A new glance at ruthenium sorption mechanism on hydroxy, carbonate, and fluor apatites: Analytical and structural studies

The sorption mechanism of Ru3+ ions on hydroxy (HAp), carbonate (CO3HAp), and fluor apatites (FAp) has been studied in detail. Ru apatites were obtained by reaction of the apatites with RuCl3 in aqueous solution. The structure and composition of the ruthenium-modified apatites were studied by several techniques: elemental analysis, XRD, EXAFS, IR, NMR, SEM-EDS, TEM, and thermal analysis. The amount of Ru in the modified apatite varies from 7.8 to 10.5 wt% and is not related to the initial composition or the specific surface area of the apatite. The different characterization techniques show that in the Ru-modified apatites Ru is surrounded by six oxygen atoms and do not contain any chlorine. For Ru-HAp and Ru-CO3HAp the new phase is amorphous whereas it is crystalline for FAp. The catalytic oxidation ability is higher for Ru-HAp and Ru-CO3HAp compared to Ru-FAp apatite in the oxidation of benzylic alcohol.     

Synthesis and Characterization of Na And Mg Containing Carbonatefluorapatites

Abstract

The apatites were precipitated in an aqueous NH₄OH-NH₄NO₃ solution with pH 9–10 at temperatures 20°C and 80°C. The synthesized materials were studied by chemical and thermal analyses (TG/DTG/DTA, TG/ETIR-EGA), IR-spectroscopy, XRD-powder analysis and specific area measurements.     

Computational study of cation substitutions in apatites

Density-functional theory plane-wave modeling of fluor- and hydroxyapatites has been performed, where one or two calcium ions per unit cell were replaced with cadmium or zinc cations. It was found that cadmium ions favor Ca(1) positions in fluorapatites and Ca(2) positions in hydroxyapatites, in agreement with experiment. A similar pattern is predicted for zinc substitutions. In the doubly substituted cases, where only hydroxyapatites were modeled, a preference for the substituting ions to be located in Ca(2) position was also observed. Displacement of the hydroxide ions from their symmetrical positions on the hexagonal axis can be used to explain the preferred configurations of substituting ions around the axis.     

Binding of SO2 by Synthetic Substituted Apatites

The reaction of SO₂ with synthetic apatites was studied by TG, XRD and IR analyses at 400-1000°C. Due to an interaction of apatite with SO₂, destruction of apatite and formation of CaSO₄ and diphosphate up to 750°C takes place. The further calcination leads to the formation of β-Ca₃(PO₄)₂ and a part of the SO₂ bound is lost again. The amount of SO₂ bound with apatite at calcination depends on the substitution ((F^- ↔ OH^-, PO₄ ^3- ↔ CO₃ ^2-, Ca²⁺ ↔ Mg²⁺) in its structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

Impact of anionic substitutions on apatite structure and properties

A review of the results of the authors on single and coupled substitutions of F for OH, and of CO₃ and SO₄ for PO₄ in synthetic and natural apatites, their influence on apatite structure and properties, studied by peak fitting FTIR, XRD, TG/DTA and TG/EGA methods, is presented. Calcination of carbonate and sulphate substituted apatites leads to the formation of stable stoichiometric apatite.     

Synergistic Effects of Fluorine and Carbonate on Cd2+Binding Properties of Apatites

Abstract

Most of the studies on heavy metals binding ability of apatites have been carried out on hydroxyapatites (HAP). (HA_p)[Ca₁₀(P0₄)₆(OH)₂]. As the chemical characteristics of apatite depend substantially on the substitutions in its structure, the apatites with F substitution for OH and CO₃ ² for PO₄ ³ were studied.