SOLID PHASE EXTRACTION OF ULTRATRACE Th(IV) IN WATER SAMPLES SOLID-PHASE USING POLIOXOMETALIC MATERIAL MODIFIED WITH SILICA AND ITS SPECTROPHOTOMETRIC DETERMINATION WITH ARSENAZO III

"Al.I. Cuza" Universityy of Iasi,, Faculty y of Chemistry, y, Carol-II No. Carol No 11, 11 Iasi 700506, 700506 Romania. Romania

Mihaela Bertescu Bertescu, Cecilia Arsene Arsene, Marius Duncianu, Duncianu Doina Humelnicu, Humelnicu Dorina Mantu, Mantu Romeo-Iulian Romeo Iulian Olariu Olariu* *[email protected] oromeo@uaic ro

ABSTRACT A simple and reliable method for rapid extraction and determination of thorium in natural waters by POM POM-SiO SiO2 sorbent and the determination of Th4+ with Arsenazo III as a chromogenic reagent is presented. presented To the best of our knowledge, knowledge modified POM material with silica have not been employed previously for the separation and concentration of thorium ion from aqueous samples. samples Extraction efficiency and the influence of type and optimum amountt off the th extracting t ti g matrix, t i , flow fl rates, t , type typ and d minimum i i amountt off inorganic i g i eluent l t were evaluated. l t d The Th limit li it off detection d t ti off the th p proposed p d method is 200 ng L-11.

INTRODUCTION

FIGURES

a

120

100

100 80

% Reco R overry

% Recovvery

80

60

60 HCl HCLO4

40

40

HNO3

SiO2/K8[SiW 11O39]

20

20

0

0

2

4

pH

6

8

0 00 0.0

10

Figure gu e 3 3. Effect ect o of p pH o of feed eed so solution ut o o on tthe e recovery eco e y of 20 µg thorium from 50 mL water by the sorbent (2 mol/L HNO3 as eluent). eluent)

05 0.5

10 1.0

1.5 1 5 conc (mol/L) conc.

20 2.0

25 2.5

30 3.0

Figure 4. Fi 4 Effect Eff t off the th concentration t ti off various i mineral acids, as stripping agents, on recovery of 20 µg thorium from a 50 mL sample p byy the sorbent. 100

100

80

%R Recove ery

80 % Re eco overy y

Presentt knowledge P k l dg off the th distribution di t ib ti off thorium th i resources is poor because of the relatively low-key low key exploration p efforts arising g out of insignificant g demand Thorium concentrations in natural surface demand. water samples p had values of 1 ÷ 0.1 ng g L-11 but are much more abundant in nature than other radionuclides such as uranium. However, highly sensitive methods are required for preconcentration and determination of thorium in water samples collected for prospecting purposes. purposes Because of their structures and properties these (iso)polyoxometalates and their SiO2 modified materials give rise to interest in interdisciplinary areas such as materials for the separation and sequestration of radioactive species [1÷3]. [1÷3] For the present study SiO2-K K8[SiW11O39] has been used as solid phase material for the preconcentration and separation of thorium ion from spiked aqueous samples. Accomplishments for the chemical characterization of the synthesized units is foreseen through the data obtained by the mean of state of art technique as Fourier Transformed Infrared Spectroscopy (FTIR), UV UV-vis vis spectrophotometer, scanning electronic microscopy (SEM) with electron diffraction X X-ray ray (EDX) detection (Figure 1) [4,5]. [4 5]

60 SiO2/K8[[SiW 11O39]

40

60 SiO2/K8[SiW 11O39]

40

20

20

0

0

0

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2 3 4 volume of HNO3 2 M (mL)

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Figure 5. Fi 5 Effect Eff t off eluent l t volume, l on recovery off 20 µg thorium from a 50 mL sample by the sorbent.

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

sorbent (g)

Figure 6. Fi 6 Effect Eff t off the th amountt off sorbent, b t on recovery of 20 µg thorium from a 50 mL sample by the sorbent.

b

Figure 1. 1 SEM images for K8[SiW11O39] (a) and SiO2/K8[SiW11O39] (b). (b)

EXPERIMENTAL A CINTRA 10e UV-vis spectrophotometer has been used d for f the th spectrophotometric p t ph t t i determination d t i ti off thorium by using 0.05% 0 05% (m/v) aqueous solution of arsenazo(III) ((III)) as a chromogenic h g i reagent g t ((Figure (Fig 2)) . A stock solution (100 ppm) of thorium was prepared by using by i g reagent g grade g d Aldrich-Sigma Ald i h Sig without ih anyy further purification. purification

Figure 2 Fi 2. UV-vis absorption p spectra of Th Th-Arsenazo Arsenazo (III) complexes complexes.

