Journal of Materials Sciences and Applications
2018; 4(1): 1-9
http://www.aascit.org/journal/jmsa
ISSN: 2381-0998 (Print); ISSN: 2381-1005 (Online)
Keywords Biosorption,
Luffa cylindrica,
Empirical Model,
Sorption Capacity,
Dosage
Received: April 30, 2017
Accepted: January 8, 2018
Published: January 25, 2018
Modelling the Effect of Dosage on the Biosorption of Ni2+ Ions onto Luffa Cylindrica
Innocent Oseribho Oboh
Department of Chemical and Petroleum Engineering, University of Uyo, Uyo, Nigeria
Email address [email protected]
Citation Innocent Oseribho Oboh. Modelling the Effect of Dosage on the Biosorption of Ni2+ Ions onto
Luffa Cylindrica. Journal of Materials Sciences and Applications. Vol. 4, No. 1, 2018, pp. 1-9.
Abstract Nickel metal contamination exists in industrial processes that use nickel catalysts, such
as coal gasification, petroleum refining, and hydrogenation of fats and oils. Therefore, a
systematic study on the removal of nickel from wastewater is of considerable
significance from an environmental point of view. Luffa cylindrica, a plant material with
wide distribution particularly in the tropical world, was characterized as the surface area,
chemical bonds, bulk density, Pore size distribution, microstructures, composition,
morphology and elemental composition were determined. Biosorption studies were
carried out with the dosage varied and the experimental data obtained were fitted to some
selected kinetic models. Non-linear regression method was used and the regressed data
obtained for the various doses studies ranged from 0.948 to unity. A kinetic model was
developed. This empirical model for predicting the sorption capacity for Ni2+
ions sorbed
by Luffa cylindrica was derived from the rate constant, equilibrium sorption capacity and
the initial sorption rate.
1. Introduction
Biosorption is an attractive technology which involves sorption of dissolved
substances by a biomaterial. It is a potential technique for the removal of heavy metals
from solutions and recovery of precious metals [1]. It is a metabolism independent
process and thus can be performed by both living and dead cells [2].
The species with the most toxicological relevance found in the industrial effluents are
the heavy metals. These species are bio-accumulative and not biodegradable over time
[3]. Water contaminated with metal ions can cause several health problems. Heavy metal
ions such as cadmium, zinc, nickel, chromium, copper and lead can bio-accumulate to be
toxic comounds through the food chain [4].
Nickel is toxic and relatively widespread in the environment. It is used in a wide
variety of industries such as plating and cadmium–nickel battery, phosphate fertilizers,
mining, pigments, stabilizers and alloys, and find its way to the aquatic environment
through wastewater discharge [5].
Activated carbon is the most employed adsorbent for heavy metal removal from
aqueous solution and have been well documented in the literature [6-7]. However, the
extensive use of activated carbon for metal removal from industrial effluents is
expensive [8], limiting its large application for wastewater treatment. Therefore, there is
a growing interest in finding alternative low-cost adsorbents for metal removal from
aqueous solution, such as: the residuals of agricultural products [9-10].
The utility of these very low cost and environmentally friendly plant materials as
biosorbents for the removal of divalent cations from aqueous solutions as the cellulose,
2 Innocent Oseribho Oboh: Modelling the Effect of Dosage on the Biosorption of Ni2+ Ions onto Luffa Cylindrica
hemicelluloses, pectin and lignin present in the cell wall are
the most important sorption sites [11]. The structure of Luffa
cylindrica for example, is cellulose based [12-13], and the
surface of cellulose in contact with water is negatively
charged. Nickel compound used in this study will dissolve to
give the cationic metal and this will undergo attraction on
approaching the anionic Luffa cylindrica structure [14]. On
this basis, it is expected that a metal cation will have a strong
sorption affinity for Luffa cylindrica.
However, some researchers have addressed the
mathematical modelling of the sorption of metal ions onto
these biosorbents. Earlier reported mathematical models for
the sorption of heavy metal ions included: surface-
complexation, cation-exchange and triple-layer models [15].
The purpose of this study is to develop an empirical model
for describing the effect of dosage on equilibrium sorption of
nickel (II) ions on Luffa cylindrica.
