『Abstract
The apparent solubility and dissolution rates of natural apatite
were measured in closed-system reactors as a function of temperature
from 5 to 50℃ and pH from 1 to 6. The temporal release rates of
Ca, P, and F during the experiments are approximately consistent
with stoichiometric dissolution in all experiments. One advantage
of closed-system experiments is that they allow determination
of reactive fluid evolution and dissolution rates at far-from
to near- to equilibrium conditions. Surface area normalized apatite
dissolution rates, r, obtained in all experiments are consistent
with
r = AAaH+nexp(EA/RT) (1 - exp(-A/σRT))
where AA stands for a rate constant equal
to 4×10-3 mol/cm2/s, aH+
denotes the activity of the aqueous H+, n designates
a reaction order equal to 0.6, EA symbolizes
an activation energy equal 11.0 kcal/mol, A refers to the chemical
affinity of the dissolving apatite, σ stands for Temkin's average
stoichiometric number equal to 5; R designates the gas constant,
and T represents absolute temperature. Logarithms of apparent
equilibrium constants obtained from experiments performed at 3≦pH≦5.6
for the apatite dissolution reaction
Ca5(PO4)3F
+ 3H+ = 5Ca2+ + 3HPO42-
+ F-
are found to be -29.5±0.6, -29.4±0.9 and -29.9±1.3 at 5, 25, and
50℃, respectively.
Keywords: Apatite; Dissolution kinetics; Equilibrium constants;
Phosphate』
1. Introduction
2. Theoretical background
3. Materials and methods
4. Results and discussion
5. Concluding remarks
Acknowledgements
References