Solid phase extraction of uranium and thorium on octadecylbonded silica modified with Cyanex 302 from aqueous solutions

A. Nilchi • T. Shariati Dehaghan •

S. Rasouli Garmarodi

Received: 22 August 2012

� Akademiai Kiado, Budapest, Hungary 2012

Abstract A simple and reliable method for rapid

extraction and determination of uranium and thorium using

octadecyl-bonded silica modified with Cyanex 302 is pre-

sented. Extraction efficiency and the influence of various

parameters such as aqueous phase pH, flow rate of sample

solution and amount of extractant has been investigated.

The study showed that the extraction of uranium and tho-

rium increase with increasing pH value and was found to

be quantitative at pH 6; and the retention of ions was not

affected significantly by the flow rate of sample solution.

The extraction percent were found to be 89.55 and 86.27 %

for uranium and thorium, respectively. The maximal

capacity of the cartridges modified by 30 mg of Cyanex

302 was found to be 20 mg of uranium and thorium. The

method was successfully applied to the extraction and

determination of uranium and thorium in aqueous solu-

tions. The percentage recovery of uranium and thorium in a

number of natural as well as seawater samples of Iran were

also investigated and found to be in the range of 85–95 %.

Keywords Solid phase extraction �Uranium and thorium �Cyanex 302 � Octadecyl bonded silica cartridge

Introduction

Uranium and thorium find extensive application as nuclear

fuel in power plants and their main sources are soil, rocks,

plants, sand and water. Uranium and thorium are known to

cause acute toxicological effects for human and their

compounds are potential occupational carcinogens [1].

These elements and compounds are highly toxic which

cause progressive or irreversible renal injury. Due to these

issues, the determination of uranium and thorium in envi-

ronmental and biological samples has considerable poten-

tial as a tool for assessment of human exposure. The low

concentration of these ions in the presence of relatively high

concentration of divorce ions makes it difficult to determine

directly uranium and thorium ions. Therefore, a separation

and preconcentration is mandatory prior to their determi-

nation by highly versatile techniques such as inductively

coupled plasma optical emission spectrometry (ICP-OES).

Many enrichment and separation techniques including

solvent extraction, coprecipitation, ion exchange and elec-

trodeposition [2–6] have been used for uranium and tho-

rium. Solid phase extraction is one of the important

preconcentration-separation procedures for trace heavy

metal ions, due to its simplicity and limited usage of the

organic solvents. Hence, solid phase extraction is the most

preferred technique, not only for enriching uranium and

thorium but also for other inorganics. Furthermore, it has

many advantages, such as high enrichment factors, absence

of emulsion, low cost due to low consumption of reagents,

flexibility and being environmentally friendly [7]. Solid

phase extraction of uranium and thorium is also a popular

subject in the analytical chemistry. Shamsipur et al. [8] have

proposed a solid phase extraction procedure for ultra trace

uranium (VI) in natural waters using octadecyl silica

membrane cartridges modified by tri-noctylphosphine

oxide. Gladis and Rao [9] have synthesized a chelating resin

by the reaction with Amberlite XAD-4 and 5-aminoquino-

line-8-ol for the uranyl ion uptake. Unsworth et al. [10] have

performed the determination of uranium and thorium in

natural waters with a high matrix concentration using

solid phase extraction inductively coupled plasma-mass

A. Nilchi (&) � T. S. Dehaghan � S. R. Garmarodi

Nuclear Science and Technology Research Institute,

P.O.Box 11365/8486, Tehran, Iran

e-mail: anilchi@aeoi.org.ir

123

J Radioanal Nucl Chem

DOI 10.1007/s10967-012-2252-6

spectrometry. Metilda et al. [11] have prepared catechol

functionalized aminopropyl silica gel for the separation and

preconcentration of uranium (VI) from thorium (IV) in soil

and sediment samples. Ghiasvand and Mottaabed [12] have

proposed a solid phase extraction procedure of ultratrace

uranium by mixtures of dicyclohexyl-18-crown-6 and tri-

n-octylphosphine oxide. Raju and Subramanian [13] have

performed the selective enrichment and separation of U

(VI) and Th(IV) in trace and macroscopic levels using

malonamide-grafted polymer from acidic matrices.

In this work, a solid phase extraction procedure for the

separation-preconcentration of uranium and thorium on

octadecyl-bonded silica modified with Cyanex 302 has

been presented prior to their inductively coupled plasma

emission spectrometry determination. The effects of ana-

lytical parameters including pH of the solution, amounts of

Cyanex 302, flow rate, sorption capacity and breakthrough

volume, were investigated. Furthermore, the procedure was

verified by determination of these elements in a number of

natural as well as seawater samples of Iran.

