Note: Descriptions are shown in the official language in which they were submitted.
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TREATMENT OF AQUEOUS COMPOSITIONS
INCLUDING FINES
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional Application
No.
62/452784, filed 31 January 2017; U.S. Provisional Application No. 62/535398,
filed 21 July
2017; U.S. Provisional Application No. 62/554220, filed 5 September 2017; and
U.S. Provisional
Application No. 62/583360, filed 8 November 2017; the entire disclosures of
each of which are
hereby incorporated by reference herein.
TECHNICAL FIELD
[0002] The present disclosure relates to dewatering and consolidation of
aqueous
compositions including fines such as tailings from processing ore.
BACKGROUND
[0003] Various mining and extraction processes produce a tailings stream
characterized
as a slurry of particulate matter in water. These tailings often contain
components that are
hazardous and cannot be discharged directly into rivers and streams. A common
practice is to
store tailings in ponds, which can be very large or encompass numerous sites.
For example, it has
recently been estimated that Canadian oil-sands tailings ponds cover an area
of about 200 square
kilometers. In the U.S., the Environmental Protection Agency has identified
more than 500 ash
and coal slurry ponds, mostly in the Appalachian coal mining region. In
Florida, phosphate
mining results in the production of approximately 100,000 tons a day of
phosphatic clays in the
form of a slurry that is also stored in ponds. It is very difficult to dewater
and the phosphate
industry leaves about 40% of mined land in unstable clay settling areas. The
processes for
mining and extracting of ores of aluminum, copper, zinc, lead, gold, silver,
etc., also create
tailing streams.
[0004] The management and sustainability of tailings ponds pose
significant and growing
problems. The dams or impoundments used to form the ponds are often
constructed from local
material and are a significant potential danger. The failure of a coal slurry
dam in West Virginia
resulted in the Buffalo Creek flood, which killed more than 125 people.
Various other, more
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recent, dam failures in tailings containment ponds have resulted in
significant if not catastrophic
environmental damage. For example, in 2016 the failure of a tailings dam in
Henan province,
China, released about 2 million cubic meters of red mud, totally immersing a
nearby village. In
2015, a waste heap from Jade mining failed in Myanmar, killing at least 113
people.
[0005] In the oil sands industry, fines are defined as particles having a
diameter equal to
or less than 44 gm. They are part of a waste stream that settles much more
slowly than coarse
sand, leaving a layer of water with some entrained fines near the surface of
the ponds. This water
is reused in the bitumen extraction process. Initially, most of the fines
(mainly silica and clay
particles) form an intermediate layer of so-called fluid fine tailings (FFT).
This fluid has a low
solids content, between 15% and 30% and is also referred to as thin fine
tailings (TFT). Over
time, additional settling occurs, but the negative surface charge of the
mineral particles limits
aggregation and a distinct layer of so-called mature fine tailings (MFT) is
formed. The solids
content of the MFT is on average about 30%, but varies with depth. It has gel-
like properties that
make it difficult to handle and dewater. It has been estimated that under the
action of gravity
alone, this tailings component could take decades to centuries to consolidate
and settle and thus
allow for land reclamation. The tailings from phosphate mining in Florida form
a similar gel-like
structure. Beneath a surface crust, these tailings have about a 25% solids
content with a fluid-
like consistency.
[0006] So-called impoundment ponds are used to store two types of waste
from coal
handling and combustion. Coal ash that is a residue of combustion is one such
material and
include several components (fly ash, bottom ash, etc.). The EPA estimated that
100 million tons
of coal ash was generated in the U.S. in 2012. There are dry methods of
disposal and coal ash
can also be recycled into building material, but for economic reasons the wet
disposal of ash into
ash ponds has been common practice. The EPA estimated that there are more than
500 units,
presumably ash ponds, at more than 200 power plants. There are increasing
environmental
concerns regarding leachate from these ponds.
[0007] The second type of impoundment pond for coal processing wastes
stores material
that is a product of coal preparation plants, where soil and rock are removed
from run-of-mine
coal to lower its ash content and increase its value. This is accomplished by
washing. However,
this coal cleaning process produces a reject stream in the form of a sludge or
slurry. This slurry
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contains very fine coal particles together with other material (such as clays)
and, as with the
tailings streams mentioned above, is very difficult to dewater economically
using standard
methods. There are now about 600 so-called slurry impoundments in the U.S.
where this waste
material is stored, mostly in the Appalachian coal mining region. The
impoundments can be as
large as 50 acres in size and contain billions of gallons of toxic sludge.
This material represents
both an economic cost in terms of the loss of a valuable resource (in the form
of coal fines) and a
major environmental hazard. The Washington Post (April 24, 2013) reported that
a study by the
Office of Surface Mining Reclamation and Enforcement found that many sludge
impoundment
walls are weak and are known to leak. Historically, a number of catastrophic
failures of ash and
sludge ponds have occurred, resulting in significant loss of life and
environmental devastation.
With the coal industry in decline and mining companies filing for bankruptcy,
the impoundment
ponds, both those that remain in use and those that have been abandoned, are a
significant and
growing problem.
[0008] The production of alumina from bauxite also results in the
generation of a large
tailings stream. Approximately 77 million tons of a highly alkaline waste
product composed
mainly of iron oxide and known as red sludge or red mud is generated every
year. This poses a
significant disposal problem and a tailings dam failure led to catastrophic
consequences, as
described above.
[0009] There is a continuing need to manage and treat aqueous fines, e.g.,
tailings, to
reduce the volume of such tailings and/or to dewater and consolidate solids in
such tailings and
in a manner preferable for land reclamation and remediation.
SUMMARY OF THE DISCLOSURE
[0010] Advantages of the present disclosure include processes to dewater
aqueous
compositions including fines, e.g., tailings, to produce high solids content
materials.
[0011] These and other advantages are satisfied, at least in part, by a
process of
consolidating solids in the aqueous composition. The process comprises
treating the
composition, which includes fines and process water, with a highly water
soluble salt.
Advantageously, the process can include treating the composition with at least
one highly water
soluble salt or solution thereof and can optionally include either or both of
(i) at least one
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polymer flocculant or solution thereof and/or (ii) optionally coarse
particles, e.g., sand, to form a
treated composition. The treated composition can include a consolidated
material in the process
water, which can then advantageously be separated from the consolidated
material.
[0012]
Implementations of the process of the present disclosure include, for example,
(i)
treating the composition with at least one highly water soluble salt to form a
treated composition
including a consolidated material in the process water, (ii) treating the
composition with at least
one highly water soluble salt and at least one polymer flocculant to form a
treated composition
including a consolidated material in the process water, (iii) treating the
composition with at least
one highly water soluble salt and coarse particles to form a treated
composition including a
consolidated material in the process water, and (iv) treating the composition
with at least one
highly water soluble salt, at least one polymer flocculant and coarse
particles to form a treated
composition including a consolidated material in the process water.
Each of these
implementations can include aqueous solutions of the salt and/or polymer
flocculant to treat the
composition. Each of these implementations can include separating the process
water from the
consolidated material. Advantageously, the consolidated material has a density
greater than the
process water.
[0013]
Embodiments of the processes include one or more of the following features
individually or combined. For example, the aqueous composition including fines
can be tailings.
In some embodiments, the at least one highly water soluble salt can have a
solubility in water (a
salt/water solubility) of at least about 5 g/100 g at 20 C, e.g., at least
about 10 g/100 g at 20 C.
In other embodiments, the at least one highly water soluble salt is a non-
hydrolyzing salt. In still
further embodiments, the at least one highly water soluble salt can have a
monovalent cation and
can include an ammonium based salt, a phosphate based salt, or a sulfate based
salt or
combinations thereof.
