Note: Descriptions are shown in the official language in which they were submitted.
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MEASUREMENT AND PROCESS CONTROL TECHNIQUES FOR DEWATERING OF
THICK FINE TAILINGS
FIELD OF THE INVENTION
The present invention generally relates to measurement and process control
techniques
for thick fine tailings, such as mature fine tailings that may be found in
tailings ponds.
BACKGROUND
Tailings derived from mining operations, such as oil sands mining, are often
placed in
dedicated disposal ponds for settling.
The settling of fine solids from the water in tailings ponds can be a
relatively slow
process. Certain techniques have been developed for dewatering thick fine
tailings.
Dewatering of thick fine tailings can include contacting the fine tailings
with a flocculant
and then depositing the flocculated fine tailings in a deposition area where
the deposited
material can release water and eventually dry.
There are several factors that may influence performance of thick fine
tailings dewatering
operations and there are various challenges related to measurement and process
control.
SUMMARY OF THE INVENTION
In some implementations, there is provided a method of treating thick fine
tailings,
including: contacting the thick fine tailings with an aqueous solution
including a
flocculating agent to disperse the flocculating agent into the thick fine
tailings and to
produce a flocculation tailings material; conditioning the flocculation
tailings material,
wherein the conditioning includes subjecting the flocculation tailings
material to shear and
modifying rheological properties of the flocculation tailings material in
order to produce
conditioned flocculated tailings; dewatering the conditioned flocculated
tailings to produce
release water and a dewatered tailings material; allowing the dewatered
tailings material
to dry to obtain a dried tailings material; and regulating treatment of the
thick fine tailings,
including: obtaining a sample of the conditioned flocculated tailings prior to
dewatering,
and determining dewatering characteristics of the sample including measuring a
Net
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Water Release (NWR) with respect to the thick fine tailings from the sample,
to thereby
obtain a measured NWR parameter; and adjusting at least one operating
condition in
accordance with the measured NWR parameter to increase the release water
produced
in the dewatering step.
In some implementations, the at least one operating condition includes: dosage
of the
flocculating agent with respect to the thick fine tailings; concentration of
the flocculating
agent in the aqueous solution; type of flocculating agent; flow rate of the
thick fine
tailings; and/or shear imparted to the flocculation tailings material.
In some implementations, adjusting the dosage of the flocculating agent with
respect to
the thick fine tailings includes modifying the concentration of the
flocculating agent on a
total clay basis of the thick fine tailings.
In some implementations, adjusting the dosage of the flocculating agent with
respect to
the thick fine tailings includes modifying the flow rate of the aqueous
solution supplied
into the thick fine tailings.
In some implementations, adjusting the dosage of the flocculating agent with
respect to
the thick fine tailings includes modifying the concentration of the
flocculating agent in the
aqueous solution.
In some implementations, adjusting the dosage of the flocculating agent with
respect to
the thick fine tailings includes modifying the flow rate of the thick fine
tailings.
In some implementations, adjusting the concentration of the flocculating agent
in the
aqueous solution includes dissolving and/or dispersing a modified amount of
the
flocculating agent into water to form the aqueous solution.
In some implementations, adjusting the type of the flocculating agent includes
selecting a
flocculating agent from a set of candidate flocculating agents.
In some implementations, adjusting flow rate of the thick fine tailings
includes modifying
the volumetric or mass flow rate of the thick fine tailings.
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In some implementations, adjusting the shear imparted to the flocculation
tailings material
includes modifying a configuration of a conditioning assembly through which
the
flocculation tailings material flows.
In some implementations, modifying the configuration of the conditioning
assembly
includes modifying a pipe length through which the flocculation tailings
material flows.
In some implementations, adjusting the shear imparted to the flocculation
tailings material
includes modifying the flow rate of the thick fine tailings.
In some implementations, obtaining the sample comprises removing a volume of
conditioned flocculated tailings from an outlet of a conditioning pipeline
that supplies the
conditioned flocculation tailings to the dewatering step.
In some implementations, determining dewatering characteristics of the sample
includes
a NWR testing scheme that includes at least one NWR test including: draining
the sample
for a given period of time; measuring an amount of water released from the
sample
during the given period of time, as a Gross Water Release (GWR); and
subtracting a
corresponding amount of added water present in the aqueous solution added to
the thick
fine tailings from the GWR, to obtain the measured NWR parameter.
In some implementations, the given period of time is at least 10 minutes, at
least 1 hour,
at least 12 hours, and/or at least 24 hours. In some implementations, the
given period of
time is between 20 minutes and 2 hours.
In some implementations, the NWR testing scheme further includes: conducting a
first
NWR test on a first portion of the sample, for a short given period of time,
thereby
obtaining a first measured NWR; conducting a second NWR test on a second
portion of
the sample, for a longer period of time, thereby obtaining a second measured
NWR;
comparing the first measured NWR and the second measured NWR, to determine
whether the dosage of the flocculating agent into the thick fine tailings is
within an optimal
range.
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In some implementations, the longer given period of time is at least 6 times
longer than
the short period of time. In some implementations, the short given period of
time is less
than 1 hour. In some implementations, the short given period of time is less
than 30
minutes. In some implementations, the longer given period of time is at least
6 hours. In
some implementations, the longer given period of time is at least 12 hours.
