THÔNG TIN TÀI LIỆU
© 2001 by CRC Press LLC Chapter Five Non-Thermal Treatment Technologies © 2001 by CRC Press LLC 5.1 Supercritical Fluid Extraction Technology for Nuclear Waste Management Chien M. Wai Department of Chemistry University of Idaho Moscow, Idaho Introduction Solvent extraction is one of the most widely used techniques for concentration, separation, and cleaning of a variety of substances in industrial operations. Conventional solvent extraction processes usually require using organic liquids, acidic or alkaline solutions, or a combination of these, generating envi- ronmental problems for handling and disposal of used solvents. In the past two decades, there has been considerable interest in developing techniques utilizing supercritical fluids as solvents for chemical extrac- tion, separation, synthesis, and cleaning. 1,2 The reasons for developing supercritical fluid extraction (SFE) technologies are mostly due to the changing environmental regulations and increasing costs for disposal of conventional liquid solvents. Supercritical fluids exhibit gas-like mass transfer rates and yet have liquid- like solvating capability. The high diffusivity and low viscosity of supercritical fluids enable them to penetrate and transport solutes from porous solid matrixes. Furthermore, the solvation power of a supercritical fluid depends on density; thus, one can achieve the optimum conditions for a particular separation process by manipulating the temperature and pressure of the fluid phase. Carbon dioxide (CO 2 ) is widely used in SFE because of its moderate critical constants (T c = 31.1°C, P c = 72.8 atm, ϕ c = 0.471 g/mL), inertness, low cost, and availability in pure form (Figure 5.1.1). In SFE processes, compounds dissolved in supercritical CO 2 are separated by reducing the pressure of the fluid phase, causing precipitation of the solutes. The fluid phase is usually expanded into a collection vessel to remove the solutes and the gas is recycled for repeated use. The unique properties of supercritical CO 2 have found many new applications in industrial operations. Typical examples of large-scale industrial applications of the SFE technology using supercritical CO 2 include the preparation of decaffeinated coffee and hop extracts. 1 Direct extraction of metal ions by supercritical CO 2 is highly inefficient because of the charge neutral- ization requirement and the weak solute-solvent interactions. However, when metal ions are chelated with organic ligands, they may become quite soluble in supercritical CO 2 . 3 Quantitative measurements of metal chelate solubilities in supercritical CO 2 were first made by Wai and co-workers in 1991 using a high-pressure view cell and UV/VIS spectroscopy. 4 In this study, the authors noted that fluorine substitution in the chelating agent could greatly enhance (by 2 to 3 orders of magnitude) the solubility of metal chelates in supercritical CO 2 (Ta ble 5 . 1.1). The demonstration of copper extraction from solid and liquid materials using supercritical CO 2 containing a fluorinated chelating agent bis(trifluoroethyl)dithiocarbamate was © 2001 by CRC Press LLC reported in 1992. 5 Since then, over 50 papers regarding SFE of metals from different systems have been published in the literature. A variety of chelating agents, including dithiocarbamates, β -diketones, organ- ophosphorus reagents, and macrocyclic ligands, have been tested for metal extraction in supercritical fluid CO 2 . 