[0014] In
certain embodiments, the treated composition can have a salt-composition
concentration of at least 0.5 wt% of the at least one highly water soluble
salt and preferably no
less than about 1 wt%, such as at least about 2 wt% and even greater than
about 3 wt%, 4 wt%, 5
wt%, etc. of the at least one highly water soluble salt. In some embodiments,
the at least one
polymer flocculant is a polyacrylamide or co-polymer thereof. The treated
composition can have
a polymer-composition concentration of the at least one polymer flocculant of
no less than about
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0.001 wt%, e.g., no less than about 0.003 wt%, 0.005 wt%, 0.01 wt% or 0.04
wt%. In other
embodiments, the composition is treated with coarse particles, e.g., sand, at
a sand to fines ratio
of less than 4:1, e.g., between about 2.5:1.0 to about 0.5:1 or between about
2.25:1 to about
0.75:1. Advantageously, the polymer flocculant forms high density flocs, e.g.,
having a density
greater than the process water, which facilitates separation and dewatering of
the consolidated
solids.
[0015] In various embodiments, treating the composition can include
combining the
composition with a solution including the at least one highly water soluble
salt and the at least
one polymer flocculant. In some embodiments, treating the composition can
include combining
a stream of the composition, e.g., tailings, with a stream of a solution
including the at least one
highly water soluble salt and a separate stream of a solution including the at
least one polymer
flocculant. Alternatively, or in combination, treating the composition can
include combining a
stream of the composition, e.g., tailings, with a stream of a solution
including both the at least
one highly water soluble salt and the at least one polymer flocculant. Coarse
particles (e.g.,
sand) can also be added to the composition or stream thereof and/or to any or
all of the solution
streams. Advantageously, the streams can be mixed inline and/or with the aid
of an inline mixer.
In certain embodiments, treating the composition can be carried out at a
temperature of no more
than 50 C, e.g., no more than about 40 C or about 30 C. In other
embodiments, treating the
composition includes using a solution of one or more highly soluble salts
sourced from a natural
or existing source such as seawater or a body of hypersaline water.
[0016] In still further embodiments, the process water can be separated
from the
consolidated material by any one or more of decanting, filtering, vacuuming,
gravity draining,
electrofiltering, etc. or combinations thereof. In various embodiments,
separating the process
water from the consolidated material can include mechanically dewatering the
consolidated
material, e.g., mechanically dewatering the consolidated material by a
dewatering screw. Once
separated, the consolidated material can be transferred for further dewatering
or disposal.
[0017] In practicing aspects of the processes of the present disclosure
and the various
embodiments thereof, the separated process water can include the at least one
highly water
soluble salt and the process can further comprise recovering at least a
portion of the separated
process water. In some embodiments, the process can further comprise recycling
at least a
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portion of the recovered separated process water to treat additional tailings.
In other
embodiments, the process can further include purifying at least a portion of
the recovered
process water.
[0018] Yet another aspect of the present disclosure includes recovering
valuable
materials from the aqueous composition of fines, e.g., tailings. The valuable
materials can
include rare earth elements (REE) associated with solids such as clays in
tailings from various
types of aqueous fines such as tailings stream. Therefore, in practicing
certain aspects of the
processes of the present disclosure and the various embodiments thereof, the
aqueous
compositions can further include rare earth element materials which can be
recovered by treating
the composition with at least one highly water soluble salt, e.g., an ammonium
based salt such as
ammonium sulfate, to form a treated composition including REE in the process
water and/or in
the consolidated materials. In some embodiments, the process further includes
separating the
process water from the consolidated material and recovering the REE from the
separated process
water and/or the consolidated materials.
[0019] Advantageously, the processes of the present disclosure can
consolidate the solids
of the composition to produce a consolidated material having a solids content
in excess of about
45% by weight, e.g., a solids content of greater than about 50% and higher
than about 60%, 65%,
70% and 75% by weight.
[0020] In practicing certain aspects of the processes of the present
disclosure and the
various embodiments thereof, the consolidated material formed in the treated
composition
according to certain embodiments can result in a high solids content after
mixing and/or
dewatering the treated composition in a short period of time. In some
embodiments, the
consolidated material can have a solids content of greater than about 50% and
at least about
60%, 65%, 70%, 75% and 80% by weight after mixing and/or dewatering.
[0021] Another aspect of the present disclosure includes an aqueous
solution for treating
aqueous fines. The aqueous solution includes a highly water soluble ammonium
based salt and a
polymer flocculant, e.g., a water soluble polymer. Embodiments include,
together or
individually, an aqueous solution of one or more of the highly water soluble
salt(s) and having a
concentration of no less than about 1 wt%, e.g., at least about 2 wt%, 5 wt%,
10 wt%, 20 wt%,
30 wt% and even as great as a 40 wt% or as an aqueous salt slurry. The aqueous
solution can
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also include one or more of the polymer flocculant(s) and having a
concentration of no less than
about 0.005 wt%, e.g. no less than about 0.01 wt%, 0.04 wt%, 0.05 wt %, 0.1
wt%, 0.2 wt%, 0.4
wt%, for example
[0022] Additional advantages of the present invention will become readily
apparent to
those skilled in this art from the following detailed description, wherein
only the preferred
embodiment of the invention is shown and described, simply by way of
illustration of the best
mode contemplated of carrying out the invention. As will be realized, the
invention is capable of
other and different embodiments, and its several details are capable of
modifications in various
obvious respects, all without departing from the invention. Accordingly, the
drawings and
description are to be regarded as illustrative in nature, and not as
restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Reference is made to the attached drawings, wherein elements having
the same
reference numeral designations represent similar elements throughout and
wherein:
[0024] Figure 1 schematically illustrates an exemplary embodiment of a
process of
consolidating an aqueous composition including fines and process water.
[0025] Figure 2 shows pictures of vials containing waste coal slurry
treated according to
an embodiment of the present disclosure. The pictures show coal slurry after
adding an ionic
solution (left), then centrifuging (middle) and after removal of supernatant
solution (right).
[0026] Figure 3 shows pictures of the dewatered coal slurry from Figure 2
after removal
from the vial (left) and subsequent hand-pressing between paper towels.
[0027] Figure 4 shows pictures of vials containing mature fine tailings
from oil sands
processing treated with an ammonium salt solution including a polyacrylamide
flocculant at the
concentrations indicated in the figure.
[0028] Figure 5 shows pictures of vials containing mature fine tailings
treated with an
ammonium salt and a polyacrylamide flocculant and illustrate effects of
increasing salt
concentration and reducing polymer concentration under the conditions tested.
[0029] Figure 6 shows a picture of vials containing mature fine tailings
from oil sands
processing treated with seawater which included varying amounts of a
polyacrylamide
flocculant.
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DETAILED DESCRIPTION OF THE DISCLOSURE
[0030] The present disclosure relates to treating aqueous composition
including fines to
consolidate and dewater the composition. Aqueous compositions of fines can be
in the form of
tailings, which are typically produced when mining and processing ores such as
metal ores, e.g.,
aluminum, copper, zinc, lead, gold, silver, etc., phosphate ore, oil sands,
etc. Aqueous
compositions of fines can also be produced when processing coal. For example,
certain
processes finely grind coal prior to combustion to more readily liberate
pyrite (a sulfur based
compound) and hence reduce sulfur emissions upon combustion of the ground
coal. Such
processes can produce fine coal particles as well as other fine mineral or
mineral matter in an
aqueous composition that are difficult to recapture and reuse.
[0031] The particulate solids in the aqueous compositions of the present
disclosure can
be minerals and mineral like materials, i.e., mineral matter, clays, slit, and
in sizes ranging from
fines to coarse solids. The term fines as used herein is consistent with the
Canadian oil sands
classification system and means solid particles with sizes equal to or less
than 44 microns (p.m).
Sand is considered solid particles with sizes greater than 44 p.m. The
composition of the fines
depends on the source of the materials, but generally fines are comprised
mostly of silt and clay
material and sometimes minerals or mineral matter, depending on the ore.
Tailings can have
various solids contents and various amounts of fines as its solids content.