In some implementations, if the first measured NWR is at least about 70% of
the second
measured NWR, the dosage of the flocculating agent into the thick fine
tailings is
considered to be within an optimal range; and if the first measured NWR is
below about
70% of the second measured NWR, the dosage of the flocculating agent into the
thick
fine tailings is considered to be outside of the optimal range, and the dosage
of the
flocculating agent is adjusted.
In some implementations, the method also includes adding an additional amount
of the
flocculating agent to the sample; measuring the NWR to determine whether the
sample is
overdosed or underdosed in the flocculating agent; and adjusting the dosage of
the
flocculating agent with respect to the thick fine tailings if the sample is
overdosed or
underdosed, in order to increase the NWR.
In some implementations, adjusting the dosage of the flocculating agent
includes
adjusting the flow rate of the thick fine tailings, adjusting the flow rate of
the aqueous
solution, and/or adjusting the concentration of the flocculating agent in the
aqueous
solution.
In some implementations, the measured NWR parameter is compared to pre-
determined
data for determining the step of adjusting the at least one operating
condition.
In some implementations, the method includes conducting a flocculant dosing
test to
determine an initial dosage approximation of the flocculating agent required
to flocculate
a sample of the thick fine tailings and obtain a positive measured NWR in
response to
shear conditioning beyond a peak static yield stress.
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In some implementations, the initial dosage approximation of the flocculating
agent is
obtained by titration.
In some implementations, the method includes conducting a dose sweep test to
determine variation of measured NWR as a function of dosage of flocculating
agent
5 around the initial dosage approximation; determining a revised dosage in
accordance
with a maximum NWR range; and utilizing the revised dosage to prepare the
aqueous
solution including the flocculating agent for the step of contacting with the
thick fine
tailings.
In some implementations, there is provided a method of treating thick fine
tailings,
including: contacting the thick fine tailings with an aqueous solution
including a
flocculating agent to disperse the flocculating agent into the thick fine
tailings and to
produce a flocculation tailings material; conditioning the flocculation
tailings material,
wherein the conditioning includes subjecting the flocculation tailings
material to shear and
modifying rheological properties of the flocculation tailings material in
order to produce
conditioned flocculated tailings; dewatering the conditioned flocculated
tailings to produce
release water and a dewatered tailings material; allowing the dewatered
tailings material
to dry to obtain a dried tailings material; performing a flocculating agent
dosage test
including determining an approximate dosage of the flocculating agent required
to
transformed a sample of the thick fine tailings into a sample conditioned
flocculated
tailings having a positive measured Net Water Release (NWR) in response to
shear
conditioning beyond a peak static yield stress, wherein the flocculant dosage
test further
comprises: conducting a first NWR test on a first portion of the sample, for a
short given
period of time, thereby obtaining a first measured NWR; conducting a second
NWR test
on a second portion of the sample, for a longer period of time, thereby
obtaining a second
measured NWR; comparing the first measured NWR and the second measured NWR, to
determine whether the dosage of the flocculating agent into the thick fine
tailings is within
an optimal dosage range; and adjusting at least one operating condition in
accordance
with the flocculating agent dosage test, to provide the flocculating agent
within the optimal
dosage range to increase the release water produced in the dewatering step.
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In some implementations, the flocculant dosage test further includes:
conducting a dose
sweep test to determine variation of NWR as a function of dosage of
flocculating agent
around the approximate dosage that is considered as an initial dosage
approximation;
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determining a revised dosage in accordance with a maximum NWR range from the
dose
sweep test; and utilizing the revised dosage to prepare the aqueous solution
including the
flocculating agent for the step of contacting with the thick fine tailings.
In some implementations, the approximate dosage of the flocculating agent is
obtained
by titration techniques.
In some implementations, the measured NWR is determined according to a NWR
testing
scheme that includes at least one NWR test including: obtaining the sample of
the
conditioned flocculated tailings; draining the sample for a given period of
time; measuring
an amount of water released from the sample during the given period of time,
as a Gross
Water Release (GWR); and subtracting a corresponding amount of added water
present
in the aqueous solution added to the thick fine tailings from the GWR, to
obtain the
measured NWR parameter.
In some implementations, the given period of time is at least 10 minutes, at
least 1 hour,
at least 12 hours, at least 24 hours, or between 20 minutes and 2 hours.
In some implementations, the NWR testing scheme further includes: conducting a
first
NWR test on a first portion of the sample, for a short given period of time,
thereby
obtaining a first measured NWR; conducting a second NWR test on a second
portion of
the sample, for a longer period of time, thereby obtaining a second measured
NWR;
comparing the first measured NWR and the second measured NWR, to determine
whether the dosage of the flocculating agent into the thick fine tailings is
within an optimal
range.
In some implementations, the loner given period of time is at least 6 times
longer than the
short period of time. In some implementations, the short given period of time
is less than
1 hour. In some implementations, the short given period of time is less than
30 minutes.
In some implementations, the longer given period of time is at least 6 hours.
In some
implementations, the longer given period of time is at least 12 hours.
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In some implementations, if the first measured NWR is at least about 70% of
the second
measured NWR, the dosage of the flocculating agent into the thick fine
tailings is
considered to be within an optimal range; and if the first measured NWR is
below about
70% of the second measured NWR, the dosage of the flocculating agent into the
thick
fine tailings is considered to be outside of the optimal range, and the dosage
of the
flocculating agent is adjusted.