Experimental

Instrumentation

An inductively coupled plasma emission spectrophotometer

Varian Liberty 150AX Turbo was used for determination of

uranium and thorium concentration. A Schott CG841 digital

pH meter was applied for pH adjustments. A Millipore vac-

uum pump was used for maintaining the sample flow rates.

Chemicals and reagents

A stock solutions of U (VI) and Th(IV) ions were prepared from

UO2(NO3)2�6H2O and Th(NO3)4�5H2O (Merck) by dissolving

appropriate amounts in slightly acidified double distilled water.

Cyanex 302 (C16H35PSO) was obtained from Cytec. All

chemicals and reagents used were of Analytical grade.

Preparation of impregnated octadecyl bonded silica

cartridge

The Cyanex302 impregnated octadecyl bonded silica car-

tridge was prepared as follows. After placing the cartridge

in the filtration apparatus, the cartridge was washed with

10 mL of HPLC grade methanol and double distilled water

repeatedly by applying a slight vacuum. After all of the

solvent had passed through the cartridge, it was dried by

passing air through it for 2 min. The cartridge was then

conditioned with 10 mL of HPLC grade methanol under a

low vacuum. The cartridge was not allowed to soak without

vacuum, and air was not allowed to make contact with the

surface of the cartridge. The cartridge was then dried under

vacuum for 5 min. Finally, a solution containing 30 mg of

Cyanex 302 in 2 mL of methanol was introduced onto the

cartridge so that the solution was spread on the cartridge

surface. The solution was allowed to penetrate inside the

cartridge completely and methanol was collected and

repeatedly passed through to ensure complete impregnation

of Cyanex 302 on the cartridge. During this entire process,

no vacuum was applied. Time required for impregnation of

Cyanex 302 on C18 cartridge was not more than 25 min.

The amount of Cyanex 302 adsorbed was evaluated by

passing methanol (20–30 mL) at high vacuum. The eluate

was then titrated against standard NaOH using phenol-

phthalein indicator.

Results and discussion

Effect of amount of Cyanex 302

A 30 mL sample solution containing 20 mg uranium and

thorium adjusted to pH 6 was studied for its sorption with

modified C18 cartridge (Fig. 1). For preparation of C18

cartridge with different amounts of Cyanex 302, a known

amount of Cyanex 302 in 2 mL methanol was passed

through cartridge as described in ‘‘Preparation of impreg-

nated octadecyl bonded silica cartridge’’ for impregnation.

Amount of Cyanex 302 lower than 30 mg resulted in an

incomplete sorption of uranium and thorium. The minimum

quantity of Cyanex 302 required for quantitative sorption of

uranium and thorium was 30 mg. Hence, for subsequent

studies 30 mg Cyanex 302 sorbed on C18 disk was used.

Effect of aqueous phase pH

A 30 mL sample solution containing 20 mg uranium and

thorium, adjusted to a pH 1.0–7.0 was passed through the

Fig. 1 Effect of amount of Cyanex 302 on extraction of uranium and

thorium

A. Nilchi et al.

123

cartridge. The amount of uranium and thorium extracted

was determined by inductively coupled plasma emission

spectrophotometer. The study indicates that the extraction

of uranium and thorium increases with increasing pH and is

found to be quantitative at pH 6 (Fig. 2). Higher pH values

([7) were not tested due to the possibility of hydrolysis of

octadecyl silica in the cartridge.

Effect of sample flow rate

The influence of sample flow rate on uranium and thorium

uptake by the cartridge at pH 6 was also investigated. It

was found that in the range of 1–7 mL/min, the retention of

these ions by cartridge was not significantly affected by the

sample solution flow rate. However, at a flow rate greater

than 7 mL/min, the sorption of uranium and thorium was

decreased, possibly due to its insufficient contact with the

sorbent. Hence, the optimum aqueous phase conditions

used were pH 6 at a sample flow rate of 5 mL/min (Fig. 3).

Breakthrough volume

Different volumes (30–2,000) mL of aqueous phase con-

taining 30 mg uranium and thorium were passed through

the cartridge to check the breakthrough volume. The

sorption of uranium and thorium was tested by the induc-

tively coupled plasma spectrophotometer. As it can be seen

from Fig. 4, the sorption of uranium and thorium was

quantitative even up to 1,500 mL.

Sorption capacity

The sorption capacity of octadecyl-bonded silica modified

with Cyanex 302 was determined by passing a 30 mL of

solutions of uranium and thorium at pH 6 with different

concentrations. The amount of uranium and thorium in the

aqueous phase was determined by ICP. The difference in

the initial amount of uranium and thorium in sample

solution and the amount found in the aqueous phase after

passing the sample solution through the cartridge was the

amount of uranium and thorium extracted on the cartridge.

