Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
1
Process for dewatering mineral tailings by the treatment of these tailings
with at least two differ-
ent polymers of different intrinsic viscosities
Description
The present invention relates to the treatment of mineral material, especially
waste mineral slur-
ries. The invention is particularly suitable for the disposal of tailings and
other waste material
resulting from mining and mineral processing operations. The invention is
particularly suitable
for the treatment of oil sand tailings and especially mature fine tailings (M
FT) derived from oil
sand tailings.
Processes of treating mineral ores or oil sands in order to extract mineral
values or in the case
of oil sands to extract hydrocarbons will normally result in waste material.
Often the waste mate-
rial consists of an aqueous slurry or sludge comprising particulate mineral
material, for instance
clay, shale, sand, grit, oil sand tailings, metal oxides etc. admixed with
water.
In some cases the waste material such as mine tailings can be conveniently
disposed of in an
underground mine to form backfill. Generally backfill waste comprises a high
proportion of
coarse large sized particles together with other smaller sized particles and
is pumped into the
mine as slurry where it is allowed to dewater leaving the sedimented solids in
place. It is com-
mon practice to use flocculants to assist this process by flocculating the
fine material to increase
the rate of sedimentation. However, in this instance, the coarse material
wills normally sediment
at a faster rate than the flocculated fines, resulting in a heterogeneous
deposit of coarse and
fine solids.
For other applications it may not be possible to dispose of the waste in a
mine. In these in-
stances, it is common practice to dispose of this material by pumping the
aqueous slurry to la-
goons, heaps or stacks and allowing it to dewater gradually through the
actions of sedimenta-
tion, drainage and evaporation.
For example in oil sands processing, the ore is processed to recover the
hydrocarbon fraction,
and the remainder, including both process material and the gangue, constitutes
the tailings that
are to be disposed of. In oil sands processing, the main process material is
water, and the
gangue is mostly sand with some silt and clay. Physically, the tailings
consist of a solid part
(sand tailings) and a more or less fluid part (sludge). The most satisfactory
place to dispose of
these tailings is, of course, in the existing excavated hole in the ground. It
turns out, however,
that the sand tailings alone from the one cubic foot of ore occupy just about
one cubic foot. The
amount of sludge is variable, depending on ore quality and process conditions,
but average
about 8.5 L (0.3 cubic feet). The tailings simply will not fit back into the
hole in the ground.
There is a great deal of environmental pressure to minimise the allocation of
new land for dis-
posal purposes and to more effectively use the existing waste areas. One
method is to load
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
2
multiple layers of waste onto an area to thus form higher stacks of waste.
However, this pre-
sents a difficulty of ensuring that the waste material can only flow over the
surface of previously
rigidified waste within acceptable boundaries, is allowed to rigidify to form
a stack, and that the
waste is sufficiently consolidated to support multiple layers of rigidified
material, without the risk
of collapse or slip. Thus the requirements for providing a waste material with
the right sort of
characteristics for stacking is altogether different from those required for
other forms of disposal,
such as back-filling within a relatively enclosed area.
In a typical mineral or oil sands processing operation, waste solids are
separated from solids
that contain mineral values in an aqueous process. The aqueous suspension of
waste solids
often contains clays and other minerals, and is usually referred to as
tailings. These solids are
often concentrated by a flocculation process in a thickener to give a higher
density underflow
and to recover some of the process water. It is usual to pump the underflow to
a surface holding
area, often referred to as a tailings pit or dam or more usually a tailings
pond in the case of oil
sands. Once deposited at this surface holding area, water will continue to be
released from the
aqueous suspension resulting in further concentration of the solids over a
period of time. Once
a sufficient volume of water has been collected this is usually pumped back to
the mineral or oil
sands processing plant.
The tailings pond or dam is often of limited size in order to minimise the
impact on the environ-
ment. In addition, providing larger tailings ponds can be expensive due to the
high costs of earth
moving and the building of containment walls. These ponds tend to have a
gently sloping bot-
tom which allows any water released from the solids to collect in one area and
which can then
be pumped back to the plant. A problem that frequently occurs is when fine
particles of solids
are carried away with the run-off water, thus contaminating the water and
having a detrimental
impact on subsequent uses of the water.
In many mineral and oil sands processing operations, for instance a mineral
sands beneficiation
process, it is also common to produce a second waste stream comprising of
mainly coarse
(>0.1 mm) mineral particles. It is particularly desirable to dispose of the
coarse and fine waste
particles as a homogeneous mixture as this improves both the mechanical
properties of the de-
watered solids, greatly reducing the time and the cost eventually required to
rehabilitate the
land. However, this is not usually possible because even if the coarse waste
material is thor-
oughly mixed into the aqueous suspension of fine waste material prior to
deposition in the dis-
posal area, the coarse material will settle much faster than the fine material
resulting in banding
within the dewatered solids. Furthermore, when the quantity of coarse material
to fine material
is relatively high, the rapid sedimentation of the coarse material may produce
excessive beach
angles which promote the run off of aqueous waste containing high proportions
of fine particles,
further contaminating the recovered water. As a result, it is often necessary
to treat the coarse
and fine waste streams separately, and recombine these materials by
mechanically re-working,
once the dewatering process is complete.
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
3
Generally oil sands tailings ponds are located within close proximity of the
oil sands mining and
extraction operations in order to facilitate pipeline transportation,
discharging and management
of the tailings. A tailings pond may be contained within a retaining structure
which may be re-
ferred to as a dyke structure. A suitable dyke structure may generally be
constructed by placing
the sand fraction of the tailings within cells or on beaches. Tailings streams
initially discharged
into the ponds may have relatively low densities and solids contents, for
instance around 0.5 to
10% by weight.
In an oil sands tailings pond, the process water, unrecovered hydrocarbons and
minerals settle
naturally to form different strata. The upper stratum can be predominantly
water that maybe
recycled as process water to the extraction process. The lower stratum can
contain settled re-
sidual hydrocarbon and minerals which are predominantly fines. It is usual to
refer to this lower
stratum as "mature fine tailings" (M FT). It is known that mature fine
tailings consolidate extreme-
ly slowly and may take many hundreds of years to settle into a consolidated
solid mass. Conse-
quently mature fine tailings and the ponds containing them are a major
challenge to tailings
management and the mining industry.
