Selective extraction of strontium with supercritical fluid carbon dioxide

Abstract

Strontium (Sr 2+ ) can be selectively extracted from aqueous solutions into supercritical fluid CO 2 at 60 °C and 100 atm with dicyclohexano-18-crown-6 (DC18C6) using CF 3 (CF 2 ) 6 CO 2 − (PFOA − ) or CF 3 (CF 2 ) 6 CF 2 SO 3 − (PFOSA − ) as a counter anion; at a mole ratio of Sr 2+ : DC18C6 : PFOA − = 1:10:50, the extraction of Sr (5.6 × 10 −5 M) from water at pH 3 is near quantitative whereas Ca 2+ and Mg 2+ at equal concentration are only extracted to a level of 7 and 1%, respectively; PFOSA − is an effective counter anion for selective extraction of Sr 2+ from 1.3 M HNO 3 with DC18C6 in supercritical CO 2 .Research in selective transport of metal ions in supercritical (sc)-CO 2 is of considerable current interest because of its potential applications in a variety of chemical processes which may be carried out in this environmentally friendly solvent. 1,2 Selective extraction of alkali metal and alkaline earth metal ions from aqueous solutions to organic solvents with crown ethers is well established in the literature. Extraction of these hard metal ions with crown ethers in scCO 2 is expected to be difficult because of limited solubilities of the resulting metal complexes in CO 2 . 3 It is known that fluorinated metal chelates are CO 2 -philic. 4 Thus, fluorination of ligands is one method of increasing solubility of metal complexes in CO 2 . This approach requires the design and synthesis of specific fluorinated macrocyclic compounds. Another method is to extract crown ether-metal complexes as ion-pairs into scCO 2 utilizing fluorinated counteranions. We report for the first time the successful extraction of Sr 2+ from aqueous media into scCO 2 utilizing a macrocyclic compound and a fluorinated counter anion.It is known that 18-membered crown ethers with cavity diameters in the range 2.6-2.8 Å are the most suitable hosts for Sr 2+ (2.2 Å). 5 For example, 90 Sr can be selectively extracted from nitric acid solutions with dicyclohexano-18-crown-6 (DC18C6) dissolved in a paraffinic or halogenated solvent, where nitrate serves as the counter anion. 6 This macrocyclic system is currently being evaluated for removing 90 Sr (t ½ = 30 years), a major uranium fission product, from the high level acidic nuclear wastes stored at the Idaho DOE site. However, disposal of organic liquid wastes generated from any solvent extraction process is a problem of environmental concern today because of changing government regulations. Supercritical fluid extraction provides several advantages over conventional solvent extraction including minimization of waste generation, allowing rapid separation of

Highly CO2-soluble 5-Amido-8-hydroxyquinoline Chelating Agents for Extraction of Metals in Sc-CO2

“…To enhance extraction efficiency, PFOSANEt 4 was chosen as a co-ligand to extract Cu(II), Co(II), Zn(II), Sr(II), and Cd(II) ions from the filter paper matrix. It is well known that PFOSANEt 4 dissociates to give a CO 2 -philic perfluorosulfonic acid anion, 23 To enhance metal extraction efficiency, we also investigated the synergistic effect of 8-HQ chelating agents on metal extraction. It has already been suggested that mixed chelating agents and other chemicals could interact with each other, thus achieving more powerful extraction ability than independent chelating agents.…”

A novel technique for modifier free delivery of ligands for supercritical fluid extraction

“…A variety of ligands such as dithiocarbamates [7,8], beta diketones [7,[9][10][11], organophosphorous reagents [12] such as TBP and TOPO, and macrocyclic compounds e.g. crown ethers [13][14][15] are used for SFE of various metal ions such as transition elements [9,16,17], lanthanides [18][19][20][21] and actinides [20][21][22][23][24][25][26][27].…”

Uranyl Extraction by TBP from a Nitric Aqueous Solution to SC-CO2: Molecular Dynamics Simulations of Phase Demixing and Interfacial Systems

“…(1)(2)(3)(4)(5)(6) This is of particular interest in the context of nuclear waste partitioning, which is generally initiated from aqueous solutions of the metal ions, obtained by dissolution of the irradiated material in concentrated nitric acid solutions. Examples of metal extraction to SC-CO 2 from solid or liquid matrices involve extraction of metallic, lanthanide and actinide cations by βdiketonate ligands, (7)(8)(9) of strontium by crown ethers (8) or of UO 2 2+ , Th 4+ , (10-15) lanthanides (16,17) or heavy metals (18) by organophosphorus ligands. Reviews can be found in ref.…”