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ADSORPTIVE REMOVAL AND RECOVERY OF AlUM INIUM (II I ), IRON
(II ) AND CHROMIUM (VI) ONTO A LOW COST FUNCTIONALI ZED
Phragmities karka WASTE
A Dissertation Submitted to the Central Department of Chemistry
Tribhuvan University, Kirtipur
Kathmandu, Nepal
In Partial Fulfillment of Requirements for the
Master's Degree in Chemistry
20010-2011
By
SHUKRA RAJ REGMI
Symbol No: 13164
Reg. No: 6-2-325-156-2005
October 2013
Central Department of Chemistry
Institute of Science and Technology
Tribhuvan University
Kirtipur, Kathmandu
Nepal
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Tribhuvan University
Institute of Science & Technology
Central Department of Chemistry
Kirtipur, Kathmandu
The dissertation entitled
ADSORPTIVE REMOVAL AND RECOVERY OF AlUMINIUM (III), IRON (II) AND
CHROMIUM (VI) ONTO A LOW COST FUNCTIONALIZED Phragmities karka WASTE
Submitted by
SHUKRA RAJ REGMI
has been accepted as a partial fulfillment of the requirements for the Master's
Degree in Chemistry
...........................................
Prof. Dr. Kedar Nath Ghimire
Head of the Department
Central Department of Chemistry
......................... .......................
External Examiner Internal Examiner
Dr. Prem Ratna Sthapit Prof. Dr. Megh Raj PokhrelM.Sc., Ph.D (U.K) M.Sc.,Ph.D.,(German)
Former Deputy Director General Tribhuwan University
Nepal Govt., Dept. of Medicinal plant
..
SupervisorProf. Dr. Kedar Nath Ghimire
Central Department of ChemistryTribhuvan University
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FOREWORD
The dissertation entitled ADSORPTION BEHAVIOUR OF AlUMINIUM(III),IRON(II)
& CHROMIUM(VI) ONTO FUNCTIONALIZED Phragmities karka ( NALKAT )STEM submitted by Mr. Shukraraj Regmi for the M. Sc. Degree in Chemistry has been
carried out under my supervision in the academic year 2010-2012. During the research
period he had performed his work sincerely & satisfactorily.
............................................
Supervisor
Dr. Kedar Nath Ghimire
Professor of ChemistryCentral Department of Chemistry
Tribhuvan University
Kathmandu,Nepal
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ACKNOWLEDGMENT
It is a matter of great pleasure to express my sincere gratitude to my research
supervisor Prof. Dr. Kedar Nath Ghimire, Head of Central Department of Chemistry,
Tribhuvan University for his valuable guidance, support, constant encouragement and
providing a great knowledge throughout this entire research work. His encouragements,
assistance at all times have been of immense value. I would like to express my sincere thanks
to Prof. Dr. Megh Raj Pokhrel, Prof. Dr Rajaram Pradhananga, Prof. Jaya Krishna shrestha
Associate. Prof. Dr Deba Bahadur Khadka, Associate. Prof. Dr. Rameshor Adhikari Asst.Prof. Mr santosh Khanal & all the supporting staffs of the Central Department of Chemistry
& Central Library. I express my sincere thanks to my wife Isha & son Heem Shankar for
helping me in preparing this Dissertation work. I would like to express sincere gratitude to
my heavenly father Sada Ananda Regmi & mother Radhika Regmi, for their co-operation
and support throughout the entire period of my study. And finally special thanks for UGC
Institutional Grant for fully supported the research of this dissertation work.
Shukra Raj Regmi
26 October, 2013, Kritipur
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ABSTRACT
Chemically modified adsorbent based onphragmitiesstem has been investigated by
treating with concentrated sulfuric acid at 2:1 weight/volume ratio. Thus prepared adsorbent
has been found to be effective in the adsorption of aluminium, iron and chromium from
aqueous medium. The maximum loading capacity for Al(III) and Fe(II) onto PCNW
adsorbent was found to be 148 mg/g and 200 mg/g, while for Cr(VI) 200 mg/g, respectively,
at their optimal pH. Similarly, it was 166.66 mg/g and 90.90 for Al (III) and Fe(II) onto the
CNW, respectively. Freundlich plot and pseudo-second order kinetic model followed the
adsorption process. The desorption of the loaded metal ions recovery was found to be to
the extent of 81%, 91% and 100% for Al(III), Fe(II) and Cr (VI), respectively.
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ABBREVIATIONS
L = Liter
N = Phragmities karka (For all CNW & PCNW)
g = Grammg = Milligram
mg/L = Milligram per liter
mL = Milliliter.
g/L = Microgram per liter
% = Percentage
mg/g = Milligram per gram
mmol/kg = Millimol per kilogram
moL/kg = Mole per kilogram
ppm = Parts per million
%A = Percentage adsorption
pHe = Equilibrium pH.
Fe(II) = Ferric iron
Al(III) = Aluminium
Cr(VI) = Hexavalent chromium.
DPCI = 1, 5-Diphenylcarbazide.
qm = Maximum adsorption capacity in mg/g
qe = Amount adsorbed at equilibrium in mg/g.
qt = Amount adsorbed at time tin mg/g.
Ce = Equilibrium concentration of metal ion in mg/L
Ci = Initial concentration of metal ion in mg/L
Ct = Concentration of metal ion at time tin mg/L
V = Volume of metal solution in Liter
W = Weight of adsorbent used in gram
1/n = Adsorption intensity
K = Adsorption capacity
KL = Langmuir equilibrium parameter
b = Langmuir constant in L/mg
K1 = Pseudo first order rate constant in min-1
K2 = Pseudo second order rate constant in in g/mg.min
K21 = Second order rate constant in g/mg.min
V0 = Initial adsorption rate in mg/g.min.
= Molar Excitation coefficien
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CONTENTS
1. Introduction Page. No
1.1 General introduction 1-8
1.2 low cost adsorbent and importance of biosorption
1.3 Batch adsorption experiment
1.4 Adsorption Isotherm
1.4.1 Langmuir adsorption isotherm
1.4.2 Freundlich Isotherm
1.5 Adsorption Kinetics
1.5.1 Pseudo first order model1.5.2 Pseudo-second order model
1.5.3 Second order model
1.6 Spectrophotometric Method
1.6.1 Spectrophotometric determination of Al(III)
1.6.2 Specrrophotometric determination of Fe(II)
1.6.3 Specrrophotometric determination of Cr(VI)1.7Interference
2. Literature Review 9-11
3. Objectives of the Research Work 124. Methodology 13-18
4.1 Instrumentation
4.2 Preparation of reagents
4.3 Preparation of bioadsorbent
4.3.1 Acid modification
4.3.2 Phosphorylation of adsorbent
4.4 Procedure for desorption studies
5.Effect of chemical modification
5.1 Effect of chemical modification on Al(III)5.2 Effect of chemical modification on Fe(II)
5.3Effect of chemical modification on Cr(VI
6. Result and Discussion for Al(III) 19-31
6.1 Determination of max for spectrophotometer for Al(III)
6.2 Construction of Calibration curve for Al(III)
6.3 Batch pH study for Al(III)
6.4 Batch kinetic study of Al(III)
6.5 Batch equilibrium time study of Al(III)
6.6 Batch Isotherm studies of Al(III)
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7. Result and Discussion for Fe(II) 32-45
7.1 Determination of max for spectrophotometer for Fe(II)
7.2 Construction of calibration curve for Fe(II)
7.3 Batch pH study for Fe(II)7.4 Batch kinetic study of Fe(II)
7.5 Batch equilibrium time study of Fe(II)
7.6 Batch Isotherm studies of Fe(II)
8. Result and Discussion for Cr (VI) 46-57
8.1 Determination of maxfor spectrophotometer for Cr(VI)
8.2 Construction of calibration curve for Cr(VI)
8.3 Batch pH study for Cr(VI)
8.4 Batch kinetic study of Cr(VI)
8.5 Batch equilibrium time study of Cr(VI)8.6 Batch Isotherms studies of Cr(VI)
9. Desorption and metal recovery 58-60
10. Conclusion 61
11. Application of the research work 62
12. Suggestion for further work 62
13. Limitation of the Present Study 63
15. References 65-67
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1. Introduction
1.1 General Introduction
Heavy metals are, high density toxic pollutants, mainly include transitional metal,
metalloids, lanthanides & actinide1, eg Cr(VI), Cd(II), Pb(II), Fe(III), Fe(II), Al(III), Ni(II),
Zn(II) Cu(II)2. Industrialization mainly concern to the chemical industry cause them to
released into aquatic ecosystem human enrollment like industrial, mining and agricultural
activities includes electroplating, leather tanning, cement, mining, dyeing, fertilizer and
photography industries. Heavy metals are non biodegradable and may cause health problem
to animal, plants, human being and environmental problem as well1.
Hexavalent Chromium is carcinogenic causes liver damage, pulmonary congestionand causes skin irritation resulting in ulcer formation1. The tolerance limit for Cr (IV) for
discharge into inland surface waters is 0.1 mgL-1and in potable water is 0.05 mgL-1. But its
concentration in industrial waste water ranges from 0.5-270 mgL-1. Hexavalent chromium,
Cr(VI) exist in the aqueous solution as oxy anions such as chromate(CrO42-),
dichromate(Cr2O72-), (HCrO4
-) and (HCr2O7-) form2.
Trivalent Aluminium is non essential to the plants & animals.excess soluble of
Al(III) in water cause the destruct food on of bone, lungs, spleen liver, & brain. It is also the
cause of Azlimers, clinically charactrrised by gradual loss of congnitive function, other
cause may be anaemia. Dentalcaries, hepatic & renal dysfunction, neuromuscular disorders,
Osteomalacia & blood cancer. UN food & agricultural organization recommended
maximum level for irrigation is 5 mg/L., In ground water its concentration should be less
than 0.1/L.
