Research Article Enhanced Viscosity of Aqueous Palygorskite

Hindawi Publishing Corporation
Advances in Materials Science and Engineering
Article ID 941580
Research Article
Enhanced Viscosity of Aqueous Palygorskite Suspensions
through Physical and Chemical Processing
Feng-shan Zhou,1 Tian-qi Li,1 Yun-hua Yan,2 Can Cao,1 Lin Zhou,1 and Yang Liu1
1
2
School of Materials Science and Technology, China University of Geosciences (Beijing), Beijing 100083, China
The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University,
Beijing 100871, China
Correspondence should be addressed to Feng-shan Zhou; [email protected]
Received 12 July 2014; Revised 14 August 2014; Accepted 14 August 2014
Academic Editor: Zhaohui Li
Copyright © Feng-shan Zhou et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Palygorskite has remarkable rheological properties and was used to increase the stability and viscosity of aqueous suspensions. The
effects of different physical and chemical processing methods on the apparent viscosity and plastic viscosity of the palygorskite
suspensions such as pressing, ultrasound scattering, acidification, and chemical additives have been released. The pressing and
ultrasound scattering indicated that the dispersed state of palygorskite could be increased effectively after treatment, and the
apparent viscosity of treated-palygorskite samples increased almost 2-3 times compared to that of before. The viscosity of the
acid-treated palygorskite suspension was not increased. The viscosity increased with the content of bentonite in the mixture of
bentonite and palygorskite in fresh water. It seemed to be not worthy to add a certain amount of bentonite to palygorskite in order
to enhance viscosity and vice versa. Chemical additives appeared to have good effects on the rheological behavior of palygorskite
suspension. Magnesium oxide revealed great contribution to viscosity enhancement. The main mechanism was the electrostatic
attractive interaction between magnesium oxide particles with positive charges and the palygorskite rods with negative charges.
This interacted force has an impact on the structural inversion of palygorskite rods and even caused the reinforcing of flocculation.
1. Introduction
Clay minerals have remarkable rheological properties and
are used to increase the stability and viscosity of flowing
suspensions. They tend to form gel-like structures at low solid
contents [1]. This property is of great importance in a very
wide range of applications for drilling fluids, paints, liquid
fertilizers, wild-fire suppressants, foundry coatings, animal
flowing feeds, molecular sieve binders, and a lot of aqueous
suspensions in which rheological properties play a significant
role [1–5].
Palygorskite forms gel structures in fresh and salt water
by establishing a lattice structure of particles connected
through hydrogen bonds. In the drilling industry, these
properties enable the clay suspension to suspend the large
dense particles of the drilling cuttings and require relatively
low pump power during water circulation [1, 7]. Palygorskite,
unlike bentonite, will form gel structures in salt water and is
used in special salt-water drilling mud for drilling formations
contaminated with salt [8]. Palygorskite particles can be
considered as charged particles with zones of positive (+) and
negative (−) charges. It is the bonding of these alternating
charges that allows them to form gel suspensions in salt and
fresh water.
Although most clay minerals form stable and viscous
suspensions when dispersed in water, the mechanisms of gel
formation for each clay mineral differ because of their unique
structures, particle size and shape, and composition [9, 10].
Unlike the swelling clay minerals such as montmorillonite, palygorskite as a fibrous nonswelling clay mineral, the
fibre length and number of silanol groups on the surface of
the fibre play an important role in aggregating fibres together
[11] and forming a random network that entraps water and
increases viscosity [12].
Neaman and Singer [13–15] systematically studied the
rheological properties of six palygorskite samples, used them
2
Advances in Materials Science and Engineering
Table 1: The chemical compositions, the physical properties, and the theoretical crystal structural formula of the palygorskite sample in
present work.
Components
SiO2
Content/wt%
64.89
Al2 O3
TiO2
Fe2 O3
FeO
MgO
CaO
Na2 O
K2 O
P2 O5
SO3
12.95
1.26
8.19
0.16
9.11
1.48
0.07
1.33
Crystal structural formula: (Mg0.81 Al0.73 Fe3+ 0.36 Ca0.09 Ti0.06 )(Si3.83 Al0.17 )O10 (OH)⋅4H2 O
Cation exchange capacity (CEC): 49.8 meq/100 g
Specific surface area: 462.0 m2 /g
0.43
0.02
as a kind of common thixotropic modifier in aqueous suspensions, and focused on the influence factors including the
ratio of crystal length to diameter, concentration of sodium
chloride (NaCl), and pH. The effects of pressing modification
and adding magnesium oxide (MgO) [16, 17], ultrasound
scattering [18, 19], acidification [6, 20], and even the mixed
palygorskite-bentonite suspensions [21] on the rheological
properties of palygorskite suspensions also have been studied.
