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Research Article
Accelerated Decolorization of Congo Red by Powdered Termite Mound†
Olushola S. Ayanda1,3,*, Ekundare A. Odo2, Dosu Malomo1, Kehinde O. Sodeinde1, Olaide S. Lawal1,
Oluwapese T. Ebenezer1, Simphiwe M. Nelana3, and Eliazer B. Naidoo3
1
Nanoscience Research, Department of Industrial Chemistry, Federal University Oye Ekiti, Oye Ekiti,
Ekiti State, Nigeria
2
Department of Physics, Federal University Oye Ekiti, Oye Ekiti, Ekiti State, Nigeria
3
Department of Chemistry, Vaal University of Technology, Vanderbijlpark, South Africa
Correspondence: Dr. O. S. Ayanda, Nanoscience Research, Department of Industrial Chemistry, Federal
University Oye Ekiti, P.M.B 373, Oye Ekiti, Ekiti State, Nigeria
Email: osayanda@gmail.com
†
This article has been accepted for publication and undergone full peer review but has not been through
the copyediting, typesetting, pagination and proofreading process, which may lead to differences between
this version and the Version of Record. Please cite this article as an ‘Accepted Article’, doi:
[10.1002/clen.201700537]
© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Received: 20 October 2017; Revised: 20 October 2017; Accepted: 20 October 2017
1
ABSTRACT
The decolorization of congo red (CR) in aqueous solution was investigated in a batch mode using termite
mound as adsorbent. Elemental analysis and identification of the mineral composition/phases in the
termite mound sample was carried out by means of X-ray fluorescence and X-ray diffraction. The optimal
percentage removal and equilibrium adsorption capacity of CR by the termite mound achieved was found
to be 95.68% and 2.30 mg/g, respectively, when 0.5 g of termite mound was added to 30 mL of 40 mg/L
CR for 60 min at 400 rpm. The decolorization of CR increased with increase in the termite mound dosage,
contact time, stirring speed, pH and temperature; however, the adsorption capacity decreased with
increase in the initial CR concentration. The adsorption process showed that CR obeyed the Freundlich
adsorption model with 0.9355 coefficient of regression, denoting multilayer formation onto the termite
mound. The adsorption kinetics followed the pseudo-second order model with a coefficient of regression
value of 0.9966, showing that chemisorption is the main rate limiting step. ∆G is negative, an indication
that the adsorption of CR onto termite mound is spontaneous. Approximately 86.6% chemical oxygen
demand reduction was achieved with real textile wastewater. This research has shown harness of termite
mound for the treatment of textile wastewater before discharged into the environment.
Abbreviations:
CR,
congo
red;
COD,
chemical
oxygen
demand;
K,
kaolin;
KC,
cetyltrimethylammonium bromide-modified kaolin; XRD, X-ray diffraction; XRF, X-ray fluorescence
Keywords: Adsorption, Azo dyes, Equilibrium, Kinetics, Thermodynamics
2
1. Introduction
The discharge of dye contaminated wastewater from textile, dyeing, printing, ink, and related industries is
detrimental and has serious environmental impact. The growing concern about environmental issues has impelled
these industries to investigate appropriate and environmentally friendly treatment methods [1]. The discharge of
dyes into streams tends to reduce sunlight transmission into water due to their intense color and hence affect the
aquatic life. Moreover, dyes are known to be carcinogenic, mutagenic and can cause allergic dermatitis and skin
irritation [2]. Numerous approaches have been reported for the removal of dyes from industrial effluents [3]. Among
these techniques, adsorption has proven to be relatively cheap, effective and attractive for the treatment of
wastewater. On the other hand, several adsorbents have been found to remove toxic pollutants from aqueous
solutions and have been used in tertiary water treatment processes, but some of these adsorbents are rather
expensive, toxic and less abundant. Hence, there is a growing interest on the use of low cost, non-toxic and abundant
adsorbents for the adsorption of environmental pollutants. Abbas et al. [4] investigated the adsorption of congo red
(CR) and brilliant green onto peanut shells. The effect of various factors on the sorption process such as contact
time, pH, agitation speed, sorption dose, particle size was studied. Their study revealed that peanut shells adsorb
dyes by both chemisorption and physisorption. The removal efficiency of CR was 15.09 mg/g and that of brilliant
green was 19.92 mg/g. Negative values of the standard free energy change (∆G°) showed that the adsorption was an
exothermic process. In 2014, Zenasni et al. [5] reported the adsorption of CR onto cetyltrimethylammonium
bromide-modified kaolin (KC) which was prepared and tested as an adsorbent for CR removal from aqueous
solutions in comparison with natural kaolin (K). The effect of various experimental parameters was investigated
using batch adsorption. In this manner, the adsorption isotherms and adsorption kinetics of CR on K and KC were
examined. It was reported that the isothermal data could be well described by the Langmuir equation and the
dynamical data fitted well with the pseudo-second order kinetic model. The adsorption capacity of modified kaolin
KC (24.46 mg/g) was found to be around four times higher than that of natural kaolin K (5.94 mg/g). The KC
demonstrated the highest adsorption capacity by removing >98% of CR after 10 min of contact. The removal of CR
from aqueous solutions by polyhedral Cu2O nanoparticles and ZIF-9@super-macroporous microsphere have been
reported by Shu et al. [6] and Dai et al. [7], respectively. Diouri et al. [8] also investigated the adsorption of CR onto
marble dust. The effect of various experimental factors; adsorbent dose, contact time (equilibrium is established
after 90 min), dye concentration and pH, were also studied by using the batch technique. The isotherms of the
adsorption data were analyzed by the Langmuir and Freundlich isotherm models.
