Developing a Fundamental Basis for the Characterization, Separation, and Disposal of Plutonium and other Actinides in High Level Radioactive Waste: The Effect of Temperature and Electrolyte Concentrations on Actinide Speciation Page: 3 of 3

                                
ML,
ML, 0

2    ML                                 1
1                                       0
10       30       50       70       90
T,  C
Figure 2: The constants of acetate protonation and complexation
with Nd(III) at variable temperatures (Ionic strength = 2.0 M).
The data at 250C are from the literature (Smith and Martell,
"Critical Stability Constants, Vol.6") for comparison.
0 04
000      ...                               ...
-0 04

12-
10-
08
06
04-
02
00-

Eu(Ac),
EU(A )
Pha

Do -> Fo Filtmg at
Ac Eu - 3 1. 25"C

EU(AC),

578 5   579 0   579 5   580 0   580 5    581 0
Wavelength, n
Figure 2: Spectral deconvolution of the 5Do -* 7F0 transition of the
Eu3* emission spectrum. The 1:1, 1:2, and 1:3 species can be
directly elucidated.
PLANNED ACTIVITIES

Table 1 Thermodynamic          parameters      of     acetate
protonation    and   complexation    with   Nd(III)   at
different temperatures (Ionic strength = 2.0 M)
T, 0C      log Ka          log 31b         log 32b         log R3
25C    4.80   0.01     1.92   0.04      3.02   0.05    3.58   0.08
45     4.76 0.01      2.05 0.03        3.40 0.05       4.36 0.12
70     4.82 0.01      2.24 0.01        3.65 0.03       4.71 0.10
a K= [HL]/([H+][L-]), where L stands for acetate. The error limits from
the data obtained in this work represent 3a.
b , = [ML,]/([M] [L]'), where i = 1, 2 and 3, M and L stand for Nd and
acetate. The error limits for the data obtained in this work represent
la.
C data at 250C are from the literature (Smith and Martell, "Critical
Stability Constants, Vol.6") for comparison.

59 C
480C
25'C

8-C

578.5    579.0    579.5     580.0    580.5    581.0
Wavelength, nm
Figure 3: High resolution spectra of the 5Do -* 7F0 transition
of the Eu3+ emission spectrum as a function of temperature.
Overall complexation increases markedly in this temperature
range, and the prominence of the 1:2 and particularly the 1:3
peaks increase significantly.

For the next fiscal year, we plan to extend our complexation studies of the trivalent actinides into more
alkaline pH regions. This is now possible based on the hydrolysis results of Prof. Wood. Prof. Wood's group will
continue to study temperature regions in excess of 1000 C. Prof. Clark's group will continue to pursue spectroscopic
studies using other ligands (oxalate, EDTA4-, nitrate, chloride, etc.). Dr. Rao is installing a calorimeter, which his
group will use to directly measure enthalpies and entropies of reaction as a function of temperature.
We will also begin to study actinides in other oxidation states. Prof. Clark's research group is setting up
potentiometric studies of the uranyl cation, and solvent extraction studies of the neptunyl cation. Prof. Wood's
group is beginning to study the solubility of Th4* in highly alkaline solutions; this work will aid in the planning of
studies with Pu in various oxidation states.
INFORMATION ACCESS - An extended summary was also submitted with this Progress Report.
"The aqueous geochemistry of the rare earth elements. IX. A potentiometric study of Nd3+ complexation with acetate in 0.1 molal NaCl
solutions from 25-225* C, Geochim. Cosmochim. Acta, in press.
"A spectroscopic investigation of temperature effects on solution complexation in the Eu3+-acetate system," M. Yeh, T. Riedener, K. Bray, and
S. B. Clark, J. Alloys Compounds, submitted.
"Temperature dependence of chloride complexation for the trivalent f-elements", M. Yeh, A. Maddison, S. B. Clark, J. Radioanalyt. Nucl. Chem.,
submitted.