In some implementations, the method includes adding an additional amount of
the
flocculating agent to the sample; measuring the NWR to determine whether the
sample is
overdosed or underdosed in the flocculating agent; and adjusting the dosage of
the
flocculating agent with respect to the thick fine tailings if the sample is
overdosed or
underdosed, in order to increase the NWR.
In some implementations, adjusting the dosage of the flocculating agent
includes
adjusting the flow rate of the thick fine tailings, adjusting the flow rate of
the aqueous
solution, and/or adjusting the concentration of the flocculating agent in the
aqueous
solution.
In some implementations, there is provided a method of determining
flocculating agent
dosage for flocculating thick fine tailings, including: obtaining a sample of
the thick fine
tailings; adding a dosage of flocculating agent to the sample of thick fine
tailings and
subjecting the same to shear conditioning to produce a shear conditioned
flocculated
sample; conducting a first Net Water Release (NWR) test on a first portion of
the shear
conditioned flocculated sample, for a short given period of time, thereby
obtaining a first
measured NWR; conducting a second NWR test on a second portion of the shear
conditioned flocculated sample, for a longer period of time, thereby obtaining
a second
measured NWR; and comparing the first measured NWR and the second measured
NWR, to determine whether the dosage of the flocculating agent is within an
optimal
dosage range.
In some implementations, each of the first and second NWR tests comprises:
draining the
shear conditioned flocculated sample for a given period of time; measuring an
amount of
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water released from the shear conditioned flocculated sample during the given
period of
time, as a Gross Water Release (GWR); and subtracting a corresponding amount
of
added water present in the aqueous solution added to the thick fine tailings
from the
GWR, to obtain the measured NWR.
In some implementations, the longer given period of time is at least 6 times
longer than
the short period of time.
In some implementations, the short given period of time is less than 1 hour.
Optionally,
the short given period of time is less than 30 minutes.
In some implementations, the longer given period of time is at least 6 hours.
Optionally,
the longer given period of time is at least 12 hours.
In some implementations, if the first measured NWR is at least about 70% of
the second
measured NWR, the dosage of the flocculating agent into the thick fine
tailings is
considered to be within an optimal range; if the first measured NWR is below
about 70%
of the second measured NWR, the dosage of the flocculating agent into the
thick fine
tailings is considered to be outside of the optimal range
In some implementations, there is provided a system for testing water release
from a
sample of flocculated thick fine tailings, including: a sample retrieval
device for retrieving
a sample of the flocculated thick fine tailings including a floc matrix and
water; a strainer
having a support surface for receiving the sample of the flocculated thick
fine tailings, the
strainer including apertures sufficiently sized such that the support surface
supports the
floc matrix and allows a portion of the water to flow through the apertures as
release
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water; a receptacle configured below on a downstream side of the strainer for
receiving
the release water passed through the apertures; and a measurement device for
measuring the amount of release water received in the receptacle over a time
period.
In some implementations, the strainer has an upward concave construction.
In some implementations, the apertures have a pre-determined size that is
sufficiently
small to prevent substantially all of the floc matrix from passing there-
through.
In some implementations, the strainer a metal mesh. In some implementations,
the mesh
is at most 1 millimeter.
In some implementations, the strainer is composed of a non-absorbent material.
In some implementations, the strainer and the receptacle are configured such
that a
substantial amount of the release water passes into the receptacle in a
downward fashion
under gravity induced drainage.
In some implementations, the measurement device includes a volumetric
measurement
device for measuring a volume of the entire contents of the receptacle.
In some implementations, the receptacle includes measurement indicia for
allowing
volumetric measurement of the release water over time. In some
implementations, the
receptacle includes a measurement cylinder. In some implementations, the
receptacle
includes a bucket.
In some implementations, the measurement device includes a drying apparatus
for drying
the contents of the receptacle to determine an amount of solids contained in
the contents
of the receptacle and thereby for determining a liquid water release value.
In some implementations, there is provided a method of treating thick fine
tailings,
comprising:
contacting the thick fine tailings with a flocculating agent;
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producing a flocculated tailings material; and
dewatering the flocculated tailings material; and
wherein the flocculating agent is added to the thick fine tailings at a dosage
within an optimal dosage range determined according to a dosage test
comprising:
conducting a first Net Water Release (NWR) test on a first thick fine
tailings sample, thereby obtaining a first measured NWR, the first
NWR test comprising:
adding a sample dosage of the flocculating agent to the first
thick fine tailings sample;
producing a first sample of flocculated material; and
draining the first sample of flocculated material for a short
period of time;
conducting a second NWR test on a second thick fine tailings
sample, thereby obtaining a second measured NWR, the second
NWR test comprising:
adding the sample dosage of the flocculating agent to the
second thick fine tailings sample;
producing a second sample of flocculated material; and
draining the second sample of flocculated material for a
longer period of time compared to the short period of time;
and
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comparing the first measured NWR and the second measured
NWR, to determine whether the sample dosage is within the
optimal dosage range.
