Soluble Catalysts for the Oxygen Reduction Reaction, and Their Application to Becher Aeration

It is shown that two water-soluble redox catalysts, namely methyl viologen dichloride and diquat dibromide, can accelerate the rate of the oxygen reduction reaction on metallic iron in aqueous solutions. It is also shown that the same catalysts can speed the removal of metallic iron from reduced ilmenite in the aeration step of the Becher process. Under industrial conditions (2% ammonium chloride and 70 °C) aeration times can be decreased from 10 h to less than 3 h without irreversible adsorption of the catalysts. In all cases where catalysts are present, the dissolved iron precipitates as magnetite (Fe3O4). This environmentally preferred product is easier to separate and faster to dewater than conventional mixtures of iron­(II,III) oxide hydroxides.