Abstract: The influence of Al on the products formed by aerial oxidation at pH 5.5–7 and 20°C of Fe(II) chloride, sulfate and carbonate solutions, was examined. In all cases Al at levels Al/Al + Fe = 0.09–0.30 inhibited the formation of γ phases (lepidocrocite and maghemite) in favor of goethite under conditions where, in the absence of Al, these γ phases formed. The influence of Al in these laboratory studies was supported by field observations.
At higher levels of Al, ferrihydrite formation was favored. This effect of Al was seen to be the result of a slowing down in the hydrolysis/oxidation rate of the Fe(II) system.
The presence of Al not only changed the direction of mineral formation, but also caused the formation of Al substitued goethites which resembled in particle size and morphology the natural aluminiferous goethite extracted from a soil.