Halons (bromofluorocarbons) are identified as ozone depleting substances and are forbidden to be produced since the end of 1993. Appropriate treatment method to decompose halon waste is required. A dry process to decompose halon with solid alkaline has been developed. Solid alkalis are prepared from reagents of CaO and MgO. Recovery of F became larger with an increase of MgO fraction in the solid alkaline. The recovery of Br became smaller with MgO fraction in the solid alkaline, since reactivity of Br with MgO was low. The diffusion of the gases produced by decomposition of halon through the product layer as well as the reactivity of the gases with the solid alkaline reactant are important for the halon decomposition treatment of the gases with the solid alkaline reactant.

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Various burning conditions of paper sludge (PS) were examined for the purpose of waste-material recycling. Relationship between burning conditions and reaction products was investigated, and based on the results, optimal condition for recycling PS to use as a filler and a pigment of recycled paper was determined.
The PS ash with high whiteness could be obtained through the general burning process at a high temperature more than 700°C for a long time more than 5 hours. However, this PS ash was not suitable for a paper-filler and a paper-pigment since the pH and electric conductivity values increased too much at the slurry-mixing step due to the formation of gehlenite with high hardness.
Chemical changes of principal components of PS under a heating condition were examined by thermal analysis. Gehlenite was possibly formed from kaolin and calcium carbonate in PS via their thermally-caused change to mata-kaolin and calcium oxide. Since decarboxylation reaction depended on the partial pressure of carbon dioxide (CO₂), transformation of calcium carbonate to calcium oxide could be suppressed by burning PS under CO₂ atmosphere, although transforming reaction of kaolin to meta-kaolin hardly could because of independently from burning atmosphere. That is, decarboxylation temperature of calcium carbonate increased up to 800°C at CO₂ concentration in air of 10% and 900°C at 100%.
Consequently, proper burning condition of PS for recycling as a paper-filler and a paper-pigment was established as follows. Burning temperature is 700 to 750°C. Burning atmosphere is 10% of CO₂ and 90% of air (20% of oxygen (O₂) and 80% of nitrogen (N₂))

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Thermal alteration of kaolins and elution properties of calcined products have been studied for Chinese kaolin and Georgia kaolin in order to obtain knowledge to apply to geopolymeric materials. TG-DTA and XRD measurements confirmed that both kaolins were transformed to metakaolin and mullite via an intermediate phase of Al-Si spinel with elevation of the calcination temperature, liberating firstly water and then amorphous silica and cristobalite.
Elution measurements were performed by leaching calcined kaolins in 0.1 N caustic soda solution at 25°C and 80°C, respectively. Leaching at 80°C produced abnormally high elution peaks for Al⁺³ and Si⁺⁴ ions, for kaolins calcined at 900°C and 1100°C, respectively. These abnormal elution peaks do not correspond to the specific surface area trends, and are discussed on the basis of phase transformations and decomposition of the kaolins. In contrast, for leaching at 25°C, no such abnormal elution peaks were found. In addition, the metakaolin prepared over the 550-800°C temperature range showed higher elution with leaching at both 25°C and 80°C, which corresponds to the specific surface area trends. The Chinese kaolin also showed high elution. even under undehydrated conditions.

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For the purpose of recovering calcium resource from such solid wastes as coal burnt ash, iron slag, paper sludge, concrete sludge and shell waste, which involve calcium-derived compounds to a large extent, an attempt was made to extract calcium component with 6 organic acids : formic acid, acetic acid, propionic acid, oxalic acid, malonic acid and succinic acid.
It was found that propionic acid was most effective among the employed 6 organic acids, in terms of extracted amount of calcium component. The CaO content in the extract was concentrated in the range of 70-94 mass% The enrichment of CaO extracted was correlated with pK_a of organic acid. The increase in pKa value resulted in higher yield of CaO content with lower amount of the impurities such as SiO₂, Al₂O₃ and Fe₂O₃.
The HCl sorption capacity of CaO obtained by calcination of calcium propionate which was extracted from calcium-derived solid wastes employed in the present study, was 0.6-3.7 times higher than that of Ca (OH) ₂. The increase in HCl sorption capacity of CaO obtained by the calcination of organic calcium compound may be attributed to a highly porous structure of the CaO.

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Increasing accumulation of coal ash have been becoming a serious social problem in view of environmental loading, and its reuse or recycling of coal ash as raw materials of ceramics products is urgently required. Since the glass-ceramics of the CaO-Al₂O₃-SiO₂ system have been promising as construction materials, we have investigated the preparation technique of the glass-ceramics of this system using coal ash by the bulk crystallization method. The glass-ceramics were investigated by means of scanning electron microscope (SEM), powder X-ray diffraction (XRD), and so on.
Batches were prepared by mixing the starting materials in the various mass ratios of MIR : SiO₂ : CaCO₃ : FeS : Na₂SO₄ : C =150 : 0-18 : 30-60 : 0-4.5 : 0-6 : 0-1.5. Glass samples were produced by melting the batches at 1450°C. By those batch compositions, the glasses were homogeneously produced. They were reheated at 850°C for 1 hr to induce nucleation in the glasses. Further, the glasses were reheated at 1100°C for 2 hr, to make them to transform into glass-ceramics. The results of SEM photographs and powder XRD patterns of the obtained glass-ceramics showed that the homogeneous precipitations of the prismatic crystals (about 1×5μm) of anorthite (CaO·Al₂O₃·2SiO₂) have occurred in the glasses by the bulk crystallization, accompanied by the precipitations of gehelenite (2CaO·Al₂O₃·SiO₂) and/or nepheline (NaO₂·Al₂O₃·25iO₂).

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It was tried to decompose benzene gas electrochemically by using electrochemical cell in the temperature range between 250 and 400°C, where 8 mol% Y₂O₃ doped ZrO₂ (YSZ) well known as oxide-ion conductor was used for the electrolyte of electrochemical cell. Benzene gas was decomposed quantitatively to CO₂ and H₂O without any byproduct. The amounts of decomposed benzene increased with increasing the cell temperature or applied voltage (0-10 V) respectively, independent on the benzene concentration. The current increased with proportion to the square value of applied voltage.

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