Kinetics and mechanism of Am(III) extraction with TODGA
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Kinetics and mechanism of Am(III) extraction with TODGA Wen-Bin Zhu • Guo-An Ye • Feng-Feng Li Hui-Rong Li
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Received: 31 March 2013 Ó Akade´miai Kiado´, Budapest, Hungary 2013
Abstract In the present paper, N,N,N’,N’-tetraoctyl diglycolamide (TODGA) as the extractant and n-dodecane as the diluent, the extraction kinetics behavior of Am(III) in TODGA/n-dodecane–HNO3 system were studied, including stirring speed, the interfacial area, extractant concentration in n-dodecane, extracted ions concentration, acidity of aqueous phase and temperature. The results show that: the extraction process is controlled by diffusion mode under 130 rpm of stirring speed and by chemical reaction mode above 150 rpm. The extraction rate equation and the apparent extraction rate constant of Am(III) by TODGA/n-dodecane in 170 rpm and at 25 °C are followed as: d½Morg: ¼ k S ½Am0:94 ½HNO3 1:05 ½TODGA1:19 r0 ¼ aq:;0 aq:;0 org:;0 V dt t¼0 k ¼ ð24:17 3:43Þ 103 mol2:18 L2:18 min1 cm; Ea ðAmðIIIÞÞ ¼ 25:94 0:98 kJ/mol: Keywords
TODGA Am(III) Extraction kinetics
Introduction The minor actinides (MA, mainly Am, Cm and Np) are the largest contributors to the long term radiotoxicity of the waste [1]. The removal of MA from the waste would reduce the necessary storage time from more than 106 years to less than 103 years. Trivalent actinides and
W.-B. Zhu (&) G.-A. Ye F.-F. Li H.-R. Li China Institute of Atomic Energy, P.O. Box 275(26), Beijing 102413, China e-mail: [email protected]
lanthanides can be co-removed from the PUREX raffinate by separation processes that utilize the chemical similarity between these groups of elements. Several processes have been developed and demonstrated, in lab scale, using simulate and genuine nuclear fuel solutions as the feed. Examples of these are: the American TRUEX (TRansUranic EXtraction) process [2–4], the Chinese TRPO process [5], the Japanese DIDPA process [6, 7], the French DIAMEX (DIAMide EXtration) process [8, 9], etc. These processes have been demonstrated with real HLLW, the results show that these processes have excellent efficiency on co-extraction actinides and lanthanides from HLLW. However, all of them are in the experimental scale stage, and have not been applied yet in industry. Each of these processes have certain limitations. The main drawbacks of the TRUEX process are (a) the poor back extraction of Am(III) and Cm(III) at lower acidity, and (b) interference due to solvent degradation products. On the other hand, DIDPA process cannot be applied to the concentrated HLW without denitration, which leads to precipitation of actinides. Similarly, TRPO solvent cannot be applied to 3–4 M HNO3 solutions which is generally encountered in HLLW. Though the completely incinerable DMDBTDMA has been reported to be a promising candidate, it is a poor extractant of Am(III)/Cm(III) from HLLW at acidity B3 mol/L HNO3. In order to increase the efficiency of diamides towards the extraction of Am(III) and Cm(III), efforts are being made towards structural modifications of diamide so as to
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