sorbent impregnated by nano manganese dioxide and its applications for uranium separation

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Synthesis of a New Amberlite 7HP Sorbent Impregnatedby Nano Manganese Dioxide and Its Applications forUranium SeparationO. A. Elhefnawy a , W. I. Zidan a , M. M. Abo-Aly b , E. M. Bakier b & G. A. Al-Magid ba Egyptian Nuclear and Radiological Regulatory Authority (ENRRA) , Cairo , Egyptb Chemistry Department, Faculty of Science , Ain Shams University , Cairo , EgyptAccepted author version posted online: 27 Feb 2013.Published online: 03 Dec 2013.

To cite this article: O. A. Elhefnawy , W. I. Zidan , M. M. Abo-Aly , E. M. Bakier & G. A. Al-Magid (2014) Synthesis of a NewAmberlite 7HP Sorbent Impregnated by Nano Manganese Dioxide and Its Applications for Uranium Separation, SpectroscopyLetters: An International Journal for Rapid Communication, 47:2, 131-146, DOI: 10.1080/00387010.2013.773519

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Synthesis of a New Amberlite 7HPSorbent Impregnated by Nano Manganese

Dioxide and Its Applications forUranium Separation

O. A. Elhefnawy1,

W. I. Zidan1,

M. M. Abo-Aly2,

E. M. Bakier2,

and G. A. Al-Magid2

1Egyptian Nuclear and

Radiological Regulatory

Authority (ENRRA), Cairo, Egypt2Chemistry Department, Faculty

of Science, Ain Shams University,

Cairo, Egypt

ABSTRACT In this work, a commercially available Amberlite 7HP has been

modified using nano-flakes MnO2 prepared by a simple reduction method.

The characterization of the new sorbent impregnated by nano manganese

dioxide was performed by scanning electron microscope, transmission elec-

tron microscope, energy-dispersive X-ray, X-ray diffraction, and Fourier

transformation infrared spectrometric analyses. The performance of the

new sorbent for UO2þ2 ion separation in aqueous medium was studied in

detail by varying the pH, contact time, initial concentration, bed height,

and flow rate. The maximum sorption has been achieved at a solution of

pH 3.1. Sorbed UO2þ2 ions were desorbed with 10mL of 1.5M HCl solution.

The kinetics and isothermal parameters of the sorption of UO2þ2 ions

onto the new sorbent have been studied. The kinetic experimental data

properly correlate with the second-order kinetic model and the time

required to reach sorption equilibrium is 240min. The sorption data

could be well interpreted by the Langmuir sorption isotherm and the mono-

layer sorption capacity was found to be 56.3mg � g�1. The sorption data

were fitted to two well-established fixed-bed sorption models, namely, Tho-

mas and Yoon–Nelson models, with a correlation coefficient, R2, �0.993.

The separation performance of the new sorbent was demonstrated by

using different real samples. Consequently, the developed sorbent resin

was successfully utilized for the separation of uranyl ions in safeguard

applications.

KEYWORDS characterization, fixed-bed sorption models, nano-flakes manganese

dioxide, nuclear safeguard applications, sorption

INTRODUCTION

Quantitative determination of uranium in nuclear materials, those from

uranium mining and processing, and through site evaluation of radioactive

waste disposal repository has received much attention.[1] Different methods

Received 14 December 2012;accepted 3 February 2013.

Address correspondence toM. M. Abo-Aly, ChemistryDepartment, Faculty of Science, AinShams University, Cairo, Egypt.E-mail: [email protected]

Spectroscopy Letters, 47:131–146, 2014Copyright # Taylor & Francis Group, LLCISSN: 0038-7010 print=1532-2289 onlineDOI: 10.1080/00387010.2013.773519

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such as solid-phase extraction, precipitation,

electrolysis, column chromatography, and ion

exchangers were used for the assessment of uranium

by extraction from interfering elements followed by

determination.[2–7] A number of analytical methods

are also reported for uranium determination,

including spectrophotometry, spectrofluorometry,

gravimetry, colorimetry, or inductively coupled

plasma–atomic emission spectrometry.[8]

Uranium uptake has also been investigated by

adsorption on a variety of economically priced sorbents

such as calcined phosphate, bone char, Bentonite,

natural scolecite, and magnetic nano-sorbents.[9–13]

Themaindefects of thesematerials are their lowadsorp-

tion capacity compared to the resins, the complexity in

removing the adsorbed uranium, the impurity of these

adsorbents, and their low selectivity.

Nanostructure materials have attracted great atten-

tion in both fundamental and applied research areas

because of their specific functionality and large specific

surface areas leading to exceptional properties and

high sorption capacities.[14] In addition, nano-sorbents

are highly mobile in porous media since they are much

smaller than the relevant pore spaces.[15]

The choice of the sorbent is a key point because it

can control the analytical parameters such as

selectivity, affinity, and capacity. In order to increase

the sorption capacity, to enhance the removal

efficiency, and to add selectivity to the solid phases,

modification and impregnation techniques have been

engaged. Therefore, new adsorbents based on mol-

ecular-imprinted polymers, activated carbon, carbon

nano-tubes, metal oxide nano-particles, and modified

silica[16–21] have been recently found as alternatives

to conventional solid-phase extraction materials.

