The aqueous suspensions containing 0.05, 0.10 and 0.20 M Fe(II) with pH 12 were subjected to oxidation with air at 20, 40, 60 and 80°C. The time duration, θ_e, needed for complete oxidation of Fe(II), which had been detected by the presence of dissolved oxygen in the suspension, was limited between 15 and 180 min by varing the oxidation rate.
Relation between the yield of Fe₃O, (X) and θ_e was obtained as follows; dX/dθ_e =k(1-X )² or 1/(1-X)=kθ_e+1, where k is a function of the oxidation temperature.
The Fe₃O₄ content of the oxidation product was affected by the oxidation rate and temperature. Settling velocity of the product became faster with increasing X for X≥0.6.