We investigated the extraction behavior of Cu(II) in the aqueous two-phase system (ATPS) formed by (L35 + MgSO4 + H2O) or (L35 +(NH4)(2)SO4 + H2O) in the presence of the extracting agent 1-(2-pyridylazo)-2-naphthol (PAN). At pH = 3 and a PAN concentration of 0.285 mmol kg(-1), both ATPS lead to the effective separation of Cu(II) from other metallic ions (Zn(II), Co(II), Ni(II) and Fe(III)). High separation factors range between 1000 and 10,000 were obtained for the extraction of Cu(II) and concomitant metallic ions. This ATPS was used for the extraction of Cu(II) from a leached ore concentrate with a extraction percentage of 90.4 +/- 1.1%; other metals were mainly located in the bottom phase. (C) 2012 Elsevier B.V. All rights reserved.