kinetic and thermodynamic modeling of cd+2 and ni+2 ion view content

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An Article Submitted to

INTERNATIONAL JOURNAL OF

CHEMICAL REACTOR ENGINEERING

Kinetic and Thermodynamic Modeling of

Cd+2

and Ni+2

Biosorption by Raw ChickenFeathers

Hilda E. Reynel-Avila∗ Guadalupe de la Rosa† Cintia K. Rojas-Mayorga‡

Irene Cano-Aguilera∗∗ Adrian Bonilla-Petriciolet††

∗Universidad de Guanajuato, helizabeth [email protected]†Universidad de Guanajuato, g dela [email protected]‡Instituto Tecnologico de Aguascalientes, [email protected]

∗∗Universidad de Guanajuato, [email protected]††Instituto Tecnologico de Aguascalientes, [email protected]

ISSN 1542-6580

Copyright c2011 The Berkeley Electronic Press. All rights reserved.



Kinetic and Thermodynamic Modeling of Cd+2

and Ni+2 Biosorption by Raw Chicken Feathers

Hilda E. Reynel-Avila, Guadalupe de la Rosa, Cintia K. Rojas-Mayorga, Irene

Cano-Aguilera, and Adrian Bonilla-Petriciolet

Abstract

Batch experiments were performed to model kinetic and thermodynamic data

for Cd+2 and Ni+2 biosorption by raw chicken feathers (CFs) under different con-ditions. Results indicated that Cd+2 and Ni+2 sorption onto CFs occurred on the

external surface of the biosorbent. Ion removal increased with pH, whereas both

endothermic and exothermic stages where observed depending on temperature.

Our calculated thermodynamic parameters showed that, below the temperature of

30 oC, the metal uptake of Cd+2 and Ni+2 ions may be mainly controlled by a

chemisorption process. However, for temperatures higher than 30oC, it is likely

that sorption of both metals onto CFs is caused by a combination of both physical

and chemical processes, especially for Ni+2 ions. Maximum sorption capacities

were of 0.039 (Cd+2 ) and 0.065 mmol/g (Ni+2) at pH 5 and 30◦C. Using 0.1 M

HCl or CH3COOH as desorbing agents, approximately a 50% recovery for Cd+2

was achieved. The pseudo-second order and the general rate law models best fitthe sorption kinetics data. The equilibrium metal uptake data was best described

by the Sips isotherm.

KEYWORDS: Chicken feathers, metal biosorption, cadmium, nickel, wastewa-

ter treatment



1

1. Introduction

Water pollution with heavy metals is one of the most severe environmentalproblems worldwide (Volesky, 2001; Sarkar, 2002; Wang and Cheng, 2009).

Although heavy metals have many useful applications, their toxicity,

accumulation in the food chain, and persistence may cause serious problems

(Volesky, 2001; Sarkar, 2002). According to the International Agency for

Research on Cancer, cadmium (Cd+2

) and nickel (Ni+2

) are two important

carcinogenic metals, despite the latter is an essential element in low doses

(Sarkar, 2002). These metals are used in several industrial activities including

metal plating, batteries, ceramic, mining, smelting, pigments, alloys, and

welding (Sarkar, 2002; Meena et al., 2005; Padmavathy, 2008; Fan et al.,

2009). A chronic exposure to Cd+2

and Ni+2

may cause adverse effects such as

kidney damage, gastrointestinal injury, lung insufficiency, extreme weakness,endocrine effects, immune system damage, and cancer (Sarkar, 2002; Meena

et al., 2005; Padmavathy, 2008).

Based on the toxicological profile of heavy metals and other pollutants,

several recommendations and regulations have been established worldwide to

improve water quality (Sarkar, 2002). In this context, the removal of heavy

metal ions from industrial wastewaters has become an important and necessary

task to protect the environment and human health. Several methods such as

ion-exchange, filtration, reverse osmosis, precipitation, coagulation, sorption,

solvent extraction and chemical oxidation-reduction have been used for heavy

metal removal from wastewaters (Volesky, 2001; Wang and Chen, 2009).

Unfortunately, some methods show technical limitations, are expensive andineffective when the metal concentrations are in the range of 1 – 100 mg/L

(Wang and Cheng, 2009). The sorption processes offer several advantages for

wastewater treatment and some are even better than other techniques due to its

effectiveness, feasibility, versatility, simplicity of design, easiness of operation

and low cost (Volesky, 2001; Doyurum and Celik, 2006; Demirbas, 2008).

A current tendency in sorption research is the use of agricultural and

industrial by-products (Demirbas, 2008; Bailey et al., 1999; Babel and

Kurniawan, 2003). This approach is competitive since these materials are

usually cheap and abundant and the costs of the removal process can be

significantly reduced as compared to those using synthetic sorbents (Volesky,

2001). Many examples of natural sorbents for wastewater treatment have been

reported in the literature and they include grape bagasse, hazelnut shells, pinus

bark, rice hulls, tea leaves, banana peels, orange, apple residues and maize

leaf, among others (Demirbas, 2008; Bailey et al., 1999; Babel and

Kurniawan, 2003). These materials contain protein, carbohydrates and

phenolic compounds with several functional groups such as carbonyl,

hydroxyl and amino, which are able to bind heavy metals (Doyurum and

Celik, 2006).

