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  • Author or Editor: V. Petkova x
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Abstract

Isothermal studies were conducted on mixtures of Fe2SO4·H2O in BaO2 in molar ratios ofn=4, 2 and 1 at temperatures of 573 and 1073 K, in a closed crucible, in air as gas medium. The solid products of decomposition were investigated by means of X-ray analysis, Mössbauer spectroscopy and electron spectroscopy.

The experiments revealed that the mechanism of the process is connected with the formation of different quantities of barium ferrites (BaFeO3, BaFe2O4 and BaFe12O19), as well as BaSO4 and Fe2O3, depending on the quantity of BaO2 in the initial mixture, the partial pressure of the gas components and temperature. Differences were found in the mechanism of the process for the same mixtures under dynamic temperature conditions.

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Abstract  

Syrian phosphorite is subjected to mechanochemical activation carried out in planetary mill. Some phase transformations are ascertained by means of powder XRD and thermal analyses. They reveal as partial transformation of carbonate fluorine apatite into carbonate hydroxyl fluorine apatite and formation of Ca(PO3)2, as well. The solubility of the activated sample in 2% citric acid is increased as a result of these changes.

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Abstract  

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.

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Abstract  

Fe2O(SO4)2 is a secondary product of the decomposition of FeSO4⋅H2O. Part I of this study presents results on the synthesis of Fe2O(SO4)2 in gaseous environment containing either low or high concentration of oxygen. In this paper the existence of differences between the structures of Fe2O(SO4)2 and Fe2(SO4)3 is proved on the basis of a detailed thermal study of Fe2O(SO4)2 upon dynamic heating (differential thermal analysis) and upon isothermal heating (thermal-analytic balance) in various gaseous environments as well as by presenting kinetic data on the processes of decomposition of both compounds.

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Abstract  

Investigations on the thermal decomposition of FeSO4H2O-BaO2 mixtures were carried out under isothermal conditions by using simultaneously solid electrolyte cell (EMF-method). Evoked interactions producing oxygen in the temperature range 553-673 K were established by means of a solid electrolyte oxygen analyzer. Based on Mssbauer spectroscopy data and X-ray analysis it was proved that these reactions were associated with the release of oxygen from barium peroxide, oxidation of ferrosulphate-monohydrate to FeOHSO4, and formation of barium ferrites such as BaFe2O4 and BaFe12O19.

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Abstract  

The thermal decomposition of FeS2 and BaO2 mixtures (mol ratio from 2 to 8) was studied in oxygen containing gas medium using dynamic heating rate. The solid decomposition products have been investigated with X-ray power diffraction and Mssbauer spectrometer. The thermal process has two main stages. In the presence of BaO2 the mixtures have a lower initial temperature of iron sulfide burning. The same time by the increasing of BaO2 content in the mixtures the diffusion difficulties are withdrawn in higher temperature ranges. It is proved that as intermediates BaSO4, nonstoichiometric sulfide, barium ferrites and Fe2O3 are formed. The content of many solid phases in the final product is in relationship with the initial ratio of BaO2 and FeS2.

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Abstract  

The thermal decomposition of tribochemically activated Al2(SO4)3 xH2O was studied by TG, DTA and EMF methods. For some of the intermediate solids, X-ray diffraction and IR-spectroscopy were applied to learn more about the reaction mechanism. Thermal and EMF studies confirmed that, even after mechanical activation of Al2(SO4)3 xH2O, Al2O(SO4)2 is formed as an intermediate. Isothermal kinetic experiments demonstrated that the thermochemical sulphurization of inactivated Al2(SO4)3 xH2O has an activation energy of 102.2 kJmol−1 in the temperature range 850–890 K. The activation energy for activated Al2(SO4)3 xH2O in the range 850–890 K is 55.0 kJmol−1. The time of thermal decomposition is almost halved when Al2(SO4)3 xH2O is activated mechanically. The results permit conclusions concerning the efficiency of the tribochemical activation of Al2(SO4)3 xH2O and the chemical and kinetic mechanisms of the desulphurization process.

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Abstract  

The data on the thermal decomposition of FeSO4⋅H2O upon various regimes of heating and gaseous environment prove the formation of intermediate products of the types Fe2O(SO4)2 and FeOHSO4, their stability and amount being determined mainly by temperature and oxygen-reduction potential. This communication aims at presenting results on the synthesis and characterization of Fe2O(SO4)2. The synthesis was carried out using a laboratory thermal equipment operating under isothermal conditions in the temperature range 713–813 K in a gaseous environment either poor in oxygen or containing 100% oxygen. The experimental conditions under which Fe2O(SO4)2 is stable are established. The effect of three basic parameters on the synthesis of Fe2O(SO4)2 is clarified: the oxygen partial pressure, the ratio PH2O/PO2 and the temperature and the mode of heating. Mssbauer spectroscopy and X-ray diffraction data for Fe2O(SO4)2 are presented.

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Abstract  

Thermochemical decomposition of pyrite in air-gas medium has been studied by means of MOM-Q 1500D Derivatograph. The derivatograms have been obtained at a heating rate of 5 K min-1 and air flowrate of 25 1 h-1 to final temperatures of 833, 933 and 1273 K, chosen on the basis of the stepwise oxidation of pyrite. The solid product is analyzed using X-ray powder diffraction and Mssbauer spectrometer techniques. The formation of nonstoichiometric sulfides (pyrrhotines) as intermediates has been confirmed. The second stage of decomposition is the oxidation of these pyrrhotines to hematite. The recorded weight losses are lower than the theoretically possible because of the formed nonstoichiometric iron sulfides. The complicated structure of the intermediate products has been confirmed by means of other techniques.

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Abstract

Thermal decomposition of different inorganic sulphates are presented. A number of techniques, but mainly TG and DTA, are used to prove the mechanism and kinetics of CaSO4, BaSO4, FeSO4·xH2O, Al2(SO4)3·xH2O under various gas atmospheres. It is shown how the partial pressure of gas components and heating rate may effect the mechanism and kinetic parameters. There are also examples on the effects of some additives and initial treatment on the thermal processes.

On the base of the results obtained some recommendations are given concerning the precautions to be taken into account in the thermal decomposition studies and the sulphur recovering.

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