Although previous research has focused on the

ability of metal oxide nano-sorbents for metal ion

sorption, few metal ions were really tested.[22–24] For

example, manganese oxide, which plays a major role

in controlling trace metal concentration via sorption

and co-precipitation processes were reported.[25]

In the present study, the new composite Amberlite

7HP impregnated by manganese dioxide

(7HPNMnO) has been prepared and characterized

as a nano-sorbent for UO2þ2 ion separation in safe-

guard applications. Separation process modeling in

both batch and dynamic modes is presented. In

addition, applications of the synthesized resin for

separation of uranyl ions of collected real samples

from Egyptian nuclear facilities and other locations

for safeguard verification purposes are examined.

EXPERIMENTAL

Instrumentation

Inductively coupled plasma optical emission spec-

trometer ICP-OES (Thermo Fisher Scientific iCAP

6500, Manchester, UK) with ITEVA operating software

for control of all instrument functions and data (maxi-

mum concentration of samples was 50mg � L�1) and

a UV-visible spectrophotometer (Thermo-Evolution

300, Thermo Scientific, Manchester, UK) were used for

determination of uranium at a wavelength of 650nm

and at a maximum concentration of 4mg � L�1. Trans-

mission electron microscope (TEM) images were

obtained using a JEOL JEM-2100 instrument (JEOL,

Tokyo, Japan) using an accelerating voltage of 200kV.

Samples were ultra-sonicated in ethanol for 15min

and then dispersed on copper grids. Structure and

purity of the modified resin was verified by means

of X-ray powder diffraction technique on a PANalyti-

cal apparatus with X’pert PRO software (PANalytical,

Almelo, The Netherlands). Surface morphology and

distribution of MnO2 on the resin was analyzed using

scanning electron microscopy (SEM), with an energy-

dispersive X-ray (EDX) detector from JEOL, 6510 LA

(JEOL, Tokyo, Japan). Fourier transform infrared

(FTIR) spectra were measured at room temperature

in the wavenumber range (400–4000 cm�1), on a Jasco

FT=IR-6100 (JASCO, Easton, Maryland, USA). The

pH values were measured on a Metrohm Herison

digital pH meter (780, Metrohm Herison, Herisau,

Switzerland). All experiments were carried out in

a safeguarded destructive analysis laboratory (ETZ-,

KMP-I) at the Egyptian Nuclear and Radiological

Regulatory Authority (ENRRA).

Reagents and Chemicals

All solutions were prepared in deionized water.

Amberlite 7HP, having 450m2 � g�1 average surface

area, was obtained from Sigma (Miami, Florida,

USA); uranyl nitrate UO2(NO3)2 � 6H2O (Mallinck-

rodt, Dublin, Ireland) was procured from local

market (U235 wt. percent, 0.07%); potassium

permanganate KMnO4, 65% nitric acid, 68%

ammonia solution, and the buffer solutions were

purchased from Merck (Darmstadt, Germany); 0.2%

O. A. Elhefnawy et al. 132

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Arsenazo (III) and ethanol were provided by Aldrich

(Taufkirchen, Germany); 36% hydrochloric acid

(Fisher Chemicals, Waltham, Massachusetts, USA)

and EDTA disodium salt (Acros, Thermo Fisher

Scientific, Geel, Belgium) were also used.

Methods

Preparation of Nano-MnO2

Nano-MnO2 was prepared by a simple reduction

method, which was previously used in preparing

manganese dioxide, as follows:[26]

2KMnO4 þ 8HCl ! 2MnO2 þ 2KClþ 3Cl2 þ 4H2O

ð1Þ

3.16 g of potassium permanganate were dissolved in

50mL deionized water in a beaker. Then, 8mL of

36% hydrochloric acid were added dropwise to this

solution with continuous stirring and heating on a

hot plate at 90�C. A suspension was then obtained

after stirring for 1 hr without heating. The formed

suspension was then washed several times using

deionized water and was air dried overnight at

90�C instead of 100�C as normally done[26] in a trial

to prepare nano-flakes of MnO2.

Preparation of 7HPNMnO

4 g of Amberlite -7HP resin were mixed in a beaker

with a heated KMnO4 solution (3.16 g in 50mL deio-

nized water) at 90�C. The mixture was then stirred

with dropwise addition of 8mL of 36% hydrochloric

acid. The formed suspension after 1 hr stirring with-

out heating was washed several times using deio-

nized water (to remove free potassium and chloride

ions), then air dried in an oven at 90�C for 24 hr

and finally stored in a polypropylene bottle for use.

pHPZC Determination of the Solid 7HPNMnO

The pHPZC value (the pH at which the surface

charge density is zero) was obtained as previously

described,[27] by dissolving 1 g of 7HPNMnO in

100mL of 0.1M KNO3 as a background electrolyte,

with initial pH range 1–12.

pHPZC was found to be 5.8; below this value, the

7HPNMnO surface is positive, and above it, the

surface becomes negative. So at a pH< 5.8, UO2þ2

ions become sorbed through a chemisorption mech-

anism, and above it, the sorption occurs through

electrostatic interactions. This suggests the possibility

of involvement of a chemisorption mechanism in this

sorption process.[28]

Static Method

0.05 g of 7HPNMnO was equilibrated with 20mL

of sample solution with initial concentration of

500 mg �mL�1 in a 100-mL well-stopped reagent bot-

tle at 100 rpm on a magnetic stirrer. Because of the

higher sorption capacity of 7HPNMnO, a small bed

height was chosen to examine its behavior against

the effect of pH, contact time, and initial metal ion

concentration. The adsorbed ions on the modified

resin were then desorbed by using HCl and

were determined spectrophotometrically using the

Arsenazo (III) method for uranium ion assay.[29]

The obtained data in batch model studies were used

to calculate the equilibrium capacities via Eq. (2):[30]

qe ¼VðC0 � CÞ1000m

ð2Þ

where qe is the equilibrium capacity (mg � g�1); V is

the sample volume (liters); C0 and C (mg � L�1) are

the initial and the effluent metal ion concentrations,

respectively; and m is the dry weight of the sorbent (g).

