Mathematical Model for the Extraction of Metal Ions using Hollow Fiber Supported Liquid Membrane Operated in a Recycling Mode

The role of cations H+ and Na+ on the transport of Nd3+ ions was investigated using microporous Hollow Fiber Supported Liquid Membrane (HFSLM) contactor. Extractant N, N, N', N'-tetraoctyl diglycolamide (TODGA) diluted with n-dodecane was used as the membrane phase. Di-n-hexyl octanamide (DHOA) was used as a phase modifier for the extractant. Transport of Nd3+ ions and HNO3 was studied at varying concentrations of NaNO3 and HNO3 while keeping total nitrate (NO3-) concentration nearly constant at 3M. The extraction equilibrium constant (K-ex) for the complexation reaction was experimentally measured for various conditions. The maximum rate of extraction of Nd3+ ions was observed at an equimolar concentration (1.5M each) of HNO3 and NaNO3 in feed solution under otherwise identical conditions. A mathematical model has also been developed to simulate this system. Mass balance equations for both acid (HNO3) and TODGA were also incorporated in the model. It was observed that the model results are in good agreement with the experimental data when diffusivity of metal-complex (D-m) and acid-complex (D-hm) through the membrane phase in the pore is 6 x 10(-12) m(2)/s and 1.2 x 10(-1)0 m(2)/s. Once the values of D-m and D-hm are estimated by simulation for one set of data, there are no further fitting parameters in the model. The model can then be used in a truly predictive mode for all the remaining data sets.