This document summarizes a study that synthesized copper oxide coated kaolinite to remove mercury ions from aqueous solution. Kaolinite was characterized and then coated with copper oxide via precipitation and thermal treatment. The coated material was then tested for removing mercury ions from water. Key findings include: 1) The copper oxide coated kaolinite was characterized through various analyses which confirmed the coating and composition. 2) Reactivity experiments determined the proton coefficient was 0.89, indicating decreased proton consumption compared to uncoated kaolinite. 3) Kinetic studies found maximum 85% mercury adsorption after 12 hours, with mass transfer rates lower than for uncoated kaolinite, possibly due to blocked reaction sites on the

1. SYNTHESIS AND CHARACTERIZATION OF KAOLINITE COATED WITH CU-OXIDE AND ITS EFFECT ON THE REMOVAL OF AQUEOUS MERCURY(II) IONS: PARTI
IRJCCS
SYNTHESIS AND CHARACTERIZATION OF KAOLINITE
COATED WITH CU-OXIDE AND ITS EFFECT ON THE
REMOVAL OF AQUEOUS MERCURY(II) IONS: PART I
Davidson E. Egirani1*, Mohamed T. LatiF2, Nanfe R. Poyi3, Napoleon Wessey1 and Shukla
Acharjee4
1Faculty of Science, Niger Delta University, Wilberforce Island, Nigeria.
2School of Environmental and Natural Sciences, National University, Malaysia.
3Nigerian Institute of Mining and Geosciences, Jos, Nigeria.
4Centre for Studies in Geography, Dibrugarh, Assam, India.
In this paper, a novel copper oxide coated kaolinite was prepared as an adsorbent of Hg(II) ions
from aqueous media. The materials used for this study were synthesized, characterised and the
product tested for mercury ion removal using standard laboratory procedures. Reactivity and
removal kinetic models derived from Freundlich isotherm were used to investigate contact time
and pH effects on the coefficient of protonation and rate of mass transfer of Hg(II) ions to the
reactive sites, Proton coefficient of 0.89 indicated a decrease in proton consumption function
when compared with uncoated kaolinite. At the 12th
h reaction time, a maximum adsorption
capacity of 85% was achieved. Mass transfer rates of 0.9359h-1
and 0.0748h-1
for the first and
second reaction phases indicated a reduction when compared with uncoated kaolinite. These
changes may be ascribed to masking of reaction sites and exposed surface area of the Cu-Oxide
coated kaolinite.
Keywords: kaolinite, Cu-Oxide, contact time, pH, reactivity, removal kinetics
INTRODUCTION
Mercury is toxic and remains a threat to environmental and
human lives. Mercury bioaccumulates in the environment
and creates neurological health impact (Cao et al., 2008:
2555–2559). Its transformation to methyl mercury
generates critical problems to humans. This is because it
is non-biodegradable in humans causing neurological
health concerns (Taman et al., 2015: 1-8.). Mercury
remains a sinister poison and can be stored in vital organs
of the human body causing several health problems (Bulut
and Tez, 2007).
Therefore, the toxic properties of mercury have attracted
considerable attention (Kannan and Malar, 2005, Husein,
2013). Kinetic studies have shown that mercury removal
involves a fast process, involving intraparticle diffusion
(Ding et al 2014: 1115-1121., Dos et al.,2015: 1230-40).
Recent studies revealed that solution dilution and
exchange stoichiometry, contact time, pH and initial metal
concentration govern mercury removal from aquatic
systems (Egirani et al 2013: 73-81.,2014:991-1005).
Most conservative techniques employed in removal of
mercury ions from aqueous solution involve chemical
precipitation, adsorption by activated carbon, ion
exchange resins and electrochemical recovery (Uzum et
al., 2009: 172–181). There is high unsuccessful rate of
these techniques particularly for low level mercury
concentrations of 1-10 mg L-1).
*Corresponding author: Dr. Davidson Egirani, Faculty of
Science, Niger Delta University, Wilberforce Island,
Nigeria. Email: eenonidavidson@yahoo.com
Research Article
International Research Journal of Chemistry and Chemical Sciences
Vol. 4(1), pp. 055-061, August, 2017. © www.premierpublishers.org. ISSN: XXXX-XXXX