Iron is also a toxic if present in excess, which cause anorexia, oliguria, diarrhea,
hypothermia, diphasic shock & metabolic acidosis & even death. In addition to these,
patients experiences vascular congestion of the gastrointestinal tract and liver toxicity via
lipid peroxidation & destruction of hepatic mitochondria. Several iron storage disease such
as cirrhosis, hepatoma siderosis, myocardial infection etc. The UN food and agriculture
organization recommended level for irrigation water is 5 mg/L. The USEPA secondary
drinking water standard MLC is 0.3 mg/L.
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1.2 low cost adsorbent and importance of biosorption
There are different methods of treatment of heavy metal contaminated water. They are
chemical precipitation, lime coagulation, ion-exchange, reverse osmosis, solvent extraction,
reduction, electro dialysis, evaporation, electrochemical precipitation. However these
methods are not widely acceptable due to high capital and operational costs and problem in
disposal of residual metal sludge.
Biosorption is an effective and versatile method for removing of these heavy metal
Al(III), Fe(II), Cr(VI) and other heavy metals from heavy metal contaminated effluents.
There are number of biosorbents which have been investigated for the removal of different
metal from aqueous solution.The chemically modified carbon is commonly used as an adsorbent for the removing
of Al(III), Fe(II), Cr(VI) because of its effective adsorption capacity in trace level at low
cost. Chemically modified carbon has been prepared from the various agriculture waste as
Phragmities karkastem, sugarcane bagasses, rice husk, coconut shell, Banana bark, pine
leaf, wood and dust, Lapsi seeds etc.1These carbon which are prepared from agriculture
waste contain high percentage of carbon and have fairly high adsorption capacity for heavy
metals including Al(III), Fe(II), Cr(VI). A great interest has been focused to understand the
mechanism of adsorption of this metal in carbon prepared from agriculture waste.1
The carbon prepared from agriculture waste can be activated by various method like
chemical modification, steam activation, thermal activation etc. By means of such
activation, the effective surface area of carbon increases and surface of the adsorbent gets
modified due to formation of different functional groups.7In Nepal lots of biomaterial like,
Phragmities karka stem, sugarcane bagasses, rice husk, maize barn, apple waste, orange
waste and banana bark are easily available as waste material
Phragmities karka stem is one of the very popular in making roof & bar in
agricultural farm, and the waste produced is abundantly found in mountain & Terai region
of Nepal, it is burnt as a less efficient fuel causing air pollution mainlyin October season.
Therefore it is quite suitable to use as an adsorbent rather than wasting. In present research
work, Phragmities karka stem is collected from periphery of Tribhuwan University Kritipur
Kathmandu has been explored to convert into cost effective environmental friendly
bioadsorbent for the removal of Al(III), Fe(II), Cr(VI) from aqueous solution.2
1.3 Batch adsorption experiment
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The phenomenon of increasing the concentration of substance on the surface of
a solid or liquid than in the bulk of solid or liquid is called adsorption.
The substance onto which adsorption takes place is called as adsorbent and which get adsorb
is called as adsorbate. The adsorption of various metals onto adsorbent can be studied by
Column and Batch experiment.
In column adsorption method, a column of adsorbent of particular length and internal
diameter is made and effluent is allowed to flow through a reservoir at the top of the column
using a flow controller. Effluent samples were collected at each interval of time and examine
for residual metal content to evaluate the efficiency of the column. The metal concentration
before and after adsorption is measured by using spectrophotometer.
In batch experiments, a definite mass of the adsorbent is agitated with the predetermined
volume of metal solution into the stopper bottle. Stopper bottle is vigorously shaken in a
mechanical shaker at room temperature for 24 h to attain adsorption equilibrium. The initial
and equilibrium concentrations of metal ions are determined using spectrophotometers. (1, 4,
8, 9)
Heavy metal adsorption onto adsorbent is affected by different parameters
such as initial concentration of metal ions (mg/L, contact time in minutes), amount of
adsorbent used (g/L), temperature (C) and pH of the solution.(4,10) To understand the
mechanism and effectiveness of adsorption, any one of the above parameter is varied by
keeping the other parameters constant.4
From the metal concentration measurement before and after adsorption,
amount of metal ion adsorption onto adsorbent is determined by using following relation
as1.
qt = VW
CCei
.......................(1)
Where, Ci and Ce are initial & equilibrium metal ion concentration in mg/L
respectively. qtis the amount of metal adsorbed at time tin mg/g. V is the volume of metal
solution in L. W is the weight of adsorbent in gm.
Metal removal percentage is calculated by using a formula.
A (%) = 001C
CC
i
ei
.......................... (2)
This is the ratio of decrease in metal ion concentration before and after adsorption
to the initial concentration. The distribution ratio (D) is defined as the ratio of the amount
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of desorption to the metal ion concentration in aqueous solution of equilibrium .It is
calculated as:
D = ci - ce/ ce = qe /ce.(3)
Where, qe is the equilibrium amount of adsorption of metal ion per unit mass of the
adsorbent and Ceis the equilibrium concentration in mg/L and D is the distribution factor
for the adsorption in L/g.
1.4 Adsorption isotherm
Adsorption isotherm is a curve which relates the amount of the adsorbedper
unit mass of adsorbent to the amount of unabsorbedadsorbate remainingin the solution at
equilibrium time. Experimentally isotherms are useful for describing adsorption capacity to
evaluate the feasibility of these processes for a given application.14
The equation parameters and the underlying thermodynamic assumption s of these
equilibrium models often provide some insight into both the sorption mechanism and the
surface properties and affinities of the sorbent. In order to describe the adsorption
characteristics of low cost sorbent used in water and waste water treatment, experimental
equilibrium data are most frequently modeled by the relationship developed by Langmuir
and Freundlich.
1.4.1 Langmuir adsorption isotherm
Langmuir adsorption isotherm is the best known of all isotherms describing
adsorption and it has been successfully applied to much adsorption process. Langmuir
isotherm is used to describe single layer adsorption characteristic of the adsorbent. The
isotherm can be represented by the following expression15.
e
e
bCaX
C ........................... (4)
Where, Ceis the concentration of adsorbate, which is in dynamic equilibrium with
the adsorbents adsorbed on charcoal, x is the amount of adsorbate adsorbed per gram
charcoal, and 'a' and 'b' are Langmuir constant.
Langmuir adsorption isotherm can be rearranged and the linear form of Langmuir
equation is given by. (2, 14, 16)
e
emaxe
bC1
bCqq
........................................ (5)
This equation can be further simplified as,
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m
e
me
e
q
C
bq
1
q
C ................. (6)
Where qe is milligram of metal accumulated per gram of the adsorbent at
equilibrium (mg/g), Ce is the equilibrium concentration of adsorbate (mg/L), qm themaximum adsorption capacity and b is the Langmuir adsorption equilibrium constant
(L/mg). When Ce/qeis plotted against Ce, then a straight line with a slope equal to 1/qmand
interceptbq
1
m
obtained from which qmvalue can be calculated.
According to Hay et.al(1996), the essential features of the Langmuir Isotherm can
be expressed in terms of a dimensionless constant separation factor or equilibrium parameter
(KL) which is defined by the following relationship.
(2,17)
KL=i
bC1
1
............................................ (7)
Where Ciis the initial concentration of the adsorbate (mg/L) and KLis the Langmuir
equilibrium parameters. The parameters KLindicate the shape of Isotherm and nature of the
adsorption process. (KL>1 for unfavorable, KL= 1 favorable, KL= zero for irreversible(2, 16)
1.4.2 Freundlich isothermThe Linear from of Freundlich model is represented by the following equation.14
qe= KCe1/n.................................. (7)
In logarithmic form,
Log qe= log k + 1/n log Ce.................................. (8)
Where, K and n are the Freundlich constant which are considered to be the
relative indicators of adsorption capacity and adsorption intensity. The value of 1/n varies
between 0-1 indicates the favorable adsorption of heavy metal.18
1.5 Adsorption kinetics
Adsorption kinetics study is the study of rate and mechanism of the adsorption
process. There are numerous adsorption kinetics models that are used to describe the uptake
of adsorbate by different adsorbent. The pseudo-first order rate equat, the pseudo second
order rate equation and second order rate equation has been used widely for the description
of adsorption kinetic model. The conformity between experimental data and the model
predicted values was expressed by the correlation coefficient (R1values close or equal to
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1). A relatively higher value indicates that the model successfully describe the kinetic of
adsorption.(1, 19)
1.5.1 The pseudo first order model
The line raised form pseudo first order model is generally expressed as follows.
)q(qKdt
dqte1
t .................................. (9)
Where qeand qtare amount of metal adsorbed at equilibrium and at time t, respectively
(mg/g). K1is the rate constant of pseudo first order adsorption (L min-1).(1, 20)
After integration and applying boundary conditions t = 0 to t = t and q t= 0 to qt= qt, the
integrated form of equation (9) becomes
Log (qe-qt) = log (qe)3032.
K1
t .......................... (10)
The plot of log (qe-qt) vs 't' should give a straight line from which k1and qecan be determined
from slopes and intercept of the plot respectively.
1.5.2 Pseudo-second order model
The pseudo second order adsorption Kinetic rates equation is expressed as (Ho et.
al.2000) (1, 20)
2
te2t )q(qk
dt
dq .......................... (11)
Where K2is the pseudo second order rate constant mg-1min-1and qeand qtare the
amount of metal ion adsorbed at equilibrium and at time t respectively (mg/g).
By applying boundary condition t= o to t = t & q t= 0 to qt= qtthe integrated from
of equation (11) becomes.
