Aim of this paper is to develop an evaluation index of desulfurization reactivity for quicklime calcined limestone that produced from eight different mining in Japan. The quicklime is calcined at 1173 K under air atmosphere, and the desulfurization reactivity is investigated by a fixed bed quartz reactor.
The desulfurization experiments are performed for 120 min at 1173 K under SO₂/N₂ atmosphere. Variation of CaO conversion during reaction obtained for eight different quicklime. Effects of physical and chemical characteristics of limestone or quicklime on CaO conversion are examined. Geological time, thermal conductivity, calcination temperature, crystal grain size, surface area and pore volume are analyzed for an investigation of the evaluation index.
The quicklime having macro-pore over 1, um shows good desulfurization reactivity. Therefore, CaO conversion, X₁₂₀, is closely connected with total macro-pore volume for over 1 μm, P_v1.0. Its cor relation coefficient, R², is 0.945. The desulfurization reactivity for various limestone is able to estimate accurately by the evaluation index, P_v1.0.

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For effective HCl gas removal from waste incineration, the effect of H₂O and CO₂ on HCl sorption with CaO and Na₂CO₃ was studied. Experiments of HCl sorption were conducted in a gas flow-type tubular reactor packed with CaO and Na₂CO₃ fine particles under 5 μm in the diameter, at the temperatures 473-1073 K. The mixed gas of HCl (1000 ppm), H₂O (10 vol%) or CO₂ (10 vol%) and N₂ (balance), was introduced into the reactor at a flow rate of 3.00×10^-4m³·min^-1.
As the results, a maximum conversion value of 0.69 for HCI sorption by CaO was obtained at 873 K in N₂ atmosphere. With the presence of H₂O and CO₂, the conversions decreased to 0.49 and 0.40, respectively. It was found that H₂O was influential on HCl sorption in whole reaction period, while the influence of CO₂ appeared after the conversion attained 0.18 A maximum conversion value of 0.76 for HCl sorption by Na₂CO₃ was obtained at 673 K in N₂ atmosphere. With the presence of H₂O, the conversion decreased to 0.64. The influence of H₂O 0n HCl sorption by Na₂CO₃ was smaller than that by CaO. Moreover, HCl sorption by Na₂CO₃ was not appreciably affected by CO₂.

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Effects of two hydrothermal processes, the room temperature and high temperature mixing method, on formation of calcium silicate hydrates were investigated at 250°C from three precursors with Ca/Si ratio of 2.0, β-Ca₂SiO₄, a mixture of CaO and fine quartz, and a mixture of CaO and amorphous silica. Nine kinds of calcium silicate hydrates were formed, depending on the hydrothermal processes and precursors. γ-C₂S hydrate was formed as an initial phase from all starting materials by the high temperature mixing method and from β-C₂S by the room temperature mixing method. Low-crystalline C-S-H gel was the initial product from lime and silica by the room temperature mixing method. After the reactions for 1 d, γ-C₂S hydrate decomposed to form C₈S₅ (Ca/Si=1.6) and reinhardbraunsite (Ca/ Si=2.5) by room temperature mixing method. On the other hand, it was first confirmed that jaffeite (Ca/Si=3.0) and kilchoanite (Ca/Si=1.5) were formed through C₈S₅ from γ-C₂S hydrate by high temperature mixing method. The reaction of a mixture of lime and silica by the room temperature mixing method gave hillebrandite (Ca/Si=2.0), but disproportionation reactions proceeded by the high temperature mixing method to form Ca-rich and Si-rich phases.

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Calcium aluminoferrite immobilizes hexavalent chromium in a liquid phase following hydration, even under the coexistence of a large quantity of sulfate ions. However, the rate of immobilization is reduced by the coexistence of sulfate ions. In addition, the rate of hexavalent chromium immobilization is significantly affected by the composition of calcium aluminoferrite. Calcium aluminoferrite simultaneously immobilized sulfate ions together with hexavalent chromium in a liquid phase. MASH rapidly decreased chromium in a liquid phase. Compared with MASH, MFSH showed a slower rate of chromium immobilization. Calcium aluminate tended to speed up the removal of chromium in a liquid phase after the generation of monosulfate was recognized. From this fact, it is considered that the reason why the rate of chromium immobilization slows down under the coexistence of sulfate ions is due to the generation reaction of ettringite, which hardly immobilizes chromium, predominantly proceeds in the initial stage of hydration through the interaction between C₃A and sulfate ions. On the other hand, in the case of calcium aluminoferrite, the timing of the formation of AFm and the timing when hexavalent chromium is in a liquid phase drastically decreased and were not always corresponding. Judging from the fact that the rate of chromium immobilization of MFSH is slower than that of MASH, AFm, which is generated from calcium aluminoferrite system compounds, is slower in the rate of chromium immobilization compared with MASH.

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Colorless and transparent corundum crystals were readily grown for the first time by a slow-cooling method of Li₂Mo₂O₇ flux. They looked blackish at a glance because they had inclusions in their center. The crystals formed as plate bounded by well-developed {0001}, {0112} and {1014} faces. They were up to 5 mm in size. The crystal habit changed to thin hexagonal plate-like crystals as they grew large. Li₂Mo₂O₇ flux was found to be a suitable flux for the growth of plate-like corundum crystals.

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Effect of Fe₂O₃ on reductive decomposition of gypsum was investigated. The experiments were carried out by employing CaSO₄ powder of the mean particle size of 80, um which was mixed with 150 mass% Fe₂O₃, under CO : 2%-CO₂ : 30%-N₂ : balance and CO : 10%-N₂ : balance atmosphere at 1273 K, in a gas-flow type tubular reactor. Furthermore, SO₂ absorption characteristic of CaO thus regenerated from CaSO₄-Fe₂O₃ mixture by CO reductive gas was studied.
It was found that the rate of reductive decomposition of CaSO₄ was drastically enhanced by addition of Fe₂O₃. Moreover, the formation of CaS was inhibited by the addition of Fe₂O₃. Calcium ferrite such as 2CaO.Fe₂O₃ was detected in the reaction product after reductive decomposition of the mixture of CaSO₄-Fe₂O₃. As the result of SO₂ absorption experiment, it was found that CaO regenerated. from CaSO₄-Fe₂O₃ by CO reductive gas had a lower SO₂ absorption performance than CaO regenerated from CaSO₄. due to a decrease in Dore volume.

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Photo-induced activity of hydroxyapatite synthesized from waste gypsum was investigated by photocatalytic decomposition of dimethyl sulfide (DMS). Hydroxyapatite samples were synthesized by the reaction of gypsum and diammonium hydrogen phosphate. The decomposition of DMS on the hydroxyapatite under UV (254 nm) irradiation was ca. 68% in the one path reaction method. The hydroxyapatite sample was very active based on photo-induced excitation under UV irradiation. It was assumed that the crystallinity of the apatite structure would influence the photocatalytic activity from the X-ray diffraction studies. The higher the pre-treatment temperature for the hydroxyapatite samples was, the lower the decomposition of DMS under UV irradiation became.

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