The current work will focus on the efficiency of termite mound as a low cost adsorbent for the decoloration of CR.
The feeding habit, food processing and mound construction operations by termites introduce significant
modifications to the soil on which the termite mound is built [9--11], consequently, termites are regarded as
ecosystem engineers. Termites are able to penetrate down forming enormous excavation capable to transport up to 1
kg/m2 per day of material from their burrows [12]. Termites in a typical mound move several tons of soil in a year to
build a giant mound, even though it may take four to five years to build a mound. Termites collect organic matter
and mineral particles from different depths and deposit them in mounds, enhancing the organic carbon content, clay
and nutrients [13] of the soil. Moreover, galleries built by termites also increase soil porosity. The mounds are
3
constructed of soil/earth particles and saliva in varying proportions. Termite mounds may reach up to 8 m in height
and 15 m in width. Termites are also capable of rebuilding their mounds as fast as the mounds are destroyed or
eroded. Hundreds of mounds could be seen in tropical grasslands. Therefore, termite mounds are cheap and
abundant; nonetheless, very limited work has been reported on the application of termite mound, most especially the
remediation of environmental contaminants. Few of the reported works are as follows: The application of termite
mound for the adsorption and removal of Pb(II) from aqueous solutions examined by Abdus-Salam and Itiola [9]. In
this study, batch adsorption experiments were carried out as a function of contact time, ionic strength and pH. The
authors reported that the maximum Pb(II) adsorption capacity of the termite mound was 15.5 mg/g and that the
equilibrium and kinetic studies fitted well with the Langmuir and Temkin isotherms and pseudo-second order
models, respectively. Russiarani and Balakrishanan [14] and Russiarani et al. [1] evaluated the efficiency of termite
soil to adsorb methylene blue and malachite green from aqueous solutions. Their aim was to find the best fitting
isotherm and kinetic model to describe the adsorption system. They reported that the equilibrium study fitted well
with the Langmuir isotherm, whereas the kinetic data fitted the pseudo-second order kinetics.
The use of termite mound for the removal of CR has not been reported in the literature. Therefore, the decolorization
of CR by the use of termite mound in a batch adsorption system was investigated in this study. The effects of termite
mound dosage, contact time, stirring speed, pH, temperature and initial concentrations were investigated, followed
by the equilibrium, kinetics and thermodynamic studies.
2. Materials and Methods
2.1. Congo red, Termite mound and Characterization
Congo red was purchased from HiMedia Laboratories, Mumbai, India. Termite mound of about 2 kg was mined
from a termite mound spotted around the main campus of Federal University Oye-Ekiti, Oye-Ekiti, Ekiti State,
Nigeria. Plant materials present in the sample were handpicked, removed, and the mound air-dried in the laboratory
at room temperature. The sample was placed in an oven set at 60°C for 3 h before crushed in a mortar and grounded.
It was sieved with a mesh of 0.5 mm pore size. Real textile wastewater containing CR was collected from a local
textile industry located at Abeokuta, Ogun State, Nigeria. Some of the properties of the textile wastewater are
chemical oxygen demand (COD) 750 ± 1.02 mg/L, pH 6.01, 30.5°C and the color is reddish brown. The wastewater
was used without any preliminary treatment.