(t)q
1
qk
1
q
t
e2e2t
...................... (12)
If initial adsorption rate vomg g-1min-1is
vo= K2qe2................................................. (13)
Then equation (13) becomes
(t)q
1
v
1
q
t
eot
................................................. (14)
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The plot of t/qt vs. t of equation (14) should give a straight line having slope 1/qe and
intercept 2e2qK
1. So the pseudo second order rate constant and amount of metal ion adsorbed
at equilibrium can be calculated.
1
1.5.3 The second order model
The second order adsorption kinetic rate equation is expressed as (Ho et. al.1996).
(t)kq
1
)q(q
1 12
3te
................................................. (15)
Where, qeand qthave their respective meaning. t is contact time and K21 is second order
rate constant (g/mg. min). The plot of (1/qe-qt) vst should be a straight line with slope
equal to K21 & intercept 1/qe.
19
1.6 Spectrophotometric method
1.6.1 Spectrophotometric determination of Al(III)
Spectrophotometric determination of aluminium ion by Erichrome cyanine R ismore superior to other. With this reagent, dilute Al solution buffered to a pH of 6.0 produced
red to a pink color complexes that exhibit maximum adsorption at near about 530 nm 37.
The intensity of the developed color is influenced by the Aluminium concentration, reaction
time, temperature, pH, alkalinity and concentration of the other ions. The minimum and
maximum concentration range detectable by this method in the absence of fluorides and
complex phosphate is approximately 6-400 g/L. A pure reagent should be brick red in
color, which fed to a pale yellow color in about two weeks.38It appears that the form of the
dye which reacts with Al(III) ion is the strongly color one. Hence, it is most important for
the optimization of the reagent that should be added in complex formation38.
1.6.2 Specrrophotometric determination of Fe(II)
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Sensitivity and detection limit for the atomic adsorption spectroscopy (AAS) methods, the
ICP methods and the phenanthroline colorimetric procedure are almost similar and generally
adequate for the analysis of natural and treated water.
Thiocynate, dipyridine, tripyridine and 1, 10 phenanthroline are important indicators for the
spectrophotometric determination of iron. The method consisting of red complex that forms between
Fe(II) and 1,10 phenanthroline seems to be more practical and sensitive.The orange red
phenanthroline complex (C12H8N2)Fe2+can be formed quantitatively in the pH range 2-9 with the
suitable reagent concentration.
Fe2+ + 3 phen Fe(phen)32+
The molar extinction coefficient of the complex (C12H8N2) Fe2+, is 11,100 at 508 nm. The
intensity of the color is independent of pH in the range of 3 to 9.The complex is very stable and the
color intensity does not change appreciably over long period of time. Color standards are stable for
at least 6 months.
The iron must be in ferrous state, and hence a reducing agent is added before the color is
developed. Hydroxylamine hydrochloride can be used to reduce ferric ion to ferrous form.
2 Fe3++ 2 NH2OH + 20H- 2 Fe2++ N2 +4H2O
The pH was adjusted at 4.5 by using the acetate buffer.
1.6.3 Spectrophotometric determination of Cr(VI)
A more sensitive method for the determination of Chromium (IV) is diphenyl carbazide
indicator (DPCI) method, in which Cr(VI) form a pink colored complexes, with 1,5-
diphenylcarbazide in acidic medium and can be spectrophotometricaly analyzed. (1, 21, 22,23)
1.7 Interference
In addition to colored ions, other ions interfere to a greater or lesser extent. Among the
interfering substances are strong oxidizing agent, cyanide, nitrite, phosphate, chromium, zinc in
concentration exceeding 10 times with that of iron, cobalt, and copper in excess of 5 mg/L and Nickel
in excess of 2 mg/L. Bismuth, cadmium, mercury, Molybdate and silver precipitate phenanthroline.
Adding excess hydroxylamine hydrochloride eliminates error caused by excessive concentrations of
strong oxidized agent. In the presence of interfering metal ions, a larger excess of phenanthroline
should be used to replace that complexes by the interfering metals. A great advantage of 1, 10-
phenanthroline over some other iron reagents lies in the possibility of using it in slightly acidic
medium. In this method, predetermine volume and concentration of iron solution mixed with
required amount of other reagents and maintained at fixed pH is subjected to spectrophotometric
measurement. This value issued to determine other parameters37,38,39.
2. Literature review
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There are different methods of the treatment of Cr(VI) contaminated water
like chemical precipitation, lime coagulation, ion exchange, reduction, reverse osmosis,
solvent extraction, electro dialysis, electrochemical precipitation, cementation etc.(1, 2, 4, 5)
However these methods are not widely acceptable due to high operational costs and problem
in disposal of residual metal sludge. Owing to this reason much attention has been given to
investigate the cheaper technique. Recently, biological waste material for the heavy metal
removal has been increasing because of their high metal binding capacity and cost effective
nature.
Adsorption process has been found to be one of the alternatives to lower down the
concentration of Chromium from aqueous solution. This can be removed by adsorption onto
various adsorbents derived from different sources. One of the most widely used adsorbent
is charcoal which can easily removed Cr(VI) from aqueous solution. Charcoal can be
prepared from various sources like sawdust, rice husk, rubber wood, fruit shell, fruit seed
etc. However, activated charcoal seems to be less effective as compare to that of
functionalized materials derived from several sources.
Dodrowolski et.al 24 studied the adsorptions of Cr(VI) from aqueous solution on activated
carbon and found that the reaction rate of ions on the surface of the activated carbon rather
than diffusion was the major process influencing the equilibrium. Surface reduction of
Cr(VI) to Cr(III) appeared to be the principal mechanism for the adsorption of chromium
on the activated carbon.
Arivoli et al. 4 studied the adsorption of chromium ion from aqueous solution by acid
activated banana bark carbon and show have effect of variable parameter on adsorption
process and maximum adsorption takes place at low and high pH value and the amount of
adsorption increased with increasing ionic strength and temperature. They calculate the
different thermodynamic parameters as H, S, G0.
Nomanbhay et.al.3 studied removal of heavy metal from industrial waste using
chatoyant coated oil palm shell charcoal and they found that chromium ion removal by using
this adsorbent was appeared to be technically feasible eco-friendly and with high efficiency.
Besides that the adsorbent can be regenerated by using sodium hydroxide and therefore can
be reused.
Hamadi et.al.25 studied the adsorption kinetics for the removal of Cr(VI) from
aqueous solution by tyres & Sawdust. They found that the removal was favored at low pH,
with maximum removal at pH 2. They found both sorbets were effective to remove Cr(VI)
from solution. The sorption kinetics was found to follow pseudo second-ordered model.
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Ahalya et.al.2studied biosorption of Cr(VI) from aqueous solution by the husk of
Bengal gram. They found that the removal was favored at pH 2. The adsorption data fit well
with the Langmuir & Freundlich Isotherm model. The biosorption of Cr(VI) was possible
due to the ion exchange with hydrogen of OH & -COOH groups presents in the
lignocelluloses moieties.
Demirabas et.al.1 studied the adsorption kinetics for the removal of Cr(VI) from
aqueous solution on the activated carbon prepared from cornelian cherry, apricot stone and
almond shells. They found that the maximum adsorption of Cr(VI) at pH 1 for all types of
carbons. The sorption reaction was found to be follow pseudo second order model.
Baral et.al.20 studied the Hexavalent chromium removal from aqueous solutionby
adsorption on sawdust. The studies were conducted by varying various parameters such as
contact time, pH, amount of adsorbent, concentration of adsorbate & temperature. They
found that the maximum removal of Cr(VI) in the pHrange 4.5-6.5 & sorption reaction was
found to be follow pseudo-second order.
Sankararamakrishnan and Sanghi 19 studied the adsorption of Cr(VI) on novel
xanthated chitosan. They found that the maximum uptake of Cr(VI) by chemically modified
chitosan at pH 3. Such chemically modified xanthated chitosan might find potential use as
adsorbent in tannery wastewater treatment.
Khan and Mohamad 5studied investigations on the removal of Cr(VI)by sugarcane
bagasse from wastewater. The effect of various parameters on the removal process and
found that removal was effective at low pH 1 and contact time 4 h. The adsorption data
obtained during the studied well fitted with the Freundlich Isotherm.
Gaupta and Babu 26 studied the adsorption of Cr(VI) by low cost adsorbent prepared
from amarind seeds. They found that the adsorbent prepared from amarind seeds can be
used for removal of Cr(VI) from aqueous solution and adsorption was favorable at low pH.
Freundlich adsorption model showed good agreement with the experimental data.
Nameni et.al.27studied adsorption of hexavalent chromium from aqueous solution
by wheat bran. They studied the effect of various parameters on Cr(VI) adsorption and found
that the adsorption of chromium by wheat barn reached to equilibrium after 60 minutes and
maximum chromium removal (87.8%) obtained at pH 2. The result showed that the
adsorption follow the pseudo second order kinetics.
Though there are several works regarding the adsorption onto either using activated
carbon or with biomaterials as such. Now a day, the great attention has been paid to remove
the heavy metals by using functionalized biopolymers. Under such circumstances, this
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dissertation has explored a possibility to derive polyphenolic / polyhydroxy functional
matrix in sugarcane waste for the purpose of chromium adsorption.
K.N Ghimire et al.prepared La(III), Ce (III) and Fe(III) loaded orange waste & used
it for the adsorption of phosphate from aquatic environment ,maximum phosphate update at
equilibrium was 13.94 mg g-1.It is noted that significant amount of phosphate was absorbed
by small amount of the modified adsorbent as compared to other adsorbents.
K.N Ghimire et al. prepared an efficient and cost effective non conventional adsorbent from
seaweed laminarriya japonica by crosslinking with epichlorohydrin .The maximum
adsorption capacity for Pb(II), Cd(II), Fe(III) was found to be 1.35 ,1.1, 1.53 mol kg-1
respectively while 0.87 mol kg-1for both La(III) & Ce(III).
