Effects of sand and flocculation on dewaterability of kaolin slurries aimed at treating mature oil sands tailings

Accepted Manuscript Title: Effects of sand and flocculation on dewaterability of kaolin slurries aimed at treating mature oil sands tailings Authors: Chandra W. Angle, Sameh Gharib PII: DOI: Reference:

S0263-8762(17)30381-7 http://dx.doi.org/doi:10.1016/j.cherd.2017.07.014 CHERD 2755

To appear in: Received date: Revised date: Accepted date:

24-2-2017 30-6-2017 6-7-2017

Please cite this article as: Angle, Chandra W., Gharib, Sameh, Effects of sand and flocculation on dewaterability of kaolin slurries aimed at treating mature oil sands tailings.Chemical Engineering Research and Design http://dx.doi.org/10.1016/j.cherd.2017.07.014 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Effects of sand and flocculation on dewaterability of kaolin slurries aimed at treating mature oil sands tailings

Chandra W. Angle*a and Sameh Ghariba

a. Natural Resources Canada, CanmetENERGY, #1 Oil Patch Drive, Devon, Alberta, T9G 1A8

*Corresponding Author - [email protected]; [email protected] ©Her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources (2017)

2 Graphical abstract

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HIGHLIGHTS HIGHLIGHTS –R2  4-5% v/v sand with kaolin in 10% v/v solids improved dewaterability significantly.  Untreated kaolin or MFT consolidated better than flocculated, with or without sand.  Starting from equal gel points MFT compressed more than kaolin but took longer.  Py () curves of flocculated kaolin and MFT crossed at 0.41 and Py=121 kPa.  Py() curves of kaolin with sand, MFT, flocculated kaolin or MFT fitted power law.

ABSTRACT In guiding dewatering of oil sands tailings we measured dewaterability of as-mined kaolin when sand was added as a process aid to both the dispersed and flocculated kaolin slurries. In batch tests, gravitational settling, inverse permeability R, and compressive yield stress Py were measured as functions of solids volume fractions , as sand increased in the mixtures. We measured Py(for flocculated kaolin with an equal sand fraction, a flocculated diluted kaolin, flocculated diluted mature fine tailings(MFT), gel-point kaolin and MFT. Results indicated that an optimal quantity of sand in mixtures with kaolin increased the consolidated volume fraction of solids at equivalent compressive yield stress, reduced hindered settling function values, and enhanced gravitational settling rate. Py() vs plots for gel-point volume fractions of kaolin and MFT showed MFT to be more compressible, but needed a much longer time to dewater. Two flocculants had similar Py() vs responses when tested with either kaolin or MFT. Flocculated kaolin and MFT exhibited rapid settling, but flocculated was less compressible than unflocculated. Py() vs plots for both kaolin and MFT that were flocculated after dilution produced a crossover at Py = 121 kPa and 0.41. The Py() vs data from all tests followed power law.

Key words: dewatering, pressure filtration, flocculation, kaolin, sand, oil-sand tailings.

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Notation T

temperature, °C

t

time, s

tf

final time, s

t0

initial time at initial volume fraction, s

V

volume, L or dm3



volume fraction

P

pressure, kPa

r()

hindered settling factor

R()

hindered settling function

R(∞) hindered settling function at final volume fraction achieved for a pressure during inverse permeability measurement Py() compressive yield stress function D( solids diffusivity as a function of volume fraction D(∞) solids diffusivity at final volume fraction f(

settling as a function of volume fraction

v∞

final settling velocity

max maximum volume fraction n

scaling factor

v/v

volume fraction

gel

volume fraction of solids at gel point

P

applied pressure, mPa

f

final volume fraction

0

initial volume fraction

∞

volume fraction of cake when no more change occurs for an imposed pressure

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H0

initial height of slurry

Hf

final height of slurry

e

effective solids stress

2

inverse slope of the linear plot of t vs V2

MPW+ model process water MTW model tap water UF

underflow

MWt molecular weight MFT

mature fine tailings in tailings ponds after bitumen extraction from oil sands

INTRODUCTION

In Canada, producers of bitumen from oil sands are required to demonstrate environmental stewardship in their commercial operations. Ideally, the fresh tailings being discharged should be treated not only to separate the water but also to remove residual diluted bitumen and solids. Demonstration of environmental sustainability requires minimizing further tailings accumulation in ponds. Technological solutions are needed(Alberta Government, 2015;Devenny, 2010). Choices are: to modify the ore processing(Li, Long, Xu, and Masliyah, 2005;Li, Long, Xu, and Masliyah, 2008) and bitumen extraction process by using solvents,(Al-Sabawi, Seth, and de Bruijn, 2011;Angle, Long, Hamza, and Lue, 2006;Long, Dabros, and Hamza, 2004;Pathak, Babadagli, and Edmunds, 2011;Sabet, Hassanzadeh, and Abedi, 2017) treat fresh tailings with process aids to enhanced water recovery, and clean up existing tailings ponds by separation methods(Matthews, Shaw, MacKinnon, and Cuddy, 2002). Thus, it is accepted that the tailings produced during the extraction of bitumen from oil sand, whether fresh or stored, require treatments to mitigate negative environmental impacts(Devenny, 2010). The tailings originate as the underflows (UFs) of separation vessels. Water, colloidal clays and minerals, surfactants, entrained residual bitumen and sand are

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discharged in the UF. These rejected materials occur mostly when the bitumen extraction from oil sands utilizes hot water and/or caustic conditioning. Tailings that are not treated immediately are stored in settling ponds. Over time, settled tailings become mature (MFT). In the settling ponds MFT is an intermediate layer between sand sediment beneath it and the free water above it. MFT can hold up to 70% w/w water and 26-30% w/w suspended solids. Some variations occur by sampling depth and the ponds. Solids concentration is at gel point where particles are networked into viscoelastic structures. The MFT network in the ponds supports the overburden pressures, is stable and does not compress further(Fine Tailings Fundamental Consortium, 1995). The water above and within the particle network has dissolved salts and surfactants. Our laboratory measured pH of pond water is 8.5 and MFT pore water 8.8. MFT can also contain 1-3% w/w residual bitumen occurring as free and entrained bitumen-in-water emulsions. The mineral content of the MFT solids is reported in the range of 50-60% w/w kaolin, 30-50% w/w illite, and about 20% w/w silica. Variations occur with the types of mined ore and bitumen extraction process producing tailings with unique flow properties (Angle, 1995;Angle and Zrobok, 1995;Angle, Zrobok, and Hamza, 1993;Angle and Hamza, 2009;Fine Tailings Fundamental Consortium, 1995). The shear and oscillatory rheological properties of MFT pose challenges for separation as network structures are also thixotropic. Therefore, both fresh and aged stable colloidal suspensions of tailings require process aids to enhance separations. Effective process aids can reduce separation times, and allow water to flow out of the sedimenting solids. When particles are not sufficiently large for solid/liquid or liquid/liquid separation to proceed on a reasonable time scale, separation aids are used. The particles can either be aggregated by coagulation using dissolved inorganic salts, or flocculated using long-chain polymers to increase the aggregate sizes (Abidin Kaya, Ali Hakan Oren, and Yeliz Yukselen, 2006;Addai-Mensah, 2007;Alberta Government, 2015;Angle CW, SmithPalmer T., and Wentzell BR, 1997;Angle and Hamza, 1987;Angle et al., 1995;Angle et al., 1993;Angle et al., 2009;Angle, Clarke, and Dabros, 2017;Besra, Sengupta, Roy, and Ay, 2002;Boger, 2009;Chalaturnyk, Scott, and Ozüm, 2002;Gregory,

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2006;Hogg, 2000;Mpofu, Addai-Mensah, and Ralston, 2003;Nasser and James, 2006b;Rao, 1980;Shouci Lu, ·Robert J.Pugh, and Eric Forssberg, 2005;Zhou, Jameson, and Franks, 2008). The physicochemical properties of the liquid continuous phase can also be modified, to increase the density differences between particles and fluid and to reduce the viscosity. Generally, water has a viscosity of about 1 mPa·s.

