Formation and Transformation of Iron Oxide–Kaolinite Associations in the Presence of Iron(II)
- Shi-Yong Weiab,
- Fan Liua,
- Xiong-Han Fenga,
- Wen-Feng Tan *ac and
- Luuk K. Koopalad
- a Dep. of Resources and Environment, Huazhong Agricultural Univ., Wuhan 430070, China
b Dep. of Chemistry and Environ. Eng., Hubei Univ. for Nationalities, Enshi, Hubei 445000, China
c State Key Lab. of Soil Erosion and Dryland Farming on Loess Plateau Institute of Soil and Water Conservation Chinese Academy of Sciences Yangling, Shanxi 712100, China
d Lab. of Physical Chemistry and Colloid Sci., Wageningen Univ., Dreijenplein 6, 6703 HB Wageningen, the Netherlands
Iron oxide–kaolinite associations are important components of tropical and subtropical soils and have significant influence on the physical and chemical properties of soils. In this study, the formation and transformation of Fe oxide–kaolinite associations as a function of pH, temperature, and time were investigated at different Fe(II)/Fe(III) molar ratios (R). Results show that the formation of crystalline Fe oxides was significantly inhibited due to the presence of kaolinite, while accelerated by Fe(II). The formation of lepidocrocite– and goethite–kaolinite associations were accelerated by Fe(II) at R = 0.04 to 0.06, an initial pH (pHi) of 5 to 8, and a temperature (T) of 50 to 70°C; the formation of hematite–kaolinite association was accelerated by Fe(II) at R = 0.06, pHi 7 to 8, and T = 60 to 80°C; magnetite–kaolinite association was obtained at R = 0.06, pHi 9, and T = 60°C or at R = 0.1 to 0.5, pHi 7, and T = 60°C. The pH as a function of time (pH t ) decreased sharply when crystalline Fe oxides were formed in the presence of Fe(II), Fe(III), and kaolinite. The decrease in pH t was slow, however, in the system with Fe(III) and kaolinite but without Fe(II) and in the system with Fe(II) and kaolinite but without Fe(III). The morphologies of lepidocrocite, goethite, hematite, and magnetite in associations are strip shaped, nanorod like, pseudo-cubic shaped, and nanosphere like, respectively. In a system with Fe(II), Fe(III), and kaolinite, Fe(II) weakened the inhibition of the formation of crystalline Fe oxides by kaolinite; the presence of kaolinite decreased the acceleration by Fe(II); and the morphologies of Fe oxides were influenced by both Fe(II) and kaolinite.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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