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- 저자 : Amalfitano, C. (검색결과 1 건)
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Stability of coprecipitated natural humic acid and ferrous iron under oxidative conditions
Colombo, C.,Palumbo, G.,Sellitto, V.M.,Cho, H.G.,Amalfitano, C.,Adamo, P. Elsevier 2015 Journal of geochemical exploration Vol.151 No.-
Goethite and lepidocrocite are considered the stable species of Fe oxyhydroxides formed from Fe<SUP>2+</SUP> oxidation in mildly acidic soil environments, while maghemite is formed in mildly alkaline conditions. Complexing ligands, especially humic acid (HA), can change the pathway formation of these iron oxyhydroxides from Fe<SUP>2+</SUP> oxidation. This research aimed to assess the influence of HA on Fe<SUP>2+</SUP> oxidation and its effect on crystalline Fe mineral products. Ferrous iron was added to HA at increasing initial COOH/Fe(II) charge ratios ® at pHs of 5.0 and 8.0 and aged at 70<SUP>o</SUP>C for 1month and up to 8years at room temperature. The precipitated products after aging were analysed using XRD, FT-IR, TEM and AFM. The results indicate that oxidation of Fe<SUP>2+</SUP> at pH5.0, in the presence of large amounts of HA (R=0.1) promoted the formation of goethite together with ferrihydrite. Oxidation of Fe<SUP>2+</SUP> in slightly alkaline conditions (pH8.0) yielded maghemite with small amounts of goethite. Further, long-term aging of HA coprecipitated with Fe<SUP>2+</SUP> perturbed the stacking of the Fe hydroxyl sheets at pH5.0, favouring the formation of ferrihydrite. At pH8.0 the presence of humic acid does not influence the crystallinity of the precipitation products and maghemite was still stable after 8years of aging. This research confirms that the oxidation of Fe<SUP>2+</SUP> in soil and its subsequent hydrolysis is a very common process of Fe hydroxides/oxide formation in acidic soil environments. The type of Fe oxide formed depends strictly on the pH and secondly on the rate of oxidation, especially on the presence and amount of organic compounds that inhibit crystal growth. Humic acid are the main organic molecules in soils, particularly in cool, humid weathering environments where they lead to a decrease in crystalline perfection and promote the formation of ferrihydrite instead of goethite or lepidocrocite. These results provide significant insights into the effect of the mobility of HA in association with Fe minerals.
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