“ Effects of polymer dosage on rheology / spread-ability of polymer-amended MFT

“Effects of polymer dosage on rheology / spread-ability of polymer-amended

MFT

Civil and Environmental Department, Carleton University

17 June 2013

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

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

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

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

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

Some pictures captured from video

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

Mixing Time & Dewaterbility

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Highest water release

Results

► Stress Growth

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ObjectiveIntroductionMethodologyResults-Rheology-Flume Test Conclusion Future Work

Shear Rate=0.1s-1 Shear Rate=1s-1

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

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

• 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

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

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

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

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

SPH flume simulation compared to lubrication theory

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Acknowledgements

► COSIA and NSERC

► Shell Canada and Barr Engineering

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