Chicken feathers (CFs) are a natural biosorbent produced in huge

quantities by the poultry industry (Banat and Al-Asheh, 2000; Barone and

1Reynel-Avila et al.: Cd and Ni biosorption modeling on chicken feathers

Published by The Berkeley Electronic Press, 2011



2

Schmidt, 2006). CFs fibers are semi-crystalline and structured by a nano-

porous network with pores of size in the range of 0.5 to 0.10 µm (Kar and

Misra, 2004). This biomass is predominantly constituted by the proteinkeratin, which can be assembled into α-helix (41%), β-sheet (38%) and

disordered structures (21%) (Barone and Schmidt, 2006). FTIR analyses

indicate that CFs contain carboxylic groups that are capable of binding metal

ions effectively (Kar and Misra, 2004). Previous studies have shown the

potential of CFs for the sorption of several metals from aqueous media (Kar

and Misra, 2004; Al-Asheh et al., 2002; Sayed et al., 2005; De la Rosa et al.,

2008). For example, Kar and Misra (2004) tested CFs to remove different

metal ions in aqueous solutions including Ni+2

and Cd+2

. Ni+2

uptake was

studied at batch conditions and pH 5 while Cd+2

sorption studies were

performed in a solution containing five metals. On the other hand, Al-Asheh et

al. (2002), studied the uptake of Ni+2

, Cu+2

and Zn+2

ions in single and binaryaqueous solutions at batch conditions and 25 °C. However, to best of our

knowledge, a comprehensive evaluation and modeling of the effect of

temperature and pH on the CFs performance for Cd+2

and Ni+2

removal has

not been reported. The evaluation and comparison of the sorption performance

is necessary in order to properly identify the relative strengths of CFs for

wastewater treatment.

In this paper, we report new experimental data for the sorption

performance of CFs in the removal of Cd+2

and Ni+2

ions from aqueous

solutions. The sorption process was investigated via batch experiments. The

effect of pH, contact time and temperature were explored. Metal desorption

conditions of saturated CFs were also studied. Our kinetic and equilibriumsorption data were fitted to several theoretical and empirical sorption models,

and the most suitable models were identified using statistical criterions.

Thermodynamic parameters of the Cd+2

and Ni+2

sorption process were also

calculated.

2. Materials and methods

2.1 Sorbent description

Raw CFs were obtained from a poultry processing plant. CFs were washed

with detergent and rinsed several times with deionized water. Subsequently,

they were washed with aqueous ethanol (20% v/v) in order to remove organic

residues, and then rinsed with deionized water. CFs were dried at 40 °C and

the barbs were carefully cut into 0.5 cm length discarding the rachis. This

biomass was used for the sorption experiments.

2.2 Kinetic and equilibrium sorption studies

Batch sorption experiments were performed using 0.06 g of dried biomass and

15 mL of either Cd+2

or Ni+2

at concentrations varying from 0.09 to 1.78, and

2



3

from 0.17 to 3.41 mmol/L, respectively. These concentration ranges were used

to achieve the saturation of the sorbent and to determine the maximum

sorption capacity of CFs. Metal solutions were prepared using deionized waterand nitrate salts, and all the reagents used in the study were of analytical

grade.

In all sorption experiments, sorbent and metal solutions at the different

concentrations were mixed, placed on a temperature-controlled shaker and

allowed to interact. First, kinetic experiments were performed to establish the

equilibrium time and to study the rate of metal uptake. In these experiments,

three concentrations of Cd+2

(0.44, 0.71, 0.89 mmol/L) and Ni+2

(0.85, 1.36

and 1.7 mmol/L) were used and samples were taken at different times

(between 0.5 to 24 h). On the other hand, Cd+2

and Ni+2

isotherms data were

measured at the equilibrium time. Kinetic and isotherm tests were performed

at pHs of 2, 3, 4, and 5, and temperatures of 25, 30, and 40o

C, in order todetermine the sorption capacity of CFs and the effect of these parameters on

Cd+2

and Ni+2

uptake. In all experiments, the initial pH of each metal solution

was adjusted to the required pH value by using diluted acid nitric. In addition,

before the sorption experiments, biomass was equilibrated at the desired pH by

using diluted nitric acid solutions. For metal quantification, samples were

filtered and the solution was then analyzed using a Perkin Elmer AAnalist 100

atomic absorption spectrophotometer equipped with an air-acetylene burner.

The amount of metal ion sorbed qt (mmol/g) at time t (h) was calculated using

equation (1)

W

V C C q t

t

)( 0 −= (1)

where C 0 is the initial metal concentration and C t is the residual metal

concentration at time t given both in mmol/L, V is the volume of metal

solution in L and W is the sorbent amount in g. All experiments were

conducted in triplicate, and the average results are reported in this study.

Reproducibility of the experiments was in general within 5%.

