adsorptive removal and recovery of aluminium (iii), iron (ii) and chromium (vi) onto a low cost...

7/25/2019 ADSORPTIVE REMOVAL AND RECOVERY OF AlUMINIUM (III), IRON (II) AND CHROMIUM (VI) ONTO A LOW COST FUNC

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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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Institute of Science & Technology


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


......................... .......................

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


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


20/77

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


21/77

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


22/77

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)


23/77

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.


24/77

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.


25/77

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


26/77

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


27/77

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


28/77

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


29/77

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


30/77

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


31/77

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


32/77

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


33/77

Table No 5. Batch kinetic study of Al(III) onto CNW

Volume of metal solution = 25 ml


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 - - - -


34/77

Table No 6. Batch kinetic study of Al(III) onto PCNW


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


35/77

4.5 Batch equilibrium time study

Table No 8. Batch equilibrium time study of Al(III) onto CNW.




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


36/77


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


37/77

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


38/77

Table No 10. Batch Isotherm study of Al(III) onto CNW




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


39/77

Table No 11. Batch Isotherm study of Al(III) onto PCNW

Volume of metal solution = 25 mlConcentration of metal solution = 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


40/77

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


41/77

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.


42/77

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


43/77

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


44/77

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




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


45/77

Table No 16. Effect of pH on the adsorption of Fe(II) onto PCNW




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


46/77

Table No 17. Batch equilibrium time study of Fe (II) onto CNW




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


47/77

Table no 18. Batch equilibrium time study Fe(II) onto PCNW




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


48/77

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


49/77

Table No 19. Batch kinetic study of Fe(II) on CNW




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


50/77

Table No 20 . Batch kinetic study of Fe(II) on PCNW




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) - - - -


51/77

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


52/77

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


53/77

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




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


54/77

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




Adjustable pH = 2.7


55/77

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


56/77

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


57/77

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


58/77

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


59/77

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


60/77




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

adsorptive removal and recovery of aluminium (iii), iron (ii) and chromium (vi) onto a low cost...

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