High-pressure homogenization process with solvent and
electrolytes with dispersion properties of palygorskite were
investigated in detail by Xu et al. [22–24]. They dispersed
the natural palygorskite in six solvents including distilled
water, methanol, ethanol, isopropanol, dimethyl formamide,
and dimethyl sulfoxide and then carried out high-pressure
homogenization. They confirmed that colloidal stability and
suspension viscosity were affected by the solvent nature,
and a much higher viscosity was obtained by dispersing
palygorskite in isopropanol, but the good colloidal stability was obtained in dimethyl sulfoxide (DMSO) solvent.
A series of palygorskite samples modified with inorganic
potassium electrolytes including KCl, KBr, KI, KH2 PO4 ,
KHSO4 , K2 HPO4 , K2 SO4 , and K3 PO4 were prepared with
the aid of high-pressure homogenization. A stable suspension
was obtained when palygorskite was dispersed in K2 SO4
solutions. Because the requirement of the viscosity is more
than the stability for palygorskite suspension, obviously, high
prices and toxic solvents in their works would be limiting the
value of industrial applications.
However, no one had systematically studied the influence
of viscosity and the methods of enhanced viscosity for palygorskite gel. The purpose of the present work is to study the
effects of different physical and chemical processing methods,
such as pressing, ultrasound scattering, acidification, and
chemical additives, on the apparent viscosity and plastic
viscosity of the aqueous palygorskite suspensions.
obtained from Beijing Taihua Bentonite Science & Technology Development Co., Ltd. (Beijing, China). Industrial
grade magnesium oxide (also named calcined magnesia;
light-burned magnesia) (MgO) and magnesium hydroxide
(Mg(OH)2 ) samples were obtained from Dandong Yilong
High Science & Technological Materials Co., Ltd. (Liaoning,
China).
2. Materials and Methods
Ultrasound Scattering. 25 g palygorskite and a certain amount
of tap-water were added into an 80 mL beaker, stirred,
and then loaded onto the platform of an ultrasonic cell
crusher. The time of ultrasound scattering on the platform of
ultrasonic cell crusher was 10 min and repeated 2-3 times to
make a better dispersion.
2.1. Materials. Palygorskite mineral sample with purity
greater than 95% was received from Mingguang Palygorskite
Mining Co., Ltd. (Anhui, China). The average length of the
palygorskite rods is around 1 m, and the average aspect
ratio is about 20. The chemical compositions, the physical
properties, and the theoretical crystal structural formula of
the palygorskite sample in present work are listed in Table 1.
There are two bentonite mineral samples used in this
work. One bentonite sample was obtained from Sinopec
Shengli Oilfield Co., Ltd. (Shandong, China). Another bentonite containing palygorskite sample from Iraq Anbar was
2.2. Instruments. The experiment of pressing palygorskite
was conducted on Jinniu JL-80 vertical grinder (1.5 KW;
Hualian Industry Co., Ltd.) (Beijing, China). The ultrasonic
dispersion test was carried out by JY92-IIDN ultrasonic cell
crusher (20–24 KHz, 650 W; Ningbo Scientz Biotechnology
Co., Ltd.) (Zhejiang, China). The modified palygorskite was
filtrated by SHB-III water circulation pumps (180 W; Xi’an
Taikang Biotechnology Co., Ltd.) (Shaanxi, China) and dried
by a 101-3 electric blast drying oven (300∘ C maximum; Shanghai Rolling-gen Equipment Co., Ltd.) (Shanghai, China).
The gelation of samples dispersion was prepared after being
stirred by GJ-2S digital display high-speed agitator (180 W,
4000–11000 rpm). The rheological parameters of suspensions
were conducted by ZNN-D6A six-speed rotary viscometer
(speed: 3, 6, 100, 200, 300, and 600 rpm, viscosity range: 0–
300 mPa⋅s). Both of the latter instruments were manufactured
by Qingdao Haitongda Special Instrument Co., Ltd. (Shandong, China).
2.3. Methods
2.3.1. Palygorskite Modification
Pressing. A certain amount of palygorskite and tap-water was
mixed and pressed by a vertical extruder. After that, the
palygorskite was collected, dried, and ground.
Acidification. The clay mineral was treated with hydrochloric
acid at a concentration of 2 mol/L by liquid and a solid ratio
of 10 to 1 in the flask, under mechanical stirring (550 rpm) in
dispersion at room temperature for 1 h. Then the sample was
filtrated, followed by washing with distilled water until a pH
value 3-4 was reached.
