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Erratum: Borrego-Sánchez, A., et al. Molecular Modeling of Adsorption of 5-Aminosalicylic Acid in the Halloysite Nanotube. Minerals 2018, 8, 61
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Minerals 2018, 8(7), 281; https://doi.org/10.3390/min8070281

Transition from Endothermic to Exothermic Dissolution of Hydroxyapatite Ca5(PO4)3OH–Johnbaumite Ca5(AsO4)3OH Solid Solution Series at Temperatures Ranging from 5 to 65 °C

Faculty of Geology, AGH University of Science and Technology, Geophysics and Environmental Protection, al. Mickiewicza 30, 30-059 Cracow, Poland
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Received: 29 May 2018 / Revised: 23 June 2018 / Accepted: 26 June 2018 / Published: 30 June 2018
(This article belongs to the Section Environmental Mineralogy and Biogeochemistry)
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Abstract

Five crystalline members of the hydroxyapatite (HAP; Ca5(PO4)3OH)–johnbaumite (JBM; Ca5(AsO4)3OH) series were crystallized at alkaline pH from aqueous solutions and used in dissolution experiments at 5, 25, 45, and 65 °C. Equilibrium was established within three months. Dissolution was slightly incongruent, particularly at the high-P end of the series. For the first time, the Gibbs free energy of formation ΔGf0, enthalpy of formation ΔHf0, entropy of formation Sf0, and specific heat of formation Cpf0 were determined for HAP–JBM solid solution series. Based on the dissolution reaction, Ca5(AsO4)m(PO4)3−mOH = 5Ca2+(aq) + mAsO43−(aq) + (3 − m)PO43−(aq) + OH(aq), their solubility product Ksp,298.15 was determined. Substitution of arsenic (As) for phosphorus (P) in the structure of apatite resulted in a linear increase in the value of Ksp: from HAP logKsp,298.15 = −57.90 ± 1.57 to JBM logKsp,298.15 = −39.22 ± 0.56. The temperature dependence of dissolution in this solid solution series is very specific; in the temperature range of 5 °C to 65 °C, the enthalpy of dissolution ΔHr varied around 0. For HAP, the dissolution reaction at 5 °C and 25 °C was endothermic, which transitioned at around 40 °C and became exothermic at 45 °C and 65 °C. View Full-Text
Keywords: solubility; apatite; stability; thermodynamic; enthalpy solubility; apatite; stability; thermodynamic; enthalpy
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Puzio, B.; Manecki, M.; Kwaśniak-Kominek, M. Transition from Endothermic to Exothermic Dissolution of Hydroxyapatite Ca5(PO4)3OH–Johnbaumite Ca5(AsO4)3OH Solid Solution Series at Temperatures Ranging from 5 to 65 °C. Minerals 2018, 8, 281.

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