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Phosphatoiron (III) and Phosphatoaluminum Complexes in Dilute Solutions
Author(s) -
Bohn H. L.,
Peech Michael
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/sssaj1969.03615995003300060022x
Subject(s) - phosphate , chemistry , ionic strength , ion , stability constants of complexes , inorganic chemistry , spectrophotometry , ultraviolet , equilibrium constant , ionic bonding , chromatography , aqueous solution , organic chemistry , materials science , optoelectronics
The phosphate complexes of iron(III) and aluminum in dilute solutions were studied by ultraviolet spectrophotometry, voltammetry, and cation exchange resins. The stability constant of the FeH 2 PO 4 2+ ion was found to be 4(± 0.8) × 10 3 at ionic strength of 0.1. Although phosphatoaluminum complexes were not directly detectable, their stability constants could be estimated as ≤ 10 3 for AlH 2 PO 4 2+ and ≤ 10 7 for AlHPO 4 + . These results indicate that, over the range of ion concentrations likely to be found in soil solutions, phosphatoiron(III) complexes are the predominant phosphate species in solutions of pH < 1.3; phosphatoaluminum complexes are the predominant phosphate species in the range of pH 1.3–4.3; and aquated phosphate ions are the predominant species in the range of 4.3–7.2. Published equilibrium constants for phosphatocalcium and phosphatomagnesium complexes and ion pairs revealed that these species are the predominant phosphate species at pH > 7.2.