Sky Journal of Soil Science and Environmental Management Vol. 4(1), pp. 016 - 019, March, 2015
Available online http://www.skyjournals.org/SJSSEM
ISSN 2315-8794© 2015 Sky Journals
Full Length Research Paper
Absorption capacity and time effect on polarity
evaluation of various solvents using natural bentonite
clay mineral
Obi C.* and Okoye I. P.
Physical Chemistry Unit, Department of Pure and Industrial Chemistry, Faculty of Chemical Sciences, University of Port
Harcourt, P.M.B. 5323, Choba, Port Harcourt, Rivers State, Nigeria.
Accepted 26 November, 2014
The rates of absorption of various solvents onto different weights of natural bentonite clay mineral were
investigated at room temperature. A column technique was adopted in the absorption process. The
physicochemical properties of the clay mineral were determined using the pH drift method, ethylene glycol
monoethylether method and atomic absorption and emission spectrophotometer. The results reveal that the
bentonite clay mineral took longer time to absorb polar solvents (1020 – 3660 s) while non – polar solvents were
3 -1
faster (120 – 600 s). The result reveal that water has the highest absorption capacity of 2.1 cm g . The degree of
polarity was observed in the order: water > ethanol > acetone > methyl chloride > petroleum spirit. The
absorption experiment proved that bentonite is a hydrophilic clay mineral. This research is a preliminary
approach to highlight the steps in the removal of hazardous wastes from landfills.
Key words: Bentonite, absorption, polarity, solvents, characterization.
INTRODUCTION
Clay is a naturally occurring aluminium silicate composed
primarily of fine - grained minerals (Grim, 1953).
Bentonite is a rock formed of highly colloidal and plastic
clays composed mainly of montmorillonite (smectite
group) (Lagaly, 1995). The industrial application of
bentonite clay depends on the composition of their clay
and non-clay minerals. The clay minerals in bentonite are
smectite such as montmorillonite, beidellite, saponite,
hectorite, etc (Grim, 1968). On the other hand, the nonclay minerals include silica (for example, quartz and
opals), feldspars, zeolites, carbonates, sulphites,
sulphides, sulphates, oxides and hydroxides (More and
Reynolds, 1997). Two types of bentonite clays exist
according to swelling and non-swelling properties.
Sodium bentonite is of swelling type while calcium
bentonite is non-swelling.
Sodium and calcium bentonite are distinctly
characterized by high ratio of their dominant
*Corresponding author. E-Mail: [email protected]. Tel:
+234-8036682351.
exchangeable base. Intermediate type bentonite may
have either sodium or calcium base dominant but in low
or nearly equal ratios mixed (Togan, 2006).
The special properties of bentonite clay minerals
include ability to form thixotrophic gels with water, ability
to absorb large quantities of water and a high cation
exchange capacity. These properties of bentonite clay
minerals are derived from the crystal structure of the
smectite group, which is an octahedral alumina sheet
between two tetrahedral silica sheets (2:1) (Yang and
Ding, 2007; Bahranowski, 1998; Brown and Anderson,
1983).
Variations in interstitial water and exchangeable cations
in the interlayer of clay affect the properties of bentonite
and thus the commercial applications of the different
types of bentonite clay minerals (Sergio et al., 2006). The
exchangeable cations are positively charged species that
are reversibly adsorbed to negatively charged clay
surfaces (Brown and Anderson, 1983). The resultant
equilibrium concentrations of the cations and their
compositions will enhance the polarities of the different
Obi and Okoye
leachates (solvents) in clay.
The adsorption kinetics of clay minerals has intrigued
soil scientists for over a century. Most investigators have
been interested in the total exchange capacity and
equilibrium exchange relationships, but few have studied
the rate of cation exchange on clay minerals (Inglezakis
et al., 2003; Obi and Okoye, 2014). In addition, literature
has shown little information concerning the impact of clay
in polarity studies.
Hence, the aim of this study is to evaluate the rate of
absorption of various solvents on natural bentonite clay
mineral and possibly determine their degree of polarity.
