Formation of cadmium, zinc-bearing ferrites in aqueous suspension by air oxidation

Abstract

Slightly oxidized cadmium, zinc-bearing and cadmium-bearing ferrites have been prepared by air oxidation of iron(II) hydroxide suspensions at initial (Cd + Zn):Fe_tot mol ratios (r_{Cd + Zn}) of 0.10:2.90–1.00:2.00 at pH 10.0 and 65 °C. The upper limit of Cd: Fe_tot mol ratio in the ferrites was found to be about 0.1:1, and for each Zn:(Cd + Zn + Fe_tot) mol ratio in the suspensions upper limits were also found, respectively. The lattice constant a₀ and Mössbauer spectra at room temperature of the cadmium, zinc-bearing ferrites suggested that at Cd²⁺:Zn²⁺ mol ratios of ⩽0.12:0.43 at the tetrahedral sites the crystal structure of the ferrites prepared at r_{Cd + Zn}= 1.00:2.00 is that of zinc-bearing ferrites and approaches that of cadmium-bearing ferrites with increasing Cd²⁺ :Zn²⁺ mol ratio. Also that at r_{Cd + Zn}= 0.10:2.90–0.80:2.20, homogenous mixtures of CdFe₂O₄–Fe₃O₄ and ZnFe₂O₄–Fe₃O₄ solid solutions are formed.