Reaction Products of Orthophosphates in Soils Containing Varying Amounts of Calcium and Magnesium

Racz, G.J.; Soper, R.J.

Canadian Journal of Soil Science 47(3): 223-230


ISSN/ISBN: 0008-4271
DOI: 10.4141/cjss67-035
Accession: 068494776

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The reaction products formed when orthophosphates (pellets) were added to 22 soils, with different calcium and magnesium contents, were identified. Di-calcium phosphate dihydrate (Ca HPO4∙2H2O) formed in the soils having a water-soluble calcium to magnesium ratio of approximately 1.5 or greater. Dicalcium phosphate dihydrate and/or dimagnesium phosphate trihydrate (Mg HPO4∙3H2O) formed in soils having a water-soluble calcium to magnesium ratio of less than 1.5. Dicalcium phosphate dihydrate and dimagnesium phosphate trihydrate precipitated in filtrates of two dolomitic soils shaken for 15 min with saturated solutions of KH2PO4 and NH4H2PO4. Octacalcium phosphate (Ca4H (PO4)3∙3H2O) and trimagnesium phosphate tetrahydrate (Mg3 (PO4)2∙4H2O) precipitated in filtrates of these soils when saturated solutions of K2HPO4 and (NH4)2HPO4 were used. Trimagnesium phosphate twenty-two hydrate (Mg3 ((PO4)2∙22H2O) formed when dimagnesium phosphate trihydrate was added to a soil containing large amounts of magnesium.