Kinetic Modeling

The pseudo-first-order,[31] pseudo-second-

order,[32,33] Elovich,[34] and intraparticle diffusion

models[35–37] were applied to interpret the experi-

mental data of the investigated sorption process.

Pseudo-First-Order Model

The pseudo-first-order equation describes the

sorption in solid–liquid systems and is based on

the sorption capacity of solids.[31] It was assumed that

one UO2þ2 ion is adsorbed by one sorption site on the

modified resin surface:

Aþ UO2þ2aq �!

k1AUO2þ

2solid phase ð3Þ

where A represents an unoccupied sorption site and

k1 is the pseudo-first-order rate constant. The linear

form of the pseudo-first-order model can be

expressed via Eq. (4):

lnðqe � qÞ ¼ ln qe � k1t ð4Þ

133 Synthesis of New Amberlite 7HP Sorbent

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where qe and q (mg � g�1) are the sorption capacities

at equilibrium and at time t (min), respectively, and

k1 is the rate constant of the first-order sorption

process (min�1).

Pseudo-Second-Order

The pseudo-second-order rate expression has

been applied for analyzing chemisorption

kinetics.[32,33] This model assumes that one UO2þ2

ion is adsorbed by two sorption sites on the modified

resin surface:

2Aþ UO2þ2aq �!

k2A2UO

2þ2solid phase ð5Þ

where A represents an unoccupied sorption site

and k2 is the pseudo-second-order rate constant

(g �mg�1 �min�1). The pseudo-second-order rate

model is linearly expressed via Eq. (6):

t

q¼ 1

k2 q2eþ t

qeð6Þ

The batch kinetic data were fitted to both of the

above models. The initial sorption rate, h (mg � g�1 �min�1), when t! 0, is expressed by Eq. (7):[38]

h ¼ k2 q2e ð7Þ

where k2q2e, h, and mg � g�1 �h�1 is defined as the

initial sorption rate.

Elovich Model

The Elovich equation[34] is applicable to the

chemisorption kinetics in solutions, involving

valence forces through sharing or exchange of

electrons between sorbent and sorbed materials.[39]

The linear form of the Elovich equation is given by

Eq. (8):[34]

q ¼ 1

b

� �lnðabÞ þ 1

b

� �lnðtÞ: ð8Þ

Intraparticle Diffusion Model

The sorption of metal ions from the aqueous

solution onto the solid phase is a multistep process

including transport of metal ions from the aqueous

phase to the surface of solid particles as a first step

(bulk diffusion), and a second step occurs by

diffusion of metal ions into the boundary layer of

the solid particles (film diffusion), followed by a

third step where transport of metal ions from the

surface to the interior pores (pore diffusion or intra-

particle diffusion) occurs. The later step is likely to

be a slow process. In addition, sorption of metal ions

by an active site on the solid-phase surface could

also occur through chemical processes. The metal

ion sorption is usually controlled by either the

intraparticle or the liquid-phase mass transport

rates.[35] The intraparticle diffusion model pro-

posed by Weber and Morris can be applied using

Eq. (9):[36]

qt ¼ Kidt0:5 þ I ð9Þ

where qt is the adsorbed amount at time t, and Kid is

the intraparticle diffusion rate constant. Values of

I give an idea about the thickness of the boundary

layer.[37]

Isothermal Modeling

Langmuir Equation Model

UO2þ2 ion isothermal sorption data using different

initial concentrations were investigated by the Lang-

muir model via Eq. (10):[40]

C

qe¼ 1

kLqmþ C

qmð10Þ

where qe is the equilibrium metal ion concentration

on the sorbent (mg � g�1), qm is the monolayer

capacity of the sorbent (mg � g�1), C is the

equilibrium metal ion concentration in solution

(mg � L�1), and KL is the Langmuir sorption constant

(L �mg�1). A plot of C=qe vs. C gives a straight line

of slope 1=qm and intercept 1=(KL qm). The Langmuir

equation is applicable to homogeneous sorption,

where the sorption of each sorbed molecule

onto the surface has equal sorption activation

energy.

Freundlich Equation Model

The logarithmic expression of the Freundlich

equation is given in Eq. (11):[41]

Log qe ¼ Log kf þ1

n

� �LogC ð11Þ


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where C is the equilibrium metal ion concentration in

solution (mg � L�1), and Kf (mg � g�1) and n are the

Freundlich constants for sorption capacity and sorp-

tion intensity, respectively. The Freundlich equation

is employed to describe heterogeneous systems

and reversible sorption and is not restricted to the

formation of monolayer.

To evaluate the nature of the adsorption reaction,

the data were analyzed with the nonlinear fitting

using Eqs. (12) and (13):[42]

Langmuir model:

qe ¼qm KLCe

1þ KLCeð12Þ

Freundlich model:

qe ¼ KFCð1=nÞ: ð13Þ

Column ‘‘Dynamic’’ Method

7HPNMnO was uniformly packed in a glass

column within the mass range (0.2–0.5 g) with

30 cm length and an internal diameter of 10mm.

