ORIGINAL PAPER

Development of Low Cost Adsorbents from Agricultural WasteBiomass for the Removal of Sr(II) and Cs(I) from Water

Bimala Pangeni • Hari Paudyal • Katsutoshi Inoue •

Hidetaka Kawakita • Keisuke Ohto •

Manju Gurung • Shafiq Alam

Received: 25 September 2013 / Accepted: 5 May 2014

� Springer Science+Business Media Dordrecht 2014

Abstract For the purpose of remediating aquatic

environment polluted by radioactive elements such as

Cs(I) and Sr(II), two types of adsorption gels were

developed using biomass wastes as feed materials: a

Ca-type pectin based cation exchanger for the removal

of Sr(II) prepared from orange waste and a polyphenol

enriched bio-sorbent for Cs(I) prepared from tea

leaves. The former was prepared by means of saponi-

fication of the methyl ester portion of orange pectin in

orange juice residue using lime water. Due to the

chemical similarity of Ca(II) and Sr(II), the Ca(II) ions

in the saponified orange juice residue (SOJR) are

easily replaced by Sr(II) during adsorption. The latter

was synthesized by means of cross-linking condensa-

tion reaction with concentrated H2SO4. The adsorption

of Sr(II) and Cs(I) increased with increasing pH of the

solution, suggesting that these metal ions were adsor-

bed onto active sites of these bio-sorbents through a

cation exchange mechanism. These modified biomass

adsorbents were found to exhibit high adsorption

capacities and fast adsorption rates for the tested metal

ions. That is, the adsorption capacity of SOJR for

Sr(II) was evaluated as 0.83 mmol/g whereas that

obtained for the cross linked tea leaves (CTL) gel with

regards to Cs was 1.22 mmol/g. In comparison to the

adsorption capacities of other adsorbents, it was con-

cluded that the SOJR and CTL displayed excellent

potential for the adsorption of Sr(II) and Cs(I),

respectively. Thus, the combined uses of SOJR and

CTL gels can be expected to work as a promising

alternative to remove radioactive Sr(II) and Cs(I) from

polluted water.

Keywords Adsorption � Orange juice residue � Strontium

removal � Tea leaves � Cesium removal

Introduction

In many countries, even those considered developing

countries, atomic energy has played an important part of

the massive amounts of energy generated with no direct

emission of CO2 gas. However, such facilities also generate

large amounts of nuclear wastes including hazardous

radioactive elements such as radioactive 137Cs and 90Sr, as

well as transuranium elements. Among radioactive fission

products, 137Cs is known as c as well as b emitter whereas90Sr is known as b emitter [1, 2]. In the unfortunate event

they are accidently released into the environment such as

during the Fukushima accident on March 11, 2011 [2] in

addition to nuclear weapon tests zones, their release poses

a considerable environmental threat due to their long half-

life (137Cs 30 years, 90Sr 29 years), high fission yield and

bio-toxicity by emitting easily penetrant (c, b) radiation [3,

4]. The released radioactive 137Cs and 90Sr persist in the

environment for extended periods thereby contaminating

the surrounding biosphere. Living organism easily adsorbs137Cs and 90Sr from contaminated water, which involves

B. Pangeni (&) � H. Paudyal � K. Inoue � H. Kawakita �K. Ohto � M. Gurung

Department of Applied Chemistry, Saga University, Honjo 1,

Saga 840-8502, Japan

e-mail: bimalapangeni@yahoo.co.in

K. Inoue

e-mail: inoue@elechem.chem.saga-u.ac.jp

M. Gurung � S. Alam

Faculty of Engineering and Applied Science, Memorial

University, St.John’s NL A1B 3X5, Canada

123

Waste Biomass Valor

DOI 10.1007/s12649-014-9309-4

serious health hazards including leukemia and cancer [1, 4,

5].

