The NiCIJNaCI separation by eleetrodialysis is studied as a function of several operating conditions such as current density, Na/Ni concentration ratio, and temperature. The experimental T(Ni/Na) separation factors are discussed, assuming a membrane-controlled process, in terms of Hittorf transport numbers and electro-osmotic coefficients for the electrically driven transport of both cations through the cationic membrane (Nation 125 from du Pont) which is assumed to be the selective component in the cell stack. Activation energy for the separation is calculated and the obtained data are compared with the values derived from membrane resistance measurements.Electrodialysis is a well-assessed technology in desalination and is still considered an interesting possibility in the field of valuable metal recovery and nuclear waste treatment (1-3). In this last field, the electrical power availability makes the energy requirements and costs for electrodialysis less conditioning parameters. In this work, the Ni/Na separation by electrodialysis in chloride media has been considered. Two commercially available membranes, the cation-selective Nation 125 (from du Pont) and the anion-selective R-5035 (from RAI Corporation) were used. The former membrane was chosen because of its high performance in many electrochemical applications (fuel cells, batteries, electrolysis) and the latter because it is specifically tailored for electrodialysis.
ExperimentalMembranes.--Nafion 125 membranes are homogeneous perfluorosulfonic acid polymeric films from du Pont. They have an equivalent weight of 1,200 and are 5 mil thick. Membrane specimens were treated with 0.1M HC1 for 48h and boiled in bidistilled water for 72h to convert the membranes to the H + form, completely wet. Mem, brane specimens of 37 cm 2 in H + form were then equilibrated with the electrolyte solution until cation exchange was complete. The R-5035 Raipore membrane (from RAI Corporation) is a quaternized vinylbenzylamine-grafted anion exchange membrane 8 mil thick. Membrane specimens were equilibrated in the electrolyte solution for 72h after 48h in boiling water.
Transport parameter measurements.--TheHittorf transport numbers (t~), the electro-osmotic coefficient (B e' ~ k cond J ~\nx \\\i \\\~ \\\\\\\x\x\x\ Fig. 1. Sketch of the experimental cell used for membrane transport parameter measurements. E', current bearing electrodes; P, pump; e', e", SCE for membrane potential measurement under flowing ~urrent (membrane ~'esistance); k, capillary for volume variation detection; cond, conductivity cell; m, stirrer; Ma, Mc, anionic and cationic ion exchange membranes; M, membrane under study.827 cm3F-'), and the membrane area resistance (R 12 em 2) were simultaneously measured for both membranes. The results are collected in Table i. A three-chamber plastic cell formed by a cathodic compartment bounded by two ion-exchange membranes of opposite charge and two measuring compartments separated by the membrane to be characterized ( Fig. 1) was used. The current delivering electrodes...