RESULTS

REMARKS

Influence of pH on feed solution was studied in th range off 2-8. the 2 8 Figure Fi 3 shows h th t thorium that th i i ion can be retained by the solid phase quantitatively i the in th p pH H range g off 4-6. 46 St i i off thorium Stripping th i i from ion f th solid the lid phase h was investigated under various condition including: diff different t volumes l and d concentration t ti off mineral i l acids such as HNO3, HCl and HClO4.

Optimal p retention p parameters: The stationary phase conditioning - 2 ml HNO3 (2M) followed by 2 ml distilled water; ►optimal quantity: solid phase 0.2g/cartridge; 0 2g/cartridge; ► pH = 4 ÷ 6 units; ► flow rate = 1.5 1 5 ml/min; ► radionuclide concentration =10 10-4 ÷10 10-7M. Optimal parameters recovery / elution: ► eluent nature/concentration = 2.0 2 0 M HNO3; ► elution l ti flow fl rate t = 1.5 1 5 mll / min; i ►optimum eluent volume = 2.0 2 0 ml. ml

The results are shown in Figure 4. 4 In comparison with ith HClO4 and d HCl, HCl HNO3 lead l d to t a quantitative tit ti elution of thorium in the 1.0 1 0 ÷ 2.5 2 5 M range. range F th elution Further l ti studies t di off thorium th i were carried i d out with 2.0 2 0 M HNO3 for both phases. phases The effect of flow rates of sample and stripping solution l ti study t d from f th sorbent the b t on the th recovery of thorium ion indicated an eluent optimal flow of 2 ml/min. l/ i Effects Eff t off the th eluent l t volume l and d the th amount of sorbents on the recovery of thorium i have ion h b been also l investigated. i tig t d Th result The lt are shown h i Figure in Fi 5 and d Figure Fi 6 6. The maximal eluent volume and optimal amount off sorbent b t studies t di shows h th t above that b 2 mll HNO3 2M and 0.2 0 2 g sorbent, sorbent recovery of extraction of th i thorium i remains ion i constant t t and dq quantitative. tit ti

REFERENCES 1. KIM, 1 KIM K.C., K C POPE, POPE M.T., M T J. J Chem. Chem Soc., Soc Dalton Trans., Trans p. p 986, 986 2001. 2001 2 KIM, 2. KIM K.C., K C GAUNT, GAUNT A., A POPE, POPE M.T., M T J. J of Cluster Science, Science 13(3), 13(3) p. p 423, 423 2002. 2002 3 ISHII, 3. ISHII Y., Y YAMAWAKI, YAMAWAKI K., K URA, URA T., T YAMADA, YAMADA H., H YOSHIDA, YOSHIDA T., T OGAWA, OGAWA M., M J. J Org. Org Chem., Chem 53, 53 p. p 3587, 3587 1998. 1998 4 OLARIU, 4. OLARIU R.I., R I HUMELNICU, HUMELNICU D., D SANDU, SANDU I., I HUMELNICU, HUMELNICU I., I ARSENE, ARSENE C., C Revista R i t de d Chimie, Chi i 60 (11), (11) p.1216, 1216 2009. 2009 5. HUMELNICU, D., OLARIU, R.I., SANDU, I., HUMELNICU, I., SANDU, A. V., ARSENE, C., Revista de Chimie, 60 ((12), ) p p.1264, 2009.

The proposed method includes extraction and preconcentration p t ti off radionuclides di lid using i g solid lid phase extraction and subsequent d t determination i ti by spectrophotometric by p t ph t t i method th d with Arsenazo (III) (ε = 49637 L M-1 cm-1). ) D Detection i limit li i ((LOD)) off the h method h d has h been b estimated at 200 ng L-11. The synthesized y material highlighted g g a high g selectivity for thorium ions. ions From the experiments e pe e ts itt was as found ou d tthat at a ca cartridge t dge (stationary phases) can be used up to eight times, having a degree of about 87.56% recovery factor. factor

ACKNOWLEDGEMENTS Financial Fi i l supportt off this thi workk from f th Romanian the R i program founding by CNCSIS-UEFISCUS CNCSIS UEFISCUS under PN PNII-ID PCE 2007 project No. No 405 is gratefully acknowledged. k l d d