Surface Decontamination of Radioactive Metal Wastes Using Acid-in-Supercritical CO₂ Emulsions

Abstract

Supercritical fluid surface decontamination (SFSD) of radioactive metal wastes was successfully demonstrated using acid-in-CO2 emulsions. NP-series(ethoxylated nonyl phenol series) formed stable acid-in-CO2 emulsions, contrary to F-AOT(sodium bis(2,2,3,3,4,4,5,5-octafluoro-1-pentyl)-2-sulfosuccinate). An ultrasonic horn was utilized to enhance mechanical and chemical reactions in Sc-CO2 emulsions. A Cu-coated specimen for a mock-up test was prepared and examined with acid-in-CO2 microemulsions. Over 90% of the Cu coating was easily dissolved away from the specimen. For actual radioactive contaminants, 6 M HNO3 in Sc-CO2 microemulsions enhanced by ultrasonic force was more than 95% decontaminated. Sc-CO2 macroemulsions were also applied with 0.1 M HNO3 or 5% oxalic acid. The decontamination efficiencies were about 90% with HNO3 and over 95% (up to background level) with oxalic acid. After decontamination, the used surfactants were recovered up to about 73% through the recovery process, and they can be reused as well as CO2. So the volume of radioactive wastes can be positively reduced. This SFSD technique may be an effective candidate for surface decontamination of radioactive metals in the near future.

Effect of Supercritical Fluid Extraction on the Reduction of Toxic Elements in Fish Oil Compared with Other Extraction Methods

“…Therefore, there is a need to produce fish oil supplements with lower levels of contamination. Supercritical fluid extraction (SFE) has been extensive ly used to remove metal ions from various solid and liquid matrices of environmental samples ( 7,19). SFE has progressed recently as an effective extraction method in food industries, mostly due to the lower health and environmental hazards involved.…”

Extraction with Water‐in‐Carbon Dioxide Microemulsions: A Case Study on Steviol Glycosides

“…In terms of extractions from a solid matrix, applications are so far restricted to metal ions. Sodium bis (2‐ethylhexyl) sulfosuccinate (AOT), fluorinated AOT, and perfluoropolyether surfactants have been used to recover metal ions that were spiked onto solid matrices such as sand, lab coat fibers, filter paper, activated carbon, wood, and cement with recoveries up to 99% in most cases (Campbell et al, ; Koh et al, ; Wang and Chiu, ; Wang et al, , ; Yates et al, ). The metals can be separated from the surfactant/CO 2 mixture by adding additional water in a later step, forcing the metal to concentrate in a water‐rich phase while the surfactant is still soluble in the CO 2 ‐rich phase.…”

Effects of Supercritical CO2 Conditioning on Cross-Linked Polyimide Membranes

“…The use of scCO 2 for essential oil and lipid extractions continues to be explored due to the low viscosity and high diffusivity of scCO 2 and its protection against thermal degradation since the supercritical temperature of CO 2 is so low. Another attractive feature of using scCO 2 for these extractions is the lack of any residual solvent with the product. − scCO 2 also continues to be studied as a solvent in polymerization reactions, especially when its use can eliminate the need for harmful additives such as fluorinated surfactants. , Another field where scCO 2 is proving useful is tool and equipment decontamination of radioactive metal salts and oxides at nuclear power facilities . Inherent in all of these processes though is the high cost of compression to reuse CO 2 when it is depressurized to separate the CO 2 from the solute.…”