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JOURNAL OF RARE EARTHS, Vol. 29, No. 5, May 2011, P. 407

Foundation item: Project supported by the grants from the National Key Technologies Research and Development Program of China (2008BAD94B09), and the

Key Grant of Education Department of Zhejiang Province, China (Z200907459)

Corresponding author: XIONG Chunhua (E-mail: xiongch@163.com; Tel.: +86-571-88932083)

DOI: 10.1016/S1002-0721(10)60469-3

Adsorption behavior of ytterbium (III) on gel-type weak acid resin

ZHENG Zhanwang (), XIONG Chunhua ()

(Department of Applied Chemistry, Zhejiang Gongshang University, Hangzhou 310012, China)

Received 11 January 2011; revised 22 February 2011

Abstract: The adsorption and desorption behaviors of Yb(III) on gel-type weak acid resin (110) were investigated. The influence of opera-

tional conditions such as contact time, initial concentration of Yb(III), initial pH of solution and temperature on the adsorption of Yb(III) were

also examined. The results showed that the optimal adsorption condition of 110 resin for Yb(III) was achieved at pH=5.5 in HAc-NaAc me-

dium. The maximum uptake capacity of Yb(III) was 265.8 mg/g at 298 K. Yb(III) could be eluted by using 3.0 mol/L HCl solution and the

110 resin could be regenerated and reused. The adsorption of Yb(III) followed the Langmuir isotherm, and the correlation coefficients were

evaluated. Various thermodynamic parameters such as standard enthalpy change (H), standard entropy change (S) and standard free energy

change (G) were evaluated. The adsorption of Yb(III) on the 110 resin was found to be endothermic in nature. Thomas model was success-fully applied to experimental data to predict the breakthrough curves and to determine the characteristics parameters of the column useful for

process design. And the resin sample both before and after adsorption was described by IR spectroscopy.

Keywords: gel-type weak acid resin (110 resin); ytterbium(III); adsorption; parameter; Thomas model; rare earths

Rare earth elements (REEs) have been regarded as the vi-

tamin of metals, which means that a minute amount of REEs

may greatly enhance the properties of metals. Ytterbium(Yb)

is one of the most significant rare earth elements, which has

attracted special attention due to its unique properties and

wide range of applications. Yb can be used in optical materi-als, dentistry as well as stainless steel to help improve the

properties of those materials; the 169Yb isotope has been used

as a radiation source substitute for a portable X-ray ma-

chine[14].

However, as industry expands, ytterbium which is also

one of the harmful elements persists in the environment and

often creates long-term contamination problems. Therefore,

extraction and preconcentration of these valuable ions from

wastes are extremely important not only from the view of

their limited resource availability, but also for the reduction

of their quantum for disposal as wastes. Different methods

have been proposed for separation and preconcentration of

REEs, such as co-precipitation, solvent extraction, ion-ex-

change and solid phase extraction[59]. Solvent extraction and

ion-exchange are the two most common methodologies for

the preconcentration and separation of trace elements from

various matrices[10]. Solvent extraction is inefficient due to

the requirement of large volume of solvent, which may cre-

ate health problem. In addition, solvent extraction proce-

dures are usually time-consuming and labor-intensive [1113].

Ion exchange resins have been used in the chemical analysis

for over 50 years[11]. They are solid and suitably insolubi-

lized high molecular weight polyelectrolytes which can ex-

change their mobile ions for ions of equal charge from the

surrounding medium. The resulting ion exchange is reversi-

ble and stoichiometric with the displacement of one ionic

species by another on the exchanger. 110 resin is a poly-

meric material containing a functional group (COOH). Ithas oxygen atom that can coordinate directly with metal

ions[14,15]. 110 resin which can be used repeatedly has the

advantages of high stability and adsorption capacity. The

high adsorption rate of 110 resin due to its unique properties

opens the door to the application in industry.

In this work, the adsorption and desorption of Yb(III) ion

on 110 resin using batch and column methods were investi-

gated. Some factors affecting adsorption, such as contact

time, initial pH of solution, initial concentration of Yb(III)

ion and temperature were examined. Furthermore, kinetics

and isotherm adsorption experiments were carried out. Tho-

mas model was applied to experimental data obtained from

column experiments. With the mentioned above, 110 resin

can be widely used in the recovery of Yb(III) from aqueous

solution.

1 Materials and methods

1.1 Apparatus

The Yb(III) ion was determined with Shimadzu UV-2550

UV-VIS spectrophotometer. Mettler toledo delta 320 pH

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408 JOURNAL OF RARE EARTHS, Vol. 29, No. 5, May 2011

meter was used for measuring pH of solutions. The sample

was shaken in a DSHZ-300A and a THZ-C-1 temperature

constant shaking machine. The water used in the present

work was purified using a Molresearch analysis-type ultra-

pure water machine.