Advances in Materials Science and Engineering
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Table 2: The effect of pressing on the rheological parameters of palygorskite suspension.
Samples of palygorskite
Unpressing
Unpressing with 1% MgO
Pressing without MgO
Pressing with 1% MgO
600
(dia)
300
(dia)
39
59
48
85
35
44
41
75
Rheological parameters
AV
PV
(mPa⋅s)
(mPa⋅s)
19.5
29.5
24.0
42.5
Chemical Additives. Certain amounts of additives were added
into 6.4 w/v% palygorskite dispersions. The dosage of chemical additives (%) in the tables and the figures was the ratio of
mass between chemicals and palygorskite.
The dispersions were stirred mechanically at 8000 rpm for
20 min at room temperature and hydration was conducted for
24 h. The term of hydration was an ageing process of water
penetrating the interlayer spaces and concomitant adsorption
with the clay swelling and colloidization.
2.3.2. Rheological Parameters Measurement. Darley and
George [8] concluded the common composition and properties of drilling and completion fluids. According to the
American Petroleum Institute (API) recommended practice
(2009) [25], the parameters of the palygorskite gel in the
drilling fluid suspension samples were prepared and measured under the specification and standard procedures. The
viscosity and gel strength of the modified gels were tested
by a rotating viscometer (ZNN-D6 S). The hydrated gels
underwent mechanical stirring at 8000 rpm for a further
20 min. This preparation step before measuring the viscosity
was to make the dispersion even and flowing. And then
the viscosity was measured at different shear rates (different
stirring velocity).
2.3.3. Rheological Theory. According to Bingham-plastic
model, the rheological parameters, including AV (apparent
viscosity), PV (plastic viscosity), YP (yield point), and RYP
(ratio of yield and plastic viscosity), were calculated with the
dial readings of 300 rpm and 600 rpm using the following
formulas according to the API recommended practice of
standard procedures [25]:
AV = 0.5600 (mPa ⋅ s)
PV = 600 − 300 (mPa ⋅ s)
YP = 0.511 (300 − PV) (Pa)
RYP =
(1)
YP
(Pa/mPa ⋅ s) ,
PV
where 600 (dia) was the dial reading of rotating viscometer
at 600 rpm and 300 (dia) was the dial reading of rotating
viscometer at 300 rpm.
2.3.4. Microscopic Examination. The morphology of the
palygorskite and modified palygorskite with additives was
4.0
15.0
7.0
10.0
YP/PV
(Pa/mPa⋅s)
15.84
14.82
17.37
33.22
3.96
2.00
2.48
3.32
Ultrasound
dispersion
Ultrasound
dispersion
Palygorskite
aggregate
YP
(Pa)
Rod bundles
Rod grains
Figure 1: The mechanism of ultrasound scattering dispersion for
palygorskite aggregates.
observed in a Quanta 200FEG environmental scanning
electron microscope (SEM). All of the raw minerals were
firstly made to powder samples, which were dried from dilute
0.2% dispersions before the SEM examination. The modified
palygorskite gel samples were also dried out from the same
concentration before SEM measurement.
3. Results and Discussion
3.1. Pressing Effect. Pressing as an effective way to break
up close and compact bulks of natural palygorskite rods
could more easily disperse palygorskite fibers in water. Experimental measurement of viscosity of pressed palygorskite
showed that the apparent viscosity increased from 19.5 mPa⋅s
to 42.5 mPa⋅s (Table 2).
Pressing can be applied as a useful approach to enhance
better dispersion of palygorskite particles, especially for raw
palygorskite aggregates. However, in our opinion, compared
to effective viscosity enlarging by using small amount of
chemical, the pressing with the inefficient and high cost
was not a suitable technique for enhanced viscosity of
palygorskite suspension in some applications with low added
value such as drilling fluids.
3.2. Ultrasound Scattering Effect. Song et al. [18] found
that after treatment with ultrasound the palygorskite crystal
bundles were crushed into crystal needles, generating palygorskite nanoparticles. What is more, Zhao et al. [19] studied
the dispersion of palygorskite in a polypropylene matrix, and
their SEM and TEM analysis results showed that ultrasonic
oscillation promoted the dispersion of palygorskite particles
(Figure 1).
Under the condition of ultrasound dispersion, the apparent viscosity was raised rapidly from 19.5 mPa⋅s to 54 mPa⋅s
(Table 3). The enhancement of viscosity was related to the fact
that ultrasonic cavitation could cause local high temperature
and high pressure. The shock wave and microjet in dispersion
brought about intense collisions of palygorskite aggregates
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Table 3: The effect of ultrasound scattering on the rheological parameters of palygorskite suspension.