The X-ray diffraction (XRD) experiment was carried out with kα1 wavelength of λ = 1.54 (GBC eMMA Xray
diffractometer). Identification of the mineral composition and phases in the sample was carried out using MATCH, a
commercial software, for phase identification from powder diffraction. Other characterizations carried out are ash
content, moisture content and the pH of the sample in 50 mL distilled water. X-ray fluorescence (XRF) analysis of
the termite mounds sample was carried out (Skyray Instrument; EDX3600B X-ray flourescence spectrometer).
2.2. Adsorption Experimental Procedure
According to the batch adsorption methods reported by Ayanda et al. [15] and Fatoki et al. [3], termite mound
(0.125--1.5 g) was added to 30 mL of 40 mg/L CR and stirred at 200 rpm for 20 min, for the effect of termite mound
4
dosage. On the effect of initial concentration, 30 mL of CR in the range of 20--200 mg/L was used in conjunction
with 0.5 g termite mound placed in a conical flask and stirred at 200 rpm for 20 min. On the effect of contact time,
0.5 g of termite mound with 30 mL of 40 mg/L CR solution was placed in a conical flask and stirred for 20--120 min
at 200 rpm. For pH, the pH of 30 mL of 40 mg/L CR solution was adjusted to pH 2 to 12 by the use of 0.01 M HCl
and NaOH. 0.5 g of termite mound with the CR solution was added into a conical flask and stirred for 20 min at 200
rpm. The effect of temperature was investigated at temperature range of 293--338 K, whereas, the stirring speed was
investigated at 100--400 rpm for 60 min.
After each of the experiments, 5 mL aliquots were withdrawn after the time elapse and the absorbance was measured
spectrophotometrically at 498 nm in the UV-vis range. The percentage CR removal was obtained with Eq. (1) and
the amount of CR adsorbed (mg dye/g termite mound) was calculated using Eq. (2).
%Removal =
qe =
Co − Ce
× 100
Co
(1)
C o −C e
V
W
(2)
where Co and Ce (mg/L) are the initial and equilibrium concentration of the CR solution. V (mL) is the volume of the
solution, W (g) is the mass of termite mound used and qe (mg/g) is the amount adsorbed.
2.3. Equilibrium Models
The initial dye concentration provides information on whether the adsorption of dye molecules on the adsorbent
surface occurs through formation of a monolayer or multilayers. Monolayer adsorption is described by Langmuir
isotherm while multilayer adsorption is given by the Freundlich isotherm.
The Langmuir isotherm is based on the theoretical principle that only a single adsorption layer exists onto an
adsorbent. The linear form of the Langmuir model is presented in Eq. (3) [16].
1
qe
=
1
1
1
+
qm K L Ce qm
(3)
where Ce is the equilibrium concentration of the dye solution (mg/L), qe is the amount of CR adsorbed per unit mass
of the termite mound (mg/g), qm is the Langmuir constant representing adsorption capacity (mg/g), and KL is the
Langmuir constant representing energy of adsorption (L/mg). A plot of
1
qe
vs.
1
Ce
is linear for a sorption process
obeying the basis of this equation with kL and qm obtained from the slope and intercept, respectively.
The Freundlich isotherm assumes that the dye uptake occurs on a heterogeneous surface by multilayer adsorption
and that the amount of the adsorbed dye increases infinitely with an increase in dye concentration. The linear form
of the Freundlich equation is written as Eq. (4) [17].
log10 qe = log10 K F +
1
log10 Ce
n
(4)
where Ce is the equilibrium concentration of CR solution (mg/L), qe is the amount of CR adsorbed per unit mass of
termite mound (mg/g), n is the number of layers, and KF is the Freundlich constant. For a sorption process obeying
5
the Freundlich isotherm, the plot of log10 q e vs. log10 C e is linear with KF and n obtained from the intercept and
slope, respectively.
2.4. Kinetic Models
The Lagergren pseudo-first order kinetic model is presented by Eq. (5) [18].
log10 (q e − q t ) = log q e +
k1
t
2.303
(5)
where qe is the equilibrium amount of CR adsorbed per unit mass of termite mound (mg/g), qt is the amount of CR
adsorbed per unit mass of termite mound at time, t (mg/g), k1 is the pseudo-first order adsorption rate constant (min1
), and t is the time (min). A linear plot of log10(qe -- qt) vs. time t gives the equilibrium adsorption capacity qe
(mg/g), as intercept while the slope gives the pseudo-first-order rate constant k1.