1.2 Materials

110 resin was supplied by The Chemical Plant of Nankai

University (Tianjin, China) and the properties are shown in

Table 1. The stock solutions of Yb(III) ion were prepared

from Yb2O3 (A.R.). HAc-NaAc buffer solution with pH=

3.506.50 and C6H15O3N-HNO3 buffer solutions with pH=

7.2 were prepared from the NaAc, HAc, C6H15O3N and

HNO3 solutions. The chromophoric reagent of 0.1% ar-

senazo-I solution was obtained by dissolving 0.1000 g ar-

senazo-I powder into 100 ml deionized water. All other

chemicals were of analytical grade and purified water was

used.

Table 1 General description and properties of 110 resin

Item Property

Resin Gel-type weak acid resin

Functional group COOH

Capacity/(mmol/ml) 12

Containing moisture/% 70.080.0

Wet superficial density/(g/ml) 0.700.80

True wet density/(g/ml) 1.101.15

1.3 Adsorption experiments

Experiments were run in a certain range of pH, tempera-

ture, initial Yb(III) ion concentrations, and contact time as

well as adsorption isotherms[16]

. The operation for the ad-

sorption and desorption of Yb(III) ion is usually carried out

in batch vessels and glass columns. Batch experiments were

performed under kinetic and equilibrium conditions. A de-

sired amount of treated 110 resin was weighed and added

into a conical flask, in which a desired volume of buffer so-

lution with pH 5.5 was added. After 24 h, a required amount

of standard solution of Yb(III) ion was put in. The flask was

shaken in a shaker at constant temperature. The upper layer

of clear solution was taken for analysis until adsorption equi-librium reached. The procedure of kinetic tests was identical

to that of the equilibrium tests. The concentrations of Yb(III)

ion of aqueous samples were measured at preset time inter-

vals. Continuous flow adsorption experiments were con-

ducted in a vertical glass column of 0.45 cm inner diameter

and 23.5 cm height filled with Yb(III) ion solution. At the

bottom of the column, a stainless sieve was attached fol-

lowed by a layer of cotton wool. The particles were dropped

in from the top of the column. Time taken by the particles to

travel a distance of 7.4 cm in vertical direction was noted.

The Yb(III) ion solution was fed from the top at a fixed flowrate. The Yb(III) ion solutions at the outlet of the column

were collected periodically and analyzed for the Yb(III) ion

concentration using a UV-visible spectrophotometer at 570 nm.

The flow through the column was continued till the outlet

and inlet concentrations were equal. All the experiments

were carried out at room temperature.

1.4 Analytical method

A solution containing lower than 75 g of Yb (III) was

added into a 25 ml colorimetric tube, and then 1.0 ml of

0.1% arsenazo-I solution and 10 ml pH 7.2 C6H15O3N-HNO3

buffer solution were added. After the addition of deionized

water to the mark of colorimetric tube, the absorbency was

determined in a 1 cm colorimetric vessel at wavelength of

570 nm and compared with blank test. The adsorption

amount (Q) and distribution coefficient (D) were calculated

with the following formulas[17,18]

:

Q=(C0Ce)V/m (1)

D=Q/Ce (2)

where C0 (mg/ml) and Ce (mg/ml) are the initial and equilib-

rium Yb(III) concentrations, respectively, V(ml) is the total

volume of solution, and m (g) is the mass of 110 resin.

2 Results and discussion

2.1 Influence of pH on the distribution coefficient for

Yb(III)

The pH of aqueous solution has been identified as the

most important variable governing the adsorption capacity of

adsorbent. The influence of pH on the adsorption behavior of

110 resin for Yb (III) is illustrated in Fig. 1.

The uptake of Yb(III) as a function of hydrogen ion con-centration was in the range of pH 3.506.50 for an initial

concentration of Yb(III) ion 5.0 mg/30.0 ml at 298 K, 100

r/min. The adsorption coefficient (D) for Yb(III) ion was the

highest when pH value was 5.50 in the HAc-NaAc medium

and decreased by either raising or lowering pH under the

experimental conditions. At lower pH values, the Yb(III) ion

uptake was inhibited in the acidic medium, which can be at-

tributed to the presence of H+ ion competing with the Yb(III)

ion for the adsorption sites. In contrast, the Yb(III) ion is

prone to precipitation at higher pH values. Therefore, all the

following experiments were performed at pH 5.5 in the

HAc-NaAc system.

