Production of Fe from Fe₂O₃ using a dry mechanical alloying process

Mechanical alloying has been, and is still being employed extensively to synthesize a variety of alloy phases. The primary interest is to produce materials for scientific research and technological applications for magnetic recording media and permanent magnetic field devices. In the present investigation however the aim was not to produce a special alloy phases but to prove the viability of the production of iron from naturally occurring hematite, using mechanical alloying. Discard fines from the biggest hematite producer, Kumba Resources, Sishen, South Africa, were obtained and mixed with aluminum powder in the ratio of 25 at.% Al, balance hematite. About 50 g of the hematite-Al mixture, to be mechanically milled, was dry milled in a planetary ball milling equipment. The milling times varied between 30 min. and 30 hours and samples for Mössbauer spectroscopy, SEM analyses and Malvern sizing were obtained for each milling interval. Milling of the fine hematite with the much coarser Al resulted in a mixture with a particle size distribution of d_0.5 = 54μm to be extracted from the mill after 30 min. The Mössbauer spectra yielded 93% Fe₂O₃ and a 7% intermetallic Fe-Al component for this milling period. A final particle size of d_0.5 = 20μm for the milled product was obtained after milling for up to 30 h. However, within an hour all the hematite was completely converted to iron (≈ 86%) and two intermetallic Fe-Al compounds of combined intensity ≈ 14%. The intensity ratio of the two intermetallic Fe-Al alloys that were observed as two doublets, changed after 3 h milling time and the averaged Mössbauer parameters for the two doublets are reported as: D₁ = (Δ = 0.50 ± 0.03 mm.s^-1 and δ = 0.24 ± 0.03 mm.s^-1) and D₂ = (Δ = 2.07 ± 0.03 mm.s ^-1 and δ = 0.98 ± 0.03 mm.s^-1) respectively.