In some implementations, there is provided a method of determining a
flocculant dosage
for a flocculating agent to add to thick fine tailings for dewatering of the
thick fine tailings,
the method comprising:
conducting a first Net Water Release (NWR) test on a first thick fine
tailings sample, thereby obtaining a first measured NWR, the first NWR
test comprising:
adding a sample dosage of the flocculating agent to the first thick
fine tailings sample;
producing a first sample of flocculated material; and
draining the first sample of flocculated material for a short period of
time;
conducting a second NWR test on a second thick fine tailings sample,
thereby obtaining a second measured NWR, the second NWR test
cornprising:
adding the sample dosage of the flocculating agent to the second
thick fine tailings sample;
producing a second sample of flocculated material; and
draining the second sample of flocculated material for a longer
period of time compared to the short period of time; and
comparing the first measured NWR and the second measured NWR to
determine whether the first measured NWR is above a threshold
percentage of the second measured NWR;
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8c
selecting the sample dosage as the flocculant dosage if the first measured
NWR is above a threshold percentage of the second measured NWR.
In some implementations, there is provided a method of determining a
flocculant dosage
for a flocculating agent to add to thick fine tailings for dewatering of the
thick fine tailings,
the method comprising:
adding a sample dosage of the flocculating agent to a thick fine tailings
sample, and producing a flocculated material sample;
allowing the flocculated material sample to release water for a short period
of time, and measuring a short-time Net Water Release (NWR);
allowing the flocculated material sample to release water for a longer
period of time compared to the short period of time, and measuring a long-
time NWR;
comparing the short-time NWR and the long-time NWR to determine
whether the sample dosage is to be used as the flocculant dosage.
In some implementations, there is provided a method of treating thick fine
tailings,
comprising:
contacting the thick fine tailings with a flocculating agent;
producing a flocculated tailings material; and
dewatering the flocculated tailings material; and
wherein the flocculating agent is added to the thick fine tailings at a dosage
determined according to the method as defined herein.
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In some implementations, there is provided a method of treating thick fine
tailings,
comprising:
contacting the thick fine tailings with a flocculating agent to disperse the
flocculating agent into the thick fine tailings and to produce a flocculation
tailings material;
conditioning the flocculation tailings material, wherein the conditioning
comprises subjecting the flocculation tailings material to shear and
modifying rheological properties of the flocculation tailings material in
order
to produce conditioned flocculated tailings;
dewatering the conditioned flocculated tailings to produce release water
and a dewatered tailings material; and
regulating treatment of the thick fine tailings, including:
obtaining a sample of the conditioned flocculated tailings prior to
dewatering, and
determining dewatering characteristics of the sample including
measuring a Net Water Release (NWR) with respect to the thick
fine tailings from the sample, to thereby obtain a measured NWR
parameter, wherein determining dewatering characteristics of the
sample comprises a NWR testing scheme that includes at least two
NWR tests, each NWR test comprising:
draining the sample for a given period of time; and
determining a net amount of water released from the sample
during the given period of time, to obtain the measured
NWR parameter; and
wherein the NWR testing scheme further comprises
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conducting a first NWR test on a first portion of the sample,
for a short given period of time, thereby obtaining a first
measured NWR;
conducting a second NWR test on a second portion of the
sample, for a longer period of time, thereby obtaining a
second measured NWR; and
comparing the first measured NWR and the second
measured NWR, to determine whether the dosage of the
flocculating agent into the thick fine tailings is within an
optimal range; and
adjusting at least one operating condition in accordance with the measured
NWR parameter to increase the release water produced in the dewatering
step.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1 represents layers for a tailings pond.
Fig 2 is a perspective view schematic of a dewatering operation.
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Fig 3 represents a schematic view of a dewatering operation.
Fig 4 represents a graph of shear yield stress versus time.
Fig 5 represents the effect of Net Water Release (NWR) on drying times.
Fig 6 represents variation of the NWR and yield stress as a function of
mixing. Fig 7
represents variations of NWR and strength versus the length of a pipeline.
Fig 8 represents a sample of flocculation tailings on a strainer.
Fig 9 represents a decision tree.
Fig 10 represents variations of the NWR versus the Clay to Water Ratio (CWR).
Fig 11 represents variations of dose on a clay basis versus yield stress.
Fig 12 represents variation of the NWR versus dose.
Fig 13 represents an embodiment of the tailing laboratory test methodology,
including
dose find test (phase I) and a dose sweep test (phase II) and optionally a
full
characterization test (phase III) and/or an optional standard drying test
(phase IV).
Fig 14 represents variations of the NWR versus the Clay to Water Ratio (CWR).
DETAILED DESCRIPTION
The present invention generally relates to measurement and process control
techniques
for dewatering operations of thick fine tailings, such as mature fine tailings
that may be
found in tailings ponds.
"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
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particles to the fines that is less than or equal to 1. The thick fine
tailings has a fines
content sufficiently high such that 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
5 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).