2. SYNTHESIS AND CHARACTERIZATION OF KAOLINITE COATED WITH CU-OXIDE AND ITS EFFECT ON THE REMOVAL OF AQUEOUS MERCURY(II) IONS: PARTI
Egirani et al 056
This is because toxic sludge is costly to dispose of it. In
addition, chemical reagents are required for mercury
recovery and this comes at a high energy cost (Arshadi et
al., 2017: 293–306., Hua et al., 2012: 317– 331). Due to
these challenges, there is need to source for cheap and
readily available modified adsorbents. Here, the use of
kaolinite coated with Cu-Oxide is being postulated.
Therefore, the aim of this paper is to use Cu-Oxide coated
kaolinite in the treatment of mercury aqueous solution.
The objectives include synthesis of the adsorbent,
characterisation of the system and the use of experimental
parameters to elucidate the removal and reactivity kinetics
of the interaction.
MATERIALS AND METHODS
All reagents used were of analytical purity. Concentrated
stock solutions were used to prepare the synthetic
solutions. Richard Baker Harrison Company (United
Kingdom) provided the kaolinite used in this study. This
was nitrogen flushed and stored in containers that were
airtight to avoid surface reaction. Hg(II) ions were sourced
from Mercuric chloride (HgCl2) obtained from Merck
(Canada).
Various concentrations of Hg(II) ions in ppm were
prepared by dissolving HgCl2 (Merck) in double distilled
water. Sodium Chloride used for potentiometric titration,
HCl and NaOH used as pH regulators were obtained from
Merck. These reagents were all analytical grade. Double
distilled water was used to prepare all the solutions.
System Characterisation
The Richard Baker Harrison kaolinite known as RBH-
kaolinite was treated with deionized water several times at
a 1:10 kaolinite/water ratio. The mixture was continuously
agitated for 3 h and set aside for 24h. This was followed
by separation, washing and drying at 60 ◦C. The percent
colloid with less than 1000 nm was estimated from the
particle size distribution curves. The particle size range of
RBH kaolinite. was determined using Coulter Laser
method. pH of RBH kaolinite suspensions and reacting
solutions were determined using the Model 3340 Jenway
ion meter. The cation exchange capacity (CEC) was
determined by Na saturation method. The specific surface
area of the RBH kaolinite mineral was measured using the
standard volumetric Brunauer, Emmett and Teller (BET)
method (Brunauer et al., 1938: 309–319). Here,
determination was by measuring the adsorption of N2 gas
on the mineral solid phase at the boiling point of liquid
nitrogen (Lowell and Shield, 1991). Spectral analysis was
done using Energy Dispersive Spectroscopy (EDS) and
Scanning Electron Microscopy (SEM) (Karickhoff and
Bailey 1973, Janaki, et al., 2014: 443-446). The uncoated
samples were viewed and secondary electron images
were acquired at low vacuum control pressure using a
JEOL JSM 5900 LVSEM with Oxford INCA EDS.
The point of zero salt effect (PZSE) of the RBH kaolinite
was carried out using standard laboratory procedures
(Alves and Lavorenti, 2005, Bolan et al., 1986: 379–388).
Potentiometric titrations involved the equilibration of 1%
(by mass) of RBH kaolinite suspensions. References
containing only a 1:1 electrolyte solution were initially
adjusted to pH range near the point of zero salt effect.
Synthesis of Cu-Oxide Coated Kaolinite
Cu-oxide-coated kaolinite was set by precipitating the
copper ions on the surface of the RBH kaolinite. This was
done using sodium hydroxide tracked by thermal treatment
[Phiwdanga, et al., 2013: 740 – 745., Eren, 2009)
20.0 g of RBH was mixed with 100 ml 1 M Cu(NO3)2
solution and 180 ml of 2 M NaOH solution. These were
freshly prepared. The mixture of the reaction was
maintained at 90 ◦C for 48 h. The RBH activated with the
NaOH solution was dispersed into 150 ml of 0.1 M
Cu(NO3)2 solution. 0.1 M NaOH aqueous solution
amounting to three hundred microliters was added
dropwise at the rate of 1 ml/h. To minimize the formation
of carbonate salts, the titration was carried out under
nitrogen flow condition (Maruthupandy et al., 2017: 167–
174., Wang et al., 2016: 328–334). Centrifugation and
washing of the precipitate was carried out to free the
content from NO3
– ions. Heating the solid for 4 h in air at
700 K led to the formation of Cu-Oxide kaolinite. RBH
kaolinite was verified from the X-ray diffraction (XRD)
patterns of the product.
H+
/M2+
Stoichiometry and Proton Exchange
Experiments
For reactivity studies to determine the proton coefficient,
the proton exchange isotherm known as change of pH
versus LogKd was determined using standard laboratory
procedure (Egirani et al., 2013: 73-81, Campos et al.,
2007). This empirical model was derived from Freundlich
isotherm, suitable for heterogenous surfaces (Egirani et
al., 2014:991-1005). A 1% RBH kaolinite coated Cu-Oxide
suspension with no added electrolyte made unto 50 ml,
were reacted with solution containing 10 ppm of Hg(II)
regulated to required pH. Experimental studies were
conducted in triplicates. Samples were stored in the dark
(23±3 ◦C). Filtration using a cellulose acetate filter (pore
size 0.2 μm) was carried out on the supernatant and
analysed for Hg(II) ions, using a Hitachi Atomic Absorption
Spectrophotometer (HG-AAS).
The proton consumption function is given (Equations 1-2):

