[SYLWAN., 159(1)]. ISI Indexed 146
Assessment of Nickel(II) Removal From Aqueous Solution Using Saudi
Bentonite
Mohamed I. Attia1*, Omar K. Alduaij
1 and Lotfi Khezami
1
1 Department of Chemistry, Science College, Al Imam Mohammad Bin Saud Islamic
University, (IMSIU), Riyadh, KSA
*Corresponding Author: Mohamed I. Attia: P.O Box 90950 Riyadh 11623 KSA, Fax:
+9662591678, Mobile : 00966532859145, e-mail:[email protected]
Abstract:
Modern Industries’ effluents cause water contamination with heavy metals. In this
work, bentonite was used for nickel(II) removal from aqueous solution compared with
commercial activated carbon. The adsorption isotherms (Langmuir, Freundlich, and
Brauner-Emmett-Teller) were applied. The rate constant of adsorption, the rate constant
for intraparticle diffusion, pore diffusion coefficient, overall reaction rate, equilibrium
constant and the thermodynamic parameters ΔGᵒ, ΔHᵒ and ΔSᵒ were evaluated. Also the
effect of time, Sorbent dose, initial concentration and the pH at different temperatures
were studied. The results were promising, indicating that bentonite is capable of
removing nickel(II) from aqueous solution. The equilibrium time for nickel(II) adsorption
by bentonite is larger than that by the powdered activated carbon and highly pH
dependent. The kinetics of adsorption were investigated as first order diffusion controlled
and spontaneous process.
Key words: Adsorption, Bentonite, Ni(II), Thermodynamic Functions, Activated Carbon,
Kinetics.
Introduction:
* Funded project No. 331207/1433 H from the Deanship of Scientific Research at Al Imam Mohammad Bin Saud Islamic University, (IMSIU), Riyadh, KSA.
[SYLWAN., 159(1)]. ISI Indexed 147
Water contamination by heavy metals in industrial effluents is a serious
environmental problem. This has led to the development of research aiming at its
reduction or elimination and at the appreciation of residues obtained through physical,
chemical, thermal, biological or mixed ways. Nickel is one of the metals found in various
raw wastewaters, e.g. of non-ferrous metals, mineral processing plants, steam-electric
power generating plants, paint formulation and porcelain enameling. [1,2] It is considered
as toxic if present in concentrations of 15 mg/l, especially in activated sludge bacteria. [3]
Its presence is detrimental to the operation of anaerobic digesters used in wastewater
treatment plants. [3-5] Nickel, copper, cadmium, lead, and zinc may be more or less toxic
to aquatic life depending on other water quality conditions, such as pH, temperature,
hardness, turbidity, and carbon dioxide content. At certain dosage levels of some heavy
metals carcinogenic effects have been observed. [6] Natural polymeric organic acids (e.g.
fulvic or humic acids) is capable of re-mobilizing it from solid phases through increasing
its solubility. [7] Removing nickel ions from wastewaters was studied either by sorption
on wollastonite (-calcium metasilicate), MnO2, activated carbon, various oxides: Fe2O3,
Al2O3, TiO2, SiO2, goethite (-FeOOH), using ion-exchange resins (Dowex 50WX8), by
precipitation or even by crystallization of nickel carbonate. [8-15] Using flyash, a cheap
industrial by-product, was investigated too, wherever the addition of flyash to the
solution raised the pH, effectively removing all of the nickel ions. [16]
The optimum binding pH, time dependency for Ni (II), Cu (II), and Pb (II)
desorption by inactivated cells of synechoccos PCC7942 (cyanobacteria) were measured
in which a high affinity for all metal ions as the pH increased from 2 to 6 with optimum
binding occurring at pH 5.5. The dependency studies showed that these cyanobacteria
had a rapid binding to all three metals. More than 90% of Ni(II), Cu(II), and Pb(II) metal
ions were recovered when treated with 0.1M HCl. [17] Activated carbon, which is
frequently used in the adsorption of pollutants, is costly both to use and to regenerate.
Therefore, there are a need for the development of low cost, easily available materials
[SYLWAN., 159(1)]. ISI Indexed 148
which can adsorb divalent nickel economically. Bentonite (montmorillonite) is a colloidal
clay (aluminum silicate), used in treating aqueous waste containing heavy metals and
organic matter. Use of clay for removal or elimination of heavy metals in effluents has
been the object of study in a great deal of research due to its several economic
advantages. [18-21] The undertaken work is devoted to investigate the performance of
local activated bentonite for Ni (II) removing from aqueous solution compared to
commercial powdered activated carbon (PAC).
