Extent and mechanism of metal ion incorporation into precipitated ferrites

The ability of many noniron metals to be incorporated into the structure of ferrites is being utilized in numerous industrial and environmental applications. The incorporation of some of these metals during Fe(II) oxidation-induced precipitation at moderate temperatures (80-100°C) appears to be limited, for reasons not fully understood, and to extents not always agreed (e.g., Ni²⁺, Cr³⁺). In this paper, the incorporation maxima of six metals into the structure of precipitated ferrites (in terms of x in Me_xFe_3-xO₄, Me represents a noniron metal) were concluded to be 1.0, 1.0, 0.78, 0.49, 0.35, and 0.0 for Zn²⁺, Co²⁺, Ni²⁺, Al³⁺, Cd²⁺ and Cr³⁺, respectively. With the exception of the much larger Cd²⁺, these values were associated with kinetic considerations controlled by the H₂O exchange rate between the hydration shells surrounding the dissolved metal ion.