Hideko koshim et al.,Iron(III) has to be collected or adsorbed to some extent by
activated charcoal, however adsorption from hydrochloric acid medium has been
overlooked. Present note will show that Fe(III) is absorbed by activated carbon from 6-10
mol dn-3 hydrochloric acid solution. Author has reported that removal up to 99% was
adsorbed from 10 M HCl solution after contact time of 19 hours.
Bozic et al. ,studied the adsorption of iron & copper ion from synthetic solution
using saw dust of beech linden, popler tree. The kinetic of adsorption was reported to be
relatively fast leaching equilibrium for less than 20 minute. The maximum adsorption
capacity was achieved at pH between 3.5 & 5 for all kind of saw dust studied. No influence
of particle size was evidenced. A degree of adsorption higher than 80% was achieved for
Cu++ ion but it is very low for Fe++ions, not exceeding 10%.
3. Objective of the research work
The objectives of this entire research work are to investigate adsorbent with suitablefunctional groups for the binding of Al(III), Fe(II) & Cr(VI) by making simple chemical
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modification of thePhragmities karkawaste. In principle, the target of this research was to
create the polyphenolic/polyhydroxy functional groups as much as possible onto the
polymer matrix ofPhragmities karkawaste.
General objectiveThe general objective of the present work was to prepare low cost bio-adsorbent
from the agricultural Phragmities karkawaste and to investigate the adsorption capacity of
the adsorbent in the removal of Al(III), Fe(II) & Cr(VI).
Specific objective
The specific objectives of the present works are
To prepare and characterize the adsorbent for absorption of Al(III), Fe(II) & Cr(VI)
from aqueous solution.
To find out the nature of adsorption Isotherm in the removal of Al(III), Fe(II) &
Cr(VI) from aqueous solution.
To investigate the effect of pH, initial concentration of absorbate and contact time
in the removal of Al(III), Fe(II) & Cr(VI) from aqueous solution.
To study the kinetics of the adsorption reaction and to find out the nature of
adsorption Isotherm in the removal of of Al(III), Fe(II) & Cr(VI) from aqueous
solution To compare the adsorption capacity of CNW & PCNW
To determine the maximum adsorption capacity of the adsorbent.
4. Methodology
4.1. Instruments
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Laboratory mill (Grinder)
Sieve no. 250 mesh, India
Weighting balance, model GT 210V, OHAUS, USA.
Hot air oven, India
Digital PHmeter, India
Magnetic stirrer hotplate, UK
Shaker, India
WPAS 104 Spectrophotometer, UK
4.2. Preparation of the reagents
4.2.1 Potassium dichromate stock solution (1000 mg/L)
Stock potassium dichromate (K2Cr2O7)solution was prepared by dissolving 2.514 gm
of potassium dichromate crystal in 1000 mL volumetric flask in 0.1 M HNO3solutions. 1mL
of stock potassium dichromate solution = 1000 g HCrO4-as in the form of Cr(VI).
4.1.2 5 M Nitric acid Solution (approx)
5M nitric acid was prepared by diluting the 32 mL of concentration. HNO3(15.66
M) in 100 mL volumetric flask in distilled water.
4.1.3 Preparation of 0.25% 1,5 diphenylcarbazide (DPCI) Solution
0.25 gm of 1.5diphenylcarbazide crystals were transferred to a 100 mL volumetric
flask and 50 mL of pure acetone was added slowly with constant striking. Then 50 mL water
was added up to the mark. Due to the high sensitivity of this solution to light, it was protectedfrom direct sunlight by wrapping the bottle containing the reagent with black paper. This
prolonged the life span of the reagent. When this solution turned faint red, it was discarded
and a fresh solution was prepared.
4.1.4 Buffer solution pH 4
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Buffer tablet of pH 4 was dissolved in a 100 mL volumetric flask and made up to
the mark in distilled water.
4.1.5 Buffer solution of pH 7
Buffer tablet of pH 7 was dissolved in 100 mL volumetric flask and made up to the
mark in distilled water.
4.1.6 Buffer solution of pH 9.2
Buffer tablet of pH 9.2 was dissolved in a 100 mL volumetric flask and made up to
the mark in distilled water.
4.1.7 Buffer solution of pH 4.5
6.5mL of 0.1M acetic acid solution and 0.1M sodium acetate solution was mixed
homogenously in 100mL volumetric flask.
4.1.8 Buffer solution of pH 6
38 g of anhydrous sodium acetate was dissolved in distilled in 1000 mL volumetric
flask.2.30 mL of glacial acetic acid was added on it . The volume was then made up to the
mark.
4.1.9 Iron(II) stock solution (1000 mg/L)
An iron (II) stock solution was prepared by dissolving 7.016 gm of Mohrs salt [Fe
(NH4)2.FeSO4.7H2O]in 1000mL volumetric flask in distilled water with volume up to the
mark.
1mL of stock solution = 1000g of Fe(II)
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4.1.10Preparation of Al(III) stock solution (1000 mg/L)
35.167 gm of potash alum (K2SO4.Al2(SO4)3.24H2O) was dissolved in 1000ml of
volumetric flask with 0.1M Nitric acid & volume was made up to the mark.
4.1.110.1M Acetic Acid
1.43 ml of glacial acetic acid was taken in 250 mL volumetric flask & volume was
made up to the mark.
1mL of stock solution = 1000 g of Al(III)
4.1.12
0.1M Sodium acetate solution
2.05 gm of anhydrous sodium acetate was taken in 250 mL volumetric flask. It was
dissolved in distilled water and volume was made up to the mark.
4.1.13 0.20% 1, 10 Phenanthrolin monohydrate solutions
0.20 gm of 1, 10-Phenanthrolin monohydrate was taken in a 100 ml, volumetric
flask. It was dissolved in distilled water by heating up to 60C but not allow boiling. After
complete dissolving, the volume made up to the mark and flask was covered by black paper
for the prevention of transmission of light.
4.1.14 10% Hydroxyl amine hydrochloride solution
10gm of solid hydroxyl amine hydrochloride was placed in 100 ml volumetric flask.
It was dissolved in distilled water & volume up to the mark.
4.1.15 0.2% of Erichrome cyanine R solution
200 gm of Erichrome cyanine R was dissolved in 100 ml volumetric flask. The
volume was then made up to the mark.
4.1.16 5 M Sulphuric acid solution (approx)
5 M of Sulphuric and solution was prepared by diluting 34.7 mL of concentration
sulphuric acid in 250 mL volumetric flask in distilled water.
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4.1.17 5M Sodium hydroxide solution (approx)
5M sodium hydroxide solution was prepared by dissolving 20 gm of sodium
hydroxide pellets in 100 mL volumetric flask in distilled water.
4.2 Preparation of bioadsorbent
4.2.1 Acid modification
Biosorbent are the biomass material which have different adsorption capacities. The
adsorption capacity of such adsorbent can be increased by different methods as thermal
activation, chemical modification & so on. Phragmities karka stem consist of cellulose,
hemicelluloses, lignin, polyphenol and many other low molecular weight compounds.8
Phragmities karka stem were collected from the periphery of Tribhuwan University. It was
washed with distilled water and dried in sunlight and finally dried in oven at 100C for 2
hours. It was cut into small pieces and grounded to powder and sieved to pass through 250
m. Chemical modification using concentrated H2SO4 at moderate temperature is supposed
to activate polyphenolic / polyhydroxy surface functional groups contained in Phragmities
karkastem. The material was mixed in a 2:1 weight : volume ratio of concentrated H2SO4
and allowed to soak for 24 hours at room temperature. The samples were then washed with
distilled water till pH of the modified carbon becomes neutral and dried at 80C for 3 hours.
CH2OH
OO
OH
OH
OOH
CH2OH
OH
Conc. H2SO4
Ring opening
OH
OH
Fig.Plausible reaction scheme after charring with acid. Ref.No.8
4.2.2 Phosphorylation of charred adsorbents
An amount of 20 g dried CNW adsorbent was soaked in 250 ml of DMF overnight
in 500 ml three naked flask. The flask was equipped with magnetic stirrer. Then 30 g of urea
was added into the flask with constant stirring followed by the addition of 40 ml of H3PO4
drop wisely with constant stirring. The mixture was refluxed for 3 hours at a temperature of
150C on paraffin bath. After cooling to room temperature, it was washed with 500 ml of
70% propanol followed by water till neutrality was obtained. The solid product was dried
in sun and then in oven for 24 hours at 60C. Thus obtained dried bioadsorbent was termed
as PCNW. The phosphorylation reaction can be expressed schematically as.
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Fig.,
Plausible phosphorylation mechanism of CNW.Ref.No 8
4.4 Procedure for desorption study
To analyzed the efficiency of adsorbent 25 mL of pH adjusted metal ion solution
to optimum value was taken in 50 ml stopper bottles with 25 mg adsorbent and shaken for
24 hours .Then the solution was filtered and analyzed for equilibrium concentration to find
out the adsorbed amount .Then the residue adsorbent was transferred into same 50 ml
stopper bottle and mixed with 25 ml 0.2 M HCl. The solution was shaken for 24 hr and then
analyzed for the metal recovery.
Again the adsorbent was washed to neutrality and administered for the same
process for the adsorption and desorption. The efficiency of the absorbents were analyzed
through the series of adsorption deposition experiments. In this study, efficiency of the
adsorbent is analyzed by the conducting desorption up to three series and % metal recovery
are analyzed. The data obtained show that the adsorbent is efficient and can be used
repeatedly for the several times. The obtained data is shown in table.