The tailings treated
according to embodiments of the present disclosure can include a significant
amount of fines by
weight (>5 wt%) as their solids content Such tailings can include at least
about 10 wt%, 20
wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt% or higher fines as their solids
content.
[0032] Advantageously, the process of the present disclosure can
consolidate the solids
of aqueous compositions including fines, e.g., tailings, to produce
consolidated material having a
solids content in excess of about 45% by weight, e.g., a solids content of
greater than about 70%
by weight.
[0033] The terms coagulation and flocculation are often used
interchangeably in the
literature. As used herein, however, coagulation means particle aggregation
brought about by the
addition of hydrolyzing salts, whereas flocculation means particle aggregation
induced by
flocculating polymers. Hydrolyzing salts undergo hydrolysis when added to
water to form metal
hydroxides, which precipitate from the solution, trapping fines and other
minerals in the
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coagulating mass. Hydrolyzing salts typically have low solubility in water and
are used as
coagulants. Aggregation induced by flocculation, in contrast, is believed to
be the result of the
polymer binding to the particles thereby tying the particles together into a
so called floc causing
aggregation of the particles.
[0034] In practicing aspects of the present disclosure, an aqueous
composition of fines
and process water can be consolidated by treating the composition with one or
more highly water
soluble salt(s) or an aqueous solution thereof to destabilize and consolidate
solids in the
composition, e.g., to destabilize and consolidate fines in the composition.
Aggregation induced
by the addition of salts is believed to be the result of destabilizing the
particles suspended in the
fluid by an alteration or a shielding of the surface electrical charge of the
particles to reduce the
inter-particle repulsive forces that prevent aggregation. In certain
embodiments, the composition
is tailings, e.g., a suspension of particulate solids in an aqueous liquid
which include fines and
process water such as tailings streams from metal extraction or a coal slurry
which includes fines
of coal and other matter. The process includes treating the composition with
the highly water
soluble salt(s) or an aqueous solution thereof to form a treated composition
including a
consolidated material, e.g. consolidated fines, in process water. The process
water can then be
separated from the consolidated material. Advantageously, the consolidated
material has a solids
content of at least 45% by weight, e.g., a solids content of greater than
about 50% and higher
than about 60%, 65%, 70% and 75% by weight
[0035] Salts that are useful in practicing the present disclosure include
salts that are
highly soluble in water. A highly water soluble salt as used herein is one
that has a solubility in
water of greater than 2 g of salt per 100 g of water (i.e., a salt/water
solubility of 2g/100g) at 20
C. Preferably the highly water soluble salt has a water solubility of at least
about 5 g/100 g at
20 C, e.g., at least about 10 g/100 g of salt/water at 20 C.
[0036] In addition, the highly water soluble salts used in the processes
of the present
disclosure are preferably non-hydrolyzing. Hydrolyzing salts undergo
hydrolysis when added to
water to form metal hydroxides, which precipitate from the solution. Such
hydrolyzing salts are
believed to form open flocs with inferior solids content and cannot be readily
recycled for use
with additional tailings in continuous or semi-continuous processes. In
addition, hydrolyzing
salts typically have low solubility in water and are used at elevated
temperatures to ensure
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sufficient solubility for aggregation, which is an energy intensive process.
See US 4,225,433
which discloses the use of lime as a coagulating agent at a temperature of 75
C.
[0037] Further, the highly water soluble salts are preferably not
carboxylate salts since
such organic acid salts tend to be more expensive than inorganic salts and can
be deleterious to
plant and/or animal life.
[0038] Highly water soluble salts that are not hydrolyzing and useful in
practicing
processes of the present disclosure include salts having a monovalent cation,
e.g., alkali halide
salts such as sodium chloride, potassium chloride; also salts with monovalent
cations such as
sodium nitrate, potassium nitrate, sodium and potassium phosphates, sodium and
potassium
sulfates, etc. are useful in practicing processes of the present disclosure.
Other monovalent
cationic salts useful in practicing processes of the present disclosure
include ammonium based
salts such as ammonium acetate (NH4C2H302), ammonium chloride (NH4C1),
ammonium
bromide (NRiBr), ammonium carbonate ((NI14)2CO3), ammonium bicarbonate
(NH4HCO3),
ammonium nitrate (N1141\103), ammonium sulfate ((N114)2SO4), ammonium hydrogen
sulfate
(NH4HSO4), ammonium dihydrogen phosphate (NH4H2PO4), ammonium hydrogen
phosphate
((NR4)2HPO4), ammonium phosphate ((N114)3PO4), etc. Mixtures of such salts can
also be used.
[0039] Ammonium based salts are useful for practicing the present
disclosure since
residual ammonium based salts on the consolidated material after combining the
salt with the
aqueous fines, e.g., tailings, can be beneficial to plant life. In fact, many
of the ammonium based
salts are useful as fertilizers, e.g., ammonium chloride, ammonium nitrate,
ammonium sulfate,
etc. Many of the monovalent sulfate and phosphate salts are also useful as
fertilizers. In certain
embodiments of the present disclosure, the highly water soluble salt or salts
used in the processes
of the present disclosure can preferably be non-toxic and beneficial to plant
life to aid in
environmental remediation and the restoration of mine sites.
[0040] In one aspect of the present disclosure, treating the compositions
of the present
disclosure with a highly water soluble salt destabilizes and consolidates
solids in the
composition. Such a process can include mixing the composition, which includes
fines and
process water, with a highly water soluble salt to consolidate the fines, and
separating the
process water from the consolidated fines to produce a high solids content,
e.g., at least 45% by
weight. In certain embodiments, the highly water soluble salt is an ammonium
based salt.
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[0041] Highly water soluble salts that can be used in practicing the
present process can
also include salts having multivalent cations. Such salts include, for
example, divalent cation
salts such as calcium and magnesium cation salts, such as calcium chloride
(CaCl2), calcium
bromide (CaBr2), calcium nitrate (Ca(NO3)2), magnesium chloride (MgC12),
magnesium bromide
(MgBr2), magnesium nitrate (Mg(NO3)2), magnesium sulfate (MgSO4); and
trivalent cation salts
such as aluminum and iron (III) cation salts, e.g., aluminum chloride (A1C13),
aluminum nitrate
(Al(NO3)3), aluminum sulfate (Al2(504)3), iron (III) chloride (FeCl3), iron
(III) nitrate
(Fe(NO3)3), iron (III) sulfate (Fe2(504)3, etc. As explained above, the highly
water soluble salts
used in the processes of the present disclosure are preferably non-
hydrolyzing. Many of the
multivalent cation salts are hydrolyzing and thus less preferred for the
reasons stated above.
Moreover, experimentation with multivalent salts showed increased fouling of
containers and
formation of less cohesive consolidated materials as compared to highly water
soluble salts
having monovalent cations. In addition, some multivalent salts, such as FeC13
and Fe2(504)3, are
particularly corrosive and Fe2(504)3 is formed from oxidizing pyrite and
results in acid mine run-
off, which make such salts less preferable for use in processes of the present
disclosure.
[0042] When a sufficiently high concentration of the highly water soluble
salt is included
in the treated composition, the salt can destabilize and consolidate solids in
the composition. For
a relatively short process times with a relatively low energy input, the salt-
composition
concentration of the at least one highly water soluble salt should preferably
be at least 0.5 wt%
and preferably no less than about 1 wt%, such as at least about 2 wt% and even
at least about 3
wt%, 4 wt%, 5 wt%, etc. The term "salt-composition concentration" as used
herein refers to the
concentration of the highly water soluble salt(s) in the treated aqueous
fines, e.g., tailings, and is
determined by taking the percentage of the mass of highly water soluble
salt(s) divided by the
combined mass of the salt(s) plus the aqueous fines and any water used to
dilute the salt(s). For
example, combining 1 part undiluted (i.e., neat) salt to 99 parts tailings by
weight results in a
salt-composition concentration of 1 wt%. Alternatively, treating tailings with
an equal weight of
a 2 wt% solution of the salt also results in a salt-composition concentration
of 1 wt% in the
treated tailings.