6 These studies provide a basis for understanding the nature of metal chelation and extraction in supercritical fluids. According to the literature, the important parameters controlling SFE of metal species appear to be: 1. Solubility and stability of chelating agents 2. Solubility and stability of metal chelates 3. Water and pH 4. Temperature and pressure 5. Chemical form of metal species 6. Matrix This in situ chelation-SFE technique may have a wide range of applications to metal related problems, including toxic metal decontamination and mineral processing. The new SFE technology appears attrac- tive for nuclear waste treatment because it can greatly reduce the secondary waste generation compared with the conventional processes involving liquid solvents. Other potential advantages of using the SFE technology for nuclear waste management include fast extraction rate, capability of penetration of solid FIGURE 5.1.1 Phase diagrams of CO 2 and H 2 O. TA BLE 5.1 .1 Solubility of Some Fluorinated Metal Dithiocarbamates Relative to their Non-fluorinated Analogues in Supercritical CO 2 Metal Dithiocarbamate a Solubility at 50°C and 100 atm Cu(DDC) 2 1.1 × 10 6 M Cu(FDDC) 2 9.1 × 10 4 M Ni(DDC) 8.5 × 10 7 M NiFDDC) 7.2 × 10 4 M Co(DDC) 3 2.4 × 10 6 M Co(FDDC) 3 8.0 × 10 4 M a DDC = (CH 3 CH 2 ) 2 NCS 2 ; FDDC = (CF 3 CH 2 ) 2 NCS 2 . Date from Reference 4. Temp ( o C) Temp ( o C) CO 2 S.F. CO 2 H 2 O P (atm)P (atm) 73 5 S L G S L G -56 31 0 374 4.6 mm 218 © 2001 by CRC Press LLC matrixes, and rapid separation of solutes by depressurization. The tunable solvation power of supercritical fluid CO 2 also allows potential separation of metal complexes based on their difference in solubility in the fluid phase or difference in partition coefficient between the fluid phase and the matrix. This unique property of supercritical CO 2 may be very useful for separating uranium and plutonium complexes without requiring chemical redox reactions as in the traditional PUREX process. This section summarizes the information regarding SFE of lanthanides, actinides, strontium, and cesium currently available in the literature to illustrate the capability of the SFE technology for removing long-lived radioisotopes from contaminated wastes. The possibility of utilizing the SFE techniques for treating mixed wastes and for reprocessing spent nuclear fuels is also discussed. Supercritical Fluid Extraction of Lanthanides and Actinides Lanthanides and actinides in solid and liquid materials can be extracted using a chelating agent such as a β -diketone dissolved in supercritical CO 2 . 6-10 Fluorine-containing β -diketones such as hexafluoroacety- lacetone (HFA) and thenoyltrifluoroacetone (TTA) are more effective than the nonfluorinated acetylac- etone (acac) for SFE of the f-block elements. In several reported SFE studies for lanthanide and uranium, TTA was used as the chelating agent. One reason for using TTA is that it is a solid at room temperature (m.p. 42°C) and is easy to handle experimentally. Other commercially available fluorinated β -diketones, often in liquid form at room temperature, have also been used for SFE of lanthanides and actinides (Ta ble 5.1.2). A strong synergistic effect was observed for the extraction of lanthanides from solid samples when a mixture of TBP and a fluorinated β -diketone was used in supercritical CO 2 . 7,8 Tributylphosphate alone is ineffective for SFE of lanthanides from solids. This is expected because TBP is neutral and trivalent lanthanide ions are not extractable by supercritical CO 2 without counteranions. However, when TBP is mixed with TTA, the extraction efficiencies of the mixed ligands for the lanthanides are drastically increased with respect to each individual ligands (Ta b l e 5. 1. 3 ). This is probably due to adduct formation, with TBP replacing a coordinated water molecule in the lanthanide-TTA complex, thus increasing the solubility of the adduct complex. Uranium and thorium in solids and aqueous solutions can also be extracted by supercritical CO 2 containing fluorinated β -diketones. For example, spiked UO 2 2+ and Th 4+ in sand can be extracted by supercritical CO 2 containing TTA with efficiencies around 70 to 75% at 60°C and 150 atm with 10 minutes of static and 20 minutes of dynamic extraction. 10 Using a mixture of TTA and TBP, the extraction efficiencies of UO 2 2+ and Th 4+ are increased to >93%. 