5. Plausible adsorption mechanismAfter charring the polymeric cellulose of phragmities become
chemically modified which provided the suitable site for the maximum possible adsorption
of the metal. After phosphorylation, adsorbent consist of phosphoric group, which
drastically alter the adsorption mechanism by many fold accordingly with cation exchange
mechanism. The metal cation Al(III) and Fe(II) is consider to be adsorbed on the phosphoric
group, while such adsorption of Cr(VI) onto phos phate group is not possible, due to the
repulsion of same charge ions. Hence, adsorption takes place through complexation with
polyphenolic group (Ghimire et al. 2002)
O
H
O
H
C
H
2
O
H
O
H
O
H C
H
H
O
H
O
HConc
.H3P
O4
O
C
H
2
O
O
H
O
H C
H
P
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5.1 Effect of chemical modification on Aluminium
Fig., plausible adsorption mechanism of Al(III) onto PCNW .Ref No.8
5.2 Effect of chemical modification on Iron(II)
Fig., plausible adsorption mechanism of Fe(II) ontoCNW & PCNW.Ref No.8
5.3 Effect of chemical modification on chromium
Based on the distribution diagram, the adsorbed chemical species of the chromium
was revealed to be HCrO4-at optimal pH 1 & 2. Since the chemically modifiedPhragmities
karkawaste possesses higher amount of polyphenolic/ polyhydroxyl functional group as
discussed in earlier section, a plausible mechanism of chromium(VI) adsorption can be
schematically represented as follows:
O
OH
CH2OH
OH
OH
OH
+ Cr O-
O
HO
O
O
OH
CH2OH
OH
O
O
Cr
O
O
+ H2O + OH-
H2
O
O
H
H
OO
H
O
H
O
H
O
C
H2O
O
H
O
H C
H
P
+Al+3
A
lH2O
O
HH O
H
C
H2 O
O
H
O
H
H
P
A
l
H2
Op
H2
O
O
H
H2
O
H2
O
H O
H
O
C
H2 O
O
HO
H C
H
P H2O
O
H
H
O
H
O
H
O
H
O
C
H2
O
O
HO
H C
H
P+F
e+2
F
eH2
O
H
2
O
OH
H
O
H
OH
O
H
O
CH2 O
O
H
O
H C
H
P+F
e+2
F
e
H2
O
O
HH O
H
C
H2 O
OH
O
H
H
P
F
e
H2
Op
H2
O
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OH
OHHCrO4
-
O
O
Cr
O
O
+ OH- + H2O
Ref No.3
Fig:. Complexation of Chromium(VI) with polyphenolic/polyhydroxyl functional moiety of modifiedPhragmities karkawaste.
6. Result and discussion for aluminium(III)
6.1. Determination of max for Spectrophotometerfor Al(III)
The adsorption spectra of Al(III)-E complex erichrome Cyanine R showed that the
maximum absorbance, at 525 nm, as shown in fig. The nature of spectra and max at 525 nm
matched with reported values.
Table No 1. Determination of maxfor Al(III).
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.80.9
1
460 480 500 520 540 560 580
[Absorbance]
[Wavelength nm]Figure 1. Maximum absorption spectrum of Al(III) erichrome cyanine
complex.
O
OH3C-
HO
HO HO O
CH3
O C
CH O
H
CH2OH
O
O
H3C-O
OH
HO
H3C-O HO
H3C-O
O
OCH3
HO
HO
H3C-O
O
OH
O OCH3
O
OH
OH
OCH3
O
O
CH3
HO
O
OCH3
O
O
HO OH
H3C-O O
O
OH
OH
OC H
C O
H
CH2OH
CH3O
O
CC
R2
HO
CH
O
OHHO
OH
OCH3
HOHO
O
O
O
HO OCH3
OH
OH
Conc. H2SO4
OH
OH
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6.2. Construction of calibration curve for Al(III)
In solution state Al occurs in +3 oxidation state between the pH 4 and forms a
complex of pink-purple colour. Alumunium as Al(III) start to form hydroxide compound
sat pH 3.5 and there is a mixture of Al(OH)2and Al(OH)3, which leads a rapid formation of
insoluble Al(OH)3Above the pH 6. The nature of the adsorption spectra and maxobtained
at 350 nm.The adsorption spectra of the pink-purple colored complex of Al(III)-ECR complex
and the calibration curve for the Al(III)-ECR complex are shown in figure.
Table No 2. Construction of Calibration curve for Al(III)
S.N Wavelength nm Absorption (O.D)
1 460 0.03
2 470 0.09
3 480 0.14
4 490 0.17
5 500 0.21
6 510 0.27
7 515 0.54
8 520 0.68
9 525 0.88
10 530 0.78
11 535 0.67
12 540 0.54
13 550 0.39
14 560 0.18
15 570 0.06
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6.3 Batch pH study for Al(III)
The maximum adsorption of Al(III) was found in the pH 6 above 6 adsorption of
Al(III) decreases, due to the rapid pre formation of of Al(OH)3 with gelly like viscus
precipitation35. It is belived that most of the metal ions including Al(III) is removed from
aquous solution by cation mechanism because at higher pH binding site of the adsorbent
start deprotonating and the metal uptake become difficult36.
S.No Wavelength nm Absorbance O.D
1 0 0
2 25 0.06
3 50 0.12
4 75 0.17
5 100 0.236 150 0.32
7 200 0.42
8 250 0.56
9 300 0.68
10 350 0.77
11 400 0.88
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Table No 3. Adsorption of Al(III) onto CNW on different pH.
Volume of metal solution = 25ml
Concentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/L
Adjustable pH = 6
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7
Adsorption[%]
[pH]
Figure 3. Effect of pH on the Percentage adsorption of Fe(II) onto CNW &
PCNW
Al(III)-CNW
Al(III)-PCNW
S.No pH Initial
concentration
Ci (mg/L)
Equililibrium
concentration
Ce (mg/L)
%
Adsorption
1 1 23.99 23.24 3.12
2 2 23.99 21.91 8.66
3 3 19.35 16.17 16.4
4 4 19.15 11.51 35.88
5 5 17.13 7.5 56.26 6 15.52 3.56 77.63
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Table no 4. Adsorption of Al(III) onto PCNW on different pH.
Volume of metal solution= 25 mlConcentration of metal solution=25 mg/L
Amount of adsorbent=25 mg/L
Adjustable pH = 6
6.4 Batchkinetic study of Al(III)
The measurement of adsorption kinetics was carried out by shaking 25 mg of
charcoal with Almunium solution of 25 g/mL 50 mL conical flask at room temperature.
The removal kinetics of Al(III) was investigated by drawing the samples after desired
contact time and the filtrate was analyzed for the remaining Al(III) concentration.
The correlation coefficient value for pseudo first order kinetic plot found for CNW
& PCNW is 0.884, 0.898 respectively by plotting log(qe-qt) Vs. time,Thus obtained value
shows for this adsorption is not flow pseudo first order kinetics.
The correlation coefficient value for pseudo second order kinetic plot found for
CNW & PCNW is 0.997, 0.986 respectively by plotting t/qt Vs.time, Thus obtained value
shows for this adsorption is not flow pseudo second order kinetics.
S.No pH Initial
concentration
Ci (mg/L)
Equililibrium
concentration
Ce (mg/L)
%
Adsorption
1 1 23.99 22.20 7.44
2 2 23.99 20.78 13.38
3 3 19.35 13.93 21.96
4 4 19.15 10.77 43.72
5 5 17.13 5.78 66.2
6 6 15.52 2.09 86.53
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R = 0.8986
R = 0.8836
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200
logqe-qt
[mg
/g]
Time [minutes]
Figure 4. Pseudo first order kinetic plot for the adsorption of Al(III) onto
CNW & PCNW
Al(III)-PCNW
Al(III)-CNW
R = 0.9867
R = 0.9978
0
2
4
6
8
10
12
0 50 100 150 200
t/qt
[g/mg]
Time [Minutes]
Figure 5. Pseudo second order kinetic for the adsorption of Al(III) onto
CNW & PCNW
Al(III)-PCNW
Al(III)-CNW
R = 0.9585
R = 0.9619
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 50 100 150 200
1/qe-
qt
[g/mg]
Time [minutes]Figure 6. Second order kinetic plot for the adsorption of Al(III) onto CNW
& PCNW
Al(III)-CNW
Al(III)-PCNW
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Table No 5. Batch kinetic study of Al(III) onto CNW
Volume of metal solution = 25 ml
Concentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/LAdjustable pH = 6
Time Initial
Concentration
Ci(mg/L)
Equilibrium
Concentration
Ce (mg/L)
qt(mg/g)
qe-qt
(mg/g)
Log(qe-qt)
(mg/g)
1/(qe-
qt)
(g/mg)
t/qt
(min.g/mg)
10 23.58 16.52 7.06 13.15 0.076 1.11 1.41
20 23.58 14.57 9.01 11.2 0.089 1.04 2.21
30 23.58 13.12 10.38 9.83 0.101 0.99 2.89
40 23.58 11.16 12.42 7.79 0.128 0.89 3.22
50 23.58 9.81 13.77 6.44 0.155 0.8 3.63
60 23.58 8.33 15.25 4.96 0.201 0.69 3.93
90 23.58 7.66 15.92 4.29 0.233 0.63 5.65
120 23.58 5.18 17.4 2.81 0.355 0.44 6.89
180 23.58 4.88 17.7 2.51 0.398 0.39 10.16
Infinite 23.58 3.37 20.21 - - - -
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Table No 6. Batch kinetic study of Al(III) onto PCNW
Volume of metal solution = 25 ml
Concentration of metal solution =25 mg/L
Amount of adsorbent = 25 mg/LAdjustable pH = 6
Table No 7. Kinetic parameter, for the Metal biosorption, with correlation coefficient for
Al+++.
