3462 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
is destabilized to generate large aggregates via the mecha-
nisms of charge neutralization, bridging, sweeping, and
patch flocculation [5]. The aggregation of fine particles can
effectively improve the filtration rate. But in practice, the
filtration efficiency could be significantly affected by the
structural properties of the aggregates (flocs). The important
properties include floc size, strength, compressibility when
subjected to pressure, and porosity distribution. Typically,
researchers discovered that inorganic coagulants can better
capture very fine solids, forming strong but relatively small
flocs [1]. The use of coagulants has the advantage of giving
better clarity of filtrate, but it may consume a large dosage
of them to guarantee an effective filtration operation. In
contrast, flocculants with long molecular chains generate
large flocs with good voids [6, 7]. However, these flocs tend
to be compressible and easily deform during the pressure
compression stage, resulting in the closure of voids and a
decrease in slurry filterability [8, 9]. Sometimes physical
filter aids such as char, fly ash, wood chips, and bagasse
are added together with chemical additives to enhance the
mechanical strength and filtration permeability of tailings
slurry [10]. Given the special characteristics of aggregates
induced by coagulants and flocculants, a combination of
them is common to aggregate fine particles before filtra-
tion. Compared to individual applications, their synergistic
effects can optimize the floc property, realizing an efficient
and cost-effective dewatering process of fine tailings by
pressure filtration.
Based on coagulation-flocculation filtration, the pres-
ent investigation aims to examine a different strategy in
terms of chemical conditioning to enhance the pressure
filtration dewatering of oil sands tailings. Oil sands tailings
are the legacy following the mining and bitumen extraction
in Alberta, Canada. It is clay-rich, containing the major
clay components of fine kaolinite, illite, and montmoril-
lonite. Besides, oil sands tailings have residual bitumen in
the forms of free droplets, water-bitumen emulsion, and
clay-bitumen associates [11]. The above two reasons con-
tribute to the colloidal stability of the oil sands tailings
suspension, making it much more challenging to dewater
versus the typical hard rock mine tailings [12]. Herein, a
new polymeric complex flocculation for oil sands tailings
is proposed. It is hypothesized that introducing a cross-
linking reagent that can interact with both coagulants and
flocculants could produce specific flocs that benefit pres-
sure filtration. In detail, we used ferric chloride (FeCl3) and
polyethylene oxide (PEO) as coagulants and flocculants,
respectively, for the chemical conditioning of tailings. A
polyphenolic compound, tannic acid (TA), was used as
an additional crosslinker with coagulants and flocculants.
The TA is selected because it can on one hand “clean” the
particle’s surface by dispersing the clays and associate bitu-
men contaminants in oil sands tailings. This cleaning effect
may help the adsorption interaction between coagulants/
flocculants and fine solids. More importantly, TA can coor-
dinate with ferric ions and form Fe-TA complexes [12,
13], meanwhile, it can also complex with PEO and form
TA-PEO associative complexes [14]. We guessed that TA
might bridge the function of FeCl3 and PEO and form
a tri-component polymeric network, which would have
advantageous effects on the mechanical properties of flocs
and the filtration process.
In this work, we first conducted batch filtration tests of
oil sands tailings under different chemical conditions. We
focused on evaluating the filtration performance with and
without tannic acid treatment in conditioning. Then we
attempted to reveal the beneficial role of tannic acid from
aspects of flocculation chemistry and floc property through
characterization techniques.
MATERIALS AND METHODS
Oil Sands Tailings and Reagents
The tailings were provided by oil sands operators in north-
ern Alberta. The received oil sands tailings were analyzed
using the Dean-Stark method to determine the content of
water, bitumen, and solid. The results show that the solid
content in the tailings sample was ca. 23.4 wt%, with 1–2
wt% bitumen and the rest of water. XRD analysis show the
mineral composition in the solids included quartz, kaolin-
ite, illite, and smectite. Hexahydrated iron (III) chloride
(FeCl3⋅6H2O, Sigma-Aldrich) was used as a coagulant.
PEO (Polysciences, Inc.) with a molecular weight of
8 MDa was used as a flocculant. Tannic acid (nominally
C76H52O46, Fisher Scientific) was used as a polyphenol
moiety acting as the crosslinker in the polymeric network.