MATERIALS AND METHODS
17
for each of the bentonite weights. Water (5 ml) was
added onto the bentonite via a pipette and immediately,
the time for the last drop of water was measured using a
stop watch. The same process was repeated for each of
the solvents at different bentonite weights. The
3
absorption capacities (cm /g) of the solvents were
determined using the equation 2:
(2)
Where qe is the absorption capacity of the solvents in
3
3
cm /g, Vi is the initial volume in cm , Ve the equilibrium
3
3
volume in cm , VT is the total volume in cm and M is the
mass of absorbent in grams.
Collection and preparation of absorbent
Natural bentonite clay mineral used in this study was
obtained from Ezinachi clay deposit in Okigwe, Imo State,
Nigeria. The sample was washed with water, dried and
sieved to remove other impurities and particles. It was
then ground to powder in a mortar and allowed to pass
through 250 µm sieve to form a homogeneous powder.
Characterization of the absorbent
Characterization of absorbents
The physical and metal oxide compositions of sample
clay mineral as determined are presented in Tables 1 and
2.
Absorption Studies
The point of zero charge (PZC) of the bentonite clay
mineral was determined using the pH drift method
(Eggleston and Jordan, 1998). The specific surface area
(SSA) of the clay mineral was determined using the
ethylene glycol monoethylether (EGME) method (Amy
and Alan, 2002) and the equation below was used for the
calculation:
SSA =
RESULTS AND DISCUSSIONS
(1)
Where W F is final weight of clay – solvent slurry in g, W S
is the initial weight of the clay sample in g, 0.000286 is a
constant known as the weight of EGME required to form
a monomolecular layer on a square meter surface in
2
g/m . The chemical composition of the clay mineral was
determined by atomic absorption and emission
spectrophotometer (Okoye and Obi, 2011).
Absorption Studies
The rates of absorption of the solvents were carried out
isothermally using burette clapped on a retort stand,
calibrated beaker and pipette. Cotton wool was placed at
the bottom of the burette. Different weights of the natural
bentonite (1.0 g, 1.5 g, 2.0 g, 2.5 g and 3.0 g) were put
into the burette. Each 5 ml of water, ethanol, acetone,
methyl chloride and petroleum spirit were measured out
The rates of absorption of the various solvents are
presented in Figure 1. The result revealed that the natural
bentonite clay took longer time to absorb water. This
could be due to the presence of only O – H bonds which
makes it extremely polar. Ethanol absorption was close to
water indicating that it is also polar. Equally acetone was
also polar. The result further revealed that the rate of
absorption of methyl chloride and petroleum spirit was
faster. This could be due to the absence of O – H bond,
thereby making it extremely non-polar. The kinetic
dynamics of these solvents could be as a result of their
varying densities and dielectric constants. Therefore, the
degree of polarity is given as: water > ethanol > acetone
> methyl chloride > petroleum spirit. The result revealed
that water has the highest absorption capacity of 2.1
3 -1
cm g .The result obtained was similar to the work done
by Brown and Anderson, (1983) on the effects of organic
solvents on the permeability of clay soils.
Conclusion
The study of effect of time on the polarity properties of
water, ethanol, acetone, methyl chloride and petroleum
spirit using natural bentonite clay mineral have shown
that the clay mineral is hydrophilic in nature. This
property makes it suitable in the paint and
pharmaceutical industries. The bentonite clay could
equally be used in the screeding of walls. In addition, the
18
Sky. J. Soil. Sci. Environ. Manage.
Table 1. Physical properties of the sample clay mineral.
2
pH
6.2
SSA(m /g)
30.00
Specific gravity
1.96
Point of zero charge
4.5
Moisture (%)
1.82
Table 2. Metal oxide composition and loss in ignition of the sample clay mineral.
Metal oxide
% Mass
SiO2
50.45
Al2O3
30.34
Fe2O3
2.78
CaO
0.10
MgO
0.23
Na2O
0.07
K2O
0.87
TiO2
0.01
MnO
0.08
Ignition loss
11.54
Figure 1. Effect of time on the absorption of the solvents at 298 K. Where A
represents petroleum spirit, B methyl chloride, C is acetone, D is ethanol and E is
water.
rate at which it absorbs non-polar solvents is faster than
polar solvents.
ACKNOWLEDGEMENTS
Authors would like to thank Mr. Peter NT of the
Department of Pure and Industrial Chemistry, University
of Port Harcourt, Rivers State for his laboratory
assistance.
Competing interests
Authors declare that there is no competing interest.
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