CA2820665C - Sub-aerial deposition and handling techniques for dewatering fine tailings - Google Patents

Abstract

Techniques for sub-aerial deposition of flocculated thick fine tailings, such as MFT, may include depositing in a laminar channel flow regime, windrowing partially dewatered deposited material and various deposition design strategies such as dedicated disposal systems provided in accordance with a pre-determined capacity of sub-aerial deposition areas based on concave beach profiles of the deposited material.

Description

SUB-AERIAL DEPOSITION AND HANDLING TECHNIQUES FOR
DEWATERING THICK FINE TAILINGS
FIELD OF INVENTION
The present invention relates to the chemical treatment and sub-aerial deposition for dewatering thick fine tailings.
BACKGROUND
Tailings derived from mining and extraction operations, e.g. oil sands mining and extraction, are often placed in dedicated disposal ponds for settling.
The settling of fine solids from the water in tailings ponds is a relatively slow process. Certain techniques have been developed for dewatering thick fine tailings, such as oil sands mature fine tailings (MFT). Dewatering of thick fine tailings can include contacting the thick fine tailings with a flocculant and then depositing the flocculated thick fine tailings in a deposition area where the deposited material can release water and eventually dry.
In the context of dewatering thick fine tailings, there are a number of challenges related to the deposition of flocculated thick fine tailings.
SUMMARY OF INVENTION
In some implementations, there is provided a process for treating thick fine tailings, including:
contacting the thick fine tailings with a flocculant to produce flocculated fine tailings;
depositing the flocculated fine tailings onto a sub-aerial deposition area, wherein the flocculated fine tailings has depositional kinetic , , ,

2 energy and yield stress to provide flow channels in a laminar flow regime;
allowing the flocculated fine tailings to flow down the deposition area where the flocculated fine tailings comes to rest, thereby forming a deposit; and allowing the deposit to dewater and dry.
In some implementations, the depositional kinetic energy on a unit volume basis is between 250 J and 1250 J and the yield stress is between 2 Pa and 175 Pa.
In some implementations, the depositional kinetic energy on a unit volume basis is between 500 J and 1000 J and the yield stress is between 10 Pa and 75 Pa.
In some implementations, the depositional kinetic energy is such that the average velocity is between 0.25 m/s and 1.25 m/s upon deposition.
In some implementations, the depositional kinetic energy is such that the average velocity is between 0.5 m/s and 1 m/s upon deposition.
In some implementations, the flocculated fine tailings have a static yield stress of at least 100 Pa and the depositional kinetic energy is such that the flow velocity is at least 0.65 m/s.
In some implementations, the depositing of the flocculated fine tailings is performed such that the deposit has a lift height of at most 30 cm.
In some implementations, the process also includes:
adjusting the yield strength of the flocculated fine tailings by:
adjusting dispersion conditions of the flocculant into the thick fine tailings;

3 adjusting clay-to-water ratio of the thick fine tailings;
adjusting dose of the flocculant relative to the thick fine tailings;
adjusting concentration of the flocculant in a flocculation solution that is contacted with the thick fine tailings; and/or adjusting shear conditioning of the flocculated fine tailings prior to deposition.
In some implementations, the process also includes:
adjusting the depositional kinetic energy by:
adjusting a flow rate of the flocculant into the thick fine tailings;
and/or adjusting the depositional kinetic energy by adjusting a deposition outlet size.
In some implementations, the depositing of the flocculated fine tailings is performed via at least one discharge outlet positioned above the sub-aerial deposition area.
In some implementations, the at least one discharge outlet is positioned above the sub-aerial deposition area sufficiently to avoid blocking or burying thereof by the deposited flocculated fine tailings.
In some implementations, the at least one discharge outlet includes a plurality of discharge outlets arranged in spaced apart relation along a header berm of the sub-aerial deposition area.
In some implementations, the flow channels have a depth of between 10 cm and cm.

4 In some implementations, the depth of the flow channels is between 15 cm and 25 cm.
In some implementations, the flow channels each have a sinuosity index between 1 and 2.5.
In some implementations, the sinuosity index of each of the flow channels is less than 2.
In some implementations, the flow channels each have a width between 0.2 m and 0.5 m.
In some implementations, the process also includes providing the sub-aerial deposition area with a sloped bottom surface.
In some implementations, the sloped bottom surface has a generally constant slope.
In some implementations, the sloped bottom surface has a slope less than 3%.
In some implementations, the sloped bottom surface has a slope between 1%
and 2%.
In some implementations, the depositing further includes overbanking a portion of the flocculated fine tailings from the flow channels over side banks thereof, thereby forming lateral aggradations.
In some implementations, the overbanking is performed periodically.
In some implementations, the overbanking is performed continuously.
In some implementations, the depositing of the flocculated fine tailings is performed at variable discharge flow rates.

In some implementations, the depositing of the flocculated fine tailings is performed at variable discharge densities.
In some implementations, the process includes:
ceasing or reducing deposition of the flocculated fine tailings;

5 forming an empty channel defined by deposited flocculated fine tailings; and re-depositing flocculated fine tailings having sufficient yield strength into the empty channel to fill the channel to side banks thereof.
In some implementations, the process includes:
forming a plunge pool of the flocculated fine tailings upon release into the sub-aerial deposition area, the plunge pool dissipating energy of the expelled flocculated fine tailings; and feeding the flow channels with flocculated fine tailings from the plunge pool.
In some implementations, the plunge pool has a depth between 10 cm and 50 cm and a length between 20 cm and 50 cm elongated in the direction of the flow channel.
In some implementations, the depositing is performed above a velocity to avoid substantial sedimentation until the flocculated fine tailings has flowed at least 40 m down the sub-aerial deposition area.
In some implementations, the sub-aerial deposition area includes an upstream region having an upstream slope and a downstream region having an downstream slope, the upstream slope being steeper than the downstream slope.

6 In some implementations, the upstream slope is between 1% and 3% and the downstream slope is between 0% and 1%.
In some implementations, at least one of the flow channels extends down the sub-aerial deposition area between 100 m and 300 m.
In some implementations, the thick fine tailings are derived from an oil sands mining and extraction operation.
In some implementations, the thick fine tailings include mature fine tailings (MFT).
In some implementations, the MFT is derived from an oil sands mining and extraction operation.
In some implementations, the MFT is retrieved from a tailings pond prior to contacting with the flocculant.
In some implementations, there is provided process for treating thick fine tailings, including:
contacting the thick fine tailings with a flocculant to produce flocculated fine tailings;
depositing the flocculated fine tailings onto a sub-aerial deposition area to form a deposited material;
allowing the deposited material to partially dewater to form a partially dewatered material having an increased yield strength;
windrowing the partially dewatered material to form a plurality of elongated piles extending down the deposition area.

,

7 In some implementations, the partially dewatered material has a yield strength of at least about 15 kPa prior to windrowing.
In some implementations, the windrowing is performed after the partially dewatered material has a solids by weight content of at least about 70% and/or of at least a re-wetting equilibrium concentration.
In some implementations, the elongated piles have a base width to height ratio sufficient to be self-supporting.
In some implementations, adjacent pairs of the elongated piles are provided with a spacing in between adjacent piles sufficient to receive a thin lift of the flocculated fine tailings.
In some implementations, the process further includes ceasing deposition of the flocculated fine tailings such that the deposited material has a lift height of at most about 100 cm.
In some implementations, the process further includes ceasing deposition of the flocculated fine tailings such that the deposited material has a lift height of at most about 75 cm.
In some implementations, the process further includes ceasing deposition of the flocculated fine tailings such that the deposited material has a lift height of at most about 50 cm.
In some implementations, the process further includes ceasing deposition of the flocculated fine tailings such that the deposited material has a lift height of at most about 30 cm.
In some implementations, the process further includes, after the windrowing step additional deposition of flocculated fine tailings in between the elongated piles to form an additional lift of deposited material.

8 In some implementations, the process further includes grading the elongated piles to enhance precipitation run-off.
In some implementations, the thick fine tailings are derived from an oil sands mining and extraction operation. In some implementations, the thick fine tailings include mature fine tailings (MFT). In some implementations, the MFT is derived from an oil sands mining and extraction operation. In some implementations, the MFT is retrieved from a tailings pond prior to contacting with the flocculant.
In some implementations, there is provided a process for treating thick fine tailings, including:
contacting the thick fine tailings with a flocculant to produce flocculated fine tailings;
depositing the flocculated fine tailings onto a sub-aerial deposition area to form a deposited material, wherein the sub-aerial deposition area includes:
a bottom surface having a downward slope and a concavity configured such that the downward slope decreases in a downstream direction;
allowing portions of the flocculated fine tailings to come to rest on the sub-aerial deposition area while advancing a front of the flocculated fine tailings down the sub-aerial deposition area, wherein the front of the flocculated fine tailings has a yield strength that decreases while advancing down the sub-aerial deposition area; and ceasing deposition of the flocculated fine tailings to form a stationary deposit on the sub-aerial deposition area.

9 In some implementations, the process further includes pre-determining a predicted beach profile of the deposited flocculated fine tailings; and configuring the concavity of the bottom surface of the deposition area to generally conform with the predicted beach profile.
In some implementations, pre-determining the predicted beach profile includes modeling using a beach profile model.
In some implementations, the beach profile model includes a stream power model.
In some implementations, the thick fine tailings are derived from an oil sands mining and extraction operation.
In some implementations, the thick fine tailings include mature fine tailings (MFT). In some implementations, the MFT is derived from an oil sands mining and extraction operation. In some implementations, the MFT is retrieved from a tailings pond prior to contacting with the flocculant.
In some implementations, there is provided a sub-aerial deposition system for receiving flocculated fine tailings, including:
a head region for receiving discharged flow of the flocculated fine tailings;
a toe region downstream from the head region;
a bottom surface having a concavity and a downward slope such that the slope decreases from the head region to the toe region.
In some implementations, there is provided a process for treating thick fine tailings, including:

contacting the thick fine tailings with a flocculant to produce flocculated fine tailings;
depositing the flocculated fine tailings into a dedicated disposal system including a plurality of sub-aerial deposition areas with sloped bottom surfaces to form lifts of deposited material in the sub-aerial deposition areas, wherein the dedicated disposal system is provided in accordance with a pre-determined capacity of the sub-aerial deposition areas based on concave beach profiles of the deposited material; and allowing the lifts of the deposited material to dewater and dry.

10 In some implementations, the sub-aerial deposition areas have lengths determined in accordance with a maximum run-out distance of the deposited material.
In some implementations, each of the sub-aerial deposition areas has a head berm and side berms.
In some implementations, at least some of the sub-aerial deposition areas have a corresponding toe berm.
In some implementations, at least some of the sub-aerial deposition areas are limited by a body of water at a downstream end thereof.
In some implementations, the depositing further includes providing the flocculated fine tailings with depositional kinetic energy and yield stress to form flow channels in a laminar flow regime down the sub-aerial deposition areas.
In some implementations, the pre-determined capacity is calculated based on a beach profile model.

, , , ,

11 In some implementations, the beach profile model includes a stream power model.
In some implementations, the thick fine tailings are derived from an oil sands mining and extraction operation. In some implementations, the thick fine tailings include mature fine tailings (MFT). In some implementations, the MFT is derived from an oil sands mining and extraction operation. In some implementations, the MFT is retrieved from a tailings pond prior to contacting with the flocculant.
It should be noted that various implementations described above may be combined with various other implementations described above and/or herein.
BRIEF DESCRIPTION OF DRAWINGS
Fig 1 is a block diagram.
Fig 2 is a graph of reaction stages for flocculated MFT.
Fig 3 is a free body diagram for a fluid in motion.
Fig 4 is a free body diagram of a fluid element on an inclined plane (steady, uniform flow).
Fig 5 is a graph showing a relationship between critical height, inclination, and yield stress.
Fig 6 is a conceptual model of momentum transfer effects in a suspension.
Fig 7 is a diagram showing scales of observation for flow testing.
Fig 8 is a graph of fitted Herschel-Bulkley flow curves for flocculated MFT
after 80, 110, and 140 seconds of mixing.

12 Fig 9 is a graph of change in rheology as measured by static yield strength and percent solids by weight.
Fig 10 is a graph of rheology as a function of solids fraction (by weight) as measured in the field and laboratory.
Fig 11 is a diagram showing general approach for field investigations.
Fig 12 is a schematic plan of typical deposition cell arrangement showing approximate boundaries of Cell D1 (5-ft interval LIDAR survey contours of fresh deposit overlaid).
Fig 13 shows typical sections for a deposition cell with (a) confining berm at the toe, and (b) the toe of the cell defined by the presence of a water body.
Fig 14 are schematics of study cells: (a) Cell 1N, (b) Cell D1, and (c) Cell illustrating the relative bed slopes and cell lengths.
Fig 15 is a perspective schematic of a monitoring set-up including a catwalk.
Fig 16 is a schematic of modified cone slump test.
Fig 17 is a graph of a field correlation established for determination of static yield stress using a modified slump test.
Fig s18a and 18b are photographs of examples of channel sinuous laminar channel flow.
Fig 19 is a graph representative of channel cross sections as measured in the field.
Fig 20 is a graph of static yield stress versus flow velocity.

=
, ,

13 Figs 21A and 216 are graphs of percentage slump or static yield stress versus distance travelled over the beach.
Fig 22 is a graph of degradation of yield strength as a function of the kinetic energy of the flowing stream.
Figs 23A to 23C are graphs of percent solids, fines, or clay content with distance travelled across the beach.
Figs 24A to 24C are graphs of percent solids, fines, or clay content with distance travelled across the beach (second round of monitoring).
Fig 25 is a diagram illustrating low or high flow and overbanking and aggradation of flocculated MFT.
Fig 26 is a graphical flow map (conceptual model) for flocculated MFT
deposited on a sub-aerial beach.
Fig 27 is a graph of field observations applied to flow map conceptual model.
Fig 28 is a graph of an integrated conceptual model for deposition of flocculated MFT.
Fig 29 is a graph of normalized beach profiles for flocculated MFT.
Fig 30 is a graph of calibrated Herschel-Bulkley model for flocculated MFT
profile.
Fig 31 is a graph of measured and predicted beach profile for fresh deposit at Cell D1 showing good model fit; Ys = 18 Pa, K=3, n=0.67.
Fig 32 is a graph of calculated and sustainable shear stress along beach length.

14 Fig 33 is a graph of measured and predicted beach profiles for Cell B1 (System 4) for validation of McPhail (1994) model.
Fig 34 is a graph of predicted fresh deposit surface vs. the measured profile at Cell 6S. The discrepancy is partially attributed to ongoing dewatering and consolidation; Ys=18 Pa, K=3, n=0.6.
Fig 35 is a graph of calculated bulk shear stress versus sustainable yield stress (based on Herschel-Bulkley model).
Fig 36 is a graph of calibration results for the McPhail model applied to Cell profile.
Fig 37 is a graph of results of verification run showing good model fit for Cell B1 (System 4).
Fig 38 is a graph of model fit results for McPhail (1994) model applied to Cell 6S
profile.
Fig 39 is a graph of beach run-out as a function of bed slope and yield stress.
Fig 40 is a graph of beach run-out as a function of bed slope and discharge rate.
Fig 41 is a graph of predicted run-out distance as a function of discharge rate on bed slopes from 0.8% to 3.5% (rheology being equal).
Fig 42 is a graph of velocity thresholds for flow of flocculated MFT.
Fig 43 is a graph of two-dimensional volume discrepancy (purple area) between a monotonic beach and a concave beach with a (a) concavity index of 2.0 and (b) concavity index of 2.5.
Fig 44 is side view schematic of a deposition cell.