2.3 Desorption studies

In order to assess the possibility of recycling the spent sorbent, 0.1 M HCl and

0.1 M CH3COOH were selected as Cd+2

and Ni+2

stripping agents. The

literature indicates that these acids are effective for metal desorption in several

sorbents (Srivastava et al., 2008). These concentrations were selected since

they do not produced physical damage to the biomass. The metal-loaded

sorbent with the maximum sorption capacity was chosen for these

experiments. Briefly, the metal-loaded sorbent was separated and rinsed with

deionized water to remove any unsorbed metal. Metal desorption experiments





4

were carried out using 0.06 g of metal-loaded sorbent, previously dried (in

order to control the biomass weight), and 15 mL of the acid solution at 30 °C,

which was identified as the temperature for obtaining the maximum metalsorption in the present study. The saturated CFs and the desorbing solution

were left in contact until they reached new equilibrium (i.e., 24 h of contact

time). The final metal ion concentration in the aqueous phase was employed

for the calculation of the desorption ratio by a mass balance. All the

experiments were carried out in triplicate and the mean values ± standard

deviations are reported. The metal desorption ratio (DR, %) was calculated

using equation (2)

⋅=

sorbedionsmetalof amount

desorbedions metalof amount100 DR (2)

2.4 Sorption data modelling

The modeling of sorption isotherms and kinetics provides valuable

physicochemical information for the design, optimization and control of

sorption processes as a unit operation. Several sorption equilibrium and kinetic

models with two or more parameters are available in the literature and have

been used for the data analysis of heavy metal removal from water using

natural and synthetic sorbents (Ho and McKay, 1998; Febrianto et al., 2008;

Liu and Liu, 2008). In this study, the equilibrium sorption data were fitted to

the Langmuir and Freundlich (two-parameter isotherm models) and theRedlich–Peterson and Sips isotherms (three-parameter models). With respect

to kinetic modeling, the pseudo first order, pseudo second order, Elovich and

General Rate Law models were considered. Most of these kinetic models have

two adjustable parameters. The exception is the General rate law model which

has three parameters. Table 1 provides the description and characteristics of

the kinetic and isotherm equations used in this study. For interested readers,

the theoretical basis, explanation, and derivation of applied models can be

found in the review reported by Liu and Liu (2008).

The parameters of kinetic and isotherm models have been determined

by minimizing the relative difference between the experimental and theoretical

data of sorption capacities (qt or qe) using the simulated annealing stochastic

optimization method (Bonilla-Petriciolet et al., 2005). Specifically, the

objective function used for data fitting in the non-linear regression procedure

is given by equation (3)

∑=

−=

ndat

i i

calcii

objq

qqF

1

2

exp,

,exp,(3)

4



5

where qi,exp and qi,calc are the experimental and predicted metal uptakes and

ndat is the overall number of experimental data, respectively. Note that two-

parameter kinetic and isotherms are the most commonly used models byseveral researchers because of their simplicity and possibility of linearization.

Unfortunately, transformation of non-linear sorption models to linear forms

usually results in parameter estimation errors and uncertainties (Kumar and

Sivanesan, 2005). In addition, the adjustable parameters of multi-parameter

sorption models cannot be estimated by linear regression. Therefore, the

adjustable parameters of all kinetic and sorption models were calculated using

a non-linear regression analysis using a stochastic optimization method since

this approach is more reliable and offers the advantage that the error

distribution is not altered as in the case of linear data fitting technique (Kumar

and Sivanesan, 2005).

Table 1. Kinetic and isotherm equations used for data modeling of Cd +2

and

Ni+2

sorption on chicken feathers in aqueous solutions.

Model Equation Description

Pseudo-First order )1( 1t k

et eqq−−=

qe is the theoretical metal uptake

(mmol/g) and k 1 is the rate constant

(h-1

).

Pseudo-Second

order t qk

t k qq

e

e

t

2

2

2

1+=

qe is the theoretical metal uptake

(mmol/g) and k 2 is the rate constant

(g/mmol h).

Elovich t k qt ln1ln1 3

+

=

α

α

α

α is the desorption constant (g/mmol)

and k 3 is the initial sorption rate(mmol/g h).

General Rate Law

−−= −n

et t k nqq 1

1

4 )))(1((1 qe is the theoretical metal uptake

(mmol/g), n is the sorption rate order,

and k 4 is the rate constant (h-1

).

Langmuir e

em

ebC

bC qq

+=

1

qm is the maximum amount of

sorption (mmol/g) and b (L/mmol) is

the sorption equilibrium constant

which is related to the affinity

between the sorbent and sorbate.

Freundlich ne f e C K q1

=

K f (mmol

1-1/n

L

1/n

g

-1

) is an indicatorof the relative sorption capacity and n

is an affinity constant which gives an

idea of the grade of heterogeneity of

the sites.

Redlich-Peterson g

e

e

e BC

AC q

+=

1

A, B and g are the three isotherm

empirical parameters.

Sipsn

es

n

esse

C a

C aqq

+=

1

qs is the monolayer sorption capacity

(mmol/g), as and n are the Sips

parameters.





6

Several statistical criterions were considered for performancecomparison of kinetic and isotherm equations. Previous studies reported the

removal of Pb using CFs (De la Rosa et al., 2008), were the coefficient of

determination ( R2), the objective function value (F obj), and the mean absolute

percentage deviation ( E ) between calculated and experimental metal uptakes

were the criterions used to measure the goodness of the fittings, and this is

given in equation (4) where

∑=

−=

ndat

i i

calcii

q

qq

ndat E

1 exp,

,exp,100 (4)

These statistics were accompanied by a study of the behavior of the relative

residuals in equation (5)

exp,

,exp,

i

calcii

iq

qqe

−=

(5)

3. Results and discussion

3.1 Sorption kinetics and isotherms

Figures 1 – 3 show the kinetics of Cd+2

and Ni+2

sorption on chicken feathers

at different pH values (Fig. 1), temperature (Fig. 2), and initial metal

concentration (Fig. 3). It is clear that pH strongly influences the Cd+2

and Ni+2

uptakes and the greatest sorption occurred at high pH as expected (Fig. 1).

