Hydrolysis is an important property that needs to be considered, since the state of hydrolysis of hydrolyzable ions is one of the controlling factors on their adsorption and desorption. For example, Matijevié et al. (1961) studying the Th adsorption of AgI sols found that the hydrolyzed species of Th are more strongly adsorbed than the simple hydrated fon. According to the ion adsorption model of James and Healy (1972), hydrolysis could bring about conditions favorable to the adsorption of lower charged species that are formed ag it progresses. This is explained by the fact that as hydrolysis proceeds, the solvation energy term in their model changes in magnitude much more than the coulombic energy term, The hydrolysis of microamounts of Am depends on its concentration and on the chemical environment such as the kind and the concentration of the acid or base electrolyte (Korotkin, 1973b, 1974). At present, the effect of an electrolyte Is attributed to the change of the activity of the dons due to the change of their state of hydration. Samartseva (1969), using the technique of sorption on Pt, determined the beginning of hydrolysis of 241am (10 1° 4) to be at pH = 2.0-2.5. Shalinets and Stapanov (1972), by electromigration technique, found the beginning to be in the similar pH range for Am at 10 > M concentration. Korotkin (1973a, 1973b, 1974), using distribu- tion chromatography and electromigration techniques, determined it to be at pH = 0.5-1.0 for 2"!Am concentration range of 10 '¥-10 § M. Obviously, there are some discrepancies, part of which may be due to experimental conditions. In any case, it would be helpful to know the state of hydrolysis of Am ab a function of pH in a complex system as a soil. Along with hydrolysis, the degree of polymerization under various conditions The beginning pH for the polymerization of Am in needs to be considered also. Some a complex system such as a soil does not appear to have been defined. An investiexperiments with simple aqueous solutions, however, have been done. gation by Samartseva (1969) on the sorption and desorption of 241am from Pt showed that up to pH = 4.0-4.5, the sorption procegs was reversible, indicating that 2"lam was fonically dispersed, whereas at pH = 5, irreversibility of Resident Am in a soil collected beneath a waste storage crib was leached by groundwater and by 1 N NaNO3 to a considerably greater extent than the resident Pu (Hajek, 1966). In the chemical extraction of soil, collected in the Pucontaminated area at the Rocky Flats Plant and assumed to be contaminated by Am and Pu in the dioxide form, the Am extraction coefficients were generally higher than the values for Pu by one or two orders of magnitude (Cleveland and Rees, 1976). Also, plant uptake studies have shown strong indication that Am is more readily taken up by the plant than is Pu (Cline, 1968; Price, 1972; Romey et at., 1975; Adams et al., 1975). The comparative environmental behavior of Pu and other transuranium elements have been discussed in an excellent review by Dahlman, Bondietti, and Eyman (1976). Few experiments that relate to the desorption of *"/Am in soils have been done. Hajek (1966) found that 7.5% of the resident Am in a soil collected under a waste storage crib was leached by 1 N NaNOq. Knoll (1969) in a soil column experiment found that the soil had little or no effect on removing the Am from any of the tagged organic compounds applied, and certain untagged organic compounds (di-(2-ethylhexy1} phosphoric acid and hydroxyacetic acid) completely leached the 7"!Am from the tagged soil. Wallace (1972a) reported that 100% of 2" am applied to a loam soil was extracted by DTPA, but not by EDDHA (ethylenediamine di-ortho-hydroxyphenol acetic acid). Apparently, certain chelates are more stable to exchange in the soil than others. Cline (1968) showed a soil type effect. In soil columns leached with 100 inches (254 cm) of irrigation water, in excess of 9B% of the Am was retained in the top 1 cm of the acid sotl, whereas only 76% was retained in the top of the alkaline soil. MATERIALS AND METHODS 24am sorption, which is a characteristic of the colloidal state, occurred. Sorption studies on Am in soils is still Sorption and Desorption in Soils. Routsen, Jansen, and Robinson (1975) determined the distribution limited, coefficients (K, values) of 24lam in subsoils of two different soils, one from the arid western United States and the other from the humid southeastern United States. The first soil, which was of neutral reaction and higher in CaCO3 content and cation exchange capacity, showed considerably higher K values (> 1,200) than the second soil, which was acidic and higher in clay content. Few comparisons of sorption with respect to other transurantum elements have been made. Routsen, Jansen, and Robinson (1975) showed that 7*!am (III) was adsorbed to soil stronger than 237Np (V). By inference from the quantitative difference of behavior between Am and Pu, it appears that in general Am may be less strongly sorbed to soils than Pu. For example, measurements of the vertical distribution of ?“!am and 239*240p,, in NTS soil profiles have found , that in some profiles, a decrease in the 2399240py/241am ratio with depth occurred, indicating greater vertical movement of 2*1!Am relative to 239*?4°py (Fowler and Essington, 1974; Gilbert et al., 1975; Essington et al., 1976). 80 The soil used for this study was Aiken clay loam (Ultisol) and its chemically treated forms. The chemical properties of these soil materials are shown in Table 1. The influences of the various soil components on the extractability of 21am were determined indirectly by chemically removing selected components and determining the effect of their removal. Except for free alumina, silica, and amorphous alumino-silicate, the procedures for the removal of the various components have been reported previously (Nishita, 1976}. In essence, treatment I was the CaClo treatment of the virgin soil, This treatment removed the water-soluble salts and organic matter, reduced the amount of exchangeable Na, K, and Mg, and retained Ca as the major (> 50% saturation of the cation exchange complex) exchangeable cation. Treatments IE through V were done in sequential manner. Treatment II was the digestion of the virgin soil with dilute HCL. This treatment removed the HCl-soluble organic matter and salts and carbonates, if present. Treatment IIT, which was the digestion of the samples in 30% H202, brought about the decomposition of organic matter, the dissolution of Mn oxides, and some residual carbonates, if present. Treatment IV 81