In order to remove 137Cs and 90Sr from water, several

physicochemical methods have been proposed, some of

which have been practically employed. Solvent extrac-

tion and ion exchange using inorganic ion exchange

materials such as Zeolites has shown to be very popular

for the effluent treatment processes employed in the

nuclear industries [6]. However, these processes suffer

from disadvantages such as incomplete removal, high

reagent cost, high energy consumption, and the genera-

tion of large quantities of toxic waste requiring further

careful disposal. In Japan, after the Fukushima accident

in particular, it has become imperative to develop new

cost-effective treatment methods for removing 137Cs and90Sr ions from water [7]. Due to low cost, functional

diversity and ease of their modification, the biomass

based adsorbents are effective for the treatment of haz-

ardous ions [8–10]. Adsorptive removal of 137Cs and 90Sr

onto adsorbents derived from biomass waste can be

expected as an excellent alternative to the above-men-

tioned conventional techniques thanks to its simplicity

and cheap production costs. Recently, much attention has

focused on evaluating the adsorption characteristics of

various biomass materials to develop efficient and low

cost adsorbents. The candidate adsorbents should be

characterized by a high stability, water insolubility and

high content of suitable active sites that effectively

interact with targeted pollutants in water.

Thus the present investigation involves the evaluation of

two novel adsorbent gels developed by the authors for

Sr(II) and Cs(I) removal and derived from orange juice

residue and tea leaves, respectively. The main component

of orange juice residue are cellulose, hemicelluloses, pec-

tin, chlorophyll, citric acid, sugar and some low molecular

organic compounds such as limonene [11]. Literature

showed that orange juice residue contains more than 12 %

pectin (called orange pectin) which was partially methyl-

ated in ester form. Because of the chemical similarity of the

Ca(II) and Sr(II) ion, it is expected that the Ca(II) ions in

the saponified product would be easily substituted by Sr(II)

ion through a cation exchange mechanism. On the other

hand, in our previous study, biomass adsorbents containing

polyphenolic compounds such as catechin and persimmon

tannin were found to be effective for Cs(I) ion removal

[12]. In the present work, we also prepared a biomass

adsorbent for Cs(I) ion from catechin rich tea leave waste

by condensation cross-linking reaction with concentrated

sulfuric acid. It is expected that the combined use of the

two types of adsorbents prepared in this study can provide

a promising technology for the treatment of waste water

polluted with either Cs(I) and Sr(II).

Materials and Methods

Chemicals and Analysis

Due to regulations regarding radioactive elements in our

laboratory, nonradioactive isotopes of strontium and

cesium were used in the present experimental work. Ana-

lytical grades of strontium chloride (SrCl2), sodium chlo-

ride (NaCl) and cesium chloride (CsCl) purchased from

Wako Chemical Co. Ltd., Japan, were used to prepare the

stock solutions (10 mmol/l). Fresh working solutions were

prepared at the time of experiment by diluting these stock

solutions. Before use, all the glass-wares and sample bot-

tles were carefully washed with double distilled water, and

finally rinsed with deionized water. The pH of the solution

was adjusted via the addition of either 0.5 M HNO3 or

0.5 M solutions. The concentration of Cs(I) was measured

using atomic absorption spectroscopy (AAS, Shimadzu

model AA6800) whereas that of Sr(II) was analyzed using

an inductively coupled plasma atomic emission spectrom-

eter (ICP-AES, Shimadzu model ICPS-8100). Fourier

Transform Infra Red (FTIR) spectra of the adsorbent were

recorded by using fourier transform infrared spectrometer

(JASCO model, FTIR-410) whereas the elemental com-

position of SOJR and CTL after the adsorption of metal

ions was measured by using an energy dispersive X-ray

(EDX) spectrometer (Shimadzu model EDX-800HS).

Preparation of Saponified Orange Juice Residue

Orange juice residue (OJR), the feed material for the

adsorbent designed for Sr(II), was kindly provided by JA

Beverage Saga Co., Ltd., Japan. The methyl ester fraction

of the orange pectin was converted into the carboxyl group

as its calcium salt by saponification reaction with lime

water for the purpose of enhancing the adsorption capacity

[13]. The procedure of saponification is exactly the same

with that adopted in our previous paper [11], which is

briefly described as follows. At first, 100 g of OJR and 8 g

of Ca(OH)2 were mixed together and grounded into fine

particles with the help of a juice mixer, followed by vig-

orous shaking for 24 h at 30 �C in order to convert the

methyl ester portion of the orange pectin into the carboxyl

O

OH

OH OO

n

COOCH3

O

OH

OH OO

n

COOCa

Ca(OH)2

Scheme 1 Saponification of the methyl ester portion of orange pectin

with lime water to produce saponified orange juice residue (SOJR)