The linear form of the Lagergren pseudo-second order kinetic model as described by Ho and Mckay [19] is given in
Eq. (6).
t
1
t
=
+
q t k 2 qe 2 qe
(6)
where qe is the equilibrium amount of CR adsorbed per unit mass of termite mound (mg/g), qt is the amount of CR
adsorbed per unit mass of termite mound at time, t (mg/g), k2 is the pseudo-second order adsorption rate constant
(g/min/mg), and t is the time (min). A linear plot of
t
vs. t gives the slope as equilibrium adsorption capacity, qe
qt
(mg/g), and the intercept pseudo-second-order rate constant k2.
2.5. Thermodynamics
Thermodynamic study gives the general information about the influence of temperature on the adsorption and
particularly is useful to predict the feasibility of the adsorption process. The standard free energy (ΔG°), enthalpy
(ΔH°) and entropy (ΔS°) changes were calculated from the Gibb’s free energy and van’t Hoff equations (Eqs. (7)-(10)) [20].
K=
Co − Ce
Ce
(7)
where C o − C e (mg/L) is the concentration after CR adsorption and Ce (mg/g) is the equilibrium concentration.
∆G° = − RT ln K
(8)
∆G° = ∆H ° − T∆S °
(9)
log K =
−∆H °
∆S °
+
2.303RT 2.303R
ΔH° and ΔS° are deduced from the slope and intercept of a plot of logK vs.
(10)
1
. R is the gas constant (8.314 J/mol/K)
T
and T is the temperature in Kelvin.
6
2.6 Application of Termite Mound for the Treatment of Real Textile Wastewater
Chemical oxygen demand is a measure of water quality; commonly used to estimate the amount of organic
contaminants present in water and wastewater. In this study, the efficiency of termite mound for the treatment of real
textile wastewater was verified. 30 mL textile wastewater was contacted with 0.5 g of termite mound for 60 min at
400 rpm, blank analysis was conducted and COD was determined in accordance with the “Standard methods for
treatment of water and wastewater” [21] before and after the treatment processes.
3. Results and Discussions
3.1. Adsorbent Characterization
Figure 1 shows the plot of XRD pattern with 17 main peaks identified. The peaks correspond to the different phases
of minerals which constitutes the clay materials. A detailed analysis of the concentrations of the different minerals
as presented in Table 1, shows that kaolinite is relatively dominant while merrillite, vermiculite and quartz appeared
in almost equal proportion. Nickelalumite and trioctahedral mica constitutes only a relative trace amount to the
overall composition. Kaolinite a major component of clay materials is long known to exhibit increasing
chemisorption characteristics [22]. The composition of kaolinite in the termite mound investigated in this work will
thus have significant contribution to the overall adoption process.
The XRF analysis of the termite mound also confirms the presence of Fe (23.8 wt %), Si (20.6 wt %) and Al (14.4
wt %). Fe, Si and Al are the three major components of the termite mound, all other constituents such as Zn, Ni, V,
K, Mg, K, P, Cu, etc., exist in trace amount, while As, Au, Ag and Cd were absent. The moisture content, ash
content and pH of the termite mound are 8.67%, 24.91% and 7.37, respectively.
3.2. Effect of Termite Mound Dosage and Initial Concentration
The results of the effect of termite mound dose on 40 mg/L CR is represented in Fig. 2. The results showed that for a
CR concentration of 40 mg/L and for a 20 min contact time, an increase of the mass of termite mound from 0.125 to
0.5 g increased the percentage of CR removed in solution from 27.5 to 62.5%. Equilibration was achieved
afterwards. The increase in decolorization and the percentage of CR removal may be due to the increase in the
number of active sites of the termite mound. The trend of the graph is similar to the results by Abbas et al. [4]. 0.5 g
of termite mound was used for further experiments due to the highest percentage CR removal (62.5%) when
compared with other termite mound dosages.
The effect of initial concentration on the adsorption of CR onto termite mound is shown in Fig. 3. Figure 3 shows
that the percentage of CR removal decreased as the initial concentration of CR increased. This phenomenon suggests
that the active adsorption sites of the termite mound became saturated as the concentration of CR increases; 82 and
45.75% removal was achieved for 20 and 200 mg/L CR, respectively, which implies that the adsorption process
depends on the initial CR concentration. The result obtained on the effect of initial concentration was utilized for the
verification of the adsorption isotherm.