[0043] The highly water soluble salt(s) can be used to treat compositions
of the present
disclosure as a solid, e.g., combining the salt as a powder with the
composition. Alternatively,
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the salt can be used to treat as a solution, e.g., combining an aqueous salt
solution with the
compositions. In some aspects of the present disclosure, an aqueous solution
of the highly water
soluble salt can be prepared having a concentration of no less than about 1
wt%, e.g., greater
than about 2 wt%, 5 wt%, 10 wt%, 20 wt%, 30 wt% and even as great as a 40 wt%
or as an
aqueous salt slurry. The composition and salt solution or slurry should be
mixed at a ratio
sufficient to destabilize the composition to cause consolidation of the solids
therein. In one
aspect of the present disclosure, the composition and the salt solution are
mixed at a ratio of
between 5.0:1.0 and 1.0:5.0, e.g., mixed at a ratio between 1.5:1.0 to 1.0:1.5
composition to salt
solution.
[0044] In some embodiments of the present processes, it can be more
advantageous to
use a natural source of a highly soluble salt or salts such as in a natural
body of water including
such salts in sufficiently high concentration such as at least about 2 wt% and
even at least about
3 wt% or greater. For example, ocean or sea water can be used as a source of
highly soluble
salts, which can significantly improve the economics of the process under
certain conditions.
The vast majority of seawater has a salinity of between 31 g/kg and 38 g/kg,
that is, 3.1-3.8%.
On average, seawater in the world's oceans has a salinity of about 3.5% (35
g/L, 599 mM).
Seawater includes of a mixture of salts, containing not only sodium cations
and chlorine anions
(together totaling about 85% of the dissolved salts present), but also sulfate
anions and calcium,
potassium and magnesium cations. There are other ions present (such as
bicarbonate), but these
are the main components. Another natural source of highly soluble salts that
can be used as a
source of highly soluble salts includes a hypersaline body of water, e.g., a
hypersaline lake,
pond, or reservoir. A hypersaline body of water is a body of water that has a
high concentration
of sodium chloride and other highly soluble salts with saline levels
surpassing ocean water, e.g.,
greater than 3.8 wt% and typically greater than about 10 wt%. Such hypersaline
bodies of water
are located on the surface of the earth and also subsurface, which can be
brought to the surface as
a result of ore mining operations.
[0045] After treating the aqueous fines with at least one highly water
soluble salt the
solids in the composition can be consolidated such as by mixing followed by
gravity
sedimentation in a settling tank or by centrifugation to increase the rate of
forming a
consolidated material in the treated composition. The consolidated material
can be separated
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from the process water by decanting, filtering, eletrofiltration, cross-flow
filtering, vacuuming,
and/or by mechanical dewatering, i.e., applying an external force to the
consolidated material.
Once separated, the consolidated material can be transferred for further
dewatering or disposal.
[0046] Although highly water soluble salts can destabilize and consolidate
solids in the
aqueous fines, it was found that the process could be significantly improved
by adding one or
more polymer flocculant(s). The addition of a polymer flocculant to the highly
water soluble salt
significantly reduced the time for consolidation of fines. In addition, the
processes of the present
disclosure can also include treating aqueous fines with coarse particles,
e.g., particles with sizes
greater than 44 gm, such as sand, to significantly increase the solids
content. Mixing with sand is
appropriate for aqueous fines that have solids mostly as fines, as the fine
particles can sit in the
voids between the coarse particles, enhancing packing and solids content. It
was found,
however, that for certain compositions such as coal slurry, the addition of
sand was not needed to
achieve a high solids content, as there were sufficient coarse particles
present in the aqueous
fines stream to give a high solids content material.
[0047] Hence, implementations of the process of the present disclosure
include, for
example, (i) treating the composition with at least one highly water soluble
salt to form a treated
composition including a consolidated material in the process water, (ii)
treating the composition
with at least one highly water soluble salt and at least one polymer
flocculant to form a treated
composition including a consolidated material in the process water, (iii)
treating the composition
with at least one highly water soluble salt and coarse particles to form a
treated composition
including a consolidated material in the process water, and (iv) treating the
composition with at
least one highly water soluble salt, at least one polymer flocculant and
coarse particles to form a
treated composition including a consolidated material in the process water.
Each of these
implementations can include aqueous solutions of the salt and/or polymer
flocculant to treat the
composition. Each of these implementations can include separating the process
water from the
consolidated material. Advantageously, the consolidated material has a density
greater than the
process water. The process water can then be readily separated from the
consolidated material
as, for example, by one or more of decanting, filtering, gravity draining,
electrofiltering, cross-
flow filtering, vacuuming and other evaporating techniques, etc. and/or by one
or more of a
device for dewatering consolidated material such as a centrifuge, decanting
centrifuge,
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dewatering screw, hydrocyclone, vacuum belt filter, filter press or pressing
devices, etc. In
addition, the separated consolidated material can be disposed or deposited in
a containment
structure which allows removal of released water from the consolidated
material.
[0048] Polymers that are useful in practicing the present disclosure
include water soluble
flocculating polymers such as polyacrylamides or copolymers thereof such as a
nonionic
polyacrylamide, an anionic polyacrylamide (APAM) such as a polyacrylamide-co-
acrylic acid,
and a cationic polyacrylamide (CPAM), which can contain co-monomers such as
acryloxyethyltrimethyl ammonium chloride, methacryloxyethyltrimethyl ammonium
chloride,
dimethyldiallyammonium chloride (DMDA AC), etc. Other water soluble
flocculating polymers
useful for practicing the present disclosure include a polyamine, such as a
polyamine or
quaternized form thereof, e.g., polyacrylamide-co-dimethylaminoethylacrylate
in quaternized
form, a polyethyleneimine, a polydiallyldimethyl ammonium chloride, a
polydicyandiamide, or
their copolymers, a polyamide-co-amine, polyelectrolytes such as a sulfonated
polystyrenes can
also be used. Other water soluble polymers such as polyethylene oxide and its
copolymers can
also be used. The polymer flocculants can be synthesized in the form of a
variety of molecular
weights (MW), electric charge types and charge density to suit specific
requirements.
Advantageously, the flocculating polymer used in practicing processes of the
present disclosure
do not include use of activated polysaccharides or activated starches, i.e.,
polysaccharides and
starches that have been heat treated, in sufficient amounts to lower the
density of the floc to
below the density of the process water from which they are separated. Such
activated
polysaccharides and activated starches when used in sufficiently high dosages
tend to form low
density flocs which rise to the surface of an aqueous composition, which can
hinder removal of
solids in large scale operations involving high solids content and can also
hinder dewatering of
consolidated material.
[0049] The amount of polymer(s) used to treat aqueous fines should
preferably be
sufficient to flocculate the solids in the composition and any added coarse
particles, e.g., sand.
The amount of polymer(s) used to treat an aqueous composition which includes
fines and process
such as tailings can be characterized as a concentration based on the total
weight of the
composition or as a dosage based on the weight percent of the solids in the
composition.
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[0050] In some embodiments of the present disclosure, the concentration of
the one or
more polymer flocculant(s) in the treated composition has a polymer-
composition concentration
of no less than about 0.001 wt%, e.g., no less than about 0.003 wt%, 0.005 wt%
or no less than
about 0.01 wt%. For relatively short processing times, consolidation of the
fines/sand mixture
can be obtained at polymer-composition concentrations no less than about 0.04
wt%. The term
"polymer-composition concentration" as used herein refers to the concentration
of the
flocculating polymer(s) in the treated composition and is determined by taking
the percentage of
the mass of the polymer(s) divided by the combined mass of the polymer(s) plus
the composition
and any water used to dissolve the polymer(s). For example, combining 1 part
undiluted (i.e.,
neat) polymer to 9999 parts tailings by weight results in a polymer-
composition concentration of
0.01 wt%. Alternatively, treating tailings with an equal weight of a 0.02 wt%
solution of the
polymer also results in a polymer-composition concentration of 0.01 wt%. In
certain
embodiments, aqueous fines are treated with at least one polymer flocculant to
yield a polymer-
composition concentration of no less than about 0.02 wt%, such as no less than
about 0.03 wt%,
0.04 wt%, 0.05 wt%, and even at least about 0.07 wt%, 0.09 wt%, 0.1 wt%, 0.2
wt%, etc. The
amount of polymer flocculant can be used in greater concentrations. However,
after certain high
concentrations it becomes difficult to dissolve the flocculant, the solution
becomes too viscous
and the process is less economical.
