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Reactions of EDTA Complexes of Fe, Zn, Mn, and Cu with Soils
Author(s) -
Norvell W. A.,
Lindsay W. L.
Publication year - 1969
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1969.03615995003300010024x
Subject(s) - ethylenediaminetetraacetic acid , chemistry , soil water , solubility , chelation , manganese , salt (chemistry) , zinc , inorganic chemistry , calcareous soils , soil ph , nuclear chemistry , environmental science , organic chemistry , soil science
The Fe, Zn, Cu, and Mn complexes and the Na salt of EDTA (ethylenediaminetetraacetic acid) were reacted with suspensions of acid, neutral, and calcareous soils. The initial concentration of chelate was 1 × 10 ‐4 M or on a soil weight basis, 11.2, 13.1, 12.7, and 11.0 ppm of Fe, Zn, Cu, and Mn, respectively. Suspensions were aerated and shaken continuously for periods of 2 hours to 30 days. At the termination of each reaction period the pH of the suspensions was measured; following centrifugation, the supernatant solutions were analyzed for Fe, Zn, Cu, Mn, Ca, and Mg by atomic absorption spectrophotometry. The concentration of 14 C‐labeled EDTA was determined by liquid scintillation. FeEDTA was stable in soil suspensions of pH 5.7 and 6.1, moderately stable at pH 6.75, and unstable at pH 7.3 and 7.85. This behavior was satisfactorily predicted using formation constants to describe equilibria of EDTA with Fe 3+ , Ca 2+ , and H + , with the assumption that the Fe 3+ concentration was controlled by the solubility of amorphous iron(III) oxides. ZnEDTA and CuEDTA were most stable in suspensions near neutrality. In acid soils Cu and Zn were increasingly displaced by Fe as pH decreased while in calcareous soils these metals were displaced by Ca as pH increased. The loss of Mn from MnEDTA was very rapid in all soils and was essentially complete in less than one day from suspensions of pH 6.1 to 7.85.