Assessment of Nickel(II) Removal From Aqueous Solution Using Saudi Bentonite

[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.


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


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


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).


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


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.


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)


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


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


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.


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

)

Assessment of Nickel(II) Removal From Aqueous Solution Using Saudi Bentonite

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