INCORPORATION OF IMPURITY METAL-IONS IN ELECTROLYTIC MANGANESE-DIOXIDE

The amounts of impurity metal ions incorporated into electrolytic mang anese dioxide (EMD) during its preparation were measured as a function of metal ion concentrations and current densities. The amount of inco rporated ions increased in proportion to the concentration in solution , and at a fixed concentration it was different from ion to ion: Ni2< Zn2+ < Co2+ < Cu2+ < Fe3+ < Pb2+. The specific surface area of the f ormed EMD was larger for impurity ions with higher incorporation affin ity. Further, the adsorption of ions on the surface of a ready-made ma nganese dioxide sample (IC12) was examined, and modeling of the adsorp tion behavior was attempted. The amounts of adsorbed ions at a fixed c oncentration in solution and pH 0.7 (where EMD is produced) were obtai ned by the ion-adsorption model. There was a strong correlation betwee n the amount incorporated and the amount of adsorption, suggesting a m echanism in which EMD is contaminated through adsorption on its new gr owing surface. The increase in specific surface area of EMD with conta minants was interpreted to be due to a suppression of the growth of EM D at the adsorbed foreign ion sites, resulting in EMD with many defect s or smaller particle sizes. The opposite effect of current density on incorporation for the two groups of metal ions was discussed.