Removal of
Sulfate from Water Using Polyaniline and Its Composites
Vahid Babaee, Hossein
Eisazadeh*and Ali Mahdavi
Babol
Noshirvani University of
Technology, P. O. Box 484, Babol, Iran
*Corresponding Author
E-mail: eisazadeh@hotmail.com
ABSTRACT:
One of the suitable methods for the removal of sulfate
from water is surface adsorption process. In this article, the preparation of
polyaniline and its composites as adsorbents are discussed and the capability
of separating sulfate from water was studied. The results compared with
anthracite, activated carbon and anion exchanger. The observations indicated
that the anion exchanger has the better sulfate removal percentage. Also the
results show that the sulfate removal percentage increased in
polyaniline-hydroxypropylcellulose/quartz composite.
1. INTRODUCTION:
There are many studies on the importance of water
quality and also on protection of different organic resources from wastewater
entrance. Sulfate is a common contaminant in industrial wastewaters, including
effluents from paper mills, fertilizer production, textile industries,
pesticide production, mining of metallif- erous sulfide deposits, root crop
processing such as ginger and beet and aluminium anodising. Sulfate causes odor
and corrosion in sewers during wastewater discharge, and leads to serious
difficulties during on-site anaerobic wastewater treatment1.
The contamination by sulfate compounds in wastewaters
and water are critical problems. High sulfate concentrations can unbalance the
natural sulfur cycle2,3. The accumulation of sulfate-rich sediments
in lakes, rivers and sea may cause the release of toxic sulfides that can
provoke damages to the environment4,5. Therefore, it is necessary
that sulfate-rich wastewaters require treatment before being released into the
environment. In order to remove sulfate in wastewater biological removal
technologies are commonly used due to lower energy consumption and operation
cost. As for sulphate-rich wastewaters, anaerobic biological treatment has been
widely used. Under anaerobic conditions, sulfate reducing bacteria (SRB)
respire sulfate as a terminal electron acceptor at the expense of the oxidation
of electron donors. Depending on the strain and species, these SRB can utilize
electron donors such as hydrogen, low molecular weight fatty acids and
alcohols, and a variety of environmental contaminants to support their
metabolism.6,7.
Therefore, SRB are commonly found in anaerobic
processes treating sulfate-rich wastewater8,9. The biological
sulfate reduction has been recognized as an efficient method for removing
sulfate from wastewater. Various aspects of this anaerobic process have been
studied10,11. Polyaniline (PAn) has a reactive NH group in a
polymer chain flanked on either side by a phenylene ring, imparting a very high
chemical flexibility. It undergoes protonation and deprotonation in addition to
adsorption through nitrogen, which, having alone pair of electrons, is
responsible for the technologically interesting chemistry and physics. Protonation
of PAn not only involves the ingress of protons, but is also accompanied by
ingress of anions, to maintain charge neutrality. This suggests that the
behavior of PAn depends on the PH and on the counterion of the Bronsted acid
used for doping.
Among conductive polymers, PAn has attracted particular
interest due to the fact that its electrical properties can be reversibly
controlled by changing the oxidation state of the main chain and by protonation
of the imine nitrogen atoms. By coupling the changes in the intrinsic oxidation
state of electroactive polymers such as PAn and it protonation/ reduction in
acid solution with the decrease in the oxidation state of the metal,
electroless precipitation of gold in elemental form from acid solution can be achieved12.
In this study various adsorbents such as anthracite,
activated carbon, anion exchanger, polyaniline and its composites were employed
to the removal of sulfate from water.
2. MATERIALS AND
METHODS:
2.1.
Instrumentation:
Magnetic mixer MK20, digital scale FR200, PH meter, and
spectrophotometer model 2100 were employed.
2.2. Reagents and Standard Solutions:
All reagents were used as received without further
purification, unless stated otherwise. Distilled deionized water was used
throughout this work. Aniline Monomer was purified by simple distillation.
Materials used in this work were anion exchanger, aniline (Aldrich), sodium
dodecylbenzenesulfonate (DBSNa) from Loba chemie, hydroxypropylcellulose (HPC,
Mw =106) from Aldrich, poly (vinyl alcohol) (PVA, Mw
=72000), poly(ethylene glycol) (PEG, Mw =35000), and KIO3
were obtained from Merck.
