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Equilibrium Relationships of Zn2+, Fe3+, Ca2+, and H+ with EDTA and DTPA in Soils
Author(s) -
Lindsay W. L.,
Norvell W. A.
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/sssaj1969.03615995003300010020x
Subject(s) - ethylenediaminetetraacetic acid , soil water , chemistry , chelation , metal , metal ions in aqueous solution , inorganic chemistry , amorphous solid , ligand (biochemistry) , equilibrium constant , crystallography , geology , organic chemistry , biochemistry , receptor , soil science
A general approach is developed by which the equilibria between chelating agents and metal ions in soils can be predicted from formation constants. Mole‐fraction diagrams are derived for EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid) in soils when the competing cations are either Fe 3+ , Ca 2+ , and H + , or Zn 2+ , Fe 3+ , Ca 2+ , and H + . These diagrams give the specific metal‐ligand complexes that form in soils and show how the concentration of each complex changes with pH. Evidence is presented to support the hypothesis that Zn reacts with amorphous SiO 2 in soils to form ZnSiO 3 . The concentration of Zn 2+ in equilibrium with solid phase ZnSiO 3 and amorphous SiO 2 is approximately 10 ‐6 M at pH 6, and decreases 100‐fold for each unit increase in pH. This concentration of Zn 2+ is approximately 100,000 times lower than that in equilibrium with ZnO or ZnCO 3 .