Separation of Co(II)/Ni(II) via micellar-enhanced ultrafiltration using organophosphorus acid extractant solubilized by nonionic surfactant

Ultrafiltration (UF) of cobalt(II) and nickel(II) in the presence of a mice lle-solubilized hydrophobic ligand has been investigated, using polyoxyethy lene nonyl phenyl ether with 10 ethylene oxide units (PONPE10) and 2-ethylh exyl phosphonic acid mono-2-ethylhexyl ester (EHPNA) as a nonionic surfacta nt and an extractant, respectively. In aqueous media, the metals are entrap ped within the surfactant micelles containing the extractant, and are effec tively rejected by UF membranes with their consequent concentration in the retentate solution. The selective rejection of Co(II) over Ni(II) can be at tained; the separation is enhanced with increasing solution pH and the extr actant concentration. On the other hand, it was found that sodium dodecyl s ulfate (SDS) as a surfactant and di-2-ethylhexyl phosphoric acid (D2EHPA) a s an extractant give no selectivity between these heavy metals in the same operation. The effects of the surfactant concentration, applied pressure, s alt addition and the membrane geometry on the rejection were also examined in the EHPNA/PONPE10 system. (C) 1999 Elsevier Science B.V. All rights rese rved.