Materials and Methods:
Materials:
Bentonite used in this study was supplied from Kholeis Provenience, Jeddah, KSA,
and was investigated for adsorption studies against a commercial Activated Charcoal in the
form of (PAC) supplied from El-Nasr Co. For Pharmaceutical Industry. The adsorbents
were dried in an oven at 105C for about one hour and then screened through a sieve 30
mesh/inch (0.1 - 0.315 mm) openings to remove any large solids. This was done to
produce a uniform material for the complete set of adsorption tests. The radius of the
adsorbents was determined using Electronic Microscope and was found to be 6.24×10−4
and 8.15×10−4 mm. for PAC and bentonite respectively i.e. approximately the same size,
hence the same surface area. All the chemicals used were of analytical grade and were
obtained from BDH, and E. Merck. A stock aqua nickel (II) solution (1000 mg Ni/L) was
prepared using nickel nitrate hexahydrate Ni(NO3)2.6H2O.
Analytical Procedures:
The adsorbents were chemically analyzed for cations; Fe, Ni, Co, Cr, Cu, Zn and Mn
using Inductively Coupled Plasma-atomic emission spectrometry (ICP). Essential chemical
[SYLWAN., 159(1)]. ISI Indexed 149
analysis methods for metal oxides, sulphates and chloride were measured. [22-25] The
analysis was listed in Table (1).
Experimental procedures
The capability of bentonite for Ni(II) removal from aqueous solution was evaluated
through adsorption kinetics. In a batch system, a working solution of Ni(II) was prepared
by diluting a sufficient volume of the stock solution to achieve the desired concentrations.
For each adsorption data point, the dry adsorbents were accurately weighed and placed
into the glass vials. The glass vials were then filled with the nickel solution (with the
specified concentration), sealed immediately and allowed to equilibrate in a water bath
shaker with a constant temperature bath at 20◦C. After each experiment the solution was
filtered and nickel concentration was determined. The following parameters were
investigated; effect of contact time (Equilibrium Time), initial concentration, mass of
adsorbents and the solution pH. All experiments were repeated at different temperatures
30, 40, 50 and 60◦C for each adsorbent. Adsorption models and adsorption dynamic
parameters were evaluated.
Results and Discussion:
Chemical Analysis of the used adsorbents:
The used adsorbents were chemically analyzed for different oxides, metal
concentrations, pH of adsorbent solution and the effect of heat, Table (1). It is obvious,
from these results that the pH of the adsorbent solutions ranges from 7 to 8. Also, these
adsorbents were free from the studied metal Ni(II).
[SYLWAN., 159(1)]. ISI Indexed 150
Evaluation of the sorption process:
Two important physico-chemical aspects of the evaluation of the sorption process
as a unit operation are the equilibrium of sorption and the kinetics. Sorption equilibrium
is established when the concentration of metal in a bulk solution is in dynamic
equilibrium with that of the interface.
Sorption equilibrium:
Critical equilibrium time and effect of initial cobalt concentration on metal adsorption:
The removal efficiency increases with time and attains equilibrium within 40 to 60
min. For both PAC and bentonite respectively, this shows that equilibrium is attained
after these periods., Fig. (1,2). However, the results indicate that the increasing in the
initial nickel concentration is accompanied by increasing in the remaining nickel
concentration in the solution at various intervals of time, and there is no dependence on
temperature change in this case.
Effect of adsorbent dose on nickel adsorption:-
The effect of the adsorbent dose indicates the decreasing in the remaining nickel
concentration by the increasing in the adsorbent doses. Isothermal data have been used
to calculate the ultimate sorption capacity of the adsorbents by substituting the required
equilibrium concentrations in the Langmuir, Freundlich and Brauner, Emmit&Teller (BET)
equations. Table (2) summarizes the Langmuir, Freundlich and BET parameters of nickel
adsorption at different temperatures. The data demonstrate that the adsorption of nickel
is effective in neutral solution in (pH 7.5-8.5). By increasing the temperatures, the
Langmuir constant, at (which is an indicative of maximum adsorption capacity), was found
to increase whilst the Langmuir constant, b (which is a measure of adsorption energy),
show a small decrease trend. On the other hand, Freundlich constant, K (which is a
measure of adsorption capacity) showed an increasing trend with increasing the
temperature. This result seems to be conflicted with the basic knowledge concerning the
[SYLWAN., 159(1)]. ISI Indexed 151
increase of desorption with increasing medium temperature, but considering that, the
temperature at which an adsorption is conducted will affect both the rate of adsorption
and the extent to which adsorption occurs. The rise of temperature affects the solubility
and the chemical potential of the adsorbate, the latter being the controlling factor for the
adsorption. If the solubility of the adsorbate increases with increase in temperature the
chemical potential decreases and both the effects, i.e. solubility and normal
temperatures, work in the same direction, causing a decrease in the adsorption. On the
other hand, if temperature has the reverse effect on the solubility, then both effects will
act in the opposite direction and the adsorption may increase or decrease depending
upon the predominant factor. [26] At the same time, the Freundlich constant, n, (a
measure of adsorption intensity), show a slight increase with increasing the temperature.