2. Materials and Methods
2.1. Preparation of Luffa cylindrica
The seeds and sponges of L. cylindrica were gathered into
a clean plastic bag. They were dried in the oven at 105°C for
24 hours and afterwards ground with a grinding mill. The
ground seeds and sponges were sieved and were of particle
size 0.3 to 0.6mm. This was to allow for shorter diffusion
path, resulting in a higher rate of biosorption [16]. The
ground seed and sponge were mixed at a ratio of 1:1.
2.2. Preparation of Aqueous Solutions
Stock solution of Nickel was prepared with distilled water
and Nickel (II) tetraoxosulphate (VI). All working solutions
were obtained by diluting the stock solutions with distilled
water. The pH of the solutions was adjusted to their respective
optimum pH. The concentration of metal ions in solutions was
analyzed by Atomic Absorption Spectrophotometer. A
duplicate was analyzed for every sample to track experimental
error and show capability of reproducing results [17].
2.3. Determination of Optimum pH
A gramme of L. cylindrica seeds and sponge mixture were
put into 250ml conical flasks containing 50 ml of the aqueous
solutions each adjusted to pH 2, 3, 4, 5, 6, 7, 7, 8, 9 and 10
for each metal ions studied. They were agitated for 2h at
25°C. The biosorbents were removed from the aqueous
solutions after biosorption using the centrifuge at 2400 rate
per minute (rpm) for 10 minutes. The final concentrations of
the metal ions remaining were determined using Atomic
Absorption Spectrophotometer (AAS).
2.4. Biosorption Experiment
The biosorption studies for evaluation of the Luffa
cylindrica mixture for removal of Nickel (II) ions from
aqueous solutions was carried-out in triplicate using the batch
biosorption procedure [9-10].
The method of least squares was used to predict the kinetic
model by linear regression method. A trial and error was
used for nonlinear regression to minimize or maximize the
objective function using the solver add-in function, Microsoft
Excel, Microsoft Corporation.
2.5. Determination of Surface Area
The Autosorb-1c was used for the determination of the
surface area of the ground Luffa cylindrica mixture under study.
2.6. Determination of Pore Size Distribution
The PoreMaster PM-60 was used to test the ground Luffa
cylindrica mixture sample. The instrument determines both
Pore volume and Pore diameter of a solid or powder by
forced intrusion of a non-wetting liquid (mercury) [18].
2.7. Determination of the Microstructures,
Composition, Morphology and Elemental
Composition of the Luffa cylindrica
Mixture
The microstructures, composition, and morphology of the
Luffa cylindrica mixture were analysed by means of scanning
electron microscopy (SEM). A Philips scanning electron
microscope (ESEM XL30) equipped with energy dispersive
X-ray spectrometer (EDX) was used to analyse the various
elemental composition found in the Luffa cylindrica mixture.
2.8. Determination of Chemical Bonds in
Luffa cylindrica Mixture
Fourier transform infrared spectroscopy (FTIR) of the
adsorbent was done by using an FTIR spectrometer (Model
FTIR 2000, Shimadzu, Kyoto, Japan) [19].
2.9. Determination of Bulk Density of Luffa cylindrica Mixture
The method of Okaka and Potter [20] was used in
determining the bulk density.
3. Results and Discussion
Table 1. Physical properties of the Luffa cylindrica biosorbent.
Specific surface area - BET (m²/g) 0.28
Total Surface area (m²/g) 1.1895
Pore Diameter Range (µm) 1051.309204 to 0.003577
Bulk density (g/cm3) 0.34
Table 1 show the bulk density, surface area and pore diameter
range for the biosorbent used for this study. The Specific surface
area using the BET method was 0.28m²/g and the Pore diameter
range was between 1051.309204 to 0.003577µm. The bulk
density was 0.34g/cm3. As observed, the surface area for the
seed and sponge mixture of L. cylindrica is relatively low, with
pore diameter values in agreement with those found for typical
mesoporous materials [21].
Journal of Materials Sciences and Applications 2018; 4(1): 1-9 3
Figure 1. SEM Scan and plot showing elemental composition of Luffa cylindrica.
Figure 1 gives the elemental composition of Luffa
cylindrica that was analysed by means of scanning electron
microscopy (SEM). The Luffa cylindrica showed it contained
a very high percentage of carbon at 79.33% followed by
oxygen, potassium, calcium, chlorine, phosphorus and
sulphur with weight % values of 12.25, 3.86, 1.58, 1.29, 0.95
and 0.75 respectively.