Special rubber tubes of 2mm internal diameter and

a calibrated peristaltic pump was used for feeding

the sample through the column using different flow

rates. The column washed several times by deio-

nized water. A stock solution of UO2þ2 ions was

prepared by dissolving an appropriate amount of

UO2(NO3)2 � 6H2O in deionized water and the initial

pH of the working solutions was adjusted by

addition of HNO3 or NH3 solution. A sample solution

containing UO2þ2 ions was passed down through the

column and desorbed with 1.5M HCl. UO2þ2 ion

concentration was determined in the aqueous phase

spectrophotometrically using the Arsenazo (III)

method at 650 nm.[29]

The loading behavior of UO2þ2 ions adsorbed from

aqueous solution onto a fixed bed is usually

expressed in terms of C=C0 as a function of time or

the volume of the sample at a constant amount of

resin, thus allowing the corresponding breakthrough

curve to be constructed. The maximum column

capacity, qtotal (mg), for a given feed concentration

and flow rate, Q, is equal to the area under the curve

of adsorbed UO2þ2 ions and obtained by plotting the

adsorbed amount, Cad (mg � L�1), versus time t (min)

as given in Eq. (14):[43]

qtotal ¼QA

1000¼ Q

1000

Z t¼t

t¼0

Ctotalad dt ð14Þ

The equilibrium capacity (qe) is the amount of

UO2þ2 ions adsorbed per unit mass of dry sorbent

(mg � g�1) in the column and is expressed via

Eq. (15):[43]

qe ¼qtotal

mð15Þ

where m is the total mass of dry sorbent in the

column.

Thomas Model

The Thomas model was used to predict the sorp-

tion performance. The nonlinear form of the model

is expressed via Eq. (16):[44]

C

C0¼ 1

1þ exp KTh

Q ðqThm� C0VÞh i ð16Þ

where kTh is the Thomas rate constant in mL �min�1 �mg�1, qTh is the uptake of UO2þ

2 ions per g of

sorbent at equilibrium (mg � g�1), and the quantities

m, C0, C, and Q are as previously defined. The

expression for the linear Thomas model is expressed

via Eq. (17):[45]

lnC0

C� 1

� �¼ KThqThm

Q� KThC0V

Qð17Þ

Thomas model parameters were obtained from the

plot of ln[(C0=C)� 1] vs. V at a given flow rate.

Yoon–Nelson Model

Yoon and Nelson were theoretically applied to

describe the sorbate diffusion inside the sorbent,

from which developed a relatively simple model

addressing the sorption and breakthrough of the

sorbate. It is expressed via Eq. (18):[46]

C

C0¼ expðKYNt�sKYNÞ

1þ expðKYNt�sKYNÞð18Þ


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The linearized Yoon–Nelson model for a

single-component system is expressed via Eq. (19):[46]

lnC

C0 � C¼ KYNt�sKYN ð19Þ

where KYN (min�1) is the rate velocity constant, and t

(min) is the time required for 50% adsorbate break-

through. From a linear plot of ln[C=(Co�C)] against

sampling time t, the sorption capacity qYN was

expressed relative to Co and Q via Eq. (20):[47]

qYN ¼ QC0 sm

: ð20Þ

Error Analysis

A nonlinear regressive method of error analysis

was employed in the present study. This method

gives the average mean square error (MSE) value,

which is the sum of the squares of the differences

between the experimental data and those calculated

from the models. MSE values were calculated using

Eq. (21):[45]

MSE ¼ 1

N

XN1

½ðCexp=C0Þ � ðCcal=C0Þ�2 ð21Þ

where (Ccal=C0) is the ratio of UO2þ2 ions effluent to

the initial concentration and was obtained by calcu-

lation from the model, and (Cexp=C0) is the same

experimentally obtained ratio.[44] If the data from

the model are similar to the experimental data,

(MSE) will have small values; in contrast, if the data

are different, then (MSE) will acquire higher values.

In order to confirm the best model for the column

sorption system, it is necessary to analyze the data

using the values of (MSE) combined with those of

the correlation coefficient (R2).

RESULTS AND DISCUSSION

Characterization Studies

Figures 1(A) and (B) show the TEM images of the

nano-MnO2, which give the morphology of the

nano-MnO2. TEM images of the nano-MnO2 show a

network-like structure and the formation of a loosely

packed microstructure in the nanometer scale.[48]

The electron diffraction pattern is shown in Fig. 2

showing bright spots in a circular pathway. This

strongly supports the crystalline nature of the

prepared MnO2.[48]

The SEM and EDX studies give information on the

surface morphology and distribution of MnO2 on the

resin. In the case of EDX spectra, a number of spots

were taken to confirm the presence of MnO2 on the

surface of the resin. Figures 3–6 show the represen-

tative SEM images and EDX spectra of the resin

before and after modification as well as after UO2þ2

ion sorption on the resin.

Figure 7 shows a comparison of the X-ray diffrac-

tion (XRD) patterns of nano-manganese dioxide (A),

7HPNMnO (B), and Amberlite 7HP (C). The rep-

resentative diffraction peaks occurring at 25.5, 37.2,

and 67.3 degrees for sample A are the characteristic

peaks of MnO2, which are also similar to the pre-

viously reported peaks for MnO2.[31] The diffraction

peaks of MnO2 are found also in sample B with a

slight shift of the 25.5-degree peak to 28.55 degrees

and the appearance of two peaks at 37.41 and

41.73 degrees and also the appearance of two other

peaks at 65.31 and 68.73 degrees in compound B,

indicating that the resin was impregnated by MnO2.

FIGURE 1 A, B: TEM images of prepared nano-MnO2.

