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Journal of Thermal Analysis and Calorimetry
Authors: Anna Kohutová, Pavla Honcová, Ladislav Svoboda, Petr Bezdička, and Monika Maříková

Introduction The biological hard tissues consist of apatitic structure in the form of hydroxyapatite (HA, Ca 10 (PO 4 ) 6 (OH) 2 ). Nevertheless, biological HA is poorly crystalline, non-stoichiometric and of submicron

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Abstract  

The sorption of strontium on synthetic hydroxyapatite was investigated using batch method and radiotracer technique. The hydroxyapatite samples were prepared by a wet precipitation process followed by calcination of calcium phosphate that precipitated from aqueous solution. Also, commercial hydroxyapatites were used. The sorption of strontium on hydroxyapatite depended on the method of preparation and it was pH independent ranging from 4 to 9 as a result of buffering properties of hydroxyapatite. The distribution coefficient K d was significantly decreased with increasing concentration of Sr2+ and Ca2+ ions in solution with concentration above 1 × 10−3 mol dm−3. The percentage strontium sorption for commercial and by wet method prepared hydroxyapatite was in the range of 83–96%, while calcined hydroxyapatite was ranging from 10 to 30%. The experimental data for sorption of strontium have been interpreted in the term of Langmuir isotherm. The sorption of Sr2+ ions was performed by ion-exchange with Ca2+ cations on the crystal surface of hydroxyapatite. Although calcined hydroxyapatite is successfully used as biomaterial for hard tissues repair, it is not used for the treatment of liquid wastes.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: J. Soriano-Rodríguez, V. Badillo-Almaraz, C. Alliot, F. Monroy-Guzmán, and P. Vitorge

Abstract  

The sorption of Pd(II) on hydroxyapatite (Ca10(PO4)6(OH)2) has been studied at 25 °C as a function of pH, in 0.01 M NaClO4, and 0.01 and 0.025 M Ca(ClO4)2 aqueous background electrolytes and Pd(II) concentration (9.3 to 47 μM), trying to minimize some types of reactions, such as solid dissolution of and metal precipitation. The radiotracer palladium, 109Pd, obtained by neutron irradiation, has been used to calculate the palladium’s distribution coefficients K d between aqueous and solid phase. A mathematical treatment of results has been made by ion-exchange theory in order to interpret palladium sorption onto treated solid. For this, we take into account the existence of active sites at the hydroxyapatite surface, and the aqueous solution chemistry of palladium as well as the effect of phosphate anions from solid dissolution. The results can be explained as evidence of sorption of the species PdOH+, and of a mixed hydroxo complex of Pd2+ like (XCaO)–PdOH+·nH2O fixed onto {≡Ca–OH} surface sites of the hydroxyapatite.

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The sorption of copper on synthetic hydroxyapatite was investigated using a batch method and radiotracer technique. The hydroxyapatite sample prepared by a wet precipitation process was of high crystallinity with Ca/P ratio of 1.688. The sorption of copper on hydroxyapatite was pH independent ranging from 4 to 6 as a result of buffering properties of hydroxyapatite. The adsorption of copper was rapid and the percentage of Cu sorption was >98% during the first 15–30 min of the contact time. The experimental data for sorption of copper have been interpreted in the term of Langmuir isotherm. The sorption of Cu2+ ions was performed by ion-exchange with Ca2+ cations on the crystal surface of hydroxyapatite under experimental conditions. The competition effect of Zn2+, Fe2+ and Pb2+ towards Cu2+ sorption was stronger than that of Co2+, Ni2+ and Ca2+ ions. The ability of the bivalent cations to depress the sorption of copper on hydroxyapatite was in the following order Pb2+ > Fe2+ > Zn2+ > Co2+ ≈ Ni2+.

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Herein, hydroxyapatite (HAP) was prepared by aqueous precipitation technique and was characterized by using FT-IR and XRD to determine its chemical functional groups and micro-structure. The removal of cobalt from aqueous solution to HAP was studied by batch technique as a function of various environmental parameters such as contact time, pH, ionic strength, foreign ions, fulvic acid (FA), and temperature under ambient conditions. The results indicated that the sorption of Co(II) on HAP was strongly dependent on pH and ionic strength. The presence of FA enhanced the sorption of Co(II) on HAP at low pH, whereas reduced Co(II) sorption on HAP at high pH. The Langmuir, Freundlich and D-R models were used to simulate the sorption isotherms at three different temperatures of 303.15, 323.15 and 343.15 K. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) calculated from the temperature dependent sorption isotherms indicated that the sorption process of Co(II) on HAP was spontaneous and endothermic. The sorption of Co(II) was dominated by outer-sphere surface complexation and ion exchange at low pH, whereas inner-sphere surface complexation or surface precipitation was the main sorption mechanism at high pH values. The results suggest that the HAP is a suitable material in the preconcentration and solidification of Co(II) from large volumes of aqueous solutions.