10 The feasibility of extracting uranyl ions from natural samples was tested using mine wastes collected from an abandoned uranium mine in the North- west region, (United States). The uranium concentrations in two mine waters tested were 9.6 µ g/mL and 18 µ g/mL, respectively. The mine waters were extracted with a 1:1 mixture of TTA and TBP in neat CO 2 TABLE 5.1.2 Properties of Some Commercially Available β -Diketone O O O OH O O || | * | * R 1 CCH 2 CR 2 ↔ R 1 CCH=CR 2 ↔ R 1 CCH=CR 2 + H + β -Diketone Abbrev. R 1 R 2 Mol. Wt. B.P. (°C) Acetylacetone AA CH 3 CH 3 100.12 139 (760 Torr) Trifluoroacetylacetone TAA CH 3 CF 3 154.09 107 Hexafluoroacetylacetone HFA CF 3 CF 3 208.06 7071 Thenoyltrifluoroacetone TTA | a | \/ S CF 3 222.18 103104 (9 Torr) Heptafluorobutanoylpivaroyl- methane FOD C(CH 3 ) 3 C 3 F 7 296.18 33 (2.7 Torr) © 2001 by CRC Press LLC at 60°C and 150 atm for a static time of 10 minutes followed by 20 minutes of dynamic extraction. Under the specific experimental conditions, the percent extraction of uranium from these samples was 81 ± 4% and 78 ± 5%, respectively. The mine waters were also added to a soil sample collected from northern Idaho. The contaminated soil samples were dried at room temperature for the SFE study. The results of extraction of uranium from the contaminated soil samples with a 1:1 mixture of TTA/TBP or HFA/TBP in supercritical CO 2 at 60°C and 150 atm are given in Ta b le 5 . 1. 4. 11 The percent extraction of uranium with HFA/TBP for both soil samples A and B is about 90%, whereas TTA/TBP shows lower percent extractions (77 to 82%) of uranium under the same conditions. The efficiency of extracting uranium from a standard uranium tailings sample obtained from CAN- MET (Canada Centre for Mineral and Energy Technology, Ottawa, Canada) with supercritical CO 2 and TTA was also evaluated. 8 The tailings sample contained 1010 ppm uranium. Repeated extraction with supercritical CO 2 containing TTA resulted in 80% of the total uranium originally present in the tailings. A fraction of the uranium in the tailings apparently could not be removed by TTA in supercritical CO 2 . TABLE 5.1.3 Synergistic Extraction of Uranyl, Thorium, and Lanthanide Ions with TTA and TBP in Supercritical CO 2 (60°C and 150 atm) Uranyl and Thorium Ions in Water a Percent Extraction (%) Extractant (UO 2 ) 2+ Th 4+ TTA 38 ± 4 70 ± 5 TBP 5 ± 2 6 ± 2 TTA + TBP 70 ± 5 87 ± 5 Lanthanide Ions Spiked on Filter Paper b,c Percent Extraction (%) Extractant Amount ( µ mole) La 3+ Eu 3+ Lu 3+ TBP 80 2 ± 13 ± 14 ± 1 TTA 80 14 ± 2 16 ± 320 ± 3 TTA+TBP 40 + 40 92 ± 3 94 ± 4 95 ± 4 a From Ref. 10. b From Ref. 9. c Filter paper sample contained 10 µ g of each lanthanide. TA BLE 5.1 .4 Extraction of Uranium from Mine Water and from Contaminated Soil with Supercritical CO 2 (60°C and 150 atm) Sample Uranium Conc. ( µ g/mL) Extractant % Extraction Mine water A 9.6 TTA+TBP 81 ± 4 Mine water B 18.0 TTA+TBP 78 ± 5 Soil A 6.3 TTA+TBP 82 ± 5 HFA+TBP 91 ± 4 Soil B 15.4 TTA+TBP 77 ± 4 HFA+TBP 89 ± 5 Note: Mine water: 4-mL sample, 200 µmole each of TTA and TBP; soil sample:100-mg sample, 200 µmole each of TTA and TBP or HFA and TBP. HFA = hexafluoroacetylacetone; TTA = thenoyl- trifluoroacetone. Data from Reference 11. © 2001 by CRC Press LLC The residue after the SFE and the original tailings were treated by the EPA Toxicity Characteristics Leaching Procedure (TCLP). The TCPL test indicated that after the SFE, most of the leachable uranium (>97%) in the tailings was removed by supercritical CO 2 . Tributylphosphate-modified CO 2 containing TTA was used by Laintz et al. 12 to extract lanthanides from an acidic aqueous matrix. Near-quantitative extraction of the trivalent Sm, Eu, Gd, Dy, Yb, Ho, and La ions from aqueous solutions using TBP-modified CO 2 was observed. Furton et al. 13 evaluated the extraction and spectrophotometric determination of UO 2 (NO 3 ) 2 ·6H 2 O from different solid matrices by liquid ethanol and by supercritical CO 2 using FOD and TBP as extractants. The highest recoveries were observed with supercritical CO 2 modified with FOD (0.1 M), TBP (0.1 M), and ethanol (5% v/v). In a comparison with liquid ethanol extraction, the SFE method required a shorter extraction time and produced higher recoveries and greater precision. In highly acidic solutions (1 to 6 M HNO 3 ), organophosphorus reagents such as TBP and TBPO dissolved in supercritical CO 2 can extract uranyl ions (UO 2 2+ ) and thorium ions (Th 4+ ) effectively (Figure 5.1.2). 