REACTION PRODUCTS OF ORTHOPHOSPHATES IN SOILS CONTAINING VARYING AMOUNTS OF CALCIUM AND MAGNESIUM

Abstract

The reaction products formed when orthophosphates (pellets) were added to 22 soils, with different calcium and magnesium contents, were identified. Di-calcium phosphate dihydrate (CaHPO 4 ∙2H 2 O) 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 (MgHPO 4 ∙3H 2 O) 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 KH 2 PO 4 and NH 4 H 2 PO 4 . Octacalcium phosphate (Ca 4 H (PO 4 ) 3 ∙3H 2 O) and trimagnesium phosphate tetrahydrate (Mg 3 (PO 4 ) 2 ∙4H 2 O) precipitated in filtrates of these soils when saturated solutions of K 2 HPO 4 and (NH 4 ) 2 HPO 4 were used.Trimagnesium phosphate twenty-two hydrate (Mg 3 ((PO 4 ) 2 ∙22H 2 O) formed when dimagnesium phosphate trihydrate was added to a soil containing large amounts of magnesium.