Synergistic coupled transport of uranyl ion across bulk liquid membrane mediated by dioxa-diazamacrocycle and oleic acid M. Soltani Behrooz 1 • J. Fasihi 2 • M. Samadfam 1 • H. Sepehrian 2 • P. Ashtari 3 • M. Mahani 4 • M. Arabieh 2 Received: 2 September 2017 Ó Akade ´miai Kiado ´, Budapest, Hungary 2018 Abstract Synergistic coupled transport of uranyl ion across a bulk liquid membrane of chloroform has been investigated using a dioxa-diazamacrocycle and oleic acid as carrier and synergistic agents, respectively. Quantitative transport of uranyl ion was achieved within 4 h when the pH of source solution was kept at 5.0–6.0 and mole ratio of carrier to synergistic agent was 1/15. It was found that overall rate and selectivity of the transport is governed by the stripping step. Finally, the influence of some foreign competitor ions including Al 3? , Ca 2? , CO 3 2- , Cu 2? , Mg 2? , Pb 2? , Zn 2? and Th 4? and also the ionic strength on the transport efficiency has been evaluated. Keywords Uranyl ion  Synergistic transport  Bulk liquid membrane  Dioxa-diazamacrocycle Introduction In comparison with the other separation techniques, espe- cially the traditional liquid–liquid extraction, the transport across liquid membranes offers some advantages including high separation factors and lower capital cost. Also, it needs a reduced amount of organic solvent which allows the use of expensive carrier molecules [1]. Among the different types of liquid membranes, the bulk liquid membrane (BLM) is utilized for preliminary and fundamental studies of certain aspects of liquid membrane transport processes such as screening of carriers and evaluating of their effectiveness. There are a number of previously reported works on the separation of uranyl ion using the bulk, supported and emulsion liquid membranes [2–7]. Due to the environmental and industrial impacts [8], investigations on the selective separation of uranyl ion by the transport across liquid membranes have received a continued interest. Var- ious macrocycles and macromolecular compounds, i.e. crown ethers [7, 9], ionizable lariat ethers [10] and cal- ixarenes [11, 12] have been used as ion carriers in transport across liquid membranes for selective removal and recovery of uranyl ion. The transport techniques which use neutral macrocyclic carriers are found to be anion dependent [13]. Meanwhile, the selectivity and efficiency of metal ion transport across the liquid membrane could be markedly influenced by the chemical structure of the carrier and sta- bility constant of the desired complexes. The stability of macrocyclic complex is dramatically governed by some structural features such as donor atoms, atom hardness and ring size [1]. Furthermore, the substitution of benzo group rises rigidity of macrocycles, which would lead to improvement of their discrimination ability [14]. Uranyl ion strongly interacts with azacrown ethers of five and six- membered ring size [15]. Due to the differences in polar- izability, nitrogen-containing crown ethers display different ionic selectivities than oxygen-containing crown ethers [16]. 5,6;14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentade- cane-5,14-diene (DBDA15C4) as a diazacrown ether derivative strongly interacts with uranyl ion [15] and could potentially be used as an effective carrier in the transport & J. Fasihi jfasihi@aeoi.org.ir 1 Department of Energy Engineering, Sharif University of Technology, Tehran, Iran 2 Nuclear Science and Technology Research Institute, Tehran, Iran 3 Radiation Application Research School, Nuclear Science and Technology Research Institute, Tehran, Iran 4 Faculty of Sciences and Modern Technologies, Graduate University of Advanced Technology, Kerman, Iran 123 Journal of Radioanalytical and Nuclear Chemistry https://doi.org/10.1007/s10967-018-5732-5