Shear-induced floc structure changes for enhanced dewatering of coal preparation plant tailings

Ofori, Philip, Nguyen, Anh V., Firth, Bruce, McNally, Clint and Ozdemir, Orhan (2011) Shear-induced floc structure changes for enhanced dewatering of coal preparation plant tailings. Chemical Engineering Journal, 172 2-3: 914-923. doi:10.1016/j.cej.2011.06.082

Author Ofori, Philip
Nguyen, Anh V.
Firth, Bruce
McNally, Clint
Ozdemir, Orhan
Title Shear-induced floc structure changes for enhanced dewatering of coal preparation plant tailings
Journal name Chemical Engineering Journal   Check publisher's open access policy
ISSN 1385-8947
Publication date 2011-08-15
Year available 2011
Sub-type Article (original research)
DOI 10.1016/j.cej.2011.06.082
Open Access Status Not yet assessed
Volume 172
Issue 2-3
Start page 914
End page 923
Total pages 10
Place of publication Oxford, United Kingdom
Publisher Oxford University Press
Language eng
Subject 1600 Chemistry
2304 Environmental Chemistry
1500 Chemical Engineering
2209 Industrial and Manufacturing Engineering
Abstract The handling and disposal of industrial waste slurries containing colloidal particulate matter, with particular reference to coal and mineral processing plant tailings with a high proportion of clay materials present significant challenge. To develop effective disposal methods requires an improved understanding of floc structure that promote better water recovery and higher sediment density during settling and consolidation of flocculated tailings. In this paper, the effect of floc structure on coal tailings dewatering and the impact of shear-induced modification of floc network structure on additional sediment consolidation and densification have been examined. Four real tailings and a high molecular weight anionic polymeric flocculant were used. Flocculation tests were conducted under reproducible hydrodynamic conditions in batch mode. Flocculated aggregates have complex structures with different sizes, shapes and voidages. The structures of the flocs were characterised by fractal analysis using light scattering technique and the dewatering characteristics of the flocs were investigated in terms of settling rates and sediment consolidation. The fractal analysis by laser scattering identified optimum mixing speed and flocculant dosage required for the production of flocs with compact structure of fractal dimensions greater than 2. It was determined that hydrodynamic conditions during flocculation have a profound impact on floc settling rates and to a lesser extent sediment consolidation. Low mixing speeds produced large flocs with high settling rates, while very high mixing speed during flocculation resulted in irreversible floc degradation leading to much reduced settling rates with some additional sediment consolidation. Application of shear to pre-sedimented flocs resulted in significant additional sediment consolidation for the tailings samples and flocculants studied. This approach would allow flocculation to be optimised for fast settling with subsequent application of shear to the settled sediment to promote the removal of inter and intra-floc liquor to improve consolidation and sediment density.
Keyword Coal tailings
Shear-induced flocculation
Fractal analysis
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Chemical Engineering Publications
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