HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Brown, W. E. Articles by Lehr, J. R. Search for Related Content PubMed Articles by Brown, W. E. Articles by Lehr, J. R. Agricola Articles by Brown, W. E. Articles by Lehr, J. R.

Application of Phase Rule to the Chemical Behavior of Monocalcium Phosphate Monohydrate in Soils¹

ABSTRACT

When a granule of monocalcium phosphate monohydrate, Ca(H₂PO₄)₂ · H₂O, dissolves in a soil system, the fraction, f, of the phosphate left at the site of the granule as a dicalcium phosphate, CaHPO₄ or CaHPO₄ · 2H₂O, is shown by the relation

f = (1 – R)/(2 – R)

where R, the mole ratio of CaO/P₂O₅ in the composite solution removed from the granule, can be determined experimentally or estimated from phase-rule data for the system CaO-P₂O₅-H₂O. The composition of the solution leaving the granule approximates the invariant-point solution in equilibrium with Ca(H₂PO₄)₂ · H₂O and either CaHPO₄ (the stable invariant point) or CaHPO₄ · 2H₂O (a metastable invariant point).

Equilibrium data from the literature suggest that a residue of CaHPO₄ will contain some 28% of the P. Experimental data are presented from which a residue of CaHPO₄ · 2H₂O is predicted to contain about 21% of the P.

Reaction of some of the solute phosphate with cations such as iron and aluminum can cause precipitation of additional calcium phosphate.

¹ Contribution of the Research Branch, Division of Chemical Development, TVA, Wilson Dam, Ala. Presented before Div. II, Soil Science Society of America, Cincinnati, Ohio, Nov. 15, 1956.

² Research Chemists. Inez Jenkins Murphy and J. W. Williard made the chemical analyses.

Received for publication May 15, 1958. Accepted for publication August 13, 1958.