The composition of mature fine tailings tends to be highly variable. The upper
part of the stra-
tum may have a mineral content of about 10% by weight but at the bottom of the
stratum the
mineral content may be as high as 50% by weight. The variation in the solids
content is believed
to be as a result of the slow settling of the solids and consolidation
occurring over time. The
average mineral content of the M FT tends to be of about 30% by weight.
The M FT generally comprises a mixture of sand, fines and clay. Generally the
sand may re-
ferred to siliceous particles of a size greater than 44 pm and may be present
in the M FT in an
amount of up to 15% by weight. The remainder of the mineral content of the M
FT tends to be
made up of a mixture of clay and fines. Generally the fines refer to mineral
particles no greater
than 44 pm. The clay may be any material traditionally referred to as clays by
virtue of its min-
eralogy and will generally have a particle size of below 2 pm. Typically, the
clays tend to be wa-
ter swelling clays, such as montmorillonites. The clay content may be up to
75% by weight of
the solids.
Additional variations in the composition of M FT maybe as a result of the
residual hydrocarbon
which may be dispersed in the mineral or may segregate into mat layers of
hydrocarbon. The
M FT in a pond not only has a wide variation of compositions distributed from
top to bottom of
the pond but there may also be pockets of different compositions at random
locations through-
out the pond.
In addition, aqueous suspensions waste solids from mining and mineral
processing operations
including mining tailings, such as M FT, held in ponds of holding areas may
also contain coarse
debris. The type and composition of this coarse debris depends on the origin
of the suspension.
In the case of M FT the coarse debris tends to be of different sizes, shapes
and chemical com-
positions. For instance, M FT may include coarse debris such as biomass, such
as wood or 0th-
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
4
er plant material; petrified matter; solids having a density low enough to
float at or near the sur-
face of the pond; glass; plastic; metal; bitumen globules; or mats. The coarse
debris found other
mining tailings may include similar debris as in the case of M FT, with the
exception of bitumen
materials and may also include other debris materials such as lumps of ore or
other masses
depending on the geology of the ore mine, the ore extraction processing
technique, or the loca-
tion of the tailings pond.
It is known that aqueous suspensions and mining tailings, such as M FT, may be
dewatered and
solidified through the action chemical treatments. A typical chemical
treatment employs the ad-
dition of chemical flocculating agents to bring about flocculation and the so
formed flocculated
suspensions can be subjected to dewatering.
It is well known to concentrate these oil sand tailings in a thickener to give
a higher density un-
derflow and to recover some of the process water as mentioned above.
For example, Xu.Y et al, Mining Engineering, November 2003, pages 33 to 39
describe the ad-
dition of anionic flocculants to the oil sand tailings in the thickener before
disposal.
The underflow can be disposed of and/or subjected to further drying for
subsequent disposal in
an oil sand tailings stacking area.
In the Bayer process for recovery of alumina from bauxite, the bauxite is
digested in an aqueous
alkaline liquor to form sodium aluminate which is separated from the insoluble
residue. This
residue consists of both sand, and fine particles of mainly ferric oxide. The
aqueous suspension
of the latter is known as red mud.
After the primary separation of the sodium aluminate solution from the
insoluble residue, the
sand (coarse waste) is separated from the red mud. The supernatant liquor is
further processed
to recover aluminate. The red mud is then washed in a plurality of sequential
washing stages, in
which the red mud is contacted by a wash liquor and is then flocculated by
addition of a floccu-
lating agent. After the final wash stage the red mud slurry is thickened as
much as possible and
then disposed of. Thickening in the context of this specification means that
the solids content of
the red mud is increased. The final thickening stage may comprise settlement
of flocculated
slurry only, or sometimes, includes a filtration step. Alternatively or
additionally, the mud may be
subjected to prolonged settlement in a lagoon. In any case, this final
thickening stage is limited
by the requirement to pump the thickened aqueous suspension to the disposal
area.
The mud can be disposed of and/or subjected to further drying for subsequent
disposal on a
mud stacking area. To be suitable for mud stacking the mud should have a high
solids content
and, when stacked, should not flow but should be relatively rigid in order
that the stacking angle
should be as high as possible so that the stack takes up as little area as
possible for a given
volume. The requirement for high solids content conflicts with the requirement
for the material to
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
remain pumpable as a fluid, so that even though it may be possible to produce
a mud having
the desired high solids content for stacking, this may render the mud
unpumpable.
The sand fraction removed from the residue is also washed and transferred to
the disposal area
5 for separate dewatering and disposal.
EP-A-388108 describes adding a water-absorbent, water-insoluble polymer to a
material com-
prising an aqueous liquid with dispersed particulate solids, such as red mud,
prior to pumping
and then pumping the material, allowing the material to stand and then
allowing it to rigidify and
become a stackable solid. The polymer absorbs the aqueous liquid of the slurry
which aids the
binding of the particulate solids and thus solidification of the material.
However this process has
the disadvantage that it requires high doses of absorbent polymer in order to
achieve adequate
solidification. In order to achieve a sufficiently rigidified material it is
often necessary to use dos-
es as high as 10 to 20 kilograms per tonne of mud. Although the use of water
swellable absor-
bent polymer to rigidify the material may appear to give an apparent increase
in solids, the
aqueous liquid is in fact held within the absorbent polymer. This presents the
disadvantage that
as the aqueous liquid has not actually been removed from the rigidified
material and under cer-
tain conditions the aqueous liquid could be desorbed subsequently and this
could risk re-
fluidisation of the waste material, with the inevitable risk of destabilising
the stack.
WO-A-96/05146 describes a process of stacking an aqueous slurry of particulate
solids which
comprises admixing an emulsion of a water-soluble polymer dispersed in a
continuous oil phase
with the slurry. Preference is given to diluting the emulsion polymer with a
diluent, and which is
preferably in a hydrocarbon liquid or gas and which will not invert the
emulsion. Therefore it is a
requirement of the process that the polymer is not added in to the slurry as
an aqueous solution.
WO-A-0192167 describes a process where a material comprising a suspension of
particulate
solids is pumped as a fluid and then allowed to stand and rigidify. The
rigidification is achieved
by introducing into the suspension particles of a water soluble polymer which
has an intrinsic
viscosity of at least 3 dl/g. This treatment enables the material to retain
its fluidity as being
pumped, but upon standing causes the material to rigidify. This process has
the benefit that the
concentrated solids can be easily stacked, which minimises the area of land
required for dis-
posal. The process also has the advantage over the use of cross linked water
absorbent poly-
mers in that water from the suspension is released rather than being absorbed
and retained by
the polymer. The importance of using particles of water soluble polymer is
emphasised and it is
stated that the use of aqueous solutions of the dissolved polymer would be
ineffective. Very
efficient release of water and convenient storage of the waste solids is
achieved by this pro-
cess, especially when applied to a red mud underflow from the Bayer alumina
process.
