Studies on thermochemistry and thermal processing of apatite; 5–18
Mihkel VEIDERMA
Abstract. A summary of the results obtained by
studies on thermochemistry of synthetic and natural apatites and thermal
processing of apatites in the presence of various inorganic compounds or
natural minerals is presented. The studies resulted in the development of
new methods for thermal processing of phosphate rocks with the purpose of
their enrichment or production of feed phosphates and phosphorus
fertilizers. Key words: apatite, synthetic, natural,
thermochemistry, thermal processing, defluorinated phosphates,
thermophosphates, sulphur dioxide.
Reaction chemistry of hydroxyapatite: Formation and decomposition; 19–28
Takafumi KANAZAWA, Hideki MONMA, and Yusuke MORIYOSHI
Abstract. The solid state formation of
stoichiometric hydroxyapatite (HAp) was investigated in detail by heating
the Ca3(PO4)2–CaO mixture and
Ca4(PO4)2O in the presence of water vapour.
HAp was an exceptionally thermally stable hydroxide even at high
temperatures above 1000 °C and at low water vapour pressures. New cementing
materials consisting of a
-Ca3(PO4)2, a
-Ca3(PO4)2 + CaHPO4×2H2O, and CaHPO4× 2H2O + CaCO3 were found
and clarified with respect to the hardening accompanying the formation of
calcium-deficient hydroxyapatite (DAp), hydration reactions with and without
additives, and mechanical strength of hardened products. The conversion of
sparingly water-soluble CaHPO4×2H2O and CaSO4× 2H2O and a calcium silicate mixture into DAp
was successfully conducted. Thermal decomposition characteristics of DAp,
HAp, HAp + SiO2, and
HAp + Ca2P2O7 were elucidated in
detail. Key words: hydroxyapatite, solid state
formation, thermal decomposition, apatitic cement.
Synthesis and structure of double phosphates of titanium and alkali
metals; 29–35
Natalya CHUDINOVA and Elena MURASHOVA
Abstract. Interaction of powdered titanium with the
polyphosphoric acid melt containing cations of alkali metals was studied at
350 °C. For the first time double condensed phosphates of titanium and
alkali metals with a composition
Na3TiIIIP8O23 and
Cs2TiIVP4O13 were obtained and
studied by XRD. Ultraphosphates
Na3TiIIIP8O23 with framework
structure contain cage-type anions. Tetraphosphate
Cs2TiIVP4O13 is of a layer
structure. Key words: phosphates, crystal
structure.
Preparation and thermal behaviour of oxovanadium(IV) phosphates and
hydrogenphosphates; 36–43
Dietmar FRATZKY, Thomas GÖTZE, Horst WORZALA, and Manfred MEISEL
Abstract. The results of a systematic study on
the conditions of the formation of different oxovanadium(IV)
hydrogenphosphate and orthophosphate hydrates in dependence on the
concentration, temperature, and pressure in the system
V2O5/H3PO4/
(COOH)2/H2O are reported. Some structural data and the
thermal dehydration of different oxovanadium(IV) orthophosphate hydrates are
discussed. Key words: oxovanadium(IV) hydrogenphosphate
hydrates, oxovanadium(IV) orthophosphate hydrates, hydrothermal synthesis,
X-ray powder diffraction, DTA.
Thermal analysis of Israeli phosphorites; 44–52
Kaia TÕNSUAADU, Mihkel VEIDERMA, Mihkel KOEL, and Yaacov NATHAN
Abstract. Thermal analysis of Israeli
phosphorites from Nahal Zin and Arad deposits was performed using the TG/DTA
method complemented with titrimetric and thermogaschromatographic
determination of the evolved gases. The amounts and temperature intervals of
H2O, CO2, and SO2 evolvement were
established, both in the oxygen-containing flow and in the inert gas
atmosphere, where additionally the organic compounds were
established. Key words: phosphorites, thermal analysis,
evolved gases, thermogaschromatography, Israel.
Modelling SO2 capture by Estonian limestones and dolomites;
53–70
Andres TRIKKEL, Ron ZEVENHOVEN, and Rein KUUSIK
Abstract. Sulphation of several chemically and
physically different Estonian limestone and dolomite samples was studied by
thermogravimetric analysis, accompanied by Hg-porosity, X-ray, and
SEM measurements. The SO2 binding capacity of the samples (particle size 125–160 mm) was analysed isothermally at 850 °C
and at 1 or 15 bar in a gas mixture of 4% O2,
15% CO2, 0.5% SO2, and N2. The
final values of conversion under these conditions were in the range of
32–66%, the amount of bound SO2 being 15.5–34 mg per
100 mg of initial sample. An attempt was made to apply an unreacted
shrinking core model with variable effective diffusivity to the CaO and
CaCO3 sulphation data under atmospheric and pressurized
conditions. The rate parameters were calculated for the sulphation reaction
and the limiting stages for the binding process were
established. Key words: sulphur binding,
thermogravimetric analysis, flue gas desulphurization.