[Wurstie]

I'm from Denmark and preparing for my exam in Chemistry, now I have about water cleaning. In water cleaning plants, you put FeCl3 into water with NPK- fertilizer to remove the phosphor. When this happens an ionic bond is created between the FeCl3 and the P, I don't know the chemical formula for this. But looking around I found Fe3(PO4)2, I just don't know you would get that from FeCl3 and phosphor. Can anybody help me? Sorry if my English terms aren't correct

[AWK]

Simply FePO4

[Wurstie]

Simply FePO4

Oh sorry, but how would you go about it. Showing how P becomes PO4-3 and then I would assume FeCl3 becomes Fe3+ and 3Cl-, but how does P become PO4-3?

[AWK]

P in NPK means calculated P₂O₅ content. But this means derivatives of phosphoric acid H₃PO₄.

[David Tan]

Ferric chloride or sulphate and ferrous sulphate are all widely used for
phosphorous removal, although the actual reactions are not fully
understood. The basic reaction is:
Fe3+ + HnPO43-n ↔ FePO4 + nH+
Ferric ions combine to form ferric phosphate. They react slowly with the
natural alkalinity and so a coagulant aid, such as lime, if added, would
raise the pH and enhance the coagulation.