Fig 45 is a side view schematic of a deposition cell.
Fig 46 is a top view schematic of a deposition cell.
Fig 47 is side view schematic of a deposition cell.
Fig 48 is side view schematic of a relocation cell.
5 Fig 49 is a top view schematic of a multi cell arrangement.
Fig 50 is perspective view schematic of a deposition cell.
Fig 51 is a side view schematic of a deposition cell.
Fig 52 is a top view schematic including a multi cell arrangement.
Fig 53 is a graph of solids by weight after re-wetting versus starting solids by 10 weight.
DETAILED DESCRIPTION
Dewatering operations for treating fine tailings, e.g. oil sands mature fine tailings (MFT) or fine tailings derived from other types of mining operations, may include flocculation of the fine tailings followed by deposition of the flocculated material

15 onto a sub-aerial deposition site where release water runs away from the flocs such that the deposited lift of material can dewater and dry.
"Thick fine tailings" are suspensions derived from a mining operation and mainly include water and fines. The fines are small solid particulates having various sizes up to about 44 microns. The thick fine tailings have a solids content with a fines portion sufficiently high such that the fines tend to remain in suspension in the water and the material has slow consolidation rates. More particularly, the thick fine tailings may have a ratio of coarse particles to the fines that is less than or equal to 1. The thick fine tailings has a fines content sufficiently high such that

16 flocculation of the fines and conditioning of the flocculated material can achieve a two phase material where release water can flow through and away from the flocs. For example, thick fine tailings may have a solids content between 10 wt%
and 45 wt%, and a fines content of at least 50 wt% on a total solids basis, giving the material a relatively low sand or coarse solids content. The thick fine tailings may be retrieved from a tailings pond, for example, and may include what is commonly referred to as "mature fine tailings" (MFT).
Before describing various techniques related to the deposition step of the dewatering operation, an example of an overall dewatering operation will be described in general terms with reference to Fig 1.
Referring to Fig 1, in some implementations, the dewatering operation includes providing thick fine tailings from a tailings source 100, which may be a tailings pond for example, from which a flow of tailings 102 is retrieved by dredge or another type of pumping arrangement. The tailings 102 may then subjected to pre-treatments, such as screening and/or pre-shearing in one or more pre-treatment units 104, for producing a pre-treated tailings flow 106 that is then supplied to a chemical addition unit 108 for contacting and mixing with a dewatering chemical 110, such as a flocculant. Once the thick fine tailings are mixed with the flocculant 110, a flocculated mixture 112 may be pipelined to a discharge assembly 114 that discharges the mixture onto a deposition site 116 for water release and drying. The flocculated mixture may be subjected to sufficient pipeline shear conditioning such that it forms a two phase material including flocs and release water. Upon deposition, the released water may flow away from the flocs and be recovered by a water recovery pipe assembly 118 for recycling into mining operations, extraction operations, water treatment facilities or other operations requiring process water.
The chemical addition unit 108 may be various kinds of devices for mixing a chemical with the shear thinned thick fine tailings and may be a solid-liquid mixer,

17 liquid-liquid mixer, in-line static mixer, impeller mixer, tank mixer, T-joint mixer, Y-joint mixer, or another type of mixer. The mixer may be selected and operated to provide rapid mixing of the chemical into the pre-treated thick fine tailings.
One or more chemical addition mixers may also be used in series or in parallel.
There may also be pre-treatment measurement devices 120 and control devices 122 for regulating the pre-treatment unit 104, and there may also be flocculation measurement devices 124 and control devices 126 for regulating the chemical addition unit 108.
The dewatering operation includes the flocculation of suspended fine particles to create a material that can be dewatered and made trafficable. The below descriptive details are generally directed to the overland flow and beaching behaviour of flocculated thick fine tailings and various enhanced deposition and farming techniques.
Introductory Information A thorough understanding of the depositional tendencies and ultimate beach profiles can aid for operational and reclamation planning purposes. Part of the context of the below description and related work was obtaining field data for the validation of beach profile models, energy-based or otherwise.
Integrated beach development models (combining beaching mechanics and elementary hydraulics, energy conservation principles, and the acknowledgement of non-linear beach profiles) may be useful at an operational level for planning and management purposes. An integrated model can also reflect the variability of a material's behaviour as process and operational conditions change. The integrated model may be based on readily obtainable field measurements and operational parameters such as flow density, static yield stress, and discharge rate.

18 The below description includes information on the flow and deposition of flocculated thick fine tailings, such as oil sands MFT, in the context of rheology and energy using obtained field measurements.
Management of Flocculated MFT
Flocculation of MFT
The following section briefly summarizes the flocculation and dewatering process. As described above thick fine tailings in some implementations are MFT
derived from an oil sands mining operation. For illustrative purposes, the techniques are described below in the context of oil sands MFT, however, it should be understood that the techniques can be applied to thick fine tailings derived from other sources.
Oil sands tailings including sand and fines fractions which meet criteria for mature fine tailings (MFT) may be treated with a high molecular weight polymer to achieve flocculation and to promote dewatering. The process may include the following steps:
- Selective dredging of MFT from active or inactive tailings ponds - Dispersion of polymer solution into MFT stream - In-line mixing and conditioning of MFT and polymer solution during transport to the deposition cell - Discharge of flocculated material from spigots to dewatering cell with sloping beds - In-situ dewatering and drying under climatic conditions

19 Additionally, under certain circumstances the following activities may be undertaken to enhance dewatering and to create new deposition area:
- In-situ mechanical working of deposited flocculated MFT
- Mechanical excavation and relocation of dewatered MFT to stockpiles The details of this process may depend on the characteristics of the feed material and may be applied on a source-by-source (pond-by-pond) basis.
Characteristics of Flocculated MFT
Dewatering Behaviour The amount and extent of dewatering is dependent on a number of factors, such as the flocculation efficacy and the shear conditioning of the material as it exits the discharge pipe and flows across the deposition cell.
Dewatering performance may be assessed using the Net Water Release (NWR) value, compared to the expected water release for a known material under laboratory conditions.
NWR is a metric that has been developed and is a measure of the differential in water between the starting solids of the thick fine tailings and the solids of treated and drained thick fine tailings after a given draining time. The draining time may be 24 hours, 12 hours, 20 minutes or 10 minutes, for example, or another representative time period for drainage in large applications. The NWR may be calculated as follows:
NWR = (Quantity of Water Recovered ¨ Quantity of Flocculant Water Added) / (Quantity of Initial thick fine tailings Water) A NWR test may be conducted using immediate drainage of a flocculation thick fine tailings sample for a drainage time of about 20 minutes. In this regard, for =
optimal dosage range and good flocculation, the water release in 20 minutes may be about 80% of the water release that would occur over a 12 to 24 hour period.
For underdosed or overdosed samples, the water release in 20 minutes may be about 20% to 60% of the water release that would occur over a 12 to 24 hour 5 period. The 20 minute NWR test may therefore be followed by a longer NWR
test, e.g. 12 hour drainage time, which may use a water volume or solids content measurement approach. It is also noted that the laboratory and filed tests described herein used a volumetric 24 hour NWR test. Referring back to Fig 5, it can be seen that a greater initial water release results in a shorter drying duration 10 that is required to achieve a certain solids target.
The NWR is dependent on several factors, including the dispersion of the flocculant into the thick fine tailings and the subsequent conditioning (including mixing) of the flocculation tailings. Rapid and thorough dispersion is preferred for increasing NWR.
15 During the flocculation process, polymer may be introduced as an aqueous solution, thereby adding water to the stream. Therefore, the performance evaluation may take into account both the MFT pore water released as well as the amount of polymer solution water recovered.
If the net water release is positive and high, then the material is relatively well

20 flocculated and should experience significant dewatering upon deposition.
Another metric for material performance is based on the measured yield stress.

The various reaction stages are delineated by yield stress limits assigned according to the measured water release after designated mixing (conditioning) times. Fig 2 illustrates an example of yield stress evolution for the reaction stages of flocculation and dewatering.
Note that the optimal water release stage may not coincide with the peak yield stress, but rather it falls behind the peak; this phenomenon may be attributed to

21 the breakage of flocculated masses ("flocs") during subsequent mixing and water release can also contribute to reduction in yield stress.
Variability Flocculated MFT is capable of exhibiting a variety of behaviours depending on several factors, for example:
- MFT source characteristics - Efficacy of the flocculation (dispersion/mixing) process - Conditioning of the flocculated material in-pipe before deposition Each of these factors contributes to the characteristics of materials deposited into dewatering cells. The process conditions are linked to flow behaviour and beaching tendencies in the deposition cells.
Sub-aerial Deposition of Flocculated MFT
Discharge and Containment Flocculated MFT may be discharged through linear spigot arrangements into deposition cells which may or may not have physical separation berms between adjacent cells. The cells may be generally rectangular, with the primary (long) axis aligned across the bed gradient and parallel to the direction of discharge.
Each cell may be typically fed by four to six spigots. The approximate footprint of the cells may vary from 100 m by 50 m (0.5 Ha) to 280 m by 80 m (2.2 Ha).
The base of the cell may be constructed with local materials, namely tailings sand and/or local clays. The cells may be graded to promote drainage and to facilitate the collection of runoff. The grade varies from site to site, and may reflect local topography with slopes of <1% to 5%, for example.

22 Perimeter berms may be provided to enclose the cells on all sides, except in the case of cells located on the perimeter of water ponds, where the water line represents the downstream limit of the cell (although materials may flow beyond this point into the water body). Header berms may be raised in the upstream or centreline manner, depending on the availability of land adjacent to the cell and the ultimate height of the berm.
Flocculated MFT can fill the cells in different manners and with different efficiencies, depending on the relationship between the fluidity of the material, the energy of the flow, and the geometry of the cell, for example. Fluidity may be defined at this point as the inverse of apparent viscosity. Highly fluid materials with low viscosity will tend to fill the furthest reaches of the cell first (achieving the lowest potential energy at the lowest elevation), and then gradually increase the deposit thickness so that the surface approaches horizontal. This filling process is limited by the downstream berm height. High viscosity materials will tend to remain near the point of discharge and build upwards (aggrade) at a geometry related to the yield strength and discharge rate of the flocculated MET among other factors. This process is limited by the upstream berm height and elevation of the discharge spigots. A combination of both these accumulation processes may be advantageous at filling the deposition cell and maximizing footprint utilization on a tonnes-per-area basis.

23 Mechanical Disturbance After having been discharged into the containment cell, flocculated MFT may be mechanically disturbed under some circumstances, for example under inhibited drying conditions where the material would benefit from over-turning to promote drying of the entire deposit profile (typically as the result of certain surface crusting that can effectively reduce or prevent evaporation).
Both of these conditions may arise due to the behaviour of high viscosity tailings, which are observed to form thick deposits near the point of discharge.
Reclamation If the flocculated MFT deposit is to remain in place, it can be anticipated that the ultimate deposit surface may require some degree of reclamation. One may thus establish the range of ultimate beach profiles expected for accurate estimates of reclaimable surface area and for design of surface water run-off and erosion control measures.
Rheology in Tailings Management Rheology in the broadest sense is the study of the flow of matter. The study of flow is a concept with broad applicability to tailings management, and more generally to design challenges for extractive industries. More technically, rheology is the quantification of a material's stress response to applied strain, or vice versa.
The two primary rheological quantities for tailings engineers both for pipeline design and deposition management are the yield stress and viscosity of the material. These two quantities can be related by fitting mathematical models to empirical data, which may be derived in the lab. Recently, however, field methods for quantifying tailings rheology have been developed and refined.
Field

24 methods can offer fast and reliable procedures for obtaining rheological data in the field. The significance of this development is that observations of field-scale flow and deposition behaviour can be readily supported by sound rheological measurements. The control of rheological behaviour is of particular significance for surface disposal of tailings.
Some work and theoretical notions Open Channel Flow Regimes Description of Open Channel Flow The present description is not restricted to the study of flocculated MFT
flowing in open channels; however, several important concepts for the description of flow can be illustrated by application of the theory. Thus, it is useful to review several relevant hydraulic principles.
Fig 3 illustrates the free body diagram for a fluid element flowing under gravitational influence where p is the fluid pressure on the upstream face, An is the depth of the fluid element, As is the length of the fluid element, W the weight, and e the inclination of the element relative to a horizontal plane (datum).
It can be shown that for an inviscous fluid, the motion of a fluid element is described by the Euler equation of motion (Equation 1):
p Vse ¨V-13 yz).= 0 at as es Equation 1: Euler equation for motion where p is the fluid mass density, 1.4 is the velocity in the s direction, t is time, and y is the unit weight of the fluid.

For the special case of steady flow, the change in velocity over time is zero and Equation 1 reduces to the Bernouilli equation for flow (Equation 2):

-2pVs- + p + yz = Constant Equation 2: Bernouilli equation for flow 5 The three left-hand terms represent the velocity head, pressure head, and elevation head, respectively. The velocity dependent term is also referred to as the dynamic pressure. In reality, this is not a pressure in the physical sense, rather the term results from a unit analysis that shows equivalence to the Pascal.
In this description, the terms dynamic pressure and unit volume kinetic energy 10 are synonymous and are defined as:
E k Equation 3: Definition of unit volume kinetic energy As a basis for comparing flocculated MFT flows with varying densities and velocities, the unit volume kinetic energy (Equation 3) was determined to be a 15 valuable descriptor.
Furthermore, the literature describes four important elements that may be used to describe the state of a fluid in motion. The classification scheme includes information on the temporal and spatial characteristics of the flow, as well as indices concerning the competition between viscous and inertial forces.
20 , The eight end-member descriptors of the four elements are provided thus:
1. Uniform or non-uniform 2. Steady or unsteady 3. Laminar or turbulent 4. Tranquil or rapid These descriptors are further examined in the following subsections as they provide a theoretical framework for documenting flow observations.
Uniformity Uniformity refers to the spatial consistency of flow geometry so that the depth, slope, and cross section of flow are identical along the entire length of the streamline. These conditions imply that the flow velocity does not change along the flow path, otherwise the flow is said to be nonuniform. A truly uniform flow is rarely observed in nature.
Steadiness A steady flow is one which does not change over time; specifically, the velocity at a fixed point of observation does not change over time. Examples of unsteady flows are surges caused by rapid upstream increases or decreases in flow rate.
Turbulence Classically, flows are described as laminar, turbulent, or transitional. In laminar flows, internal viscous forces dominate inertial forces such that the flow lines remain parallel along the length and depth of flow. Mixing in a laminar flow regime is relatively small as a result of molecular-level activity only.
Turbulent flows are characterized by a predominance of inertial forces over viscous forces, which results in instability, the random generation of eddy currents within the flow, and considerable mixing due to macroscopic particle motions.
The transition from laminar to turbulent flow is often defined by a characteristic Reynolds number (Re, Equation 4) as in pipe hydraulics, where:
pvL
Re =

Equation 4: Reynolds number calculation and L, the characteristics linear dimension for an open channel, is given by Equation 5:
A
L = Hydraulic Radi-us,Rit = ¨
P
Equation 5: Hydraulic radius formula where A is the cross sectional area of flow and P the wetted perimeter. For a circular cross-sectional area, this reduces to r/2 where r is half the width of the channel.
The value of Re at the point of transition is widely debated (ranging from 150 for open channel flow to 4000 for pipe flow), thus no numerical value is suggested here; rather, it is noted that empirical evidence must support the delineation of a transitional boundary or range for any given fluid.
Critical Flow Critical flow is a metric similar to the Reynolds number in that it provides a measure of flow stability and is used to distinguish between tranquil and rapid flows; however, its formulation is different and applies only to flows with a free surface (i.e. open channels). A flow is assessed to be sub-critical, critical, or super-critical based on the Froude number, Fr (Equation 6):
Fr= ¨
,4757 Equation 6: Calculation of the Froude number where g and y represent acceleration due to gravity and flow depth, respectively.

