Utilization of a waste from titanium oxide industry for the synthesis of sodium ferrate by gas–solid reactions

• We studied the sodium ferrate (VI) synthesis by solid–gas reactions.
• Thermal behavior of iron sulfate is followed through thermogravimetric analysis.
• Synthesis of Na–ferrate is achieved at room temperature.
• Water and chlorine content affect strongly the synthesis process.
• Conversion efficiency of Fe(II) to Fe(VI) of the proposed process is about 30%.

This work is focused on the preparation of alkali ferrates, especially sodium ferrate, using ferrous sulfate as iron bearing material and chlorine as oxidant. Ferrous sulfate heptahydrate is mainly generated during titanium oxide extraction from ilmenite through the sulfate route; it is considered as a waste for this industry. Obtained alkali ferrates belong to the compounds where iron is in the rare hexavalent state and they are becoming a substance of growing importance for water treatment and industrial effluent cleaning.Two methods are developed for the ferrate synthesis. The first method consists of simultaneous reactions of two solids (iron sulfate and sodium hydroxide) and one gaseous oxidant (diluted chlorine). The second method involves a homogenous premixing of both solids prior to the oxidation by diluted chlorine. The synthesis process is performed in a rotary reactor at room temperature; however, since the overall reaction is exothermic, temperatures as high as 150 °C are often recorded. The effects of several parameters such as hydration extent of raw materials, Na/Fe ratio, chlorine content of the reactive gases on the sodium ferrate synthesis are investigated to determine the optimal processing conditions. The conversion efficiency of Fe(II) to Fe(VI) during the sodium ferrate synthesis reaches about 30%.