Sorption of actinides

Such a mechanism would require modifications to some concepts of solubility controlled release. This report concerns a preliminary effort to determine some of the sorption properties of colloidal species representative of those formed during waste form/waste package interaction tests. Sorption of actinides and Tc on those colloids as a function of pH at 25°C was studied. 

Allard B, Olofsson U, Torstenfelt B, et al. 1982. Sorption of actinides in well-defined oxidation states on geologic media. Mater Res Soc Symp Proc 11 775-782. 

SORPTION OF ACTINIDES FROM ALKALINE PRF SALT WASTE SOLUTION AND BY SODIUM TITANATE POWER... 

Beall, G. W., and B. Allard. 1981. Sorption of actinides from aqueous solutions under environmental conditions. In Adsorption from aqueous solutions, ed P. H. Tewari, pp. 193-212. New York Plenum Press. 

It appears that both the order of sorption of actinides to colloids and their order of uptake by plants is affected by oxidation state. The postulated order of uptake by plants (Np>Am=CmHI>Pu) is approximately the inverse of their order of hydrolysis and their order of adsorption of oxidation states to colloids [Pu(IV)>U(VI)2Cm(III)=Am(III)>Np(V)]. Based on reported adsorption results for Pu(VI) (48, 49), and on preliminary results from our sorption studies dealing with oxygenated-"yl" species, the position of Pu(VI) would be between U(VI) and Np(V). Results from one study (48) showed that Pu(VI) is assimilated by barley plants more readily than Pu(IV) or Pu(III). 

The sorption of actinides on a variably charged surface sorption site can be represented as a function of pH in a generalized surface reaction demonstrated here with Np(V) ... 

McMillan, J. W., Mountfort, S. A. 1993. Measurement of the sorption of actinides on minerals using microanalytical techniques. Analyst, 118, 1241-1246. 

Geckeis H, Klenze R, Kim J1 (1999) Solid-water interface reactions of actinides and homologues sorption onto mineral surfaces. Radiochim Acta 87 13-21... 

Studies of Actinide Sorption on Selected Geologic Materials... 

The oldest, most well-established chemical separation technique is precipitation. Because the amount of the radionuclide present may be very small, carriers are frequently used. The carrier is added in macroscopic quantities and ensures the radioactive species will be part of a kinetic and thermodynamic equilibrium system. Recovery of the carrier also serves as a measure of the yield of the separation. It is important that there is an isotopic exchange between the carrier and the radionuclide. There is the related phenomenon of co-precipitation wherein the radionuclide is incorporated into or adsorbed on the surface of a precipitate that does not involve an isotope of the radionuclide or isomorphously replaces one of the elements in the precipitate. Examples of this behavior are the sorption of radionuclides by Fe(OH)3 or the co-precipitation of the actinides with LaF3. Separation by precipitation is largely restricted to laboratory procedures and apart from the bismuth phosphate process used in World War II to purify Pu, has little commercial application. 

The LiCl AIX process is based on (i) the formation of anionic chloride complexes of the tripositive actinide and lanthanide metals in concentrated LiCl solutions, (ii) the sorption of these complexes onto a strong base anion exchange resin contained in a column, and (iii) the preferential chromatographic elution of the lanthanides as a group prior to elution of the actinides. The generalized formation of the trivalent metal anionic chloride complexes is illustrated in equation (1) ... 

Silva RJ, Benson LV, Apps JA. 1979. Studies of actinide sorption on selected geologic materials. ACS Symp Ser 100 215-240. 

Sorption. In general, actinide sorption will decrease in the presence of ligands that complex with the radionuclide (most commonly humic or fulvic acids, CO3 , SO4 , E ) or cationic solutes that compete with the radionuclide for sorption sites (most commonly Ca, Mg " "). In general, sorption of the (IV) species of actinides (Np, Pu, U) is greater than of the (V) species. 

As discussed previously (Section 9.06.3.1.1), plots of pH sorption edges (see Figure 3) are useful in summarizing the sorption of radionuclide by substrates that have amphoteric sites (i.e., SOH, SO , SOHJ). The pH sorption edges of actinides are similar for different aluminosilicates (quartz, a-alumina, clinoptUolite, montmorillo-nite, and kaolinite). For example, Np(V) and U(VI) exhibit similar pH-dependent sorption edges that are independent of specific aluminosilicate identity (Bertetti et al, 1998 Pabalan et al., 1998). Under similar solution conditions, the amount of radionuclide adsorbed is primarily a function of the surface area. This observation has led several workers to propose that the amount of actinide sorption onto natural materials can be predicted from the surface site density and surface area rather the specific molecular structure of the surface (Davis and Kent, 1990 Turner and Pabalan, 1999). 

Carroll et al. (1992), Stout and Carroll (1993), Van Cappellen et al. (1993), Meece and Benninger (1993), Brady et al. (1999), and Reeder et al. (2001) summarize empirical data and theoretical models of actinide-carbonate mineral interactions. The surface PDI on carbonate minerals may be Ca or Mg " ". Increased solution concentration of Ca " will lead to decreased actinide sorption, which then leads to complex sorption behavior if the carbonate... 

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