"MFT" refers to a tailings fluid that typically forms as a layer in a tailings
pond and
10 contains water and an elevated content of fine solids that display
relatively slow settling
rates. For example, when whole tailings (which include coarse solid material,
fine solids,
and water) or thin fine tailings (which include a relatively low content of
fine solids and a
high water content) are supplied to a tailings pond, the tailings separate by
gravity into
different layers over time. The bottom layer is predominantly coarse material,
such as
sand, and the top layer is predominantly water. The middle layer is relatively
sand
depleted, but still has a fair amount of fine solids suspended in the aqueous
phase. This
middle layer is often referred to as MFT. MFT can be formed from various
different types
of mine tailings that are derived from the processing of different types of
mined ore. While
the formation of MFT typically takes a fair amount of time when derived from
certain
whole tailings supplied form an extraction operation (e.g., between 1 and 3
years under
gravity settling conditions in the pond), it should be noted that MFT and MFT-
like
materials may be formed more rapidly depending on the composition and post-
extraction
processing of the tailings, which may include thickening or other separation
steps that
may remove a certain amount of coarse solids and/or water prior to supplying
the
processed tailings to the tailings pond.
Brief overview of flocculation and dewatering operations
In some implementations, the thick fine tailings are suspensions derived from
an oil
sands mining operation and are oil sands mature fine tailings (MFT) stored in
a tailings
pond. For illustrative purposes, the techniques described below are described
in
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reference to this example type of thick fine tailings, i.e., MFT, however, it
should be
understood that the techniques described can be used for thick fine tailings
derived from
sources other than an oil sands mining operation.
Referring to Fig 1, tailings are left over material derived from mining
operations. As a non
limiting example of tailings to be considered according to the invention, the
tailings may
be produced from an extraction process, such as a process for extracting
bitumen from
the oil sands. Fig 1 displays typical settling layers for tailings ponds. The
middle layers
are composed of the fine particles including clays suspended in water.
Initially, the
tailings with a relatively low fines content may be referred to as thin fine
tailings (TFT),
which consolidate typically over the course of two to three years and become
mature fine
tailings (MFT) with higher fines contents. As mentioned above, MFT is an
example of
thick fine tailings.
Fig 2 represents a general view of a dewatering operating for the treatments
of thick fine
tailings. For illustrative purposes, the techniques and systems are described
in the
context of MFT, however, is should be understood that other types of thick
fine tailings
can be used.
More particularly, as illustrated on Fig 3, thick fine tailings 1 may be
pumped by a pump 3
from a tailing pond (as illustrated in Figs 1 and 2) and flows through a
pipeline 5 which is
provided with a chemical addition portion 7 including an injector 9 for in-
line addition of a
solution including a flocculating agent 11, forming a flocculation tailings.
The pipeline 5
may also include a downstream portion (which may also be referred to as a
"header") that
may include branches 13 allowing expelling the flocculation tailings 15 into a
deposition
cell 17.
In some implementations, the pipeline may have certain dimensions for
processing. For
example, the downstream portion of the pipeline may have a 12 inch diameter.
It may
also have an overall length from the chemical addition portion 7 to the outlet
spigots of
less than 100 meters. Various types of pumps may be used to move the fluid
through the
pipeline.
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Fig 4 illustrates general stages of the flocculation reaction over time,
particularly in
relation to static yield stress.
Fig 5 displays the effect of Net Water Release (NWR) has on the drying times
of
flocculated fine tailings. NWR is a metric that has been developed and is a
measure of
the differential in water between the starting thick fine tailings and the
treated and drained
thick fine tailings after a given draining time. In other words, NWR is a
difference in
moisture contents. The draining time may be 24 hours, 12 hours, 20 minutes, or
19
minutes, for example, or another representative time period for drainage in
commercial
applications. There are two main ways to calculate the NWR by volumetric or
solid
content difference. Example formula to calculate the NWR are as follows:
NWR(Quantity of water Recovered - Quantity of Flocculant Water Added)
=
Quantity of intial Fine Tailings Water
1 1
NWR = 1 (tMFT wt% mineral + wt% Bitumen ¨ 1) = (MFT wt% mineral + wt% Bitumen
¨ 1)
A NWR test may be conducted using immediate drainage of a flocculation
tailings sample
for a drainage time of about 20 minutes. In this regard, for optimal dosage
range and
good flocculation, the water release in 10 or 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 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 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.
CA 02820660 2013-06-20
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Fig 6 displays four stages of treated flocculated tailings (tMFT) behaviour.
Fig 6 is similar
to Fig 4, but its stages will be presented in a different manner.
As can be seen from Fig 6, the rheological evolution of thick fine tailings
that is subjected
to flocculation may include the following stages:
(a) A dispersion stage where a flocculation reagent is rapidly mixed into the
thick
fine tailings and the flocculation begins, forming the flocculation tailings
material.
(b) A floc build-up stage where the flocculation tailings increases in yield
stress. In
this stage, the flocculation tailings reaches a peak yield stress. Up to and
around
this peak yield stress the flocculation tailings material may be said to be
"under-
mixed" because insufficient mixing or conditioning has been performed to begin
to
breakdown the flocculated matrix and allow increased water release. Fig 6
shows
that the water release is effectively nil up to a certain point just after the
peak yield
stress, after which the water release increases up to an initial maximum.
Within
this floc build-up and under-mixed stage, the flocculation tailings can
resemble a
gel state material and this stage also becomes smaller with improved
dispersion.
(c) A floc breakdown stage where the flocculation tailings decreases in yield
shear
stress. This stage includes a water release zone where water is released from
the
flocculated matrix. Fig 6, for example, illustrates the water release zone
beginning
at a certain point within the floc breakdown stage, after the peak water
release,
and spanning a certain mixing time interval over which the water release
gradually
decreases. In this stage, the flocculated matrix takes on a more permeable
state
having two phases of flocs and water facilitating water to be released and
separated from the flocs.