14 Uranyl nitrate does not show an appreciable solubility in supercritical CO 2 . However, when it is coordinated with TBP, the uranyl nitrate TBP complex becomes very soluble in supercritical CO 2 . 15 The extraction efficiencies for UO 2 2+ and Th 4+ using TBP-saturated supercritical CO 2 are comparable to those observed in solvent extraction with kerosene containing 19% v/v TBP. 14 Uranyl in nitric acid solutions is extracted as (UO 2 )(NO 3 ) 2 ·2TBP in supercritical CO 2 containing TBP. 8 This is similar to the form of the uranyl complex extracted from nitric acid solutions using kerosene and TBP. 16 The extraction was found to follow first-order kinetics with a rate constant close to that reported for the solvent extraction. Meguro et al. 17 reported the equilibrium relations involved in supercritical CO 2 extraction of uranyl ions from nitric acid solutions with TBP. These results suggest that supercritical CO 2 can be used to replace the organic solvents conventionally utilized in the PUREX process. 18 Solubility of Uranyl Complexes Solubility Measurement Using Spectroscopic Techniques The solubility of a uranium complex in supercritical CO 2 is an important factor in determining its efficiency of extraction by supercritical CO 2 . Therefore, accurate measurement of the solubility of uranium complexes in supercritical CO 2 is important for developing supercritical fluid-based extraction processes. There are three traditional methods of determining solubility in supercritical fluids: gravimetric, chromatographic, and spectroscopic. Spectroscopic methods generally offer more rapid determination of solubility, with increased sensitivity, and require small amounts of compounds. If a metal complex has characteristic absorption bands in the ultraviolet-visible (UV-VIS) region, a spectroscopic method is a good choice for determining its solubility in supercritical CO 2 . A stainless steel, high-pressure view cell with quartz windows was used originally by Laintz et al. 4 in 1991 for determining the solubilities of a number of metal dithio- carbamate complexes in supercritical CO 2 . One drawback of using the high-pressure view cell for solubility measurement is its fixed pathlength (e.g., about 5 cm in the case of Laintzs original work), which limits the concentration range of the measurement. For highly soluble metal complexes, the absorbance may be out of the linear range of the Beer-Lambert law. In addition, the high-pressure view cells are expensive to fabricate, usually costing several thousand dollars each. Recently, the use of a high-pressure fiber-optic system for measurement of solubility of a uranyl complex UO 2 (NO 3 ) 2 · 2TBP in supercritical CO 2 was reported. 19 The fiber-optic system, consisting of three fiber-optic cells with pathlengths ranging from 38 µ m to 1 cm, enables compounds of high or low solubility to be measured over a concentration range of several orders of magnitude. The system is capable of withstanding pressure in excess of 300 atm, and spectra over the entire UV-VIS range (200 to 900 nm) can be obtained. The cost of manufacturing the fiber-optic system is about one tenth that for a typical high-pressure, stainless steel view cell. The structure of the fiber-optic system reported by Carrot and Wai 19 is illustrated in Figure 5.1.3. An ISCO syringe pump, model 260D (ISCO, Lincoln, Nebraska), was used to supply CO 2 at the desired pressure. Supercritical CO 2 was introduced to the saturation cell containing the test compound via a 1.5-m (1/16-in. OD × 0.03-in. ID) stainless steel equilibration coil to ensure the CO 2 was at the correct © 2001 by CRC Press LLC temperature prior to entering the cell. Either a 3.5-mL saturation vessel or a 14.9-mL view cell (5-cm pathlength) was connected to a Rheodyne 6-port valve to contain the sample. Using the view cell allowed the phase behavior of the uranyl complex under supercritical conditions to be observed. The switching