The Froude number describes the potential of downstream disturbances (waves) to migrate upstream, and hence illustrates the flow stability.
Generally, for Fr < 1 the flow is considered tranquil or sub-critical. At Fr equal to 1, the flow is critical and beyond this threshold the flow is considered as rapid or super-critical. Very rapid flows may manifest as surges in otherwise uniform flow regimes.
For the purposes of this description, and to avoid the ambiguity of the Reynolds number transitional range, the Froude number is the preferred metric of flow stability.
Open Channel Flow of Non-Newtonian Fluids Non-Newtonian fluids exhibit a viscosity that is dependent on the rate of applied shear. A Herschel-Bulkley model can be applied to laboratory-derived rheological data to describe this relationship. The Herschel-Bulkley model relates shear strain to shear stress by Equation 7:
= +
Equation 7: Herschel-Bulkley rheological model where the parameters K and n are empirically determined by curve fitting and To is the static yield stress.
The form of this mathematical relationship and the coefficients adopted will dictate the predicted flow behaviour of a non-Newtonian fluid under different hydraulic conditions. The literature provides methodologies for determining transitional boundaries for laminar and turbulent flow for a wide variety of control fluids including clay suspensions; however, this literature work is restricted to flume studies (typically 75 to 300 mm in width).
=

Haldenwang, R., Slatter, P.T. and Chhabra, R.P., 2002,"Laminar and transitional flow in open channels for non-Newtonian fluids", Hydrotransport 15: 15th International Conference on the Hydraulic Transport of Solids in Pipes, Banff, Canada, pp. 755-768, (referred to Haldenwang et at. (2002) herein) define a Reynolds number for non-Newtonian fluids based on flume testing conducted with an array of flume geometries (including semi-circular) and present the new Reynolds number, RHB, in the form of Equation 8.
8pr2 R HB ___________________________________________ Tv k Equation 8: Equation for non-Newtonian Reynolds number (Haldenwang et at., 2002) Engelbrecht, N. E., and R. A. Burger (2010), Effects of various dissipation range onset models on the 26-day variations of low-energy galactic cosmic-ray electrons, Adv. Space Res., 45, (referred to as Burger et al. (2010) herein) present results that show the onset of turbulent flow for various non-Newtonian fluids occurs at values of RHB greater than 1000 and Straub, L.G.& Silberman, E.& Nelson, H.C., "Open channel flow at small Reynolds numbers", Trans ASCE, vol. 123, 1958, p.685-706, (referred to as Straub et al. (1958) herein) show the onset of transition between a Reynolds number of 2000 and 3000.
Tailings Beaching Observations Beaching of Tailings The beaching of tailings is generally the deposition of solid particles so that they come to rest at the base of the flow. This requires that the solid particle be removed from suspension in the fluid mass, or conversely, that the volume of matrix fluid be reduced to a point where the solid structure can come to static , , 29a equilibrium. In a sub-aerial channel flowing with tailings slurry, beaching may be conceivably accomplished by several means, for example:
i. Settlement of particles through the fluid column due to a loss of buoyancy (decrease in density contrast between the solids and the carrier fluid); that is, the fluid carrier decreases in density due to addition of water or due to flocculation of fine matrix particulate;

ii.
Relaxation of the suspension structure, allowing a previously supported particle to fall through the fluid column, or such that the tailings mass can reach static equilibrium (i.e. spreading or expansion of the fluid into a vessel or channel of different geometry);
5 iii.
Decrease in carrier fluid velocity, resulting in the downward component of the gravitational force to dominate the system;
iv. Increase in the apparent size and mass of suspended particles due to flocculation, which also results in effects due to (i) and (ii); and/or or by the v. Loss of the carrier fluid through seepage to the bed, evaporation, or "run-10 away".
The term run-away is used here to describe water that is expelled from the tailings slurry and neither seeps through the bed, nor is evaporated at surface.
This water is expelled to the surface of the flow and has the ability to run down slope at a rate greater than the tailings mass due to its relatively low viscosity.

This results in an apparent increase in the slurry solids content and yield stress, and will eventually cause the mass to stop flowing. At this point, the tailings may also be considered beached.
The following sub-sections outline the general mechanisms associated with the formation of mine tailings beaches.
20 Sedimentation and Segregation Sedimentation of particles occurs when the kinetic energy (velocity) of the flow decreases to a point where the gravitational force dominates the system and the particles fall through the fluid column to settle on the channel bed or along the channel wall. The change in velocity may be the result of changes in the

25 discharge rate or by the natural loss of energy of the stream over distance.

Sedimentation requires that the free falling particles occupy a carrier fluid at a density that permits sufficient downward migration of particles over a reasonable time and distance relative to the length of the flow path.
Sedimentation is naturally accompanied by segregation, whereby low density and relatively small particles are carried further downstream than more dense, larger particles. The combination of these phenomena (sedimentation and segregation) is often cited as the dominant mechanism in beach formation for many situations.
Yield Stress Fluid Stoppage Flow of a yield stress fluid (that is, a fluid which requires some minimum stress be applied before it will move) occurs above its characteristic static yield stress.
Below that point, the fluid may exhibit some elastic behaviour, but will not yield and flow.
Hence, as a flow moves down gradient, it experiences internal and external energy losses until such point where the shear rate decreases and its stress state falls below the critical static yield stress. Below the critical static yield stress, the fluid will no longer flow along the present gradient, though it is noted that dynamic yield stress is also a useful measure for stopping fluid flow.
In the case of fluid stoppage applied to flocculated MFT, one must also conceptualize the flowing mass as a fluidized soil structure which loses moisture to the environment (through bed seepage and surface run-away) and not just as soil particles suspended in a carrier fluid.
The nature of this deposition mechanism is strongly dependant on the material rheology. It can be shown that a uniform steady flow will develop if the gravitational driving force on an element of fluid exceeds the viscous force.
For this circumstance to arise, some critical depth (and hence mass) of fluid must exist to exceed the resistive shear stress along the base of the fluid element (Fig 4).
The depth of fluid required to sustain flow is referred to as the critical height (he):
hc ¨ figsint Equation 9: Calculation of the critical height where Tc is the yield stress of the fluid, p is the fluid density, and i is the inclination of the plane with which the fluid is in contact.
An illustration of the critical height as a function of inclination and yield stress is presented in Fig 5.
Equation 9 is very similar to the method of flow depth estimate provided in literature for viscous lava flows; however, the sin(i) term is replaced by tan(i), which under relatively shallow slopes yields nearly indistinguishable results.
It should be noted that for truly uniform flow to be realized, the critical height must be observed over the entire flow length. Assuming the fluid density does not vary significantly across the length of the flow, then the beach inclination supporting the flow should be held constant over the flow distance (i.e. the previous underlying beach slope is monotonic). It will be shown in further below that this is not the case for beaches formed of flocculated MET.
Conceptual Model Fig 6 illustrates a conceptual model for momentum transfer effects in suspensions which describes the transitional boundaries between systems controlled by colloidal, Brownian, hydrodynamic, and inertial interactions.
Fig 6 suggests that the flow behaviour of a concentrated suspension will be a function of both the physical fluid characteristics and of the applied or embodied energy of the system.
Rheological Considerations for Flocculated MFT
General Considerations The rheometry (the measurement of rheological parameters) of flocculated MFT
may take into account several considerations. Specifically, a rheological measurement used to make field-scale extrapolations may be made:
-At a scale appropriate to the parameter of interest, giving consideration to the micro- and macro-scale structures observed in flocculated MET, - Over a range applied shear rates so that the energy imparted to the material most closely reflects actual field conditions;
- While taking into consideration the evolution of a dewatering material; that is, the measurement must allow for loss of moisture through drainage and to a lesser extent, by evaporation. Furthermore, moisture may be reincorporated if too much energy is applied over a given time period; and - With knowledge of the previous stress state(s) of the material.
More generally, the rheological measurement should account for the potential for thixotropy (or rheopexy), shear thinning (or thickening), and the effects of soft-jamming particles, boundary effects, shear heterogeneity, and particle settling.
Scale Effects Referring to Fig 7, a flow of flocculated MFT may be observed at several useful scales. First, the complete flow pattern may be observed, where the entire flow interacts both with itself (internal viscous forces) and with the surrounding environment (external friction forces and momentum loss). This is referred to as the flow scale. Secondly, the flow may be observed at the scale of visually discernible interactions between flocculated MFT particles (flocs) and colloidal structures (floc aggregates) that may be present. This macroscopic scale of observation focuses on internal viscous forces and particle-particle interactions that determine the rate of energy loss within the system. Finally, there are the mesoscopic and microscopic scales of observation which focus on clay-clay and clay-polymer interactions (or more generally, particle-particle, and particle-polymer) interactions.
Scale-dependant measurements may be obtained under circumstances where the scale of the instrumentation is relatively close to or below the scale of the main structural-rheological components of the system. In this case, the term Representative Elementary Volume (REV) will be used to describe the smallest element of a flocculated MFT flow that accurately describes the behaviour of the overall system. A scale-independent measurement of the rheological behaviour of flocculated MFT is desired so that upscaling is possible, thus the rheological measurement must be carried out at or above the scale of the REV.
Theoretically, measurements made below the REV scale will show variability and may not describe the entire system.
The scale of the REV will depend on numerous factors, but most significantly on the:
= Solids volume fraction, 8(VsoridsAfrotar);
= Efficacy and completeness of flocculation;
= Spatial distribution of solids, moisture, polymer, and voids; and the = Presence or absence of micro- and macrostructures (flocs and aggregates).
The scale of observation for this study covers the range of macroscopic behaviour to flow scale behaviour. The REV for rheology exists somewhere between the macroscopic and flow-scale domains depending on the heterogeneity of the deposition.
Instrument Geometry Rheological instruments vary widely in appearance and operation. The following 5 list provides the tool configurations most commonly used in a rheological study:
- Capillary tube (viscometer): for relatively low viscosity fluids with little to no macrostructure - Parallel plate: for fluids with low yield stress and little to no macrostructure - Cup-and-bob: (Couette or Searle type) for fluids with low to high viscosity 10 and varying degrees of macrostructure A cup-and-bob geometry may be used for the characterization of soil-water mixtures and granular suspensions. For tailings rheometry of tailings slurries, the standard spherical or conical bob is replaced by a rectangular 4-blade vane with an approximate 2:1 height to diameter ratio. The vane is better suited to granular 15 suspensions as it maximizes particle-instrument contact and reduces the risk of slippage and shear inhomogeneity.
Rate of Applied Shear The rate of applied shear should reflect the rate of shear experienced at the field flow scale. The rate of shear in the field will be directly related to the velocity and 20 geometry of a flowing stream of material.
For a circular cross-sectional channel flowing with flocculated MFT, the bulk shear rate can be estimated using Equation 10:
I = 2 -RN
Equation 10: Equation for calculating bulk shear rate in an open channel where v is the bulk flow velocity (in m/s) and RH is the hydraulic radius (the ratio of the cross-sectional flow area divided by the wetted perimeter).
Dewatering Dewatering of a flowing stream effectively increases the solids volume fraction of the flocculated tailings and increases its viscosity as particle-particle interactions and hydrodynamic forces predominate; however, dewatering may also result in migration of water from the internal structure of the material towards the boundaries of flow, hence lubricating the flow. This phenomenon is observed in the field where free water and residual bitumen from the flocculated MFT
migrate to the flow boundaries and reduce the friction against the channel wall.
Therefore, the net effect of dewatering may not significantly impact the behaviour of a flowing material, so long as the rate of dewatering is less than the rate of flow.
Stress History Conditioning of flocculated MFT may occur in the delivery pipe, from the point of polymer injection all the way to the point of discharge into the cell. A
flocculated MFT stream may possibly exit the discharge spigot in various states, including under-mixed, optimally mixed, and over-mixed. Furthermore, the material may be described as either optimally dispersed or under-dispersed. The conditioning of the stream will depend on the MFT-specific polymer dosage and the flow rate through the delivery piping.
The state of the discharged flocculated MFT will influence beaching behaviour and may influence the longer-term strength gain as a result of hysteresis effects.

Thixotropic and Rheopectic Behaviour Thixotropy describes the decrease in shear stress as a result of shearing and a constant rate over time. A rheopectic behaviour is one where the shear stress increases as a result of a constant shear rate over time.
Thinning and Thickening resulting from shearing degrading of flocs Shear-degrading of flocculated MFT occurs when the flocculated structure is degraded as the rate of shear is increased causing irreversible floc breakage.
In the field, this may be realized as the flow rate increases past a point where the flocculated MFT is effectively over-sheared and the viscosity decreases rapidly.
Soft-Jamming Particles Flocculated MFT tends to form agglomerated structures referred to as floc aggregates. These floc aggregate masses may range in size from several millimetres to half a decimetre, for example. Floc aggregates can be easily identified visually, and physically separated from the flowing mass. Upon inspection of a floc aggregate, it is apparent that the structure exhibits some elasticity and is easily compressed.
This type of structure can more generally be referred to as a soft-jamming particle. Two or more of these particles interacting will result in energy losses attributable to the compression of particles and the transfer of momentum between elastic media.
Boundary Effects During rheological measurements, boundary effects may influence equipment performance and the validity of measurement if certain precautions are not observed. Most critically, the gap size (the distance between the shearing and static surfaces) must be sufficient to avoid wall friction effects.
Furthermore, the gap size must be sufficiently small so that the shear zone created in the apparatus is homogenous (i.e. there is a uniform distribution of stress across the shear zone) for the analytical interpretation to be valid.
Particle Settling Particle setting can be a troublesome phenomenon observed during the rheometry of concentrated suspensions. Particle setting usually manifests during the initial stages of developing a flow-curve (shear rate versus shear stress plot), when the rate of shear is sufficiently low to allow sedimentation of once-suspended particles through the fluid column. Particle settling will typically result in a low-bias measurement of shear stress as the effective solid volume fraction of the sheared fluid is reduced along the vertical shear surface, in the case of a vane rheometer. If the shear zone is located at the lowest part of the instrument (e.g. in a parallel plate rheometer), the shear stress measurement may be biased high as the effective particle concentration increases in the shear zone.
If shear rates are maintained sufficiently high, particle settling may be avoided.
The rate of settling will also be governed by the particle shape, specific gravity, and ratio of the solid volume to the total suspension volume.
Some Laboratory Rheological Observations Extensive laboratory rheological testing of flocculated MFT over various ranges of MFT clay content, solids fraction, and degrees of flocculation, has been undertaken.
The quality of flocculation and mixing conditions are factors that dictate the form of the flow curve. Assuming that the polymer was introduced to the MFT stream appropriately, the MFT should flocculate to an optimal water release structure after conditioning; however, changes in flow rate or MFT feed quality may cause changes in in-pipe conditioning requirements and the optimal flocculation structure may not be achieved. In these cases, an optimally dosed MFT may be sub-optimally mixed. Fig 8 presents the fitted Herschel-Bulkley flow curves for flocculated MFT after varying degrees of mixing.
The empirically derived Herschel-Bulkley parameters for flocculated MFT in various states are provided in Table 1.
Table 1: Herschel-Bulkley Parameters for flocculated MFT
He rsche I-Bulkley Parameters Condition To (Pa) K (Pa.$) 80 s mixing 25.6 3.41 0.62 110 s mixing 23.3 2.99 0.77 140 s mixing 25.4 2.15 0.88 Due to the thixotropic nature of flocculated MFT, the viscosity will decrease with time under shear. This phenomenon occurs when the fluid is in motion.
Once the fluid has stopped flowing, it will continue to undergo structural changes that will influence the stress-strain relationship. First, the material will dewater under gravity drainage as well as self-weight consolidation and collapse of the soil structure. Secondly, moisture will evaporate from the surface - so long as moisture is readily supplied to surface. Both actions will act to decrease the overall moisture content, increase the solids volume fraction, and increase the yield stress.
The increase in solids content (shown as mass fraction) and increase in static yield stress (presented as peak yield strength) are illustrated in Fig 9 and Fig 10.
The relationship between yield stress and solids fraction is described by an exponential or power function with considerable scatter. The scatter is attributable to the MFT composition which can demonstrate significant variation in clay content.