In case of Brunaur- Emmett-Teller (BET) constant, A, (describe the energy of interaction
between the solute and adsorbent surface) showed an increasing trend with increasing
the temperatures indicating the increasing in the interaction between the nickel ions and
the adsorbents.
Effect of pH of the solution on nickel adsorption:-
The effect of pH change on nickel adsorption at different temperatures is
illustrated in Figs.(3), indicating that below pH=7.5, practically the Ni removal was
increased with increasing the pH, whereas above pH=7.5-8.5 the Ni removal increased
sharply and was practically 100% at pH=10-11. The results indicated that chemical
precipitation occurs after approximately pH=8 and is completed by pH>10. Similar results
were also obtained by Theis and Richer [13], where it is obvious that above pH=10
practically very little nickel exists in its Ni2+ form. Above pH=9-10, on the other hand
Ni(OH)2 only slightly soluble; in this case, its removal is due not to adsorption anymore,
but to precipitation and adsorbents may be regarded as a more filtering aids.
[SYLWAN., 159(1)]. ISI Indexed 152
Sorption kinetics:-
Determination of rate constant for nickel adsorption
The rate constant for adsorption of the nickel on different adsorbents were
determined using Lagergren’s equation and listed in Table (2). It may be concluded from
the values of Kad that the reaction may be of first orderly behavior.
Determination of rate constant for intraparticle diffusion kp:
In a batch reactor with rapid stirring, there is also a possibility that the transport
of adsorbate ions from a solution into the pores of the adsorbent is the rate controlling
step. [27,28] This possibility was tested in terms of a graphical relationship between the
amount of nickel adsorbed and the square root of time Fig.(4). The double nature of these
plots may be explained as: the initial curved portions are attributed to boundary layer
diffusion effects. [29] While the final linear portions are due to intraparticle diffusion. The
rate constant for intraparticle diffusion Kp, at different temperatures was determined
from the slopes of the linear portions of the respective plots and are given in Table (2).
Determination of pore diffusion coefficient D:
The pore diffusion coefficient D, at different temperatures was determined and
displayed in Table (2). D were found to be 6.9x10-8, 1.2x10-9 cm2 s-1 for bentonite and PAC
respectively, from the values of Kp and D, it may be indicated that the process is governed
by diffusion but pore diffusion is not the only rate limiting step. [30]
Determination of overall reaction rate K:
The kinetics of nickel adsorption by different adsorbents were investigated during
this phase of the experiment. Kinetic experiments were conducted at various
temperatures ranging between 20◦C and 60◦C. The results of the overall rate constant (K),
calculated from the negative value of the slope of the relation between Ln(1-Xa/Xac)
[SYLWAN., 159(1)]. ISI Indexed 153
versus time (t) in Figs.(5) and the results are summarized in Table (2) indicating that the
adsorption rate increase with the increasing of temperature.
Determination of activation energy E:
The values of E can be calculated by plotting the relation between LnK against the
reciprocal of the Kelvin temperature in Fig.(6). The activation energy summarized in Table
(2) for different adsorbents indicating that these values are small. Low activation energy
values are characteristic of a diffusion-controlled process. [31]
Determination of thermodynamic parameters:-
The kinetic model that was used in the research to describe this reaction rate was
based on the assumption that the adsorption of nickel onto the used adsorbents is a
diffusion controlled and first-order process. The thermodynamic parameters such as free
energy change ΔG, enthalpy change ΔH, and entropy change ΔS, were determined by
plotting the logarithmic values of the equilibrium constant Kc versus the inverse
temperature in Kelvin (1/T) in Fig.(7), revealed the values of the ΔH, and ΔS, from the
slope and the intercept respectively and hence ΔG can be calculated, summarized in Table
(2). The positive values of differential heat of adsorption ΔH, suggests that the adsorption
of nickel onto the different used adsorbents is an endothermic process. The negative
values of the free energy change ΔG, suggest the spontaneous nature of the adsorption
process. However, the negative ΔG value decreased with an increase in temperature,
indicating that the spontaneous nature of adsorption is directly proportional to the
temperature. [32]
Conclusions
Nickel removal is very important issue as it is considered as being toxic. The results
of current research indicated that: bentonite which is a very economic ore found in
Kholeis Provenience, Jeddah, KSA can indeed be used for the removal of nickel ions from
[SYLWAN., 159(1)]. ISI Indexed 154
aqueous solutions and can be used as instead of expensive absorbents such as PAC
(powdered activated carbon). The kinetics of adsorption of the studied metal onto the
utilized adsorbents was investigated as first order and diffusion controlled process.