2.3 Polyaniline preparation:
For the preparation of polyaniline (PAn), 1g KIO3
was added to 100 mL of sulfuric acid (1M) and then uniform solution was
resulted using magnetic mixer. Then, 1 mL fresh distilled aniline monomer was
added to stirred aqueous solution. The reaction was carried out for 4 h at room
temperature. Consequently, the resulted polymer was filtered on filter paper
and to separate the oligomers and impurities, product was washed several times
with deionized water and dried at room temperature.
2.4 Preparation of Polyaniline Composites:
KIO3 was used as the oxidant, with, DBSNa,
HPC, PVA and PEG as surfactants. The reaction was carried out in an aqueous
media at room temperature for 4 hours. The conditions for composite formation
are summarized in Table 1.
In a typical experiment, 1 mL of aniline monomer was
added to 100 mL stirred aqueous solution of sulfuric acid (1M) containing
0.2-0.4 g of one of the surfactants and 1 g wood sawdust or 1 g quartz
respectively. After 4 h polymer composite was filtered and to separate the
oligomers and impurities, product was washed several times with deionized water
and then dried at room temperature.
2.5 Method of sulfate Removal:
Completely mixed batch reactor (CMBR) technique was
used to remove sulfate from water. 25 milliliter of solution was added to the
beaker containing 0.25 g of one of the adsorbents and mixed for 2 h by magnetic
mixer with its rotating speed of 700 rpm. Then the adsorbent was separated from
the solution using filter. The sulfate concentration was analyzed by
spectrophotometer method.
Spectrophotometers are a standard research tool used in
biology and chemistry labs world wide.
A spectrophotometer is a device to measure light
intensity at different wavelengths. It produces light with a light source, and
after the light passes through a substra, the light is diffracted into a
spectrum which is detected by a sensor. The output of a spectrophotometer is
usually a graph of light intensity versus wavelength. The data collected to
generate this graph can typically be saved as a table of wavelengths and
intensities.Also the values of the graph can be represented as either
transmittance or absorbance.
It should be noted that the
reaction conditions such as temperature, contact time, adsorbent amount, and pH
were the same for the experiments carried out in this investigation.
3. RESULTS AND DISCUSSION:
The chemical method can be a general and useful
procedure to prepare conductive polymers and their composites. PAn composites
were prepared chemically using different surfactants. The results indicate that
the removal of sulfate from the solution is dependent on the ability of surface
absorption. Adsorption is attributed to the affinity interaction between the
adsorbent’s activated sites and the adsorbent. The adsorption capacity is
affected by the adsorbent’s properties such as its structure, size and
chemistry of surface13. The effect of various adsorbents in the
removal of sulfate demonstrated in Table II.
It has been clearly shown that surface active agents
are usually employed to affect the morphology of conducting polymers during
chemical polymerization. The total surface area increases as the particle size
decreases. DBSNa, PEG, PVA and HPC are stabilizing agents and could affect the
size, morphology and homogeneity of particles14,15, because the
surface active agents are adsorbed physically or chemically by the growing
polymer. As can be seen PAn and its composites have desired procedure in
sulfate removal in different PH of solution. The role of DBSNa, PEG, PVA and
HPC on the surface of the PAn particles has to be studied so as to clarify
their influence on the structural arrangement of the particles. The effects of
PAn and its composites for the removal of sulfate from water are shown in Table
III.
Although the sulfate removal percentage are decreased
to 85.83 and 82.38 by using PAn/quartz and PAn-DBSNa/wood sawdust composites
respectively. But due to the less consumption of polymers in unit weight, it
has economical explanation.
