Abstract
It is well known that ferric hydroxides, which is widely used as inorganic ion adsorbent, have a high adsorption capacity, and that they adsorb almost all inorganic ions on suitable conditions.
The present investigation was carried out to establish optimal conditions to prepare granular hydrated ferric oxide of high adsorption capacity, which can be used as an ion-exchanger in the form of membranes or in columns.
The results are summarized as follows;
1) The amorphous hydrated ferric oxide shows an amphoteric adsorption and has a rather high stability.
It has especially a high adsorption capacity for chloride ion.α-and βA-FeO(OH) adsorbs only chloride ion.
Their adsorption capacities are less than that of amorphous one.
2) The adsorption capacity of the amorphous hydrated ferric oxide and α-FeO(OH) are influenced by the pH of mother liquor, in which they are precipitated; that is, the adsorption capacity of α-FeO(OH) for chloride ion and the same capacity of amorphous hydrated oxide for potassium ion decreased as the pH of the mother liquor increased.
The amorphous hydrated oxide prepared in mother liquor of pH 7 indicated the highest adsorption capacity for chloride ion.
The adsorption capacity of the product decreased as the pH of the mother liquor deviates from this optimum value.
The adsorption of βA-FeO(OH) was higher, when it was prepared at the lower hydrolysis temperature.
3) It can be generally stated that the shorter the period of aging, the better the adsorption capacity. The adsorption of α-FeO(OH), however, reaches a limiting value after the aging period of five days and the adsorption of βA-FeO(OH) reaches after one day respectively, but none of them change any more.
4) It is found that there is a correlation among the adsorption capacity, crystallinity and pH of mother liquor or hydrolysis temperature; that is, the adsorption capacity decreases as the crystallinity increases, while the crystallinity increases as the pH of mother liquor in the case of α-FeO(OH) or hydrolysis temperature for βA-FeO(OH) increases.