7
3.4. Effect of pH and Contact Time
The study of the effect of pH on the adsorption of CR onto termite mound over the pH range 2--12 shows that as the
pH of the CR solution increased, decolorization of CR and hence, the amount of CR adsorbed increased as shown in
Fig. 4.
This behavior could be explained as follows; in the aqueous solution, CR is dissolved and the sulfonate groups of
the dye are dissociated and converted to anionic ions. Therefore, at low pH, the high concentration of H+ ions
promoted the protonation of CR functional groups, and the termite mound became more positively charged, which
hinders the adsorption of CR onto the adsorbent. On the other hand, when the pH of the solution increased, the OH-ions increased, resulting in the improvement of the interaction between the termite mound and the CR molecules
[15].
The contact time between adsorbent and adsorbate molecules during adsorption is used to determine the efficiency
of the adsorption process, equilibrium time and the adsorption kinetics. CR adsorption was found to slightly
decrease from 20-40 min, after which the adsorption increased rapidly from 40--120 min. The adsorption of CR with
time onto termite mound is shown in Fig. 5. In the first 20 to 40 min, the amount of CR adsorbed by the termite
mound to some extent decreased from 1.5 to 1.47 mg/g. However, there was saturation between 40 and 60 min, after
which the amount of CR adsorbed increased from 60 to 120 min.
3.5. Effect of Temperature and Stirring Speed
Temperature alters the rate of dye molecules, viscosity of solution media and surface characteristics of the
adsorbent. The effect of temperature on the adsorption of CR onto termite mound was investigated within
temperature range of 293--338 K and the results are presented in Fig. 6a.
The trend of the graph indicated that the adsorption capacity of CR onto termite mound increased with temperature.
This may be a result of the increase in the mobility of the large CR ions with temperature. An increasing number of
molecules may also acquire sufficient energy to undergo an interaction with the active sites at the surface. Likewise,
increasing temperature may produce an enormous effect within the internal structure of the adsorbent enabling large
dyes to penetrate further; the trend is similar to the work reported by Sharma et al. [23]. The result obtained on the
effect of temperature was used for the thermodynamic study.
The effect of stirring speed on the adsorption of CR onto termite mound as shown in Fig. 7 indicated that as the
stirring speed increases, the decolorization of the dye (percentage CR removal) increases. This is explained as
follows; an increasing agitation rate may reduce the film boundary layer surrounding the adsorbent particles and
thus, increase the external film diffusion rate and uptake rate.
The optimal CR adsorption achieved was 95.68%, when 30 mL of 40 mg/L CR was added to 0.5 g termite mound
agitated for 60 min at 400 rpm. CR solution (40 mg/L) before and after treatment with powdered termite mound is
presented in Supporting Information Fig. S1.
8
3.6. Isotherm, Kinetic and Thermodynamic Studies
The regression coefficient (R2 = 0.8147) confirms that the adsorption does not follow the Langmuir model. The
slope and intercept to Eq. (3) as depicted in Supporting Information Fig. S2 gave the Langmuir monolayer
adsorption constant, qm as 3.755 mg/g and Langmuir energy of adsorption constant, KL = 0.0945 L/mg for CR
adsorption onto termite mound.
The Freundlich isotherm assumes that dye uptake occurs on a heterogeneous surface by multilayer adsorption and
that the amount of the adsorbed adsorbate increases with an increase in adsorbate concentration. A plot of log10qe vs.
log10Ce is linear (Fig. 8a) with KF (2.417 mg/g (L/mg)1/n) and n (1.8996) obtained from the intercept and slope,
respectively. The result shows that CR obey the Freundich isotherm due to the high regression coefficient value of
0.9355.The results of Langmuir and Freundlich isotherm plots on CR adsorption onto powdered termite mound are
presented in Table 2.
The pseudo-first order and pseudo-second order kinetics as tested on the adsorption of CR onto powdered termite
mound is represented in Supporting Information Fig. S3 and Fig 8b, respectively. The adsorption kinetics followed
the pseudo-second order equation having coefficient of regression value of 0.9966, showing that chemisorption is
the main rate limiting step. Table 2 presents the calculated kinetic parameters and regression coefficient. k2 and qe
obtained for the pseudo-second order equation are 0.1361 g/(mg min) and 1.6436 mg/g, respectively.