[0051] In some embodiments of the present disclosure, the concentration of
the one or
more polymer flocculant(s) in the treated composition, e.g., tailings, has
dosage (weight of the
flocculant(s) to weight of the solids in the composition, e.g., tailings) of
no less than about 0.005
wt%, e.g., no less than about 0.01 wt% and preferably no less than about 0.015
wt%, 0.020 wt%,
0.025 wt%, 0.03 wt%, or 0.04 wt%.
[0052] The amount of polymer flocculant can be reduced if the salt-
composition
concentration is increased. While the reason for this effect is not clear, a
very low polymer-
composition concentration of no less than about 0.001 wt%, e.g. no less than
about 0.003 wt%,
0.005 wt%, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt %, for example, can
achieve
reasonably fast consolidation of solids in composition, e.g., tailings, if the
salt-composition
concentration is increased.
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[0053] Coarse particles useful for practicing certain processes according
to the present
disclosure are preferably sand and when used in treating compositions the
amount of such
particles are preferably in a sand to fines ratio (SFR ratio) of less than
4:1, e.g., between about
2.5:1.0 to about 0.5:1 or between about 2.25:1 to about 0.75:1. The SFR ratio
is calculated by
determining the amount of sand added to an estimated amount of solid fines in
the aqueous fines
on a weight basis. It is believed that the use of coarse particles facilitates
packing of the
consolidated fines which advantageously increases the solids content and can
even form a
jammed structure of consolidated solids, i.e. a structure in which generally
individual particles of
the consolidated solid can no longer move freely relative to other particles.
[0054] Treating an aqueous composition including fines and process water,
e.g., tailings,
with at least one highly water soluble salt and optionally with either or both
of at least one
polymer flocculant and/or optionally sand can be carried out in a number of
ways. In certain
embodiments, treating the composition includes combining and/or mixing the
various
components. In addition, the at least one salt can be added directly to the
composition either as
an undiluted solid in powder form or as a solution; the at least one polymer
flocculant can be
added directly to the composition either as an undiluted material or as a
solution, and the sand
can be added to the composition directly or with the salt and/or polymer or
solutions thereof.
The salt and polymer can be combined in a single solution, with or without
sand, and combined
with the composition. The order of combining the salt, polymer and sand to the
composition can
give equivalent results and optimization of the process will depend on the
type of composition,
and the scale and equipment used in the process.
[0055] However, it tends to be more convenient to first prepare one or
more solutions
including the one or more highly water soluble salt(s) and the one or more
polymer flocculant(s)
followed by combining the one or more solutions with the composition and sand.
In certain
embodiments, an aqueous solution of one or more highly water soluble salt(s)
can be prepared
having a concentration of no less than about 0.5 wt% or 1 wt%, e.g., at least
about 2 wt%, 3
wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 10 wt%, 20 wt%, 30 wt% and even as great as a
40 wt% or
as an aqueous salt slurry for use in treating the composition. The one or more
polymer
flocculant(s) can also be included in the aqueous solution of the salt(s) and
can have a
concentration of no less than about 0.005 wt%, e.g., no less than about 0.01
wt%, 0.04 wt%, 0.05
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wt %, 0.1 wt%, 0.2 wt%, 0.4 wt%, for example. The aqueous solution of the
highly water
soluble salt(s) and polymer flocculant(s) can be used to treat the composition
and can be
combined with such compositions at a ratio of between 5.0:1.0 and 1.0:5.0,
e.g., at a ratio
between 1.5:1.0 to 1.0:1.5 of composition to aqueous solution. Sand can be
combined with the
composition before, during, or after combining the composition with the
solutions.
[0056] Because highly water soluble salts and polymer flocculants that are
preferably
water soluble are used in the process of the present disclosure, the
temperature of the treated
aqueous fines need not be elevated above ambient to practice the process. In
certain
embodiments, treating the composition according to the various embodiments
herein can be
carried out at a temperature of no more than 50 C, e.g., no more than about
40 C or about 30
C. In other embodiments, such as oil sands froth tailings consolidation, the
tailings stream may
already be warm or hot as a result of prior processing. The processes of the
present disclosure
can be applied directly to these tailings streams.
[0057] In practicing aspects of the present disclosure, compositions,
e.g., a suspension of
particulate solids in an aqueous liquid which include fines and process water,
can be
consolidated by treating such compositions with at least one highly water
soluble salt or aqueous
solutions thereof and can optionally include either or both of at least one
polymer flocculant,
e.g., a water-soluble flocculating polymer, or aqueous solutions thereof,
and/or optionally coarse
particles, e.g., sand to form a treated composition. Treating compositions,
e.g., tailings, in this
manner can cause destabilization and consolidation of the solids, e.g., fines
and sand, in the
treated composition to form a consolidated material, which can settle under
gravity relatively
quickly, in the process water.
[0058] The treated compositions and/or consolidated material can be
further dewatered to
further separate the process water from the consolidated material and, in some
instances, further
consolidate the solids. In some embodiments, the consolidated material formed
in the treated
compositions can be separated from the process water by any one or more of
decanting, filtering,
e.g., electrofiltering, cross-flow filtering, gravity draining, vacuuming and
other evaporating
techniques, etc. and/or by any one or more of a mechanical dewatering, i.e.,
applying an external
force to the consolidated material, with a device for dewatering consolidated
material such as by
applying a centrifuge, decanting centrifuge, dewatering screw, hydrocyclone,
filter press,
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pressing device, etc. or combinations thereof. In one aspect of the processes
of the present
disclosure, the process water can be separated from the consolidated material
by passing a stream
of treated composition through a cross-flow filter, e.g., a porous or slotted
pipe, which filters and
dewaters the treated composition stream to separate the process water from the
consolidated
material. The process water can then be readily separated from the
consolidated material. In
another aspect of the processes of the present disclosure, the process water
can be separated from
the consolidated material by gravity draining to achieve a solids content of
at least about 70%
within about a month after treating the tailings, e.g., within about two weeks
or within about one
week of gravity draining after treating the tailings. In still further aspect
of the processes of the
present disclosure, the consolidated material can be further dewatered after
separating from the
treated composition by depositing the separated consolidated material in a
thin lift deposition.
[0059] The consolidated material formed in the treated compositions can
advantageously
have a high solids content, e.g., a solids content of greater than about 50%
and at least about
60%, 65%, 70% and 75% by weight In addition, the consolidated material formed
in the treated
compositions according to certain embodiments can result in a high solids
content after mixing
and/or dewatering the treated compositions in a short period. In embodiments
of the present
disclosure, the consolidated material can have a solids content of greater
than about 50% and at
least about 60%, 65%, 70%, 75% and 80% by weight after mixing and/or
dewatering. In certain
embodiments a solids content of at least about 70 % is achieved within about
one month of
gravity draining after treating the composition, e.g., within about two weeks
or within about one
week of gravity draining after treating the composition.
[0060] In an embodiment of the present disclosure, the process includes
mixing the
composition with a highly water soluble salt, e.g., an ammonium based salt, a
water soluble
polymer, e.g., a polyacrylamide, and optionally sand, such as in a sand to
fines ratio of between
about 2.25:1 to about 0.75:1 to form a treated composition including a
consolidated material
having a high solids content, e.g., a solids content of greater than about 50%
by weight, e.g., at
least about 60%, 65%, 70 wt% or higher in less than 10 minutes, depending on
the dewatering
method used.