Waste Biomass Valor

123

group by means of a saponification reaction as shown in

Scheme 1. After 24 h of shaking, the mixture was washed

with distilled water several times via decantation followed

by filtrations until a neutral pH was obtained, after which it

was dried in a convection oven at 70 �C. The final product

obtained in such a manner was termed saponified orange

juice residue, abbreviated as SOJR hereafter.

Preparation of Cross-Linked Tea Leaves

The adsorbent derived from cross-linked tea leave was

prepared according to the procedure described in our pre-

vious paper [12] which is described briefly as follows. 15 g

of dried powder from the green tea leave was mixed

together with 30 ml of concentrated sulphuric acid (96 %)

in a 250 ml eggplant flask after which the mixture was

refluxed for 24 h at 100 �C in oil bath to complete the

cross-linking condensation reaction between the various

polyphenol and alcoholic hydroxyl functional groups con-

tained in the tea leaves and to prevent the dissolution of the

products in water. After the completion of the reaction, the

black product thus obtained was washed several times with

deionized water until a neutral pH of the washing water

was attained. The black product was then dried in a con-

vection oven at 70 �C for 24 h. The final product thus

obtained was designated as cross-linked tea leave and

abbreviated as CTL hereafter.

Batch Wise Adsorption of Cs(I) and Sr(II) ion

The adsorption of Cs(I) and Sr(II) were carried out by

means of standard batch method. The adsorption of Sr(II)

and Cs(I) was carried out by shaking 10 mg of SOJR

together with 10 ml of the metal solutions at different pH

ranging from 2 up to 9 for 24 h at a shaking speed of

150 rpm and temperature of 30 �C to ensure complete

equilibrium. Similarly, adsorption test of Na(I) and Cs(I)

(0.1 mmol/l metal solution each) were conducted using the

CTL with a solid liquid ratio of 1 g/l at 30 �C, and at

varying pH from 2 to 7. After shaking, the equilibrated

solution was filtered and analyzed for the metal concen-

trations using either ICP-AES or AAS. The percentage

adsorption of the metal ions (%A) and metal uptake

capacity (q) were calculated according to the following

equations.

%A ¼ Ci � Ce

Ci

� 100 ð1Þ

q ¼ Ci � Ce

m� V ð2Þ

where, Ci and Ce are the initial and equilibrium concen-

tration of metal ions (mmol/l), respectively, V is the

volume of the metal solution (l) and m is the dry weight of

the adsorbent (g).

Kinetic measurements were performed by changing

contact time between the adsorbents and metal solutions at

a solid liquid ratio of 1 g/l. The adsorption isotherm test for

Sr(II) on SOJR were carried out by varying the Sr(II)

concentration (0.5–6 mmol/l) at a pH of *5.6 and solid

liquid ratio of 1.33 g/l, whereas that for Cs(I) on CTL was

performed by varying the Cs(I) concentration

(0.2–8 mmol/l) at a pH of 6.5 and solid liquid ratio of 1 g/l.

Except for the kinetics tests, the mixtures used for the

adsorption isotherm tests were stirred for 24 h at 30 �C.

The metal ion concentrations in the tested samples were

then measured before and after adsorption by ICP-AES or

AAS.

