Current-voltage characteristics in a hybrid electrodialysis-ion exchange system for the recovery of cesium ions from ammonium molybdophosphate-polyacrylonitrile

A hybrid electrodialysis-ion exchange (EDIX) method was investigated for the recovery of cesium from cesium-sorbed ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) ion exchange resin. Concentration polarization was studied by observing current-voltage (I-V) characteristics of a three compartment electrodialysis cell containing AMP-PAN in the middle compartment. The effect of process parameters such as flow rates of electrolytes and anolyte concentration on the current-voltage behavior was examined. Limiting currents, determined using Cowan plots, increased with electrolyte flow rates and anolyte concentration. In the present study, limiting current density (LCD) was measured for the electrodialysis system as a function of linear velocity and anolyte concentration using the equation ilim = aCub. Coefficients a and b for relating limiting current density and flow velocity were evaluated for different anolyte concentrations and electrolyte flow rates. Application of overlimiting currents resulted in lower recovery of cesium from AMP-PAN. During continuous operation of the cell, the onset of concentration polarization was detected by observing the pH of the acidic catholyte which turned to alkaline.