Specifically, a significant increase in Cd+2

and Ni+2

uptakes was observed at

pH 5. However, it appears that Cd+2

sorption is more sensitive to pH changes.

The increase in metal sorption capacity as the pH increases can be explained

by changes in the chemical nature of the metal (e.g., charge density, solubilityand degree of hydrolysis) and in the sorbent surface properties, among other

factors (Al-Asheh and Duvnajk, 1997; Meena et al., 2005). At pH below 3, the

metal sorption performance of CFs is significantly affected given that H+

ions

compete with Cd+2

and Ni+2

for the active sites in CF (De la Rosa et al., 2008;

Farinella et al., 2007). It is important to note that the pH value in all

experiments was measured after equilibrium because metal solutions were not

buffered. The final pH in metal solutions after sorption process ranged from

1.9 to 5.4 for both metals and there was no physical evidence of metal

6



precipitation. Further

are the only ionic spec

Figure 1. Effect of p

conducted at a T o

Initial Cd+2

and

respectively. Data r

Figure 2 show

Ni+2

sorption by CF.

°C caused an increase

ore, according to speciation diagrams, Cd

ies present in solution at pH < 6.

H on Cd+2

and Ni+2

sorption by CFs. Experi

30 °C and pH values of (●) 2, (∆) 3, (■) 4, a

i+2

concentrations were of 0.89 and 0.85 m

epresents mean of three replicates. Error bar

standard deviation.

s the effect of temperature on the kinetics

or both metals, the rise in temperature from

in the metal uptake, indicating an endother

7

+2and Ni

+2

ents were

nd (◊) 5.

ol/L,

indicate

f Cd+2

and

25 °C to 30

ic sorption





8

process at this temperature range. This increase may be attributed to the

increase in the number of active surface sites available for sorption on the

sorbent caused by the stretching of the feather fibers and the decrease in thethickness of the boundary layer which surrounds the sorbent reducing the mass

transfer resistance (Banat and Al-Asheh, 2000; Meena et al., 2005; De la Rosa

et al., 2008). However, from 30 °C to 40 °C both, Cd+2

and Ni+2

uptake

decreased. At this temperature range, it appears that metal sorption is

exothermic.

As indicated by De la Rosa et al. (2008), this behavior could be caused

by an increased mobility of metals in solution that affects the metal binding to

active sites of CFs. It is important to note that this dual effect of temperature

on sorption performance has been also reported for the removal of Pb+2

ions

using CFs (De la Rosa et al., 2008). This unusual behavior cannot be attributed

to experimental errors since the decrease and increase in the metal uptake isgreater than the magnitude of the uncertainty of sorption experiments (see

standard deviations reported in Figure 2).

Finally, Figure 3 shows the effect of contact time and initial metal

concentration on the sorption kinetics of Cd+2

and Ni+2

using CF at 30oC and

pH 5, which are the conditions for maximum metal removal determined in the

present investigation. As expected, the metal sorption rates show that the

sorbed amount increased with an increase in the metal concentration and

contact time. In particular, the initial metal concentration provides the

necessary force to overcome the resistance to the mass transfer, which allows

metals to pass from the solution to the particle surface and favors the

interaction between metal and sorbent enhancing the metal uptake (Al-Ashehand Duvnjak, 1997; De la Rosa et al., 2008). Thus, there is an increase in the

mass transfer driving force caused by the increase in the Cd+2

and Ni+2

contents. For both metals, kinetic studies confirmed that Cd+2

and Ni+2

sorption onto CFs is quite rapid indicating that most of the sorption process

occurs on the external surface of the sorbent where the binding sites of CFs

that might be responsible for heavy metal removal are more accessible (Kar

and Misra, 2004). Typically, 30 – 90% of the metal removal occurs within the

first hours of contact time and it is evident that saturation is reached after 24 h.

This trend is similar to that obtained by other studies including our results

reported for Pb+2

sorption using CFs (Kar and Misra, 2004; De la Rosa et al.,

2008).In summary, kinetics results indicated that the Cd

+2and Ni

+2sorption

on CFs is described by the following three stages: a) a very rapid external

surface sorption, b) a gradual increase in sorption due to intraparticle

diffusion, and c) a last stage where metal sorption becomes asymptotic caused

by equilibrium between metal ions and sorbent. The data presented herein

suggest that particle diffusion is not the rate-controlling step at the tested

conditions.

8



Figure 2. Effect of Treacted with a) 0.89

temperatures of: (▲)

n Cd+2

and Ni+2

sorption by CFs. Sorbent (mmol/L Cd

+2; and b) 0.85 mmol/L Ni

+2a

5, (●) 30, and (□) 40 °C.

9

0.06 g) waspH 5 and





Figure 3. Effect of iCFs. Experiments wer

(♦) 0.44, (■) 0.71, and

() 1.70 for Ni+2

. Dat

standard deviation.