W02004/060819 describes a process in which material comprising an aqueous
liquid with dis-
persed particulate solids is transferred as a fluid to a deposition area, then
allowed to stand and
rigidify, and in which rigidification is improved whilst retaining the
fluidity of the material during
transfer, by combining with the material an effective rigidifying amount of an
aqueous solution of
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
6
a water-soluble polymer. Also described is a process in which dewatering of
the particulate sol-
ids is achieved.
Canadian patent application 2512324 describes a process for the rigidification
of a suspension
which is or comprises oil sand tailings. The process involves transferring the
suspension as a
fluid to a deposition area in which an effective rigidifying amount of an
aqueous solution of a
water-soluble polymer is combined with the suspension during transfer and then
allowing the so
treated suspension to stand and rigidify. The rigidification is improved
whilst retaining the fluidity
of the material during transfer. The process was particularly suited to the
treatment of tailings as
they are produced from the oil sands processing operation.
WO 01/05712 Al discloses a process for treating an aqueous suspension of
suspended solids
by adding a concentrated polymer solution and a dilute polymer solution. This
process is con-
ducted to treat mineral tailings in general, tailings comprising very small
particles like oil sand
tailings, especially M FT, are not mentioned.
However, suspensions which contain a very high proportion of fine solids and
clays, such as
M FT, are particularly difficult to dewater and generally require very high
doses of chemical
treatment aids.
Therefore it is an objective of the present invention to achieve a more
efficient process for de-
watering a suspension containing high levels of fine solids and clays,
especially M FT derived
from oil sand tailings. In particular it would be desirable if such a process
required reduced total
amounts of chemical treatment aids. Moreover, it would be desirable for the
process of remov-
ing water or dewatering process is a rigidification process.
According to the present invention we provide a process of dewatering a
suspension comprising
particulate solids dispersed in an aqueous liquid, said particulate solids
comprises clay and
mineral particles of size below 50 pm, which process comprises the steps of,
(a) Addition of at least one first polymer and of at least one second
polymer to the suspen-
sion; and
(b) Dewatering the polymer treated suspension of step (a),
wherein the at least one first polymer and the at least one second polymer
have different intrin-
sic viscosities IV.
The process brings about significant improvements in removing water from the
suspension us-
ing lower levels of treatment chemicals than previously possible.
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
7
By mineral particles of particle size below 50 pm, we mean solid mineral
particles that are not
water swelling clays that may generally be referred to as fines. Often these
mineral particles
may be referred to as silt. Usually these mineral particles have a size of no
greater than 44 pm.
Typically, they will have a size between 2 pm and 44 pm, although their size
may be smaller.
The mineral origin of the particles often will be silica and/or quartz and/or
feldspar.
The mineral particles may typically be present in the suspension in an amount
of at least 10%
by weight of the mineral content. Often the particles may be present in amount
of at least 15%,
more often of at least 20% by weight of the solids content. In some cases the
solids content of
the suspension may be made up of 50 or 60% by weight.
The clay may be any material traditionally referred to as clays by virtue of
its mineralogy and will
tend to have a particle size of below 2 pm. Generally the clays may tend to be
a mixture of
clays. Typically the clay component may comprise kaolinite; illite; chlorite;
montmorillonites; kao-
linite-smectite mixtures; illite-smectite mixtures. The clay content of the
suspension would usual-
ly be at least 20% by weight of the solids and may be up to 75% by weight of
the solids.
Without being limited by theory the inventors believe that suspensions which
contain a high
proportion of very small sized mineral particles and clay particles,
especially where they have
been held in tailings ponds over a considerable time, even many years, such as
oil sands de-
rived MFT, exhibit three-dimensional particle network structure based on the
clays. These net-
work structures are believed to include clay-clay intra-particle networks and
clay-inter-particle
network structures which incorporate the fine mineral particles. The inventors
believe that these
network structures comprise clay particles linked to each other and network
structures where
clay particles and the fine particles are linked together by clay particles.
Further, it is believed
that this network structure is responsible for retaining more water than in
suspensions of equiva-
lent solids. Furthermore, it is considered that the electrostatic forces
within the clay inter-particle
structure may be responsible for the difficulty in achieving adequate water
release with conven-
tional doses of chemical treatment aids.
Unexpectedly, the inventors have discovered that applying at least two
polymers with different
intrinsic viscosities IV provides a polymer treated suspension which is
significantly more con-
ducive to releasing water by chemical treatment. The inventors believe that
the polymer having
a lower intrinsic viscosity IV preferably binds to the mineral and renders it
more receptive for the
polymer having the higher intrinsic viscosity IV. Therefore, a better mineral
polymer interaction
is received and lower total amounts of polymers have to be used in order to
obtain the desired
rigidification and water release.
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
8
Preferably, the suspension comprises mature fine tailings derived from oil
sands tailings.
The process of the present invention involves addition of at least one first
polymer and at least
one second polymer, wherein the at least one first polymer and the at least
one second polymer
-- have different intrinsic viscosities IV.
According to a preferred embodiment, the process of the present invention
involves the addition
of the at least one first polymer as at least one first, preferably aqueous,
solution and of the at
least one second polymer as at least one second, preferably aqueous, solution.
The addition of polymers with different intrinsic viscosities facilitates the
removal of water in the
dewatering step.
The dewatering of the polymer treated suspension according to step (b) may
employ any known
-- dewatering method. For instance the dewatering step may involve
sedimentation of the polymer
treated suspension to produce settled sediment. Such a process may be carried
out in a vessel
for example a gravimetric thickener or in a settlement pond. Alternatively the
dewatering pro-
cess may involve pressure dewatering, for example using a filter press, a belt
press or a centri-
fuge.
According to a first preferred embodiment of the present invention, dewatering
in step (b) of the
process according to the present invention is conducted by sedimentation.
Preferably the dewatering process is a process of rigidification of the solids
in the suspension
-- and the dewatering step is part of the rigidification process. Thus in a
preferred form of the in-
vention the polymer treated suspension is transferred as a fluid to a
deposition area, then al-
lowed to stand and rigidifying, in which the at least one first polymer and at
least one second
polymer are added to the sheared suspension during the transfer of the
suspension.