The van't Hoff plot for the adsorption of CR onto termite mound is shown in Fig. 6b. The standard free energy
(ΔG°), enthalpy (ΔH°) and entropy (ΔS°) changes for the termite mound were obtained using equilibrium constant K
and the data are given in Table 3. The negative value of free energy change (ΔG°) shows that the adsorption process
is spontaneous at low and high temperature, and has good feasibility for CR adsorption onto termite mound. The
positive value of ΔH° as presented in Table 3 showed that the adsorption process is endothermic.
Preliminary authentication experiments with textile wastewater revealed the reduction of COD from 750 ± 1.02 to
85.50 ± 1.32 mg/L. The treatment reduced the COD to <250 mg/L, the upper limit for effluent disposal into surface
water [24]. The slight decrease in the percentage treatment of the textile wastewater (88.60% COD reduction) when
compared to the simulated CR solution (95.68%) may be due to the presence of other contaminants present in the
textile wastewater.
4. Conclusion
In the present study, the ability of powdered termite mound to decolorize CR was investigated. The research has
shown that termite mound will serve as a cost effective alternative adsorbent for the decolorization of dyes and
could be used for the treatment of textile wastewater before discharged into the environment. Experimental results
showed that the decolorization of CR increases with increase in the termite mound dosage, contact time, stirring
speed, pH and temperature but decreases with increase in the initial CR concentrations. The adsorption obeyed the
Freundlich adsorption model while the adsorption kinetics followed the pseudo-second order equation. Moreover,
the thermodynamic parameters showed that the adsorption process is endothermic and spontaneous. The mineral
phases of the termite mound used in this study are kaolinite, merrillite, vermiculite, quartz, nickelalumite and
trioctahedral mica, in addition, XRF analysis confirms the presence of Fe, Si and Al as the major constituent of the
9
mound. Hence, the effectiveness and speedy decolorization of CR and COD reduction of the textile wastewater
could be attributed to the abundance of primary and secondary minerals present in the termite mound.
The authors have declared no conflict of interest.
References
1. S. Russiarani, K. Balakrishnan, V. Nandhakumar, Termite soil as a potential low-cost adsorbent for the removal
of methylene blue and malachite green dyes, J. Adv. Appl. Sci. Res. 2016, 1, 53--74.
2. S. K. Bhoi, Adsorption characteristics of congo red dye onto PAC and GAC based on S/N ratio: A Taguchi
approach, BSc Thesis, National Institute of Technology, Rourkela, India 2010, 32pp.
3. O. S. Fatoki, O. S. Ayanda, F. A. Adekola, B. J. Ximba, Sorption of Triphenyltin Chloride to nFe3O4, Fly ash and
nFe3O4/fly ash Composite Material in Seawater, Clean – Soil Air Water 2014, 42, 472--479.
4. A. Abbas, S. Murtaza, K. Shahid, M. Munir, R. Ayub, R. Akbe, Comparative study of adsorptive removal of
congo red and brilliant green dyes from water using peanut shell, Middle-East J. Sci. Res. 2012, 11, 828--832.
5. M. A. Zenasni, B. Meroufel, A. Merlin, B. George, Adsorption of Congo Red from Aqueous Solution using
CTAB-kaolin from Bechar Algeria, J. Surf. Eng. Mater. Adv. Technol. 2014, 4, 332--341.
6. J. Shu, Z. Wang, Y. Huang, N. Huang, C. Ren, W. Zhang, Adsorption removal of Congo red from aqueous
solution by polyhedral Cu2O nanoparticles: Kinetics, isotherms, thermodynamics and mechanism analysis, J. Alloy
Compd. 2015, 633, 338--346.
7. J. Dai, S. Xiao, J. Liu, J. He, J. Lei, L. Wang, Fabrication of ZIF-9@super-macroporous microsphere for
adsorptive removal of Congo red from water, RSC Adv. 2017, 7, 6288--6296
8. K. Diouri, A. Kherbeche, A. Chaqroune, Kinetics of Congo Red Dye Adsorption onto Marble Powder Sorbents,
Int. J. Innov. Res. Sci. Eng. Technol. 2015, 4, 267--274.
9. H. O. Maduakor, A. N. Okere, C. C. Oneyanuforo, Termite Mounds in Relation to the Surrounding Soil in the
Forest and Derived Savanna Zones of Southeastern Nigeria, Biol. Fertil. Soil 1995, 20, 157–162.
