FePO42H2O

FePO4·2H2O, commonly written FePO4·2H2O, is iron(III) phosphate dihydrate. It is an inorganic salt formed from ferric ions (Fe3+) and phosphate (PO4^3−). In nature, it occurs as the mineral strengite in iron-rich soils and in oxidizing phosphate-bearing environments.

The compound consists of Fe3+ centers coordinated to oxygen from phosphate groups, with two water molecules incorporated into the crystal lattice as waters of hydration. It is a solid that displays very low solubility in water, making it effectively sparingly soluble under normal conditions. Its solubility and stability are influenced by pH; it tends to dissolve only under acidic conditions where phosphate and iron ions can be released.

FePO4·2H2O can be prepared by precipitation from aqueous solutions containing Fe3+ salts (such as ferric chloride or ferric sulfate) and phosphate under near-neutral to mildly basic conditions, allowing crystalline dihydrate to form and be isolated by filtration and drying. It can also be produced by dehydration of the dihydrate upon heating, which yields the anhydrous ferric phosphate.

Applications of FePO4·2H2O are largely related to its role as a mineral form of ferric phosphate rather than a widely used commercial reagent. It is of interest in studies of phosphate minerals, soil chemistry, and environmental processes involving iron and phosphate cycling. Safety data align with typical inorganic phosphates: it is relatively insoluble and of low acute toxicity, though handling should follow standard inorganic salt precautions.