Authors:Kaia Tõnsuaadu, Kārlis Agris Gross, Liene Plūduma, and Mihkel Veiderma
The multifunctionality of calcium apatite is attributed to a large capability for elemental substitution, the active surface and a range in crystal perfection (low to high crystallinity). Harnessing these
Authors:Sergei N. Danilchenko, Aleksei N. Kalinkevich, Roman A. Moskalenko, Vladimir N. Kuznetsov, Aleksandr V. Kochenko, Evgenia V. Husak, Vadim V. Starikov, Fuyan Liu, Junhu Meng, and Jinjun Lü
Recent investigations [ 1 , 2 ] and earlier works [ 3 , 4 ] have shown that the mineral of cardiovascular pathological deposits consists of poorly crystalline carbonate-substituted apatite. However, the chemical
Two types of thermal effects, caused by substitutions (Ca2+↔ Na+, ↔ CO32-, SO42-, OH-↔ F-) in synthetic precipitated apatites as well as by sorption of Cd2+, Zn2+, and Cr3+ ions from the solutions were studied by TG/DTA, XRD and FTIR analysis. The temperatures of exothermic effect at 330-340°C
and of decomposition of carbonate and sulfate apatites at 650-950°C were shown to depend on the substitutions in the apatite
Authors:V. Petkova, E. Serafimova, N. Petrova, and Y. Pelovski
comprehensive utilization of the mineral raw materials, the product quality, and the environmental protection.
Natural apatite is the main raw material for production of mineral fertilizers. The application of traditional technologies for acidic receipt
Authors:M. Fedoroff, L. Debove, and Ch. Loos-Neskovic
The radioisotope18F with a half-life of 110 min is produced in order to determine fluorine and oxygen by γ photon or charged particles activation.
This radioisotope is a β+ emitter and must be separated from other radioisotopes produced from the analysed matrix. The separation was achieved by
fixation of fluorine on a plombo-stronsic hydroxyapatite, prepared by synthesis in aqueous medium. Studies of the distribution
of radioactive fluorine between the apatite and solutions of variable compositions, showed the optimal conditions, for the
separation from the following metals: Al, Mg, Fe, Mo and from the Al−Mg alloy. The separation was applied to the determination
of fluorine by γ irradiation and of oxygen by3He irradiation. Due to the great selectivity of this separation, radiochemically clean fluorine is obtained and the limit
of detection is lowered.
Authors:K. Tõnsuaadu, M. Peld, V. Bender, and M. Veiderma
The reaction of SO2 with synthetic apatites was studied by TG, XRD and IR analyses at 400-1000C. Due to an interaction of apatite with SO2, destruction of apatite and formation of CaSO4 and diphosphate up to 750C 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-, PO43- ↔ CO32-, Ca2+ ↔ Mg2+) in its structure.
The phase transformations of Syrian phosphorite upon mechanochemical activation are examined in the present work. The latter
is carried out in planetary mill equipped with 20 mm steel milling bodies and duration from 30 to 300 min. The established
by means of DTA, DTG, TG analyses transformation of non-activated carbonate fluorine apatite type B into the carbonate hydroxyl
fluorine apatite (COHFAp) mixed type A2-B leads to substantial changes in the properties of the activated samples expressed
in lowering the degree of crystallinity, strong defectiveness of the structure, and increase of the citric solubility. The
thermal analysis gives evidence for the decomposition of the carbonate-containing component within the phosphorite, as from
the positions placed in the vicinity of the hexagonal 63 axis (type A2), as well as from the positions of the phosphate ion (type B), and from the free carbonates. The data from
the thermal analysis, the powder X-ray analysis and the infrared spectroscopy give also evidence for phase transformations
of the activated apatite (with admixtures of quartz and calcite) into Ca10FOH(PO4)6, β-Ca3(PO4)2, Ca4P2O9, Ca3(PO4)2 · Ca2SiO4 and for that one of the quartz—into larnite and wollastonite. The influence of the α-quartz as a concomitant mineral is considered
to be positive. The α-quartz forms Si–O–Si–OH bonds retaining humidity in the solid phase thus facilitating the isomorphous
substitution OH− → F− with the subsequent formation of partially substituted COHFAp. Calcium silicophosphate and Ca4P2O9 are obtained upon its further heating. The presented here results settle a perspective route for processing of low-grade
phosphate raw materials by means of tribothermal treatment aiming at preparation of condensed phosphates suitable for application
as slowly acting fertilizer components.
Authors:Kaia Tõnsuaadu, J. Pelt, and Maria Borissova
Summary Thermal reactions in natural fluorapatite or fluorcarbonate apatite and ammonium sulfate mixtures with mole ratio 1:4 at calcination up to 500°C were studied by simultaneous thermogravimetry and FTIR analysis of the evolved gases. The composition of natural apatite has little impact on the release of NH3. Upon the evolution of NH3 nitrous oxides were found in minor amounts. The release of SO2 at temperatures above 400°C is more intensive and occurs at lower temperatures in the case of fluorapatite than of carbonate containing apatites. Evolution of CO2 starts at 250°C with maximum at 350-360°C.
Authors:M. Veiderma, M. Pyldme, K. Tynsuaadu, and K. Utsal
The thermal interaction of Kovdor apatite, calcite, dolomite and forsterite with calcium polyphosphate up to 1200 °C were studied by chemical, thermal (under dynamic and quasiisothermal and isobaric conditions), X-ray, electronmicroscopic and chromatographic methods. It was found that the accompanying minerals of apatite react with calcium polyphosphate at lower temperature in comparison with apatite, complicating the process of thermal defluorination of papatite.
Nuclear quadrupole interaction study using Time Differential Perturbed Angular Correlation technique has been carried out
to identify the sites where hafnium can reside in hydroxyapatite in order to mimic the behavior of plutonium adsorption on
hydroxyapatite. Hf(IV) has been found to occupy three sites with the quadrupole interaction frequency(ωQ) and its asymmetry(η): (i) ωQ = 136.7(5) Mrad/s, η = 0.54(1); (ii) ωQ = 300.1(9) Mrad/s, η = 0.35(2); (iii) ωQ = 124.6(5), η = 0.0(1). Narrow frequency distributions indicate the sites are well-defined. This study has been extended
to barium orthophosphate to confirm our inference for the apatite structure.