The results fo

Ni+2

sorption isother

correspond to a favor

uptake ranged from

itial metal concentration on Cd+2

and Ni+2

run at 30 °C and pH 5 at initial metal conc

(▲) 0.89 mmol/L for Cd+2

, and (◊) 0.85, (

represents mean of three replicates. Error

the isotherm studies are shown in Figure

s can be classified as Langmuir-type isothe

ble sorption process. In general, the equili

.0005 to 0.039 mmol/g for Cd+2

and fro

10

sorption byntrations of

) 1.36, and

ars indicate

. Cd+2

and

m and they

rium metal

0.0005 to

10



0.065 mmol/g for Ni

present research wer

respectively, at the co

Figure 4. Isotherms

and b) Effect of

Temperature. pHs: (

The maximum

this study are higher

sorbents. For exampl

reported for exhausted

et al., 1999), rice hu

Moringa oleifera see

copra meal: 0.016 m

higher than clinoptilol

niger : 0.03 mmol/g [1

and appears to be co

0.016 mmol/g (Sharm

+2. The maximum sorption capacities obta

e of 0.039 and 0.065 mmol/g, for Cd+2

ditions of pH 5 and 30 °C.

or Cd+2

and Ni+2

sorption by CFs. Cd+2

: a) E

emperature, Ni+2

: c) Effect of pH and d) Ef

●) 2, (∆) 3, (■) 4, and (◊) 5. Temperatures: (

30, and (□) 40 °C.

sorption capacities of Cd+2

and Ni+2

ions

than those reported for other synthetic

, the Cd+2

metal uptakes of CFs are highe

coffee: 0.013 mmol/g, waste tea: 0.015 mm

k ash: 0.026 mmol/g (Srivastava et al., 20

s: 0.009 mmol/g (Sharma et al., 2007),

ol/g [27]. In the case of Ni+2

, the removal

ite: 0.008 mmol/g (Ofojama and Ho, 2007),

], chitosan: 0.04 mmol/g (Babel and Kurnia

petitive with respect to shelled Moringa ole

et al., 2007), petiolar felt-sheath of palm:

11

ined in the

and Ni+2

,

ffect of pH

ect of

) 25, (○)

obtained in

and natural

than those

l/g (Bailey

8), shelled

nd coconut

with CFs is

Aspergillus

wan, 2003),

ifera seeds:

.12 mmol/g





12

(Iqbal et al., 2002), and rice husk: 0.094 mmol/g (Krishnani et al., 2008). Even

when a proper comparison of sorption capacities is not completely possible

due to the broad diversity of experimental conditions including sorbentparticle size, pH, temperature, and chemical modifications, these data serve as

reference. According to our results, it can be concluded that raw CFs display

acceptable metal uptakes for Cd+2

and Ni+2

ions in aqueous solutions.

3.2 Thermodynamic parameters

Based on the results of the equilibrium studies, we calculated the

thermodynamic parameters for Cd+2

and Ni+2

sorption process. The enthalpy

change ( ∆ H 0) and entropy change ( ∆S

0) were determined from the slope and

intercept of the plot ln K eq versus 1/ T , or better known as van’t Hoff plot,using equation (6):

R

S

RT

H K eq

00

ln∆

+∆−

= (6)

where K eq = C se / C e is the distribution coefficient which was calculated from

experimental data, C se is the concentration of sorbed solute on sorbent at

equilibrium in mmol/L, T is temperature in Kelvin and R is universal gas

constant (8.314×10−3

kJ/mol K).

Thermodynamic parameters were calculated using Eq. (6) and results

are reported in Table 2 for both metals. The positive value in enthalpy change

from 25 to 30 °C for both metals suggests the endothermic nature of theprocess and possible strong bonding between the metal and sorbent (Uslu and

Tanyol, 2006). Also, for this temperature increment, a positive entropy change

value reflects the affinity of the sorbent to Cd+2

and Ni+2

ions since there may

be an increase in randomness at the sorbent/solution interface during the

process (Uslu and Tanyol, 2006; De la Rosa et al., 2008). Table 2 shows that

enthalpy and entropy changes of Ni+2

uptakes are higher than those obtained

for Cd+2

suggesting a more strong metal-sorbent interaction. However, at

temperatures between 30 to 40 °C, the negative enthalpy values indicate that

sorption process is exothermic for both metal ions. This suggests that there is a

weak bonding between the sorbate and sorbent surface at these operating

conditions (Febrianto et al., 2008). Also, negative entropy changes correspond

to a decrease in the degree of freedom of the sorbed metal, which could be

attributed to the ions displaying a higher level of order on the solid phase (i.e.,

biomass) compared to that in the aqueous phase, this being a result of the loss

of mobility when the ions are attached to the biomass surface (Khazali et al.,

2007). In conclusion, calculated thermodynamic parameters are in agreement

with the experimental data.

Generally, physical sorption involves an enthalpy change from 2 to 21

kJ/mol, while enthalpy change of chemisorption falls in the range of 80 – 200

kJ/mol (Liu and Liu, 2008). In addition, as indicated by other authors (e.g.,

12



13

Febrianto et al, 2008) if a physical sorption process is involved, a decrease of

this process with an increase in temperature should be expected. When

chemisorption is involved, it is usually favored with rises in temperature.According to these observations and our calculated thermodynamic

parameters, the results showed that, below the temperature of 30oC, the metal

uptake of Cd+2

and Ni+2

ions may be mainly controlled by a chemisorption

process. However, for temperatures higher than 30oC, it is likely that sorption

of both metals onto CFs is caused by a combination of both physical and

chemical processes, especially for Ni+2

ions. According to Kar and Misra

(2004), the physisorption process may occur by the trapping of metal ions in

the nano-porous network of CFs while chemisorption is believed to occur at

the carboxylic binding sites of CFs. These thermodynamic trends have been

also observed for Pb+2

removal from aqueous solutions using CFs (De la Rosa

et al., 2008).

