Influences of Ni²⁺, Co²⁺, Cu²⁺ and Pd²⁺ Ions on Hydrothermal Synthesis of Magnetite

Abstract

A new approach for the synthesis of spinel-type ferrites under hydrothermal conditions has been investigated using the Schikorr reaction method. Magnetite was synthesized using ferrous sulfate solution containing small amounts of metal ions, including Ni²⁺, Co²⁺, Cu²⁺ and Pd²⁺ ions, respectively. Other workers have achieved the synthesis of magnetite above 160 °C by the Schikorr reaction, but the present work shows addition of Ni²⁺ ions is the most influential factor effecting acceleration of the reaction. In this study, low temperature (at 110 °C) magnetite synthesis was achieved by addition of Ni²⁺ (Ni / Fe = 0.34 mol%). Ni²⁺ is likely to be reduced by H₂ generated during the Schikorr reaction, with the newly formed Ni metal providing the catalyst to accelerate the dehydrogenation reaction. The most effective reaction mechanism for synthesis of magnetite above 150 °C is the Schikorr reaction, although other magnetite formation mechanisms may be effective at reaction temperatures less than 150 °C. During the Schikorr reaction, Fe²⁺ in solution is oxidized to Fe³⁺ accompanying the oxidation of Fe²⁺ to Fe³⁺ due to reduction of SOM₄^2-.