Electrode graphite powder beds were interposed between anode and cathode as intermediate electrodes inside an electrolytic setup. Due to electrostatic shielding they eliminate the applied electric field and therefore stop the electromigration of ions within their mass. It was found that the intermediate electrodes can act as ionic current sinks-ion concentrating compartments and therefore cause a new type of a membrane-less electrodialysis/electrodeionization process. The proposed electrostatic shielding based coupled electrodialysis/electrodeionization treatment of synthetic cobalt plating rinse water containing 300 mg L(-1) Co(2 + ) ions produced a low-volume Co(2 + ) concentrate which could be recycled to the electroplating bath for reuse and a diluate containing 43.8 mg L(-1) Co(2 + ) ions. The diluate was then used as feed in the subsequent electrostatic shielding electrodeionization process which produced pure water with a cobalt ion concentration less than 0.1 mg L(-1). The current efficiency was 22-29%, the enrichment factor 13.5-26.1, the current density 20-40 A m(-2) and the flow rate 1.54 × 10(-4)-4.06 × 10(-4) dm(3) s(-1). The proposed membrane free electrostatic shielding electrodialysis/electrodeionization process could be developed into a new alternative electrochemical method of cobalt or other heavy metal removal and water purification and recycling from industrial effluents laden with heavy metals.

We constructed electrostatic shielding zones made of electrode graphite powder and used them as a new type of ionic and electronic current sinks. Because of the local elimination of the applied electric field, voltage and current within the current sinks, ions are led inside them and accumulate there. The sinks become ion concentrating compartments whereas the adjacent compartments become ion depleting compartments. The proposed electrodeionization process uses no permselective ion exchange membranes. We implemented it in electrodialysis desalination of a synthetic brackish 0.03 M NaCl solution and obtained potable water with a NaCl concentration <500 mg L -1 . Furthermore, we performed electrodialysis of 0.002 M NiSO 4 and electrodeionization of 0.001 M NiSO 4 solutions with simultaneous electrochemical regeneration of the used ion exchange resin beds. By the continuous mode of electrodeionization of the 0.001 M NiSO 4 solution we obtained pure water with a Ni 2+ ion concentration of less than 0.5 mg L -1 at a flow rate of 2.3 x10 -4 L s -1 diluate stream