Centrifugation is

sometimes used to increase the rate of settling and study compressibility (Curvers, Saveyn, Scales, and Van der Meeren, 2009;Garrido, Concha, and Bürger, 2003;Miller, Melant, and Zukoski, 1996;Stickland, Burgess, Dixon, Harbour, Scales, Studer, and Usher, 2008;Usher, Studer, Wall, and Scales, 2013;Wakeman, 2007). For our particular study, centrifugation was not useful. We used pressure filtration. Pressures imposed normal to the fluid cause the water to flow through the pores of the solids networks and the filter medium. The end result is that solids consolidate into a cake on the filter medium and water is expelled through both the cake and filter medium. Solid/liquid separations by using pressure filtration and aids are shown below as viable options for the oil sands tailings systems. The following paper shows results obtained for dewatering of several slurries made up in model process water (MPW+) and model tap water (MTW) while using process aids such as sand and polymer flocculation. Slurries are: kaolin, kaolin and sand, sand and flocculated kaolin, MFT, flocculated diluted MFT and flocculated diluted kaolin.

2. THEORY OF DEWATERING In context for this work, dewatering refers to water separation from solids in both dilute and concentrated suspensions (Bürger and Concha, 2001;Curvers et al., 2009;Garrido et al., 2003;Miller et al., 1996;Stickland et al., 2008;Usher et al., 2013;Wakeman, 2007). Gravity settling and pressure filtration are methods used. Dewatering occurs in three zones of separations in a vessel. These are: 1. Initial free settling of solids when followed over time would give initial settling rates; 2. Hindered settling of particles, where rates of solids separation from water are reduced (Figure 1 a); 3. Consolidation or cake formation

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zone, where fluid in compacting solids would flows out through network pores and the filter membranes, often aided by imposed pressure (Figure 1 b-c). The scholarly development of theory and practical tools for obtaining separation parameters for use in the predictive modeling of solid/liquid separations have been a focus for use in the mineral industry(Concha and Bustos, 1991;Davies, Dollimore, and Sharp, 1976;Davis and Gecol, 1994;Green, Eberl, and Landman, 1996;Green, Landman, de Kretser, and Boger, 1998;Kynch, 1952;Landman K.A and L.R.White, 1992;Landman, White, and Eberl, 1995;Michaels and Bolger, 1962;Nasser and James, 2006a;Raha, Khilar, Pradip, and Kapur, 2005;Ruth, 1935;Ruth, 1946;Skinner, Studer, Dixon, Hillis, Rees, Wall, Cavalida, Usher, Stickland, and Scales, 2015;Stickland, 2015;Stickland et al., 2008;Tiller and Khatib, 1984). These tools have been used extensively to determine parameters required for modeling the separations of mineral tailings and biological sludges (de Kretser, Usher, Scales, Boger, and Landman, 2001;Stickland et al., 2008;Toorman, 1996;Toorman, 1999). To date, there are still insufficient published experimental findings on such separation parameters for fresh oil sands tailings and MFT (Angle et al., 2017;Eckert, Masliyah, Gray, and Fedorak, 1996;Matthews et al., 2002;Xu and Hamza, 2003;Xu, Dabros, and Kan, 2008). Recently published reviews of compressional rheology, sedimentation and filtration addressed historical developments, theory and analysis for dewatering sludges (Skinner et al., 2015;Stickland, 2015;Stickland, Irvin, Skinner, Scales, Hawkey, and Kaswalder, 2016;Stickland et al., 2008). The following is a short explanation of how the dewatering parameters are obtained and used for determining the material properties in the solid/liquid separation in our work. 2.1. Compressive Yield Stress and Pressure filtration. Pressure filtration is used to obtain the network strength or compressive yield stress that characterizes a material at starting volume concentration of particles  at or above the gel pointgel. The particle network structure remains unchanged until the applied stress

P exceeds the compressive yield stress. Figures 2 and 2a show a schematic and picture of a filtration rig that was built and customized for performing pressure filtration for our

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tailings applications (University of Melbourne, Australia)(de Kretser et al., 2001). Figure 3 is a screen capture picture of water removal in time as clay slurry dewatered during compression by applied stepped pressures. As a constant pressure is applied, time t as a function of filtrate volume squared V2 is recorded and plotted. The t vs V2 data for the stepped increases in pressure are used in calculations of the parameters. Using built-in software, for a given pressure t vs V2 data are recorded as the curve reaches a plateau. The volume fraction of solids f is calculated for that condition. When the imposed pressure P results in no further compression it is recorded as the compressive yield stress Py for that equilibrium volume fraction of solids (  ) . In order for further compression to occur the pressure P is stepped up and data collection is repeated until the full geometric series of pressures have been applied and the cake has reached its maximum compression. Corrections are made for presence of dissolved solids and cake moisture after cake and permeate are weighed and dried. Thus, for the pressure filtration cell, equation 1.1 describes the relationship for the final volume fraction ffor one pressure step, proportional to the initial volume fraction 0of the slurry times the ratio of the initial height H0 and the final height Hf. The heights are measured by a sensor on the tip of the piston after the initial calibrations are performed to teach the linear encoder the zero-height position:

 f  0

H0 Hf

1.1

Py() is also referred to as e the effective solids stress in equation 1.2. It measures the strength of the solid network formed with increased local volume fraction of particles: P  Py ()   e ( f )

The network partially collapses at the next higher imposed pressure and consolidation begins within a smaller volume, where more interparticle contacts occur. 2.2. Hindered Settling Function and Stepped Pressures.

1.2

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As the volume fraction and number of particles increase within a given cylinder volume, the hydrodynamic interactions between particles, and consequently the drag on a given particle, increase (Figure 1 (a)). The hindrance of particle movement by the fluid is described by the parameter r(thehindered settling factor, which increases nonlinearly with volume fraction (Buscall and White, 1987). Details on the derivations are given elsewhere (de Kretser et al., 2001;Landman K.A and L.R.White, 1992;Landman et al., 1995). The hindered settling function R(), is obtained from the measured slope of the linear part of the time t vs V2 plot for one imposed pressure. The slope of the plot is linear within the cake formation region. 



is the inverse of this slopeRis often

referred to as the inverse permeability. In equation the slope of a plot of vsP is used to obtain r(When the piston meets the cake which forms from the membrane upwards,is non-uniform. In time, and for a given imposed pressure, when no more change occurs in the cake, sediment volume fraction becomes final at (  ) . The function R (  ) in equation 1.3 is used to produce the hindered settling parameters.  1 1 d  2 1 R(  )  r (  )    2[(  )(1    )2 ( ) ] V    d  P p 0   

1.3

Vp is the volume of a particle and is a Stokes drag coefficient for a single particle in an infinite medium. 2.3. Solids Diffusivity. The solids diffusivity D (  ) is related to both Py (  ) and R (  ) in equation 1.4. D() is interpreted as the overall rate of dewatering that is dependent on the solids volume fraction. Higher values of D indicate easier dewatering. D(  )  (

dPy (  ) d 

)(R(  ))1 (1    )2

1.4

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According to de Kretser et al. (de Kretser et al., 2001) one can directly use the experimental data collected from the filtration rig to obtain D() function. The slope of the plot of  2 vs   in equation 1.5 is utilized to give this material property. Data from initial to final volume fractions at a given pressure are used: 1 d 2  1 1  D(  )     2 d    0   

1

One can directly use the experimental data collected from the filtration rig to obtain D() function. Further details on the functional theory are found in published papers (de Kretser et al., 2001;Landman K.A and L.R.White, 1992). Separate independent runs using stepped-up pressure filtration were replicated to collect the data for determining the parameters, R() and Py(). The solids diffusivity function D (), which describes the overall rate of dewatering was calculated using the Py() and R() datasets. In selected cases the Py() functions for both as-received and diluted then flocculated MFT, were compared with those for kaolin and sand combinations.

