Formation of a chromium-bearing ferrite, Cr0.42Fe2.56O4.00, in aqueous suspension by nitrate oxidation

Abstract

The title ferrite has been obtained by nitrate oxidation of an aqueous suspension containing a Cr³⁺ : Fe_total ratio of 0.16 : 1.00 and an optimum sulphate concentration (SO₄^2– : Cr³⁺= 1.0 : 1.0) at pH 7.0 and 80 °C. When the sulphate concentration in the initial suspension is low or high (SO₄^2– : Cr³⁺= 0.2 or 5.0 : 1.0), the incorporation of Cr³⁺ into the spinel-type ferrite is suppressed (Cr³⁺ : Fe_total= 0.01 : 1.00 to 0.03 : 1.00). The ferrite is formed via an intermediate compound which is a complex of chromium(III) and iron(II) hydroxides and SO₄^2–.