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On the Solubility Constant of Strengite
Author(s) -
Iuliano Mauro,
Ciavatta Liberato,
De Tommaso Gaetano
Publication year - 2007
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/sssaj2006.0109
Subject(s) - solubility , solubility equilibrium , chemistry , dilution , equilibrium constant , absorption (acoustics) , analytical chemistry (journal) , inorganic chemistry , chromatography , thermodynamics , materials science , physics , composite material
Strengite, FePO 4 ·2H 2 O, commonly occurs in soils and represents a source of P for plants. The solubility of strengite is thus considerably important in the field of agriculture and environmental geochemistry, but few solubility data are available. Using absorption spectrophotometric techniques, the solubility equilibrium was studied at 25°C by measuring the total Fe(III), m Fe(III) , dissolved while keeping strengite in contact with H 3 PO 4 solutions. The acid concentration, m P , ranged from 0.001 to 0.1 mol kg −1 In solutions of m P ≤ 0.01 mol kg −1 m Fe(III) , results were constant within the limits of experimental error. This was ascribed to the predominance of a soluble species FePO 4 (aq). Soluble complexes, mainly Fe(H 2 PO 4 ) 3 (aq) and FeH 3 (PO 4 ) 2 (aq), were responsible for the increased solubility at m P ≥ 0.02 mol kg −1 , as evidenced in previous investigations. Using the constants evaluated in these investigations, the solubility data can be explained with the ion product equal to 10 −6.70 mol −1 kg at the infinite dilution reference state.