3. EXPERIMENTAL In this study, dewatering is defined as the removal of water from suspensions. We used two separation processes and process aids that included sand and two cationic polymers. The first process was gravitational settling, for which generally the solids separate from the suspending liquid leaving behind a relatively clarified continuous liquid phase. The supernatant or continuous phase that suspends the solids is displaced by the sedimenting solids. The subject of gravitational settling and the associated physics have been thoroughly studied and reported in textbooks(Coulson, Richardson, Backhurst, and Harker, 2001). Dewaterability parameters were measured for: 1) Varied volume ratios of sand added to kaolin for a fixed total of 10% v/v solids equilibrated in model process water (MPW+), at pH 8.5; 2) Flocculated kaolin and added sand suspended in a model tap water (MTW) at equal kaolin to sand volume ratio, v/v = 0.5:0.5; 3) Compressive yield stresses as a function of solids volume fraction Py() for initial 10% v/v kaolin in MPW+

1.5

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were compared to similar data collected for a typical 10% v/v MFT in its own water. 4) Py() for diluted then flocculated kaolin in MTW were compared with those of similarly treated MFT in MTW at the starting solids concentration of 5% w/w, as used generally in standard flocculation tests. The physical properties such as density differences between the solid particles and the suspending liquid, particle sizes, viscosity of the liquid, and particle concentrations were obtained before dewatering tests. 3.1 Materials and Methods In addressing clean energy production mandate Alberta kaolin was used as a model material in the experiments designed to understand some fundamentals of oil sand tailings dewatering. The kaolin (Pioneer Kaolin), a ceramic quality clay used in pottery and mined near Medicine Hat, Alberta, Canada, was used as received. The kaolin was purchased from Plainsman Clays Ltd. in Edmonton, Alberta. The choice of kaolin as a model material for tailings was made after comparing the zeta potentials  of the kaolin and MFT solids in the same aqueous buffer and as pH varied. The data would indicate similarities in the electrokinetic charge of the materials. Coarse white Ottawa sand, (U.S Silica, Ottawa, Illinois) was used after sieving through a 50-70 mesh Tyler sieve. The coarse sand was used as a dewatering aid when mixed with fine slurried kaolin, and selectively with flocculated kaolin. MFT was obtained from Suncor Inc. (Ft McMurray, Alberta) as part of our long term study of MFT physicochemical properties. There were two batches. The first was used as received for comparing its compressibility with that of kaolin at gel point solids concentrations. Dean-Stark analysis of this sample revealed 26.88% w/w solids, 2.91% w/w bitumen and 68.82% w/w water. The second sample was taken from another shipment bucket and Dean-Stark analysis was 46.61% w/w solids, 3.61% w/w bitumen and 52.09% w/w water. This sample was used later on for flocculation tests after dilution

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in MTW. The average density of kaolin particles obtained by null pycnometry was 2.62 g/cm3. The averaged specific surface area for the kaolin by BET-nitrogen methods was 22.12 m2/g. The density of sand as measured by null pycnometry was 2.65 g/cm 3. Density of Dean-Stark extracted MFT solids by the same method was 2.54 g/ cm3 for batch 1 and 2.62 g/cm3 for batch 2 solids. Quantitative x-ray diffraction analysis of kaolin (Rigaku Corporation, Japan) was performed by specialists in-house. The Rigaku D/MAX Rapid-II rotating anode powder diffractometer, equipped with an imaging plate detector was used. Diffraction data were obtained using CrKα radiation at 35 kV and 25 mA, scanning from 5° to 150° 2θ with a scan step of 0.045° 2θ for 0.2 s. Quantification of the mineral species in the randomly oriented specimen was carried out using the Rietveld least square refinement program, AUTOQUAN™. The mineral content of the kaolin was 82.6 ± 2.8% w/w kaolinite, 7.24 ±0.9% w/w muscovite, 6.34±2.5% w/w chlorite, 1.82±0.48% w/w anatase, 1.13 ±1.05% w/w schorl, and 0.69±0.45% w/w zircon. Size analyses of kaolin, sand and MFT particles were performed by laser diffraction techniques using Malvern Mastersizer MS2000 (Malvern USA). The d 50 for kaolin was measured at 6 m. Kaolin was suspended in a 2.5% w/w sodium hexametaphosphate which was also the carrier fluid. The sample was pre-sonicated in the sampler before the size measurement. Size measurements of kaolin in several other carrier fluids were reported in our earlier work. The d50 of MFT batch 1 particles was 5.75 m. MFT was suspended and measured in its own water as carrier fluid. Sizes of coarse white sieved Ottawa sand were measured in model process water after sonication. Sizes were d50 = 303 m, d10 = 22 m, d90 = 413, d32 = 294 m. The Malvern Zeta–Nano (Malvern, USA) with disposable cuvettes and gold-plated electrodes was used for determination of the zeta potential as a function of pH. Generally, the colloidal particles of a typical MFT (Suncor, batch 2) and the as-mined kaolin were dispersed in an electrolyte solution made of 10 mM NaHCO 3 and 1 mM NaCl, prior to measurements. MFT supernatant was used to measure zeta potential of the as-

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received MFT particles as required. Subsamples were placed in the cuvettes and inserted into the sampling compartment of the instrument. A lazer-light directed at the cuvette of the suspended particles caused their scattering and movements through Brownian diffusion or from an imposed electric field, were detected and recorded. Details of measurement techniques are found in the Zeta-Nano manual (Malvern, USA). 3.3 Chemicals, Waters and Slurries All chemicals were ACS grade obtained from Fisher Scientific: NaHCO3, K2CO3, NaCl, CaCl2, and pH buffers (4.0, 6.0, and 10.0) for calibration of a Fisher AR50 research-grade pH meter (Fisher Scientific, Edmonton, Alberta). A combination glass electrode, HCl, and NaOH were used for pH adjustments. All slurries used in this work were at pH 8.5. Electrolyte solutions were prepared by dissolving the appropriate mass of salts in deionized water taken from a laboratory installed Millipore RO-Milli-Q system (Millipore Inc., USA). Model process water (MPW+) was made by dissolving 0.01M CaCl2 in a buffer solution made of 9.39 mM NaHCO3 and 0.137 mM K2CO3. Model tap water (MTW) was made similarly and consisted of 2.54 mM NaHCO3, 1.17 mM CaCl2, and 5.8 mM MgCl2. The filtration membrane used was a Whatman grade 17 filter paper of thickness 940 x 10 6

m (Fisher Scientific, Edmonton, Alberta). Two cationic polymeric flocculants Zetag 7557 and Zetag 8160 (BASF-Global,

Germany) were used based on success from our earlier in-house studies. Preliminary tests showed that these cationic polymers were effective flocculants for clays. Molecular weights (MWts) of Zetag 7557 and Zetag 8160 were 6-7 x106 Da and 10-15x106 Da respectively. The charge density of both was 60 %. The dosages (100 ppm, 1000 ppm and 2000 ppm (based on mg polymer/Kg solids in the sample) were preselected based on our earlier preliminary in-house studies. Their best activity was observed in model tap water (unpublished). Polymer stock solutions (1% w/w) were freshly prepared as needed. The polymer powder was dissolved in deionized water by slowly adding the grains to the surface of a spinning vortex of preweighed water that was magnetically stirred in a 125-

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mL glass jar. The solutions were used immediately after preparation and, if needed, could be stored safely at 4°C in a refrigerator for up to three days. 3.3.2 Slurry Preparation The 10% v/v clay slurry was prepared by adding the preweighed powdered clay slowly into the premeasured MPW+ electrolyte solution in a 2-L pail while mixing continuously at 400 rpm using a 2.7-inch diameter stainless steel marine impeller attached to a Lightnin (L1U08- Lightnin, USA) mixer. The off-bottom clearance was L/3, where L = liquid height. The masses of clay and water were increased proportionately if larger quantities of slurry were needed. In preparations of the clay-sand slurries, the designated proportions of kaolin and sand were added simultaneously and slowly while mixing the water at 400 rpm. Mixing continued for approximately 30 min after all solids were added. The slurry was then allowed to stand for 12 h to equilibrate and the pH was readjusted to 8.5±0.05 before testing. Prior to the tests, the slurry was remixed at 400 rpm and was subsampled during mixing. As indicated earlier, the total solids content in kaolin-sand mixtures was always 10% v/v. The combinations of kaolin:sand were, by %v/v ratio, 10:0, 9:1, 8:2, 7:3, 6:4, and 5:5. The greatest amount of sand tolerated in the mixture before segregation became visible in the timescale of the experiment was 5:5 %v/v. Any greater sand fraction resulted in segregation and difficulty performing measurements.