Pressure Filtration Unit and Procedure
Fig.1 shows the chemical conditioning setup (on the left)
and Millipore filtration unit (on the right). Before the fil-
tration, 250 grams of raw oil sands tailings were weighed
and conditioned in a 2-L beaker with an agitation speed of
250 rpm. The tannic acid, ferric chloride, and PEO were
added in sequence according to the experimental condi-
tions. The conditioning time with each chemical was deter-
mined from the real-time torque values on the stirrer as
described in previous work [15]. After conditioning, the
chemical-treated tailings were transferred to the cylindrical
vessel of the filtration unit. The filtration time was set at
30 min with a constant pressure of 600 kPa. During the
process, the accumulative filtrate weight versus filtration
is destabilized to generate large aggregates via the mecha-
nisms of charge neutralization, bridging, sweeping, and
patch flocculation [5]. The aggregation of fine particles can
effectively improve the filtration rate. But in practice, the
filtration efficiency could be significantly affected by the
structural properties of the aggregates (flocs). The important
properties include floc size, strength, compressibility when
subjected to pressure, and porosity distribution. Typically,
researchers discovered that inorganic coagulants can better
capture very fine solids, forming strong but relatively small
flocs [1]. The use of coagulants has the advantage of giving
better clarity of filtrate, but it may consume a large dosage
of them to guarantee an effective filtration operation. In
contrast, flocculants with long molecular chains generate
large flocs with good voids [6, 7]. However, these flocs tend
to be compressible and easily deform during the pressure
compression stage, resulting in the closure of voids and a
decrease in slurry filterability [8, 9]. Sometimes physical
filter aids such as char, fly ash, wood chips, and bagasse
are added together with chemical additives to enhance the
mechanical strength and filtration permeability of tailings
slurry [10]. Given the special characteristics of aggregates
induced by coagulants and flocculants, a combination of
them is common to aggregate fine particles before filtra-
tion. Compared to individual applications, their synergistic
effects can optimize the floc property, realizing an efficient
and cost-effective dewatering process of fine tailings by
pressure filtration.
Based on coagulation-flocculation filtration, the pres-
ent investigation aims to examine a different strategy in
terms of chemical conditioning to enhance the pressure
filtration dewatering of oil sands tailings. Oil sands tailings
are the legacy following the mining and bitumen extraction
in Alberta, Canada. It is clay-rich, containing the major
clay components of fine kaolinite, illite, and montmoril-
lonite. Besides, oil sands tailings have residual bitumen in
the forms of free droplets, water-bitumen emulsion, and
clay-bitumen associates [11]. The above two reasons con-
tribute to the colloidal stability of the oil sands tailings
suspension, making it much more challenging to dewater
versus the typical hard rock mine tailings [12]. Herein, a
new polymeric complex flocculation for oil sands tailings
is proposed. It is hypothesized that introducing a cross-
linking reagent that can interact with both coagulants and
flocculants could produce specific flocs that benefit pres-
sure filtration. In detail, we used ferric chloride (FeCl3) and
polyethylene oxide (PEO) as coagulants and flocculants,
respectively, for the chemical conditioning of tailings. A
polyphenolic compound, tannic acid (TA), was used as
an additional crosslinker with coagulants and flocculants.
The TA is selected because it can on one hand “clean” the
particle’s surface by dispersing the clays and associate bitu-
men contaminants in oil sands tailings. This cleaning effect
may help the adsorption interaction between coagulants/
flocculants and fine solids. More importantly, TA can coor-
dinate with ferric ions and form Fe-TA complexes [12,
13], meanwhile, it can also complex with PEO and form
TA-PEO associative complexes [14]. We guessed that TA
might bridge the function of FeCl3 and PEO and form
a tri-component polymeric network, which would have
advantageous effects on the mechanical properties of flocs
and the filtration process.
In this work, we first conducted batch filtration tests of
oil sands tailings under different chemical conditions. We
focused on evaluating the filtration performance with and
without tannic acid treatment in conditioning. Then we
attempted to reveal the beneficial role of tannic acid from
aspects of flocculation chemistry and floc property through
characterization techniques.
MATERIALS AND METHODS
Oil Sands Tailings and Reagents
The tailings were provided by oil sands operators in north-
ern Alberta. The received oil sands tailings were analyzed
using the Dean-Stark method to determine the content of
water, bitumen, and solid. The results show that the solid
content in the tailings sample was ca. 23.4 wt%, with 1–2
wt% bitumen and the rest of water. XRD analysis show the
mineral composition in the solids included quartz, kaolin-
ite, illite, and smectite. Hexahydrated iron (III) chloride
(FeCl3⋅6H2O, Sigma-Aldrich) was used as a coagulant.
PEO (Polysciences, Inc.) with a molecular weight of
8 MDa was used as a flocculant. Tannic acid (nominally
C76H52O46, Fisher Scientific) was used as a polyphenol
moiety acting as the crosslinker in the polymeric network.
Pressure Filtration Unit and Procedure
Fig.1 shows the chemical conditioning setup (on the left)
and Millipore filtration unit (on the right). Before the fil-
tration, 250 grams of raw oil sands tailings were weighed
and conditioned in a 2-L beaker with an agitation speed of
250 rpm. The tannic acid, ferric chloride, and PEO were
added in sequence according to the experimental condi-
tions. The conditioning time with each chemical was deter-
mined from the real-time torque values on the stirrer as
described in previous work [15]. After conditioning, the
chemical-treated tailings were transferred to the cylindrical
vessel of the filtration unit. The filtration time was set at
30 min with a constant pressure of 600 kPa. During the
process, the accumulative filtrate weight versus filtration