Fig 1: Effect of type and stabilizer concentration on the
removal percentage
Table 1: Preparation of Polyaniline Composites
|
Type of composite
|
Surfactant concentration (g/L)
|
Aniline
(mol/L)
|
KIO
(g/L)
|
Reaction time (h)
|
Temperature
|
|
Polyaniline
|
-------
|
0.107
|
10
|
4
|
Room temperature
|
|
Composite of PAn and PEG
|
2
|
0.107
|
10
|
4
|
Room temperature
|
|
Composite of PAn and DBSNa
|
2
4
|
0.107
|
10
|
4
|
Room temperature
|
|
Composite of PAn and HPC
|
2
4
|
0.107
|
10
|
4
|
Room temperature
|
|
Composite of PAn and PVA
|
2
|
0.107
|
10
|
4
|
Room temperature
|
|
Composite of PAn and quartz
|
-------
|
0.107
|
10
|
4
|
Room temperature
|
|
Composite of PAn-DBSNa/quartz
|
4
|
0.107
|
10
|
4
|
Room temperature
|
|
Composite of PAn-HPC/quartz
|
4
|
0.107
|
10
|
4
|
Room temperature
|
|
Composite of PAn and wood sawdust
|
-------
|
0.107
|
10
|
4
|
Room temperature
|
|
Composite of PAn-HPC/wood sawdust
|
4
|
0.107
|
10
|
4
|
Room temperature
|
|
Composite of PAn-DBSNa/wood sawdust
|
4
|
0.107
|
10
|
4
|
Room temperature
|
Table II: The effect of various adsorbents in the
removal of sulfate
|
Adsorbent
|
Initial concentration of sulfate (ppm)
|
Final concentration of sulfate (ppm)
|
Removal Percentage (%)
|
|
Anthracite
|
66.21
|
4.95
|
92.52
|
|
Granular activated carbon
|
66.21
|
2.60
|
95.89
|
|
Powder activated carbon
|
66.21
|
2.33
|
96.48
|
|
Anion exchanger
|
66.21
|
1.23
|
98.15
|
As it can be seen, the maximum and minimum adsorption
percentage are obtained for anion exchanger and anthracite with 98.15 and 92.52
%, respectively.
Table III: The effect of Polyaniline and its composites
in the sulfat removal
|
Removal percentage (wt %)
|
Final concentration (ppm)
|
Initial concentration (ppm)
|
Concentration of adsorbent (g/L)
|
PH of solution
|
Surfactant concentration (g/L)
|
Type of adsorbent
|
|
90.87
|
6.04
|
66.21
|
2.5
|
7
|
-------
|
Polyaniline
|
|
87.34
|
8.38
|
66.21
|
2.5
|
7
|
2
|
Composite of PAn with PEG (Mw=35000)
|
|
76.71
89.33
|
15.42
7.06
|
66.21
66.21
|
2.5
|
7
|
2
4
|
Composite of PAn and DBSNa
|
|
69.94
80.87
|
19.9
12.66
|
66.21
66.21
|
2.5
|
7
|
2
4
|
Composite of PAn and HPC
|
|
81.72
|
12.04
|
66.21
|
2.5
|
7
|
2
|
Composite of PAn and PVA
|
|
85.53
|
9.58
|
66.21
|
2.5
|
7
|
-------
|
Composite of PAn and quartz
|
|
87.43
|
8.32
|
66.21
|
2.5
|
7
|
4
|
Composite of PAn-DBSNa/quartz
|
|
91.82
|
5.42
|
66.21
|
2.5
|
7
|
4
|
Composite of PAn-HPC/quartz
|
|
88.76
|
7.44
|
66.21
|
2.5
|
7
|
-------
|
Composite of PAn and wood sawdust
|
|
85.62
|
9.52
|
66.21
|
2.5
|
7
|
4
|
Composite of PAn-HPC/wood sawdust
|
|
82.38
|
11.66
|
66.21
|
2.5
|
7
|
4
|
Composite of PAn-DBSNa/wood sawdust
|
The results show that PAn and PAn-HPC/quartz composite
have desired procedure in sulfate removal with 90.87 and 91.82 %, respectively.
The role of DBSNa, HPC, PVA and PEG on the surface of
the PAn particles has to be studied so as to clarify their influence on the
structural arrangement of the particles. As can be seen in figure 1, sulfate removal increases
by increasing concentration of stabilizer, because particle size decreases and
total surface area of particles increase by increasing concentration of
stabilizer
4. CONCLUSIONS:
In this study the effect of PAn and its composites on
the removal of sulfate from water was investigated and results compared with
various adsorbents such as anthracite,
activated carbon and anion exchanger. The observations show that the sulfate
removal percentage increased in PAn-HPC/quartz composite. Also adsorbent type,
type, and concentration of surface active agents have a great effect on the
removal of sulfate from the solution.
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