Adsorption Test Using Fixed Bed Column

Two types of dynamic adsorption tests using a fixed bed

column were carried out in a glass column of 20.0 cm

height and 0.8 cm inner diameter as shown in Fig. 1. Ini-

tially, since the SOJR was found to be selective for the

Sr(II) ion in the batch experiments, the adsorbent was

packed in this column for the mutual separation of Sr(II)

from Cs(I). The feed solution contained approximately

0.02 mmol/l of Sr(II) and Cs(I) each and the inlet pH was

maintained at 5.6 using a 0.5 M HNO3 solution. The feed

solution was percolated at room temperature (23 ± 1 �C)

through the bed using an Iwaki model 100 N peristaltic

pump in the up-flow mode to avoid possible short-

d. glass beade. cotton layer

c. glass filter

a. influent solnb. peristaltic pump

h. stand

f. adsorbent

P

g. effluent soln

b

h

g

c

d

ef

e

d

a

Fig. 1 Schematic diagram of column experiment

Waste Biomass Valor

123

circuiting. The flow rate was adjusted to approximately

6.1 ml/h and the effluent samples were collected at regular

time intervals using a Bio-Rad model-2100 automatic

fraction collector. Similarly, another dynamic adsorption

test was carried out using the same column packed with

CTL for the mutual separation of Cs(I) from Na(I). Here,

the feed solution contained 0.1 mmol/l of Cs(I) and

0.6 mmol/l of Na(I) and the inlet pH was adjusted at 6.5.

The solution was percolated at a feed rate of 5.4 ml/h

through the bed of the CTL. The concentrations of the

metal ions were measured by the same method as men-

tioned earlier.

Results and Discussion

Spectroscopic Characterization

Fourier transform infra red spectroscopy is one of the

useful tools to identify the surface functional groups of the

adsorbent so that FTIR spectra of the SOJR and the CTL

were recorded and presented in Fig. 2. In the case of SOJR,

the absorption band at 3,380, 2,913, and 1,683 cm-1 were

observed which are due to stretching vibration of OH, CH,

and C = O groups in addition to the peaks of carboxylate

salt at 1,642 and 1,439 cm-1 which is attributed to the

existence of O–Ca bond whereas in the case of CTL, the

broad band of phenolic ydroxyl groups was appeared at

around 3,460–3,280 cm-1 in addition to the peak at around

2,952, (1,450–1,400 and 1,380), and 1,073 cm-1 which are

due to CH stretching, OH bending and C–O–C linkage.

The existence band corresponding to ether bond linkage

(C–O–C) in FTIR spectra of CTL is the indication that two

hydroxyl groups of different polyphenol were cross-linked.

This indicates that, the hydroxyl functional groups are the

main functional groups in CTL whereas carbonyl and

hydroxyl groups are major in the case of SOJR.

To show the direct evidence for the adsorption of Sr(II)

and Cs(I) onto SOJR and CTL gel, the various elements

present in the samples of Sr(II) loaded SOJR and

Cs(I) loaded CTL were measured and the results are pre-

sented in Fig. 3a, b, respectively. In the case of Sr(II)

loaded SOJR (Fig. 3a), the intense peaks of adsorbed

strontium were observed at energy values from 14.24 to

15.63 keV in addition to C (0.25 keV), O (0.32 keV), Na

(1.14 keV), Si (1.82 keV), P (2.04 keV), S (2.31), K

(3.34 keV), Ca (3.83 and 4.02 keV), Fe (6.45 keV) and Cu

% T

4000 3100 4001300

Wave number [cm-1]

SOJR

CTL

2200

Fig. 2 FTIR spectra of saponified orange juice residue (SOJR) and

cross-linked tea leave (CLT)

(a)

(b)

Ca

0 3 6 9 12 15 18

Inte

nsi

ty

keV

Sr

Sr

Fe CuCa

SP

CONa

Si

K

0.015

0.15

1.5

0 3 6 9 12 15 18

Inte

nsi

ty

keV

C

S

Na

S

Fe

Fe Cu

CsCs

Cs

Cs

Cs

Si

O

Fig. 3 Energy dispersive X-ray (EDX) spectra of (a) SOJR after

Sr(II) adsorption and (b) CTL after Cs(I) adsorption

Waste Biomass Valor

123

(8.01 keV). Similarly, the intense peaks of adsorbed

cesium were observed at 4.21, 4.57, 4.90, 5.26, and

5.56 keV together with C (0.27 keV), O (0.39 keV), Na

(1.13 keV), Si (1.76 keV), S (2.32, 2.53), Fe (6.44 and

6.94 keV) and Cu (8.04 keV) in the case of CTL gel

(Fig. 3b). These result provides the strong evidence that

Sr(II) and Cs(I) were effectively adsorbed onto SOJR and

CTL, respectively.