3.3.2.1 Settling Tests For each settling test an aliquot of mixed slurry was subsampled and placed in the 250 – mL graduated settling cylinder. The cylinder was capped and mounted on a Stuart rotator (Fisher Scientific, Edmonton, AB). Each cylinder was inverted 10 times at 20 rpm to thoroughly remix the slurry. The cylinder was placed vertically on the lab bench at room temperature. The descent of the solid/liquid interface (mudline) in time was followed visually or with a video camera. The initial settling data were recorded immediately.

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Interface height vs time was plotted to obtain each settling curve. The initial settling rate was simply the slope of the linear part of the descending interface height vs time curve. 3.3.2.2 Preparation of Samples for Flocculation and Settling Tests In order to perform similar experiments on flocculated kaolin, the condition of 5:5 %v/v ratio kaolin:sand was used. In this case, the solids were mixed in MTW, which was deemed in our preliminary studies to be the best water for activity of these polymeric flocculants. The slurry was prepared by adding 196.52-g kaolin slowly to 1350.91g MTW while mixing at 400 rpm with Lightnin mixer and a 2.7-in diameter stainless steel marine impeller for 30 min. The sample was allowed to stand overnight. While mixing the slurry, subsamples of 80 mL was removed for pressure filtration and 100 mL for settling tests. Adjustment of the kaolin slurry pH to 8.5 was done prior to testing. The samples were mixed with a Stuart rotator for 10 rotations at 20 rpm, and allowed to stand for 15 min. A volume of supernatant equal to that to be added for the selected flocculant dosage was removed. Next, dosages of 1000 or 2000 ppm flocculant (mg polymer/Kg solids) were added to the top surface of the kaolin slurry and left undisturbed for 15 min. The cylinder was mixed gently in ten end-to-end-inversions at 20 rpm using the Stuart rotator, then gently poured into the pressure filtration cell or left for settling. The pre-weighed sand was added to the flocculated clays and all materials were remixed once more by 10 rotations at 20 rpm before performing either a settling test or stepped pressure filtration. When sand addition was not a factor, 100 ppm polymer was added to 5% w/w kaolin in MTW or to 5% w/w solids of MTW-diluted MFT. Before sub-sampling of MFT from the bucket, MFT was stirred manually for 5 minutes and sampled into a 2-L bucket. Then, MTW was added to the sampled MFT and mixed by a Lightnin Lab Mixer (Lightnin, USA) at 300 rpm for 5 minutes. Next, 82±1 g of the resulting slurry (4.9% w/w solids) was subsampled into 100 mL graduated cylinders for testing. After polymer addition the sample was mixed for 10 rotations at 20 rpm and transferred to the measurement cell. After 15 min of standing in the measurement cell of the filtration unit, the compression test was started.

17

3.3.3 Pressure Filtration For pressure filtration tests, the sample was placed in the sampling cell of the previously readied pressure filtration rig (see Figure 2). Geometrically increasing pressure steps were entered and the program was initiated to begin a run. Typical pressure steps were 20, 40, 80, 160 kPa. For higher pressures 225, 250, 300 kPa were included in the jobstream when possible, depending on the material properties. A pressure transducer flush on the face of the piston, monitored the pressure of filtration and a linear encoder monitored rate of movement of the piston from the detected height (or volume). In precalibration, the height zero was set to the base of the filter support membrane. The initial piston height at the sample surface was detected by the software. The linear encoder in Figure 2 measured the displacement of the piston to a resolution of 10 m, thus ensuring accuracy of position and the volumetric flow of filtrate. A pressure controller (Bronkhurst EL Press) controlled the pressure in the pneumatic cylinder. The pressure range normally used for our test materials with this filtration rig was 20 to 300 kPa. Each compression experiment was performed in triplicate, with the exception of the gel- point MFT. After the compression test both the solid cakes and collected waters were removed, weighed, dried at 110°C overnight, cooled and reweighed. The final volume fraction solids content were corrected after the stepped test. Datasets for obtaining the rates of filtration from hindered settling function (inverse permeability) and compressive yield stress (compressibility) were obtained using this rig. Other details of both equipment design and theory development are found in earlier papers (de Kretser et al., 2001;Landman et al., 1995). Results by other comparative methods, apparatus and theory have been discussed and reported previously in earlier studies (Angle et al., 2017). In independent runs, the hindered settling function tests (inverse permeability) and compressibility tests were performed for the same series of pressure steps. In the inverse permeability case, as soon as the slope of time (t) vs volume squared (V2) was linear and stable, and while taking precautions to stay in the cake formation region of filtration, the pressure was stepped up to the next value. The process was repeated at the

18

next pressure to obtain the next slope. In this technique, the program collects the data before the cake compression phase. The increase in pressure results in a transition region, where the cake formation occurs for that pressure, and so forth. In the consolidation region or for the compressive yield stress measurements, the slurry was allowed to dewater into the cake compression phase for the selected pressure. After compression had reached set criteria for equilibrium at that applied pressure, the pressure was stepped up. Solids diffusivity (D) as a function of solids volume fraction  was calculated using the data acquired from both the inverse permeability and the compressibility tests. Further details are found in the results section.

4. RESULTS AND DISCUSSION 4.1.

Zeta Potential and pH

The zeta potential vs pH curves of the as-mined kaolin and MFT in a buffer are shown in Figure 4. The two curves show almost identical responses especially at pH 8.5. A pH 8.5 is a typical condition for oil sand tailings and MFT process water. Thus all our dewatering experiments were conducted at pH 8.5. The high negatively charged particles meant significant interparticle repulsive energy. The zeta potential values also suggested that the particles in the slurry could be relatively dispersed and stable. Without process aids, dewatering these stable suspensions is challenging. When MFT’s particles were suspended in its own extracted water we measured a zeta potential of -33.4 mV.

4.2. Settling Rates in Model Process Water 4.2.1. Kaolin and Sand Mixtures

Figure 5 shows five settling curves for 10% v/v solids consisting of increasing volume ratios of kaolin to sand. The bottom curve represents the 5% v/v kaolin plus 5% v/v sand that levels off at the 10.4-cm (110-mL) mark in the vessel. As the proportion of kaolin in the mixture increased by 1% v/v, the sediment height increased. Consequently the

19

settling curves change shapes and are higher along the y-axis on the graphs. The kaolin in the mixtures significantly influences the responses. The shapes of the settling curves remain similar and parallel up to the 7% v/v kaolin plus 3% v/v sand. The next two curves above show greater hindered settling. For the same time frame the largest settled volumes of sediment still did not reach constant values or approach equilibrium. Figure 6 shows bar graphs indicating that the initial settling rates decrease with increasing proportions of kaolin in the mixture. Sand in the mixture enhanced the settling rates. Photographs of the pre-and post- settling of slurries in the cylinders are shown in Figures 7a-b for initial time 0 h, 4 h and 1 week later. 4.2.2. Hindered Settling Function Figure 8 shows the hindered setting function R( vs solid volume fraction (curves for the combined initial 10% v/v of kaolin-plus-sand mixtures in MPW+ compared to that for kaolin only at 10% v/v. The results represent the measured values obtained using stepped pressure increases. Initially the settling cylinders for the mixture of 5% v/v sand plus 5% v/v kaolin show no segregation (Figure 7a), but appears after 4h (Figure 7b). This indicated that no segregation would occur for the experimental time taken for measurements of the hindered settling. This combination of kaolin and sand appears to be the most permeable (Figure 8). As the fraction of kaolin in the mixture increases, curves of R( vs systematically shift up to higher values. The 7% and 8% v/v kaolin start at the same value then diverge after the second pressure step. Kaolin-only at 10% v/v shows the highest values for R( vs Thus the data indicate that sand mixed with the clays causes the hindered settling function to decline significantly, before segregation. Before segregation occurs the clay structures can hold the sand more or less homogeneously. From these curves one can conclude that the water can easily flow out (permeate) without segregation of sand when the 10% v/v solids comprises 6% v/v kaolin and 4% v/v sand.

