Abstract
Measurements of membrane potentials across nickel, hydroxide precipitate membranes have been made to estimate the transport number of anions, the order of selectivity for anions, and the fixed charge concentration. The membranes show a high selectivity for anions; from the measurements of the membrane potentials, the transport number for anions evaluated to be 0.98 in sodium chloride, nitrate, perchlorate, and sulphate solutions. The order of the selectivity for anions determined with the biionic potentials is OH->SO42->Br->I->Cl->NO3->ClO4-. This order of the selectivity is the same as that of the mobility in aqueous solutions, but the difference in the selectivity for these anions is greater in the membranes than in aqueous solutions. Nickel cations on nickel hydroxide precipitates constitute the fixed ion matrix characterizing the membranes as an anion exchanger, and its concentration is determined to be about 0.4g equiv./liter by comparing the experimental membrane potentials with the theoretical values according to the fixed charge theory of membranes.
