Synthesis of Calcium Ferrite Monosulfate Hydrate and Rehydration of Its Thermally Treated Intermediates

This paper describes the synthesis of pure calcium ferrite monosulfate hydrate (abbr. CFMSH), the thermal decomposition process of CFMSH, the rehydration of its intermediates thermally treated at various temperatures and the reconstruction of initial layer structure. These results obtained are compared with results of literatures on hydrotalcite. To remove CaSO4·2H2O being contained as mixture in CFMSH specimen obtained at optimum compounding molar ratios (CaO/Fe2(SO4)3) of 7.0, decarbonated water warmed to 40 °C was used. Synthesis of pure phase CFMSH was identified by XRD and FT-IR. The results obtained by thermal analysis, XRD and FT-IR showed the following. The host layer structure of pure CFMSH obtained in this way was destroyed by heating until 400 °C. At ca. 610 °C, 2CaO. Fe2O3, CaO and CaSO4 (type II) were crystallized. The thermal decomposition of CaSO4 occurred at ca. 1200 °C releasing SO3. All rehydration products of intermediates thermally treated under 1200 °C s howed roentgenographically the same layer crystal structure as initial CFMSH. Therefore, it was found that the temperature range of reconst ruction of CFMSH by rehydration method was more wide than that of hydrotalcite. On the other hand, the XRD result of rehydration product of i ntermediate thermally treated at 1400 °C did not show the initial layer structure, but showed the presence of Ca3Fe2(OH)12 of cubic system and Ca(OH)2.