Naphthol- and resorcinol-based azo dyes as metal ion complexants in aqueous biphasic systems

Aqueous biphasic systems (ABS) are comprised of both a polymer-rich phase ( e.g., polyethylene glycol, PEG) and a salt-rich phase [e.g., (NH4)(2)SO4] s uch that both phases are 80% water on a molar basis. ABS have demonstrated applications as environmentally-friendly methods to separate relatively hyd rophobic anionic species, such as pertechnetate and mercury halide anionic complexes, from high ionic strength solutions although partitioning of hydr ated metal ions, such as Fe3+ and actinides, to the PEG-rich phase is negli gible without the addition of a metal ion complexant to the system. Four na phthol- or resorcinol-based dyes; 1-(2-pyridylazo)-2-naphthol (PAN), 1-(thi azolylazo)-2-naphthol (TAN), 4-(2-pyridylazo)-resorcinol (PAR) and 4-(2-thi azolylazo)-resorcinol (TAR), each incorporating a naphthol or resorcinol wi th an ortho azo functional group, have been studied as metal ion extractant s in ABS as a function of pH. In the PEG-2000/ (NH4)(2)SO4 ABS, the distrib ution ratios of Fe3+, Co2+ and Ni2+ were enhanced by several orders of magn itude at high pH in contrast to the behavior of Cs+, Cd2+ and EU3+ whose pa rtitioning behavior was largely unaffected by the presence of these extract ants at: any pH. The three extracted metal ions, Fe3+, Co2+ and Ni2+, could be stripped by contact with a fresh salt phase at low pH. (C) 2000 Elsevie r Science B.V. All rights reserved.