Applied predictive thermodynamics (ThermAP). Part 2. Apatites containing Ni2+, Co2+, Mn2+, or Fe2+ ions

Abstract

Additive model Enthalpy Gibbs free energy Stability Nickel apatite Cobalt apatite Manganese apatite Iron apatite ThermAP a b s t r a c tApatites are minerals encountered in many fields including geochemistry, nuclear and environmental sciences as well as medicine. This ubiquity is likely related to the diversity of ion substitutions that the apatite structure can accommodate, making of it an excellent ''ion reservoir'' either in natural settings or for the intentional production of doped systems with tailored properties. Despite this widespread interest for apatite compounds, however, only few studies are dedicated to study their thermodynamic properties. Yet, their knowledge becomes necessary for assessing stability domains and understanding evolutionary trends in solution or upon heating, for example. Recently, the experimental thermodynamics of 33 phosphate apatite compounds (deriving from the composition M 10 (PO 4 ) 6 X 2 ) have been reviewed and their comparison allowed the development of the additive predictive model ''ThermAP'' (Applied Predictive Thermodynamics) capable of adequately predicting properties such as standard enthalpies (DH f ), Gibbs free energies of formation (DG f ), or entropies (S°) at T = 298 K, for any composition involving ions among M 2+ = Ca 2+ , Ba 2+ , Sr 2+ , Mg 2+ , Cd 2+ , Pb 2+ , Cu 2+ , Zn 2+ and X À = OH À , F À , Cl À or Br À . Although experimental data for apatites involving other divalent cations such as Ni 2+ , Co 2+ , Mn 2+ or Fe 2+ do not seem to be available, the exploration of apatites doped with these ions is appealing from a practical and fundamental viewpoint, for example for understanding geochemical events, or when using apatite precipitation for the elimination of metal cations from industrial wastewaters, or else for conferring magnetic properties to apatite systems in medicine. Based on multiple physico-chemical correlations, the present contribution extends the additive predictive model ThermAP to Ni-, Co-, Mn(II)-and Fe(II)-doped apatites. It provides for the first time estimations of enthalpies, Gibbs free energies of formation and entropies, unveiling the general stability ranking Mn(II)-apatite > Fe(II)-apatite > Coapatite P Ni-apatite. This additive approach also allows one to estimate these properties for any composition in view of enabling thermodynamic calculations for applicative or fundamental purposes.

Thermodynamic Modeling of Integration of Strontium into Bone Tissue Hydroxyapatite

“…Software Th erm' AP was used [15,16]. Th is software allows to evaluate thermodynamic functions of phosphates with an apatite structure.…”

On the occurrence of jahnsite/whiteite phases on Mars: A thermodynamic study

“…where v i denotes the stoichiometric coefficient for ion i in the chemical formula, g i is the Gibbs free energy contribution of this ion, and a corr,Gi is a corrective factor applicable to the simplest oxide formed with ion i (for halides, the diatomic molecule is taken as reference). This approach, inspired from other works on predictive thermodynamics (e.g., La Iglesia 2009) but further investigated, has been particularly developed so far in the illustrative case of phosphate apatites and led to G f°, H f° and S° estimates generally within 0.5 to 1% of relative error (Drouet 2019(Drouet , 2015. For simplification of use, in the ThermAP formalism, each ion in the chemical formula is associated with a triplet (g i , h i , s i ) denoting…”

“…These factors were shown to be directly related to physicochemical characteristics of the elements considered, e.g. in terms of electronegativity (Drouet 2019(Drouet , 2015.…”

“…In practice, the corrective factors to apply for a given family of compounds are accessed by multiple iterations (ion by ion) comparing the ThermAP-calculated values of G f°, H f° or S° to data accessible as "reference" in the literature. However, when no reference data are available, as is the case of Jahnsites and Whiteites, it remains possible to consider a subpopulation of related solid phases sharing similar compositional features (Drouet 2019). The 23 phosphate phases taken into account in the present work for assessing the (g i , h i , s i ) values to apply to Jahnsites/Whiteites are listed in Table S1 (Supporting Information); they were selected on the basis of their chemical composition involving ions relevant to Jahnsites/Whiteites (essentially based on Table 1) and for their known thermodynamic properties, including in the extensive and updated Thermoddem database of mineral phases (Blanc et al 2012) usable in PHREEQC calculations.…”

“…Since no experimental data are available to assess directly the thermodynamic properties of these compounds, we expanded here the "Applied Predictive Thermodynamics" model ThermAP (Drouet and Alphonse 2015) to such phases. This model was previously set up and applied successfully to the phosphate apatite group of minerals (Drouet 2015(Drouet , 2019. To this aim, the model was based here on known thermodynamic data from a series of related mineral compounds (generally phosphates) involving ions relevant to the Jahnsite/Whiteite system and included in the Thermoddem mineralogical database, allowing calculations with speciation programs such as PHREEQC.…”