Uranium desorption

The complexation of U by humic substances from soils contaminated by natural processes is also being studied. Gel permeation chromatography has been used to show that different fractions of humic substances vary greatly in their effectiveness as ligands. These studies have also shown that uranium desorption is redistributed slowly between different fractions of humic substances following its initial adsorption. 

Since uranium is present in sea water in such low concentrations as 3.2 pig/1, adsorption recovery could become a feasible method of extraction and concentration for further utilization. Amidoxime resin is one of the promising adsorbents for this purpose and in fact after contact with sea water for more than one hundred days the resin can accumulate several hundred mg/1 of uranium in the bed. The resin also adsorbs alkaline earth metals such as calcium and magnesium, which must first be removed by a weak acid solution. Desorption of uranium by hydrochloric acid solutions of different concentrations and the resultant equilibrium relations are shown in Fig. 9.5. From this result, hydrochloric acid of one molc/1 was selected as an eluant. Acid elution and uranium desorption are solved simultaneously by a similar set of... 

Erdal, B.R. Aguilar, R.D. Bayhurst, B.P. Daniels, W.R. Duffy, C.J. Lawrence, F.O. Maestas, S. Oliver, P.Q. Wolfsberg, K. "Sorption-Desorption Studies on Granite. I. Initial Studies of Strontium, Technetium, Cesium, Barium, Cerium, Europium, Uranium, Plutonium, and Americium", in "Proceedings of the Task 4 Waste Isolation Safety Assessment Program Second Contractor Information Meeting", Vol. II, Report PNL-SA-7352, Battelle Pacific Northwest Laboratory, 1978, pp. 7-67. 

In comparison to the bismuth molybdate and cuprous oxide catalyst systems, data on other catalyst systems are much more sparse. However, by the use of similar labeling techniques, the allylic species has been identified as an intermediate in the selective oxidation of propylene over uranium antimonate catalysts (20), tin oxide-antimony oxide catalysts (21), and supported rhodium, ruthenium (22), and gold (23) catalysts. A direct observation of the allylic species has been made on zinc oxide by means of infrared spectroscopy (24-26). In this system, however, only adsorbed acrolein is detected because the temperature cannot be raised sufficiently to cause desorption of acrolein without initiating reactions which yield primarily oxides of carbon and water. 

The sorption and desorption behavior of uranium is similar to neptunium. Figure 3 shows that hysteresis is more important for uranium sorption under reducing conditions than under oxidizing conditions. Values of Ng/Nd are 10 and approximately 200 for oxidizing and reducing conditions, respectively. 

Figure 3. Sorption and Desorption Isotherms for Uranium Sorption on Mabton Interbed Solids, (a) Oxidizing Conditions, (b) Reducing Conditions.

Another example is found in the analysis of the mineral zircon. We had previously published [4] a spectrum of a positive ion laser desorption spectrum of a sample of the mineral zircon (zirconium silicate) showing uranium as 238U+, present in the sample at a level of approximately 15 parts-per-million [41]. The spectrum, which showed mixed zirconium oxides and hydroxides as the most intense peaks in the spectrum, was taken with a four second delay between the laser pulse and ion detection, in order to allow neutrals to be pumped out of the cell. These conditions had been found adequate for analysis of organic compounds. However, it was found that the reactivity of zirconium was such that the mixed oxides and hydroxides were produced as ion-molecule reaction products during the long trap period. 

In addition to the migration of dissolved or suspended uranium due to the movement of water in the environment, the transport and dispersion of uranium in surface water and groundwater are affected by adsorption and desorption of the uranium on surface water sediments. On the other hand, migration of uranium in soil and subsoil and uptake in vegetation are usually quite local involving distances from several centimeters to several meters. 

