Transport of Ag+ through tri-n-dodecylamine supported liquid membranes

Silver (I) has been transported from feed in to strip solution via tri-n-dodecylamine-cyclohexane-polypropylene supported liquid membrane (SLM). The transport of Ag+ has been found to be dependent on different parameters such as concentration of H+ in feed solution, tri-n-dodecylamine (TDDA) concentration in membrane phase, stripping phase composition and membrane thickness. The optimized conditions obtained for Ag+ transport are: 0.75 mol/dm3 of HNO3 in feed solution, 0.788 M of TDDA in cyclohexane in membrane phase and 1.0 mol/dm3 of NH3(aq) in stripping phase. The stoichiometry of the complex was calculated from the flux data of Ag+ transport across the membrane. The complex responsible for the transport of Ag+ has been investigated to be (LH)·Ag(NO3)2. Recovery of more than 98% of silver has been observed from feed solution at optimized conditions. Stability of this SLM system has been studied and found stable for 120 h.

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► Complex (LH)n·Ag(NO3)n+1formation at feed membrane interface.
► Diffusion of (LH)n·Ag(NO3)n+1 to strip membrane interface.
► Dissociation of complex at strip membrane interface due to NH3(aq).
► Release of Ag+ in strip phase and diffusion of TDDA back to feed membrane interface.