Tailings Beach Profile Models General Researchers have approached the problem of tailings beach profile modeling, with a multitude of motivations and to varying degrees of success. Approaches 5 are both theoretical and semi-empirical. Some models are described and compared in the following sections.
Melent'ev et al. (1973) The Melent'ev et al. (1973) model has been successfully applied to profile prediction of both hydraulic fills and mine tailings. The empirical model is based 10 on curve fitting to the cross sectional profiles of hydraulic fill beaches. The empirical relationship is provided in Equation 11:
z = ze - -L) Equation 11: Empirical equation for the Melent'ev (1973) profile where z is the elevation along the beach, zo is the elevation at the beach head, x 15 is the distance along the beach measured from the point of discharge to the end of the beach at a distance L.
The parameter n is dependent on the fill characteristics, namely particle size distribution and specific gravity.
The profile equation is easily differentiated to illustrate the change in slope (S) 20 over the beach length:
S = st, (1 - Ly-Equation 12: Slope as a function of beach position (Melent'ev et al., 1973) The work of Melent'ev et al. (1973) on hydraulic fill beaches has been subsequently validated on both sub-aerial and sub-aqueous tailings beaches.
See Melent'ev, V.A., Kolpashnikov, & N.P., & Volmin, B. A. (1973), Hydraulic fill structures. Energy, Moscow, English translation, ed. D. van Zyl, 1-240 (referred to as Melent'ev et al. (1973) herein). Williams and Morris (1989) Morris and Williams (1998) identify that the empirical equation originally introduced by Williams and Morris in 1989 (reproduced here as Equation 13) provides a reasonable fit to measured beach profiles of coal and metalliferous tailings.
z = Ae(-4r Equation 13: Empirical fit equation from Williams and Morris (1989) where:

A = __________________________________________ Equation 14: Equation for the A parameter in Williams and Morris (1989) and w is an empirically determined parameter.
Morris and Williams offer a statistical treatise on beach profile fitting and demonstrate that an exponential function provides a superior fit to the majority of profiles in a database of 46 surveys from coal mines and metal mines.
Furthermore, the researchers discourage the use of a power-law for profile fitting as it has no theoretical basis and overlooks basic hydraulic principles.
See Morris, P.H. (2004), Mine waste beach profile and flow resistance equations.
International Journal of Mining, Reclamation and Environment, 18(4), 253-272, Morris, P.H., & Williams, D.J. (1998), A comparison of two mine waste beach equations, International Journal of Surface Mining, Reclamation and Environment, 12(3), 97-100, and Morris, P.H., & Williams, D.J. (1996), Prediction of mine tailings delta profiles, Transactions of the Institute of Mining and Metallurgy, (Section A: Mining Industry), 105, A63-8.
Fitton (2007) An equilibrium slope is a slope at which material is neither added nor removed from the channel bed and is identified as a general predictor of deposit slope.
Fitton proposes that the slope of a tailings deposit can be equated to the equilibrium slope achieved by channels that run across the beach and provides three models for calculating this unique slope. The simplified and semi-empirical models will not be discussed here; however, the a priori model is discussed as it is based on widely accepted hydraulic principles and is most easily generalized to describe a variety of tailings.
The a priori model requires the following inputs:
= Q, the flow rate (m3/s) = Cv, the concentration of the tailings slurry in terms of volume (fraction) = d50, the median particle diameter of the tailings slurry (m) = d90, the 90th percentile particle diameter of the tailings slurry (m) = pw, the density of the carrier fluid of the tailings slurry (kg/m3) = Ps, the density of the solid particles in the tailings slurry (kg/m3) = Ty, K, and n (rheological parameters for a Herschel-Bulkley slurry model) Fitton (2007) introduces a straight-forward spreadsheet algorithm to calculate the equilibrium slope as:
1. Guess an initial value of the flow depth 2. Calculate the cross sectional area of flow, A, and the wetted perimeter, P, as a function of the 3. geometry of the channel cross-section 4. Calculate RH (the ratio of A/P) 5. Calculate V, the mean velocity in the channel (equal to Q/A) 6. Calculate Vc, the minimum transport velocity 7. Repeat steps 1 to 5, adjusting the depth value (in step 1) until V and Vc in steps 4 and 5 equate 8. Calculate ReHB using a modified Reynolds number equation 9. Calculate a friction factor (f) for the channel based on Step 7 10. Calculate So (the equilibrium slope) using the Darcy-Weisbach equation:
pis so ¨ _________________________________________ gRial Equation 15: Darcy-Weisbach equation The equilibrium model presented suffers from several key shortcomings, namely:
= The analysis is restricted to a fixed channel geometry both spatially and temporally = The analysis is data intensive, requiring delineation of the d50 and d90 particle sizes = Strict definition of the laminar-turbulent transition is required = The model outcome is a unique slope value The final point addressed in this list is without question the most detrimental for this model; that is, the non-monotonic beach profile of flocculated tailings cannot be described with a monotonic model.
See Fitton, T. (2007), Tailings beach slope prediction, PhD dissertation, RMIT
University. Henriquez, J. And Simms, P. 2009. Dynamic imaging and modelling of multilayer deposition of gold paste tailings. Minerals Engineering, 22(2):

139., (referred to as Simms & Henriquez (2009) herein).
Lubrication theory in the context of tailings engineering is explored by Simms and Henriquez. The theory is limited in that, by principle, it is only applicable to the deposition of tailings by uniform sheet flow. The theory also requires the following conditions be met:
= The ratio between the thickness of the flow and the horizontal extent of the flow is small.
= The flow velocity is low and the flow state is laminar.
Although the uniform sheet flow condition is rarely met by flocculated MET, this description will present the theory as it offers some theoretical background for the flow and stoppage of a yield stress fluid on an inclined plane.
First, the shear stress profile through a slow flowing, laminar flow can be written as:
r(z) = (it ¨ co56 (tan ¨ai)]
dx.
where h is the flow depth, z is the vertical distance measured upward from the channel bed, 6 the bed inclination measured from the horizontal, and x is the displacement along the inclined plane.
At the base of a channel, the shear stress can be replaced by the yield stress (thus requiring that the flow is at equilibrium and has stopped flowing) and the expression can be written to express the tailings profile explicitly (Equation 16):

2r,, Pg(x )C0) Equation 16: Fluid profile determined from lubrication theory where ry is the yield stress of the fluid.
Simms & Henriquez (2009) show examples of laboratory and field scale 5 measurements which are fitted to theoretical profiles.
McPhail (1994) McPhail and Blight suggest the introduction of a power law or exponential function to empirically capture the profile of beaches forming under natural conditions of energy loss. Where the system is constrained (i.e. the beach length 10 is defined), the beach profile may be best described by a function similar in construction to the Melent'ev et al. (1973) equation; however, where the profile is dictated by the loss of energy down the beach, an exponential function (in the form of Equation 17) best fits measured beach profiles.
Tr= 1 -e 15 Equation 17: The normalized profile equation where the concavity parameter, c, is a function of the material properties and discharge conditions. The terms yN and x/H are the normalized vertical and horizontal coordinates which together describe the profile in two dimensions.
The term x/H increases from 0 to 1 from the point of discharge to the end of the 20 deposit and the term yN decreases from 1 to 0 from the point of discharge to the lowest elevation of the deposit.
The development of tailings beaches can be a chaotic, random, natural process;

therefore the exact profile of a tailings beach at equilibrium cannot be wholly satisfied by deterministic models. The stream power approach (McPhail, 1994;
McPhail & Blight, 1998) applies the basic principles of open channel hydraulics and entropy theory to estimate the distribution of stream power along the tailings flow path. The stream power is calculated on the basis of a uniform flow rate, density, and driving gravitational (elevation) head. As the stream (channel) meanders down the length of the deposition cell it experiences frictional energy losses; hence, the velocity approaches zero and the flow eventually stops. The rate of the dissipation of energy can be calculated with known rheological behaviour and flow geometry. The dissipated energy as a function of distance down the beach can be seen as a naturally occurring process and can be probabilistically modelled using Shannon entropy theory.
Several notable model assumptions that may be made are:
1. Deposition along and within the flow channel is gradual and slow compared to the flow rate so that for all practical purposes the flow rate can be kept constant down the beach.
2. Built into this first assumption is the assumption that the slurry properties remain essentially constant down the beach (i.e. particle size distribution, percent solids, and rheology do not change significantly).
3. The reduction in stream power down the beach is as a result of frictional loss and is represented by a change in flow velocity.
4. The flow channel is circular.
5. The Bernoulli equation applies to the circular flow channel without modification.

Stream power, P, is calculated as follows:
P= P9Q11 Equation 18: Stream power formula where Q is the volumetric flow rate and H is the total head difference between the point of discharge and the end of the beach.
After the flocculated tailings are discharged from the pipe, they fall with some horizontal momentum supplied by the pressure difference between the pipe and the discharge environment. The stream will fall with some vertical momentum as a result of gravity and thus strike the beach at some nominal distance from the end of the pipe. For flocculated tailings, this distance is typically small for discharge rates up to 450 m3 per hour ¨ in the order of 0.2 to 0.5 metres ¨
and henceforth will be considered negligible when compared to the total flow distance (in the order of 100 to 300 metres). At this discharge rate, the flocculated MFT
will scour the bed material of the cell to create a depression. This depression is referred to as the plunge pool, and may vary in size from approximately 10 to centimetres in depth and 20 to 50 centimetres in diameter (elongated in the direction of flow). The exact dimensions will vary as a function of the bed material and the energy of the flowing tailings stream. The role of the plunge pool is essentially that of an energy dissipater ¨ reducing the velocity of the tailings as it contacts the beach head.
At the downstream lip of the plunge pool, the stream power for a flow of volumetric rate Q is given the notation P0 and the head term (H) is the elevation difference between the discharge and the toe of the cell, or the ouffall to the pond. This signifies that the stream power will be a function of the overall gravitational potential of the flow, or put another way, the average bed inclination of the disposal cell. The expression for stream power is subject to loose boundary conditions in a naturally formed channel under gravity flow from the plunge pool, such that the stream power at any distance x from the downstream lip of the plunge pool will be a function of the velocity head at distance x (Equation 19):
Px = PQiv Equation 19: Stream power as a function of velocity head The initial stream power, Po, is thus taken to be a function of the average velocity at the lip of the plunge pool, and not that of the initial discharge from the pipe.
The change in stream power along the beach is derived from Shannon entropy theory for a discrete random variable (P in this case) at a distance, x, from the source. Simplified, the Shannon entropy model asserts that at the system's lowest energy state, the degree of disorder, or entropy, will be maximized.
McPhail defines the most probable distribution of energy losses down the beach, from an initial stream power of Po to a final power equal to zero (where the stream stops flowing). The entropy-maximized stream power expression is given as:
P (x) = - ¨1 In (1 - exp'"P )2-c + exp-"
Equation 20: Entropy-maximized stream power as a function of distance from the plunge pool The parameter p is related to the stream's rheology. All other inputs are determined by the physical layout of the disposal cell (L, the effective length of the cell) and the initial discharge conditions (flow rate, density, and plunge pool characteristics).

Holistically, this model represents the rate of energy losses in the flowing stream as an exponential decay with shape parameters that can be defined based on a rheological model.
The profile of stream power can be differentiated to find the slope of the stream power profile at any distance along the beach and the slope of the stream power profile will parallel the slope profile of the final beach surface. The beach profile is offset vertically by the upstream restriction (e.g. the header berm height, or elevation of the discharge pipe relative to the cell base). The slope of the stream power profile at distance x from the discharge (SBA, and hence of the final beach is then calculated as follows:
- exp.'" ) sB (x)- - L /I exp-pyx) Equation 21: Slope of the stream power profile The complete beach profile can thus be constructed with any number of discrete slope calculations along the beach length. This model can be easily coded into a spreadsheet program and the p term solved by iteration.
A procedure is included in the algorithm to verify that the calculated shear stress of the fluid (as a function of the computed flow velocity and channel geometry) is consistent with the sustainable shear stress which is determined from an assumed Herschel-Bulkley model.
See McPhail, G.I. (1994), Prediction of the beaching characteristics of hydraulically placed tailings. PhD dissertation, University of Witwatersrand, and McPhail, G.I, & Blight, G.E. (1998), Predicting tailings beach profiles using energy and entropy, Proceedings from Tailings and Mine Waste '98, 19-25.

Field Setting and Methods General Field monitoring of flow conditions occurred over a period of two deposition seasons (each season being approximately April through October) at several 5 locations at an oil sands mine. Quantitative flow monitoring and sampling was restricted to the second field season, when access to deposition cells was made possible by the installation of scaffolding structures. Beach profiles were also obtained at a number of full-scale deposition cells.
An overview of the general method employed for the qualitative and quantitative 10 assessment of flow and deposition at the various study cells is outlined in Fig 11.
The following sub-sections describe the field setting and methods employed.
Deposition Cells Flocculated tailings are deposited on sloping beds near, or on, existing tailings impoundments; these areas are generally referred to as deposition cells herein.
15 The cells, taken in aggregate, form what is referred to as a Dedicated Disposal Area (DDA), or Dedicated Disposal System (DDS). The cells, which may be generally rectangular in plan, range in length from 150 to 300 metres and in width from 50 to 80 metres, approximately. The initial bed slope depends on the underlying topography, but generally ranges from 1% to 5%, sloping away from 20 the point of tailings discharge to facilitate tailings distribution and dewatering. In many cases, these cells are not truly isolated on all sides, but the arrangement of spigots at the header berm may imply lateral boundaries. Typically, a linear arrangement of multiple spigots, e.g. four spigots, designates the extent of one cell. A number of cells may be constructed in series to allow efficient distribution 25 of the tailings to those cells (see Fig 12). The downstream boundary of the cell may be supplied by a standing pool of water (either the supernatant pool of the impoundment, or stored water at the toe of the cell resulting from dewatering and run-off collection), or by a soil berm constructed to retain the tailings (see Fig 13).
Qualitative observations of flow behaviour and beaching tendencies were undertaken at numerous locations, while quantitative observations and sampling was focused in three primary deposition cells. Table 2 describes main key locations for data collection. The location names in the second column refer to nomenclature for the deposition areas, and are provided only for completeness.

Fig 14 provides schematics for these deposition cells.
Table 2: Description of main deposition cells used in this study Cell Approximate Approximate Purpose / main length x width Bed Slope observations (m) A 250 x 50 3.5% Flow monitoring /
sampling 270 x 70 0.8 to 1% Profile surveys /
flow observations 150 x 50 (max, 1 to 3% (variable) Profile surveys triangular) Various cells 250 x 50 0.8 to 1% Profile surveys The study cells demonstrate the range of physical constraints on deposition, covering a bed slope range of approximately 1 to 3.5% and a range in cell length from 150 to 270 metres.
The geographic location of the cell is relevant in that it can determine the specific tailings stream that it receives. For instance, Cells A, B and C received tailings feeds from different MFT sources (tailings impoundments). It should be noted that the compositional differences in MFT between sources can influence the flocculated MFT characteristics and the flocculation and dewatering operation may be adjusted in accordance with different source MFT properties.

, , ' The majority of the flow behaviour monitoring was conducted at Cell A, while beach profile data was readily obtained from Cell B, Cell C, and various other cells.
Deposition Conditions The monitoring occurred during regular operation of the production of flocculated MFT. This allowed the following:
- Permit observation of the operational range of discharge conditions;
- Allow flexibility in terms of monitoring location and duration; and to - Facilitate completion of this work within the constraints of the operating season.
The result of this methodology is observations and measurements that span a range of a large scale operating conditions.
Monitoring Methods Overview A combination of qualitative and quantitative observations and measurements were undertaken. Flow monitoring was aided by the installation of a scaffolding structure ("catwalks") that permitted safe access to the interior of deposition cells during operation. Fig 15 depicts the field setting at Cell A, including the scaffolding structure.
Some of the field methods for sampling and monitoring that were adopted are discussed in the following sections.

Qualitative Monitoring Time-lapse photography, video, and digital photography were undertaken to document flows of flocculated MFT over periods as long as 24 hours. Video was used in some instances to verify measured flow velocities.
Flow Classification & Quantitative Monitoring During field monitoring, observed flows were visually classified into one of four main flow regimes:
- Stacking flows - Sheet flows - Laminar channel flows - Turbulent channel flows Stacking flows and sheet flows are easily distinguished from channelized flow in the field; however, the distinction between laminar and turbulent channel flows requires a more strict qualitative definition.
For the purposes of first identifying the channel flow regimes, and to later compare the qualitative and quantitative observations, the following guidelines were used to distinguish laminar and turbulent regimes.
Laminar flows were generally characterized by:
- Relatively slow-moving, stable channels;
- Higher degrees of sinuosity on shallow slopes;
- Easily distinguished parallel flowlines at surface (e.g. may be delineated by the residual bitumen expelled to the surface of the flow); and - Little evidence of channel erosion.

