Uptake of Fe(II) onto hematite (α-Fe{sub}2O{sub}3), corundum (α-Al{sub}2O{sub}3), amorphous ferric oxide (AFO), and a mixture of hematite and AFO was measured. Uptake was operationally divided into adsorption (extractable by 0.5 N HCl within 20 h) and fixation (extractable by 3.0 N HCl within 7 d). For 0.25 mM Fe(II) onto 25 mM iron(III) hematite at pH 6.8:(i) 10 of Fe(II) was adsorbed within 1 mm; (ii) 20 of Fe(II) was adsorbed within 1 d; (iii) uptake slowly increased to 24 of Fe(II) during the next 24 d, almost all adsorbed; (iv) at 30 d, the uptake increased to 28 of Fe(II) with 6 of total Fe(II) fixed; and (v) uptake slowly increased to 30 of Fe(II) by 45 d with 10 of total Fe(II) fixed. Similar results were observed for 0.125 mM Fe(II) onto 25 mM iron(III) hematite, except that percent of adsorption and fixation were increased. There was adsorption but no fixation for 0.25 mM Fe(II) onto corundum 196.2 mM Al(III) at pH 6.8, for 0.125 mM Fe(II) onto 25 mM iron(III) hematite at pH 4.5, and for 0.25 mM Zn(II) onto 25 mM iron(III) hematite at pH 6.8. A small addition of AFO to the hematite suspension increased Fe(II) fixation when 0.25 mM Fe(II) was reacted with 25 mM iron(III) hematite and 0.025 mM Fe(III) AFO at pH 6.8. Reaction of 0.125 mM Fe(III) with 2.5 mM Fe(III) AFO resulted in rapid adsorption of 30 of added Fe(II), followed by conversion of AFO to goethite and a decrease in adsorption without Fe(II) fixation. The fixation of Fe(II) by hematite at pH 6.8 is consistent with interfacial electron transfer and the formation of new mineral phases. We propose that electron transfer from adsorbed Fe(II) to structural Fe(III) in hematite results in oxidation of Fe(II) to AFO on the surface of hematite and that solid-phase contact among hematite, AFO, and structural Fe(II) produces magnetite (Fe{sub}3O{sub}4). The unique interactions of Fe(II) with iron(III) oxides would be environmentally important to understand the fate of redoxsensitive chemicals.
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