Plutonium sorption

Neptunium and plutonium sorption behaviors were remarkably similar, implying that they had similar sorption reactions and solution species. Both NaOH and NaA102 decreased neptunium and plutonium sorption. Several explanations can be offered to rationalize this behavior. First, NaOH and NaAlO, may have reacted with the sediment minerals to yield solids of lower sorptive capacity. Aluminate ion, as an anionic species, also may have competed with the similar neptunate and plutonate anions for sorption sites. Finally, sodium hydroxide may have stabilized the hydrolyzed Np02(0H) and Pu02(0H)2" species in solution, as was shown in the solubility tests, and prevented sorption. Explanation of the effect of NaOH and NaA102 on neptunium and plutonium sorption will require further investigation. 

The presence of either HEDTA or EDTA resulted in significantly lower neptunium and plutonium sorption. Complexation of the neptunium and plutonium by HEDTA and EDTA may have caused the reduced sorption. However, this evidence for complex formation was not consistent with the observations made in the solubility studies (HEDTA increased and EDTA decreased neptunium solubility neither affected plutonium solubility). Thus, HEDTA and EDTA may have decreased neptunium and plutonium sorption through some undetermined effect on the sediment minerals. 

Sorption Prediction Equations. Equations predicting radioelement distribution coefficients, K s, as arithmetic functions of component concentrations were obtained for sorption of strontium, neptunium, plutonium, and americium on two Hanford sediments. These equations, presented in Table VH and derived from statistical fits of Box-Behnken experimental designs, were generated for strontium in terms of sodium ion, HEDTA, and EDTA concentrations. Prediction equations for neptunium and plutonium sorption were derived from NaOH, NaA102, HEDTA, and EDTA concentrations. Americium sorption prediction equations were based on NaOH, HEDTA, and EDTA concentrations. 

M, or 4x10 Bq/m. This is below the lowest ALI value presently used. Considering the selected conditions — highest possible plutonium solubility and lowest observed Kd-value for plutonium sorption on rock — this value contains a considerable safety margin ... 

Studies of the sorption of plutonium are complicated by the high redox reactivity of plutonium. Sorption of Pu(V) by pure aluminosilicates and oxyhydroxide phases is usually characterized by initial rapid uptake followed by slow irreversible sorption and may represent a reductive uptake mechanism catalyzed by the electrical double layer of the mineral surface (Turner et al., 1998 Runde et al., 2002a). In Yucca Mountain waters, the ranges for Pu(V) uptake by hematite, montmorillonite, and silica colloids were 4.9xl0 mLg to 1.8 X 10 mL g 5.8 X 10 mL and 8.1 X 10 mL g, respectively. These are much higher than those observed for Np(V) in the same waters as described previously. High surface redox reactivity for... 

Table II shows that the plutonium sorption onto A190 is around 87% and it was demonstrated that with the aid of fluoride ions the recovery of plutonium traces from waste solutions was possible.

All plutonium solutions, except where pH was a variable, were buffered at pH 7 with phosphate. The final concentration of the phosphate, as KH2P04, was typically 0.001M. Experiments on the effect of phosphate on plutonium sorption indicated that there should be no increase in sorption resulting from formation of a plutonium-phosphate complex at this concentration. All experiments, except where temperature was a variable, were carried out at room temperature, which was usually between 24° and 26 °C. 

Plutonium sorption onto Yucca Mountain tuff. A major challenge in environmental... 

Heterogeneous plutonium sorption on Yucca Mountain tuff. APS Forefront (ANL/APS/TB-42). 18-21... 

Wildung R, Garland T, Rogers J. 1987. Plutonium interactions with soil microbial metabolites Effect on plutonium sorption by soil. In Pinder J, et al., eds. Environmental research on actinide elements. U.S. Department of Energy, Washington, DC. 

Fig. 2. Isotherm data for radium, uranium(VI) and plutonium sorption onto haematite (using the batch-sorption technique, liquid solid ratio indicated on diagrams). The general form of the data is consistent with a linear sorption mechanism. For information, error bars corresponding to 40% of the measured value are shovra (see text for further discussion of experimental variability).

Fig. 7. Results illustrating the effect of organic degradation products on plutonium sorption onto BVG tuff. Range of ISA concentrations studied, 10 M to 10 M. The data shown are for a tuff sample taken from 577 m (below the rotary table), Borehole 2, Sellafield.

Experimental results suggest that thorium, uranium(VI) and plutonium sorption within the ADZ surrounding a cementitious repository will be the same as or higher than sorption in the undisturbed geosphere. 

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