Abstract
There are two factors preventing ion permeation during electrodialysis using porous anodic alumina membranes-electrostenolysis in the pores, and sealing of the pores by a hydration reaction.
The mechanism of occurrence of electrostenolysis was investigated using an electrodialysis cell of the construction Pt/NiSO4/sulfuric acid membrane/H2C2O4 or Na2SO4/Pt.
With an oxalic acid catholyte at a pH value of 2∼6.5, ions were unable to permeate the membrane as an insoluble nickel compound (NiC2O4) precipitated into the pores, but with a sodium sulfate catholyte and a pH range 1∼65 they were able to permeate.
Electrodialysis was carried out by using membranes treated to different sealing times in boiled water, and the amount of Ni ions permeated to the cathode compartment was measured. Ni ion permeation ceased for sulfulic acid membranes in 2 minutes, and for Kalcolor membrane in 10 minutes.
SEM observations revealed that the pores of sulfulic acid films were completely sealed, however those of Kalcolor films had become smaller but were not completely sealed.
