Grantee Research Project Results
Supercritical Fluid Extraction of Actinide Surrogates fFrom Environmental MatricesEPA Grant Number: U914940
Title: Supercritical Fluid Extraction of Actinide Surrogates fFrom Environmental Matrices
Investigators: Anderson, Wendy A.
Institution: University of Colorado at Boulder
EPA Project Officer: Packard, Benjamin H
Project Period: January 1, 1996 through January 1, 1999
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1996) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Safer Chemicals , Fellowship - Analytical Chemistry
The objective of this research is to explore the use of chelating agents in combination with supercritical CO2 extraction to remove actinide surrogates from contaminated soils, sediments, aqueous systems, and wastes generated in the nuclear industry.
Supercritical fluid extraction has gained popularity as a separation technique because it avoids the use of hazardous solvents and reduces the volume of material for waste disposal. Moreover, this method is appropriate for the treatment of mixed radioactive and hazardous organic wastes that cannot be disposed under current regulations. In addition to dissolving chelated metals, the solvating power of CO2 can be "tuned" as a function of temperature and pressure to dissolve many classes of hazardous organic compounds.
Extraction efficiency depends on the solubility of both the chelating agent and the metal chelate in supercritical CO2. By measuring the solubility of various metal chelates in CO2, we can determine which chelating agents will be the most efficient for extraction studies, and can use the solubility information to optimize future extraction parameters. We have developed a method to determine the solubility of highly colored metal chelates in supercritical CO2 by near infrared spectroscopy. The beta-diketone ligand, 2,2,7-trimethyl-3,5-octandione, H(tod), shows promise as an inexpensive and effective chelating agent for supercritical fluid extraction. Solubility results for Fe(tod)3 show that this metal chelate is within an order of magnitude as soluble as highly fluorinated metal chelates. Currently extraction studies are being performed on surrogate waste samples to optimize the extraction efficiency of the system in terms of pressure, temperature, mixing, pH, and solvent modifiers. Additional experiments will analyze the performance of a two-step extraction process to separate mixed radioactive and hazardous wastes. In this method, an initial extraction will be performed with neat supercritical CO2 to separate hazardous organic compounds. Then, a batch of supercritical CO2-containing chelating agents will be used to extract metals from the waste sample.