Study of the effects of the applied current regime and the concentration of chromic acid on the transport of Ni2+ ions through Nafion 117 membranes

In the present work galvanostatic experiments are conducted with an electrodialysis cell in order to study the passage of Ni2+ ions present in chromic acid solutions through a Nafion cation-exchange membrane. The competing transport between H+ and Ni2+ ions through the membranes has been studied under the imposition of under- and overlimiting currents. Results show an increasing competence between both ions when the concentration of protons exceeds that of the Ni2+ ions. Increased nickel removal rates and current efficiency values were achieved with intensive current regimes due to the onset of electroconvection. However, at low values of the [Ni2+]/[H+] ratio, this improved transfer through the membrane implies high values of specific energy consumption due to increased membrane voltage drops, thus decreasing the convenience of applying overlimiting currents. The obtained results are related to the values of plateau length calculated from the polarization curves of this membrane/electrolyte system and prove that Ni2+ ions promote the arising of electroconvective vortices, whereas H+ ions hamper electroconvection.

► Overlimiting currents can imply improved specific energy consumption values.
► Increased Ni(II) removal rates are obtained at overlimiting currents.
► Arising of electroconvection improves the current efficiency of the nickel removal.
► Electroconvection is enhanced at high [Ni2+]/[H+] ratios.
► The plateau length, electroconvection and energy consumption are strongly related.