The precipitation reaction between aminotri(methylenephosphonic
acid) (ATMP), a phosphonate used
for scale prevention in high-water-volume industrial processes such as
petroleum production, and calcium
was systematically studied. By varying the precipitating
conditions, three distinct precipitates formed:
a crystalline, sheetlike, 1:1 calcium−ATMP precipitate; an amorphous,
spherical-shaped, 2:1 calcium−ATMP precipitate; and an amorphous, spherical-shaped, 3:1 calcium−ATMP
precipitate. Corresponding
batch dissolution experiments showed that as the precipitate
calcium−ATMP molar ratio increased from
1:1 to 2:1 to 3:1, the rate of dissolution and the equilibrium
solubility limit decreased significantly. The
significance of these observations was evident when the release
characteristics of each precipitate from
porous media were studied as related to ATMP use in oil-recovery
systems. The 3:1 calcium−ATMP
precipitate was released from porous media in a much slower manner than
the other two precipitates,
strongly suggesting that the 3:1 precipitate is most suitable for use
in oil recovery.
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