Fig. 1 Influence of pH on the distribution coefficient of Yb(III)

(Resin 15.0 mg, C0=5.0 mg/30.0 ml, T=298 K, 100 r/min)

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ZHENG Zhanwang et al.,Adsorption behavior of ytterbium (III) on gel-type weak acid resin 409

2.2 Isotherm adsorption curve

The Langmuir model perhaps is the best known isotherm

to describe adsorption from a liquid solution. The Langmuir

model assumes uniform energies of adsorption on the sur-

face and no interaction between adsorbed molecules. The

model also assumes that adsorption is limited to completesurface coverage by a monomolecular layer and can be rep-

resented by the following equation[19,20]:

e e

e m m

1=

C C

Q Q bQ (3)

where Ce (mg/ml) is equilibrium concentration of Yb(III), Qe

(mg/g) the adsorbing capacity in equilibrium state, Qm (mg/g)

the saturated adsorption capacity and b the Langmuir con-

stant which reflects quantitatively the affinity between the

110 resin and Yb(III) ions. It is used to analyze batch equi-

librium data by plotting Ce/Qe versus Ce, which yields a lin-

ear plot if the data conform to the Langmuir isotherm. Ac-cording to the experiment data, plotting of Ce/Qe versus Ce

gave a straight line and the correlation coefficient R2

(R2288

K=0.9913, R2298 K=0.9869, R

2308 K=0.9958) were high as

shown in Fig. 2. This was indicative of applicability of the

proposed model for the process undertaken. In other words,

the Langmuir-type adsorption isotherm was suitable for

equilibrium studies. This indicates that the adsorption of Yb

(III) ion by 110 resin is of monolayer-type[21]

.

2.3 Determination of adsorption rate constant at dif-

ferent temperatures and apparent activation energy

The influence of contact time on the adsorption of Yb(III)

ion onto 110 resin (Fig. 3) was investigated at various tem-

peratures, i.e., 288, 298 and 308 K. The amount of adsorp-

tion increased with increasing contact time. Further, the

loading half time t1/2 was 7 h and the maximum adsorption

was observed after 36 h, beyond which there was almost no

further increase in the adsorption. Therefore, this interaction

time could be well taken as equivalent to the equilibrium

time. Meanwhile, the equilibrium adsorption capacity of

Yb(III) ion onto 110 resin was found to increase with in-

creasing temperature, indicating that the adsorption of Yb(III)

ion onto the adsorbent was favored at higher temperatures.

Fig. 2 Langmuir isotherm curves (Resin 15.0 mg, C0=5.0 mg/30.0

ml9.0 mg/30.0 ml, pH=5.5, 100 r/min)

Fig. 3 Adsorption capacity (Q)at different contact time and tem-

peratures (Resin=15.0 mg, C0=18.0 mg/60.0 ml, pH=5.5,

100 r/min)

This effect suggests that the adsorption mechanism associ-

ated with Yb(III) ion onto 110 resin involves a temperature

dependent process.

According to Brykina method, the adsorption rate constant

kcan be calculated from[22,23]:

ln(1F)=kBt (4)

whereF=Qt/Qe, Qt (mg/g) and Qe (mg/g) are the adsorption

amounts at certain time and at equilibrium, respectively. The

experimental results accord with the equation and a straight

line is obtained by plotting ln(1F) versus t(Fig. 4) and the

adsorption rate constants of 110 resin for Yb(III) can be

found from the slope of the straight line, which are shown in

Table 2. According to Boyd equation, it can be deduced

from the linear relationship of ln(1F) versus tthat the liq-

uid film spreading is the controlling step in the adsorptionprocess.

According to the formula of Arrhenius[24]:

alg lg

2.30

Ek A

RT (5)

where A is the Arrhenius factor. The relationship between

Fig. 4 Determination of adsorption rate constant (Resin=15.0 mg,

C0=18.0 mg/60.0 ml, pH=5.5, 100 r/min)

Table 2 Adsorption rate constants of 110 resin for Yb (III)

T/K Linearity relation ofln(1F) and t k/(10

5

s

1

) R

2

288 y=0.0833x0.0385 2.31 0.9924

298 y=0.0882x0.0294 2.45 0.9934

308 y=0.0912x+0.0223 2.53 0.9959

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410 JOURNAL OF RARE EARTHS, Vol. 29, No. 5, May 2011

lgkand 1/Tis shown in Fig. 5, and the slope of the straight

line Kslope=174.97. So the apparent activation energy Ea=

3.35 kJ/mol can be calculated. It can be seen from the rate

constant that the adsorption speed accelerates when the tem-

perature increases within the scope.