20

4.2.3. Compressive Yield Stress Figure 9 shows the curves for compressive yield stress measured as a function of solids volume fraction (explained earlier) for stepped increases in pressure for each kaolin-sand combination. Lines are the power law fits to the data points. Table 1 is a summary of the fitted parameters. There is a systematic shift in compressibility as the proportion of sand in the mixture reaches kaolin:sand = 5:5 %v/v. When sand is present there appears to be improvements in the dewaterability of suspensions for the higher pressures. Compare the respective kaolin-plus-sand volumes in the mixture: 6% v/v plus 4% v/v and 5% v/v plus 5% v/v. The scaling factor b is highest for these combinations of kaolin and sand. The data indicate that it is advantageous to add sand to the kaolin for dewatering the total 10% v/v solids in slurry. From our previous in-house studies 10% v/v was measured as the gel point of this kaolin. Figure 10 shows plots for the final volume fractions of compressed solids for each compressive yield stress, plotted against the sand content in the mixture. The data indicate that addition of sand to clay for the same initial total solids content in the slurry causes increased volume fraction of final compressed solids for each compressive yield stress Py. 4.2.4. Solids Diffusivity In order to obtain a composite measure of the dewaterability of the material, the solids diffusivity D was determined as a function of volume fraction of solids  (equation 1.5). As indicated earlier D is generally calculated using a function that combines compressibility and permeability (equations 1.2, 1.3 and 1.4). Figure 11 shows the plotted curves for D as a function of for five combinations of kaolin and sand discussed above. The curves indicate that the 5% v/v kaolin plus 5% v/v sand display the highest dewatering rate, which is useful and important, especially if process time is limited. The D() for 6% v/v kaolin plus 4% v/v sand is significantly less than the case for 5% v/v kaolin

21

plus 5% v/v sand. There appear to be no gains in dewatering rate by adding between 1 and 3% v/v sand in a 10% v/v total solids fraction. The data show that significant enhancements in dewatering rate are achieved for 4% to 5% v/v sand additions. 4.3. Compressive Yield Stress for Sand added to Flocculated Kaolin The effects of adding 5% v/v sand to 5% v/v flocculated kaolin are shown in Figures 12-13 for two dosages,1000 and 2000 ppm of the two polymeric flocculants. The photographs of the mixtures in respective cylinders of Figure 13 show that the flocs are coarser for the 2000-ppm samples. However, flocs formed by both dosages, segregated from the sand after being allowed to settle out. Figure 12 shows the Py() vs  graphs for each flocculant. The five compressibility curves fitted to scaling law (lines) show the effects of the two flocculants at 1000 and 2000 ppm relative to the unflocculated kaolin–plus–sand control. Figure 12 indicates that there is virtually little difference between the effects of the two polymeric flocculants, even though the molecular weight of one is twice that of the other. There is only a slight shift to higher compressed volume fraction with Zetag 8160, the higher-molecular-weight flocculant. However the difference is not very significant as values fall within the error bars for . By comparing the data for the compressive yield stress function of unflocculated kaolin and sand in MPW+, it can be seen that the materials in the mixtures are less compressible when the kaolin is flocculated. Cationic flocculants interactions with such minerals determine their floc structures and properties. Morphologies and behaviors are often linked to the mechanisms of adsorption, charge neutralization and bridging phenomena (Fleer, 2010;Gregory, 2006;Hogg, 2000;Tadros, 1986;Tadros and Zsednai, 1990). The accompanying photographs of the flocculated kaolin and sand mixtures in Figures 13 indicate that, at this composition, sand segregates after standing awhile and can complicate the process. It was not possible to obtain reproducible hindered settling function data for these flocculated kaolin-sand slurries. Settling of flocculated clay

22

occurred too quickly and it was not possible to measure the initial settling rates.

4.4. Compressibility of Kaolin vs MFT before and after Flocculation Figure 14 compares the compressive yield stress curves for equal initial volume fractions of untreated kaolin in model process water (MPW+) and undiluted Suncor MFT (batch 1) as received. The latter appears to be more compressible. However, the experimental time scale for MFT was exceedingly long (weeks) due to gradual blinding of the filter medium by residual oil in the MFT. Figure 15 shows compressive yield stress curves for MFT (batch 2) and kaolin starting at equal solids concentrations in MTW, and after flocculation by 100 ppm Zetag 7557 and Zetag 8160. Both kaolin and MFT were diluted in MTW to 5% w/w solids respectively, then flocculated by 100 ppm (based on solids) of either Zetag 7557 or Zetag 8160. The kaolin flocculated by both polymers responded identically. The responses for the flocculated diluted MFT were also similar in both cases. These responses suggest that the molecular weights differences of the polymers were not significant for floc behaviors in these systems. When compressive yield stress curves Py() vs functions for flocculated diluted MFT are compared with those for flocculated kaolin, there appeared to be a crossing point of identical compressive yield stress 121 kPa at solids volume fraction 0.41. This could suggest that the materials behaved similarly in the MTW or oil was less of a factor. MFT behaved like the model kaolin after flocculation. In MTW the unflocculated kaolin was more compressible than the flocculated kaolin, as shown by the green curve in Figure 15. All materials followed a power law scaling function Py = ab, as seen by the fitted lines (Buscall and Mills, 1988;Konnur, 2006;Konnur and Raha, 2007a;Konnur and Raha, 2007b;Scales, 2006).The scaling function fits for diluted flocculated MFT and kaolin had different coefficient and power b values than those for the gel point MFT and kaolin (see

23

Tables 3 and 4). Diluted kaolin showed larger b values than diluted MFT, yet b values for untreated gel point kaolin were larger than those for gel point MFT.

5. CONCLUSIONS The results of this study provided a fundamental understanding of dewatering oil sands tailings. We indicated choices of possible treatments and their limitations in enhancing the dewatering of tailings. Our experimental results indicated that kaolin and oilsands tailings can be dewatered with some ease when sand and flocculants are process aids. In a total 10% v/v solids, addition of 4-5% v/v sand to kaolin improved dewaterability

of

the

mixtures

significantly.

Improvements

in

settling

rate,

compressibility, and solids diffusivity as well as reduction of the hindered settling function were shown. Sand and dispersed kaolin or MFT consolidated better than sand and the flocculated. Flocculation of 5% v/v kaolin using 1000 and 2000 ppm cationic polymeric flocculants Zetag 7557 or Zetag 8160, and mixing with 5% v/v sand reduced the final compressed volume fraction of solids for the same compressive yield stress as the untreated. Kaolin flocculated by 1000 and 2000 ppm of the two flocculants Zetag 7557 or Zetag 8160 settled rapidly and neither settling rate nor hindered settling function values could be measured. Although the morphology of flocs appeared slightly different for these flocculants, the compressive yield stress functions were similar. Testing at lower dosages produced similar responses. Compressive yield stress functions for 5% w/w mature fine tailings (MFT) diluted in model tap water (MTW) and flocculated by 100 ppm of the two polymers Zetag 7557 or Zetag 8160 were identical. The flocculated 5% w/w kaolin in MTW responded similarly. However, as before, the flocs were less compressible than the untreated materials. Both flocculated MFT and kaolin showed a common yield stress at 121 kPa at volume fraction 0.41.

24

Kaolin in model process water (MPW+) starting at its gel point concentration compressed readily but the final compressed volume fraction of solids was less than that for the same gel point concentration of MFT. Although MFT was more compressible than kaolin, consolidation time was longer. We found that pressure filtration and compression of as-received MFT were difficult and time consuming. Partial blinding of the filter medium can occur when residual oil is present in the slurry. Compressive yield stress vs final solids volume fraction curves, for all materials tested followed power law functions, as for mineral sludges.

A fundamental

understanding of oil sands tailings characteristic material properties was shown in this paper. Thus, by using the appropriate technology, it is possible to achieve both environmental sustainability and tailings separability in clean bitumen extractions.

6.

ACKNOWLEDGEMENTS

Funding for this work was provided by the government of Canada Panel on Energy Research and Development (PERD) and EcoEII (Energy and Environment Innovation Initiative) grant U0S1009. We thank: Dr Ross de Kretser of the University of Melbourne Chemical and Biological Engineering dewatering group for rig customization and training on its processing software; Behnam Namsechi for XRD analysis; Drs Hassan Hamza and Tadeusz Dabros (deceased) for support.

