[APD] Re: Triple PO4 and Apatite solubility

["A.Kumar" <aar111 at yahoo_com>]

Hi,
        I did some calculations on the fluorapatite
(Ca5(PO4)3F) solubility using my old textbooks. The
solubility product, Ksp=3.16E-60 for fluorapatite. 
The ions (Ca++, PO4--, F-) are in the ratio 5:3:1. Let
S represent one ionic concentration. Then we would get
the equation Ksp=(5S)^5(3S)^3(S). If you do the math,
you will get 6.94E-8 M. Multiply by 3 (because we have
3 phosphates) and you get 2.1E-7 M. The ?M? stands for
molar which is moles/Liter. PO4 weighs 95g/mol. 
        After some more number crunching, I end up
with a value of .02mg/L, or .02ppm phosphate.
	This seems to be kind of low. However, the 0.02ppm
phosphate will be constantly maintained (by
dissolution) even as the plants uptake phosphate.
Also, there will be some pH effects and I think an
acidic pH will increase dissolution. Hope this helps,
AK


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