[0061] Another advantage of the processes of the present disclosure is the
recovery of
materials from tailings that include rare earth elements. For example, certain
tailings can include
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valuable minerals that include rare earth elements. A rare earth element
(REE), as defined by
IUPAC, is one of a set of seventeen chemical elements in the periodic table,
specifically the
fifteen lanthanides, as well as scandium and yttrium. Scandium and yttrium are
considered rare
earth elements because they tend to occur in the same ore deposits as the
lanthanides and exhibit
similar chemical properties. Many of the REE are used in electronic devices,
magnets, high
performance coatings. Such REF, include cerium (Ce), dysprosium (Dy), erbium
(Er), europium
(Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium
(Nd),
praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium
(Tb), thulium
(Tm), ytterbium (Yb) and yttrium (Y).
[0062] REE in aqueous fines are typically in the form of an ion or oxide.
For example,
zirconium can be present as zircon, ZrSi0.4, titanium can be present as the
minerals ilmenite,
leucoxene and rutile. Coal ash and coal cleaning wastes contain rare earth
elements. Fire clay
coal ash has unusually high concentrations of Yttrium and zirconium. Oil sands
tailings also
contain REE.
[0063] The processes of the present disclosure are useful in recovering
REE. It is
believed that in some tailings, REEs absorb on the surface of clays in
tailings. In other tailings,
REEs are predominately included among the solids of the tailings but can also
be in the process
water. Absorbed REEs can be exchanged with the highly water soluble salts of
the present
disclosure, e.g., ammonium based salts due to an exchange of ammonium ions for
the REE ions.
REEs from the solids of the tailings can be obtained by leaching the solids
with acid followed by
extraction and precipitation or by caustic decomposition followed by acid
leaching.
[0064] Another aspect of processes of the present disclosure includes
consolidating an
aqueous composition including fines and process water, e.g., tailings, which
include REE
materials by treating the composition with at least one highly water soluble
salt, e.g., an
ammonium based salt such as ammonium sulfate, to form a treated composition
including a
consolidated material in process water which includes the REE materials in the
process water
and/or among the consolidated materials. In one aspect of the present
disclosure, the treated
composition consolidates the fines and also separates REE materials from the
solids and into the
process water. The process water can then be separated from the consolidated
material and the
REE materials can be recovered from the separated process water. The REE
materials can be
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recovered from the process water by precipitation, e.g., using oxalic acid, or
extraction. Other
methods for recovering REE from the process water include mineral processing
and physical
beneficiation, deep eutectic solvents/ionic liquids extraction, acid
dissolution, high temperature
phase separations, use of REE selective sorbents, photophoresis, in-situ brine
injection and
extraction, reactive grinding, etc. In other aspect of the present disclosure,
the treated
composition consolidates the fines and REEs are among the consolidated
materials. The process
water can then be separated from the consolidated material. The consolidated
material can then
be leached with acid, e.g., nitric acid, sulfuric acid, etc., followed by
extraction with solvent
and/or ion exchange resins and precipitated. Alternatively, the consolidated
material can then be
treated with a caustic reagent such as sodium hydroxide to decompose certain
of the materials to
form hydroxides of the REEs followed by leaching in acid, e.g., HC1.
[0065] In addition, the composition which includes REE materials can be
treated with at
least one polymer flocculant and optionally sand to form the treated
composition. The treated
composition can have a salt-composition concentration of at least 0.5 wt% of
the at least one
highly water soluble salt and preferably no less than about 1 wt%, such as at
least about 2 wt%
and even greater than about 3 wt%, 4 wt%, 5 wt%, etc. of the at least one
highly water soluble
salt
[0066] The process of the present disclosure allows for large scale
treatment of aqueous
fines in a continuous or semi-continuous process with further recovering,
recycling and purifying
at least a portion of the process water in the aqueous fines and optionally
recovering REE
materials. When non-hydrolyzing, highly water soluble salts are used in the
processes of the
present disclosure, the process water separated from an initial treated
composition can
advantageously include a significant amount of the one or more highly water
soluble salt(s)
initially used to treat the composition. In certain embodiments, the separated
process water
includes the at least one highly water soluble salt and the process includes
recovering at least a
portion of the separated process water; recycling at least a portion of the
recovered separated
process water to treat additional aqueous fines; and/or purifying at least a
portion of the
recovered process water. In other embodiments, the separated process water
includes REE
materials salt and the process further includes recovering at least a portion
of the separated
process water; recycling at least a portion of the recovered separated process
water to treat
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additional aqueous fines; recovering the REE materials and/or purifying at
least a portion of the
recovered process water.
[0067] Figure 1 schematically illustrates such an exemplary continuous or
semi-
continuous process. As shown in the figure, aqueous compositions including
fines and process
water are treated with one or more highly water soluble salt(s), and
optionally one or more
polymer flocculant(s) and optionally coarse particles (sand) by combining a
stream of the salt(s)
(101a), which can be an aqueous solution with a stream of the composition
(103a). For this
embodiment, the composition is a tailings composition but other aqueous fines
compositions can
be processed in the same manner. Optionally, the composition can also be
treated with one or
more polymer flocculant(s) by combining a stream of the flocculants(s) (102a),
which can be as
an aqueous solution, with the composition stream (103a). Alternatively, the
salts(s) and
flocculant(s) can be combined together as a solution to treat the tailings as
a stream thereof.
Coarse particles (sand) can also be added to the composition or stream thereof
and/or to any or
all of the solution streams.
[0068] The solution streams of salt(s) and polymer(s) can be sourced from
holding tanks
101 and 102 and the streams of aqueous fines and sand can be sourced from
holding tanks 103
and 105, respectively. Alternatively, the Tailings can be sourced from an oil
sands extraction
operation.
[0069] For this embodiment, the stream of salt(s) (101a) and polymer(s)
(102a) and
tailings stream (103a) are carried to mixing device 107 where a stream of sand
(105a) is added
and the combination mixed. Mixing device 107 can be an inline mixer, a mixing
tank, ribbon
mixer or other mixing device that can mix streams 101a, 102a, 103a and 105a.
For this
embodiment, the aqueous fines are combined with the salt(s) and polymer(s) as
solutions
followed by addition of sand to treat the aqueous fines. However, the order
can be changed, e.g.,
the sand can be combined with the aqueous fines (105b) followed by mixing with
the salt(s) and
polymer(s) solutions. The sand can be added as a wet or dry stream. In some
embodiments, the
combination of the streams in a line can cause sufficient mixing to eliminate
the need for a
separate mixing device, e.g., inline mixing, and the combined streams can be
carried directly to a
mechanical dewatering device to separate consolidated material from process
water and, in some
instances, to further consolidate the solids in the consolidated material.
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[0070] As shown in the embodiment of Figure 1, after mixer 107, the
treated aqueous
fines, which include a consolidated material and process water, is transferred
to dewatering
device 109 to separate the process water from the consolidated material. Such
dewatering
devices include, for example, one or more of a decanting, filtering,
electrofiltering, cross-flow
filtering, gravity draining, or vacuuming device or combination thereof and/or
by one or more of
a device for dewatering consolidated material such as a centrifuge, decanting
centrifuge,
dewatering screw, hydrocyclone, vacuum belt filter, filter press or pressing
devices, etc. or
combinations thereof
[0071] Separated process water can be recovered and collected in tank 111
and separated
consolidated material can be recovered and collected in container 113. For
this embodiment, the
recovered process water in tank 111 includes the process water from the
aqueous fines, e.g.,
tailings, diluted with stream 101a and thus includes residual salt(s) from the
one or more highly
water soluble salt(s) and can possibly include residual polymer(s) from the
one or more polymer
flocculant(s) as well as contaminants from the aqueous fines. If the aqueous
fines include REE
materials, the recovered process water in tank 111 and/or the consolidated
material in 113 can
also include REE materials. There are also highly water soluble salts that are
constituents of the
original aqueous fines and these become part of the recovered process water.