7.0 REFERENCES 1. Abidin Kaya, Ali Hakan Oren, Yeliz Yukselen, 2006. Settling of Kaolinite in different aqueous environment. Marine Georesources&Geotechnology 24, 203-208. 2. Addai-Mensah, J., 2007. Enhanced flocculation and dewatering of clay mineral dispersions. Powder Technology 179, 73-78. 3. Al-Sabawi, M., Seth, D., de Bruijn, T., 2011. Effect of modifiers in n-pentane on the supercritical extraction of Athabasca bitumen. Fuel Processing Technology 92, 1929-1938.

25 4. Alberta Government. Lower Athabasca Region - Tailings Management Framework for the Mineable Athabasca Oil Sands. Framework- aep.alberta.ca/lands-forests/.../LARPTailingsMgtAthabascaOilsands-Mar2015.pdf, 1-52. 2015. Edmonton, Alberta, Alberta Government. aep.alberta.ca/lands-forests/.../LARP-TailingsMgtAthabascaOilsandsMar2015.pdf. Ref Type: Report 5. Angle CW, SmithPalmer T., Wentzell BR, 1997. The effects of cationic polymers on flocculation of a coal thickener feed in washery water as a function of pH. J. of Applied Polymer Science 64, 783-789. 6. Angle, C.W., 1995. Fundamental Properties of Fine Tails -Part 2. Electrokinetics and surface properties in Mature Fine Tailings Stability and Structure. In: Hamza, H.A. (Ed.), Advances in Oil Sands Tailings Research Alberta Department of Energy, Oil sands Research Division, Edmonton, pp. 60-64. 7. Angle, C.W., Hamza, H.A., 1987. The effects of selected polymers on the electrokinetics properties of fine coal particles and silica in washery water . Flocculation and Biotechnology and Separation Systems Elsevier, Science, New York, pp. 75-93. 8. Angle, C.W., Zrobok, R., 1995. Fundamental Properties of Fine Tails -Part 1. Rheology. In: Hamza, H.A. (Ed.), Advances in Oil Sands Tailings Research Alberta Department of Energy, Oil sands Research Division, Edmonton, pp. 59-60. 9. Angle, C.W., Zrobok, R., Hamza, H.A., 1993. Surface properties and elasticity of oil-sandsderived clays found in a sludge pond. Applied Clay Science 7, 455-470. 10. Angle, C.W., Hamza, H.A. Effects of clay-organics on structure and rheology of mature fine tailings. The Joint International JCIS - ACIS symposium, Adelaide, Australia, February 16,2009. Rheology 0C021. 2009. Adelaide, Australia. Ref Type: Conference Proceeding 11. Angle, C.W., Clarke, B., Dabros, T., 2017. Dewatering kinetics and viscoelastic properties of kaolin as tailings model under compressive pressures. Chemical Engineering Research and Design 118, 286-293. 12. Angle, C.W., Long, Y., Hamza, H., Lue, L., 2006. Precipitation of asphaltenes from solventdiluted heavy oil and thermodynamic properties of solvent-diluted heavy oil solutions. Fuel 85, 492-506. 13. Besra, L., Sengupta, D.K., Roy, S.K., Ay, P., 2002. Polymer adsorption: its correlation with flocculation and dewatering of kaolin suspension in the presence and absence of surfactants. International Journal of Mineral Processing 66, 183-202. 14. Boger, D.V., 2009. Rheology and the resource industries. Chemical Engineering Science 64, 4525-4536.

26 15. Bürger, R., Concha, F., 2001. Settling velocities of particulate systems: 12: Batch centrifugation of flocculated suspensions. International Journal of Mineral Processing 63, 115-145. 16. Buscall, R., Mills, P.D.A., 1988. Scaling Behaviour of the Rheology of Aggregate Networks formed from Colloidal Particles. Journal of the Chemical Society, Faraday Transactions 1 84, 4249-4260. 17. Buscall, R., White, L.R., 1987. The consolidation of concentrated colloidal suspensions. Part 1 The theory of sedimentation. J, Chem. Soc. Faraday Trans. , 83, 873-891. 18. Chalaturnyk, R.J., Scott, J.D., Ozüm, B., 2002. Management of Oil Sands Tailings. Petroleum Science and Technology 20, 1025-1046. 19. Concha, F., Bustos, M.C., 1991. Settling velocities of particulate systems, 6. Kynch sedimentation processes: batch settling. International Journal of Mineral Processing 32, 193-212. 20. Coulson, J.M., Richardson, J.F., Backhurst, J.R., Harker, J.H., 2001. Chemical Engineering Vol 2. Particle Technology and Separation Processes. Butterworth-Heinemann, London. 21. Curvers, D., Saveyn, H., Scales, P.J., Van der Meeren, P., 2009. A centrifugation method for the assessment of low pressure compressibility of particulate suspensions. Chemical Engineering Journal 148, 405-413. 22. Davies, L., Dollimore, D., Sharp, J.H., 1976. Sedimentation of Suspensions: Implications of Theories of Hindered Settling. Powder Technology 13, 123-132. 23. Davis, R.H., Gecol, H., 1994. Hindered settling function with no empirical parameters for polydisperse suspensions. AIChE J. 40, 570-575. 24. de Kretser, R.G., Usher, S., Scales, P.J., Boger, D.V., Landman, K.A., 2001. Rapid Filtration Measurement of Dewatering Design and Optimization Parameters. AIChE J. 47, 17581769. 25. Devenny, D.W. A screening study of oilsands tailings technologies and practices. AERI. AERI Contract Number -20080326, 1-22. 2010. Alberta, Alberta Energy Research Institute. Ref Type: Report 26. Eckert, W.F., Masliyah, J.H., Gray, M.R., Fedorak, P.M., 1996. Prediction of sedimentation and consolidation of fine tails. AIChE J. 42, 960-972. 27. Fine Tailings Fundamental Consortium, 1995. Advances in Oil Sands Tailings Research. Alberta Department of Energy Oil Sands and Research Division, Edmonton. 28. Fleer, G.J., 2010. Polymers at interfaces and in colloidal dispersions. Advances in Colloid and Interface Science 159, 99-116.

27 29. Garrido, P., Concha, F., Bürger, R., 2003. Settling velocities of particulate systems: 14. Unified model of sedimentation, centrifugation and filtration of flocculated suspensions. International Journal of Mineral Processing 72, 57-74. 30. Green, M., Eberl, M., Landman, K.A., 1996. Compressive Yield Stress of Flocculated Suspensions: Determination via Experiment. AIChE J. 42, 2308-2318. 31. Green, M., Landman, K.A., de Kretser, R.G., Boger, D.V., 1998. Pressure Filtration Technique for Complete Characterization of Consolidating Suspensions. Ind. Eng. Chem. Res. 37, 4152-4156. 32. Gregory, J., 2006. Chapter 3: Floc formation and floc structure. In: Gayle Newcombe and David Dixon (Ed.), Interface Science and Technology Interface Science in Drinking Water Treatment - Theory and Application Elsevier, pp. 25-43. 33. Hogg, R., 2000. Flocculation and dewatering. International Journal of Mineral Processing 58, 223-236. 34. Konnur, R., 2006. Methods for the rapid characterization of dewaterability of particulate suspensions. International Journal of Mineral Processing 80, 79-87. 35. Konnur, R., Raha, S., 2007a. Parameter estimation and simulation of dependence of constant pressure batch dewatering on initial solids concentration. International Journal of Mineral Processing 81, 248-255. 36. Konnur, R., Raha, S., 2007b. Scaling behavior in constant pressure batch dewatering of fine particle suspensions. International Journal of Mineral Processing 83, 28-35. 37. Kynch, G.J., 1952. A theory of sedimentation. Transactions of the Faraday Society. 38. Landman K.A and L.R.White, 1992. Determination of the Hindered Settling Factor for Flocculated Suspensions. AIChE J. 38, 184-192. 39. Landman, K.A., White, L.R., Eberl, M., 1995. Pressure Filtration of Flocculated Suspensions. AIChE J. 41, 1687-1700. 40. Li, H., Long, J., Xu, Z., Masliyah, J.H., 2005. Synergetic Role of Polymer Flocculant in LowTemperature Bitumen Extraction and Tailings Treatment. Energy Fuels 19, 936-943. 41. Li, H.H., Long, J., Xu, Z., Masliyah, J.H., 2008. Novel polymer aids for low-grade oil sand ore processing. The Canadian Journal of Chemical Engineering 86, 168-176. 42. Long, Y., Dabros, T., Hamza, H., 2004. Structure of water/solids/asphaltenes aggregates and effect of mixing temperature on settling rate in solvent-diluted bitumen. Fuel 83, 823-832. 43. Matthews, J.G., Shaw, W.H., MacKinnon, M.D., Cuddy, R.G., 2002. Development of Composite Tailings Technology at Syncrude. International Journal of Mining, Reclamation and Environment 16, 24-39.