-- According to a second preferred embodiment of the present invention,
dewatering in step (b) of
the process according to the present invention is conducted by rigidification.
Rigidification is a term that refers to a networked structure of particulate
solids. Compared with
settling or sedimentation, rigidification is faster, produces more recovered
water and results in a
-- chemically bonded tailings that occupy a smaller surface area, which is
more quickly
rehabilitated. Rigidified tailings are also less likely to spread laterally
after deposition enabling
more efficient land use; and would more rapidly form a solid structure in the
form of a beach or
stack; and have a greater yield stress when deposited, with increased
uniformity or homogenity
of coarse and fine particles. Further by reason of its heaped geometry as a
beach or stack such
-- rigidified material would result in downward compression forces, driving
water out of the stack
and more rapid release of water, with better clarity.
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
9
Therefore, dewatering in step (b) of the process according to the present
invention is preferably
conducted by sedimentation and/or rigidification.
Desirably, the at least one first polymer and at least one second polymer may
be added to the
suspension in the form of aqueous solutions either simultaneously or
separately. The addition of
at least one first polymer and at least one second polymer, preferably as
aqueous solution(s),
allows the suspension to retain sufficient fluidity during transfer and then
once the material is
allowed to stand it will form a solid mass strong enough to support subsequent
layers of rigidi-
fied material. We have unexpectedly found that the addition of the at least
one first polymer and
at least one second polymer, preferably as aqueous solutions of the polymers,
to the suspen-
sion does not cause instant rigidification or substantially any settling of
the solids prior to stand-
ing.
The at least one first and the at least one second polymer may be metered
directly into the sus-
pension as separate materials, preferably as separate solutions. By
substantially simultaneously
the two polymers should be added at approximately the same dosing point. Where
the at least
one first polymer and the at least one second polymer are added to the
suspension separately,
they may be added in either order. For instance if the at least one first
polymer is added first,
the at least one second polymer may be added after the effective adsorption of
the at least one
first polymer onto the mineral surface. Preferably, the at least one second
polymer shall be
added before the dewatering stage. When the at least one first and the at
least one second pol-
ymers are added separately, it may be appropriate to allow or apply some
degree mixing be-
tween the dosing stages in order to allow the first polymer dose to become
distributed through-
out the suspension solids. This mixing may for instance include allowing the
treated suspension
to pass some distance along a flow line which optionally contains bends,
baffles, constrictions
or other features which induce gentle mixing.
Preferably the at least one first polymer and the at least one second polymer,
more preferably
solutions thereof, are introduced separately, more preferably the at least one
first polymer is
added first, and the at least one second polymer is added afterwards.
The aqueous solution of the at least one first polymer comprises the at least
one first polymer in
an amount of from 1 to 99% by weight, preferably 25 to 75 % by weight, in each
case based on
weight of polymer.
The aqueous solution of the at least one second polymer comprises the at least
one second
polymer in an amount of from 1 to 99% by weight, preferably 25 to 75% by
weight, in each case
based on weight of polymer.
According to a further embodiment, the at least one first polymer and the at
least one second
polymer are added as one aqueous composition comprising both.
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
If an aqueous solution is used comprising both, the at least one first polymer
and the at least
one second polymer, the at least one first polymer is present in an amount of
1 to 99 % by
weight, preferably 25 to 75 % by weight, and the at least one second polymer
is present in an
amount of 99 to 1 % by weight, preferably 75 to 25 % by weight, in each case
based on the
5 whole aqueous solution.
According to the invention the at least one first polymer may be either
cationic, anionic or non-
ionic. Further, according to the present invention, the at least one first
polymer and the at least
one second polymer are both anionic, cationic or non-ionic.
The present invention therefore preferably relates to the process according to
the present inven-
tion, wherein both, the at least one first polymer and the at least one second
polymer are anion-
ic, cationic or non-ionic. According to the invention the at least one second
polymer may be ei-
ther cationic, anionic or non-ionic. The at least one first polymer is
preferably either co-ionic with
the at least one second polymer or non-ionic. In another preferred form the at
least one first
polymer is non-ionic and the at least one second polymer is cationic, anionic
or non-ionic.
Suitable doses of polymer range from 10 grams to 10,000 grams per tonne of
material solids.
Generally the appropriate dose can vary according to the particular material
and material solids
content. Preferred doses are in the range 30 to 3,000 grams per tonne, while
more preferred
doses are in the range of from 60 to 200 or 400 grams per tonne, in each case
in respect of the
sum of all polymers and in different solutions.
In some instances better results may be obtained when the suspension,
particular the oil sands
derived M FT, is relatively concentrated and homogenous. It may also be
desirable to combine
the addition of at least one first polymer and at least one second polymer
with other additives.
For instance the flow properties of the material through a conduit may be
facilitated by including
a dispersant. Typically where a dispersant is included it would be included in
conventional
amounts. However, we have found that surprisingly the presence of dispersants
or other addi-
tives does not impair the rigidification of the material on standing. It may
also be desirable to
pre-treat the material with either an inorganic or organic coagulant to pre-
coagulate the fine ma-
terial to aid its retention in the rigidified solids.
Thus in the present invention the at least one first polymer and at least one
second polymer,
preferably as aqueous solutions, are added directly to the aforementioned
suspension. The pol-
ymer solution may consist wholly or partially of water-soluble first and/or
second polymers. Thus
the polymer solutions may comprise a blend of cross-linked polymer and water
soluble polymer,
provided sufficient of the polymer is in solution or behaves as though it is
in solution to bring
about rigidification on standing.
According to a preferred embodiment of the present invention the at least one
first polymer and
the at least one second polymer dilute solution may comprise one or more
polymer(s).
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
11
According to a preferred embodiment of the present invention, in the process
according to the
present invention the at least one first polymer and the at least one second
polymer are of the
same type.
The present invention therefore preferably relates to the process according to
the present inven-
tion in which the at least one first polymer and the at least one second
polymer are of the same
type.
According to the present invention "polymers of the same type" means that both
polymers are
built up of the same or at least similar monomers, but have different
intrinsic viscosities IV. Ac-
cording to a further preferred embodiment the at least one first polymer and
the at least one
second polymer are of different types.
The present invention therefore preferably relates to the process according to
the present inven-
tion in which the at least one first polymer and the at least one second
polymer are of the same
type, wherein the at least one first polymer and the at least one second
polymer are built up of
the same or similar monomers, but have different intrinsic viscosities.
