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

The distribution behaviour of Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), 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 or 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 phase predominantly as Cu(SCN)42−, Zn(SCN)42− and Co(SCN)42− and Fe(III) as Fe(SCN)4−, respectively. On the other hand, Cd(II) is extracted as Cd(SCN)2 in the SCN− system, while as CdI42− in the I− system. The extractabilities of the metal ions depend not only on the stabilities of the metal thiocyanate or iodide complexes but also on those of their sulphate complexes. A selective separation of Cd(II) from the other metal ions studied 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 reagent for Cu(II).