valve enabled the sample cell to be switched in or out of the flow path without the need for depressurizing the entire system and also facilitated the cleaning and flushing of the fiber-optic cells. Three high-pressure UV-VIS cells, with pathlengths of 38 µ m, 733 µ m, and 1 cm were used for the solubility measurements. Flow of the saturated supercritical solution through the cell was controlled via a high-pressure valve connected to the outlet of the optical cell manifold. Pressure was maintained in the system using a crimped stainless steel restrictor manufactured from 1/16-in. × 0.01-in. ID tubing to give a flow of 100 mL/min at 300 atm and room temperature. The tip of the restrictor was housed in a heated aluminum block to minimize plugging during depressurization. All components of the apparatus, except the view cell, were housed in an Eldex HPLC oven to allow precise control of the temperature (±0.1°C). Heating of the external view cell was maintained by a digital temperature controller. A Cary 1E UV-VIS spec- trometer and fiber-optic interface (Varian Instruments) was used for spectroscopic measurements in the work of Carrott and Wai. 19 To determine the solubilities of metal chelates in supercritical CO 2 , both the pathlength of the fiber- optic cells and the molar absorptivity of the complex must be known. First the pathlength of each of the optical cells was determined. The 1-cm pathlength cell was constructed by simply measuring the distance between the fibers during assembly; however, this is impossible for the cells with a pathlength less than 1 mm. The pathlength of these cells was determined using a series of standard anthracene solutions with FIGURE 5.1.2 A high-pressure fiber-optic reactor with CCR array UV/VIS spectrometer. (From Ref. 20.) Nitrate Concentration (M) Nitrate Concentration (M) (UO 2) 2+ Extraction from Nitric Acid Th 4+ Extraction from Nitric Acid % Extraction % Extraction 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 01234 5 678910 01234 5 678910 © 2001 by CRC Press LLC a known molar absorptivity. The molar absorptivity of anthracene at 359 nm was calculated using the Beer-Lambert law where the pathlength was 1 cm. The pathlengths for the two remaining cells were calculated from the slope of linear calibration curve of absorbance (at 359 nm) vs. concentration using the calculated molar absorptivity. The molar absorptivity for each complex was determined using stan- dards of the metal chelate in hexane in the 1-cm pathlength cell. Hexane was used because it has a similar polarity to CO 2 and because solutes exhibit similar extinction coefficients and negligible wavelength shifts in absorption maxima. 19 The molar absorptivities for all complexes measured were calculated from the slope of a linear calibration curve of absorbance (at one wavelength) vs. concentration. Recently, a high-pressure fiber-optic reactor was used by Hunt et al. 20 to measure the dissolution rate of some organic compounds in supercritical CO 2 . The basic structure of this reactor (Figure 5.1.4) is similar to the fiber-optic solubility cell reported by Carrott and Wai. 19 The fiber-optic system can be connected to a CCD array UV/VIS spectrometer to obtain absorption spectra rapidly. The high-pressure fiber-optic system reported by Hunt et al. 20 is capable of obtaining one UV/VIS spectrum per second over the entire UV-VIS range. This type of fiber-optic reactor system will be very useful for studying the rates of fast dissolution processes and chemical reactions in supercritical fluids. Solubility Data and Modeling The solubilities of (UO 2 )(NO 3 ) 2 ·2TBP in supercritical CO 2 in the temperature range 40 to 60°C and pressure range 100 to 300 atm are shown in Figure 5.1.5. 