According to the present
invention the wording "similar monomers" relates to monomers belonging to the
same class of
monomers like styrene type monomers comprising styrene and substituted
equivalents thereof,
(meth)acrylic acid, substituted equivalents and derivatives thereof like
amides, (meth)acrylic
acid esters and substituted equivalents thereof etc.
According to the present invention at least one first polymer is added in step
(a), for example
one, two, three, four etc. polymers, more preferably one first polymer is
added in step (a). Ac-
cording to the present invention at least one second polymer is added in step
(a), for example
one, two, three, four etc., more preferably one second polymer is added in
step (a).
Both polymers, preferably both solution(s), according to the present
invention, may comprise a
physical blend of swellable polymer and soluble polymer or alternatively a
lightly cross-linked
polymer for instance as described in EP202780. Although the polymers may
comprise some
cross-linked polymer it is preferred to the present invention that a
significant amount of water
soluble polymer is present. When the polymers comprise some swellable polymer
it is desirable
that at least 80% of the polymer is water-soluble.
Preferably the polymers are wholly or at least substantially water soluble.
The water soluble
polymer may be branched by the presence of branching agent, for instance as
described in
WO-A-9829604, for instance in claim 12, or alternatively the water soluble
polymer is substan-
tially linear.
An essential feature of the present invention is that the at least one first
polymer and the at least
one second polymer have different, preferably significant different, intrinsic
viscosities. Prefera-
bly the at least one first polymer has a lower intrinsic viscosity than the at
least one second pol-
ymer. More preferably the at least one first polymer has a significantly lower
intrinsic viscosity
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
12
than the at least one second polymer. According to the present invention
"significantly different"
or "significantly lower" means a difference in intrinsic viscosity of for
example at least 5%, more
preferably at least 10%, most preferably at least 20%.
According to the present invention the difference of intrinsic viscosity IV of
the at least one first
polymer and the at least one second polymer is preferably at least 5, dL/g,
more preferably at
least 10 dL/g, particularly preferably at least 15 dL/g.
The present invention therefore preferably relates to the process as mentioned
above, wherein
the difference of intrinsic viscosity IV of the at least one first polymer and
the at least one sec-
ond polymer is at least 5, dL/g, more preferably at least 10 dL/g,
particularly preferably at least
dL/g.
According to the present invention, the at least one first polymer has
preferably an intrinsic vis-
15 cosity IV of 0.1 to 8 dL/g, more preferably 0.1 to 5 dL/g, and the at
least one second polymer
has preferably an intrinsic viscosity IV of 5 to 30 dL/g, more preferably 8 to
30 dL/g, particularly
preferably 15 to 25 dL/g.
The present invention therefore preferably relates to the process as mentioned
above, wherein
the at least one first polymer has an intrinsic viscosity IV of 0.1 to 8 dL/g,
preferably 0.1 to 5
dL/g, and the at least one second polymer has an intrinsic viscosity IV of 5
to 30 dL/g, prefera-
bly 8 to 30 dL/g, more preferably 15 to 25 dL/g.
Intrinsic viscosity IV of polymers may be determined by preparing an aqueous
solution of the
polymer (0.5 to 1% w/w) based on the active content of the polymer. 2 g of
this 0.5 to 1% w/w
polymer solution is diluted to 100 ml in a volumetric flask with 50 ml of 2M
sodium chloride solu-
tion that is buffered to pH 7.0 (using 1.56 g sodium dihydrogen phosphate and
32.26 g disodium
hydrogen phosphate per litre of deionised water) and the whole is diluted to
the 100 ml mark
with deionised water. The intrinsic viscosity of the polymers is measured
using a Number 1 sus-
pended level viscometer at 25 C in 1M buffered salt solution.
The polymers may be a natural polymer, for instance polysaccharides such as
starch, guar gum
or dextran, or a semi-natural polymer such as carboxymethyl cellulose or
hydroxyethyl cellu-
lose. Preferably the polymers are synthetic and preferably they are formed
from an ethylenically
unsaturated water-soluble monomer or blend of monomers.
The polymers may be cationic, non-ionic, amphoteric, or anionic. Preferably,
the at least one
first polymer and the at least one second polymer are both anionic, cationic
or non-ionic.
The polymers may be formed from any suitable water-soluble monomers. Typically
the water
soluble monomers have solubility in water of at least 5 g/100 ml at 25 C.
Particularly preferred
anionic polymers are formed from monomers selected from ethylenically
unsaturated carboxylic
acid and sulphonic acid monomers, preferably selected from (meth) acrylic
acid, ally! sulphonic
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
13
acid and 2-acrylamido-2-methyl propane sulphonic acid (AMPS), and their salts,
optionally in
combination with non-ionic co-monomers, preferably selected from (meth)
acrylamide, hydroxy
alkyl esters of (meth) acrylic acid and N-vinyl pyrrolidone.
Preferred non-ionic polymers are formed from ethylenically unsaturated
monomers selected
from (meth) acrylamide, hydroxy alkyl esters of (meth) acrylic acid and N-
vinyl pyrrolidone.
Preferred cationic polymers are formed from ethylenically unsaturated monomers
selected from
dimethyl amino ethyl (meth) acrylate - methyl chloride, (DMAEA.MeCI) quat,
diallyl dimethyl
ammonium chloride (DADMAC), trimethyl amino propyl (meth) acrylamide chloride
(ATPAC)
optionally in combination with non-ionic co-monomers, preferably selected from
(meth) acryla-
mide, hydroxy alkyl esters of (meth) acrylic acid and N-vinyl pyrrolidone.
In some instances, it has been found advantageous to separately add
combinations of polymer
types. Thus an aqueous solution of an anionic, cationic or non-ionic polymer
may be added to
the above mentioned material as at least one first polymer first, followed by
a second dose of
either a similar or different water soluble polymer of any type as at least
one second polymer.
In the invention, the polymers may be formed by any suitable polymerisation
process. The p01-
ymers may be prepared for instance as gel polymers by solution polymerisation,
water-in-oil
suspension polymerisation or by water-in-oil emulsion polymerisation. When
preparing gel pol-
ymers by solution polymerisation the initiators are generally introduced into
the monomer solu-
tion.
Optionally a thermal initiator system may be included. Typically a thermal
initiator would include
any suitable initiator compound that releases radicals at an elevated
temperature, for instance
azo compounds, such as azo-bis-isobutyronitrile. The temperature during
polymerisation should
rise to at least 70 C but preferably below 95 C. Alternatively
polymerisation may be effected
by irradiation (ultra violet light, microwave energy, heat etc.) optionally
also using suitable radia-
tion initiators. Once the polymerisation is complete and the polymer gel has
been allowed to
cool sufficiently the gel can be processed in a standard way by first
commuting the gel into
smaller pieces, drying to the substantially dehydrated polymer followed by
grinding to a powder.