Batch Wise Studies

Kinetic Experiments

Kinetic measurements are necessary for determining the

optimal contact time required to reach equilibrium. The

relationship between the degree of adsorption of Sr(II) on

the SOJR and contact time is shown in Fig. 4a. It is seen

from this figure that adsorption of Sr(II) onto the SOJR

increases sharply at the beginning of contact and then

gradually slows down, finally reaching equilibrium within

2 h. Similarly, adsorption of Cs(I) onto the CTL also

showed an initially rapidly increased during the initial

0.5 h, eventually attaining equilibrium at around 1 h as

shown in Fig. 4b. However, to ensure complete equilib-

rium, the solid–liquid mixtures were shaken for 24 h (far

more than 1–2 h) for all the subsequent experiments.

Effect of pH and Adsorption Mechanism

In adsorption processes, the pH of an aqueous solution is an

important controlling parameter. The % adsorption of

Sr(II) and Cs(I) onto the SOJR is shown in Fig. 5a as a

function of pH, where it is evident that the % adsorption of

Sr(II) is clearly affected by pH. That is, the % adsorption of

Sr(II) increases with increasing pH in the low pH region (at

pH = 2–5), and then approaches a constant value at pH

values greater than 5. At alkaline pH Sr(II) was

precipitated so that adsorption test were carried out only up

to pH 7. It is also clear from this figure that the SOJR

negligibly adsorbs Cs(I), indicating the low affinity of the

SOJR towards the Cs(I) ion. Such pH dependency on the

adsorption of Sr(II) is typical of the adsorption of other

divalent and trivalent metal ions on the SOJR as observed

in our previous work [14]. Similarly, in the case of the

CTL, the % adsorption of Cs(I) rapidly increased from 6.9

to 71.6 % with increasing pH in the pH range from 1.5 to 4

and then gradually increases at pH values greater than 4 as

shown in Fig. 5b. In both cases, the results of increasing %

adsorption of metal ions with increasing pH of the solution

suggest that these cationic metal ions are adsorbed

according to the cation exchange mechanism as shown in

Scheme 2a, b. That is, as the pH of the solution increases,

the concentration of hydrogen ion in the solution which

potentially competes with the Cs(I) and Sr(II) ions during

adsorption process is decreased, thus the consumption of

proton by competitive adsorption onto the active sites of

SOJR and CTL is also decreased, which leads to the

increase in % adsorption of metal ions with increasing

solution pH.

Adsorption Isotherm of Cs(I) and Sr(II)

The adsorption isotherm plots of Sr(II) on the SOJR is

illustrated in Fig. 6a, b. It is clear from this figure that the

adsorption of Sr(II) onto SOJR (Fig. 6a) and Cs(I) onto

CTL (Fig. 6b) rapidly increases with increasing concen-

trations within the lower concentration region whereas it

tends to approach a constant value at higher concentrations,

suggesting the monolayer adsorption of these metal ions on

the tested adsorbents. In order to evaluate the best fit

adsorption model, the experimental data were analyzed by

using well known Freundlich and Langmuir isotherm

model. The Langmuir isotherm equation can be expressed

in its linear form as shown below (Eq.3)

(a)

0

0.02

0.04

0.06

0.08

0.1

0 2 4 6 8 10

Cs(

I) u

ptke

cap

acit

y[m

mol

/g]

Time (h)

0

0.05

0.1

0.15

0.2

0.25

0 1 2 3 4

Sr(I

I) u

ptak

e ca

paci

ty [

mm

ol/g

]

Time (h)

(b)Fig. 4 Time variation of the

adsorption of (a) Sr(II) onto the

SOJR, and (b) Cs(I) onto the

CTL. Conditions: Solid–liquid

ratio = 1 g/l, metal

concentration = 0.1 mM

Cs(I) and 0.27 mM Sr(II),

pH = 5.6 for Sr(II) and 6.5 for

Cs(I), temperature = 30 �C

Waste Biomass Valor

123

O

OH

OH OO

n

COOCa

O

OH

OH OO

n

COOSr

Sr (II) solution

Ca(II)