Turbulent flows were generally characterized by:
- Fast-moving, unstable flows;
- Generally straight, down-gradient channels on all slopes (low degree of sinuosity);
- No or very few distinguishable flow-lines at surface due to macroscopic mixing; and - Evidence of channel erosion and sediment transport down-slope.
Flow Velocity In the field, flow velocity is most readily quantified by the surface velocity of the flowing stream (or the displacement of the mass with time for stacking or sheet flow). While velocity is assumed to vary with depth through a flow profile according to classical hydraulic theory, the use of surface velocity measurement provides an easily obtained, practical metric for flow velocity. Acoustic profilers or other instruments could be used, for example. In addition, surface velocity may be measured using a physical floating tracer (50 mm diameter low-density polyethylene disk) placed in the flow centreline. A chronometer may be used to measure the time required for the tracer to pass between measuring staffs placed along the flow path at measured intervals. The floating tracer method was used for various examples described herein.
Sampling Sampling along the flow path was accomplished by inserting a four-litre sampling vessel into the flow as the physical tracer passed established benchmarks (typically surveyed wooden stakes) within the deposition cell. The four-litre sample was sufficient to complete the density and yield stress testing along with retention of approximately 500 mL of sample for laboratory analysis. This method may use the assumption that the tailings mass flows essentially as a plug of material.

Rheology & Density Measurement Yield stress can be readily estimated using a simple slump test. The test procedure and apparatus is modified from the traditional concrete slump test as outlined in ASTM C143/C143M ¨ 10a (ASTM, 2010). A modified slump test (see 5 Figure 16, for example) may be used for determination of the static yield stress of slurries. Figure 16 provides an illustration of the slump test and the yield stress distribution associated with this method.
A standardized four inch inside diameter, smooth-walled, open-ended cylinder with height-to-diameter aspect ratio of 1:1 was used for all testing.
Flocculated 10 tailings were sampled from the flowing stream using a long-reach sampling pole, and carefully poured to completely fill the cylinder. The slump cylinder rested on a portable Mettler-Toledo bench scale so that the sample mass could be measured for density calculation.
The cylinder was lifted vertically to allow the material to slump and the change in 15 height of the specimen was recorded (S). From this, a percentage slump value was calculated (Equation 22).
Ws ¨SI
= _____________________________________ x100%
Ho Equation 22: Calculation of percentage slump The slump values were correlated to static yield stress measurements using a manual shear vane (GeonorTM H-60) rotated through the tailings in a smooth-20 walled sample pail. The vane geometry is regarded as well suited for determining the yield stress of mine tailings. Samples were sub-divided for slump testing and vane testing.
The use of a so-called "bucket rheometer" set-up was used for vane testing.
The nominal pail diameter was 265 mm with a depth of 385 mm and the vane diameter was 150 mm with a height-to-diameter ratio of 2:1. The total volume of sample tested during each measurement was approximately 20 litres. Attention was paid to insert the vane to a position no less than 50 mm from the bottom of the pail to avoid boundary effects. A gap spacing of more than 10 times the largest particle size in the system to preclude the influence of particle-wall effects on the rheological measurement may be used. The gap spacing for the sidewall and bottom surface was a minimum of 50 mm in both instances. The vane was rotated at according to the manufacturer's recommendation, and the instrument reading was converted to yield stress using the manufacturer's correlation factor.
The resulting yield stress measurement was recorded and correlated to the parallel slump test results (see Fig 17).
Field Beach Profiles Profiles of flocculated MFT deposits were obtained from a variety of deposition areas by optical and laser measurement techniques over the course of two deposition seasons (summer 2010 and summer 2011). A discussion of the observed and measured profiles is provided further below.
Field Observations of Flow and Deposition of Flocculated Mature Fine Tailings Flow Regimes General The spectrum of flow regimes observed over several years of large scale production has been broad, reflecting the variability of the tested process inputs and outputs. The flow categories can range from high yield stress stacking behaviour to low viscosity turbulent channel flow. The shear stress incurred by the flocculated tailings varies according to the flow velocity, flow geometry, flow stability, and rheological properties, for example. Hence, an understanding of the , range and frequency of these flow regimes over any period of deposition aids interpreting the deposit formation processes and performance.
Table 3 provides a concise reference for the classification of flow regimes and the observed relative frequency of occurrence.
Table 3: Classification of flocculated MET flows Condition /State RegimeRelative Uniformity Steadiness Turbulence Tranquility Frequency Primary Secondary A A Vt = V Re Fr Stacking Non-uniform Steady to non-steady n.a. n.a. Common Sheet Uniform Steady Laminar Tranquil Rare Laminar Uniform Steady to non-steady Laminar Tranquil Common Channel Turbulent Non-uniform Non-steady Turbulent Rapid Common The following subsections detail the generalized flow regimes observed.
Stacking Flow Stacking flows are generally characterized by a rising stack or cone of material that rapidly accumulates after contacting the beach. The movement of material is generally upwards with outward migration as a result of increased vertical stress on the lower stack layers and failure radially outwards (analogous to a failing cone from a concrete slump test). The discharge is generally characterized by a low velocity, high density stream of material exiting the pipe with very little horizontal momentum.
Stacking flows may be indicative of an under-sheared or over-dosed MFT.
Indeed, this high yield stress, high viscosity, low velocity deposition regime can negatively impact operations. For example, such under-sheared or over-dosed material that has not been sufficiently shear conditioned (e.g. by pipeline conditioning) is a one-phase matrix that is gel-like and from which water release by run-away or separation of water from the flocs does not occur. In addition, stacking can negatively impact operations by jeopardizing the freeboard on the discharge berm and by blocking and burying the discharge spigot.
In some implementations, dewatering operations are conducted so as to avoid stacking flow and deposition.
Laminar Channel Flow Many examples of laminar channel flow have been observed across all deposition cells and beaches. Laminar channels develop during periods of relatively low velocity and stable discharge with well flocculated MFT.
However, under certain conditions (low velocity), laminar channel flow have been observed with relatively poorly flocculated material as well.
Laminar channel flows tend to follow the underlying beach gradient and maintain a Sinuosity Index (SI), length of actual channel divided by down-gradient travel distance approximately equal to 1 but ranging to 2.5. See Figs 18a and 18b (SI
=
1.3). A measure of sinuosity is relevant for correcting the flow path length for average flow velocity calculations.
Length of Actual Channel Streamline Sinuosity Index (5) = ___________________________________________ Downgradtent (Shortest) Length Figure 5-1:3 Examples of channel sinuous laminar channel flow Laminar flows typically vary in width from 0.2 to 0.5 metres in width and 10 to 30 centimetres in depth with an approximately semi-circular cross-section.
Several representative channel cross-sections as measured in the field are presented in Fig 19. These measurements were taken in dried channels where tailings were known to have flowed. An image of a flowing laminar channel is shown in Fig 19.
Laminar channel flows tend to develop on slopes less than 3% and consistently on slopes between 1 and 2%.

, Turbulent Channel Flow Turbulent channels develop when frictional forces within the fluid are overwhelmed by inertial forces that de-stabilize the flow. Such flows are typically observed when discharge rates are high and when low density material is produced.
Turbulent channels may be identified in the field by the presence of standing waves, hydraulic jumps, as well as pools and riffles along the flow path.
Turbulent channels tend to assume a geometry so that the sinuosity index (SI) is much greater than 1 (SI in the order of SI = 2 to 4). Turbulent flow channels will form on practically any bed slope given the right conditions. Turbulent flows are dominant on bed slopes greater than 3.5%.
Both laminar and turbulent channel flows are responsible for distributing material down and across the beach; however, the different depositional mechanics at play are discussed herein.
Uniform Sheets and Coating Flows Uniform sheet flows demonstrate similar thickness across the majority of the sheet so that the material uniformly blankets or coats the surface onto which it is deposited. It is rarely observed in the field. When confined by higher-strength material, the uniform sheet may approximate the behaviour of a laminar channel;
however, the apparent cross section will be different with a depth much less than the radius.

Rheological Observations Relationships between Flow Velocity and Yield Stress The series of flow observations conducted at Cell A are summarized in Table 4.

Where channel flow is indicated with no laminar or turbulent qualifier, the flow 5 was not easily distinguished as having characteristics of either.
Table 4: Summary of flow monitoring from Cell A
Measured Yield Stress Measured Surface Dynamic from Slump Density Visual Assessment , Velocity, v Pressure, Test ID Test (Pa) (kg/m3) of Flow (m/s) pv2/2 (Pa) 1 20.0 1100 channel 1 550.0 2 40.0 1100 channel 2.5 3437.5 3 120.0 1300 stack . 0.4 104.0 4 100.0 1250 sheet 0.4 100.0 5 60.8 1268 channel (laminar) 0.66 276.2 6 17.7 1195 channel (turbulent) 1.5 1344.4 ; 7 17.7 1195 channel (laminar) 1 597.5 8 22.8 1210 channel (turbulent) = 2.22 2981.7 9 102.6 1299 channel (laminar) , 1.08 757.6 10 1.6 1054 channel (turbulent) ' 2.15 2436.1 11 7.9 1147 channel (laminar) 1.06 644.4 12 255.6 1353 stack-sheet 0.61 251.7 13 36.6 1238 channel (laminar) 0.85 447.2 Measurements obtained at Cell A suggest a relationship between the flow velocity and yield stress (see Fig 20) which is consistent with qualitative 10 observations. Generally, high yield stress materials flow slowly down the beach, if at all, while low yield stress tailings flow relatively quickly.

Change in Yield Stress with Flow Distance Select flows were also monitored along the length of their flow path as a basis for determining the effects of flow on the tailings behaviour and rheological properties. As the flocculated MFT flows down the beach at a pseudo-constant rate, the static yield stress of the material will tend to decrease in most cases. In essence, the flocculated structure is subjected to energy inputs over time and the structure is degraded. Fig 21 illustrates this phenomenon based on field monitoring of flocculated MFT flows.
Field monitoring of static yield stress in samples extracted from active flows suggest that most flows undergo structural degradation over the beach;
however, there was one example (A2 Trial) where the static yield stress was shown to increase marginally. In this isolated case, the measured yield stress increased from 76 Pa to 81 Pa over a distance of 34 metres.
For all other monitored flows in Table 4, the degree of degradation was variable and shown to be related to the flow velocity. Figs also illustrate the degree of degradation of the material as a function of the velocity (or kinetic energy) of the flow.
The vertical axis of Fig 22 plots the fraction of the initial static yield stress lost over time in which the material flowed down the beach. Generally, the degree of strength loss over time was relatively small with a maximum degradation rate of 1.4% of the initial static yield stress per second of flow. Furthermore, the decrease in static yield stress was more apparent at higher flow velocities, suggesting enhanced degradation of the flocculated MFT over time.
Variability In the case of greater variability of process inputs and the sensitivity of flocculation implementations, one may observe some or all of the aforementioned =
flow regimes during a deposition period (typically four to sixteen hours in duration).
Well-flocculated material that is deposited by means of a stacking or quiescent channel flow can easily be eroded and carried downstream by a subsequent high energy stream. In contrast, a relict channel may be in-filled by subsequent stacking or low energy channel deposits.
The variability in flow regime allows for the movement of materials away from the point of discharge and leads to a highly heterogeneous distribution of materials across the final deposit.
5.4 Process Controls on Flow The kinetic energy of the discharge stream is dictated by the flow rate and density of the stream. The velocity and density of the stream are dependent on the feed MFT characteristics and the capacity for the pumping system to deliver the treated material to the cell. Oscillations in the system may occur, for example due to variable source streams and flocculation.
The initial kinetic energy is a relevant component of the system as it represents the potential for generation of free flowing channels, sheet, or stacking flows and the maximum amount of energy imparted to those various systems. Along the course of flowing downstream, the system is continuously losing energy to internal and external frictional forces as well as losing potential energy as the flow loses elevation head (potential energy).
Flow Specific Deposition Mechanisms for Flocculated Mature Fine Tailings Sedimentation & Segregation Field sampling and monitoring suggest that particle settling is not a predominant mechanism of deposition for at least the first 45 metres of beach where bulk =

shear rates are sufficiently high to retain solids in suspension. Samples were taken from the same section of flow as it progressed down the beach. The results of the field sampling and laboratory analyses are presented in Table 5 and Figs 23A to 23C. The Location column refers to the distance along the flow path, relative to the discharge spigot. Each Trial (e.g. A, B, C, and so on) refers to a single flow channel that was monitored.
Table 5: Summary of laboratory results from initial round of flow monitoring at Cell A
BmW %Fines (<44 urn), as MB Slurry Trial Sample Location% Bitumen %Mineral %Water Total Percentage of method % Clay CWR
(m) .tal or Is , 111141 _ A 1 2 2.38 25.59 71.42 99.38 79.91 1500 64.58 0.231 A 2 26 2.96 24.96 72.04 99.96 78.64 1367 58.88 0.204 A ' 3 44 2.49 25.35 71.67 99.50 81.82 1479 63.68 0.225 B 1 2 2.89 26.35 70.26 99.50 79.33 1277 55.00 0.206 B 2 26 2.93 25.40 71.05 99.38 82.92 1137 49.02 0.175 B 3 44 2.94 26.17 70.25 99.36 83.22 1414 60.91 0.227 1 2 2.09 26.37 71.04 99.49 80.15 1055 45.50 0.169 C 2 26 2.16 24.42 74.23 100.80 81.45 1112 47.93 0.158 C 3 44 2.31 24.51 73.10 99.93 80.81 1558 67.05 0.225 1 2 2.70 25.60 71.62 99.92 79.86 1236 53.26 0.190 D 2 26 3.09 24.92 72.09 100.11 84.35 799 34.54 0.119 D 3 34 3.12 24.33 71.98 99.42 78.15 800 34.59 0.117 E 1 1 2 2.12 24.83 72.31 99.27 88.02 1021 44.02 0.151 E 2 26 1.68 24.63 72.94 99.25 88.79 950 41.01 0.138 E 3 34 1.42 23.88 74.93 100.24 91.14 1271 54.78 0.175 AVERAGE 2.49 25.15 72.06 ' 99.70 82.57 1198.49 51.65 0.18 Note here that the physical composition of the flowing mass does not change significantly over the intervals sampled. While there are variations in the reported parameters over the flow length, those differences may be attributable to measurement error. By weight, the percent mineral solids does not change considerably in any flow observation (different flows are denoted by the Trial identifier). This indicates that the moisture content of the flow is not changing considerably over these intervals. The relative percent of fines (<44pm) and clay =
=

content (calculated from the Methylene Blue Index test) do not show increase as one might expect if the coarser fractions were settling out.
A second round of monitoring and sampling was conducted under similar flow conditions to verify the results of the initial observations. The laboratory results are summarized in Table 6 and Figs 24A to 240.
Table 6: Summary of laboratory results for second round of flow monitoring at Cell A
% Fines BMW by closure (<44 urn), as MB Slurry Location Percentage of method % Clay Trial Sample % Bitumen %Mineral %Water Total CWR
(m) Total Solids YVIMINIWA*Ifikaft41;--0.; 4Vittilt A 1 4 1.48 26.35 71.18 99.01 85.82 1370 58.98 0.218 A 2 30 2.12 27.90 69.22 99.23 89.04 1082 46.65 0.188 A 3 ao 2.45 32.11 64.55 99,12 86.66 976 42.11 0.209 13 1 4 1.49 27.51 70.97 99.96 87.53 1173 50.56 0.196 13 2 30 1.58 27.93 69.93 99.44 86.52 1189 51.25 0.205 C 1 4 1.71 26.75 71.13 99.59 86.24 1108 47.76 0.180 2 30 1.75 27.99 69.41 99.15 88.90 830 35.86 0.145 D 1 4 2.02 30.20 67.76 99.98 77.35 1232 53.07 0.237 2 30 1.89 25.91 71.27 99.07 81.48 1413 60.83 0.221 AVERAGE
1.83 28.07 69.49 99.39 85.51 1152.43 49.68 0.20 The second set of results confirms that there is no apparent sedimentation over the first 30 metres of beach within the flowing channels; however, sedimentation is likely to have occurred beyond at lower reaches of the cell as the flow velocity decreases. One notable exception is Trial A (Table 6), where there is an apparent 6% increase in solids content. This flow does represent the lowest recorded velocity on this monitoring occasion, with a measured surface velocity of 0.67 m/s. It is conceivable that this represents the critical velocity for the onset of sedimentation.