Time Initial
Concentratio
n
Ci(mg/L)
Equilibrium
Concentratio
n
Ce (mg/L)
qt(mg/g
)
qe-qt
(mg/g
)
Log(qe
-qt)
(mg/g)
1/(qe-
qt)
(g/mg
)
t/qt
(min.g/mg
)
10 23.58 11.48 12.1 8.5 0.117 0.92 0.82
20 23.58 10.32 13.26 7.34 0.136 0.86 1.5
30 23.58 9.26 14.32 6.28 0.159 0.79 2.09
40 23.58 8.22 15.36 5.24 0.19 0.71 2.6
50 23.58 7.64 15.94 4.66 0.214 0.66 3.13
60 23.58 5.34 18.24 2.36 0.423 0.37 3.28
90 23.58 5.04 18.54 2.06 0.485 0.31 4.85
120 23.58 4.7 18.88 1.72 0.581 0.23 6.38
180 23.58 4.18 19.04 1.2 0.833 0.07 9.24
Infinit
e
23.58 2.68 20.6 - - - -
Adsorbent qexp(mg/g)
Pseudo- first
order
Pseudo-
Second
order
Second order
K1
min-1(10-
3)
qe R2 K2
min-1(10-
3)
qe Vo R2 K21
min-1(10-
3)
qe R2
CNW 20.21 2.92 7.88 0.883 9.774 2.71 0.112 0.997 0.406 1.055 0.958
PCNW 20.6 2.45 11.80 0.898 10 3.39 0.98 0.986 0.812 1.12 0.961
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4.5 Batch equilibrium time study
Table No 8. Batch equilibrium time study of Al(III) onto CNW.
Volume of metal solution = 25 ml
Concentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/L
Adjustable pH = 2.7
Table No 9. Batch equilibrium time study of Al(III) onto PCNW.
0
5
10
15
20
25
0 100 200 300 400 500 600
qt
[mg/g]
Time [minutes]
Fig 7. Effect of contact time on the adsorption of Al(III) onto CNW &
PCNW
Al(III)-CNW
Al(III)-PCNW
S.NO Time (minutes) Initial
concentration
Ci (mg/L)
Equilibrium
concentration
Ce (mg/L)
qt (mg/l)
1 10 23.58 16.52 7.06
2 20 23.58 14.57 9.01
3 30 23.58 13.12 10.38
4 40 23.58 11.16 12.42
5 50 23.58 9.81 13.77
6 60 23.58 8.33 15.25
7 90 23.58 7.66 15.92
8 120 23.58 5.18 17.4
9 180 23.58 4.88 17.7
10 240 23.58 3.37 20.21
11 300 23.58 3.37 20.21
12 360 23.58 3.37 20.21
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Volume of metal solution = 25 ml
Concentration of metal solution = 25 mg/LAmount of adsorbent = 25 mg/L
Adjustable pH = 6
S.NO Time (minutes) Initial
concentration
Ci (mg/L)
Equilibrium
concentration
Ce (mg/L)
qt (mg/l)
1 10 23.58 11.48 12.1
2 20 23.58 10.32 13.26
3 30 23.58 9.26 14.32
4 40 23.58 8.22 15.36
5 50 23.58 7.64 15.94
6 60 23.58 5.34 18.24
7 90 23.58 5.04 18.54
8 120 23.58 4.7 18.88
9 180 23.58 4.18 19.04
10 240 23.58 2.26 20.6
11 300 23.58 2.26 20.6
12 360 23.58 2.26 20.6
13 420 23.58 2.26 20.6
14 500 23.58 2.26 20.6
13 420 23.58 3.37 20.21
14 500 23.58 3.37 20.21
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6.6 Batch isotherm study
R = 0.9661
R = 0.9769
0
1
2
3
4
5
6
0 100 200 300 400 500
Ce
/qe
[g/L]
C e [mg/l]
Figure 8. Langmuir adsorption plot for the adsorption of Al(III) onto
CNW & PCNW
Al(III)-CNW
Al(III)-PCNW
R = 0.9666
R = 0.995
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5 3
log
qe
[mg/g]
log Ce [mg/L]
Figure 9. Freundlich adsorption plot for Al(III) onto CNW & PCNW
Al(III)-CNW
Al(III)-PCNW
0
20
40
60
80
100
0 100 200 300 400 500
qe
[mg/L]
Ce [mg/L]
Figure 10. Adsorption isotherm for adsorption of Al(III) onto CNW &
PCNW
Al(III)-CNW
Fe(II)-PCNW
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Table No 10. Batch Isotherm study of Al(III) onto CNW
Volume of metal solution = 25 ml
Concentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/L
Adjustable pH = 6
S.NO Ci
(mg/L)
Ce
(mg/L)
qe
(mg/g)
Ce/qe
(l/g)
log Ce
(mg/L)
log qe
(mg/L)
%
adsorption
1 7.48 1.19 6.59 0.18 0.075 0.81 84.00
2 16.63 4.59 12.04 0.38 0.66 1.08 72.37
3 37.18 16.12 21.06 0.76 1.20 1.32 56.62
4 69.00 35.32 33.68 1.04 1.54 1.52 48.00
5 83.18 47.92 35.26 1.35 1.68 1.54 42.38
6 173.44 120.67 52.77 2.28 2.08 1.77 30.42
7 239.40 174.30 65.10 2.67 2.24 1.81 27.19
8 280.63 209.77 70.86 2.96 2.32 1.85 25.25
9 367.00 291.48 75.52 3.87 2.46 1.87 20.57
10 485.22 401.96 83.26 4.82 2.60 1.92 17.15
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Table No 11. Batch Isotherm study of Al(III) onto PCNW
Volume of metal solution = 25 mlConcentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/L
Adjustable pH = 6
S.NO Ci
(mg/L)
Ce
(mg/L)
qe
(mg/g)
Ce/qe
(L/g)
log Ce
(mg/L)
log qe
(mg/L)
%
adsorption
1 7.5 1.05 6.45 0.16 0.021 0.8 86.00
2 16.61 3.79 12.82 0.29 0.57 1.10 77.18
3 37.22 14.05 23.17 0.60 1.14 1.11 62.24
4 68.10 33.36 34.74 0.96 1.52 1.54 51.00
5 84.20 47.99 36.21 1.32 1.68 1.55 43.00
6 172.53 113.86 58.67 1.94 2.05 1.76 34.00
7 236.18 165.95 67.22 2.46 2.21 1.82 30.32
8 280.16 202.12 81.35 2.48 2.30 1.91 27.85
9 370.00 282.71 87.29 3.23 2.45 1.94 23.59
10 487.17 394.17 93.00 4.23 2.59 1.96 19.08
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Langmuir and Freundlich parameters shown in figures were determined from the slope and intercept
of their respective plots. The values of Langmuir equilibrium parameters which lied between 0 and
1 indicated that equilibrium data fits well with langmuir adsorption isotherm. The values of 1/n lied
between 0 and 1 indicated that adsorption process was favorable.
Correlation coefficient values for Freundlich isotherms were found to be greater than that
of Langmuir Isotherms indicating that the adsorption process is better defined by the Freundlich
adsorption Isotherm model than by the Langmuir, which indicated the homogenous distribution of
active sites of the adsorbent surface. Therefore from the above data, it is concluded that the
adsorption capacity of PCNW > CNW.
Another parameter qmaxwhich is the maximum quantity of metal ions per unit mass of
adsorbent to form a complete monolayer on the surface. Higher the value of qmax , higher is the
amount of metal ions adsorbed, qmax value obtained for Al onto CNW is 90.90 mg/g & for PCNW
is 142.85 mg/L
Table No 12. Langmuir and Freundlich parameters and correlation coefficient R2
with the Expt.qmaxfor the adsorption of Al(III) onto CNW & PCNW.
Adsorbent qmexp.
(mg/g)
Langmuir parameter Freundlich parameter
qm
(mg/g)
b
(L/mg)
R2 K (mg/g) 1/n R2
CNW 94 90.90 0.019 0.976 5.78 0.475 0.966
PCNW 82 142.85 0.017 0.966 6.15 0.450 0.995
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7 . Result and discussion for iron(II)
7.1. Determination of maxand construction of calibration
First of all 1000 mg/L stoke solution was diluted to 25 mg/L in a 500 ml . From
25mg/L Fe(II) solution, 0.5,1,2,3,4,5,6,7,8 ml solution were kept in 25ml V.F respectively
to prepare 0.5 to 8 mg/L solution ,to this solution, 5ml of acetate buffer of pH 4.5, 2.5 ml
of the 0.2% 1,10-phenanthrolin solution, 2.5 ml 10% hydroxylamine hydrochloride solution
were added and the remaining volume was made up to the mark by distilled water. Then the
solution was allowed to stand for 20 min for color development. Blank solution was
prepared by adding the other entire reagent except iron solution.
The solution having intermediate concentration (5 mg/L) was taken for the
determination of max. The measurement was started from 420 nm after setting the
wavelength for blank solution was used to set zero absorbance value in the
spectrophotometer, after that blank solution was taken out and the absorbance of the Fe(II)
solution was measured. Then the wavelength was increased, from the peak shaped plot of
absorbance versus wavelength for maximum absorbance, i.e, maxcan be evaluated.
After finding the max value i.e., 510 nm the wave length is set at 510 nm and the
absorbance of solution of different concentration was measured . Thus obtain plot between
absorbance and concentration of the solution is known as calibration curve.
0
0.2
0.4
0.6
0.8
1
1.2
400 450 500 550 600
[Absorption]
[Wavelength nm]
Figure 11. Absorption spectrum of Fe(II)complex with phenanthroline
showing absorption vs.wavelength.
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Table No.13 Determination of max for Spectrophotometer for Fe, 1, 10 phenanthrolin
complex.