10. S. Konate, X. Le Roux, D. Tessier, M. Lepage, Influence of Large Termiteria on Soil Characteristics, Soil Water
Regime and Tree Leaf Shedding Pattern in a West Africa Savanna, Plant Soil 1999, 206, 47–60.
11. N. Abdus-Salam, A. D. Itiola, Potential Application of Termite Mound for Adsorption and Removal of Pb(II)
from Aqueous Solutions, J. Iran Chem. Soc. 2012, 9, 373–382.
12. S. M. Awadh, Geochemistry of Termite Hills as a Tool for Geochemical Exploration of Glass Sand in the Iraqi
Western Desert, Int. J. Geosci. 2010, 1, 130-138.
13. T. S. Sarcinelli, C. E. G. R. Schaefer, L. de Souza Lynch, D. H. Arato, J. H. M. Viana, M. R. de Albuquerque
Filho, T. T. Gonçalves, Chemical, Physical and Micromorphological Properties of Termite Mounds and Adjacent
Soils along a Toposequence in Zona da Mata, Minas Gerais State, Brazil, Catena 2009, 76, 107–113.
14. S. Russiarani, K. Balakrishanan, Adsorption of Methylene Blue Dye on Termite Soil, Int. J. Biosci. Nanosci.
2015, 2, 175--184.
15. O. S. Ayanda, O. S. Fatoki, F. A. Adekola, B. J. Ximba, Utilization of nSiO2, Fly ash and nSiO2/fly ash
10
Composite for the Remediation of Triphenyltin (TPT) from Contaminated Seawater, Environ. Sci. Pollut. Res. 2013,
20, 8172–8181.
16. I. Langmuir, The Adsorption of Gases on Plane Surfaces of Glass, Mica and Platinum, J. Am. Chem Soc. 1918,
40, 1361--1403.
17. H. M. F. Freundlich, Über die Adsorption in Lösungen, Phys. Chem. 1906, 57, 385--470.
18. A. K. Singh, D. P. Singh, K. K. Pandey, V. N. Singh, Wollastonite as Adsorbent for Removal of Fe(II) from
Water, J. Chem. Technol. 1988, 42 (1), 29--49.
19. Y. S. Ho, G. McKay, Pseudo-second Order Model for Sorption Processes, Process Biochem. 1999, 34, 451--465.
20. M. G. Sujana, H. K. Pradhan, S. Anand, Studies on Sorption of some Geomaterials for Fluoride Removal from
Aqueous Solutions, J. Hazard. Mater. 2009, 161, 120--125.
21. American Public Health Association (APHA), Standard Methods for the Examination of Water and Wastewater,
20th Ed., American Public Health Association (APHA), American Water Works Association (AWWA), Water
Environment Federation (WEF), Washington DC, USA 1999.
22. H. Hanlie, F. Zhengyi, M. Xinmin, The Adsorption of [Au(HS)2]- on Kaolinite Surfaces: Quantum Chemistry
Calculations, Can. Mineral. 2001, 39, 1591--1596.
23. Y. C. Sharma, U. S. N. Upadhyay, F. Gode, Adsorptive Removal of a Basic Dye from Water and Wastewater by
Activated Carbon, J. Appl. Sci. Environ. Sanit. 2009, 4, 21--28.
24. G. B. Adebayo, G. A. Otunola, T. A. Ajao, Assessment and Biological Treatment of Effluent from Textile
Industry, Afr. J. Biotechnol. 2010, 9 (49), 8365--8368.