15 This important uranyl complex is highly soluble in supercritical CO 2 , reaching a solubility of approximately 0.4 mol/L at 40°C and 300 atm. This solute concentration range is similar to those found in the PUREX process. The leveling off at pressures above 200 atm at 40°C was due to the complete dissolution of the UO 2 (NO 3 ) 2 ·2TBP solid placed in the reaction cell. At higher temperatures, the density decreases at a given pressure, correlating with decreased solubility of UO 2 (NO 3 ) 2 ·2TBP as the temperature is increased. The solubilities of several uranyl-TTA-X complexes at 40°C and various pressures are given in Figure 5.1.6, where X = TBP, TEP (triethyl phosphate), TOPO (trioctylphosphine oxide), TBPO (tributylphosphine oxide), and H 2 O. In this group of uranyl-TTA adduct complexes, UO 2 (TTA) 2 ·TBP is the most soluble in supercritical CO 2 at each FIGURE 5.1.3 Extraction of uranyl and thorium ions from nitric acid solutions with supercritical CO 2 containing TBP. ( l ) Solvent extraction with 19% TBP in kerosene; ( n ) SFE. (Data from Ref. 14.) © 2001 by CRC Press LLC pressure, followed by UO 2 (TTA) 2 ·TEP and UO 2 (TTA) 2 ·TOPO. All of these compounds showed an increase in solubility in CO 2 with increasing pressure. The solubilities of UO 2 (TTA) 2 ·TBPO, and UO 2 (TTA) 2 ·H 2 O are significantly less than those of the other three complexes. UO 2 (TTA) 2 ·H 2 O, the least soluble uranyl-TTA complex in this series, was used as the starting material to synthesize the remaining UO 2 (TTA) 2 ·X adduct complexes. Replacing the coordinated water molecule with an organophosphorus ligand would significantly increase the solubility of the resulting complex. The most soluble adduct complex studied, UO 2 (TTA) 2 ·TBP, is 2 orders of magnitude more soluble than the maximum concen- tration of UO 2 (TTA) 2 ·H 2 O. In comparison with UO 2 (NO 3 ) 2 ·2TBP, the solubility of UO 2 (TTA) 2 ·TBP in supercritical CO 2 is approximately an order of magnitude lower. A simple model, which relates the solubility of a compound to the solvents density and the absolute temperature, was used by Waller et al. 21 to predict the solubility of the uranyl complexes in supercritical CO 2 . According to this model, the molecules of the solute and those of the solvent would associate with one another to form a solvato complex. The presence of this complex in the supercritical fluid at equilibrium is represented by the following reaction: A + kB ↔ AB k (5.1.1) FIGURE 5.1.4 A high-pressure fiber-optic system for solubility measurements in supercritical CO 2 . (From Ref. 19.) To Pump Fiber-Optics (a) (b) (c) #1 #2 #3 #4 Injection Loop Pump CO 2 Hot /Stir Plate To a CCD Array UV - Vis spectrometer #1 1/16 inch Valco Nut #2 1/16 in PEEK Tubing #3 Fiber Optic #4 1/16 Valco Ferrule ????? ??????? ?????? © 2001 by CRC Press LLC Equation (5.1.1) is interpreted as one molecule of solute A associating with k molecules of a solvent B to form one molecule of a solvato complex AB k . The equilibrium constant, K, is represented by Equation (5.1.2): (5.1.2) Equation (5.1.2) can be expressed in logarithmic form as: ln[AB k ] = k ln[B] + ln[A] + ln K (5.1.3) The equilibrium constant (K) can be expressed as a function of the enthalpy of solvation ( ∆ H solv ): (5.1.4) FIGURE 5.1.5 (a) Solubility of UO 2 (NO 3 ) 2 ·2TBP in supercritical CO 2 ; (b) ln S vs. ln D plot for the solubility data. (Data from Ref. 15.) Pressure, atm In D (g/L) of SF CO 2 Concentration, MIn S (g/L) (a) (b) 0 100 200 300 6.25 6.5 6.75 7 0 1 2 3 4 5 6 7 0 0.1 0.2 0.3 0.4 0.5 40 50 60 T, o C K AB k [] A[]B[] k = Kln ∆H solv RT q s += [...]... the system pressure and eliminating the air sparge to facilitate higher NO⋅ and NO2⋅ concentrations in solution Data reflecting the oxidation behavior of polyethylene is shown in Figure 5. 2.2.1 Oxidation of Polyethylene Reaction % Complete 120 20 0-2 05oC 1 0-1 5 psig 100 80 18 5- 1 90oC 0 -5 psig 17 0-1 75oC 0 -5 psig 60 PVC 18 5- 1 90oC 0 -5 psig 40 20 0 0 100 200 300 400 Time (mins) FIGURE 5. 2.2.1 Oxidation behavior... Co(III), and Ce(IV), J Appl Electrochem., 25, 846,19 95 7 G Pillay and J Birmingham, Catalyzed electrochemical oxidation and gas-phase corona reactor for chemical and biological warfare agent and hazardous organic destruction, presented at ACS (INEC Division) Symposium, Emerging Technologies in Hazardous Waste Management VIII, Birmingham, AL, Sept 9-1 1, 1996 8 J.C Farmer, F.T Wang, P.R Lewis, and L.J... up to 148 g/L HNO3 at 155 °C and 20 g/L HNO3 at 1 85 C The solubility of © 2001 by CRC Press LLC TABLE 5. 