The recovered
process water in tank 111 can then be transferred to a water purifying system
115 to purify at
least a portion of the recovered process water which is transferred to tank
117. Water purifying
systems that can be used for embodiments of the processes of the present
disclosure include
reverse osmosis systems, vacuum distillation systems, electrodialysis,
filtration systems, etc.
The remaining, non-purified recovered process water is transferred to tank 119
to recover
process water including the one or more highly water soluble salt(s) and
highly water soluble
salts that are constituents of the original aqueous fines. This remaining, non-
purified recovered
process water can be recycled back to the treatment process. For this
embodiment, at least a
portion of the non-purified recovered process water can be recycled back to
holding tank 101 and
deficiency in the concentration of the salt(s) or polymer(s) can be corrected
by adding additional
highly water soluble salt(s) or polymer flocculant(s) from one or more make-up
tanks such as
make-up containers 121 and 122.
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[0072] The process of the present disclosure can also include recovering
REE materials
from recycled separated process water or from the consolidated solids. The REE
materials can
be recovered from the process water by precipitation, e.g., using oxalic acid,
or extraction. Other
methods for recovering REE from the process water include mineral processing
and physical
beneficiation, deep eutectic solvents/ionic liquids extraction, acid
dissolution, high temperature
phase separations, use of REE selective sorbents, photophoresis, in-situ brine
injection and
extraction, reactive grinding, etc. The process of the present disclosure can
also include
recovering REE materials from the consolidated solids by acid leaching or
caustic
decomposition.
[0073] The process of the present disclosure can include adding an organic
solvent (e.g.,
naphtha, kerosene or a C5-8 hydrocarbon, such as pentane, hexane, heptane,
benzene, toluene, etc.
or mixtures thereof) to dilute organic material included with the aqueous
fines, e.g., tailings such
as residual hydrocarbons, organic solvents, oil, bitumen. The addition of an
organic solvent
forms an organic mixture with the organic material which can be removed.
[0074] In addition, the consolidated solids can be recovered. The
recovered consolidated
solids can include residual highly water soluble salt(s) from the treatment of
the tailings. When
the salt used in treating the tailings are beneficial to plant life, such as
an ammonium based salt
or sulfate based salt or phosphate based salt, the residual salt can act as a
fertilizer with the
consolidated solids. The recovered consolidated solids can include REE
materials which can be
separated from the consolidated solids as explained elsewhere.
EXAMPLES
[0075] The following examples are intended to further illustrate certain
preferred
embodiments of the invention and are not limiting in nature. Those skilled in
the art will
recognize, or be able to ascertain, using no more than routine
experimentation, numerous
equivalents to the specific substances and procedures described herein.
[0076] Coal Ash Slurry Consolidation
[0077] An initial sample of a coal ash slurry was analyzed by infrared
spectroscopy to
determine the content of solids content. Further, the sample was estimated to
have 30% or more
coal fines present, i.e., a mixture of fine coal particles and fine mineral
particles. Approximately
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g of the coal slurry was placed in a vial and an equal weight of an aqueous
ionic solution was
added and the diluted slurry shaken to mix the components. The ionic liquid
was composed of
water, 10 wt% ammonium sulfate and 0.1 wt% polyacrylamide (PAM). Settling
started
immediately, as can be seen in the picture on the left in Figure 2. The vial
was then centrifuged
for 30 seconds at 3000 rpm and the particles consolidated into a compact mass,
as shown in the
picture in the center of Figure 2. The supernatant liquid appeared to be
clear, with no visible
suspended particles. Upon removal of the liquid it was found that the
compacted solids have
enough cohesive strength to hold their shape when the vial was inverted, as
can be seen in the
picture on the right in Figure 2.
[0078] The material was removed from the vial (Figure 3, left) and a
portion dried. The
consolidated material had an initial solids content of 54%. Some of the
remainder was pressed
(by hand) between paper towels (Figure 3, right). This pressed material had a
solids content of
74%.
[0079] Varying Salt and Salt Concentration in Treating Oil Sands Tailings
[0080] Additional experiments were carried out with various highly water
soluble salts
and in different concentrations and with and without sand to treat oil sands
tailings. A series of
salt/polymer solutions were prepared. All of the salt/polymer solutions
included 0.1 wt% of
polyacrylamide (PAM) but varied the type and concentration of the salt. For
example, a series of
wt%, 5 wt% and 2 wt% calcium chloride solutions each with 0.1 wt% of PAM were
prepared
and used to treat MFT. Other 10 wt%, 5 wt% and 2 wt% salt solutions of
ammonium sulfate,
potassium chloride, etc. were prepared each with 0.1 wt% of PAM. An equal
weight of a
particular salt/polymer solution was then combined with MFT, with or without
sand, in a vial
followed by vigorous mixing. The vials were then centrifuged at 3000 rpm on a
LW Scientific
laboratory centrifuge for 30 seconds to form a consolidated material in the
form of a slurry.
After centrifugation, the supernatant liquid was separated from the
consolidated material by a
pipette. The consolidated material was then weighed, dried and reweighed to
determine a solids
content of the consolidated material. The various salts and their
concentrations which were used
to treat MFT and the resultant solids content data are summarized in Tables 1
and 2 below.
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Table 1: Solids content of MET treated with an equal weight of a salt/PAM
solution without the
addition of sand and after centrifugation.
Salt 10% Concentration' 5% Concentration2 2%
Concentration3
(+ 0.1 wt% PAM)
No Sand
Ferric Chloride (FeCl3) 34.9% 35.6%
Aluminum Sulfate 33.1% 34.1%
(Al2(504)3)
Calcium Chloride 36.8% 37.1% 35.8%
(CaCl2)
Ammonium Sulfate 33.1% 31.8% 31.4%
(NE-14SO4)
Potassium Chloride 35.4% 32.4% 33.5%
(KCl)
Table 2: Solids content of MFT treated with an equal weight of a salt/PAM
solution with the
addition of sand (SFR ratio 1:1) after centrifugation.
Salt 10% Concentration' 5% Concentration2 2%
Concentration3
(+ 0.1 wt% PAM)
With Sand
Ferric Chloride 45.7% 52.8%
FeCl3)
Aluminum Sulfate 51.4% 53.7%
(Al2(504)3)
Calcium Chloride 58% 56.8% 56.1%
(CaCl2)
Ammonium Sulfate 53.6% 52.3% 53.5%
(NH4SO4)
Potassium Chloride 53.4% 52.5% 53.9%
KCl)
1. The salt-tailings concentration was about 5 wt%.
2. The salt-tailings concentration was about 2.5 wt%.
3. The salt-tailings concentration was about 1 wt%.
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[0081] Table 1 reports the solids content of dried consolidated material
following treating
of MFT with the various salt/polymer solutions without sand. After
centrifugation for just 30
seconds, the highly water soluble salts gave solids contents for the
consolidated materials in a
range between about 31%-37%. However, the use of highly water soluble salts
having a
multivalent cation such as the aluminum and ferric cations appeared to cause
fouling of the vial
walls and gave a less cohesive consolidated material as compared to highly
water soluble salts
having a monovalent cation under the tested conditions. In some tests using
salt concentrations
of 10%, the clarified water sitting on top of the consolidated materials were
removed using a
pipette and the wet solids pressed between paper towels. It was found that the
salts with
multivalent cations, aluminum chloride (A1C13), ferric chloride (FeCl3) and
calcium chloride
(CaCl2), which all gave significant deposits of a slimy material on the vial
walls, were less
cohesive than the pressed solids obtained using salts with monovalent cations,
such as the
ammonium salts NH4C1 and (NI-14)2SO4.