7.2.Construction of Calibration curve for Fe(II)
y = 0.202x + 3E-16
R = 0.9943
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 1 2 3 4 5 6
[Abs
orbance]
Concentration [ppm]
Figure 12.Calibration curve for the determination of concentration
of Fe(II) phenanthriline complex.
S.NO Wavelength nm Absorption1 440 0.62
2 450 0.68
3 460 0.74
4 470 0.78
5 480 0.8
6 490 0.8
7 500 0.82
8 510 0.98
9 520 0.88
10 530 0.66
11 540 0.44
12 550 0.22
13 560 0.16
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Table no 14. Construction of Calibration curve for Fe(II).
7.3. Effect of pH on the adsorption of Fe(II) onto CNW & PCNW
The pH of the aqueous solution is an important parameter in the removal of metal
by adsorption. The metal removal capacity generally increases with the increases in the pH.Figure shows that % adsorption of Fe(II) increased up to the pH 2.7. The hypothesis
0
20
40
60
80
100
120
0 0.5 1 1.5 2 2.5 3
Adsorption[%]
[pH]
Figure 13. Effect of pH on the percentage adsorption of Fe(II) onto CNW
& PCNW
Fe(II)-CNW
Fe(II)-PCNW
S.NO. Concentration ppm Absorbsorption
1 0 0
2 1 0.18
3 2 0.41
4 3 0.62
5 4 0.85
6 5 0.98
7 6 1.22
8 7 1.34
9 8 1.44
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possesses a greatest in the adsorptive removal of iron. The figure also shows that %
adsorption of Fe(II) greater for PCNW than CNW respectively. The optimum pH for the
adsorption of Fe(II) was found to be 2.7.
The increase in the percentage adsorption with the increase of pH indicates that
the adsorption process involves the cation exchange mechanism there is competition
between Fe(II) and H+ions for the adsorption sites. At low pH value, there are high H+ ions
for adsorption sites. At low pH value, there is high H+ion concentration than Fe(II) ions and
lead to the low adsorption of Fe(II) ions. But at high pH, the concentration of H+ions is less
and they are easily replaced by the metal ions onto the adsorbent by the ion exchange process
.
Table No 15. Effect of pH on the adsorption of Fe(II) onto CNW
Volume of metal solution = 25 ml
Concentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/L
Adjustable pH = 2.7
S.No pH Initial
concentrationCi (mg/L)
Equililibrium
concentrationCe (mg/L)
% Adsorption
1 0.5 22.77 22.21 2.44
2 1 22.52 20.79 7.68
3 1.5 22.77 19.45 14.56
4 2 21.53 13.68 36.44
5 2.5 21.28 3.76 82.32
6 2.7 20.79 2.42 88.33
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Table No 16. Effect of pH on the adsorption of Fe(II) onto PCNW
Volume of metal solution = 25 ml
Concentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/L
Adjustable pH = 2.7
7.4. Batch equilibrium time study.
Figure shows that the adsorption of Fe(II) onto CNW & PCNW from 5 min to
infinite time. It was found that optimum time for the adsorption of Fe(II) ions onto CNW
& PCNW 3 hours, respectively. From this data, it can be concluded that PCNW is better
adsorbent than others as it brings equilibrium quickly.
S.No pH Initial
concentration
Ci (mg/L)
Equililibrium
concentration
Ce (mg/L)
% Adsorption
1 0.5 22.77 21.95 3.6
2 1 22.52 20.38 9.48
3 1.5 22.77 18.59 18.32
4 2 21.53 11.95 44.48
5 2.5 21.28 2.17 89.77
6 2.7 20.79 0.83 96
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Table No 17. Batch equilibrium time study of Fe (II) onto CNW
Volume of metal solution = 25 ml
Concentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/L
Adjustable pH = 2.7
0
5
10
15
20
25
0 100 200 300 400 500 600
qt
[mg/g]
Time [minutes]
Figure 14. Effect of contact time on the adsorption of Fe(II) onto CNW &
PCNW
Fe(II)-CNW
Fe(II)-PCNW
S.NO Time(minutes)
Initialconcentration
Ci (mg/L)
Equilibriumconcentration
Ce (mg/L)
qt (mg/l)
1 10 24 10.5 13.5
2 20 24 9.3 14.7
3 30 24 8.1 15.9
4 40 24 7.5 16.5
5 50 24 6.2 17.8
6 60 24 5.4 19.65
7 90 24 4.35 20.9
8 120 24 3.1 21.82
9 180 24 2.18 23.65
10 240 24 1.37 23.65
11 300 24 1.37 23.65
12 360 24 1.37 23.65
13 420 24 1.37 23.65
14 480 24 1.37 23.65
15 540 24 1.37 23.65
16 600 24 1.37 23.65
17 1440 24 1.37 23.65
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Table no 18. Batch equilibrium time study Fe(II) onto PCNW
Volume of metal solution = 25 ml
Concentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/L
Adjustable pH = 2.7
S.NO Time (minutes) Initialconcentration
Ci (mg/L)
Equilibriumconcentration
Ce (mg/L)
qt(mg/l)
1 10 23.76 12.88 10.88
2 20 23.76 11.26 12.44
3 30 23.76 10.56 13.2
4 40 23.76 9.14 14.62
5 50 23.76 8.04 15.72
6 60 23.76 6.44 17.26
7 90 23.76 5.5 18.26
8 120 23.76 4.7 19.06
9 180 23.76 3.5 20.26
10 240 23.76 2.84 21.92
11 300 23.76 2.84 21.92
12 360 23.76 2.84 21.92
13 420 23.76 2.84 21.92
14 480 23.76 2.84 21.92
15 540 23.76 2.84 21.92
16 600 23.76 2.84 21.92
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7.5. Batch kinetic study.
Kinetic data for the adsorption of Fe(II) onto CNW & PCNW were analyzed by
using pseudo-first order, pseudo-second order, and second order kinetic models. On
studying these plots, it was found that the adsorption of Fe(II) onto all these adsorbents
follow Pseudo second order kinetic model with high correlation coefficient (R2) value.
R = 0.9697
R = 0.9648
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200Logqe-qt
[mg/L]
Time [minutes]
Figure 15. Pseudo-First order kinetics for adsorption of Fe(II) on to CNW &
PCNW
Fe(II)-PCNW
Fe(II)-CNW
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Table No 19. Batch kinetic study of Fe(II) on CNW
Volume of metal solution = 25 ml
Concentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/L
Adjustable pH = 2.7
R = 0.9962
R = 0.9973
01234
56789
10
0 50 100 150 200
t/qt[g
/mg]
Time [Minutes]
Figure 16. Pseudo-second order kinetic plot for the adsorption of Fe(II)
onto CNW & PCNW
Fe(II)-PCNW
Fe(II)-CNW
R = 0.9734
y = 0.003x + 0.0258
R = 0.913
y = 0.0063x - 0.0786
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 50 100 150 200
1/qe-qt[g/mg]
Time [minutes]
Figure 17. Second order kinetic plot of Fe(II) onto CNW & PCNW
Fe(II)-CNW
Fe(II)-PCNW
Time Initial
Concentration
Ci(mg/L)
Equilibrium
Concentration
Ce (mg/L)
qt (mg/g) qe-qt
(mg/g)
Log(qe-qt)
(mg/g)
1/(qe-
qt)
(g/mg)
t/qt
(min.g/mg)
10 23.76 12.88 10.88 11.04 0.09 1.04 0.91
20 23.76 11.26 12.44 9.48 0.1 0.97 1.6
30 23.76 10.56 13.2 8.72 0.11 0.94 2.25
40 23.76 9.14 14.62 7.3 0.13 0.86 2.73
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Table No 20 . Batch kinetic study of Fe(II) on PCNW
Volume of metal solution = 25 ml
Concentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/L
Adjustable pH = 2.7
Time InitialConcentration
Ci(mg/L)
EquilibriumConcentration
Ce (mg/L)
qt (mg/g) qe-qt(mg/g)Log(qe-qt)
(mg/g)
1/(qe-qt)
(g/mg)
t/qt(min.g/mg)
10 24 10.5 13.5 9.13 0.1 0.96 0.74
20 24 9.8 14.7 7.93 0.12 0.89 1.36
30 24 8.1 15.9 6.73 0.14 0.82 1.83
40 24 7.5 16.5 6.13 0.16 0.78 2.42
50 24 6.2 17.8 4.83 0.2 0.68 2.8
60 24 5.4 16.6 4.03 0.24 0.6 3.22
90 24 4.35 19.65 2.98 0.33 0.47 4.58
120 24 3.1 20.9 1.73 0.57 0.23 5.74
180 24 2.18 21.82 0.81 1.23 0.1 8.24
Infinite 24 1.37 22.63(qe) - - - -
Table No 21. Kinetic parameter, for the Metal biosorption, with correlation coefficient for
Fe++
50 23.76 8.04 15.72 6.2 0.16 0.79 3.18
60 23.76 6.44 17.26 6.66 0.21 0.66 3.47
90 23.76 5.5 18.26 3.66 0.27 0.56 4.92
120 23.76 4.7 19.06 2.87 0.34 0.45 6.29
180 23.76 3.5 20.26 1.66 0.6 0.22 8.8
Infinite 23.76 1.84 21.92(qe) - - - -
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7.6 Batch isotherm study
The effect of concentration on the adsorption of Fe (II) on to different parameter
from CNW & PCNW is shown in the table. The data shows that the percentage of adsorption
decreases with increases in the concentration of Fe(II) ion.