Samples of palygorskite
600
(dia)
300
(dia)
No ultrasound scattering
Ultrasound scattering
39
108
35
92
in aqueous suspensions just like the same dispersion mechanism in polypropylene matrix described in Figure 1.
3.3. Acidification Effect. Many practices using acid to purify
palygorskite have been reported in the literature. For example, Neaman and Singer [20] used acid to remove carbonates and other cement impurities. Other researchers used
acidification to break up the cluster of closely bound fibers
to increase specific surface area for good dispersion and
absorption. The raw material in the experiment was of high
purity. Octahedral cations dissolved and crystal structure
was even changed because of the high concentration of acid
and reaction time. Chen et al. [6] investigated the structural
changes of palygorskite with reaction to acid; their results
indicated that dissolution of octahedral reactions increased
with an increase in acid concentration and reaction time.
When octahedral cations were dissolved completely, the final
product was mesoporous amorphous silica-fiber (Figure 2).
The study showed that the gel of the acidified palygorskite
in dispersion came to serious sedimentation after hydration.
Initially, with the ratio of acid to palygorskite being 10 to 1 and
concentration of HCl being 2 mol/L, the apparent viscosity
value was only 5 mPa⋅s. By reducing the concentration and
amount of acid solution (weight ratio of acid to palygorskite
was 4 to 1; concentration of HCl was 1 mol/L), the AV still
measured only 10 mPa⋅s. Obviously, acidizing palygorskite
viscosity was not enhanced in the present work; the opposite
is the case.
3.4. Effects of Bentonite. Several studies have been carried
out in the past to understand the rheological properties of
standard clays [9, 10, 13–15, 26–28]. However, there are a
lot of works on the rheological properties of mixed clay
suspensions in recent years. The influence of montmorillonite
addition on the rheological behaviour of palygorskite suspensions was investigated by Neaman and Singer [13–15].
Rheological properties of palygorskite-bentonite mixed clay
suspensions were studied by Chemeda et al. [21].
The limited information is considered important because
most clay used such as in drilling fluid applications usually
contains more than one type of clay minerals along with
nonclay minerals. For example, palygorskite occurs in association with smectite in most of the known world palygorskite
deposits [6]. Therefore it is worthwhile to understand the
rheological behavior of suspensions containing mixtures of
clay minerals.
The most difference of rheological properties between
palygorskite and bentonite was that palygorskite can be used
in fresh water and salt water, but the bentonite is only
Rheological parameters
AV
PV
(mPa⋅s)
(mPa⋅s)
19.5
54.0
4
16
YP
(Pa)
YP/PV
(Pa/mPa⋅s)
15.84
38.84
3.96
2.43
used in fresh water. Figure 3 shows the effects of bentonite
addition on the viscosity of bentonite-palygorskite mixture.
The viscosity of the mixture increased with the increase
of content of bentonite in mixture in fresh water. But the
viscosity of the mixture decreased with the increase of content
of bentonite in mixture in salt water because of the poor
salt tolerance of bentonite. Taking into account the effect,
nature, and the price ratio, it was not worthy to add a certain
amount of bentonite to palygorskite, because the palygorskite
is normally used in salt water condition. For the same reason,
it was also worthless to add a certain amount of palygorskite
to bentonite.
In contrast to the admixture of bentonite and
palygorskite, some kinds of natural coexisting bentonitepalygorskite clay mixture would have a very high viscosity
(Figure 4), because their random network structures were
formed more easily which entrapped water and increased
viscosity. But for some others, the same viscosity behavior
does not appear [6]; the real reason is still unknown.
3.5. Effects of Magnesium Oxide. The experimental measurements of samples with chemical additives (Figure 5) exhibited
that the sample added MgO showed an increased viscosity
value with lower MgO content. This higher viscosity value
exhibited better cuttings suspension and carrying capacity in
drilling fluids.
When MgO particles were added to water, the reaction
happened as follows:
MgO + H2 O  Mg(OH)2  Mg2+ + 2OH−
(2)
The cation exchange ability of Mg2+ was better than
Na . The Mg2+ entered into the channels of clay mineral
particles and caused shrinkage of the electrical double layer.
The shrinkage of the electrical double layer easily formed
face-face aggregation. At the same time, the absorbed Mg2+
bridged edge and face formed edge-edge and edge-face
flocculation.
As already stated above, the PV reflected the internal
friction of suspended particles, the liquid phase, and their
interface. Flocculation reinforced the suspension network
structure with expression of an increase on viscosity.