(d) An over-shear zone, which is avoided, where the flocs are broken down to a
point that the material generally returns to a similar states as the initial
thick fine
tailings. Little to no water can release from the broken down flocculation
matrix.
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In order to facilitate efficient dewatering operations, the flocculation
tailings may be
consistently deposited within the water release zone.
Testing and control methodologies
Various testing and control methodologies will be described in further detail.
Net Water Release (NWR)
One test method includes determining the NWR of a sample of flocculation
tailings. It
should be noted that determining the NWR may be done in connection with a
process
control technique for adjusting or controlling a dewatering operation.
Determining the
NWR may also be done in the design or conception stage of a thick fine
tailings
dewatering plant, where sample of the thick fine tailings are treated at
laboratory or pilot
scale in order to determine certain process variables to be used for scale up
to
commercial applications.
The method for determining the NWR may first include obtaining a sample of
flocculation
tailings. The sample of flocculation tailings may be obtained from a
commercial or pilot
scale dewatering operation, for example from the outlet of the conditioning
pipeline that
supplies the flocculation tailings into the deposition cell or from freshly
deposited
flocculation tailings within the deposition cell proximate or advancing away
from the
outlets. More particularly, the flocculation tailings are deposited in thin
lifts on a beach of
the deposition cell. Alternatively, the sample of flocculation tailings may be
prepared in
the laboratory by mixing of a flocculant into a sample of thick fine tailings.
Once the flocculation tailings sample is obtained, the method then includes
straining the
sample for a given period of time.
Referring to Fig 8 shows an example setup for straining the flocculation
tailings sample.
The sample may be placed on a strainer. The strainer may have an upward
concave
construction or may be flat. An upward concave construction may prevent the
sample
from flowing off of the strainer in the event the sample has sufficiently low
yield stress.
The strainer may have a pore size that is pre-determined and sufficiently
small to prevent
CA 02820660 2013-06-20
substantially all of the flocs of the sample from passing through. The pore
size of the
strainer may vary depending on the flocculant, the type of tailings, and the
dispersion and
conditioning steps. For example, the pore size of the strainer may be between
about 0.1
mm to 10 mm. In one scenario, an 18 mesh (1 mm sieve size) flat screen was
employed.
5 The pore size is sufficient to allow release water to drain out of the
flocculation tailings
and pass through the strainer into a receptacle, as illustrated schematically
in Fig 8.
The strainer may be composed of a variety of materials and may have various
configurations. For example, it may include a metal mesh or a mesh composed of
another material. In some implementations, the parts of the strainer that are
in contact
10 with the sample are composed of a non-absorbent material, e.g. metal or
plastic.
The strainer may have a configuration such that a substantial amount of the
release
water passing through it is downward and due to gravity induced drainage
mechanism.
Alternatively, if the strainer is configured to be at least partially in
contact with side
portions of the sample, a portion of the release water may pass through the
strainer as
15 lateral release.
The release water is allowed to drain through the strainer and then can be
collected in a
receptacle. The receptacle may include a collection bucket or a measuring
cylinder, for
example. The measuring cylinder may be configured to allow measuring water
release
rate over time, as the volume of water may be taken from the level of the
measuring
cylinder. The method then includes measuring an amount of water released from
the
sample during the given period of time, as a Gross Water Release (GWR). This
measurement may be conducted in a number of ways. For example, the measurement
may be done by determining the volume in the receptacle into which the release
water
was collected. This collected material contains mainly water, but may also
contain an
amount of suspended solids that were not captured in the flocculation
tailings. Thus a
simple volumetric measurement may be considered as an estimate of the release
water
but can be used as the measured GWR. Another method of measuring the amount of
release water is by using a drying technique, e.g. by collecting all of the
passing material
collected in the receptacle, weighing it, and subjecting it to evaporation to
determined
CA 02820660 2013-06-20
16
how much water was contained in the material. It is understood that the first
method
would be a faster way of estimating the GWR compared to the second, and the
second
method may allow greater accuracy. It is also noted that both methods may be
performed
for a same NWR determination scheme, and they may be compared to determine the
amount of solids contained in the material passed through the strainer.
The method for determining the NWR also includes subtracting an amount of
added
water present in the flocculating agent solution from the GWR, to obtain the
measured
NWR. Since the flocculant may be added as part of an aqueous solution,
dissolved
and/or dispersed in the solution, water may be added to the thick fine
tailings upon
addition of the flocculant. This amount of water may thus be subtracted from
the GWR to
obtain an estimate of the net amount of water that was released from the
flocculation
tailings.
In one example of determining NWR, a 300 ml to 500 ml flocculation tailings
sample may
be obtained from flocculation tailings that is flowing, depositing or has been
deposited on
the deposition area. The sample is then poured over a strainer, e.g. as
illustrated in Fig 8,
and allowed to drain for a period of time such as 24 hours. The water release
is then
measured, for example using a graduated cylinder.