Cs(I)

OH

OH

Cs

O

OH

+ H+

(a) (b)

Scheme 2 Hypothesized mechanism of Cs(I) adsorption onto (a) SOJR and (b) CTL

(a)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1 2 3 4 5 6 7 8 9

q[m

mol

/g]

Ce/[mmol/l]

Cs

Na

0

0.3

0.6

0.9

0 2 4 6

q [m

mol

/g]

Ce [mmol/l]

(a) (b)Fig. 6 Adsorption isotherms of

(a) Sr(II) on the SOJR, and of

(b) Cs(I) and Na(II) on the CTL

Conditions: Dry weight of

added adsorbent = 10 mg,

volume of metal

solution = 10 ml, pH = 5.6 for

Sr(II) and 6.5 for Cs(I) and

Na(I), shaking = 24 h, and

temperature = 30 �C

0

10

20

30

40

0 2 4 6 8

Ce/

q e[g

/l]

Ce [mmol/l]

Cs

Na

0

2

4

6

8

0 1 2 3 4 5 6

Ce/

q e[g

/l]

C

(a) (b)

e [mmol/l]

Fig. 7 Langmuir plots for the

adsorption of (a) Sr(II) on the

SOJR, and for those of

(b) Cs(I) and Na(I) on the CTL

(a) (b)

0

20

40

60

80

100

1 2 3 4 5 6 7

Ads

orpt

ion

of m

etal

ions

[%

]

pH

Cs

Na

0

20

40

60

80

100

1 2 3 4 5 6 7 8 9

Ads

orpt

ion

of m

etal

ion

[%]

pH

Sr

Cs

Fig. 5 Effect of initial pH on

the adsorption of metal ions

onto the (a) SOJR and (b) CTL.

Conditions: Weight of

gel = 10 mg, volume of metal

solution = 10 ml, metal

concentration = 0.1 mmol/l

and temperature = 30 �C

Waste Biomass Valor

123

Ce=q ¼ 1= bqmaxð Þ þ Ce=qmax ð3Þ

where, Ce (mmol/l) and qe (mmol/g) are equilibrium

concentration and amount of adsorption, respectively,

while qmax is the maximum uptake capacity. The binding

constant, b (l/mmol), is the adsorption equilibrium con-

stant, which is related to the binding energy associated

with the adsorption process. The experimental data

shown in Fig. 6 were replotted according to Eq. (3) as

presented in Fig. 7. As seen from Fig. 7a, b, the values

are clustered on straight lines as expected from Eq.(3).

The values of qmax and b were evaluated from the slope

and intercept of the straight line for the plots of Ce/qe

versus Ce, respectively, according to Eq. (3) and as listed

in Table 1.

Freundlich isotherm model is basically an empirical

model and employed to describe non ideal adsorption on

heterogeneous surface. The heterogeneity is caused by the

presence of different functional groups on the adsorbent

surface. It is expressed by following equation

log qe ¼ log kF þ 1=nð Þ log Ce ð4Þ

where, kF and n are the Freundlich constants related to

adsorption capacity and adsorption intensity, respectively.

The magnitude of n provides the indication of the favour-

ability of the adsorption. Freundlich parameters kF and n

were evaluated from the intercept and slope for the plot of

log qe versus log Ce, respectively [Fig 8a, b] according to

Eq. (4). The values are also listed in Table 1.

The table shows that experimental data was well fitted

with the Langmuir isotherm model with very high corre-

lation regression coefficient ([0.99) for both the adsorbent

than Freundlich isotherm model (\0.91) suggesting that the

adsorption of Sr(II) and Cs(I) onto the tested adsorbents

takes place according to Langmuir type monolayer

adsorption. The maximum adsorption capacity of SOJR for

Sr(II) was found to be 0.83 mmol/g whereas that of CTL

for Cs(I) and Na(I) was evaluated to be 1.22 and

0.24 mmol/g, respectively.