FIGURE 2 Electron diffraction pattern of prepared nano-MnO2.


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Figure 8 shows the FT-IR spectra of the samples

A, B, and C. In sample A, several absorption bands

can be observed at 3408.57, 1624.7, 1406.82,

1023.05, 516.829, and 453.19 cm�1. The band at

3408.57 cm�1 should be attributed to the –OH

stretching vibration, and the bands at 1624.7,

1406.82, and 1023.05 cm�1 are usually attributed to

the –OH bending vibrations bonded to Mn atoms,

while the bands at 516.829 and 453.19 cm�1 rep-

resent normal stretching and bending modes of

the Mn–O bond, respectively.[48] The peaks of

MnO2, which are found in sample B (7HPNMnO)

with slight shifts at 3415.2, 1608.8, 1453.75, 1004,

555.2, and 418.4 cm�1, can be assigned to MnO2

loaded on Amberlite 7HP; the slight shifts in normal

stretching and bending modes of the Mn–O bonds

suggest that nano-MnO2 particles are distributed

throughout the pores of Amberlite 7HP as a

composite material.

Factors Affecting theSeparation Process

Effect of pH

Experiments were performed to find the optimum

pH of the sorption of UO2þ2 ions onto 7HPNMnO

nano-sorbents using a range of initial pH values from

0.5 to 3.7. A pH value of 3.7 was not exceeded, since

increasing pH to 4.0, at fixed values of other vari-

ables, resulted in the precipitation of uranyl ions.[49]

Therefore, it was not possible to carry sorption

experiments for UO2þ2 ions at pH> 3.7. Figure 9

shows the effects of pH on the sorption of UO2þ2

ions. As seen, the removal of UO2þ2 ions is clearly

pH dependent with a maximum removal efficiency

of 66.5% at pH¼ (3.1� 0.3). Due to the optimum

pH<pHpzc, the surface of the resin was positive,

which suggests the possibility of involvement of a

chemisorption mechanism in the sorption process.[28]

FIGURE 3 A: SEM and photographs of prepared nano-MnO2. B: EDX spectrum of prepared nano-MnO2. (Color figure available online.)

FIGURE 4 A: SEM photographs of Amberlite 7HP. B: EDX spectrum of Amberlite 7HP. (Color figure available online.)


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FIGURE 6 A: SEM photographs of 7HPNMnO and after UO2þ2 ion sorption. B: EDX spectrum of 7HPNMnO and after UO2þ

2 ion sorption.

(Color figure available online.)

FIGURE 7 XRD patterns of samples. A: Prepared nano-MnO2.

B: 7HPNMnO. C: Amberlite 7HP. (Color figure available online.)

FIGURE 8 FTIR spectra of samples. A: Prepared nano-MnO2.

B: 7HPNMnO. C: Amberlite 7HP.

FIGURE 5 A: SEM photographs of 7HPNMnO. B: EDX spectrum of 7HPNMnO. (Color figure available online.)


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Effect of Contact Time

The effect of contact time on the UO2þ2 ions sorp-

tion on 7HPNMnO was investigated by mixing 20mL

of 500mg � L�1 uranyl solution at pH of 3.1 with

50mg of 7HPNMnO. The removal of UO2þ2 ions by

the sorbent as a function of contact time is shown

in Fig. 10. It was observed that the amounts of

UO2þ2 ion sorption increases with contact time

increase.

Modeling of Sorption Kinetics

In order to determine the kinetics of the sorption

process, the pseudo-first-order, pseudo-second-

order, and Elovich models were fitted to the experi-

mental data. The resulted values of the regression

coefficient (R2) for these models are given in

Table 1. The sorption kinetics of UO2þ2 ions onto

7HPNMnO were investigated by mixing 20mL of a

solution containing 500mg � L�1 UO2þ2 ions with

50mg of 7HPNMnO at pH of 3.1. The sorption

capacity was obtained by determining the amount

of uranium remained in the solution. In this experi-

ment, the time required to reach sorption equilib-

rium is 240min. The results of the kinetic

parameters of the pseudo-first-order model are

calculated by Eq. (4) and indicated in Table 1.

The pseudo-second-order kinetic model fits at cor-

relation coefficient R2¼ 0.999, higher than that

derived from pseudo-first-order model fits. The good

agreement between this model and the experimen-

tally observed equilibrium sorption capacity suggests

that UO2þ2 ion sorption follows pseudo-second-order

kinetics and UO2þ2 ions were sorbed onto

nano-MnO2 surface via chemical interaction. The

results of the kinetic parameters for UO2þ2 ion sorp-

tion are calculated by Eqs. (6) and (7) and are given

in Table 1.

Elovich parameters and the corresponding corre-

lation coefficient value (R2) calculated by Eq. (8)

are given in Table 1. This table confirmed that the

Elovich model also fits well with the experimental

data with a high correlation coefficient. This suggests

that the sorption of the studied systems may be of a

chemisorption type involving valence forces through

sharing or exchange of electrons between sorbent

and sorbed.FIGURE 10 Effect of contact time on the sorption of UO2þ

2 ions

on 7HPNMnO.

