Interdiffusion in alkali ion sorption from mixed-solvent solutions on hydrous stannic oxide II. Na +/H + exchange

Abstract

The Na +-working capacity of hydrous stannic oxide mostly increases on addition of methanol, ethanol or propan-1-o1. The largest increase is obtained with ethanol and the smallest one is obtained with propan-1-o1. Considering the previous results of Li + exchange, it can generally be said that the change of interdiffusion coefficient D̄ i on addition of alcohol is the result of the effect of this addition on counterion-solvent, counterion-exchange site and alkali ion-coion interactions. The first factor contrary to other factors, enhances diffusion due to a dehydration (decrease of size) of diffusing counter ions. On going from one alcohol to the other in the purely hydroxide solutions, the decrease of the size of counter ions is the dominant factor, and D̄ i decreases in the order: propan-1-o1>ethanol>methanol. As with the aqueous medium, D̄ i increases on addition of NaCl to the alcoholic hydroxide solution due to a weaker interaction with Cl − coions, compared to OH − coions, inside the oxide pores. The order of D̄ i in the alcohols is mostly reversed on adding Cl −, which is probably connected with Na +Cl − interactions. Differences in the diffusion behaviour of Li + and Na + are discussed.