[0082] Table 2 reports the solids content of dried consolidated material
following treating
MFT with the various salt/polymer solutions and sand. Sand was added with a
1:1 sand to fines
ratio (i.e., 1.5 g of sand was added to the 5 gm of MET having 30% solids to
give a 1:1 ratio of
the weight of sand to that of the solids in the MFT). After centrifugation for
just 30 seconds, the
highly water soluble salts gave solids contents for the consolidated materials
in a range between
about 46%-58%, which was significantly higher than the range of solids
contents without use of
sand. Although the solids content of the vials containing added sand is twice
those without sand,
the volume of the centrifuged slurry is about the same.
[0083] The data in Tables 1 and 2 show that addition of 2 wt% salt
solution to treat MFT
was as effective as a 10 wt% salt solution. That is, a 1 wt% salt-tailings
concentration was as
effective as a 5 wt% salt-tailings concentration. Since an equal weight of the
salt/polymer
solution was used to treat MFT, the salt concentration of the added salt in
the treated tailings is
one-half of the concentration in the salt/polymer solution, i.e., the added 2
wt% salt solution
provided a 1 wt% salt-tailings concentration and the 10 wt% salt solution
provided a 5 wt% salt-
tailings concentration. The salt-tailings concentration in treated MFT can be
achieved in a
number of ways. For ease of handling in the foregoing vial tests, it was
convenient to combine
equal weights of salt/polymer solutions to MFT. However, smaller amounts of
salt/polymer
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solutions with higher concentrations thereof to give the same salt-tailings
concentration give
equivalent results of consolidated materials.
[0084] Centrifuging in flat-bottomed vials is not as effective in terms of
producing a high
solids material as using centrifuge tubes. It should be kept in mind that for
all sets of laboratory
vial and tube tests, there is always solution remaining in the voids between
the particles. It will
be shown later that the solids content of the consolidated material can easily
be increased from
the 46%-58% range by simply draining or the use of mechanical dewatering
methods known to
the art, such as filter presses, belt filters, cross-flow filtering,
dewatering sand screws, decanting
centrifuges, hydrocyclones, etc.
[0085] Varying Salt Concentration and Polymer Concentration in Treating
Oil Sands
Tailings
[0086] When salt, polymer and sand are used together, salt-tailings
concentrations in
excess of 0.5 wt% and preferably no less than about 1% should be used to
achieve reasonably
fast consolidation of the solids in the tailings. In addition, although a
degree of consolidation of
the fines/sand mixture is obtained at polymer-tailings concentrations as low
as 0.01 wt% for
relatively short processing times, superior results are obtained at polymer-
tailings concentrations
of 0.05% and higher. These preferences were determined by a set of vial
experiments. The top
set of vials in Figure 4 shows results obtained by adding 5 g of a 2 wt%
ammonium sulfate
((NH4)2SO4) solution containing PAM to 5 g of MFT. Sand was also added to give
a sand-to-
fines ratio of 1:1 (i.e., 1.5 g of sand was added). The amount of PAM in the
solutions was varied
between 0.1% (by weight) and 0.02% (by weight). The bottom set of vials show
what is
observed when a 1 wt% of the ammonium sulfate was used. The vials were
centrifuged at 3000
rpm for 30 seconds to accelerate settling.
[0087] It can be seen that for all the vials treated with the 1 wt%
(NR4)2504 solutions,
there is a degree of settling of the fines and sand, but the supernatant
liquid contains a significant
amount of suspended particles. In addition, visually there appears to be a
degree of segregation
of the sand and fines. In contrast, the MFT treated with a 2 wt% (NI-14)2504
solution containing
0.1 wt% PAM showed settled and compacted solids in contact with a clear
supernatant. As the
amount of polymer in the solution is reduced from vial A4 to E4, the clarity
of the supernatant
decreases, as more suspended particles remain in the liquid phase. Greater
clarity of the
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supernatant liquid should be achievable at longer centrifuge times, but for
short processing times,
treating MFT to result in a salt-tailings concentration of no less than about
0.5 wt% and a
polymer-tailings concentration of no less than about 0.04 wt% are preferable.
[0088] The solids contents of the consolidated materials in each of the
vials shown in
Figure 4 was determined by drying, i.e., the centrifuged consolidated material
was separated
from its supernatant liquid, the wet mass weighed, dried and reweighed to
determine a solids
content. The solids content of the consolidated materials for the sets of
vials are summarized in
Table 3.
Table 3: The solids content of centrifuged ammonium sulfate/PAM treated MFT as
determined
by separating and drying consolidated material.
0.1% PAM 0.08% PAM 0.06% PAM 0.04% PAM 0.02% PAM
% Solids % Solids % Solids % Solids % Solids
2% (NF14)7SO4 60.3% 58.8% 58.1% 52.0% 48.5%
1% (NH4)2504 54.4% 57.2% 58.1% 56.3% 44.6%
[0089] It can be seen that for the 2 wt% (NI-14)2504 solution containing
0.1 wt% PAM, a
solids content of just over 60% was achieved. This decreased only slightly
when treating MFT
with solutions including PAM concentrations of 0.08 wt% and 0.06 wt%, but
significantly at
lower PAM concentrated solutions. Treating MFT with an equal weight of the (NI-
14)2504
polymer solutions resulted in a salt-tailings concentration of about 1 wt% for
each of vials A4-
E4, and for vial A4, a polymer-tailings concentration of about 0.05 wt% PAM,
for vial B4 a
polymer-tailings concentration of about 0.04 wt% PAM, for vial C4 a polymer-
tailings
concentration of about 0.03 wt% PAM, for vial D4 a polymer-tailings
concentration of about
0.02 wt% PAM, and for vial E4 a polymer-tailings concentration of about 0.01%
PAM. For the
1 wt% (N1-14)2504 solutions, the solids content was very variable, reflecting
the problems with
segregation of coarse and fine particles in the consolidated materials in
these experiments.
[0090] Increased Salt Concentration Allows for Lower Polymer Concentration
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[0091] When salt, polymer and sand are used together to treat tailings, it
was observed
that the polymer-tailings concentration can be reduced if the salt-tailings
concentration is
increased under certain circumstances. Thus, very low polymer-tailings
concentration can
achieve reasonably fast consolidation of solids in the tailings if the salt-
tailings concentration is
increased. Figure 5 illustrates that as the salt concentration increases, less
polymer flocculant is
needed to obtain clear supernatant solutions. For these tests, the polymer-
tailings concentration
increases from 0.01% to 0.05% in 0.01% increments from right to left while the
salt-tailings
concentration increases from 1% to 2% from top to bottom.
[0092] Varying Polymer Concentration in Treating Oil Sands Tailings with
Seawater
[0093] For these experiments, solutions of seawater (sourced from the U.S.
eastern shore
of the Atlantic Ocean) were prepared with various concentrations of a nonionic
polyacrylamide
(available from SNF as FA920) between 0.1% (by weight) and 0.02% (by weight).
The
concentration of highly soluble salts in the seawater is believed to be
greater than 3 wt%. The
seawater-polymer solutions were used to treat MFT from oil sands processing.
An equal amount
of seawater ¨polymer solution was used to treat MFT (about 5 g of seawater
¨polymer solution
to about 5 g of MFT) in a vial. The treated mixtures were first stirred and
then the vials were
centrifuged at 3000 rpm for 30 seconds to accelerate settling. The results are
shown in the
picture of Figure 6. From left to right, the seawater used to treat the MFT
included about 0.1
wt%, 0.08 wt%, 0.06 wt%, 0.04 wt% and 0.02 wt% of the polymer flocculant,
respectively.
These experiments show that a mixture of highly soluble salts sourced from an
ocean can be used
in the process of the present disclosure.
[0094] Only the preferred embodiment of the present invention and examples
of its
versatility are shown and described in the present disclosure. It is to be
understood that the
present invention is capable of use in various other combinations and
environments and is
capable of changes or modifications within the scope of the inventive concept
as expressed
herein. Thus, for example, those skilled in the art will recognize, or be able
to ascertain, using
no more than routine experimentation, numerous equivalents to the specific
substances,
procedures and arrangements described herein. Such equivalents are considered
to be within the
scope of this invention, and are covered by the following claims.