TABLE 1 The Kinetic Parameters of UO2þ2 Ion Sorption on

7HPNMnO, at pH 3.1 and qe¼ 53.2mg �g�1

Model Parameters Value

Pseudo-first-order K1 (min�1) 0.010

qe (mg �g�1) 18.306

R2 0.942

Pseudo-second-order K2 (g �mg�1 �min�1)(�10�4) 0.003

qe (mg �g�1) 54.525

h (mg �g�1 �min�1) 9.531

R2 0.999

Elovich a (mg �g�1 �min�1) 5.125

b (g �mg�1) 0.196

R2 0.987

Intraparticle diffusion Kid1 (mg �g�1 �min�0.5) 1.750

I1 6.874

R2 0.992

Kid2 (mg �g�1 �min�0.5) 0.34

I2 13.4

R2 0.995

FIGURE 9 Effect of pH on the sorption of UO2þ2 ions on

7HPNMnO.


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Finally, intraparticle diffusion parameters were

calculated from the slope and the intercept of the

linear plot as expressed in Eq. (9) and reported in

Table 1. Fig. 11 displays the plot of qt vs. t0.5 and

shows that the obtained straight lines do not pass

through the origin (I> 0). The deviation of straight

lines from the origin as shown in the figure may be

because of the difference between the rate of mass

transfer in the initial and final steps of the sorption

process; such deviation of straight line from the ori-

gin indicates the greater effect of the boundary layer

thickness.[37] From Fig. 11, it may be seen that there

are two separate regions: the first region was attribu-

ted to the film diffusion, which has higher intraparti-

cle diffusion rate constant Kid1 and lower I1, while

the second region is due to intraparticle diffusion,

which has a lower intraparticle diffusion rate

constant Kid2 and higher I1, indicating that the film

diffusion occurs faster than the pore diffusion.[50]

This means that the intraparticle diffusion, although

important over longer contact time periods, is not

the rate-limiting step in the sorption process.[51–53]

Isothermal Modeling

The isothermal sorption experiments were con-

ducted by mixing 20mL of different concentrations

of uranyl solution at pH 3.1 with 50mg of

7HPNMnO; the data was then modeled by using a

nonlinear form of Langmuir equation as shown in

Fig. 12. The Langmuir isotherm is valid for mono-

layer sorption due to a surface composed of a finite

number of identical sites and is expressed in the

linear form using Eq. (10). This suggests that the

sorption of UO2þ2 ions by the 7HPNMnO was homo-

geneous, forming a monolayer on the adsorbent sur-

face. It is noteworthy that the Langmuir model

assumes that sorption occurs on a homogeneous

surface. The data may also be explained by the

Freundlich equation, as in Eq. (11). The values of

qm, KL, Kf, 1=n, and the correlation coefficient (R2)

for Langmuir and Freundlich models are reported

in Table 2. The data in Table 2 indicate that the sorp-

tion of UO2þ2 ions on 7HPNMnO correlate well with

the Langmuir model (R2¼ 0.999) as compared to the

Freundlich one (R2¼ 0.949) and also as shown in

Fig. 12. These results strongly support that the

Langmuir model is the best-fitting one within the

experimental conditions considered in this study.

Effect of Various Parameters on

Breakthrough Curves

Operational parameters such as bed height (Z),

flow rate (Q), and initial concentration (Co) are

important factors in column design, so the effect of

these parameters on the sorption capacity of

7HPNMnO was studied for the UO2þ2 ions’ uptake.

FIGURE 11 The intraparticle diffusion model for adsorption of

uranyl ions on 7HPNMnO.FIGURE 12 Nonlinear fit of Langmuir and Freundlich

isothermal models. (Color figure available online.)

TABLE 2 Calculated Parameters of the Langmuir and

Freundlich Isotherm Models

Langmuir constants Freundlich constants

qm (mg �g�1) KL (L �mg�1) R2 1=n Kf (mg �g �1) R2

56.275 0.042 0.999 0.402 6.208 0.949


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Breakthrough curves representing the effects of (Q)

on column performance with experimental data are

shown in Fig. 13. It is obvious that the breakthrough

and exhaustion times shifted to earlier time scale by

the effect of increasing (Q). The sorption capacities

also increased with decreasing (Q). The sorption

capacity was found to have the 59.147, 56.745, and

55.137mg � g�1 values at (Q) of 1, 2, and 3mL.min�1,

respectively, and is given in Table 3. This may be

due to insufficient residence time of the solute in the

column at higher (Q) values.

Figure 14 shows the breakthrough curves

obtained for UO2þ2 ion sorption on the 7HPNMnO

at different (Z) values of 1, 2, and 3 cm, at a constant

(Q) of 1mL.min�1 and UO2þ2 ion inlet concentration

of 540 (mg � L�1). From Fig. 14, the breakthrough

time increased with increasing Z. As Z increased,

the UO2þ2 ions had more contact time with

7HPNMnO, which leads to higher removal efficiency

of UO2þ2 ions from the column. Higher bed column

resulted also in a drop of the solute concentration

in the effluent at the same time. The slope of break-

through curves was slightly decreased with increas-

ing Z, leading to a broad mass transfer zone.[54]

In order to investigate the effect of Co on the sorp-

tion of UO2þ2 ions onto 7HPNMnO, Z and Q values

were kept constant at 3 cm and l mL.min�1, respect-

ively, while the value of Co was varied in the range of

400–700 (mg � L�1). Results are depicted in Fig. 15. It

was found that the uptake capacity increased with an

increase in Co. The larger the Co, the steeper is the

slope of the breakthrough curve and the smaller is

the sorption time. This can be explained by the fact

that more sorption sites are being covered with

increasing Co. These results demonstrate that the

change in concentration gradient affected the satu-

ration rate. As the Co increases, the UO2þ2 ion loading

rate increases, as does the driving force or mass

transfer, which results in a decrease in the sorption

zone length.[55]

FIGURE 13 Breakthrough curves for UO2þ2 ion sorption at

different flow rates. (Color figure available online.)

