EFFECTS OF SILICATE AND PHOSPHATE IONS ON THE FORMATION OF FERRIC-OXIDE HYDROXIDE PARTICLES

The effects of silicate and phosphate ions on the formation of alpha- and beta-FeOOH particles were studied. The formation and crystallization of alpha-FeOOH particles were inhibited by both the anions, and their particle size decreased with increasing concentration of the anions added. This inhibition was caused not only by complexing with ferric ions but also by adsorption on the particle surface. For alpha-FeOOH the amorphous particles were formed at a higher concentration of these anions. On the other hand, in the case of beta-FeOOH the effects of both the anions were little, especially for silicate ions. This difference between alpha- and beta-FeOOH particles could be explained by the difference between their preparation pH. The alpha-FeOOH particles prepared in the presence of these anions showed a microporosity.