2.2.1 HNO3 Solubility in Concentrated H3PO4 Pressure Temperature 155 °C 170°C 1 85 C 0 psig 10 psig 20 psig 148 g/L 1 95 g/L 252 g/L 64 g/L 107 g/L 147 g/L 20 g/L 46 g/L 73 g/L 190°C 2 05 C 220°C 40 g/L 15 g/L 1.3 g/L 15 psig HNO3 in H3PO4 increases with increasing pressure (Table 5. 2.2.1) While pressurization... H 5) 4 = CF 3(CF 2 ) 6 CF2SO 3 [N(C 2H 5) 4]; PFOSA-K = CF3(CF 2)6CF2SO 3K Data from Reference 23 TABLE 5. 1.7 Extraction of Sr2+, Ca2+, and Mg2+ from 1.3 M HNO3 by Supercritical Fluid CO2 Containing DC18C6 and PFOAH or PFOSA Salt at 35 C and 200 atm Mole Ratio Sr2+:DC18C6:PFOA-H 1 1 10 0 10 50 Sr2+:DC18C6:PFOSA-K 1 10 50 1 20 50 Sr2+:DC18C6:PFOSAN(C 2H 5) 4 1 10 50 % Extraction Sr2+ Ca2+ Mg 2+ 1 18 ±... acids and oxidants (e.g., H2O2 and HNO3) at elevated pressure (100 to 150 psig) and temperature ( 150 to 200°C) to digest organic samples When 0.1-g samples of aliphatic compounds and 5 mL 70% nitric acid are placed in a 100-mL digestion vessel, the samples dissolve in 5 to 10 min Rapid dissolution was demonstrated on PVC, low- and high-density polyethylene, polypropylene, and Tygon The role of the microwave... of Mixed Wastes (PCB(BZ #54 ) + Uranium) with Supercritical CO2 Sample First Extraction Neat CO2 for PCB Second Extraction CO 2+TTA+TBP for Uranium Sand Idaho soil UTS-4 tailings 98 97 98 94 75 86 Note: 200 µg BZ #54 (2,2′,6,6′-tetrachlorobiphenyl), 200 µg U, 300 mg TTA, and 200 µL TBP; UTS-4 tailings contained 1010 µg uranium/g tailings (from CANMET) 150 °C and 200 atm for PCB extraction, 80°C and 200... clean-up of low-level radioisotope-contaminated materials generated by a wide range of facilities, including nuclear power plants, government and defense laboratories and reactors, hospitals, and industrial plants The waste takes a variety of forms, such as medical treatment and research materials, contaminated wiping rags and paper towels, used filters and filter sludge, protective clothing, hand tools,... fluorinated βdiketones and tributyl phosphate, Anal Chem., 66, 197119 75 (1994) 10 Yuehe Lin, R.D Brauer, K.E Laintz, and C.M Wai, Supercritical fluid extraction of lanthanides and actinides from solid materials with a fluorinated β-diketonate, Anal Chem., 65, 254 9 255 1 (1993) 11 Yuehe Lin, C.M Wai, F.M Jean, and R.D Brauer, Supercritical fluid extraction of thorium and uranium ions from solid and liquid materials... Efficiency, % 100 99 98 97 96 95 40 50 60 70 80 90 Coulombic Efficiency, % 100 FIGURE 5. 2.1.2 Relationship between current and destruction efficiencies for bench-scale tests of trimsol Cellulose Destruction Efficiency, % 100 99 .5 99 98 .5 98 97 .5 97 40 50 60 70 80 90 100 Coulombic Efficiency, % FIGURE 5. 2.1.3 Relationship between current and destruction efficiencies for bench-scale tests of cellulose there... experiments, dicyclohexano-21-crown-7 (DC21C7) was found more effective than 18C6, DC18C6, and DB24C8 (dibenzo-24-crown-8) for Cs+ extraction from aqueous solutions The efficiency of SFE of cesium from water (pH 2.9) using DC21C7 and a fluorinated counteranion such as PFOA or PFOSA-N(C2H5)4 depends on temperature, the initial concentration of cesium, and the amount of the counteranion Table 5. 1.7 shows some . supercritical CO 2 with DC18C6 and perfluoro-1-octanesulfonic acid tetraethylammonium salt (PFOSA-N(C 2 H 5 ) 4 ) or its potassium salt (PFOSA-K) was observed in 1.3 M HNO 3 (Tab le 5. 1. 7 ). 23 The extraction. (M) 0 0.000 05 0.000 15 0.000 25 0.000 35 0.0001 0.0002 0.0003 0.0004 0.000 45 0 100 200 300 400 © 2001 by CRC Press LLC 5. 1.7). The slope (k) and intercept (C), calculated using Equation (5. 1 .5) , are shown in Table 5. 1 .5 for each compound at 40°C 89 ± 5 Note: Mine water: 4-mL sample, 200 µmole each of TTA and TBP; soil sample:100-mg sample, 200 µmole each of TTA and TBP or HFA and TBP. HFA = hexafluoroacetylacetone; TTA = thenoyl- trifluoroacetone. Data
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