TABLE 3 Column Data Parameters Obtained at Different Initial

UO2þ2 Ion Concentrations Co, Bed Heights (Z), and Flow Rates (Q)

C0 (mg � L�1) Z (cm) Q (mL �min�1) qe (mg �g�1)

400 3 1 56.019

540 3 1 59.147

700 3 1 63.960

540 1 1 50.692

540 2 1 53.050

540 3 1 59.147

540 3 1 59.147

540 3 2 56.745

540 3 3 55.137


different bed heights. (Color figure available online.)


different initial concentrations. (Color figure available online.)


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Breakthrough Modeling

The Thomas model was applied to the data for C=Co

ratios between 0.08 and 0.99.[42] A linear plot of ln[(Co=

C)� 1] against V enabled the determination of (KTh)

and (qTh) according to Eq. (17). (KTh) and (qTh) values

are given in Table 4. Values of R2 were found to be

�0.995. Figures 16–18 display the experimental and

theoretical breakthrough curves obtained at different

operating conditions by the Thomas model. It can be

observed from Table 4 that the values of (qTh) generally

increase with an increase in the value of Z and Co and

with the decrease in the value of Q. Table 4 also shows

that the values of (KTh) are inversely proportional to Z

and Co and directly proportional to Q.

Applying the Yoon–Nelson model to the experi-

mental results, the values of the Yoon–Nelson model

rate constant (KYN, min�1) and the time in minutes

(t) required for 50% sorbed breakthrough are indi-

cated in Table 5. The values of (KYN) and (t) were

determined from plotting ln[C=(Co �C)] versus t as

given in Eq. (19) at variable operating conditions.

Figures 19–21 display the experimental and theoreti-

cal breakthrough curves obtained at different operat-

ing conditions by the Yoon–Nelson model. Both the

Thomas and Yoon–Nelson models could be used to

TABLE 4 Parameters Calculated from Thomas Model for Removal of UO2þ2 Ions on Fixed-Bed Column at Different Initial Concentrations

Q (mL �min�1) Z (cm) C0 (mg � L�1) KTh (L �mg�1 �min�1 � 10�5) qCale (mg �g�1) qExp

e (mg �g�1) R2 MSE

1 3 400 13.685 57.213 56.019 0.995 0.0006656

1 3 540 9.896 60.596 59.147 0.999 0.0009552

1 3 700 8.425 64.806 63.960 0.995 0.0009949

1 1 540 16.059 50.652 50.692 0.997 0.0007531

1 2 540 14.847 53.772 53.050 0.998 0.0003567

1 3 540 9.896 60.596 59.147 0.997 0.0009552

1 3 540 9.896 60.596 59.147 0.999 0.0009552

2 3 540 14.083 56.907 56.745 0.999 0.0005009

3 3 540 20.412 53.963 55.137 0.999 0.0004084

FIGURE 16 Breakthrough curves for UO2þ2 ions sorption at

different bed heights calculated by Thomas model. (Color figure

available online.)


different flow rates calculated by Thomas model. (Color figure

available online.)


different initial concentrations calculated by Thomas model.



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describe the behavior of the sorption of UO2þ2 ions in

a modified fixed-bed column. When the experi-

mental and the calculated data from the two models

were compared in terms of MSE, lower MSE values

were obtained from both the Thomas and Yoon–

Nelson models vs. experimental data and also a

higher value of R2 was found.

Elution Study

Quantitative recovery of the metal ions from the

solid support is necessary for repeated use of the same

solid phase. Table 6 gives the data related to efficiency

of the two eluents HNO3 and HCl at three different

concentrations for recovery of UO2þ2 ions from

packed column. Recovery of UO2þ2 ions was quantitat-

ive (99%) only with 10mL of 1.5M HCl solution. Elu-

ent flow rates greater than 1mL.min�1 decreased the

recovery of uranium (VI) due to insufficient contact

time between the eluent and UO2þ2 ions sorbed on

the nano-MnO2-modified Amberlite 7HP. Hence,

1mL.min�1 flow rate was considered in this study.

Analytical Applications

Effect of Interfering Ions

The effect of various cations and anions on the

recovery of 500mg � L�1 of uranium ions by the

TABLE 5 Parameters Calculated from Yoon–Nelson Model for Removal of UO2þ2 Ions by Fixed-Bed Column at Different Initial

Concentrations

Q (mL �min�1) Z (cm) C0 (mg � L�1) KYN (min�1) s (min) qCale (mg �g�1) qExp

e (mg �g�1) R2 MSE

1 3 400 0.055 71.516 57.213 56.019 0.995 0.000676

1 3 540 0.054 55.938 60.413 59.147 0.997 0.000937

1 3 700 0.059 46.287 64.802 63.96 0.995 0.000995

1 1 540 0.087 18.759 50.651 50.692 0.993 0.0007

1 2 540 0.080 29.810 53.659 53.05 0.998 0.0003

1 3 540 0.054 55.938 60.413 59.147 0.995 0.000937

1 3 540 0.054 55.938 60.413 59.147 0.997 0.000937

2 3 540 0.076 26.346 56.908 56.745 0.999 0.000501

3 3 540 0.110 16.655 53.962 55.137 0.999 0.000408


different bed heights calculated by Yoon–Nelson model. (Color

figure available online.)


different flow rates calculated by Yoon–Nelson model. (Color

figure available online.)


different initial concentrations calculated by Yoon–Nelson model.