 

HMSOHMSOH )(2
…….. (1)
LogKd=log(Kp{SOH} )+pH……………...............(2)
Here, SOH denotes the mineral surface-binding site, M2+
denotes the soluble metal species,
MSOH )( denotes

3. SYNTHESIS AND CHARACTERIZATION OF KAOLINITE COATED WITH CU-OXIDE AND ITS EFFECT ON THE REMOVAL OF AQUEOUS MERCURY(II) IONS: PARTI
Int. Res. J. Chem. Chem. Sci. 057
Table 1: Summary of system characterisation
Components of Characterisation Values
SiO2 (%) 47.00
Al2O3 (%) 38.00
Moisture content (%) 1.50
Specific gravity 2.60
Water soluble salt (%) 0.20
CEC (mmols/kg) 170.00
% (<1000 nm) colloid 3.00
Particle size range (μm) 0.60-20.01±0.5
pH ± σ 6.05±0.05
Surface Area(SSA±σ) (m2
/g) 47.01± 0.24
Point of Zero Salt Effect (PZSE) 7.00
the surface bound metal, logKp denotes the apparent
equilibrium-binding constant and  denotes the
coefficient of protonation. This represents the number of
protons displaced when one mole of metal binds to the
mineral surface (Egirani et al., 2013: 73-81., Contescu et
al., 1993: 1754–1765). Proton coefficients were obtained
by graphical analysis using logKd versus pH plots. A
regression analysis of the plot gave  the proton
coefficient as its slope.
Kinetic Experiments
Kinetic experiments for Hg(II) removal were conducted,
using 1% Cu-Oxide coated kaolinite. This system was
reacted with solution containing 10ppm of Hg(II) ions
regulated to required pH. Amounts of Hg(II) ions remaining
in solution after 2ndh, 4thh, 6thh, 8th h, 12thh, 18th h, and 24th
h reaction was determined using Hitachi Atomic
Absorption Spectrophotometer (HG-AAS). Kinetic studies
were conducted in 24h because adsorption reactions take
place rapidly (Egirani et al., 2013: 73-81).
The amount of metal sorbed (Qt) on a mineral at time t, is
given by the following mass-balance (Equation.3):
Qt(mg/kg) = [Co-Ct] V/m………………………………….. (3)
Here, Co denotes the initial metal concentration (mgL-1) at
time t=0; Ct denotes the concentration (mgL-1) at time t; V
denotes the total Cu-Oxide coated kaolinite suspension
volume and m is the weight of the sorbent (kg) (Egirani et
al., 2013: 73-81., Vijayakumar et al., 2012: 157-170). The
mass transfer constant Kf determines the transport of
adsorbate from external layers to the mineral surface
binding sites. This is obtained from the slopes of the curve
derived from plotting Ct/ Co vs. time based on equation 4
(Egirani et al., 2005: 319–325):
sf
t
t
SK
dt
C
Cd



















