Neil G. Smart

Supercritical fluid extraction of uranium and thorium from nitric acid solutions with organophosphorus reagents

Extraction techniques for the recovery of uranium and transuranic elements from acid waste solutions are important in nuclear waste management. This paper examines the feasibility of extracting uranyl and thorium ions from nitric acid solutions with supercritical CO{sub 2} containing the different organophosphorus reagents. In this study, an organophosphorus reagent is dissolved in supercritical CO{sub 2} by passing the fluid through a reagent vessel placed upstream of the sample vessel in the extractor. Using TBPO or TOPO in supercritical CO{sub 2}, effective extraction of uranyl and thorium ions can be achieved even in dilute HNO{sub 3} solutions, thus yielding the possibility of reducing acidic waste volumes in nuclear waste treatment. The results may form the basis of a novel extraction process for the treatment of acidified nuclear wastes, while minimizing the production of secondary wastes. 12 refs., 2 figs., 2 tabs.

Supercritical fluid extraction and chromatography of metal chelates and organometallic compounds

Abstract Metal ions in solid and liquid materials can be extracted by supercritical CO 2 containing a suitable ligand. Fluorine substituted ligands are particularly effective because of the high solubilities of fluorinated metal chelates in CO 2 . Organometallic compounds can be extracted by supercritical CO 2 with or without derivatization. This in situ chelation-supercritical fluid extraction technique followed by supercritical fluid chromatography of the extracted metal chelates may have important applications for environmental trace metal analysis.

APPLICATION OF SUPERCRITICAL FLUIDS TO THE REACTIVE EXTRACTION AND ANALYSIS OF TOXIC HEAVY METALS FROM ENVIRONMENTAL MATRICES–SYSTEM OPTIMISATION

The extraction of Cu2+, Pb2+, Cd2+ and Zn2+ utilising supercritical fluid carbon dioxide containing dissolved organophosphorus reagents is shown to be feasible. Using the solubility parameter concept and investigation of a variety of physical parameters favourable extraction conditions of 60 °C and 400 atm pressure were determined. Cyanex 302 was found to be the most favourable ligand in terms of stability and ability to complex a range of metal ions. A soil containing substantial amounts of Pb2+ and Cd2+ was studied using SFE and the technique was found to reduce the levels of leachable metal ions to near US EPA regulatory levels.

STUDIES ON IN-SITU CHELATION/SUPERCRITICAL FLUID EXTRACTION OF LANTHANIDES AND ACTINIDES USING A RADIOTRACER TECHNIQUE

Radioisotope tracer techniques were used to study the process of in-situ chelation / supercritical fluid extraction (SFE) of La3+ and Lu3+ from a solid matrix using mixed ligand hexafluoroacetylacetone (HFA) and tributylphosphate (TBP) as chelating agents. A lab-built SFE extractor was used in this study and the extractor design was optimized based on the experimental results. Quantitative recovery of La and Lu was achieved when the extractor design was optimized. Extraction of uranium from real world samples was also investigated to demonstrate the feasibility of this chelation / SFE technology for environmental remediation applications. A novel on-line back extraction technique for the recovery of metal ions and regeneration of ligands is also reported.

Modelling of the extraction of uranium with supercritical carbon dioxide

A model is presented for the analysis of the results of extraction of uranium in a flow system by supercritical fluid modified with tributylphosphate from a nitric acid matrix, in which the extraction is not limited by the solubility of the uranium species. The model used is that of diffusion out of a sphere into a medium in which the extracted uranium is infinitely dilute. Although not a completely accurate representation of the liquid-supercritical fluid system, the model is shown to be a reasonable representation and some conclusions discussed.

Prediction of retention behavior of ferrocene derivatives in supercritical fluid chromatography

Abstract The retention behavior in capillary supercritical fluid chromatography (SFC) of a range of ferrocene derivatives is demonstrated. Prediction of retention times and hence elution order of the ferrocene derivatives based on a knowledge of solute molar volume, solute solubility parameter and the physical parameters of the chromatography column system is shown to be feasible using this procedure.