The results indicate that the amount of uranium and

Fig. 2 Effect of aqueous phase pH on extraction of uranium and

thorium

Fig. 3 Effect of aqueous phase flow rate on the recovery of uranium

and thorium ions

Fig. 4 Breakthrough volume for extraction of uranium and thorium

ions

Fig. 5 Effect of amount of uranium/thorium in sample solution on

the extraction of uranium/thorium

Solid phase extraction of uranium and thorium

123

thorium extracted on the modified cartridge was constant,

thus the maximum sorption capacity of this modified solid

support for uranium and thorium was 20 mg (Fig. 5).

Applications for analysis of natural water samples

capacity

The applicability of the proposed method for preconcen-

tration and determination of uranium and thorium in nat-

ural water samples were carried out under optimum

conditions. Natural water samples were collected from (1)

Alamot Spring (Ghazvin, Iran); (2) Persian Gulf; (3) Jujrod

Stream water; (4) Tap water from the Atomic Energy

Organization (Isfahan, Iran) and (5) Well water from the

Atomic Organization (Tehran, Iran).

Table 1 shows the results of percentage recovery of

uranium and thorium from natural water samples to be in

the range of 85–95 %, and the relative standard deviations

were in the range of 1.5–7.5 %. It is worth pointing out that

the results obtained were the average of three replicate

analyses with confidence level of 95 %.

Conclusion

This work presents a new method involving the extraction

and determination of uranium and thorium in aqueous

solutions using octadecyl bonded silica cartridge impreg-

nated with Cyanex 302. The extraction percent were found

to be 89.55 and 86.27 % for uranium and thorium,

respectively. The results showed that uranium and thorium

ions can be sorbed at pH 6 and the sorption capacity of the

functionalized silica gel was 20 mg for both ions. Fur-

thermore, the applicability of proposed method was veri-

fied for uranium and thorium in a number of water samples

of Iran, which their percentage recovery and their relative

standard deviations were in the range of 85–95 and

1.5–7.5 %, respectively.

References

1. Jain VK, Pandya RA, Pillai SG, Shrivastav PS (2006) Talanta

70:257–263

2. Torgov VG, Demidova MG, Saprykin AI, Nikolaeva IV, Us TV,

Chebykin EP (2002) J Anal Chem 57:303–310

3. Dojozan D, Pournaghi-Azar MH, Toutounchi-Asr J (1998)

Talanta 46:123–130

4. Miura T, Morimoto T, Hayano K, Kishimoto T (2000) Bunseki

Kagaku 49:245–252

5. Kato K, Ito M, Watanabe K (2000) Fresenius J Anal Chem

366:54–62

6. Pretty JR, Van Berkel GJ, Duckworth DC (1998) Int J Mass

Spectrom 178:51–60

7. Rao TP, Metilda P, Gladis JM (2005) Talanta 65(1): 1047–1053

Table 1 Determination of U

and Th in various water samplesSample Element Amount

added

lg/L

Amount

found

lg/L

Recovery

(%)

Alamot spring (Ghazvin) U 10 11.0 ± -1.4 95

1.4 ± -0.6

Persian Gulf 10 11.3 ± -1.6 87

2.3 ± -0.6

Jajrod Streamwater 10 11.4 ± -1.7 89

2.5 ± -0.7

Tapwater (Isfahan, AEOI) 10 10.2 ± -0.6 92

1.0 ± -0.2

Well (Tehran, AEOI) 10 11.5 ± -1.5 85

3.0 ± -0.1

Alamot spring (Ghazvin) Th 10 9.8 ± -0.7 86

1.1 ± -0.2

Persian Gulf 10 12.9 ± -0.3 91

3.8 ± -0.1

Jajrod streamwater 10 13.1 ± -0.4 92

3.9 ± -0.1

Tapwater (Isfahan, AEOI) 10 9.9 ± -0.6 93

0.6 ± -0.1

Well (Tehran, AEOI) 10 12.9 ± -0.4 88

2.2 ± -0.2

A. Nilchi et al.

123

8. Shamsipur M, Ghiasvand AR, Yamini Y (1999) Anal Chem

71:4892–4897

9. Gladis JM, Rao TP (2002) Anal Bioanal Chem 373:867–871

10. Unsworth ER, Cook JM, Hill SJ (2001) Anal Chim Acta

442:141–147

11. Metilda P, Gladis JM, Rao TP (2005) Radiochim Acta

93:219–225

12. Ghiasvand AR, Mottaabed K (2005) Asian J Chem 17:655661

13. Raju CSK, Subramanian MS (2005) Microchim Acta 150:

297–303

Solid phase extraction of uranium and thorium

123