Table 2. Thermodynamic parameters for Cd +2

and Ni+2

sorption in aqueous

solutions using chicken feathers

T,oC Metal ion ∆H

0, kJ/mol ∆S

0, kJ/mol K

25 – 30 Cd+2

100.86 0.32

Ni+2

127.92 0.40

30 – 40 Cd+2 -18.44 -0.07

Ni+2

-61.19 -0.22

3.3 Data modeling

Results of kinetic and isotherm data modeling are reported in Figures 5 and 6

and Table 3. For both metals, the statistical analysis indicated that the pseudo-

second order and the General Rate Law models describe the rate of metal

uptakes better than that of pseudo first-order and Elovich kinetic equations

(see Figure 5 and Table 3). According to the literature, the pseudo-second

order model assumes that two surface sites could be occupied by one sorbate

ion (Onyango et al., 2003). Therefore, it would be expected that this model is

applicable and suitable for modeling the sorption of divalent metal ions as

Cd+2

and Ni+2

. On the other hand, the general rate law equation considers that

sorption reaction on the surface of the sorbent is the rate-controlling step. This

model assumes that sorption rate varies with the effective concentration of

binding sites and it is unnecessary to link the sorption kinetics to the possible

sorption mechanism because sorption process is extremely complex and

various mechanisms would be involved (Liu and Shen, 2008). This kinetic

equation establishes that it is possible the existence of mixed-order reactions

with a fractional order for their rate. Liu and Shen (2008) suggested that it is

more convenient to determine the order of sorption process using the general

rate law equation instead of using a preset-order kinetic equation. Overall,

these two models showed a mean error from 0.51 to 7.52% and high values of





14

the correlation coefficients ( R2

> 0.88) in the data modeling. Model parameters

of these kinetic expressions are given in Tables 4 and 5 for all the tested

conditions explored in the present study.

Table 3. Results of data modeling using kinetic and isotherm models for Cd +2

and Ni+2

sorption on chicken feathers from aqueous solutions.

Statistical analysis

Metal Model R2

E, % Fobj

Cd+2

Pseudo-first order 0.68 - 0.98 3.64 - 11.94 1.47×10-2

– 1.65×10-1

Pseudo-second order 0.88 - 0.99 1.18 - 6.13 1.73×10-3

– 6.56×10-2

Elovich 0.77 - 0.98 2.03 - 12.21 5.67×10-3

– 1.48×10-1

General rate law 0.91 - 1.00 0.61 - 7.52 4.60×10-4

– 9.15×10-2

Langmuir 0.13 - 0.98 5.96 - 39.55 8.51×10-2

- 3.19

Freundlich 0.20 - 0.95 6.94 - 38.90 1.03×10-1

– 3.13

Redlich-Peterson 0.13 - 0.96 5.96 - 38.91 8.51×10-2

- 3.13

Sips 0.96 - 0.99 4.70 - 6.94 4.64×10-2

- 0.11

Ni+2

Pseudo-first order 0.71 - 0.98 2.14 - 8.51 4.87×10-3

– 7.00×10-2

Pseudo-second order 0.90 - 0.99 0.65 - 6.62 6.19×10-4

– 7.09×10-2

Elovich 0.73 - 0.97 2.33 - 10.65 5.91×10-3

– 1.23×10-1

General rate law 0.94 - 1.00 0.51 - 2.61 2.79×10-4 – 7.00×10-3

Langmuir 0.72 - 0.97 5.70 - 26.66 7.29×10-2

- 1.45

Freundlich 0.68 - 0.92 9.29 - 27.54 1.70×10-1

- 1.47

Redlich-Peterson 0.72 - 0.97 5.70 - 26.67 7.29×10-2

- 1.45

Sips 0.95 - 0.98 5.45 - 13.21 6.82×10-2

- 0.54

Table 3 and Figure 6 display the results for the isotherm data

modeling. Figure 6 shows that our data was better correlated to the Langmuir

and Redlich-Peterson models as compared to the Freundlich isotherm.

However, Langmuir, Freundlich and Redlich-Peterson isotherms were

incapable of fitting satisfactorily the metal uptakes at pH 2, 3 and 25 °C for

Cd+2

and at pH 2 and 25 °C for Ni+2

ions. It is clear that Sips isotherm

generally gave better fits than the rest of the isotherm equations used for

modeling both Cd+2

and Ni+2

sorption data. Sips isotherm is an empirical

model that incorporates the features of both Langmuir and Freundlich

isotherms (Sips, 1948). At low concentrations, the Sips model reduces to the

Freundlich isotherm while a higher concentrations it may predict a monolayer

14



15

Table 4. Parameters of the pseudo-second order model for Cd +2

and Ni+2

sorption kinetics using raw chicken feathers.