A variety of time periods may be used for allowing the sample to release
water. Different
release water times may also provide an indication as to whether flocculant
dosage may
be improved. For example, for optimal flocculant dosage range and good
mixing/flocculation, the water release in 20 minutes has been found to be
about 80% of
the water release that would occur over a 12 to 24 hour period. At better
flocculant
dosage, dispersion and handling conditions, water releases faster and the NWR
over a
shorter period of time is closer to the total water that is released from the
flocculation
tailings. For underdosed or overdosed samples, the water release in 20 minutes
may only
be about 20% to 60% of the water release that would occur over a 12 to 24 hour
period.
A 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.
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In some scenarios, the NWR testing scheme may include one or more individual
NWR
tests on the same or different samples. In some cases, the NWR at different
drainage
times may be tracked for a dewatering operation, and one or more operating
parameters
may be adjusted based on the NWR measurements. For example, if the measured
NWR
starts to decrease, operating parameters may be adjusted until the NWR
increases.
Flocculent dosage testing
Another test method includes determining optimal flocculant dosage ranges for
flocculating and dewatering the thick fine tailings.
In general, the flocculant dosage testing may include determining an amount of
the
flocculating agent required to transformed a sample of the thick fine tailings
into a sample
flocculation tailings having a positive measured Net Water Release (NWR) in
response to
shear conditioning beyond a peak static yield stress.
In particular, the dosage testing may include a dose find test (Phase I) and a
dose sweep
test (Phase II).
The Phase I test may include incremental addition of an amount of flocculant
to the
sample of thick fine tailings until flocculation and water release are
observed. For
example, 1 to 5 ml of flocculant solution may be incrementally added to the
thick fine
tailings sample. The sample is subjected to mixing during the flocculant
addition, which
may be constant rotations per minute of an impeller mixer blade. Each
increment of
flocculant is well mixed into the sample before adding the next amount of
flocculant.
Incremental addition may be viewed as a titration to determine an approximate
dosage of
flocculant for flocculating the given sample and achieving a water release
zone. The
incremental addition is repeated until a change in the structure of the sample
and water
release is observed. The water release may be measured by various means,
including
one of the NWR tests described herein and/or a Capillary Suction Time (CST)
test.
The Phase II test may be conducted where the flocculant for a given
approximate dosage
(e.g. determined in Phase I or previously estimated from data sets) is
injected all at once.
CA 02820660 2013-06-20
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The flocculant may be added to a thick fine tailings sample and then the
sample may be
subjected to mixing, which may be a two stage mixing of rapid shear mixing to
induce
dispersion of the flocculant into the sample followed by a slower mixing to
shear condition
the flocculation sample until it reaches the water release zone. NWR may be
determined
for each dosage of the sweep. For example, dosages 100 PPM either side of the
approximate dosage from Phase I may be determined to produce a dosage curve
for
each sample (e.g. NWR vs. dosage). Additional dosages beyond those may also be
tested to provide a more complete curve. The Phase II dose results may be a
reasonable
indicator of the dosage requirements in up-scaled commercial application of
flocculation
and dewatering operations. Fig 12 illustrates NWR as a function of dose of
flocculant
according to dose find test (Phase I) and dose sweep test (Phase II). It is
noted that the
dose is slightly higher in Phase I than in Phase II, and consequently the NWR
can be
slightly lower. NWR may also be lower in Phase ll if dispersion in not
effective in Phase II.
Thus, the flocculant dosage test may include conducting a first dosage test
(e.g. Phase I)
to identify an initial dosage approximation at which positive NWR occurs and a
second
dosage sweep test (e.g. Phase II) to determine variation of NWR as a function
of dosage
of flocculating agent around the initial dosage approximation. The next step
may include
determining a revised dosage in accordance with a maximum NWR range or value
from
the dose sweep test. The dosage giving the maximum NWR value may also be
extrapolated from the dosage sweep curve if it appears that the maximum dosage
would
be between two adjacent doses that were actually tested. The revised dosage
can then
be used for implementing and/or adjusting a flocculation and dewatering
operation.
Optionally, as illustrated in Fig 13, the dosage test (e.g. Phase I) and the
dosage sweep
test (e.g. Phase II), may be followed by full characterization tests (e.g.
Phase III) and/or a
standard drying test (Phase IV). The full characterization tests (e.g. Phase
III) allow the
determination of the water release, YS, Viscosity and/or CST in different
mixing zones. A
single injection may be used. The standard drying test (e.g. Phase IV) allows
the
determination of the effect of dose and water release on drying rates and
rheology.
CA 02820660 2013-06-20
,
19
It is also noted that flocculant dosage is dependent on clay content of the
thick fine
tailings. An increase in clay content will often result in an increase in
flocculant dosage
requirements, unless other process variables are modified.
Water release has also been correlated with clay to water ratio (CWR). The
optimal dose
may be correlated with the `)/0 clay and the static yield stress of the thick
fine tailings
and/or the amount of shearing imparted to the thick fine tailings prior to
flocculation (pre-
shearing, which reduces yield stress). Also, it has been noted that the static
yield stress
of the flocculation tailings may be correlated with CWR. The dose find test
may therefore
be used to determine a particular thick fine tailings sensitive to dose of
flocculating agent.
Fig 10 illustrates NWR as a function of CWR. Water release for the laboratory
mixer at an
initial mixing rate of 320 rpm is a function of the CWR. A high NWR was
observed at
lower CWR. It is also noted that the NWR in commercial operations has been
noted to be
higher than the laboratory settings. Fig 14 illustrates further data regarding
NWR as a
function of CWR.
