Americium kinetics

Kelman BJ, Sikov MR. 1984. Transplacental movements of americium-241 in the guinea pig and early distribution kinetics in the dam. Teratology 29(2) 40A. 

Schmidt CT, Durbin P. 1985. A five-compartment model for the kinetic distribution of americium in man. Health Phys 49(1) 161. 

Sontag W. 1986. Multicompartment kinetic models for the metabolism of americium, plutonium and uranium in rats. Hum Toxicol 5 163-173. 

Schuessler, W., Artinger, R., Kienzler, B. KlM, J. I. 2000. Conceptual modeling of the humic colloid-borne americium(III) migration by a kinetic approach. Environmental Science and Technology, 34, 2608-2611. 

In previous work (l.> > ) it was found that the kinetics of sorption was an important parameter affecting the migration of nuclides in geologic media. For example, in experiments designed to measure the kinetics of reaction for radionuclides in solution with tablets of rock, it was found that periods from several minutes to several hours were required for the radionuclides to reach steady state concentrations on the rock tablets and in the solutions. Figure 1 shows the reaction curves found for the sorption of plutonium and americium from solution by a tablet of granite. The reaction rates for the sorption of plutonium and americium from solution are not the same, and both require a number of hours to reach steady state concentrations. 

T. W. Newton, The Kinetics of the Oxidation Reduction Reactions of Cranium, Neptunium, Plutonium, and Americium in Aqueous Solution, TID-26506, U.S. Energy, Research, and Development Administration (ERDA) Technical Information Center, Washington, D.C., 1975. 

Weigl, M., Geist, A., Mullich, U., Gompper, K. 2006. Kinetics of americium(III) extraction and back extraction with BTP. Solvent Extr. Ion Exch. 24 (6) 845-860. 

Tin and americium were so extensively sorbed under all conditions that isotherm data could not be obtained. These elements are not significantly mobile in the Mabton Interbed aquifer. Values of Freundlich constants for technetium, radium, uranium, neptunium, and plutonium are given in Table IV. The Freundlich equation did not fit the selenium sorption data very well probably because of slow sorption kinetics or precipitation. Precipitation was also observed for technetium at 23°C for concentrations above 10 7M. This is about the same solubility observed for technetium in the sandstone isotherm measurements. Linear isotherms were observed only in the case of radium sorption. In general, sorption on the Mabton Interbed was greater than on the Rattlesnake Ridge sandstone. This is probably due to the greater clay content of the Mabton standard. 

Mikheeva, M.N., Novicoov, P., Myasoedov, B.F., and Tikhomirov, S.V., Kinetics of americium(VI) mass transfer through solid supported liquid membrane with HDEHP. J. Radioanal Nucl Chem., 1994, 185 265-271. 

In conclusion, we can state that additions of small amounts of phosphoric acid increase the rate of Am (III) oxidation by Ag + ions without drastically changing the distribution coefficients of the species involved, because no complexation of Am occurs in these solutions, contrary to what occured in the extensive studies of Myassoeodov et al. (12, 13) in more concentrated phosphoric acid, where the kinetic effects must be attributed to changes in americium and silver (II) ionic species. In our Am-Cm separations we added phosphoric acid, which accelerates the oxidation rates of Am (III), solubilizes argentic oxide, and makes it possible to obtain Am (VI) quantitatively and rapidly at room temperature. 

Actinides.— A kinetic study has been made of the reduction of neptunium(vn) and americium(vi) by bromide ion. In both cases two moles of oxidant are consumed in the production of a mole of Brj. The rate law governing the neptunium(vii) reduction is of the form... 

An excellent extractant for Am is bis(2-ethylhexyl) phosphoric acid (HDEHP). This extractant is commercially available in large quantities, can be readily purified, and has been widely used for both analytical and plant-scale recovery and purification of americium [48,49]. Extraction of Am(iii) is very sensitive to the nature of the diluent [49]. Kinetics of extraction were studied by Choppin and Nash [336]. 

Species (e.g. hydrogen peroxide and HO2 radicals) produced by radiolysis of water by alpha particles reduce the higher oxidation states of americium to Am(iii). Because of its lower specific addvity, the rates of autoreduction of Am species are much less than those of Am species. Zaitsev et at. [2S9] account for the kinetics of autoreduction of aqueous AmOl and AmO ions by assuming that H2O2 is consumed only in reducing Am(vi), Am(v) is reduced only by HO2 radicals, but Am(v) may be oxidized to Am(vi) by OH radicals. 

All investigators concur that autoreduction of Am(vi) is kinetically zero order with respect to the AmO ion and first order with respect to total americium concentration ... 

Extensive treatments of oxidation-reduction kinetics of the aqueous ions of uranium through americium are found in Chapters 5-8, in the critical monograph of Newton [264], and in a recent review [273]. 

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