Yield Stress Fluid Stoppage Several observations were made during the course of field activities, for example:
= At some point along the beach length, and preferentially where the slope of the bed flattens and approaches zero, flocculated tailings will slow 5 down, spread out laterally, and come to rest;
= The distance at which this occurs, relative to the discharge point, appears to be a function of the flow rate within the channel, and inversely related to the relative yield strength of flocculated MFTs;
= For observations of sheet flow, the run-out distance appears to be limited 10 and related to the internal strength of the material; that is, sheet flows were observed to continue expanding across the deposition cell until a channel broke through and spread material further down-slope.
Overbanking & Lateral Aggradation Overbanking indicates the occurrence in unsteady, non-uniform flows when the volume of water and sediments passing through a channel increases such that the flow depth exceeds the channel depth, and hence water and sediments are carried over the banks and deposit on adjacent floodplains as flows recede.
Fig 25 presents schematic cross sections of a flow of material through a channel as it experiences overbanking.
20 The phenomenon of overbanking is the predominant deposition mechanism observed in flocculated MFT channel flows experiencing highly variable discharge rate and density on sloped beaches. The flooding of the channel promotes lateral and vertical growth of the deposit while still allowing for down-gradient movement away from the point of discharge.

The yield stress of a flow based on the measured geometry of the levees that border an open channel may be determined by calculations, for example. For flows of high yield stress materials, the width of those levees will be larger than for flows of a lower yield stress material. According to such calculation methods as well as observations, flocculated MFT can build expansive levees near the head of the deposit when high yield stress material is discharged.
Overbanking processes, along with chaotic scrolling of the channels across the deposition area, constitutes can provide a significant depositional mechanism for this material.
The Flow Map ¨ A Rheology-Energy Conceptual Model Conceptualization of the Flow Map A conceptual model was developed to describe the relationship between rheology and energy in the context of the overland flow of flocculated tailings.
Flow maps have been applied by fluid dynamicists to the description of multiphase liquid-gas flows restricted to pipes or channels; however, in the present description, the concept of a flow map is applied to a yield stress fluid (flocculated MFT). The flow map relates the characteristic static yield stress of the tailings to the energy associated with the flowing mass and is generalized to include observed flow regimes (Fig 26).
The flow map may be interpreted by considering system energy as a combination of potential and kinetic energy embodied in the flow. If the flows are observed at a constant elevation along the flow path (that is, a set of observations of different flow regimes are made from the same place along the stream), then the flow systems can be compared on the basis of kinetic energy alone. The effects of gravitational head are thus ignored and velocity head defines the system.

, In this conceptual model, as system energy increases for lower yield stress materials, the dominant flow regime is observed to be laminar channel (including particles undergoing Brownian motion and experiencing hydrodynamic effects), while at higher energy levels the flow changes to a more turbulent regime dominated by inertia. At the highest yield stresses, flocculated MFT forms stacks or lobes. In flocculated MET, this can be interpreted as the result of a higher solids volume fraction generated through flocculation of once-dispersed particles.
However, as the system's energy level is increased (e.g. the rate of discharge is increased), the stacking regime transitions to sheet flow and eventually to channelling flow, moving once again into an inertia-dominated system.
Fig 26 was developed after field observations of numerous hours of active discharge to containment cells. Quantification of the major boundaries could provide operators numerical guidance for managing the overland flow of tailings in their facilities.
Development of Numerical Boundaries For quantification of system energy in Fig 26, the unit volume kinetic energy was used.
The initial observations and measurements are summarized above (see Table 4).
Where the visual flow assessment states only 'channel', the flow was not easily defined as either turbulent or laminar. For these observations, the measured flow velocity and dynamic pressure were later used to assign the specific flow regime on the basis of trends from the other data.
Fig 27 plots the field observations and measurements with the conceptual boundaries superimposed. For consistency, all of the data plotted here represent measurements taken at the initiation of flow, that is, within approximately two metres of the discharge spigot. This distance allows for the stabilization of the flow after leaving the plunge pool which may be turbulent. For this reason, these , = 68 data can be taken to represent the initial rheological-energetic state of the material and the point at which the maximum unit volume kinetic energy (dynamic pressure) is achieved in the flow. Field data suggests that the conceptual model depicted in the flow map satisfies the range of observed field conditions.
The boundary separating laminar and turbulent channel regimes is situated at 1050 J/m3 to separate the data; however, the data collected did not provide a sufficiently dense distribution of data points to allow the exact determination of this transition.
Given a typical measured density of 1100 kg/m3, the flow velocity at this transition will be approximately 0.95 m/s. Furthermore, by assuming a typical channel flow depth of 10 centimetres, a Froude number of 0.96 is computed.
This calculation suggests that the sub-critical to critical transitional boundary should be positioned closer to 1.0 m/s or 1100 J/m3, thereby expanding the laminar channel domain slightly. The Froude criterion introduced previously appears to be a good indicator of the observed transitional flow region.
An Integrated Conceptual Model Based on the nature of flocculated MFT, an integrated conceptual model for the deposition of solids was developed. In some instances, fluid stoppage is predominant and may disperse solids over a large areal extent of the beach, yet in other instances a variable flow rate will cause channel overbanking and confine deposition to relatively narrow corridors down the beach.
The depositional process to dominate a flow will be based on the plotting position of the flocculated MFT in the rheology-energy space (see flow map conceptual model in previous section). A hybridized conceptual model is provided in Fig and a predictive model for this behaviour may be developed.

Note the appearance of an erosion space in the high energy, low yield stress region. While erosion of underlying materials is conceivable across almost all regions of the flow map, deep channels are primarily observed to form in the turbulent regime.
Beach Profile Modeling Background Beaches created by natural processes have long been known to form non-monotonic, concave-up surfaces. The beach profiles of hydraulically placed sediments in marine environments have also been analysed and reflect the same geometry.
More recently, the surfaces created by the sub-aqueous and sub-aerial deposition of mine tailings have also been studied and have been shown to demonstrate the same characteristics as naturally formed beaches and hydraulically-placed sediments.
Observations Profiles All fully developed deposits (i.e. filled to capacity) were characterized by concave-up geometry; however, due to the variable beach length and thickness of deposit, direct comparison is difficult.
Fig 29 shows a representative set of normalized profiles, converted from raw field measurements. The horizontal axis represents the relative horizontal distance from the point of discharge to the end of the deposit (either the end of the flow or a body of water) while the vertical axis plots the vertical relief of the deposit surface relative to the total elevation difference between the point of discharge and the end of the deposit. The survey stations measured along the profiles are plotted without interpolation for later comparison to theoretical profiles (solid lines). A perfectly planar slope is provided for reference (dashed grey).
Henceforth, the area of the deposit proximal to the point of discharge will be referred to as the head and the most distal point as the toe.
5 The selected profiles plotted in Fig 29 represent a range of deposits with total lengths from 118 to 275 metres, maximum thicknesses (as measured at the head) from approximately 1.0 to 3.5 metres, and bed inclinations ranging from 0.8% to 3.5%. For reference, Profile S5A is taken from Cell D1 and profile is taken from Cell 6S. Furthermore, the profiles reflect various MFT source ponds 10 and variable discharge conditioning. The range of expected deposit profiles of flocculated MFT is demonstrated by Fig 29.
Note that all profiles clearly demonstrate a non-planar, concave-up surface.
The clustering of data points suggests the following form for description of the normalized profile according to Equation 21. The best-fit value of the concavity 15 index, c, varies but clusters around a nominal value of 2Ø Note that the divergence of the measured values beyond 70% of the beach length (x/H = 0.7) is due to the inherent difficulty in defining the end of the deposit and the influence of the variable extent of the water pool that accumulates at the downstream berm. Furthermore, the largest divergence from the master profiles is observed in 20 deposits that were surveyed remotely while the deposit was actively dewatering and subsiding, while profiles that adhere more stringently to the empirical curves were more completely dewatered and trafficable by foot. This introduces the observation of time-dependency of the profiles.
A power law function would be better suited to match the observed profiles of 25 S4A/B and S5A/B for example; however, as a logarithmic function has no theoretical basis, the exponential curve is preferred.

Energy-Based Profile Modelling Modeling Objective The objective of this modeling exercise is to assess the validity of the McPhail (1994) stream power approach as a predictive tool for estimating the two-dimensional beach profile of a flocculated MFT deposit.
Model Selection The McPhail (1994) model was selected as it requires only the input of deposition cell geometry, operational discharge parameters (flow rate, density) and an estimate of the rheological properties which can be obtained through laboratory and field measurements. The hydraulic theory applied in the McPhail (1994) model is valid for steady, uniform, laminar flow. While these conditions do not always apply in the field given variations in feed quality and flocculation efficacy, these conditions are met more frequently than unsteady, surging flows when the system is operated diligently.
Conceptual Model The conceptual model for flow and deposition is best illustrated by Fig 26 which presents the predominant flow regimes for flocculated MFT. The McPhail (1994) model is applicable, in theory, only to the laminar channel regime. In this regime, the loss of kinetic energy from a slowing stream must be counterbalanced by a potential energy increase which indicates that the channel base, and hence the beach surface, aggrades with time.
Data Review During the course of field investigations, beach profiles from both fresh and dewatered deposits were obtained through level profiling and remote sensing with Light Detection and Ranging (LIDAR) techniques. LIDAR surveys were conducted by MDH Engineered Solutions (Sasktatoon, Canada) along with post-processing. Generally, level profiling was used for short beaches (less than metres) while longer beaches, up to 300 metres, were surveyed using stationary, land-based LIDAR equipment.
Baseline rheological data was provided for use in this modeling effort. The baseline data provides a range of plausible rheological parameters that are not easily obtained in the field (namely, dynamic viscosity and coefficients for the Herschel-Bulkley model). This baseline data was fitted with Herschel-Bulkley parameters for use in the McPhail (1994) model.
Application of the McPhail (1994) Profile Model Rationale Given the inherent variability in process and discharge conditions, the most robust beach profile prediction model is preferred. The McPhail (1994) stream power-entropy approach allows for profile predictions based on assumed average or back-analyzed rheological parameters. In reality, the beach will be formed by a variety of materials with varying rheological behaviours; however, the majority of the beach profile will reflect the average rheological behaviour which may be difficult to determine experimentally.
In this case, the energy-rheology flow map was used to determine the appropriate rheological parameters to apply. Upon examination, it is apparent (based on the distribution of field observations) that an average flow condition may be best described by a laminar channel regime. Stacking flows are limited in influence to several tens of metres from the point of discharge (assuming a header height of 1 to 4 metres). Sheet flows are more rarely observed and will thus not be considered. Turbulent flows, while prevalent under high discharge conditions, will tend to flow all the way to the toe of the cell and have little positive contributions to the beach building process.

Conveniently, a laminar channel regime will be accurately reflected in the hydraulic theory employed in the McPhail (1994) model.
General Assumptions for Model Runs Beyond the hydraulic and rheological assumptions required for the McPhail (1994) model, several assumptions regarding operational parameters were required. These assumptions were supported by observations, field measurements, and laboratory analysis wherever possible.
For all model runs, unless otherwise noted, a discharge rate of 450 m3/hr (divided between 4 spigots) was used. During field observations, this was the operational flow rate target. There is uncertainty associated with this parameter;
hence its effect was evaluated in further sensitivity analysis.
A density of 1150 kg/m3 was used for all model runs, unless otherwise noted.
This density represents the average measured field density at the point of discharge at Cell 1N and corresponds to a mineral concentration of approximately 21% (assuming a specific gravity of solids of 2.65). This value is somewhat lower than the lab measured values during this investigation in the range of 23% to 26% solids. Furthermore, this range is lower than operational targets, but represents the reality of a variable discharge. The low solids content and density represent a conservative parameter which results in the development of long, flat beaches. For modeling purposes, the field measurements of density are considered to be more reliable. Within the range of observed field values, the beach profile is relatively insensitive to the density.
The Herschel-Bulkley rheological parameters were assumed from laboratory results presented above as an initial best-guess. The values of the coefficients were adjusted within a reasonable range during the calibration process to achieve the best fit for the measured beach profiles. For consistency, the same calibrated Herschel-Bulkley model parameters were assumed for all modeled õ

profiles to demonstrate the predictive capability of the model. The effect of varying the yield stress is examined below.
Calibration and Application to Fresh Deposits Although numerous beach profiles were measured during field investigations, few exhibit ideal boundary conditions for back-analysis and calibration. The effects of boundary conditions may also be regarded as a potential source of uncertainty.
Due to the deposition history and boundary conditions at Cell D1 (rectangular geometry, near-uniform 1% bed slope, and a fully developed profile), calibration was first carried out on this surface.
During calibration, average rheological parameters (Herschel-Bulkley model) from laboratory testing were used as initial best-guess values. From there, the average empirical rheological values were determined by fitting the stream-entropy profile to the measured profile elevations. Equation 23 and Fig 30 present the Herschel-Bulkley model resulting from calibration of the McPhail profile to the measured beach profile.
T = 23 + 3y 47 Equation 23: Herschel-Bulkley model assumed for McPhail beach profile modeling The fitted beach profile is provided in Fig 31 and shows good agreement between the surveyed profile (red squares) and the simulated profile (blue crosses). Note that there is an apparent discrepancy between the measured and simulated beach run-out distance. The model fits a beach with a total length of approximately 190 metres, while the apparent measured beach is 250 metres in length. At these distances from discharge, defining the extent of the deposit becomes difficult. Errant product (poorly flocculated MFT) tends to run to the toe of the cell, filling the lower reaches with a shallowly-sloping, near horizontal deposit that is often water-covered. Extrapolation of the bed shows that the measured deposit thickness beyond 190 metres is no more than 0.2 m (or less than 0.1% of the run-out distance and no more than 5.7% of the maximum 5 deposit thickness.
Within the McPhail (1994) model, the calculated bulk yield stress and the yield stress sustainable by the fluid are calculated at each point down the beach according to the calculated flow velocity and shear rate in a laminar channel of assumed geometry. The values shown in Fig 32 demonstrate reasonable 10 agreement.
The McPhail (1994) stream power model provides a good fit with the fully-developed, field-measured profile with reasonable rheological parameters assumed from laboratory and field testing.
Verification and Validation 15 To verify the model calibration, another profile (not used in calibration) was selected to assess the goodness of fit. A typical deposit from the System 4 deposition area was selected for analysis as this was the only other fully developed deposit with boundary conditions consistent with ongoing deposition cell construction (i.e. long cells with relatively shallow bed slopes).
20 The same Herschel-Bulkley model was used and the bed slope and header height parameters were adjusted to reflect the conditions at the System 4 site.
The resulting profile is presented in Fig 33.
Application to Dewatered Deposits Due to safe access concerns and the limited availability of remote surveying 25 equipment, many of the deposit profiles were obtained some time after the discharge and deposition period. After periods of days and weeks, the deposits show significant signs of settlement and consolidation due to dewatering and evaporative drying. This change in volume over time must be considered if these dewatered-deposit surveys are to be used for validation of the model.
Using the assumed flow curve from the calibration discussed herein, the following initial deposit profile is generated (Fig 34). It should be noted that the bed slope was not known definitively but was assumed to vary between 1% and 3%. During modeling, the most reasonable profile was achieved using a 1% bed slope.
Once again, the calculated shear stress and sustainable shear stress show reasonable agreement (Fig 35).
Upon closer inspection of the profile, the discrepancy between the predicted fresh deposit profile and the as-measured field profile is evident. The date of surveying was approximately one month after deposition of the uppermost 0.5 metres of flocculated MFT (full deposit was placed in lifts of approximately 0.5 metres thickness at the head).
The average settlement across this section is in the range of 10 to 20 centimetres which is reasonable for a deposited layer of approximately 50 centimetres initial thickness (20% to 40% settlement). Note also that the proportion of settlement is greater near the toe of the cell where the deposit thickness decreases. The greater overall volume reduction is likely attributable to evaporative losses and the nearly complete desiccation of the flocculated MFT
near the toe as no water was retained at the lower portion of this cell.
Some Results During the calibration stage, the McPhail profile was successfully fitted to the field-measured profile of Cell D1 using a Herschel-Bulkley rheological model õ =