Figure 1: Plot of the XRD diffraction pattern with the different phases
Figure 2: Effect of termite mound dosage on the adsorption of CR (Co = 40 mg/L, contact time = 20 min, stirring
speed = 200 rpm, pH 7)
Figure 3: Effect of initial concentration on the adsorption of CR onto termite mound (Dosage = 0.5 g, contact time =
20 min, stirring speed = 200 rpm, pH 7)
Figure 4: Effect of pH on the adsorption of CR onto termite mound (Co = 40 mg/L, dosage = 0.5g, contact time = 20
min, stirring speed = 200 rpm)
Figure 5: Effect of contact time on the adsorption of CR onto termite mound (Co = 40 mg/L, dosage = 0.5 g, stirring
speed = 200 rpm, pH 7)
Figure 6: Effect of temperature (a) and van't Hoff plot (b) on the adsorption of CR onto termite mound (Co = 40
mg/L, contact time = 60 min, dosage = 0.5 g, stirring speed = 200 rpm, pH 7)
Figure 7: Effect of stirring speed on the adsorption of CR onto termite mound (Co = 40 mg/L, contact time = 60 min,
dosage = 0.5 g, pH 7)
Figure 8: Freundlich isotherm (a) and pseudo-second order kinetics (b) of CR adsorption onto termite mound
11
Table 1: Phases matched in the diffraction pattern and their relative percentage contributions
Phase
% Contribution
Empirical formula
With Fe component
1
Kaolinite
29.0
Al2Si2O5(OH)4
Al2H4O9Si2
2
Merrillite
22.9
Ca9NaMg(PO4)7
Ca9.45Fe0.22Mg0.78O28P7
3
Vermiculite
22.1
(Mg,Fe2+,Al)3(Al,Si)4O10(OH)2 · 4 (H2O)
Al1.68Ca0.43Fe0.207Mg2.022O15.16Si2.764Ti0.042
4
Quartz
21.2
SiO2
SiO2
5
Nickelalumite
2.9
(Ni,Cu)Al4[(SO4),(NO3)2](OH)12 · 3 (H2O)
Al4Fe0.01H18Ni0.55O19SV0.02Zn0.39
6
Trioctahedral
1.9
Al0.24Fe3.76H2KO12Si3
mica
Table 2: Isotherm and kinetic parameters for CR adsorption onto termite mound
Isotherm
Langmuir model
Freundlich model
2
q m (mg/g)
K L (L/mg)
R
3.755
0.0945
0.8147
1/n
K F (mg/g (L/mg) )
n
R2
2.417
1.8996
0.9335
Kinetic model
Pseudo-first order
Pseudo-second order
k1 (min −1 )
q e (mg/g)
R2
k 2 (g/mg/ min)
q e (mg/g)
R2
0.0037
0.4829
0.5941
0.1361
1.6436
0.9966
Table 3: Thermodynamic parameters of CR adsorption onto powdered termite mound
T (K)
293
ΔH° (kJ/mol)
5.882
ΔS° (J/(mol K))
22.722
ΔG° (J/mol)
--736.4
298
--876.2
303
--1153.3
308
--1172.4
313
--1055.1
318
--1350.5
323
--1371.8
328
--1688.1
333
--1562.9
338
--1895.3
12
Peak area of phase A (Kaolinite) 29.0%
B (Merrillite) 22.9%
C (Vermiculite) 22.1%
D (SiO2) 21.2%
E (Nickelalumite) 2.90%
F (trioctahedral mica) 1.9%
Intensity (a.u)
400
200
0
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
Figure 1:
13
Congo red removal (%)
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Termite mound dose (g)
Figure 2:
14
90.0
Congo red removal (%)
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
0
50
100
150
200
250
Concentration (mg/L)
Figure 3:
15
1.8
1.6
1.4
qe mg/g
1.2
1
0.8
0.6
0.4
0.2
0
0
2
4
6
8
10
12
14
pH
Figure 4:
16
Congo red removal (%)
70.0
65.0
60.0
55.0
50.0
45.0
40.0
0
20
40
60
80
100
120
140
Contact time (min)
Figure 5:
17
67.0
66.0
65.0
64.0
63.0
62.0
61.0
60.0
59.0
58.0
57.0
0.35
a)
0.30
y = -307.23x + 1.1867
0.25
log K
Congo red removal (%)
0.20
0.15
0.10
0.05
290
300
310
320
330
Temperature (K)
340
350
0.00
0.0028
0.0030
0.0032
1/T
0.0034
0.0036
(K-1)
b)Figure 6:
18
120.0
Congo red removal (%)
100.0
80.0
60.0
40.0
20.0
0.0
100
150
200
250
300
350
400
450
Stirrimg speed (rpm)
Figure 7:
19
0.6
70
y = 0.5264x - 0.3832
R² = 0.9355
60
t/qt(gmin/mg)
0.7
80
a)
0.8
log qe
0.5
0.4
0.3
50
30
0.2
20
0.1
10
0.0
0.8000
0
1.3000
1.8000
2.3000
0
50
100
150
time(min)
log Ce
Figure 8:
y = 0.6084x + 2.7191
R² = 0.9966
40
b)
20
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