Comparisons with Other Adsorbents

The comparison of the maximum adsorption capacity of

various adsorbents [15–19] for Sr(II) with that of the SOJR

investigated in this work is presented in Table 2. It is clear

Table 1 The evaluated

Langmuir and Freundlich

parameterss for the adsorption

on the SOJR and CTL

Experimental conditions Langmuir parameters Freundlich parameters

Adsorbents Metal

ion

pH qmax (mmol/g) b (l/mmol) r2 kF (mmol/g) n r2

SOJR Sr(II) 5.6 0.83 2.40 0.99 0.74 2.96 0.97

CTL Cs(I) 6.5 1.22 1.52 0.99 0.77 2.30 0.93

CTL Cs(I) 6.5 0.24 0.79 0.99 0.35 1.67 0.86

-2

-1.5

-1

-0.5

0

0.5

-2 -1.5 -1 -0.5 0 0.5 1 1.5

log

q e

log Ce

Cs

Na

-0.8

-0.6

-0.4

-0.2

0(a) (b)

-1.5 -1 -0.5 0 0.5 1

log

q e

log Ce

Fig. 8 Freundlich plots for the

adsorption of (a) Sr(II) on the

SOJR, and (b) for those of

Cs(I) and Na(I) on the CTL

Table 2 Comparative study of the adsorption potential of the SOJR

for Sr(II) with other adsorbents

Adsorbents q (mmol/g) Reference

SOJR 0.83 This study

Imprinted palygorskite 0.52 [15]

Nano hydroxyappatite 0.56 [16]

Activated carbon 0.49 [17]

Plant root tissue 0.14 [18]

Dolomite powder 0.013 [19]

Phosphate modified montmorilonite 0.15 [25]

Waste Biomass Valor

123

from this table that the adsorption capacity of the SOJR for

Sr(II) is higher than that observed with other adsorbents

reported in the literatures, thereby demonstrating the

potential of the SOJR prepared from orange waste as an

effective adsorbent for the removal of Sr(II) from water.

Similarly, the maximum adsorption capacity of the CTL

for Cs(I) was also compared with other adsorbents reported

in literatures [20–25] as shown in Table 3. This table

suggests that Zeolite A; a conventional inorganic adsor-

bent, exhibits a higher adsorption capacity than CTL.

However, porous materials such as Zeolite and Prussian

blue generally suffer from the clogging of their micro-pore

during the treatments of waste water usually containing

very fine solid particles, potentially lowering their

adsorption capacity and are typically considerably more

expensive. In the contrary, the CTL produced from bio-

mass waste is a low cost adsorbent because the feed

material for CTL is waste tea leaves itself and its produc-

tion process is very simple. Although the maximum

adsorption capacity of CTL is slightly lower than that of

Zeolite A, the difference between is not considerable.

Consequently, the CTL can effectively remove Cs(I) from

water with sufficiently higher adsorption capacity at low

cost.

Adsorption of Metal Ions in Fixed Bed Systems

From the results obtained in this study, it appears that the

SOJR is capable of selectively adsorbing Sr(II) whereas

Cs(I) can be effectively adsorbed on the CTL. The waste

water containing both radioactive ions, Sr(II) and Cs(I),

can be expected to be treated initially with the SOJR to

remove the Sr(II) ions, leaving Cs(I) in the solution which

can be subsequently removed using the CTL. Thus, the

combined use of SOJR and CTL can be expected to pro-

vide an easy, convenient and promising technology for the

treatment of water containing both of Sr(II) and Cs(I).

Figure 9 shows the breakthrough profiles of Sr(II) and

Cs(I) ions through the bed of the SOJR. It is seen that the

breakthrough of Cs(I) occurs immediately just after the

initiation of the flow of feed solution, likely attributed to

the weak affinity of the SOJR for the Cs(I) ion, whereas

that of Sr(II) occurs at around 2,700 bed volumes (B.V.),

likely attributed to the high affinity of the SOJR for the

Sr(II) ion. Figure 10 shows the breakthrough curves of the

Cs(I) and Na(I) ions from the bed packed with CTL. It is

evident from this figure that the breakthrough of

Na(I) occurs at 41 B.V. whereas that of Cs(I) occurs at 281

B.V., thereby indicating that the Cs(I) ion was effectively

adsorbed onto the CTL even in the presence of co-existing

Table 3 Comparative study of the adsorption potential of the CTL

for Cs(I) with other reported adsorbents

Adsorbents q (mmol/g) Reference

CTL 1.22 This study

Prussian blue alginate bead 1.07 [21]