SEM micrographs of the palygorskite with Mg(OH)2 and
MgO (Figure 6) revealed that the palygorskite had a fibrous
morphology and that Mg(OH)2 and MgO particles with positive charge dispersed in the palygorskite scaffolding structure
with negative charge. The electrostatic attractive interaction
also reinforced the palygorskite structure, confirming the
increase in viscosity.
+
5
a axis
a axis
Advances in Materials Science and Engineering
c axis
c axis
(a)
(b)
Figure 2: The channel structure change of palygorskite with acidification treatment [6]. (a) The original channel structure of palygorskite.
(b) The channel structure of palygorskite after acidification with hydrochloric acid.
30
Apparent viscosity (mPa·s)
Fresh water
25
20
API
15
4% NaCl salt water
10
5
0
0
20
40
60
80
100
Content of bentonite in the bentonite-palygorskite mixture (%)
Figure 3: The effects of bentonite addition on the viscosity of suspension of bentonite-palygorskite mixture in fresh water and salt water.
50
3.0
40
30
2.5
20
API
2.0
10
0
1.5
0.0
0.5
1.0
1.5
2.0
Content of Na 2 CO3 (%)
(a)
2.5
3.0
35
60
30
50
25
40
20
30
15
20
10
10
5
Ratio of YP/PV (Pa/mPa·s)
3.5
Yield point (mPa·s)
60
40
70
4.0
Plastic viscosity (mPa·s)
Apparent viscosity (mPa·s)
70
0
0
0.0
0.5
1.0
1.5
2.0
Content of Na 2 CO3 (%)
2.5
3.0
(b)
Figure 4: The viscosity of a natural coexisting clay mixture sample with 7% palygorskite and 57% sodium-calcium based hybrid bentonite
from Iraq Anbar. (a) The apparent viscosity and plastic viscosity of the natural coexisting clay mixture. (b) The yield point and ratio of YP/PV
of the natural coexisting clay mixture.
Advances in Materials Science and Engineering
21
18
20
3.5
19
3.0
18
2.5
16
28
14
26
12
24
10
22
8
6
20
4
18
Yield point (mPa·s)
30
4.0
20
Plastic viscosity (mPa·s)
Apparent viscosity (mPa·s)
32
17
2.0
16
1.5
15
14
1.0
13
0.5
Ratio of YP/PV (Pa/mPa·s)
6
0.0
12
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Content of MgO (%)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Content of MgO (%)
(a)
(b)
Figure 5: The effects of MgO on the rheological parameters of palygorskite suspension. (a) The apparent viscosity and plastic viscosity of
palygorskite suspension. (b) The yield point and ratio of YP/PV of palygorskite suspension.
(a)
(b)
Figure 6: The change of scanning electron microscope photograph of palygorskite processed with magnesium oxide. (a) SEM micrograph of
original unmodified palygorskite. (b) SEM micrograph of palygorskite modified adding MgO.
4. Conclusions
The results of the pressing and ultrasound scattering effect
studies indicated that the dispersed state and increasing
viscosity of clay mineral gel could be adjusted by the two
methods effectively. The mechanisms were that pressing
broke up close and compact palygorskite rods clusters, and
ultrasonic cavitations caused intense collisions within the
palygorskite aggregate. Consequently, pressing and ultrasound scattering could be used as useful modification methods for improving the viscosity of the aqueous suspension of
palygorskite.
The acidification effect would not increase the viscosity
of palygorskite, perhaps because the high concentration
acidification was harmful for gelation and dispersion of
palygorskite.
The viscosity of the mixture of bentonite and palygorskite
increased with the increase of content of bentonite in fresh
water. But the viscosity of the mixture decreased with the
increase of content of bentonite in salt water because of the
poor salt tolerance of bentonite. It seemed to be not worthy
to add a certain amount of bentonite to palygorskite in order
to enhance viscosity.
Chemical additives showed good effects on the rheological and thixotropic behavior of palygorskite suspension.
The results of adding MgO revealed that the contribution
of MgO to viscosity caused the reinforcing of flocculation.
Furthermore, the analysis showed that electrostatic attractive
interaction between MgO particles dispersed in the scaffolding structure with positive charges and the palygorskite
rods with negative charges had impact on the inversion of
palygorskite rods configuration. In drilling applications, this
higher viscosity value will provide better cuttings suspension
and carrying capacity.
Conflict of Interests
The authors declare that there is no conflict of interests
regarding the publication of this paper.
Advances in Materials Science and Engineering
Acknowledgment
Thanks are due to Dr. Susan Turner (Brisbane) for the
helpful comments on the paper and for improving the English
language.
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