Scanning electron microscopy (SEM) of the Luffa
cylindrica biosorbent was taken in order to verify the
presence of macropores in the structure of the fiber. In the
micrographs presented, Figure 2 shows the fibrous structure
of Luffa cylindrica, with some fissures and holes, which
indicate the presence macroporous structure. These, should
contribute a little bit to the diffusion of the Ni (II) ions to the
Luffa cylindrica biosorbent surface [22-25]. The small
number of macroporous structure is confirmed by the low
specific surface area of the biosorbent (see Table 1). As the
biosorbent material presents few numbers of macroporous
structure, it adsorbed low amount of nitrogen, which led to a
low BET surface area [22-25]. Therefore the major
contribution of the Ni (II) ions uptake can be attributed to
micro- and mesoporous structures (see Figure 2).
Figure 2. Scanning electron microscopy of Luffa cylindrica biosorbent:
Transversal view of the mixture of seed and sponge 4000×.
4 Innocent Oseribho Oboh: Modelling the Effect of Dosage on the Biosorption of Ni2+ Ions onto Luffa Cylindrica
Figure 3a. FTIR spectrum of the mixture of seed and sponge of L. cylindrica biosorbent before biosorption.
Figure 3b. FTIR spectrum of the mixture of seed and sponge of L. cylindrica biosorbent after biosorption of Ni2+ ions.
Journal of Materials Sciences and Applications 2018; 4(1): 1-9 5
Figures 3a and 3b show the FTIR spectral. The functional
groups on the binding sites were identified by FTIR spectral
comparison of the free biomass with a view to understanding the
surface binding mechanisms. The significant bands obtained are
shown in Figure 3a and 3b. Functional groups found in the
structure include carboxylic, alkynes or nitriles and amine
groups [26]. The stretching vibrations of C-H stretch of -CHO
group shifted from 2847.05 to 2922.20, 2852.58, 2852.46 and
2852.43 cm-1
after Ni2+
ions biosorption. The assigned bands of
the carboxylic, amine groups and alkynes or nitriles vibrations
also shifted on biosorption. The shift in the frequency showed
that there was biosorption of Ni2+
ions on the L. cylindrica
biosorbent and the carboxylic and amine groups were involved
in the sorption of the Ni2+
ions [11].
Figure 4. A plot showing the pore size distribution of the biosorbent - L. cylindrical.
Table 2. Kinetic models and parameters for Ni (II) ions using L. cylindrica
as biosorbent.
Kinetic parameters Dosage
Pseudo-first order 0.3g 0.5g 0.7g 0.9g
qe(mg/g) 12.88 7.859 5.673 4.446
kf(min-1) 0.194 0.165 0.148 0.136
R2 0.981 0.983 0.983 0.983
Pseudo-Second order
qe(mg/g) 13.27 8.126 5.883 4.622
ks(g/mg/min) 0.030 0.040 0.048 0.054
Kinetic parameters Dosage
R2 1.000 1.000 1.000 1.000
Intra-particle diffusion
Ki(mg/g min-0.5) 0.284 0.184 0.148 0.125
C 10.04 5.780 3.990 3.010
R2 0.965 0.957 0.952 0.948
Avrami
qe(mg/g) 12.88 7.859 5.673 4.446
Ka(min-1) 0.029 0.024 0.022 0.020
na 6.602 6.911 6.851 6.843
R2 0.984 0.983 0.983 0.983
6 Innocent Oseribho Oboh: Modelling the Effect of Dosage on the Biosorption of Ni2+ Ions onto Luffa Cylindrica
The pore size distribution of the Luffa cylindrica sample
was obtained by Mercury intrusion method, and it is shown
in Figure 4. The distribution of average pore diameter curve
presents a maximum with an average pore diameter of about
30 µm. The amount of pores seen in the Luffa cylindrica
biosorbent; decreases for average pore diameters ranging
from 30 to 1000 µm. On the other hand, the amount of
average pores ranging from 3.0 x 10-03
to 30 µm is
predominant. Therefore, this biosorbent can be considered
mixtures of micro- and mesoporous materials [22-25].
Some selected set of kinetic reaction models [27-31] were
used to fit the experimental data but the correlation
coefficients were not as high as the rate law for a pseudo-
second order (Table 2).
The qe values found in the pseudo-second-order for Table
2 were in good agreement with the experimental qe values.