Thermodynamic functions H, G and S were evaluated and indicated that the
processes of adsorption of nickel is endothermic. Nickel adsorption was highly pH
dependent and the removal of hydrolyzed heavy metal cation at high pH was preferred
than the heavy metal cation itself. The most suitable pH for its removal was found to be
7.5-8.5. The effect of temperature on the adsorption is conflicted with the basic
knowledge concerning the increase of desorption with increasing the medium
temperature, but the exerogenicity of the process reflect that the adsorption capacity
may increase with rise in temperature.
Acknowledgement:
The researchers thank the Deanship of Scientific Research at Al Imam Mohammad Bin
Saud Islamic University, (IMSIU), Riyadh, KSA for funding this project No. 331207/1433 H.
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Figures Captions:
Fig. (1) Effect of Time on Nickel Adsorption by PAC
Fig. (2) Effect of Time on Nickel adsorption by Bentonite
Fig. (3) Effect of pH on Nickel Adsorption
Fig. (4) Determination of rate constant for intraparticle diffusion kp
Fig. (5) Determination of overall reaction rate K
Fig. (6) Determination of Activation Energy
Fig. (7) Determination of thermodynamic parameters
[SYLWAN., 159(1)]. ISI Indexed 158
Table (1): Characteristics and Chemical Composition Of Used Adsorbents
Analyte % Bentonite PAC
SiO2
CaO
MgO
Na2O
K2O
Al2O3
SO2-
4
Cl-
P2O5
Fe
Cu (ppm)
Cr (ppm)
Ni (ppm)
Co (ppm)
Zn (ppm)
Mn (ppm)
pH
Loss of weight at:
100C
1000C
Particle Size:
>0.315 mm
<0.100 mm
57.27
3.54
1.54
1.02
0.42
18.39
7.65
0.15
0.25
1.98
0.02
0.01
0.00
0.00
0.04
10.01
7.30
8.30
16.53
0.22% max.
2.15% max.
2.14
0.51
0.60
1.65
0.90
0.14
0.00
0.00
0.00
0.60
0.03
0.00
0.00
0.00
0.01
21.29
7.80
2.10
94.96
0.20% max.
2.00% max.
[SYLWAN., 159(1)]. ISI Indexed 159
Table (2) Adsorption parameters of nickel by powdered activated carbon (PAC) and bentonite
Para- Powdered Activated Carbon (PAC) Bentonite
meter T=20C T=30C T=40C T=50C T=60C T=20C T=30C T=40C T=50C T=60C
L a b
0.077 13x10
-3
0.580 7.5x10
-3
1.86 6.5x10
-3
5.39 6.7x10
-3
7.30 7.1x10
-3
-0.056 -1x10
-3
-0.046 -2x10
-3
-0.035 -5x10
-3
-0.008 -0.137
-0.017 -0.009
F n k
1.23 0.813
2.20 2.51
2.66 3.67
2.87 5.30
3.24 5.84
0.394 0.008
0.539 0.034
0.518 0.091
0.645 0.181
0.586 0.234
BET A 2.0 22.60 32.94 64.10 65.30 -1.492 -0.584 -0.796 -0.047 -1.10
Kad 0.157 0.090 0.131 0.070 0.085 0.069 0.075 0.94 0.108 0.114
K 0.156 0.228 0.247 0.303 0.341 0.073 0.081 0.96 0.115 0.119
Kc 6.04 6.46 7.47 8.09 9.00 3.64 4.18 5.60 6.00 6.88
Kp 0.84 0.63 0.39 0.49 0.85 1.12 1.50 1.25 1.37 1.00
G -1.035 -1.138 -1.240 -1.343 -1.446 -0.590 -0.882 -1.052 -1.117 -1.28
H 1.977 2.852
S 0.01 0.009
E 4.83 3.025
D 1.2x10-9
6.9x10-8
ro 6.24x10-4
3.85x10-3
L a: Langmuir constant (mg/g) Kp: Rate constant of intraparticle diffusion (min
-1)
b: Langmuir constant (l/mg) G: Free energy change (kcal/mol)
F n: Freundlich constant H: Enthalpy change (kcal/mol)
k: Freundlich constant (mg/g) S: Entropy change (kcal/mol) BET A: Brunaur-Emmet-Teller constant E : Activation energy(kcal/mol) Kad : Lagergren’ rate constant (min
-1) D : Pore diffusion coeffecient (cm
2 s
-1)
K : Overall reaction rate (min-1
) ro : Radius of adsorbent (cm)
Kc: Equilibrium constant (min-1
)
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