which is considered reasonable when compared to laboratory and field measurements. A direct comparison of measured and predicted surface elevations are provided in Fig 36. The results show good model fit, with all predicted points within 40 cm of the measured elevations. An acceptable error of 10 to 15% of the maximum deposit thickness was deemed acceptable for this exercise.
The stream power model is applicable directly to fresh deposits that have not experienced significant settlement or consolidation due to dewatering. Beyond this timeframe, one should consider consolidation and settlement effects. The applicability of this model to fresh deposits may range from a period of hours in optimal water release material to a period of weeks for sub-optimal water release material. During the validation stage of modeling, the McPhail model was successfully applied to a measured profile of a fresh deposit from the System Cell B1 deposition area. A comparison of the predicted and measured deposit surface elevations is presented in Fig 37. There was a local area where the measured beach profile was more than 50 cm below the predicted profile, but generally the model provides an acceptable fit.
To assess how a dewatered deposit profile compares to a fresh deposit, and whether the McPhail (1994) model could still describe the surface, the model was applied to the Cell 6S profile. The analysis suggests that the profile can still be explained using the McPhail (1994) model and that back-analysis of older deposits may be possible if the effects of dewatering and consolidation are understood. Fig 38 illustrates the goodness of fit for this exercise.
As there is some uncertainty regarding the operational parameters assumed in this study, and as the nature of the flocculated MET could change over time and as the process is developed, a sensitivity analysis was undertaken to evaluate the effect of discharge rate, bed slope, and flocculate MFT yield stress on the beach profile. As the profile presents a complex geometry, a simplification was required to compare the modeled deposits. To achieve this, the run-out distance of the beach was taken as the basis for comparison. For high concavity beach profiles, the run-out distance will tend to be shorter than for beaches of low concavity, owing to the relationship between yield stress and concavity.
The effect of yield stress was first analyzed by systematically changing the yield stress component of the Herschel-Bulkley model used in the McPhail (1994) calculations. The run-out distance was predicted for four different yield stresses over four different bed slopes, producing a total of 16 sensitivity runs. For all runs, the discharge rate was held at 450 m3/hr and the height of the discharge point above ground surface was 3.5 metres. The results of these runs are presented in Fig 39.
Two main observations are apparent from the compilation of Fig 39, namely:
= Predicted run-out distance (and hence beach profile) is strongly influenced by basal slope when the yield stress is less than 50 Pa and this sensitivity increases as the yield stress decreases; and = Predicted run-out distances for materials with a yield stress above 100 Pa are relatively insensitive to basal slope, and are not predicted to achieve run-out distances greater than 50 m on bed slopes up to an including 3.5%.
In addition to yield stress, the effect of discharge rate was examined with an additional eight sensitivity runs. These run results are presented in Fig 40.
Observations from Fig 40 include the following:
= Predicted run-out distance is positively correlated (non-linearly) and highly sensitive to discharge rate; and that = A theoretical maximum run-out distance at the current operational discharge rate (450 m3/hr) is approximately 400 m on a 3.5% slope.

When the run-out distance is expressed as a function of discharge rate, the utility of the data becomes more apparent (Fig 41).
Some Discussion Three full-scale beach profiles were used to calibrate and validate the McPhail (1994) model for flocculated MFT beach profile prediction. All model runs showed good correlation with the field-surveyed beach profiles. The apparent discrepancy in run-out distance is attributable to observation of errant product filling the lower reaches of the cell, which is not representative of the overall deposit geometry.
The McPhail (1994) model may be used to back-analyze dewatered and consolidated deposits in order to ascertain the original rheology of the tailings;
however, fresh deposits should be used for analyses wherever possible.
Furthermore, a sensitivity analysis of key operational parameters has revealed that the dependence of run-out distance on discharge rate and basal slope is strongest when the yield stress of flocculated MET is below 50 Pa.
Application and Discussion of Results Flow Control General In some scenarios, flow control may refer to the management of discharge rates such that the tailings are deposited to a cell in a manner which precludes unnecessary shearing of the material, erosion of the previous beach surface, or stacking of high viscosity tailings requiring mechanical intervention.
On the basis of the flow map that has been created for flocculated MET in the present description, guidelines can be established for the effective management , of tailings discharge rates to the receiving cell. For example, both stacking flows and turbulent flows are undesirable for everyday operation.
Stacking may be avoided by increasing the energy inputs which can be achieved by increasing the discharge rate at the spigot. This may be achieved in two main 5 ways, namely:
= Increase the flow rate to the entire cell, or = Increase the flow rate through individual spigots by restricting or preventing flow through neighbouring spigots.
These operational changes could increase the dynamic pressure of the flow and 10 move it into a channel flow regime; however, increases in the pressures for spigots and distribution lines have to be maintained within their safe operating limits and pump capabilities.
For turbulent flows, the solution is more easily achieved. The operator should reduce the flow rate through each spigot such that the velocity of flow on the 15 beach falls back to within the limits established for laminar flow.
Reducing the flow rate to the cell may not be desirable for production purposes or for hydraulic reasons; however, additional spigots could be introduced to the system thereby reducing the average flow rate through each outlet. These additional spigots could be opened or closed depending on the requirements of the system.
20 Laminar flows may be routinely achieved by managing the discharge rate such that it is tailored to the yield stress and density of the material that is produced as a result of the flocculation process.
=

Sustaining a Laminar Channel Flow A laminar flow regime will be sustained when the tailings embody sufficient energy to preclude stacking and back-up without exceeding some critical value above which turbulent flow is initiated.
If the flow velocity measurements embodied in the flow map are assessed directly (Fig 42), a range of Froude numbers from 1.11 to 1.36 is computed (assuming a mean flow depth of 10 cm) between the laminar and turbulent observation points. This value range likely exhibits some density dependence, and hence the laminar-turbulent boundary would not be vertical in the flow map, as it is depicted in Fig 42 (density effects have been eliminated from this plot by assuming a constant density).
For flocculated tailings with a static yield stress equal to or above 100 Pa, the minimum flow velocity required to sustain channel flow (and avoid stacking) is shown to be approximately 0.65 m/s. Assuming a channel radius and depth equal to 15 cm, this equates to a minimum required flow rate of 83 m3/hr supplied by the spigot to the beach channel when the material yield stress is above 100 Pa.
To preclude turbulent flow of materials below 100 Pa, the channel velocity on the beach should not exceed a nominal range of 0.95 to 1.2 m/s. Again, assuming the channel geometry as above, each spigot should supply between 120 and 150 m3/hr to the beach.
For the purposes of flow control, findings would suggest that an ideal operating range for discharge to a deposition cell, as currently configured, would be from 330 to 480 m3/hr. By operating below or above this range, the operator is , exposed to risk of frequent back-ups and turbulent channel flows.
=

Profile Control Data presented above, suggests that many of the measured beach profiles, when compared on a normalized basis, exhibit the same degree of concavity although the scale of those deposits varies considerably. From an operational perspective, the control of the deposit profile may be practically difficult to achieve given the variability of feed and discharge conditions, and the chaotic nature of beach formation; however, several conclusions may be drawn from the present description to direct operators in controlling run-out distance and maintaining effective cell coverage.
The run-out distance of a tailings beach is shown to be highly sensitive to discharge rate and sensitive to slope when the tailings yield stress is low (below 50 Pa). The higher the slope of the beach, the more prudent the operator must be when regulating the discharge rate. Second, stacking and back-up is more probable when the tailings yield stress exceeds 100 Pa; a pseudo-uniform sheet flow may be achievable between 50 and 100 Pa on bed slopes between 1 and 3.5%, but this yield stress range may be practically difficult to maintain.
Design of Deposition Cells Although sheet flow or pseudo-sheet flow may be considered ideal, predictions based on the McPhail (1994) model show run-out distances (for the yield stress range defined in the flow map, and assuming current discharge practices) no greater than about 100 metres. For the design of a deposition cell, the designer should consider selecting the bed slope and cell dimensions that accommodate deposits formed by laminar channel flows.
The sensitivity analysis introduced herein suggest that a 3.5% bed slope produces a wide range of deposit lengths and implies that this bed slope is inappropriate for tailings with yield stress values lower than 50 Pa. A more appropriate bed slope for a robust design would likely lie between 1.5 and 2%.

The length of the deposition cell should be based on the anticipated maximum run-out distance of the tailings. The reason for this is so that the lowest reaches of the cell can be used for the collection and control of water (derived from the dewatered tailings and from surface run-off), and so that this body of water does not adversely impact the dewatering and drying of material near the end of the deposit. Based on an assumed header height of 3.5 metres and a bed slope ranging between 1.5 and 2%, a minimal cell length of between 220 and 270 metres should be adopted (allowing for up to 20 metres of horizontal space for water management).
Storage Estimation This application provides estimates of cell storage based on various geometries and assumptions regarding beach concavity. Estimates of storage capacity can be made by estimating the area of a longitudinal cross-section and multiplying by the cell width. There are three primary methods for estimating the cross-section of a sloping deposit, namely:
= Assume a monotonic beach slope and approximate the deposit volume using a wedge-shape;
= Assume a concavity index, c, and use Equation 21 to estimate the cross sectional area of the deposit (through integration of the exponential function); or = Integrate a polynomial function that is fitted to the McPhail (1994) beach profile.
Concavity indices typical of flocculated MFT deposits range from approximately 2.0 to 2.5 based on observations presented herein. This concavity leads to a discrepancy between monotonic storage calculations and those that accommodate concave beaches. This discrepancy is independent of the beach length, bed slope, or header height, and is dependant only on the degree of concavity.
Table 7 presents estimates of deposition cell storage based on an assumed length and width, and varying degrees of cell usability (dictated by water control measures), header height, and beach concavity. The measured range of concavity translates into a discrepancy of 14 to 27% when compared to monotonic storage estimates.
Table 7: Disposal cell capacity for deposits with monotonic (planar) and concave profiles Usable Cell Concave Monotonic Cell Cell Deposit Cell Header Fill Calc.
% Monotonic Length, I Width, w Concavity Length Height, H
Capacity Capacity Over-Estimate (m) (m) Index, c (%) (m) (m3) (m3) 200 50 85 1 2 3,675 4,250 14%
200 50 85 2 2 7,350 8,500 14%
200 50 85 3 2 11,024 12,750 14%
200 50 100 1 2 4,323 5,000 14%
200 50 100 2 2 8,647 10,000 14%
200 50 100 3 2 12,970 15,000 14%
200 50 85 1 2.5 3,121 4,250 27%
200 50 85 2 ; 2.5 6,242 8,500 27%
200 50 85 3 2.5 9,363 12,750 27%
200 50 100 1 2.5 3,672 5,000 27%
200 50 100 2 2.5 7,343 10,000 27%
200 50 100 3 2.5 11,015 15,000 27%
Fig 43 illustrates the volume discrepancy in two-dimensions.
The apparent increased storage volume in the toe of the deposit (x/H= 0.8 to 1.0) is the result of the exponential representation of the profile and accounts for only 2.5 to 5% of the total volume estimate. It can thus be expected that a monotonic beach profile used for storage estimates will overestimate flocculated MFT
capacity by approximately 10 to 20%.
The most accurate estimate of deposition cell capacity may be achieved by examining the volume captured by a McPhail (1994) beach profile. The simplest method for determining this volume is by fitting an appropriate function through the beach profile, integrating that function and evaluating it at the limit of the beach length, correcting for the bed slope, and multiplying by the cell width.

Polynomial functions (second-order) are fitted to McPhail (1994) beach profiles in the Figs. These functions are easily integrated to determine the cross-sectional area. Table 8 presents a comparison of volume estimates for deposits represented by monotonic, concave, and McPhail (1994) model profiles for some study cells.
Table 8: Comparison of volume estimates for study cells Concavity Concavity Monotonic Estimate Estimate McPhail Study Cell Estimate (c = 2.0) (c = 2.5) Estimate D1 16,625 14,298 12,136 13,957 65 8,000 6,880 5,840 4,865 B1 20,000_ 17,200 14,600 16,523 This application shows that integration of a McPhail (1994) profile provides a reasonably conservative estimate of storage volume.
Additional Remarks The flow and deposition of flocculated MET on a sloping beach can be described in the context of a rheology-energy conceptual model. The conceptual model, or 20 flow map, can provide designers and operators with a useful framework for managing beach development in a sub-aerial deposition cell.

Beach surveys demonstrate the trend of strongly concave profiles which has significant repercussions for tailings planning and may be considered when calculating storage volumes.
Furthermore, the McPhail (1994) stream power model can provide a robust tool for estimating final beach profiles developed from the sub-aerial discharge of polymer-flocculated mature fine tailings. The model has been validated against field-scale measurements and is consistent with the rheology-energy conceptual model developed to describe the flocculated MFT beaching behaviour.
The entropy-based stream power model is capable of predicting fresh deposit profiles with knowledge of discharge conditions and rheological parameters derived from standard laboratory testing that are validated with field measurements. The model can be used for back-analysis and determination of flow-scale rheological behaviour.
The utility of the flow map conceptual model and the field-validated profile model can help in the design and operation of a sub-aerial disposal cell for flocculated tailings.
The boundaries or transitional regions between the observed flow conditions may be determined to complement the above approaches. The flow map concept could also be applied to other tailings which exhibit variable flow behaviours due to flocculation or thickening processes.
Incorporating changes of rheology as a function of flow distance could also complement model.
There is some evidence to suggest that slopes near the boundaries of large disposal cells may be influenced by adjacent containment berms. This may be due to wall friction effects at the field scale, changes in dewatering and settlement behaviour near the containment berms, or variability in the discharge quality near the beginning or end of the delivery pipes. This boundary effect may be factored in for storage estimates.
Some measured profiles after a winter were noted to have a remarkably planar surface. Visually, this observation is applicable to other similar deposits on a 4%
slope. This may indicate a slow creep phenomenon or differential consolidation as the result of freeze-thaw action on a relatively steep inclination. If underlying materials remain at sufficient moisture content on a steep gradient, the deposit could very slowly flow down-gradient, much as a glacier flows down-valley under the influence of gravity. Observations show that freeze depth in these deposits is typically no more than one metre; hence deposits over one metre in thickness could experience creep, even when the deposit pore water is frozen near-surface.
The McPhail (1994) entropy model could be adapted to produce a three-dimensional surface representing the ultimate deposit surface. The model would require an algorithm for lateral distribution of material through channel meandering, an inherently stochastic process. A correction would be required for the reduced gradient as the assumed path of the channel deviates from the discharge centreline (and hence the maximum gradient of gravitational potential).
A three-dimensional model may further help determine capacity estimates for containment facilities.
Further findings, techniques and implementations Referring to Fig 44, it has been found that the slope and height of the initial upstream portion 200 of the deposition cell 116 does not significantly affect the beach profile further downstream of the outlet 202. The initial upstream portion 200 may thus be provided and configured such that the deposited flowing flocculation material can rapidly release water without being oversheared. The profile of the deposited material that flows down the deposition cell 116 is concave up.
It has also been found that steep slopes of deposition cells combined with low yield stress material can result in dendritic flows patterns leading to inefficient use of the entire deposition area.
It has also been found that basal permeability can be reduced due to the presence of bitumen and/or flocculant in the water which can result in clogging.
Thus, effective water release in the form of run-off can further aid in dewatering the material since basal drainage may be reduced in some implementations.
Referring to Fig 45, in some implementations the dewatering operation may be performed to deposit a first thin lift 204 followed by a second thin lift 206 and a final third thin lift 208, in a deposition cell 116 defined in part between a head berm 210 and a toe berm 212. The lifts may be deposited such that the third thin lift 208 reaches to or proximate the toe berm, as illustrated. The slope of the bottom of the cell, the lift thickness, the flow regime and rheology of the deposited material may be managed to achieve three subsequent lifts in a season.
Referring to Fig 46, deposited -material that has flowed down the deposition cell and undergone dewatering may be windrowed into multiple elongated piles 214.
In some implementations, the deposited material is substantially all windrowed into the piles 214 to expose elongated areas 216 into which further deposition may occur. In some implementations, the windrowed piles 214 are between 1 and 2 meters high. In some implementations, before windrowing, the deposited material is left for a sufficient amount of time in order to enter an evaporation dominated drying phase. The deposited material may be left until it has an increased yield stress, e.g. above 10 or 15 kPa, and a high solids content, e.g. at least about 70 wt%. The windrowed piles 214 may have increased surface area compared to the lift within the deposition cell, thus increasing the evaporative drying of the material during the evaporation dominated phase of drying.
It is noted that a challenge in deposition activities is caused by re-wetting of previously dried material by a subsequent lift of flocculated fine tailings.
Referring to Fig 53, it has been observed that dried material can be re-wetted and will decrease in solids content until reaching an apparent equilibrium solids content of approximately 70 wt%. When deposited material having below 70 wt% solids is subjected to rewetting, the material tends to not decrease in solids content after 1 or 5 days and is thus not significantly impacted by re-wetting. When deposited material having above 70 wt% solids, e.g. above 95 wt% solids, the material decreases in solids content and tends toward a lower solids content equilibrium point, which in some examples may be about 70 wt%. Thus, secondary lifts placed on dried material can cause re-wetting of the dried material back down to 70 wt% solids. Windrowing may be implemented to displace material of 70 wt% solids or above off of the main surface of the deposition cell and allow a subsequent lift of flocculated fine tailings to be deposited onto the cleared surface, thereby reducing re-wetting of the windrowed material. In some implementations, the step of windrowing may be conducted once the deposited material has partially dried to have a solids content above the re-wetting equilibrium concentration, e.g. above 70 wt%.
Referring to Fig 46, in some implementations, outlet switching may occur, where a first deposition is done at a first outlet 202a at one berm 210 followed by a second deposition at a second outlet 202b at the opposite berm 212, thereby forming a first lift 218 and a second lift 220.
Referring to Fig 48, deposited material may also be relocated once it has at least partially dewatered. The relocated material 222 may be placed in a disposal cell 224, which may have the appropriate berm structures 226 for the type and strength of the material.