Metal C0, mmol/L T, °C pH qe mmol/g k2,g/mmol h R

2

Fobj Cd+2

0.44 30 2 6.10×10-3

277.67 0.97 1.45×10-2

3 1.26×10-2

47.28 0.98 2.25×10-2

4 1.47×10-2

49.58 0.99 2.09×10-2

5 1.70×10-2

112.98 0.96 1.63×10-2

25 5 1.10×10-2

146.65 0.99 5.36×10-3

40 5 1.57×10-2

37.80 0.96 5.06×10-2

0.71 30 2 6.71×10-3

259.70 0.88 6.56×10-2

3 1.93×10-2

152.78 0.93 1.40×10-2

4 2.24×10-2

64.91 0.97 1.45×10-2

5 2.53×10-2

106.71 0.96 9.52×10-3

25 5 1.87×10-2

107.68 0.98 9.40×10-3

40 5 2.19×10-2

68.63 0.94 3.37×10-2

0.89 30 2 6.97×10

-3120.37 0.98 1.48×10

-2

3 2.39×10-2

149.25 0.99 1.73×10-3

4 2.96×10-2

36.15 0.94 5.64×10-2

5 3.04×10-2

128.45 0.96 5.05×10-3

25 5 2.50×10-2

65.20 0.98 8.15×10-3

40 5 2.71×10-2

82.79 0.96 1.35×10-2

Ni+2

0.85 30 2 5.44×10-3

787.76 0.90 9.77×10-3

3 7.82×10-3

283.16 0.97 9.78×10-3

4 1.50×10-2

75.39 0.97 2.49×10-2

5 1.98×10-2

52.02 0.99 8.18×10-3

25 5 1.55×10-2

37.14 0.97 7.09×10-2

40 5 1.41×10-2

61.14 0.99 9.86×10-3

1.36 30 2 8.70×10-3

287.36 0.98 6.37×10-2

3 1.27×10-2

190.41 0.98 4.51×10-3

4 2.68×10-2

328.30 0.96 1.27×10-3

5 3.97×10-2

57.50 0.96 1.26×10-2

25 5 2.94×10-2

66.39 0.98 5.11×10-3

40 5 2.53×10-2

118.30 0.98 4.72×10-3

1.70 30 2 1.07×10-2

161.06 0.98 7.54×10-3

3 1.63×10-2

221.90 0.96 7.82×10-3

4 3.61×10-2

115.55 0.97 4.12×10-3

5 4.87×10-2

72.18 0.97 5.55×10-3

25 5 4.09×10-2 54.99 0.98 5.28×10-3 40 5 3.84×10

-2137.35 0.99 6.19×10

-4





16

Table 5. Parameters of the general rate law model for Cd +2

and Ni+2

sorption

kinetics in aqueous solution using raw chicken feathers.

Metal C0, mmol/L T, °C pH qe, mmol/g k4, h

-1

n R

2

Fobj Cd+2

0.44 30 2 7.39×10-3

2.97 4.00 0.98 6.43×10-3

3 1.48×10-2

1.23 4.00 0.97 3.44×10-2

4 1.59×10-2

1.57 3.27 1.00 3.40×10-3

5 2.06×10-2

3.43 4.00 0.99 3.89×10-3

25 5 1.14×10-2

3.00 2.65 0.99 2.16×10-3

40 5 1.85×10-2

1.21 4.00 0.96 9.15×10-2

0.71 30 2 8.07×10-3

3.21 4.00 0.91 4.17×10-2

3 2.27×10-2

6.08 4.00 0.99 2.60×10-3

4 2.72×10-2

2.49 4.00 0.99 6.26×10-3

5 2.55×10-2

4.49 2.32 0.97 6.58×10-3

25 5 2.08×10-2

3.58 3.31 0.97 1.02×10-2

40 5 2.41×10-2

2.72 3.23 0.92 4.54×10-2

0.89 30 2 7.77×10

-31.66 3.38 0.98 1.31×10

-2

3 2.42×10-2

5.68 2.35 0.99 1.47×10-3

4 2.77×10-2

2.82 2.11 0.99 4.70×10-3

5 3.44×10-2

9.25 3.79 1.00 4.60×10-4

25 5 3.02×10-2

2.79 3.92 0.99 3.72×10-3

40 5 3.23×10-2

4.28 3.98 0.96 9.12×10-3

Ni+2

0.85 30 2 6.06×10-3

10.31 3.65 0.94 6.11×10-3

3 7.97×10-3

3.85 2.48 0.97 7.00×10-3

4 1.49×10-2

2.50 2.47 0.99 3.31×10-3

5 2.42×10-2

1.79 4.00 0.99 5.48×10-3

25 5 1.60×10-2

1.48 3.09 0.99 5.19×10-3

40 5 1.54×10-2

1.74 3.27 1.00 2.52×10-3

1.36 30 2 9.54×10-3

4.53 3.20 0.97 5.62×10-3

3 1.39×10-2

4.27 3.20 0.99 1.87×10-3

4 2.80×10-2

25.00 3.09 0.99 2.79×10-4

5 3.83×10-2

4.30 1.92 1.00 3.54×10-4

25 5 3.46×10-2

3.45 3.78 1.00 1.04×10-3

40 5 2.60×10-2

4.96 2.50 0.98 3.43×10-3

1.70 30 2 1.20×10-2

3.03 3.26 0.98 5.39×10-3

3 1.83×10-2

8.16 3.69 0.98 3.83×10-3

4 3.75×10-2

7.38 2.72 0.97 4.00×10-3

5 4.76×10-2

5.48 1.89 0.99 1.14×10-3

25 5 4.09×10-2 3.96 2.29 0.99 1.72×10-3 40 5 3.93×10

-28.79 2.53 1.00 3.12×10

-4

16



Figure 5. Experim

chicken feathers in aq

Pseudo-seco

sorption capacity char

n in the Sips equation

equation. In general, t

isotherms of both Cd+

n was considered as

were imposed for itsempirical and n has n

sorption process is a

binding sites of the s

due to geometric fact

there are external an

capacity. As a conse

challenging at some o

ntal and calculated (□) Cd+2

and (●) Ni+2

up

ueous solutions. Kinetic model: a) Pseudo-fi

nd order, c) Elovich, and d) General Rate La

cteristic of the Langmuir isotherm. When th

is equals to 1.0, this model is reduced to th

e exponent value n was found to be greater2

and Ni+2

ions (see Table 6). It is important

an empirical adjustable parameter (i.e. no

values during data fitting) given that thisclearly defined physical meaning. As state

fected by several factors and is complex

rbent are not all identical; there is sorptio

rs and to the affinity of sorbate and sorbe

internal mass transfer factors that limit t

uence, the modeling of the sorption proc

erating conditions.

