2004 Fiscal Year Final Research Report Summary
The Thermodynamic Study on the Solvent Extraction Behavior of EDTA and its Complexes
| Project/Area Number |
14540555
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
分離・精製・検出法
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| Research Institution | Niigata University |
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Principal Investigator |
SATOH Keiichi Niigata University, Faculty of Science, Associate Professor, 理学部, 助教授 (60225935)
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| Project Period (FY) |
2002 – 2004
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| Keywords | Ethylenediamine tetraacetate / Ion-pair extraction / Thermodynamic constnats / Hydrolysis of EDTA complex / Mixed-ligand complex / Hydrolysis of metal ion / Steric effect / Total hydrophobisity |
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| Research Abstract |
In the ion-pair extraction of EDTA alone by quaternary tetraalkylammonium ion, edta^<4->, the most negatively charged species of EDTA, is effectively extracted into organic solvents. This phenomenon is due to the increased hydrophobicity of the ion-pair formed with the large numbers of tetraalkylammonium ion.
For the extraction of Co(II),Ni(II),Cu(II), Zn(II),Cd(II),and Pb(II) complexes, the species of [M(edta)]^<2-> and [(edta)(OH)]^<3-> were extracted. The extraction constants for [M(edta)]^<2-> did not differ so much with the change of metal ion except for Pb(II), while of [(edta)(OH)]^<3-> differ with one logarithmic unit. The difference of the extraction constants between [M(edta)]^<2-> and [(edta)(OH)]^<3-> was small. There is no significant correlation between the extraction constants and the formation constants of EDTA complexes, ionic radius of metal ions, nor the hydrolysis constants. For Fe(III) system, the dimeric species, [Fe_2(edta)_2(OH)_2]^<4->, is extracted along with the hydrolysis of [Fe(edta)]-at about pH 7. For Al(III),In(III),and lanthanide(III),[M(edta)]-and [M(edta)(OH)]^<2-> were extracted but the dimeric species was not formed and not extracted. Ga(III)-EDTA complex was dissociated by the hydrolysis of aqua ion of Ga(III). Co(III)-EDTA forms mixed-ligand complex with co-existing ligand, but the dimeric species was not formed and not extracted. The formation and the extraction of dimeric species of Fe(III) is specific behavior for the solvent extraction. These results suggest that the extraction separation of divalent and trivalent metals is possible. The separation of divalent metals each other is, however, quite difficult and the use of chromatographic technique is required.
The extractions with symmetric tetraalkylammonium ions are quite low irrespective of their high hydrophobicity. These results suggest the steic effect on the formation and extraction of ion-pair for the anion of complex structure.
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Research Products
(11 results)
