Thermochemical and kinetic study of the attack of fluorapatite by sulfuric acid solution at different temperatures

  • Hadir Aouadi-Selmi
  • Kaïs AntarEmail author
  • Ismail Khattech


The thermochemical and kinetics study of the attack of a synthetic fluorapatite (Fap) by a 10 mass% H2SO4 sulfuric acid solution was performed first at 25 °C using C-80 SETARAM microcalorimeter with reversal cells. The results are repetitive only for few amounts of Fap and the global enthalpy of the attack equals − 401.4 ± 9.7 kJ mol−1. The recorded curves and thermogenesis show one peak corresponding to the formation of anhydrous calcium sulfate (AH). The Avrami model has been used in order to determine the Avrami constants (k and n). The deconvoluted curves agree with a homogeneous kinetic scheme based on two successive reactions of order 1 with respect to calcium involving dissolution and precipitation phenomena. The precipitation enthalpy of AH deduced from iteration is close to the one determined experimentally and the sum of the reaction enthalpies does not differ from the global enthalpy determined by integrating the rough signal by more than 2.8%. Increasing temperature led to an increase in the attack rate, and kinetic results agree with the shrinking core model with a mixture of both diffusion through an ash layer and chemical reactions control. The two resulting apparent activation energies are 34.4 and 41.0 kJ mol−1, which are in the range determined by the isoconversional model [16.7–48.8 kJ mol−1].


Fluorapatite Microcalorimetry Kinetics Dissolution Precipitation enthalpy 



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© Akadémiai Kiadó, Budapest, Hungary 2019

Authors and Affiliations

  1. 1.LR15ES01, Materials, Cristallochemistry and Applied Thermodynamics Laboratory, Chemistry Department, Faculty of Science of TunisUniversity of Tunis El ManarTunis El ManarTunisia

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