Uranium oxides have been investigated as catalysts and catalyst components for selective oxidation. They are more commonly used as catalyst components, but there are also reports of uranium oxide alone as a selective oxidation catalyst The oxidation of ethylene over UO3 has been studied by Idriss and Madhavaram [40] using the technique of temperature programmed desorption (TPD). Table 13.3 shows the desorption products formed during TPD after ethylene adsorption at room temperature on UO3. The production of acetaldehyde from ethylene indicates... 

One of the key problems with many ion-exchange materials, including the polyamidoxime sorbents used for uranium extraction is encountered in the desorption (elution) stage. With the polyaminodimer, the HCl elution of uranium is usually carried out in two steps. The removal of calcium and magnesium with dilute HCl solution ( 0.01 M) is followed by uranium elution with 0.3-1.0 M HCl [212, 213]. The concentrated efSuent contains tens to hundreds of milligrams of uranium per liter and the removal of uranium reaches 93%. However, the elution with HCl seriously reduces the sorbent capacity [198, p. 213 163, 207, 208], e.g., a six-day treatment of the fibrous amidoxime sorbents with 1 M HCl... 

The results of sorption and desorption of uranium are shown in Table 2. As shown in Table 2, the desorbed percentages of uranium from the granite sur ces are somewhat greater than sorbed percentages of uranium on granite surfaces. Thus, the results show that the sorption process of U(V1) is a little irreversible for the two types of granite surfaces depending on pH and surface type. This may be due to the frict that small amount of a mineral such as chlorite mainly contribute to the sorption of uranium and the uranium sorbed on this mineral is hard to be desorbed from the mineral sur ce. 

Figure 3 Sorption and desorption edges for uranyl on goethite. Each sample contained 60m L goethite and 100p,gmL uranium. The sorption edge was measured 2 d after uranium addition desorption samples were contacted with the uranyl solution at pH 7 for 5 d, the pH was adjusted to cover the range of interest, and the samples were re-equilihrated for 2 d prior to sampling (see also Bryan and Siegel, 1998).

Laboratory experiments, transport modeling, field data, and engineering cost analysis provide complementary information to be used in an assessment of the viability of an MNA approach for a site. Information from kinetic sorption/ desorption experiments, selective extraction experiments, reactive transport modeling, and historical case analyses of plumes at several UMTRA sites can be used to establish a framework for evaluation of MNA for uranium contamination (Brady et al, 1998, 2002 Bryan and Siegel, 1998 Jove-Colon et al, 2001). The results of a recent project conducted at the Hanford 100-N site provided information for evaluation of MNA for a °Sr plume that has reached the Columbia River (Kelley et al, 2002). The study included strontium sorption-desorption studies, strontium transport and hydrologic modeling of the near-river system, and evaluation of the comparative costs and predicted effectiveness of alternative remediation strategies. 

Madhavaram H, Idriss H (1997) Temperature programmed desorption of ethylene and acetaldehyde on uranium oxides. Evidence of furan formation from ethylene. Stud Surf Sci Catal 110 265... 

Non-aqueous Process. A halide volatility process has been extensively studied among the dry reprocessing processes. The chloride distillation using carbon tetrachloride has been studied in applying to the treatment of irradiated uranium dioxide (32). In a proposed flow-sheet, chlorination and distillation processes are followed by the sorption and desorption process of uranium chloride on a barium chloride bed. Fundamental data of decontamination for the fission products have been accumulated, showing that excellent purification of uranium is achieved. 

In an effort to understand adsorption mechanisms, Waite et al. (1994) (see also Chisholm-Brause and Morris 1992) examined the character of U(V1) adsorption sites on the HFO surface with uranium EXAFS spectroscopy. They concluded that a single inner-sphere, mononuclear, bidentate complex, (sFe02)U02, could explain their low pH-adsorption results and that U(VI) desorption at alkaline pH s could be modeled assuming a (sFe02)U02C03 surface species. Waite et al. (1994) used the DL model in their study and assumed the existence of both weak and strong adsorption sites (see Fig. 13.14 and Chap. 10). 

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