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RESEARCH PRODUCT

Trace metal partitioning in Fe–Mn nodules from Sicilian soils, Italy

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Concentrations of 20 elements (Mn, Fe, Na, Mg, Al, K, Ca, V, Co, Ni, Cu, Zn, Rb, Sr, Cd, Cs, Ba, La, Ce, Pb) were determined in 18 Fe–Mn nodules from two alfisols, which are subject to periodic waterlogging. The nodules are significantly enriched in most trace metals relative to the host soil, with Mn, Co, Ce, Pb, Ba, Cd, Ni more enriched than Fe, V, La, Cu, Sr, Zn. Cesium and rubidium show poor or no enrichment in the nodules, consistent with their aluminosilicate affiliation. Scanning electron microscopy (SEM) examination and energy dispersive X-ray spectrometer (EDS) microprobe analysis have shown different microstructures (an undifferentiated fabric and a distinctive Fe–Mn banded structure) in the nodules from the two soils. A clearer partitioning of trace elements between Mn and Fe oxide phases is observed in the nodules showing the Fe–Mn banded structure, with Ba, Sr, Ni, Cu, and Cd correlated with Mn, V, and Pb with Fe. The nodules with undifferentiated fabric exhibit lower element/Mn molar ratios, which could reflect a minor adsorption of trace elements by MnO2 in relation to a more rapid growth of the nodules. As shown by elemental associations, the Cd and Ce distribution appears to be closely linked to the redox cycling of Mn.