Fig 11 shows that the dose on a clay basis is correlated with the static yield
stress of the
thick fine tailings. Modeling may be performed to determine the approximate
dose from
the static yield stress and % SBW of the fine tailings. Thick fine tailings
can also be "pre-
sheared" lowing the yield stress and dose.
Some integrated testing methods and process control
Implementation and/or adjustment of operating parameters of the flocculation
and
dewatering operation may be performed in light of various test methodologies.
Various
tests may be conducted in order to determine whether to adjust one or more
operating
parameters of the dewatering process.
When flocculation tailings are not optimal with respect to expected or desired
NWR
values, then a collected sample can be further treated to determine an
appropriate
adjustment measure to take in order to improve dewatering performance.
CA 02820660 2013-06-20
For example, the collected sample may be further treated with additional
mixing and/or
flocculant addition according to one or more steps as outlined in the decision
tree
illustrated in Fig. 9. This decision tree can enable determining if the
flocculation tailings
are under-dosed in flocculant, over-dosed in flocculant, under-mixed or over-
mixed.
5 Dosage, mixing and shear conditioning are factors that can influence the
flocculation and
dewatering performance. Upon determining one or more probable causes of lower
water
release, appropriate changes or adjustments to one or more operating
parameters of the
process can be determined and implemented.
Referring still to Fig 9, a sample of flocculation tailings may be collected
and first
10 evaluated to determine if the sample have good flocs and/or good NWR
(see Fig 6 for
images and qualitative descriptions of the flocs). In some implementations,
the
macroscopic structure of the flocs may be observed to determine whether good
flocs are
present. It may also be possible to conduct microscopic observations of the
floc structure
to make this determination. If good flocs and water release are observed, the
sample may
15 be considered to be optimally dosed and mixed. However, when the sample
does not
have optimal NWR and/or good flocs, then the sample may be subjected to the
following
set of steps:
Scenario A (if the sample does not have a poor floc structure)
A sample having good floc structure may be stirred (e.g. in a lab mixer to
impart addition
20 shear conditioning) until some thinning occurs (e.g. reduction in yield
stress), and
determine whether there is water release. If so, then the original sample was
likely
properly dosed but under-mixed. The additional shear conditioning was
sufficient to reach
the water release zone to enable water to separate from the flocs. The
commercial
application may be adjusted in order to impart additional shear conditioning
to the
flocculation tailings, e.g. by flowing the flocculation tailings through a
longer pipeline
section prior to deposition.
If additional mixing does not result in water release, additional flocculant
may be added to
the sample. The amount of flocculant may be 10 ml, for example. The new
mixture is then
stirred (e.g. in a lab mixer to impart addition shear conditioning). If there
is water release,
CA 02820660 2013-06-20
21
then the original sample was likely under-dosed in flocculant. One may then
take note of
the additional polymer that was added in order to achieve a dose enabling
increased
water release. The commercial application may be adjusted in order to increase
the
dosage, e.g. by increasing the flocculant concentration in the flocculant
solution added to
the tailings and/or by increasing the flow rate of the flocculant solution
relative to the
tailings.
If the first increment of additional flocculant does not lead to water
release, incremental
addition may continue as per the above paragraph, in order to gradually
increase the
flocculant dosage in the sample and observe the effect on water release after
imparting
shear to the mixture. If many increments of additional flocculant are added
without any
observed increase in water release, this indicates that the original sample
was likely
marginally over-dosed. The commercial application may be adjusted by lowering
the dose
slightly.
Scenario B (the sample has a poor floc structure)
A sample having poor floc structure may be stirred (e.g. in a lab mixer to
impart addition
shear conditioning) until thinning occurs. An amount of flocculant may then be
added to
the thinned mixture, for example 10 ml of flocculant. The resulting mixture is
then stirred
again to disperse the flocculant into the sample.
If the sample thickens, one may observe whether there is any water release. If
there is
water release, then the original sample was likely under-dosed in flocculant
and the
commercial application may be adjusted in order to increase the dosage. If
there is little
to no water release, then the step of adding an amount of flocculant (e.g. 10
ml) followed
by stirring may be repeated. If a subsequent iteration results in observed
water release,
then the original sample was likely under-dosed in flocculant. The added
amount of
flocculant to enable water release may be noted and used to adjust and/or
design the
commercial operation.
If the sample, after repeated iterations of flocculant addition and stirring,
does not release
water, then it can be considered as over-dosed in flocculant. At this stage,
certain
CA 02820660 2013-06-20
22
observations can be made regarding the sample. For example, if the floc
structure
changed without an increase in yield stress, the original sample was likely
over-dosed
and the commercial application may be adjusted in order to reduce the dosage.
If the
sample is shiny, then the original sample was likely over-dosed and the
commercial
application may be adjusted in order to reduce the dosage.
On the other hand, if the floc structure did not change without an increase in
yield stress,
or the sample is not shiny, then the original sample was likely at an
appropriate dose but
was entering or within an oversheared zone. One may take note whether there
was water
release in the original sample, to determine to what approximate extent the
additional
stirring may have caused the sample to be oversheared.
