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“Effects of polymer dosage on rheology / spread-ability of polymer-amended
MFT
Civil and Environmental Department, Carleton University
17 June 2013
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Team managerSahar SoleimaniPhD Environmental Engineering3 years experience in Civil EngineeringProjectsExpertise in numerical modelling
Bereket Fisseha (at U of A)5 years experience with Golder in Mining Geotechnical Services
Shabnam Mizani3 years experience with AMEC
Tariq Bajwa 5 years in Civil and Hydropower Engineering
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Project Background
► Part of a larger project funded by COSIA looking at optimization of polymer-amended mature fine tailings
► Optimization includes:
► i) Short-term dewatering due to action of polymer and consolidation under self-weight in a thin (< 1 m ) lift
► ii) Dewatering due to desiccation
► Iii) Dewatering and geotechnical behaviour after consolidation under addition of new lifts
► Iv) Spread-ability (rheological behaviour after material emerges from the pipe)
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Objective – Improve understanding of “out of pipe” rheologyControlling stack geometry (slope and lift heights)
- Designing deposition cells
- Trade off between deposition and dewaterability
Flow Behaviour of the Amended Oil Sand Tailings upon Deposition
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Objective Introduction Methodology Results Conclusion Future Work
Rheology
Topography
Operational Parameters
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Introduction
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Flocculation: Aggregation Process
Alters the Rheology significantly (Yield Stress, Viscosity)Mixing intensity and duration (shear caused during transportation can disintegrate the flocs)
ObjectiveIntroduction Methodology Results Conclusion Future Work
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Rheological Behaviour
► Tailings show Non-Newtonian behaviour
► Polymer amended MFT especially sensitive to aging and
shearing
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Rheology ??
ObjectiveIntroduction Methodology Results Conclusion Future Work
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Methodology► Slump Tests
► Back analysis of bench /field scale deposition
► Rheometer (Anton Paar Physica MCR301)
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A.Stress growth (Rate control mode)
B. Stress relaxation
C. Creep (Stress controlled mode)
Application of constant stress
Application of constant stress rate
ObjectiveIntroductionMethodology Results Conclusion Future Work
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Some pictures captured from video
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In Line Mixing
In Field► rapid mixing of polymer occurs in a 17 ft pipeline
In LaboratoryI. First a four blade impeller with radius of 8.5 cm was immersed in
1,800 g of MFT.
II. The mixing was then started at a fixed speed of 250 rpm.
III. The flocculant solution was then added but was mainly directed near the impeller during mixing.
IV. After adding the 0.4% flocculant solution the mixing was continued for another 10 seconds
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ObjectiveIntroductionMethodology Results Conclusion Future Work
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Mixing Time & Dewaterbility
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Highest water release
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Results
► Stress Growth
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ObjectiveIntroductionMethodologyResults-Rheology-Flume Test Conclusion Future Work
Shear Rate=0.1s-1 Shear Rate=1s-1
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Constant stress test (Decreasing)-850gr/ton30s each step (800-5Pa) 10min each step (250-30Pa)
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Flume / 3-D bench deposition tests► Using Funnel-9L of flocculated Tailings
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ObjectiveIntroductionMethodologyResults-Rheology-Spreadibility Conclusion Future Work
Dosage (g/ton) Yield stress (Pa)600 60
725 95850 104
1,000 110
Yield stress from best fits of lubrication theory – JNNFM 2013
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Comparison With Field Data (Pilot scale Test Oct2012)► Stress Growth Shear rate=0.1s-1
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mixing time and intensity used to prepare the flocculated MFT in the laboratory was representative of field mixing conditions
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• Shell Atmospheric Drying cell during the autumn 2010
• Total volume of tailings deposited in this cell was 7953 m3
• average slope of 2.1%.
15287.00
288.00
289.00
290.00
291.00
292.00
293.00
0 50 100 150 200 250
Heig
ht(m
)
Run-Out( m)
Deposited Tails
Topography
LT prediction, 100 Pa yield stress
LT prediction 240 Pa yield stress
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Summary & Conclusion
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ObjectiveIntroductionMethodologyResults-Rheology-SpreadibilityConclusion Future Work
Dosage (g/ton)
Method of Measurement
Slump (Pa)From Lubrication
Theory
(Pa)
Stress growth Decreasing shear stress Stress Relaxation
Shear rate
(S-1)
Max stress
(Pa)
Starting shear stress
(Pa)
Interpreted yield stress
(Pa)
Ave Stress
(Pa)
MFT - -0.1 28.8
100 10 5.521 28.0
600 92 600.1 169 250 50-1001 207 200 50-100
725 125 950.1 255
450 50-1001 323
850 154 1040.1 333
700 50-100 16.71 510
1,000 163 1100.1 988
1,000 2501 1,020
1,200 187 -0.1 1,000
1,300 -*1 1,180
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Microstructure SEM► Scanning electron microscopy (Vega-II XMU VPSEM, Tescan)
► speed of 148 µs/pixel and a working distance of 6-8 mm.
► acceleration voltage of 20 kV using a cold stage to freeze the samples(prevent excessive water withdrawal during the observation under the vacuum condition of the SEM chamber)
Raw MFT 1000 g/ton
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ObjectiveIntroductionMethodologyResultsConclusionFuture Work
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Microstructure: MIP
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0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02
0.01 0.1 1 10
Incr
emen
tal p
ore
volu
me
(ml/
g)
Pore diameter (microns)
MFT
1500 ppm
700 ppm
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Summary & Conclusion
► Laboratory prepared samples could mimic field samples in the stress growth tests
► Yield stress calculated from the flume and other tests employing lubrication theory was in best agreement with slump and controlled decreasing shear stress test.
► Lift thickness control likely needs to consider increase in effective yield stress of the deposit over deposition time
► Even high sheared polymer amended MFT still manifests a significant yield stress
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Future/Ongoing WorkRheology Characterise the dependence of spreadability on both aging
and shearing (i.e. Coussot Model )
Spreadibility finite element non-Newtonian flow codes such as ANYS Polyflow
or ANSYS CFX 14 (Finite Volume)
SPH – smooth particle hydrodynamics
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ObjectiveIntroductionMethodologyResults-Rheology-SpreadibilityConclusion Future Work
.1
dt
d
Characteristic time
Rate of shear
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SPH flume simulation compared to lubrication theory
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Acknowledgements
► COSIA and NSERC
► Shell Canada and Barr Engineering
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