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Abstract  

The synthesis of four types of hydroxyapatite synthesized from calcium chloride and four different organic phosphites is presented. The method of synthesis chosen is the sol–gel route, which has a number of advantages compared to other methods, like the intimate contact between reactants and the milder synthesis conditions. The samples were thermally treated, the TG/DTG/DTA curves being obtained at four heating rates, namely: 7, 10, 12 and 15 °C min−1. The samples were characterized before and after the thermal treatment using FT-IR analysis. The FT-IR spectra certified that the formed compounds represent hydroxyapatite. Based on the information from the TG curves and IR spectra interpretation, a reaction mechanism was proposed.

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In this research, a new composite, poly (hydroxyethylmethacrylate-hydroxyapatite) [P(HEMA-Hap)], was synthesized and its adsorptive features for natural radionuclides (TI+, Ra2+, Bi3+and Ac3+ in a leaching solution) were investigated at differing initial pH, concentration and temperature ranges. The natural radionuclides were counted by gamma spectrometer using a type NAI (Tl) detector. The adsorption data obtained were well represented by Langmuir and Freundlich type isotherms. The magnitude of determined monolayer adsorption capacities (X L) for the adsorbed radionuclides were TI+ = Ac3+ > Ra2+ = Bi3+. These results demonstrated that P(HEMA-Hap) had high affinity to the natural radionuclide. The thermodynamic parameters indicated that the adsorption mechanisms were spontaneous (ΔG < 0) in terms of adsorption free enthalpy, and changes in the enthalpy and entropy values showed that the overall adsorption process was endothermic (ΔH > 0), thus increasing entropy (ΔS > 0).

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In this work, hydroxyapatite (HAP) was prepared by aqueous precipitation technique and was characterized by using FT-IR to determine its chemical functional groups. A series of batch experiments were carried out to investigate the effect of various environmental factors such as contact time, pH, ionic strength, foreign ions, fulvic acid (FA) and temperature on the sorption behavior of HAP towards radionuclide 109Cd(II). The results indicated that the sorption of 109Cd(II) on HAP was strongly dependent on pH and ionic strength. A positive effect of FA on 109Cd(II) sorption was found at pH <7.0, whereas a negative effect was observed at pH >7.0. The Langmuir, Freundlich and D-R models were used to simulate the sorption isotherms at three different temperatures of 298.15, 323.15 and 343.15 K. The thermodynamic parameters (ΔH0, ΔS0 and ΔG0) calculated from the temperature dependent sorption isotherms indicated that the sorption process of 109Cd(II) on HAP was spontaneous and endothermic. At low pH, the sorption of 109Cd(II) was dominated by outer-sphere surface complexation and ion exchange on HAP surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. From the experimental results, it is possible to conclude that HAP has good potentialities for cost-effective treatments of 109Cd(II)-contaminated wastewaters.

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A novel composite adsorbent, magnetite/hydroxyapatite (Fe3O4/HAP) composites, was prepared by biowaste chicken eggshell for the purpose of removing radiocobalt from aqueous solutions. It highlighted that more than 92% Co(II) could be removed by using the developed composites under the experimental conditions. The maximum sorption capacity of Co(II) on Fe3O4/HAP composites was 6.9 × 10−4 mol/g. The coexisted foreign ions, e.g., ClO4 , NO3 , Cl, Na+ and K+, did not interfere the elimination of Co(II) from aqueous solutions, while Mg2+ did. The sorption process was found to be controlled well by pseudo-second-order and intra-particle diffusion models, and the equilibrium data were simulated by Langmuir model very well with high correlation coefficients. The thermodynamic parameters confirmed the spontaneity and endothermic nature of Co(II) sorption processes. After sorption, the Fe3O4/HAP composites could be effectively and fleetly separated from aqueous solutions by magnetic separation technique in large scale. The Fe3O4/HAP composites are suitable materials in the preconcentration of Co(II) from large volumes of aqueous solutions.

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) Degradation of hydroxyapatite, fluorapatite and fluorhydroxyapatite coating of dental implants in dogs. J. Biomed. Mater. Res. 48 , 224–234. Frayssinet P. Degradation of hydroxyapatite

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