R = 0.9748
R = 0.9803
0
0.5
1
1.5
2
2.5
0 50 100 150 200 250 300 350
Ce
/qe
[g/L]
Ce [mg/L]Figure 18. langmuir adsorption isotherm of Fe(II) onto CNW and PCNW
Fe(II)-PCNW
Fe(II)-CNW
Adsorbent qexp
(mg/g)
Pseudo- first
order
Pseudo-
Second order
Second order
K1
min-1(10-3)
qe R2 K2
min-1(10-3)
qe Vo R2 K21
min-1(10-3)
qe R2
CNW 21.92 0.101 2.63 0.964 0.872 1.55 0.111 0.997 0.609 0.92 0.973
PCNW 22.63 0.812 2.84 0.969 0.913 1.73 0.310 0.996 0.121 1.02 0.913
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Langmuir and Freundlich parameters shown in table were determined from the
slope and intercept of their respective plots. The values of Langmuir equilibrium parameters
which in table lied between 0 and 1 indicated that equilibrium data fits well with language
adsorption Isotherm. The values of 1/n lied between 0 and 1 indicated that adsorption
process was favorable.
R = 0.9829
R = 0.9829
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5 3
logqe
[mg/g]
log Ce [mg/L]
Figure 19. Freundlich adsorption isotherm of fe(II) onto CNW and PCNW
Fe(II)CNW
Fe(II)PCNW
0
50
100
150
200
250
0 100 200 300 400
qe
[mg/L]
Ce [mg/L]
Figure 20. Adsorption isotherm for adsorption of Al(III) onto CNW &
PCNW
Fe(II)-CNW
Fe(II)-PCNW
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Correlation coefficient values for Langmuir isotherms were found to be greater than
that of Freundlich isotherms indicating that the adsorption process is better defined by the
Langmuir adsorption Isotherm model than by the Freundlich, which indicated the
homogenous distribution of active sites of the adsorbent surface. K value is an indicator of
adsorption capacity. Therefore from the above data, it is concluded that the adsorption
capacity of PCNW > CNW.
Another parameter qmaxwhich is the maximum quantity of metal ions per unit mass
of adsorbent to form a complete monolayer on the surface. Higher the value of qmax, higher
is the amount of metal ions adsorbed, qmax value obtained for Fe++onto CNW is 166.66
mg/g & for PCNW is 200 mg/g
Table No. 22 Langmuir and Freundlich parameters and correlation coefficient R2
with the Expt. qmaxfor the adsorption of Fe(II) onto CNW & PCNW.
Table No 23 .Batch isotherm study of Fe(II) onto CNW
Volume of metal solution = 25 ml
Concentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/L
Adjustable pH = 2.7
Adsorbent qmexp.
(mg/g)
Langmuir parameter Freundlich parameter
qm
(mg/g)
b
(L/mg)
R2 K (mg/g) 1/n R2
CNW 165 166.66 0.028 0.974 10.59 0.527 0.980
PCNW 190 200 0.039 0.978 13.96 0.490 0.987
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S.NO Ci(mg/L)
Ce(mg/L)
qe(mg/g)
Ce/qe(l/g)
log Ce
(mg/L)
log qe(mg/L)
%
adsorption
1 5.66 0.41 5.57 0.077 -0.387 0.721 92.66
2 10.61 0.92 9.69 0.099 -0.036 0.986 91.26
3 15.2 1.78 13.42 0.132 0.25 1.384 88.28
4 31.6 4.46 27.14 0.164 0.649 1.433 85.47
5 71.36 15.54 65.79 0.236 1.191 1.818 74.22
6 85.66 22.63 63.03 0.359 0.354 1.435 68.58
7 158.41 59.15 99.26 0.595 0.771 1.512 62.66
8 231.5 112.43 119.07 0.944 2.05 2.075 51.43
9 317.82 168.14 149.68 1.123 2.225 2.175 47.08
10 403.17 233.33 170.81 1.366 2.367 2.232 42.12
11 495.44 313.41 182.03 1.721 2.496 2.26 36.74
Table No 24. Batch Isotherm study of Fe(II) onto PCNW
Volume of metal solution = 25 ml
Concentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/L
Adjustable pH = 2.7
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8. Result and discussion for chromium
8.1 Determination of maxfor Spectrophotometric determination of Cr(VI).
Absorbance Spectra and Calibration Curve for Cr(VI) complex with DPCI. Represents
the absorption spectra of the pink-colored complex of Cr(VI) - diphenylcarbazide complex
in 5 M H2So4solution. The nature of spectra and maxat 540 nm matched with the reported
value. (1, 2, 22)
Figure represents the Lambert - Beer's plot for Chromium (VI)-diphenycarbazide
complex at 540 nm. A linear relation was found between the absorbance of Cr(VI)
diphenylcarbazide complex and the concentration of chromium.
S.NO Ci
(mg/L)
Ce
(mg/L)
qe
(mg/g)
Ce/qe
(l/g)
log Ce
(mg/L)
log qe
(mg/L)
%
adsorption
1 5.66 0.17 5.51 0.03 -0.76 0.74 96.88
2 10.61 0.6 10.01 0.059 -0.22 1 94.28
3 15.2 1.31 13.89 0.094 0.11 1.14 91.36
4 31.6 3.27 28.33 0.115 0.51 1.45 89.64
5 71.36 10.58 60.78 0.174 1.02 1.78 85.16
6 85.66 20.08 65.58 0.306 1.3 1.81 76.55
7 158.41 52.71 105.7 0.498 1.72 2.02 66.72
8 231.5 100.93 130.57 0.772 2 2.11 56.4
9 317.82 145.46 172.36 0.843 2.16 2.23 54.23
10 403.17 222.21 180.93 1.228 2.34 2.25 44.88
11 495.44 302.84 192.6 1.926 2.48 2.28 38.87
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Chromium(VI)solution of 25 mg/L of volumes 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 mL
were taken in a different 25 mL volumetric flask and was acidified with 1 mL of 5 M
H2SO4solution. Then 1 mL of 0.25% DPCI solution was added to each volumetric flask
and shaken well for 20 minutes. The volume was made up to the mark by adding water.23
The absorption spectra of pink colored Chromium (VI) diphenylcarbazide complex was
recorded by using systonic spectrophotometer-103 against blank solution. At max the
absorbance of all the solution were measured against reagent black using same
spectrophotometer and calibration curve was drawn. The absorbance spectra and calibration
curve
Table 25. Determination of maxof Cr(VI) with DPCI complex.
0
0.1
0.2
0.3
0.4
0.5
0.6
400 450 500 550 600
[Absorbance]
[Wavelength nm]
Figure 21. Plot of absorbane Vs. wavelength for the determination
of max.
S.N. Wave length
(nm)
Absorbance
1 400 0.06
2 410 0.07
3 420 0.09
4 430 0.1
5 440 0.1
6 450 0.13
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8.2 Construction of calibration curve for Cr(VI)
7 460 0.15
8 470 0.18
9 480 0.22
10 490 0.26
11 500 0.29
12 510 0.34
13 520 0.42
14 530 0.48
15 540 0.56
16 550 0.49
17 560 0.38
18 570 0.27
19 580 0.13
20 590 0.09
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Table No 26. Construction of calibration curve for Cr(VI)
8.3. Effect of pH studies
R = 0.9994y = 0.6933x + 0.006
0
0.1
0.2
0.3
0.4
0.5
0.6
0 0.2 0.4 0.6 0.8 1
[Absorban
ces]
[Concentration ppm]
Figure 22. Calibration curve for the determination of concentration of Cr(VI) DPCI
complex.
S.NO Concentration in g/L Absorbance
1 0.1 0.08
2 0.2 0.14
3 0.3 0.22
4 0.4 0.29
5 0.5 0.35
6 0.6 0.42
7 0.7 0.49
8 0.8 0.56
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Figure shows the effect of pH in the adsorption of Cr(VI) onto CNW at an initial
concentration of 25 ppm at laboratory temperature. The amount of adsorption decreases
from 100 to 26.66 %. When the pH of the solution increased from 1 to 6. This indicates that
the adsorption of chromium is clearly dependent on pH. It is obvious that pH determines the
extent of the Cr(VI) removal as well as providing a favorable removal adsorbent surface
charge for the adsorption to occur. At low pH, chromium exists as HCrO4-. The reason of
maximum adsorption at low pH is due to the favourable complexation of the chromium with
polyphenolic/ polyhydroxy functional groups of the CNW. From the batch pH studies it was
found that the adsorption of Cr(VI) is found to be effective at pH 1 & 2.
Table No 27. Batch pH study for Cr(VI) onto CNW
0
20
40
60
80
100
120
0 1 2 3 4 5 6 7
Adsorption[%]
[pH]
Figure 23. Effect of pH on removal of Cr(VI) on to CNW
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Volume of metal solution = 25 ml
Concentration of metal solution = 25 mg/L
Amount of adsorbent = 25 mg/L
8.4. Batch kinetic studies
Kinetic studies for the adsorption of Cr(VI) onto CNW studied using pseudo-first
order (Lagergren, 1989) pseudo-second order (Ho, et. al.1995 and Ho and Mckay et. al.
2000) and second order (Lagergren, 1898) model. It was observed experimentally from the
present studies that the adsorption kinetics behavior of Cr(VI) onto these adsorbent was
found to follow only pseudo-second order kinetic model but not pseudo-first order model
and second order model.
For 1st order model the plot of log [qe-qt] versus t should be a straight line with -
ve slope value but when we plot this values we get a line with +ve slope value. Similarly
for second order when we plot a graph between1/[qe-qt] versust we should not get a
straight line with +ve value of slope. So we concluded that the adsorption process does not
follow pseudo 1storder model and second order model.
But when we plot a graph for t/qt versust we get a straight line with slope having
+ve value according to pseudo second order model. So adsorption studies of Cr(VI) on
CNW follow pseudo-second order kinetic model. This is represented in Figure .
S.NO pH Initialconcentration