These results indicate that the pseudo-second- order kinetic
model should be taken into account for explaining the
biosorption process of Ni (II) ions removal by the L.
cylindrica biosorbent.
When analyzing the values of the kinetic parameters
depicted on Table 2, it should be mentioned that the ks values
strongly depend on the initial concentration, since its units is
gmg−1
min−1
. Table 2 shows that the kinetic results obtained
fitted very well to the pseudo-second-order kinetic model for
the nickel (II) ions studied with R2 values of unity for the
various dosages under consideration. The sorption of Ni (II)
ions onto Luffa cylindrica could be a pseudo-second order
process.
3.1. Derivation of Empirical Model
Luffa cylindrica contains polar functional groups such as
aldehydes, ketones, and acids. These groups can be involved
in chemical bonding and are responsible for the cation
exchange capacity of the Luffa cylindrica [28]. It appears
reasonable that in many cases ion exchange rather than
sorption to free sites is the relevant overall-mechanism for
the binding of metal ions in biosorption. Since the overall
charge of the biomass particle has to be neutral, any binding
of one cation must be accompanied by either a stoichiometric
release of other cations or by the binding of anions [32]. Thus,
the Luffa cylindrica-metal reaction may be represented in two
ways:
2L- + Ni2+ → NiL2 (1a)
and
2HL + Ni2+ → NiL2 + 2H+ (1b)
where L and HL are polar sites on the Luffa cylindrica
surface.
In developing the mathematical description of this sorption
process, certain assumptions were made:
a. The process may be pseudo-second order and the rate
limiting step may be chemical sorption or
chemisorption;
b. there is a monolayer of metal ion on the surface of Luffa
cylindrica;
c. the energy of sorption for each ion is the same and
independent of surface coverage;
d. the sorption occurs only on localised sites and involves
no interactions between sorbed ions;
e. the rate of sorption is almost negligible in comparison
with the initial rate of sorption.
The rate of pseudo-second order reaction may be
dependent on the amount of divalent metal ion on the surface
of Luffa cylindrica and the amount of divalent metal ion
sorbed at equilibrium. The sorption equilibrium, qe, is a
function of, for example, the initial metal ion concentration,
the Luffa cylindrica dose and the nature of solute-sorbent
interaction [28].
The rate expression for the sorption described by
Eqs (1a) and (1b) is:
or
where (L)t and (HL)t are the number of active sites occupied
on the Luffa cylindrica at time t, (L)0 and (HL)0 are the
number of equilibrium sites available on the Luffa cylindrica
[28].
The kinetic rate equations can be rewritten as follows:
(2)
where k is the rate constant of sorption, (g/mg min), qe is the
amount of divalent metal ion sorbed at equilibrium, (mg/g),
qt is amount of divalent metal ion on the surface of the
sorbent at anytime, t, (mg/g).
Separating the variables in Eq. (2) gives:
integrating this for the boundary conditions t= 0 to t = t and qt
= 0 to qt = qt, gives:
(3)
this is the integrated rate law for a pseudo-second order
reaction.
Eq. (3) can be rearranged to obtain:
(4)
(5)
( ) ( )[ ]2
0
)(t
t LLkdt
Ld−=
( ) ( )[ ]2
0
)(t
t HLHLkdt
HLd−=
( )2te
t qqkdt
dq−=
( )kdt
dq
te
t =− 2
( ) ktqqq ete
+=−
11
( )ee
tqtkq
tq
//1 2 +=
2ekqh =
Journal of Materials Sciences and Applications 2018; 4(1): 1-9 7
Substituting Eq. (5) into Eq. (4), gives:
(6)
Although there are many factors which will influence
sorption, contact time, pH, temperature, sorbent
concentration, nature of the solute and its concentration, a
kinetic model is concerned only with the effect of observable
parameters on the overall rate. These include initial metal ion
concentration, temperature, Luffa cylindrica dose and nature
of solute [28].
3.2. Effect of Luffa cylindrica Dose and
Nature of Solute
Figures 5 and 6 show typical sorption curves for effect of
Luffa cylindrica dose on the sorption kinetics of zinc, nickel,
copper and lead ions onto Luffa cylindrica at temperature of
25°C and initial ion concentration of 100 mg/l. The plotted
experimental data (Figure 5) also gave a good fit with the
pseudo-second order equation and the regression coefficients
for the linear plots were very close to 1.00 as can be seen in
Table 3.
