mudlines then determined from image capture and bed profiles byc-attenuation.The use of wide columns minimised wall effects that can limit consolidation, while simultaneous effortsto maximise measurement reproducibility and sensitivity led to a greater ability to distinguish subtleimpacts from variations in flocculation. Duplicate columns with detachable lower sections enable directvane yield stress measurement at known bed depths and thereby plots of yield stress vs. solids fraction.Modelling of such data will be described in subsequent publications, with the present study focusing onkey experimental requirements and limitations, the form of data outputs and insights into flocculationimpacts. For the latter, off-line determination of individual aggregate settling rate vs. size after bed sampling confirmed that higher solids volume fractions low within beds occurred through removal ofboth inter- and intra-aggregate liquor, i.e. there is a contributi
Subject Water Treatment Processes
Keyword(s) Aggregate
Attenuation
Bed profiling
Flocculation
Sedimentation
DOI - identifier 10.1016/j.ces.2018.03.037
Copyright notice Crown Copyright © 2018 Published by Elsevier Ltd. All rights reserved.
ISSN 0009-2509
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