28 44. Michaels, A.S., Bolger, J.C., 1962. Settling Rates and Sediment Volumes of Flocculated Kaolin Suspensions. Ind. Eng. Chem. Fund. 1, 24-33. 45. Miller, K.T., Melant, R.M., Zukoski, C.F., 1996. Comparison of the Compressive Yield Response of Aggregated Suspensions: Pressure Filtration, Centrifugation, and Osmotic Consolidation. Journal of the American Ceramic Society 79, 2545-2556. 46. Mpofu, P., Addai-Mensah, J., Ralston, J., 2003. Investigation of the effect of polymer structure type on flocculation, rheology and dewatering behaviour of kaolinite dispersions. International Journal of Mineral Processing 71, 247-268. 47. Nasser, M.S., James, A.E., 2006a. Settling and sediment bed behaviour of kaolinite in aqueous media. Separation and Purification Technology 51, 10-17. 48. Nasser, M.S., James, A.E., 2006b. The effect of polyacrylamide charge density and molecular weight on the flocculation and sedimentation behaviour of kaolinite suspensions. Separation and Purification Technology 52, 241-252. 49. Pathak, V., Babadagli, T., Edmunds, N.R., 2011. Heavy oil and bitumen recovery by hot solvent injection. Journal of Petroleum Science and Engineering 78, 637-645. 50. Raha, S., Khilar, K.C., Pradip, Kapur, P.C., 2005. Rapid determination of compressive yield stress of dense suspensions by a mean-phi () model of high pressure filtration. Powder Technology 155, 42-51. 51. Rao, S.R., 1980. Flocculation and dewatering of Alberta oil sands tailings. International Journal of Mineral Processing 7, 245-253. 52. Ruth, B.F., 1935. Studies in Filtration III. Derivation of General Filtration Equations. Ind. Eng. Chem. 27, 708-723. 53. Ruth, B.F., 1946. Correlating Filtration Theory with Industrial Practice. Ind. Eng. Chem. 38, 564-571. 54. Sabet, N., Hassanzadeh, H., Abedi, J., 2017. Selection of efficient solvent in solvent-aided thermal recovery of bitumen. Chemical Engineering Science 161, 198-205. 55. Scales, P., 2006. Chapter 13: Dewatering of water treatment plant sludges. In: Gayle Newcombe and David Dixon (Ed.), Interface Science and Technology Interface Science in Drinking Water Treatment - Theory and Application Elsevier, pp. 225-243. 56. Shouci Lu, ·Robert J.Pugh, Eric Forssberg, 2005. Chapter 7 Flocculation with polymers. In: Shouci Lu, R.J.P. (Ed.), Studies in Interface Science Interfacial Separation of Particles Elsevier, pp. 354-414. 57. Skinner, S.J., Studer, L.J., Dixon, D.R., Hillis, P., Rees, C.A., Wall, R.C., Cavalida, R.G., Usher, S.P., Stickland, A.D., Scales, P.J., 2015. Quantification of wastewater sludge dewatering. Water Research 82, 2-13.

29 58. Stickland, A.D., 2015. Compressional rheology: A tool for understanding compressibility effects in sludge dewatering. Water Research 82, 37-46. 59. Stickland, A.D., Irvin, E.H., Skinner, S.J., Scales, P.J., Hawkey, A., Kaswalder, F., 2016. Filter Press Performance for Fast-Filtering Compressible Suspensions. Chemical Engineering & Technology 39, 409-416. 60. Stickland, D., Burgess, C., Dixon, D.R., Harbour, P.J., Scales, P.J., Studer, L.J., Usher, S.P., 2008. Fundamental dewatering properties of wastewater treatment sludges from filtration and sedimentation testing. Chemical Engineering Science 63, 5283-5290. 61. Tadros, T., 1986. Control of the properties of suspensions. Colloids and Surfaces 18, 137173. 62. Tadros, T., Zsednai, A., 1990. Application of depletion flocculation for prevention of formation of dilatant sediments. Colloids and Surfaces 43, 105-116. 63. Tiller, F.M., Khatib, Z., 1984. The Theory of Sediment Volumes of Compressible, Particulate Structures. Journal of Colloid and Interface Science 100, 55-67. 64. Toorman, E.A., 1996. Sedimentation and self-weight consolidation: general unifying theory. Géotechnique 46, 103-113. 65. Toorman, E.A., 1999. Sedimentation and self-weight consolidation: constitutive equations and numerical modelling. Géotechnique 49, 709-726. 66. Usher, S.P., Studer, L.J., Wall, R.C., Scales, P.J., 2013. Characterisation of Dewaterability from Equilibrium and Transient Centrifugation Test Data. Chemical Engineering Science. 67. Wakeman, R.J., 2007. Separation technologies for sludge dewatering. Journal of Hazardous Materials 144, 614-619. 68. Xu, Y., Hamza, H.A., 2003. Thickening and disposal of oil sand tailings. Mining Engineering 55, 33-39. 69. Xu, Y., Dabros, T., Kan, J., 2008. Filterability of oil sands tailings. Journal of the European Federation of Chemical Engineering Part B: Process Safety and Environmental Protection 86, 268-276. 70. Zhou, Y., Jameson, G.J., Franks, G.V., 2008. Influence of polymer charge on the compressive yield stress of silica aggregated with adsorbed cationic polymers. Colloids and Surfaces A: Physicochemical and Engineering Aspects 331, 183-194.

30

t = tf

t=0

P H0

Φ0

0 (a)

Hf Φf 0

(b)

(c)

Figure 1: Schematic of (a) hindered settling of particles in water in a cylinder (b, c) Consolidation under imposed pressure from initial volume fraction 0 at time t zero to final f at time f.

31

Digital Connection Linear Encoder Pressure Controller

P Pneumatic Cylinder

Pressurized Air Line

Bleed Line Valve

Pressure Transducer

Sample Membrane

Computer Filtrate Collector

Figure 2. Schematic of the pressure filtration rig in our laboratory.

32

Figure 2a. Photograph of our pressure filtration rig (built by University of Melbourne).

33

Figure 3. Screen picture of a typical t vs V2 plot at various pressures P, used in calculations of Py() after a run. Each rise represents a constant volume or volume fraction with time at a given pressure step.

34

-30

Zeta potential (mV)

-35

Plainsman kaolin Suncor MFT

-40

-45

-50

-55

-60 5

6

7

8

9

pH

Figure 4. Zeta potential vs pH for colloidal Plainsman kaolin and Suncor MFT(batch 2) in a background electrolyte consisting of 10 mM NaHCO3 and 1 mM NaCl.

35

30

Height of Sediment (cm)

28

5 %v/v Sand+ 5 %v/v Kaolin 4 %v/v Sand+ 6 %v/v Kaolin 3 %v/v Sand+ 7 %v/v Kaolin 2 %v/v Sand+ 8 %v/v Kaolin 1 %v/v Sand+ 9 %v/v Kaolin

26 24 22 20 18 16 14 12 10 8 0

10

20

30

40

50

60

70

Time of Settling (h)

Figure 5. Settling curves for kaolin and Ottawa sand mixtures in MPW+ at pH 8.5.

36 5% v/v sand 4% v/v sand 3% v/v sand 2% v/v sand 1% v/v sand

0.06

Settling Rate (m/h)

0.05

+ 5% v/v kaolin + 6% v/v kaolin + 7% v/v kaolin + 8% v/v kaolin + 9% v/v kaolin

0.04 0.03 0.02 0.01 0.00 0

2

4

6

Sand proportion (% v/v)

Figure 6. Initial settling rates for kaolin + sand in MPW+ at pH 8.5.