Referring now to Fig 49, flocculation material may be deposited into a multi-cell arrangement 228 that is configured such that outlets 230 expel the flocculation material onto beaches or cells sized and configured to facilitate release water to flow and accumulate into channels. Some channels 232a may receive release 5 water from two opposed areas where the flocculation material has dewatered, and they may flow and join together to form combined channels 232b. Combined channels 232b may connect with other channels to form a final release water channel 232c that is collected by a collection device 234. The accumulated release water 236 may be transported back to water ponds, tailings ponds, water 10 treatment and/or extraction facilities for reuse.
Referring to Fig 50, in some implementations, a flume 238 may be provided at a downstream end of the deposition cell 116. The flume 238 has an opening through which the water is allowed to flow, in order to facilitate forming a release water channel and/or measurement of water release. The flume 238 may be 15 provided spanning between two side berms 240a and 240b.
In some implementations, the dewatering operation may be seasonally optimized by laying down lifts of the flocculation tailings into the deposition cell during pre-determined seasons or seasonal conditions. For example, a first lift may be provided during spring, followed by a second lift in summer. A third lift is provided 20 in the fall, and it is allowed to undergo freeze-thaw.
Referring to Fig 51, jetties may be provided. The jetties may include coke and/or sand. Jetties may provide for improved distribution of material throughout the cell, for example.
In some implementations, various swales may be provided around the deposition 25 cells in order to recover release water.
In some implementations, a deposited lift of flocculation tailings is allowed to form an upper crust. In some implementations, the dewatering operation is managed so as to adapt the deposition and farming with the quality of flocculation.
For example, for well flocculated material with elevated NWR, a lift of about 25 to 35 cm may be laid out for dewatering and eventual drying without farming. For variable quality of the flocculation tailings, thinner lifts of between 10 and 20 cm are laid out and are windrowed prior to laying down a second lift, and/or a lift between 15 and 45 cm is laid down and subjected to spreading to even out the thickness. In some implementations, a crust may provide strength to the overall deposit.
Flocculation operations In some implementations, thick fine tailings that may or may not be pre-treated are subjected to a chemical aided dewatering operation such as flocculation.
The thick fine tailings may have been screened to remove coarse debris, aerated or subjected to gas injection, and/or shear thinned. The thick fine tailings may be subjected to a recovery process to recover one or more valuable substances included in the tailings, such as metals, hydrocarbons, residual ore, and the like, that may benefit the pre-treatment operation. The thick fine tailings may be subjected to a chemical treatment to alter its chemistry, such as its pH or salt content.
After the pre-treatment, the pre-treated thick fine tailings have a composition allowing improved mixing and processing with dewatering chemical additives (e.g. flocculant).
In some implementations, the dewatering operation includes chemical addition to react with the fine solid particles in the tailings followed by deposition of the tailings. The chemical addition may include addition of a flocculant, such as a long chain polymer, in the form of solid particles, an aqueous solution or a dispersion of particles in a liquid medium.

Referring to Fig 1, the pre-treated fine tailings 106 is supplied to the chemical addition unit 108. A chemical additive 110, such as a flocculant, may be added to the pre-treated tailings for mixing in the chemical addition unit. The flocculant may be added in the form of an aqueous solution where the flocculant is at least partially dissolved. The flocculated mixture 112 is then transported and deposited to form a lift of deposited material.
In some implementations, the thick fine tailings may be treated with a flocculant solution. Since the extent and quality of the flocculation reaction depends on the mixing of the flocculant into the thick fine tailings, the thick fine tailings may be shear thinned to provide improved mixability. Thus, initial dispersion stage of the flocculant solution into the thick fine tailings is enhanced. The next stage of the dewatering operation includes conditioning the thick fine tailings by inputting a sufficient energy to cause the formation and rearrangement of flocculated fine tailing solids to increase the yield shear strength. The next stage is the water release stage. The flocculated tailings are thus subjected to sufficient energy such that the floc network structure allows water release. The input energy should not be so great as to over-shear the flocculated material. The water release stage should be attained without over-shearing the flocculated structure that can then be deposited. The flocculated thick fine tailings may be deposited to allow the water release and the formation of a deposit which can be allowed to dewater and dry.
The chemical addition unit may be any kind of device for mixing a chemical with the pre-treated tailings and may be a solid-liquid mixer, liquid-liquid mixer, in-line static mixer, impeller mixer, tank mixer, T-joint mixer, Y-joint mixer, or another type of mixer. The mixer may be selected and operated to provide rapid mixing of the chemical into the pre-treated fine tailings. One or more mixers may also be used in series or in parallel.

One example implementation of a mixer configuration is a pipeline reactor design that enables rapid mixing thick fine tailings, such as MFT, and flocculant solution.
The MFT is supplied from an upstream pipeline into a mixing zone. The mixing zone includes an injection device for injecting the flocculant solution. The injection device may also be referred to as a "mixer". The injection device may include an annular plate, injectors distributed around the annular plate and a central orifice defined within the annular plate. The MFT accelerates through the central orifice and forms a forward-flow region and an annular eddy region made up of turbulence eddies. The injectors introduce the flocculant solution directly into the eddy region for mixing with the turbulent MFT. The recirculation of the MFT eddies back towards the orifice results in mixing of the flocculant solution into the MFT forward-flow. The forward-flow region expands as it continues along the downstream pipe. For some mixer embodiments, the forward-flow region may be a vena-contra region of a jet stream created by an orifice or baffle. The main flow of the MFT thus draws in and mixes with the flocculant solution, causing dispersion of the flocculant solution, and flocculation thus commences in a short distance of pipe. This example injection device may also be referred to as an "orifice mixer". A range of orifice diameter "d" to downstream pipe diameter "D"
may be 0.25 ¨ 0.75.
In some implementations, the flocculant added to the thick fine tailings may be a polymer flocculant with a high molecular weight. The polymer flocculant may be anionic in overall charge, e.g. approximately 30% anionicity, which may include certain amounts of cationic monomer and may be amphoteric. The polymer flocculant may be water-soluble to form a solution in which the polymer is completely dissolved. It is also possible that the polymer is mostly or partly dissolved in the solution. The polymer flocculant may be composed of anionic monomers selected from ethylenically unsaturated carboxylic acid and sulphonic acid monomers, which may be selected from acrylic acid, methacrylic acid, allyl sulphonic acid and 2-acrylamido-2-methyl propane sulphonic acid (AMPS), etc., and the salts of such monomers; non-ionic monomers selected from acrylamide, methacrylamide, hydroxy alkyl esters of methacrylic acid, N-vinyl pyrrolidone, acrylate esters, etc.; and cationic monomers selected from DMAEA, DMAEA.MeCI, DADMAC, ATPAC and the like. The polymer flocculant may also have monomers enabling interactions that results in higher yield strength of the flocculated MFT. Synthetic polymers such as thickeners maybe used, and may have hydrophobic groups to make associative polymers such that in aqueous solution the hydrophobic groups join together to limit water interactions and stick together to provide a desired shear, yield stress or viscosity response in solution and when reacted with the MFT. The polymer flocculant may also have a desired high molecular weight, for instance over 10,000,000, for certain flocculation reactivity and dewatering potential. The polymer flocculant may be generally linear or not according to the desired shear and process response and reactivity with the given MFT.
Other chemical enhanced dewatering operations may also be employed and may use organic and/or inorganic and/or organic-inorganic hybrid chemical additives.
It is noted that the thick fine tailings may be derived from an oil sands mining and extraction operation, but may also be derived from other types of mining and extraction operations. It should be noted that while various implementations describe herein refer to thick fine tailings, such techniques may also be applied to other thick fine suspensions in general.
Any one of the various pre-treatment techniques and various deposition techniques may be used in combination with one or more other techniques, for example in an overall thick fine tailings dewatering operation.

Claims (37)

95

1. A process for treating thick fine tailings, comprising:
contacting the thick fine tailings with a flocculant to produce flocculated fine tailings;
depositing the flocculated fine tailings onto a sub-aerial deposition area, wherein the flocculated fine tailings has depositional kinetic energy and yield stress to provide flow channels in a laminar flow regime;
allowing the flocculated fine tailings to flow down the deposition area where the flocculated fine tailings comes to rest, thereby forming a deposit; and allowing the deposit to dewater and dry.

2. The process of claim 1, wherein the depositional kinetic energy on a unit volume basis is between 250 J and 1250 J and the yield stress is between 2 Pa and 175 Pa.

3. The process of claim 1 or 2, wherein the depositional kinetic energy on a unit volume basis is between 500 J and 1000 J and the yield stress is between 10 Pa and 75 Pa.

4. The process of any one of claims 1 to 3, wherein the depositional kinetic energy is such that the average velocity is between 0.25 m/s and 1.25 m/s upon deposition.

5. The process of any one of claims 1 to 4, wherein the depositional kinetic energy is such that the average velocity is between 0.5 m/s and 1 m/s upon deposition.

6. The process of any one of claims 1 to 5, wherein the flocculated fine tailings have a static yield stress of at least 100 Pa and the depositional kinetic energy is such that the flow velocity is at least 0.65 m/s.

7. The process of any one claims 1 to 6, wherein the depositing of the flocculated fine tailings is performed such that the deposit has a lift height of at most 30 cm.

8. The process of any one claims 1 to 7, further comprising:
adjusting the yield strength of the flocculated fine tailings by:
adjusting dispersion conditions of the flocculant into the thick fine tailings;
adjusting clay-to-water ratio of the thick fine tailings;
adjusting dose of the flocculant relative to the thick fine tailings;
adjusting concentration of the flocculant in a flocculation solution that is contacted with the thick fine tailings; and/or adjusting shear conditioning of the flocculated fine tailings prior to deposition.

9. The process of any one of claims 1 to 8, further comprising:
adjusting the depositional kinetic energy by:
adjusting a flow rate of the flocculant into the thick fine tailings;
and/or adjusting the depositional kinetic energy by adjusting a deposition outlet size.

10.The process of any one of claims 1 to 9, wherein the depositing of the flocculated fine tailings is performed via at least one discharge outlet positioned above the sub-aerial deposition area.

11. The process of claim 10, wherein the at least one discharge outlet is positioned above the sub-aerial deposition area sufficiently to avoid blocking or burying thereof by the deposited flocculated fine tailings.

12. The process of claim 10 or 11, wherein the at least one discharge outlet comprises a plurality of discharge outlets arranged in spaced apart relation along a header berm of the sub-aerial deposition area.

13. The process of any one of claims 1 to 12, wherein the flow channels have a depth of between 10 cm and 30 cm.

14. The process of any one of claims 1 to 13, wherein the depth of the flow channels is between 15 cm and 25 cm.

15. The process of any one of claims 1 to 14, wherein the flow channels each have a sinuosity index between 1 and 2.5.

16. The process of claim 15, wherein the sinuosity index of each of the flow channels is less than 2.

17. The process of any one of claims 1 to 16, wherein the flow channels each have a width between 0.2 m and 0.5 m.

18. The process of any one of claims 1 to 17, further comprising:
providing the sub-aerial deposition area with a sloped bottom surface.

19.The process of claim 18, wherein the sloped bottom surface has a generally constant slope.

20. The process of claim 18 or 19, wherein the sloped bottom surface has a slope less than 3%.

21. The process of any one of claims 18 to 20, wherein the sloped bottom surface has a slope between 1% and 2%.

22. The process of any one of claims 1 to 21, wherein the depositing further comprises:
overbanking a portion of the flocculated fine tailings from the flow channels over side banks thereof, thereby forming lateral aggradations.

23.The process of claim 22, wherein the overbanking is performed periodically.

24.The process of claim 22, wherein the overbanking is performed continuously.

25. The process of any one of claims 1 to 24, wherein the depositing of the flocculated fine tailings is performed at variable discharge flow rates.

26. The process of any one of claims 1 to 25, wherein the depositing of the flocculated fine tailings is performed at variable discharge densities.

27.The process of any one of claims 1 to 26, further comprising:
ceasing or reducing deposition of the flocculated fine tailings;
forming an empty channel defined by deposited flocculated fine tailings; and re-depositing flocculated fine tailings having sufficient yield strength into the empty channel to fill the channel to side banks thereof.

28. The process of any one of claims 1 to 27, further comprising:
forming a plunge pool of the flocculated fine tailings upon release into the sub-aerial deposition area, the plunge pool dissipating energy of the expelled flocculated fine tailings; and feeding the flow channels with flocculated fine tailings from the plunge pool.

29. The process of claim 28, wherein the plunge pool has a depth between 10 cm and 50 cm and a length between 20 cm and 50 cm elongated in the direction of the flow channel.

30. The process of any one of claims 1 to 29, wherein the depositing is performed above a velocity to avoid substantial sedimentation until the flocculated fine tailings has flowed at least 40 m down the sub-aerial deposition area.

31. The process of any one of claims 1 to 30, wherein the sub-aerial deposition area includes an upstream region having an upstream slope and a downstream region having an downstream slope, the upstream slope being steeper than the downstream slope.

32. The process of claim 31, wherein the upstream slope is between 1% and 3% and the downstream slope is between 0% and 1%.

33. The process of any one of claims 1 to 32, wherein at least one of the flow channels extends down the sub-aerial deposition area between 100 m and 300 m.

34. The process of any one of claims 1 to 33, wherein the thick fine tailings are derived from an oil sands mining and extraction operation.

35. The process of any one of claims 1 to 33, wherein the thick fine tailings comprise mature fine tailings (MFT).

36. The process of claim 35, wherein the MFT is derived from an oil sands mining and extraction operation.

37. The process of claim 35 or 36, wherein the MFT is retrieved from a tailings pond prior to contacting with the flocculant.