0
0
……………… (4)
Here, Ct and C0 denote the initial concentrations of Hg(II)
at time t, Ss denotes the exposed external surface area of
the adsorbent, and Kf denotes the mass transfer coefficient
(Tang et al., 2011: 689- 697). The Freundlich isotherm was
adopted to describe sorption of Hg(II) ions because this is
appropriate for heterogeneous surfaces over a wide range
of solute concentrations (Vijayakumar et al., 2012: 157-
170).
RESULTS AND DISCUSSION
RESULTS
In this study, RBH kaolinite was characterised by RBH as
containing 47% SiO2 (%), 38% Al2O3 (%), 1.5% moisture
content, 2.6 specific gravity, 0.2(%) water soluble salt (%).
This paper reported 0.60-20µm particle size range 3%
colloid, 6.00 pH, 47.00 surface area(m2/g), 170.00 CEC
and 7.00 point of zero salt effect. The systems involved in
this study have been characterized and summarized
(Table 1, Figures. 1-4). The X-ray diffraction spectrum
indicated kaolinite as the key constituent. The EDS
spectrum and SEM morphology indicated the presence of
hydrous alumino silicates (Al, Si and K). This agrees with
the chemical constituents of the RBH kaolinite and micron
range values of the particle sizes. The point zero charge
pHpzc also known as point of zero salt effect and the
surface area of adsorbents are important characterization
concerning adsorption. Here, the amount of negative
charges on the surface of the adsorbent equals the
quantity of positive charges. Therefore, it determines the
positive and negative charge divide on the mineral surface.
The external surface area of the adsorbent controlled the
quantity of exposed mineral surface available for reaction.
Proton coefficient (α) was based on a theoretical
framework given by equations (1, 2), predicted and derived
from the regression value of the plot (Figures 5-6), (Table
2). The value was 0.89, < 1. Mass transfer coefficient (Kf)
was based on a theoretical framework given by equation
(5), predicted and derived from the regression value of the
plot (Figure 8), (Table 3).

4. SYNTHESIS AND CHARACTERIZATION OF KAOLINITE COATED WITH CU-OXIDE AND ITS EFFECT ON THE REMOVAL OF AQUEOUS MERCURY(II) IONS: PARTI
Egirani et al 058
Figure 1: X-ray diffraction of kaolinite Figure 2a: EDS for kaolinite showing element peaks
Figure 2b: SEM for kaolinite showing particle sizes. Figure 2c: X-Ray spectra of synthetic CuO-Kaolinite matrix showing
peaks of kaolinite and Cu at a and b respectively
Figure 3: Particle size distribution of kaolinite Figure 4: Point of Zero Salt Effect of Kaolinite
0
500
1000
1500
2000
0 20 40 60 80 100
Degree
CPS
a
b
c

5. SYNTHESIS AND CHARACTERIZATION OF KAOLINITE COATED WITH CU-OXIDE AND ITS EFFECT ON THE REMOVAL OF AQUEOUS MERCURY(II) IONS: PARTI
Int. Res. J. Chem. Chem. Sci. 059
Table 2: Statistical presentation of proton coefficient
Equation Y=a+b*x
Proton coefficient α 0.891
Residual Sum of Squares 0.019
Pearson’s r 0.939
Adj. R-Square 0.843
Value Standard Error
Log Kd(L/kg) Intercept 1.946 0.755
Slope 0.605 0.127
Table 3: Mass transfer rates for Hg(II) sorbed on Cu-Oxide coated kaolinite
Slope I(hr-1
) SlopeII(hr-1
) Exposed Surface Area (cm2
) KfI (cm2
hr-1
) KfII (cm2
hr-1
)
0.935 0.074 4700 1.990e-4 1.590e-5
Figure 5: Plot of distribution coefficient versus pH for proton coefficient Figure 6: Plot of logKd versus Final Ph
Figure 7: Plot of Hg adsorption % versus contact time(h) Figure 8: Plot of Ct/Co versus contact time (h)
The mass transfer coefficient derived from the slope were
0.935h-1 and 0.074h-1 This plot consists of two linear parts.
The mass transfer rate predicted from equations (3, 4) and
derived. from Figure. 8 are given (Tables 3). Also, this
consist of two linear parts with the first part lower than the
second. The second linear part started after the 15th h.
There was increase in capacity of adsorption as pH was
increased. Distribution coefficient increased from 215 to
340 mg/kg over the range of pH investigated (Figure 5).
The maximum distribution coefficient occurred at pH=8.
Figure. 7 consists of two linear parts. Percent adsorption
increased from 58% to 88%. There was increase in %
adsorption as contact time was increased. At the 10th h,
the second linear part of adsorption began plateauing over
the rest of contact time investigated.
DISCUSSION
In previous studies without coated Cu-Oxide on kaolinite,
proton coefficient was greater than one (Egirani et al 2013:

6. SYNTHESIS AND CHARACTERIZATION OF KAOLINITE COATED WITH CU-OXIDE AND ITS EFFECT ON THE REMOVAL OF AQUEOUS MERCURY(II) IONS: PARTI
Egirani et al 060
73-81). Here, α for Cu-Oxide coated kaolinite was less
than one (Table 2). Differences may be ascribed to
differences in the availability of strongly acidic sites in the
two systems. This suggested that protonation was lowered
in the presence of Cu-Oxide coating. Acidic sites present
on kaolinite planar surfaces could be masked by the
presence of a coated medium.
The dependent on time attitude of Hg(II) removal was
assessed at different time intervals ranging from 2 to 24h
at 23ºC. This was at initial Hg(II) concentration of 10 mgL-
1 at pH 4. Based on Figure 7, the percent of Hg(II) ions
removed increased with increase in contact time. This
reaction pattern plateaued after the 12th h at 85%
adsorption. The adsorption rate was initially fast and the
capacity of adsorption increased over time. The initial
speedy adsorption of Hg(II) in the first step may be
ascribed to larger numbers of active adsorption sites
(Egirani et al., 2013: 73-81., Tuzun et al., 2005).
The mass transfer rate derived from equation 4 is provided
(Figure 8 and Table 3). Adsorption kinetics indicated a two-
phase process ascribed to outer sphere and inner sphere
complexation. Here, intra-particle diffusion was probably
minimal. In previous studies (Egirani et al., 2013: 73-81),
mass transfer rate for the first (Kf1) and the second reaction
phase(Kf1I) were higher when compared with rates
observed in the presence of Cu-Oxide coating. Mass
transfer rate is a function of exposed surface area.
Decrease in mass transfer rate could be ascribed to
complex reduction in the exposed surface area of the
coated Cu-Oxide RBH kaolinite.
CONCLUSIONS
Synthesis, characterisation and application of Cu-Oxide
coated kaolinite in Hg(II) removal was investigated. Using
empirical models derived from Freundlich isotherm, proton
coefficient for mercury sorbed on Cu-Oxide coated RHB
kaolinite was less than one. This suggested a lowering of
protonation during the adsorption process when compared
with uncoated kaolinite. Attenuation of protonation may be
ascribed to masking of reaction sites. In addition, mass
transfer rates for coated RBH kaolinite were lower when
compared with uncoated kaolinite. Here, complex
reduction in exposed surface area may account for this
decrease. The observed reaction plateau after the 12th h,
may account for the limited available reactive sites after
the initial fast reaction phase.
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Accepted 3 August, 2017
Citation: Egirani DE, Latif MT, Poyi NR, Wessey N, Acharjee
S (2017). SYNTHESIS AND CHARACTERIZATION OF
KAOLINITE COATED WITH CU-OXIDE AND ITS EFFECT
ON THE REMOVAL OF AQUEOUS MERCURY(II) IONS:
PARTI. International Research Journal of Chemistry and
Chemical Sciences, 4(1): 055-061.
Copyright: © 2017 Egirani et al. This is an open-access
article distributed under the terms of the Creative Commons
Attribution License, which permits unrestricted use,
distribution, and reproduction in any medium, provided the
original author and source are cited.