2.4 Influence of adsorption temperature on distribution

ratio and determination of thermodynamic pa-

rameters

The distribution coefficient (D) of the 110 resin for Yb (III)

in the temperature range of 288308 K was measured, and

the result is shown in Fig.6. A straight line was obtained by

plotting lgD against 1/T with a correlation coefficient of

0.9908. The result obviously indicates that it is favorable for

the adsorption with the temperature increasing. It implies

that the adsorption process is endothermic. So the adsorption

reaction is a chemical adsorption.

The vant Hoff equation given below, can be used to cal-culate the enthalpy changes associated with the adsorption

process of the metal ions.

lg2.30 2.30

H SD

RT R

' ' (6)

whereR is the universal gas constant,D the distribution co-

efficient and T(K)the absolute temperature. The plot of lgD

versus 1/Tgives a straight line, from which H(the enthalpy

variation) and S(the entropy variation) were deduced from

the slope and intercept of the line, respectively. And the

Fig. 5 Relationship between lgkand 1/T(Resin=15.0 mg, C0=18.0

mg/60.0 ml, pH=5.5, 100 r/min)

Fig. 6 Influence of temperature on distribution ratio (D) (Resin=

15.0 mg, C0=5 mg/30 ml, pH=5.5, 100 r/min)

free energy variation, G was calculated from:

G=HTS (7)

The thermodynamic parameters of the sorption of Yb(III)

were calculated and given in Table 3. The positive values of

Hindicate the endothermic character of the solid phase ex-

traction and sorption process, but the negative value ofG

indicates the spontaneous nature of Yb(III) sorption. The

positive entropy change (S) value corresponds to an in-

crease in the degree of freedom of the adsorbed species.

2.5 Desorption and regeneration studies

Whether an adsorbent is an appropriate material in re-

moval of metal ions from aqueous solutions depends not

only on its adsorptive capacity, but also on its regeneration

ability. For repeated use of an adsorbent, adsorbed metal

ions should be easily desorbed under suitable conditions. In

this work, 15.0 mg 110 resin was added into a mixed solu-

tion composed of pH 5.5 buffer solution and desired amountof Yb(III) ion solution. After the equilibrium was achieved,

the concentration of Yb(III) ion in the aqueous phase was

determined, and the adsorption capacity of the 110 resin for

Yb(III) ion was obtained. Then, the 110 resin separated from

aqueous phase was washed three times with pH 5.5 buffer

solution. The 110 resin adsorbed Yb(III) ion was shaken

with 30.0 ml HCl eluant. After equilibrium was achieved,

the concentration of Yb(III) ion in aqueous phase was de-

termined and then the percentage of elution for Yb(III) ion

was obtained.

The results shown in Fig. 7 indicate that the percentage ofelution for Yb(III) ion is different when the concentration of

HCl is changed. It is evident that the 3.0 mol/L HCl solution

is suitable to be the eluant.

Table 3 Thermodynamic data calculated for adsorption of Yb(III)

on 110 resin

T/K G/(kJ/mol) H/(kJ/mol) S/(J/(molK))

288 22.80

298 24.45

308 26.10

24.59 164.56

Fig. 7 Desorption of Yb(III) from 110 resin by HCl in varying con-

centrations (Resin=15.0 mg, pH=5.5, T=298 K, 100 r/min)

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ZHENG Zhanwang et al.,Adsorption behavior of ytterbium (III) on gel-type weak acid resin 411

2.6 Dynamic adsorption and desorption

2.6.1 Dynamic adsorption curve The performance of

packed beds is described through the concept of the break-

through curve. The breakthrough curve shows the loading

behavior of Yb(III) to be removed from solution in a fixed

bed and is usually expressed in terms of adsorbed Yb(III)concentration (Cad=inlet Yb(III) concentration (Co) outlet

Yb(III) concentration (Ce)) or normalized concentration de-

fined as the ratio of effluent Yb(III) concentration to inlet

Yb(III) concentration (Ce/Co) as a function of time or volume

of effluent for a given bed height[25]. The area under the

breakthrough curve obtained by integrating the adsorbed

concentration (Cad, mg/L) versus the throughput volume (V,

ml) plot can be used to find the total adsorbed Yb(III) quan-

tity (maximum column capacity). Total adsorbed Yb(III)

quantity (Q, mg/g) in the column for a given feed concentra-

tion and flow rate is calculated from Eq. (8):

e dV ( C )

V

0

C0

=C

Qm (8)

where m (g) is the mass of the adsorbent. The capacity value

Qc (mg/g) was obtained by graphical integration as 305 mg/g.