37

Figure 7a. Initial 10% v/v solids of slurries of kaolin and sand in MPW+ show no segregation. Volume % ratios of kaolin:sand (left) 7:3, 8:2, and 9:1; (right) 6:4, 5:5. %v/v K:S = 9:1

After

8:2

(c)

7:3

4h

6:4

5:5

9:1

8:2

7:3

(d)

1 week

6:4

5:5

Figure 7b. Settling cylinders of K = kaolin plus S = sand slurries after settling (c) for 3-4 h as segregated sand becomes apparent at bottom for %v/v K:S = 5:5. (d) sediments after 1 week.

38

1.0E+13 9.0E+12 8.0E+12

R (Pa.s/m2)

7.0E+12

5% v/v Kaolin + 5% v/v Sand 6% v/v Kaolin + 4% v/v Sand 7% v/v Kaolin + 3% v/v Sand 8% v/v Kaolin + 2% v/v Sand 9% v/v Kaolin + 1% v/v Sand 10% v/v Kaolin

6.0E+12 5.0E+12 4.0E+12 3.0E+12 2.0E+12 1.0E+12 0.0E+00 0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

Solids volume fraction (v/v = )

Figure 8. R( (hindered settling function) vs solids volume fraction) in stepped pressure inverse permeability measurements of kaolin-sand mixtures at pH 8.5 in MPW+.

39

350 300

Py (kPa)

250

10%v/v Kaolin 5 %v/v Kaol +5%v/v Sand 6 %v/v Kaol + 4%v/v Sand 7 %v/v Kaol+ 3 %v/v Sand 8 %v/v Kaol+ 2 %v/v Sand 9 %v/v Kaol+1 %v/v Sand

200 150 100 50 0 0.35

0.40

0.45

0.50

0.55

0.60

Volume fraction solids (v/v)

Figure 9. Compressive yield stress (Py) as a function of solids volume fraction of kaolinsand mixtures in MPW+. Lines indicate the scaling function Py = ab fitted to the data.

Compressed volume fraction solids ( = v/v)

40

0.75

Py = 20 kPa Py = 40 kPa Py = 80 kPa Py = 120 kPa Py = 160 kPa Py = 200 kPa

0.70 0.65 0.60 0.55 0.50 0.45 0.40 0.35 0.30 0

1

2

3

4

5

Sand in Mix (% v/v)

Figure 10. Plots for final compressed volume fraction of solids (vs % v/v sand in the 10% v/v kaolin-sand mixtures, for each compressive yield stress Py.

41

4.0E-07 3.5E-07

D (m2s-1)

3.0E-07 2.5E-07

5% v/v Kaolin + 5% v/v Sand 6% v/v Kaolin + 4% v/v Sand 7% v/v Kaolin + 3% v/v Sand 8% v/v Kaolin + 2% v/v Sand 9% v/v Kaolin + 1% v/v Sand 10% v/v Kaolin

2.0E-07 1.5E-07 1.0E-07 5.0E-08 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 Solids volume fraction (v/v = )

Figure 11. Solids diffusivity (D) plotted as a function of solids volume fraction for kaolinsand mixtures in process water at pH 8.5.

42

Compressive Yield Stress,Py (kPa)

350 300

2000 ppm Zetag 7557 in 5% v/v Kaolin + 5% v/v Sand in MTW 2000 ppm Zetag 8160 in 5% v/v Kaolin + 5%v/v Sand in MTW 1000 ppm Zetag 8160 in 5% v/v kaolin + 5% v/v Sand in MTW 1000 ppm Zetag 7557 in 5% v/v Kaolin + 5% v/v Sand in MTW 5 %v/v Kaolin + 5 %v/v Sand in MPW+

250 200 150 100 50 0 0.2

0.3

0.4

0.5

0.6

Volume Fraction Solids ( = v/v)

Figure 12. Compressive yield stress as a function of solids volume fraction for 1000 and 2000 ppm Zetag 7557 and Zetag 8160 flocculated kaolin and sand in MTW; and 5% v/v unflocculated kaolin plus 5% v/v sand in MPW+. Lines are power law fits to data (Table 2).

43

Zetag 5775

1000 ppm, 2000 ppm

Zetag 8160

1000 ppm

2000 ppm

Figure 13. Photographs of flocculated kaolin in MTW mixed with sand, each at 5% v/v, in cylinders after Zetag 7557 and Zetag 8160 at 1000 and 2000 ppm (based on solids).

44

Compressive Yield Stress (kPa)

350 300

Kaolin (initial v/v =0.11 in MPW+) Suncor MFT (iniital v/v = 0.11)

250 200 150 100 50 0 0.3

0.4

0.5

0.6

Volume fraction solids ( = v/v)

Figure 14. Comparing compressive yield stress curves of equal volume fractions (at gel point) of kaolin in MPW+ and Suncor MFT as received. Lines are power law fit to data.

45

Compressive yield stress (kPa)

350 300

5% w/w kaolin in MTW, 100 ppm Zetag 7557 5% w/w kaolin in MTW, 100 ppm Zetag 8160 5% w/w Suncor MFT in MTW, 100 ppm Zetag 8160 5% w/w Suncor MFT in MTW,100 ppm Zetag 7557 5% w/w kaolin in MTW

250 200 150 100 50 0 0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

Volume fraction solids ( = v/v)

Figure 15. Compressive yield stress curves for solids in MTW: 5% w/w kaolin (control), 5% w/w kaolin flocculated, and 5% w/w Suncor MFT flocculated by 100 ppm Zetag 7557 and 8160. Lines are power law fits to data.

46

Table 1: Fitted parameters for power law scaling function in Figure 9. MPW+ Kaolin + Sand, %v/v 10 + 0 5+5 6+4 7+3 8+2 9+1

a Value 4.67E+04 2.86E+05 3.28E+04 2.07E+04 4.00E+04 3.09E+04

a Standard Error ± 4.70E+03 8.56E+04 6.33E+02 1.21E+03 4.00E+03 1.81E+03

b Value 8.01 14.04 10.01 8.36 9.00 8.11

b Standard Error ± 0.14 0.56 0.04 0.10 0.16 0.09

Statistics Reduced Chi-Sqr 3.21 14.91 0.12 1.36 3.07 1.13

Statistics Adj. RSquare 0.999 0.997 1.000 1.000 0.999 1.000

47

Table 2: Fitted parameters for power law scaling function in Figure 12. MTW 5% v/v Kaolin + 5%v/v Sand 1000 ppm Zetag 7557 2000 ppm Zetag 7557 1000 ppm Zetag 8160 2000 ppm Zetag 8160 Control in MPW+

a

a

b

b

Statistics

Statistics

Value

Standard Error ±

Value

Standard Error ±

Reduced Chi-Sqr

Adj. Square

4.09E+05

2.82E+04

10.77

0.94

69.80

0.985

6.00E+05

6.10E+04

10.84

0.12

0.27

1.000

1.87E+05

4.17E+04

9.79

0.32

18.20

0.997

7.64E+05

3.95E+05

11.26

0.63

5.79

0.995

2.85E+05

7.69E+04

14.02

0.50

12.29

0.997

R-

48

Table 3: Parameters for power law fitted lines of Figure 14. Parameters

a

Figure 14 Value Kaolin in MPW+ 3.74 E+04 =0.11

MFT as rec'd, 3.56E+04  = 0.11

a Standard Error ±

b

b Standard Error ±

Statistics Reduced Chi-Sqr

Statistics Adj. RSquare

3.32E+03 8.04

0.14

3.0

0.999

7.13E+03 9.60

0.38

39.0

0.997

Value

49

Table 4: Parameters for power law fitted lines of Figure 15. Parameters Figure 15

a

5% w/w solids 100 ppm polymer Kaolin+MTW + Zetag 7557 Kaolin+MTW Zetag 8160 MFT+MTW Zetag 8160 MFT+MTW Zetag 7557

Value

a

b

b

Statistics Statistics

Standard Error ± 2.21E+04 2.10E+03

Value 5.80

Standard Error ± 0.11

Reduced Chi-Sqr 6.72

Adj. Square 0.999

2.32E+04 2.17E+03

5.88

0.01

4.05

0.999

5.74E+03 3.28E+02

4.30

0.07

2.85

0.999

6.22E+03 2.10E+02

4.37

0.04

1.69

1.000

R-