DOI: 10.1007/s10967-007-0717-9 Journal of Radioanalytical and Nuclear Chemistry, Vol. 273, No.1 (2007) 99–102

0236–5731/USD 20.00 Akadémiai Kiadó, Budapest © 2007 Akadémiai Kiadó, Budapest Springer, Dordrecht

Synthesis of a new microporous indium sulphide and its capabilities to the separation of strontium

Ying Lan, Zhe Su, Xingliang Li, Zhaoqun Jiang, Jun Jin, Jiali Xie, Shoujian Li*

School of Chemistry, Sichuan University, Chengdu, 610064, P.R. China

(Received June 30, 2006)

A new crystalline microporous inorganic ion-exchanger, indium sulphide, was synthesized and characterized. Elemental analysis suggests that the probable composition of this exchanger is [In10.5S14.5].[(H2NCH2CH2–NHCH2)2]2.5. This exchanger is stable in dilute acid (<2M) has strong binding ability with Sr2+, and a quicker exchange kinetic equilibrium taking its crystalline nature into account.

Introduction

Transforming high level radioactive liquid waste (HLLW) into low-/mid-level liquid waste can decrease the radioactivity of the dangerous waste effectively, reduce the storage time and cut down the cost for the stockpile of the waste. Both high thermal release components, 90Sr and 137Cs, are present in large proportion of radioactivity in HLLW. Thus, for almost 50 years, much attention has been focused on the removal of the two hazardous species from HLLW.

Inorganic ion-exchangers, due to their superior resistance to radiation and usually higher thermal stability as compared to organic ion-exchange resins and carcinogenic solvent used in conventional liquid–liquid extraction, and moreover, their compatibility with potential immobilization matrices, find specific applications in the treatment and disposal of nuclear liquid wastes. A variety of inorganic ion-exchangers have been reported and reviewed in the past 4 decades. The typical examples are acidic salts of multivalent metals of group III and IV metals,1–6 salts of heteropolyacids,1,3,7,8 insoluble ferrocyanides,2,3 and natural mineral exchangers like zeolites, micas2,9 and so on. However, most of them are used for selective concentration of 137Cs. Good exchanger for the removal of 90Sr, especially from acidic solution, is still lacking.1

In the present investigation, an attempt has been made to synthesize a new member, crystalline microporous indium chalcogenide, for the inorganic ion-exchanging material family, which might be expected to achieve reasonable separation of 90Sr. Hydrothermal method was employed in our experiments, and the Sr ion-exchanging behavior of the as-synthesized material was also determined.

* E-mail: sjli000616@163.com

Experimental

Reagents and instruments

All the chemicals were of analytical grade and were used without further purification. Powder X-ray diffraction analyses were made on a D/max-rA X-ray diffractometer with graphite-monochromated Cu Kαradiation. The elemental analysis of the exchangers was done by Carlo, Erba1106 element analyzer and EDX attachment on a scanning electron microscope. A Perkin Elmer IR-843 spectrometer was used for IR studies. Thermogravimetric analysis was performed on a Dupout1090 (EXATAR 6000) at a heating rate of 10 °C.min–1 with 300 ml.min–1 of N2 flow. Ion concentration was measured using inductively coupled plasma spectrophotometer (ICP), Perkin Elmer Model 5500.

Synthesis of indium sulphide

Indium metal (57.5 mg), sulfur (40 mg), potassium chloride (75 mg), and distilled water (3 ml) were placed into a 23-ml Teflon-lined stainless steel vessel, followed by triethylenetetramine (0.58 ml, ~4 mmol). The mixture was stirred for 15 minutes, and the vessel was sealed, and then heated to 170 °C for 5 days. After that the reaction was cooled to room-temperature, the slightly yellow octahedral-shaped crystals (65% yield based on In) were mechanically separated from a small amount of yellow solid and then washed with distilled water and ethanol and dried in air.

Determination of ion-exchange capacity (IEC)

The IEC of the exchanger was determined by equilibrating nearly 10 mg solid (<80 mesh) with 20 ml of the solution containing given amount of metal ions with specified acidity in a HCl system. After shaking,

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typically, at the rate of 175 rpm for 2 hours, the solid from solution was separated and the ion concentration was determined by ICP. IEC of the resulting material can be calculated by:

Q = [(C0–C1).V]/W mmol/g

where C0 is the ion concentration in initial solution, mmol/l; C is the ion concentration after equilibrium with the exchanger, mmol/l; V is the volume of testing solution, l; W is the weight of the exchanger in contact with the testing solution, g.

Results and discussion

Characterization of indium sulphide

Powder XRD patterns (Fig. 1) show that the resulting material is a typical crystalline in nature.

