ENVR 211 |
| Nikolla P. Qafoku1, Calvin C. Ainsworth1, Dhanpat Rai2, and Dean Moore2. (1) Environmental Dynamics and Simulation Group, Pacific Northwest National Laboratory, MSIN: K3-61 902 Battelle Boulevard, P.O. Box 999, Richland, WA 99352, (2) Chemical Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Bldv, P7-50, Richland, WA 99352 |
| Siderophores, such as rhodotorulic acid (RA), are organic ligands secreted by some microorganisms to mobilize Fe(III) from the environment and use it for their metabolic needs. The stability constants of most siderophore - Fe(III) complexes are very high. Thorium may also form strong complexes with siderophores. The positive aspect of this phenomenon is that siderophores may be successfully used in decontamination processes. The negative aspect, however, is that actinide mobility may be drastically increased in the presence of siderophores. Only a few examples can be found in the literature where stability constants for the Th-siderophore complexes have been reported. Several carefully conducted macroscopic solubilization batch experiments with ThO2 (am) were conducted under controlled atmosphere conditions at room temperature in the presence of RA. The RA concentration in the contact solutions varied in the range from 0.1 mM/L to 2.554 mM/L. These experiments were conducted over a pH range from 2 to 14, for 6 to more than 100 days. Results showed that ThO2 (am) solubility drastically increased in the presence of RA. The trends of changes in ThO2 (am) solubility with pH were significantly different at pH > 4, in the presence of RA. Thorium was massively mobilized into the aqueous phase, and the amount of Th released increased with the RA concentration up to a RA concentration of 1.333 mM/L. An increase beyond this point appeared to have no further effect on ThO2(am) solubilization. ThO2 (am) solubility decreased slowly in the pH range from 4 to 9.6, in the experiments conducted with RA concentrations of 1.33 mM/L or greater. It followed a more rapid decreasing slope from pH=9.6 to approximately 12 and ThO2 (am) solubility became independent of pH at pH values between 12 and close to 14. A coupled, non-linear, least-squares and chemical equilibrium program (INSIGHT) will be used to calculate complexation constants for the Th-siderophore aqueous complexes and to calculate the ThO2 (am) solubility constants in the presence of RA. |
|
Biogeochemistry of Chelating Agents
6:00 PM-8:00 PM, Wednesday, September 10, 2003 Javits Convention Center -- North Pavillion, Poster
Division of Environmental Chemistry |