Harouiya,N., Chairat(iの頭は¨),C., Kohler(oの頭に¨),S.J., Gout,R. and Oelkers,E.H.(2007): The dissolution kinetics and apparent solubility of natural apatite in closed reactors at temperatures from 5 to 50 ℃ and pH from 1 to 6. Chemical Geology, 244, 554-568.

『5〜50℃の温度と1〜6のpHにおける閉鎖型反応器での天然産アパタイト(燐灰石)の溶解カイネティックス見かけの溶解度』


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



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