Effect of the Presence of Aluminum Ions in Iron Solutions on the Formation of Iron Oxyhydroxides (FeOOH) at Room Temperature Under Acidic Environment
The hydrolytic behavior of Fe solutions at room temperature under acidic conditions was investigated. In the presence of Al ions, with Cl and NO3 as associated anions, the Fe hydrolysis began almost instantaneously and a crystalline β-FeOOH (akaganeite) was formed in the AlCl3/FeCl3 system within a short period. Initially the particles were small with large surface area. However, with time the particles grew in size and the surface area decreased. After about 42 days of equilibration, the akaganeite particles grew to 60–300 nm long, 10–50 nm wide and with a surface area of 55 m2/g, which is similar to other reports for akaganeite prepared at higher temperatures. In the NO3 system [Al(NO3)3/Fe(NO3)3], lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) were formed. In a mixed anion system (Cl/NO3) solid phases identified were akaganeite (β-FeOOH) and lepidocrocite (γ,-FeOOH). The introduction of poly-nuclear hydroxy-Al along with monomer Al in Cl and NO3 systems of Fe affected the quantity and quality of the solid phase. The crystallinity of β-FeOOH formed in the presence of polynuclear hydroxy-Al ions in a Cl-system was more disordered than when it formed in the presence of monomer Al-ions alone. In NO3 systems, polynuclear hydroxy-Al hindered the formation of goethite (α-FeOOH). Our experiments showed that Fe oxyhydroxides crystallize readily under acidic conditions in the presence of Al ions and the data also indicated that the Cl was essential for the crystallization of akaganeite, whereas goethite was formed in those systems when Cl was absent.
Key WordsAkaganeite Aluminum Hydroxy-aluminum ions Iron hydrolysis Transmission electron microscopy X-ray diffraction
Unable to display preview. Download preview PDF.
- Burns, R.G. and Burns, V.M. (1977) Mineralogy: in Manne Manganese Deposits, G. P. Glasby, ed., Elsevier, Amsterdam. 18. pp.Google Scholar
- Cornell, R. M. and Giovanoli, R. (1989) Effect of cobalt on the formation of crystalline iron oxides from ferrihydrite in alkaline media: Clays and Clay Minerals 36: 358–390.Google Scholar
- JCPDS (1989) Mineral Powder Diffraction: File, 34–1266. International Centre for Diffraction Data, Swarthmore, Pennsylvania, U.S.A.Google Scholar
- Mackenzie, R. C. (1970) Differential Thermal Analysis, Vol. 1, Academic Press, London.Google Scholar
- Paterson, E., Swaffield, R., and Clark, D.R. (1982) Thermal decomposition of synthetic akaganeite (β-FeOOH): Ther-mochimica Acta 54: 210–211.Google Scholar
- Schwertmann, U. and Taylor, R. M. (1977) Iron oxides: in Minerals in Soil Environments, J. B. Dixon and S. B. Weed, eds., Soil Science Society of America, Madison, Wisconsin, 379–438.Google Scholar