Zeolite A 1.57 [22]

Natural clinoptilolite zeolite 0.37 [23]

Brewery waste biomass 0.07 [24]

Phosphate modified montmorilonite 0.42 [25]

0

0.2

0.4

0.6

0.8

1

0 900 1800 2700 3600 4500

Ct/C

i[-

]

B.V. [-]

Cs

Sr

Fig. 9 Breakthrough profile of Sr(II) and Cs(I) ions through the bed

packed with SOJR Conditions: Flow rate = 6.1 ml/h, metals concen-

tration = 0.02 mmol/l, dry weight of the packed adsorbent = 0.5 g

Fig. 10 Breakthrough profile of Cs(I) and Na(I) ions through the bed

packed with the CTL Conditions: Flow rate = 5.4 ml/h, metal

concentration = 0.1 mmol/l of Cs(I) and 0.6 mmol/l of Na(I), dry

weight of the packed adsorbent = 0.1 g

Waste Biomass Valor

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Na(I). The result indicates that aqueous solution containing

Sr(II) and Cs(I) can be effectively treated by SOJR fol-

lowed by CTL which is similar type of treatment strategy

as investigated by Wiley, 1978 by using commercially

available Duolite ARC-359 and Chelax 100 cation

exchange resins where decontamination of alkaline radio-

active waste containing 137Cs, 90Sr and Pu in fixed bed

column was carried out first treating with Duolite ARC-359

(a phenolsulphonic acid type cation-exchange resin) to

removes 137Cs and Pu leaving 90Sr in the effluent which

was further treated by Chelax 100 bed (iminodiacetate type

chelating resin) to remove residual 90Sr from the effluent

[26].

Hence, it is expected that the radioactive waste water

polluted with 90Sr(II) and 137Cs(I) can be efficiently treated

using the bioadsorbents investigated in this study. The

waste water was first treated with the SOJR to remove

radioactive 90Sr(II) leaving 137Cs(I) in the solution, which

can be removed by subsequent treatment with the CTL.

The ease of incineration is one of the most important and

advantageous characteristic of adsorbents prepared from

biomass waste, that makes post-treatment much easier

compared with organic and inorganic ion-exchangers pro-

duced from plastics and refractory materials. Natural

polymer contained in waste biomass like orange juice

residue and tea leaves are partly deteriorated by irradiation.

Thus, application of the adsorbent prepared from biomass

material for long period by repeated adsorption and elution

is unsuitable during the treatment of radioactive wastes.

For such cases, the best option is one time adsorption

without elution, but followed by incineration of the

adsorbents loaded with radioactive elements that dramati-

cally reducing their toxic volume and become easier for

their extended safe storage.

Conclusions

In the present paper, it was found that SOJR containing

calcium pectate as one of major components preferentially

adsorbed Sr(II) over Cs(I). On the other hand, CTL which

was rich in polyphenolic compounds effectively adsorbed

Cs(I). The amount of adsorbed metal ions was shown to

increase with the solution pH value, in the 2–5 range for

both metal ions, from which the adsorption of these metal

ions was inferred to take place according to a cation

exchange mechanism. The adsorption isotherms of these

metal ions were interpreted in terms of the Langmuir

adsorption model, from which the maximum adsorption

amount of Sr(II) on the SOJR was evaluated as 0.83 mmol/

g, whereas that of Cs(I) on the CTL was 1.22 mmol/g. For

waste water containing both of Sr(II) and Cs(I), it was

proposed that the Sr(II) was selectively adsorbed at first

onto SOJR at first leaving the Cs(I) in the solution that

could be subsequently adsorbed onto the CTL.

Acknowledgments This study was financially supported by Grant-

in-Aid for Exploratory Research by the Japan Society for the Pro-

motion of Science (JSPS) (KAKENHI No. 24656551).

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