Successful design of a column adsorption process requires

prediction of the concentration versus time profile or break-

through curve for the effluent. The maximum sorption ca-

pacity of 110 resin is also in design.

Traditionally, the Thomas model is used to fulfill the pur-

pose. The model has the following form[26]:

0 T e

1=

1 + exp[ ( )/ ]V T 0

eC

C K Q m C

(9)

where KT (ml/(minmg)) is the Thomas rate constant,

(ml/min) the volumetric flow rate, and QT (mg/g) the theo-

retical maximum sorption capacity value. The linearized

form of the Thomas model is as follows:

T 0T T

eln ( 1) = V

0

e

K CC K Q m

C(10)

The kinetic coefficient KT and the adsorption capacity of

the bed QTcan be determined from a plot of ln [(Co/Ce)1]

versus tat a certain flow rate as shown in Fig. 8. The Tho-

mas equation coefficients for Yb(III) ion adsorption were

KT=9.7102

ml/(minmg) and Qc=311 mg/g. The theoreticalpredictions based on the model parameters were compared

Fig. 8 Thomas model for the continuous adsorption of Yb(III)

(Resin=150.0 mg, C0=0.1 mg/ml, pH=5.5, flow rate=0.28 ml/min)

with the observed data as shown in Fig. 9.

The Thomas model was found in a relatively good fitness

with breakthrough curve for sorption of Yb(III) on 110 resin

with a R2 value 0.9869. In addition, theoretical maximum

adsorption capacity value QT was very close to the experi-

mental one Qc. Therefore, it can be concluded that the ex-

perimental data fitted well to the Thomas model, which in-

dicates that this model was successfully used for the predic-

tion of the breakthrough curves and can be employed to de-

termine the characteristics parameters of the column process

design.

2.6.2 Dynamic desorption curve Efficient elution of ad-

sorbed solute from 110 resin in column was essential to en-

sure the recovery of metal ions as well as the reuse of resin

for repeated adsorption/desorption cycles. With respect to

the stripping of Yb(III) from 110 resin, 3.0 mol/L HCl eluant

was employed. Desorption curve was formed by plotting the

effluent concentration (Ce) versus elution volume (ml) fromthe column at a certain flow rate. It can be seen from Fig. 10

that the desorption flow rate was less so that the volume of

elution was less which helped in easy handling and high

concentration for economical recovery of Yb(III). It was ob-

served that the total volume of eluent was 175 ml, after

which further desorption was negligible. Therefore, the 3.0

mol/L HCl eluant could help in easy handling and recover-

ing of Yb(III).

Fig. 9 Dynamic adsorption curves of 110 resin for Yb(III)

(Resin=150.0 mg, C0=0.1 mg/ml, pH=5.5, flow rate=0.28 ml/min,

T=298 K)

Fig. 10 Dynamic desorption curve of 110 resin for Yb (III)

(Resin=150.0 mg, CHCl=3.0 mol/L, flow rate=0.25 ml/min, T=298 K)

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412 JOURNAL OF RARE EARTHS, Vol. 29, No. 5, May 2011

Fig. 11 Infrared spectra of 110 resin

(1) Before adsorption; (2) After adsorption

2.7 IR spectra

The IR spectra of resin samples both before and after

Yb(III) was adsorbed, detected and identified by IR spec-

trometer. From the results above (Fig. 11), it can be deduced

that the sorption of Yb(III) by 110 resin can be classified as

chemical sorption by ion exchange (H>0). And the func-

tional group of 110 resin (C=O) and Yb(III) formed chemi-

cal bonds. It was found that the characteristic absorption

peak of the bond C=O (1710.77 cm1) was sharply weakened,

and the new peak (1544.62 cm1) formed. The result shows

that there are coordination bonds between oxygen atoms and

Yb(III).

3 Conclusions

Yb(III) could be optimally adsorbed on 110 resin in HAc-

NaAc medium at pH 5.50. The statically saturated adsorp-

tion capacity of Yb(III) was 265.8 mg/g 110 resin at 298 K.

The adsorption behavior of 110 resin for Yb(III) obeyed the

Langmuir isotherm. The adsorption rate constant was k298 K=

2.45105 s1 and the apparent activation energy was Ea=

3.35 kJ/mol. Thermodynamic parameters, S, Hand G,

on the adsorption for Yb(III) indicated that the adsorption

process was spontaneous and endothermic. The Yb(III) ad-

sorbed on 110 resin could be eluted by using 3.0 mol/L HCl

solution as an eluant. Infrared spectra of 110 resin adsorbed

Yb(III) showed that the functional group of resin was coor-

dinated with Yb(III) to form coordination compound.

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