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Supercrltlcal Fluid Extraction of Lanthanldes and Actinides from Solid Materials with a Fluorlnated @-Diketone Yuehe Lin, R. D. Brauer, K. E. Laintz: and C. M. Wai' Department of Chemistry, University of Idaho, Moscow, Idaho 83843 procedure outlined in the literature.? Solutions of La3+,Eu3+, and Lu3+were prepared from their nitrates, also obtained from Aldrich. Uranyl [(UOZ)~+] solutions were prepared from the Supercritical fluid extraction (SFE) offers several advanacetate salt obtained from Baker. Lanthanum and europium tages over conventional solvent extraction, including the FOD complexes were obtained from MTM Research Chemicals minimization of organic liquid waste generation and exposure (Windham,NH). Allother chemicalsused were analyticalreagent of personnel to organic vapors.' The high diffusivity, low grade. Filter papers used as the sample matrix were obtained viscosity, and temperature-pressure dependence of solvent from Whatman Ltd. (Maidstone, England). Samples were strength are some attractive properties which make superprepared by spiking 10 pg each of a mixture of La3+,Eu3+, and critical fluids excellent candidates for extraction and recovery L U ~solution + or 10pg of a uranyl acetate solution on prewashed filter papers (Whatman No. 42, 0.5 cm X 2 cm in size, washed of organic compounds from solid materials.2 Carbon dioxide with Ultrex HNOs and rinsed with deionized water). The spiked is a solvent of choice in SFE because of its moderate critical filter papers were allowed to air dry at a room temperature of 23 constants, inertness, and availability in purified form. How"C. ever, direct extraction of metal ions by supercritical C02 is All experiments were performed with a laboratory-built SFE highly inefficient because of the charge neutralization reapparatus. SFC-grade C02 or C02 with 5 mol % methanol quirement and the weak solute-solvent interactions. One modifier (Scott Specialty Gases, Plumsteadville, PA) was desuggested approach of extracting metal ions by supercritical livered to the SFE system using a Haskel pump (Haskel Inc., COSis to convert the charged species into metal chelates using Burbank, CA). The system pressure was monitored to f 5 psi using a Setra system (Acton, MA) pressure transducer. The a chelating agent in the fluid phase.3 Recently, Wai and coextractor consisted of an inlet valve (Supelco, Bellefonte, PA) workers have demonstrated that copper ions (Cu2+)in liquid and an outlet valve connected to a commercial extraction cell and in solid materials can be extracted by supercritical carbon (Dionex, Sunnyvale, CA) having a volume of 3.5 mL. The dioxide containing a fluorinated chelating agent, lithium bisextractioncell was placed in an oven with temperature controlled (trifluoroethy1)dithiocarbamate(LiFDDC).4 The choice of to fO.1 "C by an Omega (Stamford, CT) CN9000A temperature the fluorinated ligand was based on the fact that the controller. A fused-silica tubing (Dionex, 50-pm i.d. and 20 cm solubilities of metal-FDDC complexesare significantly higher in length) was used as the pressure restrictor for the exit gas. The SFE system allows static and dynamic extraction steps to be (2-3 orders of magnitude) than the nonfluorinated analogues.5 carried out by closing and opening of the inlet and outlet valves. This in situ chelation-SFE technique may have a wide range A glass tube (0.5-cm i.d. and 3 cm in length) was plugged at of applications, including the preconcentration of trace metals one end with a piece of glass wool, previously cleaned with Ultrex for analytical purposes and the treatment of metal-contamnitric acid. To the open end of the glass tube was inserted a inated waste materials. SFE of lanthanides and actinides spiked filter sample. About 20 pL (80 pmol) of FOD was are particularly interesting because of its potential applicaintroduced to the sample, and the open end was plugged with a tions to nuclear waste analysis and management. The success piece of clean glass wool. The sample tube was placed immeof this in situ chelation-SFE approach for metal extraction diately into the extraction cell and installed in the SFE oven. depends largely on the effectiveness of the ligand. A suitable The temperature of the oven was set at 60 O C , and the cell was pressurized to 150 atm. The chelation and the extraction chelating agent should have a reasonable solubility in the processes were allowed to occur under a static SFE condition for supercritical fluid and form stable and extractable chelates 10min. After that, the exit valve was opened and the samplewas with the metal ions of interest. LiFDDC is not an effective extracted and flushed under dynamicconditionfor 10min. When ligand for complexation with the f-block elements.6 This the dynamic extraction step was completed, the sample was paper describes a method of extracting lanthanide and uranyl removed from the SFE system and the filter paper was analyzed ions from a solid material by supercritical COOcontaining a by a nondestructive neutron activation analysis (NAA). A fluorinated &diketone, 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro- standard filter paper containing the same amount of the lanthanide or uranyl ions was irradiated and counted with the 3,boctanedione (FOD). Potential applications of this SFE sample under identical conditions. The extraction efficiencies method for separating the f-block elements from environwere calculatedbased on the amountof the lanthanideor uranium mental samples are discussed. found in the filter paper before and after the extraction. The extracted lanthanide complexes were also collected in a glass vial EXPERIMENTAL SECTION containing 5 mL of chloroform. The lanthanides trapped in the chloroform solution were determined by back-extraction with The fluorinated 8-diketone FOD was purchased from the 50% HN03 followed by NAA of the acid solution. Aldrich Chemical Co. and used without further purification. The solubilities of La(FOD)3and Eu(F0D)s in supercritical LiFDDC was synthesized in our laboratory according to a COz were determined by placing a weighed amount of the lanthanide complex in a glass tube with both ends plugged with t Current address: Japan Atomic Energy Research Institute, Tokaiglass wool. The sample tube was placed in an extractor of known mura. Ibaraki-kan. JaDan. ~volume and then installed in the extraction oven. The sample (IjEckert, C. A:; V& Alsten, J. G.; Stoicos, T. Enuiron. Sci. Technol. was heated at 60 OC and 150 atm for 30 min. After this static 1986.20. ----. --, 319. heating, the fluid phase was vented into the collection vial (2) Hawthorne, S. B. Anal. Chem. 1990,62, 633A. containing5 mL of chloroform and the sample tube was removed (3) Laintz, K.E.; Yu, J. J.; Wai, C. M. Anal. Chem. 1992, 64, 311. (4) Laintz, K.E.;Wai, C. M.; Yonker, C. R.; Smith, R. D. Anal. Chem. from the extraction cell. The empty cell without the sample 1992,64, 2875. tube was reinstalled into the oven and the system was flushed
INTRODUCTION
(5) Laintz, K. E.; Wai, C. M.; Yonker, C. R.; Smith, R. D. J. Supercrit. Fluids 1991, 4, 194. (8) Alfassi, Z. B.; Wai, C. M. Preconcentration Techniques for Trace Elements; CRC Press: Boca Raton, FL, 1992; pp 101-132.
0003-2700/93/0365-2549$04.00/0
(7) Laintz, K. E.; Shieh, G. M.; Wai, C. M. J. Chromatogr. Sci. 1992, 30,120.
0 1993 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 65, NO. 18, SEPTEMBER 15, 1993
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Table I. Percent Extraction of La3+, Ed+, and Lus+ from a Cellulose-Based Filter Paper with Supercritical C02 Containing FOD at 60 O C and 150 atm extraction ( % ) matrix ligand amt fluid phase condition (FODpmol) La3+ Eu3+ Lu3+ (a) Spiked with 10 pg Each of the Lanthanides at pH 6.5 dry or wet 0
