ORGANO-METALLIC INTERACTIONS IN SOILS

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Abstract
An ion-exchange equilibrium method was used to determine stability constants of complexes formed between a Podzol fulvic acid (F.A.) and Pb++, Ni++, Mn++, Co++, Ca++, and Mg++ at pH 3.5 and 5.0. At pH 3.5, log stability constants for the different metal-F.A. complexes were as follows: Ni-F.A., 3.47; Pb-F.A., 3.09; Co-F.A., 2.20; Ca-F.A., 2.04; Mn-F.A., 1.47; Mg-F.A., 1.23. At pH 5.0, log K values were: Pb-F.A., 6.13; Ni-F.A., 4.14; Mn-F.A., 3.78; Co-F.A., 3.69; Ca-F.A., 2.92; and Mg-F.A., 2.09. The results of this and of a previous investigation indicated the following order of stabilities of complexes formed between a soil fulvic acid and 9 divalent metal ions: Cu++>Fe++>Ni++>Pb++>Co++>Ca++>Zn++>Mn++>Mg++ at pH 3.5. At pH 5.0, the order changed to: Cu++>Pb++>Fe++>Ni++> Mn++>Co++>Ca++>Zn++>Mg++. Both orders deviated substantially from the Irving-Williams series.

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