Table 3. The effect of dosage on metal ions biosorption data.
Dosage (g) r2 qe (mg/g) k (g/mgmin) h (mg/gmin)
0.3 1.000 13.2687 0.0371 6.4899
0.5 1.000 8.1256 0.0487 3.1907
0.7 1.000 5.8826 0.0582 1.9987
0.9 1.000 4.6216 0.0666 1.4093
Figure 6 show that for all the various doses, the amount of
the divalent metal ions sorbed increases rapidly with time in
the beginning and very slowly towards the end of the reaction.
Furthermore, a large fraction of the total amount of metal
was removed within a short time that is before 20 minutes.
The plot as seen in Figure 6 also showed that sorption
capacity increased for lower Luffa cylindrica dosages at any
specific time. There were effects on the contact time required
to reach saturation due to the variation in Luffa cylindrica
doses. It was found that the equilibrium sorption of metal
ions studied was a function of Luffa cylindrica doses. The
rate constant, k, the equilibrium sorption, qe and the initial
sorption rate, h, of sorption at different Luffa cylindrica doses
were calculated from the intercept and slope of the straight
line plots of t/qt versus t. The initial sorption rate decreased
with an increase in the Luffa cylindrica dose from 0.2 -1.0 g.
The corresponding linear plots of the values of qe, k and h
against m (dosage) were regressed to obtain expressions with
exponents for these values in terms of the m parameters for
all the metal ions studied.
Figure 5. The sorbed capacity against time for the effect of varied doses on
the sorption kinetics of Nickel (II) ions onto Luffa cylindrica at pH= 8.0.
Figure 6. The sorbed capacity against time for the effect of varied doses on
the sorption kinetics of Nickel (II) ions onto Luffa cylindrica at pH= 8.0.
The expression
x = Amb (7)
Where x= qe, k or h
Table 4. Empirical parameters for predicted qe, k and h.
M2+ Aq bq r2 Ak bk r2 Ah bh r2
Ni 4.177 - 0.96 1.000 0.0704 0.5331 1.000 1.2174 - 1.39 1.000
Table 4 shows the empirical parameters for predicted qe, k and h and their corresponding correlation coefficients.
Substituting the values of Aq, Bq, Ah and Bh from Table 4 in Eq. (6), the rate law for a pseudo-second order reaction and the
relationship between qt, m and t can be represented as:
(8)
( )e
tqth
tq
//1 +=
96.039.1 177.42174.11 −− +=
mtm
tq
t
8 Innocent Oseribho Oboh: Modelling the Effect of Dosage on the Biosorption of Ni2+ Ions onto Luffa Cylindrica
Figure 7. Effect of L. cylindrica dose on nickel (ii) ions sorption at various times.
These equations can then be used to derive the sorption
amount of nickel at any given dosage and the reaction time.
The three-dimensional plot of the Equation (8) is shown in
Figure 7.
The Equation represent a generalised predictive model for
the amount of metal ion sorbed at any contact time and
involved L. cylindrica dose. It indicates that the metal sorbed
at any contact time is higher as the L. cylindrica dose is
decreased. This is due to the fact that increasing the L.
cylindrica dose increases the surface area for sorption and
hence the rate of metal sorption is increased when the initial
metal ion concentration is constant.
A kinetic model has been derived for the sorption of the
nickel (II) ions onto L. cylindrica. The parameter which has
the greatest influence on the kinetics of the sorption reaction
was sorption equilibrium; qe is a function of L. cylindrica
dose and nature of solute and this is in agreement with
previous research [28].
4. Conclusion
A kinetic study was carried out and the experimental data
fitted into Pseudo-first order, Pseudo-second order, Intra-
particle diffusion and Avrami models using the non-linear
regression method to obtain the kinetic parameters.
A kinetic model has been developed and fitted for the
sorption of the divalent nickel ions onto L. cylindrica. The
results showed sorption for Ni (II) ions onto L. cylindrica
during agitation by suspended shaking; the process can be
described by all kinetic models with pseudo-second order
having the R2 value of unity for all the doses studied. The
experimental data fits the pseudo-second order model based
on the assumption that the rate limiting step may be chemical
sorption involving ion exchange between sorbent and sorbate.
The parameter which has the influence on the kinetics of the
sorption reaction was the sorption equilibrium capacity, qe, a
function of initial metal ion concentration, Luffa cylindrica
dose and the nature of solute ion.
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