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proposed method was studied and the obtained data

are reported in Table 7. Most of the examined cations

and anions do not interfere with the separation and

determination of uranium, and many of them are

tolerated at high levels. However, to study the inter-

ference of various metal ions such as Co2þ, Cd2þ,

and Zr4þ, 10mL of a solution containing 500mg � L�1

of the UO2þ2 ions was mixed with the interfering ions

and subjected to the extraction process. The inter-

ference effect of these elements could be eliminated

by adding 20mL of 60mM of EDTA solution as a

proper masking agent.

Analysis of Uranium in the Real Samples

The new sorbent 7HPNMnO was utilized for UO2þ2

ion separation in real samples collected from some

Egyptian nuclear locations for safeguard verification

purposes; 5mL of the samples were adjusted to pH

3.1 and passed through 0.5 g of 7HPNMnO at a rate

of 1mL.min�1. Based on the optimum conditions of

the experimental separation process, the quantitative

results are given in Table 8. To verify the measured

results, the standard addition method was applied,

and 5mL of the samples were adjusted to pH 3.1

and spiked with 5mL of different concentrations of

uranyl solutions (5, 20mg � L�1), then passed through

0.5 g dry weight of the 7HPNMnO column at a rate of

1mL.min�1 followed by elution with 10mL of 1.5M

HCl. Samples are diluted to reach a maximum con-

centration of 50mg � L�1 to be measured. The results,

which are given in Table 8, point to the efficiency

and accuracy of the procedure for the separation

and determination of UO2þ2 ions from aqueous

solution.

CONCLUSION

In this study, a new sorbent impregnated by nano

manganese dioxide (7HPNMnO) based on a cheap

and commercially available Amberlite 7HP has been

TABLE 6 Recovery of UO2þ2 Ions using Different Concentra-

tions of HNO3 and HCl acids (n¼ 3)

Eluent Volume (mL) Recovery %�RSD (%)

0.5M HNO3 10 65.4� 1.0

1M HNO3 10 77.6� 1.7

1.5M HNO3 10 81.4� 1.2

0.5M HCl 10 80.5� 0.7

1M HCl 10 89.0� 1.2

1.5M HCl 10 99.8� 0.4

Initial sample, 10mL of 500mg � L�1 UO2þ2 ions.

TABLE 7 Effect of Different Anions and Cations on the

Sorption Recovery of UO2þ2 Ions on 7HPNMnO

Ion Added salt

Cations and

anions concentration

(mg � L�1)

Recovery

(%)�RSD (%)

Naþ NaCl 500 99.2� 1.4

Kþ KCl 500 99.3� 1.5

Mgþ2 MgCl2 200 98.4� 1.7

Caþ2 CaCl2 100 98.3� 1.2

Alþ3 AlCl3 100 97.0� 0.9

Coþ2 Co(No3)2 50 90.3� 1.7

Cdþ2 Cd(No3)2 50 88.7� 1.3

Zrþ4 ZrOCl2 50 80.1� 1.6

Cl� KCl 500 99.3� 1.0

SO�24 Na2SO4 100 98.3� 1.1

NO�3 KNO3 500 99.6� 0.5

After removing the interfering effects by 60mM EDTA

(20mL)

Ion

Cations and anions

concentration (mg � L�1)

Recovery

(%)�RSD (%)

Coþ2 50 99.2� 1.1

Cdþ2 50 99.1� 1.3

Zrþ4 50 99.4� 1.5

TABLE 8 Determination of UO2þ2 Ions in Real Samples (n¼ 3)

Sample

ID

Sample

(mg � L�1)

Spiked

(mg � L�1)

Total

(mg � L�1)

Measured

conc.

(mg � L�1)

Recovery

(%)�RSD

1 519 0 519 515 99.2� 0.3

519 20 539 537 99.6� 0.4

519 5 524 521 99.4� 0.4

2 615 0 615 610 99.1� 0.2

615 20 635 631 99.4� 0.2

615 5 620 615 99.2� 0.2

3 640 0 640 635.4 99.2� 0.3

640 20 660 656 99.4� 0.2

640 5 645 640 99.2� 0.2

4 574 0 574 570 99.3� 0.3

574 20 594 593 99.8� 0.3

574 5 579 576 99.5� 0.2

5 505 0 505 501.4 99.3� 0.3

505 20 525 524.5 99.9� 0.3

505 5 510 507 99.4� 0.4

6 545 0 545 540 99.1� 0.3

545 20 565 561 99.3� 0.3

545 5 550 545 99.1� 0.2


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prepared using a simple reduction method. The new

sorbent was characterized using different spectro-

metric techniques. It was found suitable for UO2þ2

ion separation in aqueous solution within the experi-

mental conditions of contact time, initial concen-

tration, bed height, and flow rate considered in this

study. The kinetic experimental data were properly

tested by the pseudo-first-order, pseudo-second-

order, and Elovich kinetic models. The experimental

results were also analyzed using the Langmuir and

Freundlich isotherm models. Error analysis showed

that the Thomas and Yoon–Nelson models were

applied to the experimental data to predict the

breakthrough curves and to determine the kinetic

parameters for the column. EDTA was found to be

suitable for UO2þ2 ion separation from Co(II), Cd(II),

and Zr(IV) in aqueous solution using the new sor-

bent. Furthermore, the developed sorbent resin

was successfully applied for the separation of uranyl

ions in safeguard applications.

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sorbent impregnated by nano manganese dioxide and its applications for uranium separation

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