Modelling the Effect of Dosage on the Biosorption of Ni 2 ...article.aascit.org/file/pdf/8910896.pdf · by Luffa cylindrica was derived from the rate constant, equilibrium sorption

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×.


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.


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


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

qq

dq

te

t =− 2

( ) ktqqq ete

+=−

11

( )ee

tqtkq

tq

//1 2 +=

2ekqh =


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


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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