Alternatively polymer gels may be supplied in the form of polymer gels, for
instance as neutron
type gel polymer logs.
Such polymer gels may be prepared by suitable polymerisation techniques as
described above,
for instance by irradiation. The gels may be chopped to an appropriate size as
required and
then on application mixed with the material as partially hydrated water
soluble polymer particles.
The polymers may be produced as beads by suspension polymerisation or as a
water-in-oil
emulsion or dispersion by water-in-oil emulsion polymerisation, for example
according to a pro-
cess defined by EP-A-150933, EP-A-102760 or EP-A126528.
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
14
Alternatively the polymers may be provided as dispersion in an aqueous medium.
This may for
instance be a dispersion of polymer particles of at least 20 microns in an
aqueous medium con-
taining an equilibrating agent as given in EP-A-170394. This may for example
also include
aqueous dispersions of polymer particles prepared by the polymerisation of
aqueous monomers
in the presence of an aqueous medium containing dissolved low IV polymers such
as polydial-
lyldimethyl ammonium chloride and optionally other dissolved materials for
instance electrolyte
and/or multi-hydroxy compounds e. g. polyalkylene glycols, as given in WO-A-
9831749 or WO-
A-9831748.
The, preferably aqueous, solutions of polymers are typically obtained by
dissolving the polymers
in preferably water or by diluting a more concentrated solution of the
polymer. Generally solid
particulate polymer, for instance in the form of powder or beads, is dispersed
in preferably water
and allowed to dissolve with agitation. This may be achieved using
conventional make up
equipment. Desirably, the polymer solution can be prepared using the Auto Jet
Wet (trademark)
supplied by BASF. Alternatively, the polymer may be supplied in the form of a
reverse phase
emulsion or dispersion which can then be inverted into preferably water.
According to a preferred embodiment, the at least one first polymer and the at
least one second
polymer are added simultaneously. According to this embodiment, the aqueous
composition
comprising the at least one first polymer and the at least one second polymer
may be formed by
introducing the solution of at least one first polymer into a flowing stream
of the solution of the at
least one second polymer. For instance in one method of preparing the
composition a solution
of at least one first polymer is introduced directly into a conduit through
which the solution of at
least one second polymer is being conveyed towards the dosing point where the
composition
comprising both polymers are metered into the suspension of solids in order to
effect dewater-
ing.
A suitable and effective rigidifying amount of the at least one first polymer
and of at least one
second polymer, preferably as aqueous solutions, can be mixed with the
suspension prior to a
pumping stage. In this way the polymer solutions can be distributed throughout
the suspension.
Alternatively, the polymer solutions can be introduced and mixed with the
suspension during a
pumping stage or subsequently.
According to a preferred embodiment of the present invention the at least one
first polymer and
the at least one second polymer are added sequentially, for example the at
least one first poly-
mer is added prior to a pumping stage, and the at least one second polymer is
added after the
pumping stage, more preferably during the optional shearing stage. The most
effective point of
addition will depend upon the substrate and the distance from the kinetic
energy stage to the
deposition area. If the conduit is relatively short it may be advantageous to
dose the polymer
solutions close to where the modified, preferably sheared, suspension flows
from the preferably
used kinetic energy device. On the other hand, where the deposition area is
significantly remote
from the preferably used the kinetic energy device it may be desirable to
introduce the polymer
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
solutions closer to the outlet. In some instances in may be convenient to
introduce the polymer
solutions into the preferably modified, preferably sheared, suspension as it
exits the outlet.
Preferably the polymer treated suspension will be pumped as a fluid to an
outlet at the deposi-
5 tion area and the so treated suspension allowed to flow over the surface
of rigidified material.
The suspension is allowed to stand and rigidify and therefore forming a stack
of rigidified mate-
rial. This process may be repeated several times to form a stack that
comprises several layers
of rigidified solids of the suspension. The formation of stacks of rigidified
material has the ad-
vantage that less area is required for disposal.
The rheological characteristics of the polymer treated suspension as it flows
through the conduit
to the deposition area is important, since any significant reduction in flow
characteristics could
seriously impair the efficiency of the process. It is important that there is
no significant settling of
the solids as this could result in a blockage, which may mean that the plant
has to be closed to
allow the blockage to be cleared. In addition it is important that there is no
significant reduction
in flow characteristics, since this could drastically impair the pumpability
on the suspension.
Such a deleterious effect could result in significantly increased energy costs
as pumping be-
comes harder and the likelihood of increased wear on the pumping equipment.
The rheological characteristics of the suspension as it rigidifies is
important, since once the pol-
ymer treated suspension is allowed to stand it is important that flow is
minimised and that solidi-
fication of the polymer treated suspension proceeds rapidly. If the polymer
treated suspension is
too fluid then it will not form an effective stack and there is also a risk
that it will contaminate
water released from the suspension. It is also necessary that the rigidified
material is sufficiently
strong to remain intact, but must be compressable, and withstand the weight of
subsequent lay-
ers of rigidified suspension being applied to it.
Preferably the process of the invention will achieve heaped disposal geometry
and will co-
immobilise the fine and any coarse fractions of the solids in the suspension
and also allowing
any released water to have a higher driving force to separate it from the
suspension by virtue of
hydraulic gravity drainage. The heaped geometry appears to give a higher
downward compac-
tion pressure on underlying solids which seems to be responsible for enhancing
the rate of de-
watering. We find that this geometry results in a higher volume of waste per
surface area, which
is both environmentally and economically beneficial.
A preferred feature of the present invention is the release of aqueous liquor
that often occurs
during the rigidification step. Thus in a preferred form of the invention the
suspension is de-
watered during rigidification to release liquor containing significantly less
solids. The liquor can
then be returned to the process thus reducing the volume of imported water
required and there-
fore it is important that the liquor is clear and substantially free of
contaminants, especially mi-
grating particulate fines. Suitably the liquor may for instance be recycled to
the mining opera-
tion, for instance oil sands operation, from which the suspension originates.
Alternatively, the
liquor can be recycled to the spirals or other processes within the same
plant.
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
16
According to a preferred embodiment the present invention relates to a process
according to the
present invention in which before, during or after step (a) kinetic energy is
applied to the sus-
pension.
