Mobile Carrier Properties of N2O2- and N3O2-Type Schiff Base Molecules Towards Copper(II) Ions

Mobile carrier properties of two schiff base ligands, named bis(2-hydroxypropiophenone)-1,2-propanediimine (N2O2) and bis(1'-hydroxy-2'-acetonaphthone)-2,2'-diiminodiethylamine (N3O2), dissolved in dichloromethane for the extraction of copper(II) ions from an ammonium buffer feed phase into a nitric acid solution (receiving phase) were investigated and compared. The parameters influencing the transport efficiency such as pH of the feed phase, chemical composition of the receiving phase, carrier concentration in the membrane and time dependency of the process were studied and discussed. Addition of sodium dodecysulfate (SDS), an anionic surfactant, to the receiving phase enhances significantly the process efficiency. This reveals that the transport is controlled by the kinetics of decomplexation at the stripping interface. The transported amount of copper ions from ammonium buffer (pH 7) into the receiving phase including HNO3 and SDS across a dichloromethane layer containing N2O2 and N3O2, at 20 ºC, was found to be 90.6 (±0.7) % and 97.4 (±0.4) % after 4 h, respectively. The selectivity of the processes towards copper ions were tested by performing the competitive transport experiments on the mixture containing Pb2+, Ni2+, Cd2+, Zn2+ and Co2+ ions. Although N3O2 possess higher transport efficiency with respect to that of N2O2, both ligands present adequate selectivity for separation of Cu(II) ions.