Influence of Mn2+ and pH on the Formation of Iron Oxides from Ferrous Chloride and Ferrous Sulfate Solutions1

G. S. R. Krishnamurti and P. M. Huang
Department of Soil Science, University of Saskatchewan Saskatoon, Saskatchewan S7N 0W0, Canada
1 Contribution No. R. 609, Saskatchewan Institute of Pedology, University of Saskatchewan, Saskatoon, Saskatchewan S7N 0W0, Canada.

Abstract: The influence of Mn2+ on the formation of Fe oxides at pHs of 6.0 and 8.0 and varying Mn/Fe molar ratios (0, 0.1, 1.0, and 10.0) in the FeCl2-NH4OH and FeSO4-NH4OH systems was studied by X-ray powder diffraction (XRD), infrared absorption, transmission electron microscopic, and chemical analyses. In the absence of Mn2+, lepidocrocite (γ-FeOOH) and maghemite (γ-Fe2O3) were the crystalline species formed at pHs of 6.0 and 8.0, respectively, in the FeCl2 system, whereas lepidocrocite and goethite (α-FeOOH) and lepidocrocite were the crystalline species formed at pHs of 6.0 and 8.0, respectively, in the FeSO4 system. The amount of Mn coprecipitated with Fe (as much as 8.1 mole % in the FeCl2 system and 15.0 mole % in the FeSO4 system) increased as the initial solution Mn/Fe molar ratio increased from 0 to 10.0, resulting in the perturbation of the crystallization processes of the hydrolytic products of Fe formed. At pH 6.0, the perturbation led to the formation of poorly ordered lepidocrocite, as reflected in the increasing broadening of its characteristic peaks in the XRD patterns. At pH 8.0, poorly ordered iepidocrocite and a honessite-like mineral (Mn-Fe-SO4-H20) formed in the FeCl2 and FeSO4 systems, respectively.

Key Words: Goethite • Infrared spectroscopy • Iron oxides • Lepidocrocite • Maghemite • Manganese • Synthesis • X-ray powder diffraction

Clays and Clay Minerals; October 1989 v. 37; no. 5; p. 451-458; DOI: 10.1346/CCMN.1989.0370509
© 1989, The Clay Minerals Society
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