IR spectrums of samples were measured by the standard KBr disc method in the range of 400–4000 cm–1 and are shown in Fig. 2. The broad peak at ~3400 cm–1 in the pattern is due to N–H present in the crystal and the distinct peak at 2800 cm–1 represents methyl and methylene, which proves the amine is present in the product. The amine molecules are free or bound in the holes or cavities of the crystal and their roles are to adjust crystal holes’ size and balance the crystal’s charge. The peaks at ~2452 cm–1 and 1642 cm–1 are due to CO2 in the atmosphere and interstitial water (bound water), respectively.

Thermograms of the crystal are represented in Fig. 3 which indicates three main weight loss events. The first, the weight loss of 3.72% occurred between 72 and 150 °C, and is attributed to the loss of external water and crystal water molecules. The second and third events, which begin at approximately 200 and 300 °C, respectively, sum to about 20% of the mass of the

sample. These can be assigned to a two-stage loss of the organic amine (BP. 267 °C) used as a model in the experiment. A weight loss of this amount is roughly equivalent to the loss of 3 organic amine per experiential formula unit.

After pretreated at 140 °C under vacuum for 2 hours, the specific surface area of the exchanger sample was measured and its pore structure was analyzed by static sorption technique in the atmosphere of liquid nitrogen. The results show that the sample possesses a specific surface area of 10.3 m2/g, a micropore volume of 0.03 cm3/g and a framework density of 2.1 g/ml. The median pore diameter was calculated as 9.0 Å, porosity of 6.0%.

The exchanger is stable in water, ethanol, methanol, acetone and DMF even after several days. It is also stable in normal chemical environment. From the test of soaking about 0.05 g of the exchanger in 10 ml of acidic solutions with different HCl concentration up to 3M for periods of 8 hours, followed by the determination of the percentage of indium dissolved in that medium, it was found that less than about 5% In was leached out from the exchanger under the condition of 1M acid, and nearly 8% at 2M acid. The solid slightly decomposed when use of 3M HCl acid.

Composition

According to carbon, hydrogen and nitrogen elemental analyses for the amine-containing crystal and the results from EDX analysis for the major species, indium and sulfur, in the exchange material, the composition of the material nearly corresponds to: In: 57.15; S: 22.04; C: 8.36; N: 6.42; H: 2.62. Based on these data, it might be concluded that the formula of the exchanger is:

[In10.5S14.5].[(H2NCH2CH2–NHCH2)2]2.5.

Fig. 1. XRD powder pattern of indium sulphide ion-exchanger

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Fig. 2. IR spectra of triethylenetetramine (a) and indium sulphide exchanger (b)

Fig. 3. TG and DTG curves for indium sulphide ion-exchanger

Ion-exchange capability

It has been observed that almost all metal ions including Sr2+, Cs+, Co2+, Mn2+, Cr3+, Zn2+, were adsorbed by the exchanger at the acidic conditions in the range from pH 4 to [H+] = 1M in HCl system, keeping arelatively stable adsorbing level. Adsorption decreased while acidity of the testing solution reached up to more than 1.5M. The ion-exchange isotherm for Sr2+ ion at

pH 1 is given in Fig. 4. As it can be seen, the IEC of the exchanger approaches or reaches the maximum value after the initial Sr2+ ion concentration increases to 2.25M or over. The highest exchange capacity was found to be 0.71 mmol/g. IEC values of the exchanger with different metal ions is presented in Table 1. It is interesting to note that the IEC of Sr (0.68 meq/g) is even higher than that of Cs and those of transition metals (<0.14 meq/g) under the same test condition.

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Fig. 4. Isotherm of Sr2+ sorption by indium sulphide ion-exchanger at pH 1

Table 1. Ion-exchange capacity of the exchanger for different metals

Metal Exchange capacity, mmol/g Co2+ 0.044 Mn2+ 0.080 Cr3+ 0.028 Zn2+ 0.14 Sr2+ 0.68 Cs+ 0.31

pH 1, C0 = ~2.75 mmol/l, shaking overnight.

The effect of exchanging time was also investigated by shaking the mixture of metal ion containing solution and the exchanger for the time varied from 10 minutes to 24 hours, followed by separation of solid from solution and measurement of metal concentration.

The results showed that the exchanging equilibrium was completed within 1 hours. These suggest that the process of diffusing and exchanging of the metal ion(s) in the crystalline indium sulphide should be in a rapid manner. This may be owed to the microporous framework structure of the new material.

Conclusions

The synthesis of the new exchanger and its characterization has implied the prospect of this kind of chalcogenides towards attaining a novel separation and confinement of strontium radionuclides. It is also predicted that this exchanger might be useful for the separation of other alkaline earth metals from transition metals.

*

The financial support from the National Natural Science Foundation of China (Grant 20471039 and 20571053) is gratefully acknowledged. The authors express thanks to GUANGLEI CHEN,XIAOHONG ZHU and XIAOYANG JI, Scientific Researchers of Aanalytical and Testing Centre of Sichuan University, for kind supplying the data on metal ion composition, IR and XRD analyses.

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