Formation of aluminium-bearing ferrite in aqueous suspension by air oxidation

Abstract

Aluminium-bearing ferrites and Al-bearing goethites are formed by air oxidation of Fe[OH]₂ suspensions containing aluminium(III) ions, with the mol ratio, AI^III: Fe_total(r_Al), in the range 0.03–0.40 : 1 at pH 10.5 and 65 °C. The amount of Al-bearing ferrites in the products decreases with increasing r_Al, whereas that of the Al-bearing goethites increases. At r_Al= 0.60 : 1 only the Al-bearing goethite, Fe_0.71Al_0.29O(OH), is formed. The chemical composition of the Al-bearing ferrite formed at r_Al= 0.03 : 1 is that of the stoicheiometric ferrite (Fe_2.95Al_0.05O_4.00). The values of r_Al in the Al-bearing ferrites are approximately half of those in the Al-bearing goethites.