In order to utilize the fiber-cement-stabilized mud as landfill materials, it is very important to know the durability of the soils. Therefore, repeated cycle tests of drying and wetting were carried out by using the cement-stabilized mud and the fiber-cement-stabilized mud, and the durability of the modified soils was experimentally investigated. It was confirmed that the cement-stabilized mud deteriorated with increasing the cycle number. This result was not inconsistent with the results obtained by the previous researches. On the other hands, it was confirmed that the fiber- cement-stabilized mud did not deteriorate even if the cycle number increased. In order to explore the reason why the fiber-cement-stabilized mud shows high durability, the observation of the inside and the surface of specimens was carried out by using the microscope. Furthermore, the unconfined compression tests were carried out and failure strains were measured for both the cement-stabilized mud and the fiber-cement-stabilized mud. It was found from the unconfined compression tests that the failure strains of fiber-cement-stabilized mud were much larger than those of cement-stabilized mud. Therefore, it was confirmed that the reason why the fiber-cement-stabilized mud did not deteriorate was that the fiber-cement-stabilized mud forms the complicated structure which the soil particles and fiber are intertwined, and this complicated structure strengthens the combined force between soil particles and restrains the deterioration of the modified soils.

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Methane hydrate is one of the potential resources of natural gas in the near future, because a large amount of reservoir exists in marine sediments and permafrost regions worldwide. It is very important to investigate physical phenomena in hydrate reservoirs, especially for developing an extraction system for gas hydrates, and in considering the environmental impacts by the development.
In this study, we carried out an experimental research on hot water injection process as one of the thermal stimulation methods, using a special-type apparatus designed for simulating hydrate reservoir. As a result of the experiments, it was found that the dissociation process by hot water injection consisted of the following four stages, such as (1) displacement of free methane gas due to water injection, (2) additional hydrate formation at downstream zone due to migration of dissociated gas and water, (3) actual dissociation, (4) completion of dissociation. In addition, the permeability of the hydrate reservoir was observed as a function of time that, tended to decrease during the additional hydrate formation period and increase during the actual hydrate dissociation period. Based on experimental data of temperature distribution during dissociation, the reservoir could be divided into three zones from upstream edge, and dissociation zone was extremely narrow area depending on the dissociation rate. Furthermore, we discussed the effect of injected water temperature, reservoir pressure and hydrate saturation on the movement of dissociation front and gas production behavior.

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The main issues of conventional explosion-proof enclosures for methane gas, which are mainly used in coal mines, are their high cost, the difficulty of visualization of a display device, and an inaudible sound of a speaker put in them.
In order to solve these issues, the authors fabricated three test vessels (8, 16 and 32 cubic cm), which have a clearance of 1.2 mm, a width of joint of 50 mm, and several total width of clearances. The materials used for fabricating them were thin steel and acryl resin plates. Methane gas explosion tests and tests for non-transmission of an internal ignition were conducted at a gas concentration of 9 and 7.5 vol. % using them. The test results revealed that all test vessels had an explosion-proof function similar to the conventional explosion-proof enclosure. In addition, it became clear that the maximum explosion pressures in the test vessels at 9 % were considerably low (about 5 to 130 kPa).
From the test results, it is judged that the test vessels have the potential for solving the issues mentioned above. Because we would be able to fabricate explosion-proof enclosures with lower resisting pressures and with a wider clearance when compared to the conventional ones, using inexpensive thin steel and transparent materials.

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For the removal of acid gases discharged from municipal solid waste incineration, simultaneous / individual sorption of HCl and / or SO₂ by using Na₂CO₃ was investigated in the temperature range of 473-1073K. The tested gas mixture in N₂ balance was set to the respective concentrations as follows: 1000ppm HCl, 200ppm SO₂, 5% O₂ for simultaneous sorption; 1000ppm HCl for individual HCl sorption; 200ppm SO₂, 5% O₂ for individual SO₂ sorption. The sorption capacity as well as sorption rate for HCl / SO₂ sorption of Na₂CO₃ fine particle (d_p <5 μ m) was evaluated by the gas inlet-outlet measured by material balance.
As a result, the total capacity of simultaneous sorption of HCl and SO₂ was lower than that of individual sorption of HCl or SO₂, in the temperature range of 473-673K. On the other hand, the total capacity of HCl and SO₂ for simultaneous sorption of HCl and SO₂ was increased with temperatures of the range of 873-1073K. The sum of HCl and SO₂ sorption amount was about 1.4 times larger than that of individual sorption of HCl or SO₂ at 1073K. SEM / EDS analysis revealed that the amount of Cl distributed on the surface of the particle was about 20 times larger than that of S heated at 673K. This result indicated that sodium chloride formed on the surface of particles prevented SO₂ to react with Na₂CO₃.
An effective diffusion coefficient of HCl for chlorination of Na₂CO₃ was in the magnitude 10^-11, which was about twice higher than that of SO₂ under simultaneous sorption of HCl and SO₂.

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Leaching process by ammonium thiosulfate and solvent extraction by trioctylmethylammonium chloride (TOMAC, (C₈H₁₇)₃CH₃NCl) to recover gold from ores and waste was developed in our laboratory. In this report, the effects of gold, pH, ammonia, thiosulfate and cupric (Cu₂₊) ion concentration of ammonium thiosulfate solution, organic and water phase ratio were investigated to obtain a high recovery of gold with TOMAC. Under the constant condition of TOMAC (0.18mol/l, n-octane diluent + 10vol% 1-hexanol (in organic phase)) as discussed in the 1^st report which is related with this work, it was found that extraction efficiency increased with the thiosulfate ion to form a (TOMAC)₃-Au(S₂O₃)₂^3- ion at the condition of 0.01 to 0.03mol/l Cu²⁺ ion and 1.0 to 3.0mol/l NH₃/NH₄⁺. From the experimental results, it is indicated that this process can recover gold effectively and directly from ammonium thiosulfate solution by TOMAC. In addition, the advantage of this process is that the extraction can be conducted without pH and other adjustment.

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The phase relation between the CaO-SiO₂-FeO_X slag and the Fe-O-S melt saturated with solid iron has been investigated at 1573 and 1473K by a quench-chemical analysis method. The oxygen potentials of the melts were also measured by an EMF method. The miscibility gap between oxide and sulfide was illustrated as a function of oxygen potential. The solubility of sulfur in the CaO-SiO₂-FeO_X slag determined from the phase relations increased with the increase of basicity of the slag. The interaction between sulfur and oxygen in the CaO-SiO₂-FeO_X system has been discussed, and the following equation is derived as log P₀₂ = log P°₀₂ - 0.096 (mass%S) + 0.0052 (mass%S)²
(0.8<%S<10) at 1573K, where P₀₂ , P°₀₂ and (mass%S) are the oxygen partial pressure, the oxygen pressure for the CaO-SiO₂-FeO_X system and mass% of S in the slag, respectively.

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