Extraction behaviour of metal ions in aqueous polyethylene glycol-sodium sulphate two-phase systems in the presence of iodide and thiocyanate ions

The distribution behaviour of Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(I I), Cd(II) and Li(I) was studied in an aqueous two-phase system formed from a polyethylene glycol and sodium sulphate in the presence of thiocyanate o r iodide ion. From the distribution ratios determined as a function of the iodide or thiocyanate concentration, the extracted species were assumed. In the SCN- system Cu(II), Zn(II) and Co(II) distribute into the PEG-rich pha se predominantly as Cu(SCN)(4)(2-), Zn(SCN)(4)(2-) and Co(SCN)(4)(2-) and F e(III) as Fe(SCN)(4)(-), respectively. On the other hand, Cd(II) is extract ed as Cd(SCN)(4)(2) in the SCN- system, while as CdI42- in the I- system. T he extractabilities of the metal ions depend not only on the stabilities of the metal thiocyanate or iodide complexes but also on those of their sulph ate complexes. A selective separation of Cd(II) from the other metal ions s tudied was accomplished in the aqueous two-phase system by using iodide ion as an extracting reagent for Cd(II) and an ammonium buffer as a masking re agent for Cu(II). (C) 2001 Elsevier Science B.V. All rights reserved.