According to a particularly preferred embodiment, the present invention
relates to a process
according to the present invention in which before, during or after step (a)
the suspension is
subjected to a kinetic energy stage to produce a modified suspension, wherein
the kinetic ener-
gy stage is a shearing stage and/or the application of ultrasonic to the
suspension.
According to a further preferred embodiment, the present invention relates to
the process ac-
cording to the present invention which the shearing stage comprises subjecting
the suspension
to shearing employing a shearing device and in which the shearing device is
selected from the
group consisting of:
a shearing device comprising moving elements which rotate, preferably
impellers, kneading
components, or moving plates;
a milling device comprising moving elements;
a static mixer,
preferably in which the operation of the moving elements is at least 5 cycles
per second.
The inventors believe that the action of the kinetic energy on the suspension
directly interacts
with the clay-clay intra-particle network structures and the clay inter-
particle network structures.
In fact it is believed that the kinetic energy will at least partially
breakdown these network struc-
tures.
By kinetic energy we mean that suspension is subjected to some energy which is
or induces
motion within the suspension. In one form the kinetic energy may be ultrasonic
energy. General-
ly it is expected that the application of ultrasonic energy will induce
vibrations which will at least
partially break down the network structures. Other forms of kinetic energy may
be alternative
means for inducing vibrations.
Kinetic energy may be applied before, during and/or after the addition of at
least one first poly-
mer and at least one second polymer according to step (a) of the process
according to the pre-
sent invention. Preferably, kinetic energy is applied before step (a) of the
process according to
the present invention. According to this preferred embodiment, a modified,
preferably sheared,
suspension is introduced into step (a) of the process according to the present
invention.
One particularly suitable form of kinetic energy is shearing.
The shearing may be carried out in a shearing vessel before being transferred
to the next step
of the process. Alternatively, the shearing may be carried out in line as the
suspension is being
transferred.
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
17
Any conventional shearing device may be employed as such devices are very well
known in the
industry and also described in the literature. Industrial scale shear devices,
for instance shear
mixing devices or shear pumps are available from a variety of manufacturers,
for instance IKA
which manufactures Ultra Turrax high shear devices, for instance the devices
in the Ultra Turrax
UTL 2000 range; Fluko-high shear mixers; SiIverson high shear mixers, for
instance Ultramix
mixers or In-line mixers; Euromixers; Greaves; Admix Inc which manufactures
Rotosolver high
shear devices; Charles Ross and Son Company which manufactures Ross high shear
mixers;
Robbins Myers which manufactures Greerco high shear mixers; Powershear Mixers.
Suitable shearing devices generally have moving elements: such as rotating
components, for
instance impellers; kneeding components; or moving plates. The mixing pumps
may also con-
tain static elements such as baffles or plates, for instance containing
orifices. The moving ele-
ments will tend to move quite rapidly in order to generate shear. In general
this will depend up-
on the mode of action within the shearing chamber and the size of the volume
that is being
sheared. This may be for instance at least 5 cycles per second (5 s-1),
preferably at least 6 cy-
cles per second (6 s-1), more preferably at least 7 cycles per second (7 s-1),
most preferably at
least 8 cycles per second (8 s-1), even more preferably 9 cycles per second (9
s-1), and usually
at least 10 cycles per second (10 s-1), suitably at least 20 cycles per second
(20 s-1). Typically
this may be up to 170 s-1, up to 200 s-, or up to 300 s-, or more.
When the suspension, for instance oil sands derived M FT, is subjected to
shearing, the period
of shearing may be referred to as the residence time. The residence time in
the shearing device
may be, for instance at least 1 second. Often it will be at least 5 seconds
and sometimes at
least 10 seconds. It may be up to 30 seconds or more or it may be up to 15
seconds or up to 20
seconds. In some situations it may be at least 20 seconds, for instance at
least 1 min and often
may be several hours, for instance up 10 hours or more. Suitably the residence
time may be at
least 5 min, suitably at least 10 min and often at least 30 min. In many cases
it may be at least
one hour. In some cases the residence time may be up to 8 hours but desirably
less than this.
The shearing device may even be a milling device. Milling devices include
colloid mills, cone
mills and rotor mills etc. In general milling devices tend to have moving
elements, for instance
cones, screens or plates containing gaps, grooves, slots or orifices which
move against other
static elements. The moving elements may move instance by rotation. These
devices tend to
generate a high level of shear stress on liquids and other materials passing
through them. The
moving elements tend to combine high-speed with a very small shear gap which
produces in-
tense friction on the material being processed. The friction and shear that
result is commonly
referred to as wet milling. In one form the milling device may contain a rotor
and a stator which
are both cone shaped and may have one or more stages of fine grooves, gaps,
slots or orifices.
This stator can be adjusted to obtain the desired gap setting between the
rotor and stator. The
grooves, gaps, slots or orifices may change direction in each stage to
increased turbulence. The
moving elements will tend to move quite rapidly in order to generate
sufficient shear. This may
be for instance at least 5 cycles per second (5 s-1), preferably at least 6
cycles per second
(6 s-1), more preferably at least 7 cycles per second (7 s-1), most preferably
at least 8 cycles per
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
18
second (8 s-1), even more preferably 9 cycles per second (9 s-1), and usually
at least 10 cycles
per second (10 s-1), suitably at least 20 cycles per second (20 s-1).
Typically this may be up to
170 s-1, up to 200 s-, or up to 300 s-, or more.
Alternatively the suspension may be passed through a static mixer or other
static elements
which bring about a shearing action, for instance baffles in a pipeline or
alternatively a con-
striction in a pipeline.
The inventors have noted that during the application of kinetic energy, for
instance by shearing
of the suspension, in particular the oil sands derived M FT, a notable
reduction in viscosity of the
suspension can occur. The inventors considered that this may be as a result of
the clay-clay
intra-particle network structures and clay inter-particle network structures
being broken down
and releasing water previously entrained within these networks. It is thought
that this availability
of the water may bring about a reduction in viscosity. Typically viscosity may
be measured by
an instrument called a controlled stress rheometer, such as Brookfield RS.
Viscosity may be
measured at 25 C.
