5,6,14,15-Dibenzo-1,4-dioxa-8,12-diazacyclopentadeca-5,14-diene (DBDA15C4) as a mobile carrier and histidine as a stripping agent were used for the selective uphill and proton driven transport of Zn2+ ions through a bulk liquid membrane. A study of different parameters on zinc transport has been carried out. This include the pH of the feed phase, amount of DBDA15C4 in the liquid membrane, type and concentration of acid and amino acid in the strip phase and transport. In the optimum procedure conditions, the maximum transport of Zn2+ ions at 3 h was observed (96.2 +/- 1.2%). With this system, Zn2+ as Zn-histidine complex could be separated from Cu2+, Cd2+, Pb2+, Mn2+ Cr3+, Al3+, Co2+, Ni2+, Ca2+, Mg2+ and Fe3+. The transport mechanism of this system has been described. (C) 2005 Elsevier B.V. All rights reserved.