17

takes by

st order, b)

.

e parameter

e Langmuir

than 1.0 for

to note that

restrictions

isotherm isd early, the

ecause the

resistance

nt. Besides,

he sorption

ss may be





Figure 6. Experim

chicken feathers in

Freu

Table 6. Parameters

aqueous solution usin

Metal T, °C pH

Cd+2

30 2

3

4

5 125 5

40 5

Ni+2

30 2 1

3

4

5 1

25 5

40 5

ntal and calculated (□) Cd2+

and (●) Ni2+

up

aqueous solutions. Isotherm model: a) Lang

dlich, c) Redlich-Peterson, and d) Sips.

f the Sips isotherm model for Cd +2

and Ni+2

raw chicken feathers.

s, mmol/g as n R2

.02×10-3

265.47 3.26 0.96

.96×10-2

5.30 1.97 0.99

.07×10-2

1.25 1.20 0.97

.39×10-1

0.32 0.76 0.98.30×10

-23.46 2.11 0.99

.85×10-2

0.96 1.11 0.97

.31×10-2

1.37 1.96 0.98

.77×10-2

0.38 1.07 0.97

.25×10-2

0.32 1.54 0.97

.17×10-1

0.32 1.47 0.98

.48×10-2

0.34 1.72 0.96

.71×10-2

0.33 1.57 0.95

18

takes by

muir, b)

sorption in

Fobj

.64×10-2

6.49×10-2

1.07×10-1

8.91×10-2

.38×10

-2

.30×10-2

6.85×10-2

6.82×10-2

.05×10-1

1.28×10-1

5.36×10-1

3.48×10-1

18



19

In the absence of a theoretical model that could account for the

chemical heterogeneity of the sorbent and the simultaneous prevalence of

different sorption mechanisms, it is reasonable to use the Sips model withoutany mathematical restriction for its parameters during the data fitting

procedure. In general, the performance of the isotherm equations for the metal

sorption data modeling of CFs is given by: Sips > Redlich-Peterson ≅

Langmuir > Freundlich.

3.4 Desorption studies

Desorption studies indicated that the maximum desorption was achieved with

0.1M acetic acid for Cd+2

with a DR of 51.7 ± 0.9%, which is slightly higher

than that obtained for HCl (44.7 ± 1.2%). For Ni+2

desorption, the DR was

around 14.6 ± 1.8% and 12.2 ± 3.1% for both desorbing agents, respectively.In literature, a number of desorbing agents has been tested for metal recovery

and sorbent regeneration and they include both inorganic and organic agents

such as HCl, HNO3, H2SO4, CH3COOH, EDTA, and NaOH. The performance

of these desorbing agents depends on the sorbent type, the concentration of

sorbed metals, and operating conditions (e.g., concentration of desorbing

agent, temperature, and sorbent dosage). Usually, the metal recovery

efficiencies reported in literature range from 5 to 70%, where the best

desorbing ratios are obtained especially for Cd+2

. Therefore, our results

indicate that both HCl and CH3COOH solutions at low concentration are

suitable for Cd+2

desorption but they are ineffective for desorbing Ni+2

ions

from CFs. However, other stripping agents should be explored in order todetermine if higher recoveries are possible. It appears that there may be a

strong Ni+2

–CF interaction.

Thermodynamic parameters indicate that chemisorption process is

more predominant for Ni+2

ions and, under these conditions, low DR would be

expected. Usually, the metal sorption process is not completely reversible

given that the metal ions may become entrapped in the nano-porous network

of the sorbent, some of the metal ions may be incorporated onto the biomass

or because of the presence of a re-sorption process. The DR obtained for Cd+2

could mean that external surface sorption was predominant on CFs and

suggests that it is possible the sorbent regeneration, at least, for this metal.

4. Conclusions

The capacity of CFs for sorbing Cd+2

and Ni+2

ions was considerably

dependent on pH and temperature. The sorption capacity for both metals

exhibited a maximum at pH of 5, and temperature of 30 °C. Thermodynamic

calculations suggest that Cd+2 and Ni+2 removal by chicken feathers may be

controlled by a chemisorption process, or by a combination of both physical

and chemical processes depending on temperature. The pseudo-second order

and general rate law models were suitable for modeling the Cd+2

and Ni+2





20

uptakes by CFs, whereas equilibrium sorption data were properly adjusted by

the Sips model. The desorption process of Cd+2

is feasible using CH3COOH

and HCl at low concentration. However, these stripping agents were notsuitable for Ni+2

desorption. It is convenient to study other desorption

conditions to improve the desorption ratio of both metals especially for Ni+2

.

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