Generally the viscosity of the modified (for instance sheared) suspension
would often be below
90% of the viscosity of the suspension prior to the application of kinetic
energy, such as the
shearing stage. Preferably the viscosity of the modified suspension, for
instance sheared sus-
pension, is no more than 80% of the viscosity of the suspension before the
application of kinetic
energy, such as shearing and more preferably no more than 70%. More preferably
still the mod-
ified suspension, for instance sheared suspension, viscosity will be up to 60%
and in particular
less than 50% of the suspension before the application of kinetic energy, for
instance un-
sheared suspension. In some cases the viscosity of the modified suspension,
for instance
sheared suspension, may be as little as 0.001% of the suspension before the
application of ki-
netic energy, for instance shearing, or even below. Often the modified
suspension, for instance
sheared suspension, will be at least 0.05% or 0.1% of the suspension before
the application of
kinetic energy, for instance un-sheared suspension. In many cases the modified
suspension, for
instance sheared suspension will be at least 1%, at least 5% or at least 10%
of the suspension
before the application of kinetic energy, for instance un-sheared suspension.
Generally the change in viscosity from the suspension before the application
of kinetic energy,
for instance without the application of shear, to the modified suspension, for
instance after the
application of shear, tends to increase as the clay content of the suspension
increases.
The present invention also includes a test method for evaluating suspensions
which contain fine
mineral particles and clay, especially mature fine tailings derived from oil
sands tailings.
A further aspect of the invention defines a method of testing a suspension
which comprises par-
ticulate solids dispersed in an aqueous liquid, said particulate solids
comprises clay and mineral
particles of size below 50 pm, which method comprises the steps of,
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
19
(a) Addition of at least one first polymer and of at least one second
polymer to the suspen-
sion;
(b) Transferring the polymer treated suspension of step (a) onto a mesh; and
(c) Measuring the water drained through the mesh and measuring the angle
formed between
the base of the solids retained on the mesh and a line drawn between the
perimeter of the
solids at the highest point in the center of the solids,
wherein the at least one first polymer and the at least one second polymer
have different intrin-
sic viscosities IV.
The suspension may be in accordance with the suspension already defined
herein. Preferably
the suspension comprises mature fine tailings (M FT) that have been derived
from oil sands tail-
ings.
The present invention further preferably relates to the method according to
the present invention
in in which the at least one first polymer is added as an, preferably aqueous,
solution, and the at
least one second polymer is added as, preferably aqueous, solution. General
and preferred
embodiments in respect of at least one first polymer, at least one second
polymer, solutions and
ways of addition are outlined above.
Preferably, the present invention relates to the method according to the
present invention in
which before, during or after step (a) kinetic energy is applied to the
suspension. According to a
further preferred embodiment, the present invention relates to the method
according to the pre-
sent invention in which the kinetic energy is shearing.
By kinetic energy we mean that suspension is subjected some energy which is or
induces mo-
tion within the suspension. In one form the kinetic energy may be ultrasonic
energy. Generally it
is expected that the application of ultrasonic energy will induce vibrations
which will at least par-
tially break down the network structures. Other forms of kinetic energy may be
alternative
means for inducing vibrations.
General and preferred embodiments of the application of kinetic energy, in
particular shearing,
are outlined above.
The present invention preferably relates to the method according to the
present invention in
which the kinetic energy is shearing and the modified suspension is a sheared
suspension.
The shearing may be carried out by any suitable shearing devices that may be
employed in a
laboratory. Typically such shearing devices may be domestic or laboratory
shearing devices,
such as those manufactured by SiIverson or Moulinex. One particularly suitable
shearing device
comprises a flat paddle impeller.
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
The present invention preferably relates to the method according to the
present invention in
which before, during or after step (a) the suspension is subjected to a
kinetic energy stage to
produce a modified suspension, wherein the kinetic energy stage is a shearing
stage and/or the
5 application of ultrasonic to the suspension.
Suitably a sample of the suspension, desirably M FT, may be placed into a
beaker or other con-
venient receptacle, suitably having a circular cross-section. The shearing
member of the shear-
ing device should then be inserted into the suspension. When the shearing
device comprises a
10 flat paddle impeller it is preferred that the length of the paddle fits
substantially across the diam-
eter of the beaker or receptacle. By this we mean that there may be up to 1,
2, or 3 mm clear-
ance between the wall of the beaker or receptacle and the ends of the flat
paddle.
Desirably the sample should be sheared by operating the shearing device at a
rate of at least
15 200 rpm, preferably at least 300 rpm and more preferably at least 400
rpm, especially at the 450
rpm. There is no upper limit to the rate of shearing but generally this would
tend to depend on
the type of shearing device and this would tend not to be greater 10,000 rpm
or 20,000 rpm. In
the case of the shearing device with the flat paddle impeller the upper rate
of shearing may be
no more than 1000 rpm and usually less than this. A desirable rate of shearing
when using the
20 flat paddle impeller may be in the range of between 200 and 800 rpm,
preferably between 300
and 700 rpm, more preferably between 400 and 600 rpm, especially between 450
and 550 rpm.
The duration of the shearing will tend to be at least 1 or 2 seconds and
usually at least 5 sec-
onds and in some cases at least 30 seconds or at least 1 min. The period of
shearing may be
longer than this, for instance up to 30 min or more. Generally the period of
shearing would be
up to 20 min.
Typically the at least one first polymer, preferably in solution, and the at
least one second poly-
mer, preferably in solution, will normally be used at a concentration as
mentioned above. Fol-
lowing the addition of the polymers, in particular as solutions, to the
preferably modified, more
preferably sheared, suspension, it may be desirable to assist the polymer
treated suspension to
be integrated throughout the solids of the suspension. This may be achieved by
stirring. Alterna-
tively the polymer treated suspension may be transferred to a sealed container
and inverted
several times, for instance between 2 and 10 inversions, suitably between 3
and 5 inversions.
The present invention preferably relates to the method according to the
present invention in
which the at least one first polymer is added as an, preferably aqueous,
solution, and the at
least one second polymer is added as, preferably aqueous, solution.
The mesh onto which the polymer treated suspension is applied maybe any
suitable mesh
which allows water to drain through it and retain the solids on top of it. The
mesh may be part of
a sieve. The mesh may be made from metal or other material such as plastic.
CA 02939319 2016-08-10
WO 2015/173728
PCT/1B2015/053481
21
The test method is useful for determining which polymer products are likely to
be most effective
for the treatment of the suspension. The method should also be useful in
determining the opti-
mal doses of polymers, intrinsic viscosities of polymers, or preferably
solutions thereof.
The general and preferred embodiments that have been mentioned in respect of
the process of
dewatering a suspension according to the present invention also apply to the
method of testing
a suspension according to the present invention.
