Recent trend of Rare Metal Recycling in Japan is described from the viewpoints to develop the new recycling industrial system called“ Rare Metal Recovery Complex” (RMRC). The novel recycling technologies of typical wastes such as cemented carbide tools, neodymium magnets, lithium ion batteries and printed circuit boards are reviewed as well as the latest achievements of industrial applications for rare metal recycling. The necessity to organize the venous economic system is emphasized for establishing a logistic supply-chain of collection, dismantle, intermediate treatment, urban mining and re-manufacture. The first step to fulfill such an industrial development in Japan is to accomplish the domestic flow circulation of rare metals in the industrial scraps and household wastes by promoting recycling activities, followed by the next step of international development and cooperation for a sustainable resources management. The introduction to a new concept of RMRC and its concrete image are also described along with the milestone to the RMRC goal.

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Borehole breakout, which is shear failure of the borehole wall, is one of the serious problems in drilling wells for oil/gas exploration and production. Investigation of stress condition causing breakout helps to avoid this problem. Conventionally, simple failure criteria, such as Mohr-Coulomb, which disregard the effect of the intermediate principal stress, were used to evaluate the stress condition. However, many researchers have reported that the intermediate principal stress affects the stress condition causing breakout. In this paper, the authors conducted true triaxial experiments using cubic rock specimens with a borehole to investigate the effect of the intermediate principal stress. In these experiments, measurements of tangential strains around the borehole wall and a weight of failed rock fragments by the scale, and observation of the wall using video camera were conducted to detect the failure development process. The effect of the intermediate principal stress was evaluated in five points along failure development detected by the measurements and the observations described above. The experimental results elucidated that the magnitudes of stress causing breakout clearly increase with increase of the intermediate principal stress in the all points along the failure development. However, when the authors compared the results with the three failure criteria, Modified-Lade, Drucker-Prager and Mogi, which consider the effect of the intermediate principal stress, the three failure criteria underestimated the stress condition causing breakout.

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In a project of methane gas extraction from a methane hydrate (MH) bearing sand formation in marine sediments, a production well is drilled into the sea floor from a marine platform. The depressurization method has been proposed for extracting methane gas. During the depressurization operation, sediment deformation and consolidation occurs because of MH dissociation and increases in the effective stress. This ingenerates friction on the production well, and shear failure may occur. These problems may cause gas leakage and depressurization impediment. Therefore, to ensure reliability of the well, it is very important to understand the frictional strength between the well and the sediments. The well consists of casing and cement, and it has three interface types: casing-cement, casing-sediment (sand or clay), and cement-sediment. In this study, we prepared simulated interface samples using steel rods (surface roughness: R_z = 2.7, 14.7, and 30.0 μm) and Class G cement. Moreover, a pushout test was carried out on these samples under different effective confining pressures. The test results showed that the maximum friction is not affected by the water-cement ratio of the cement, but it tended to increase depending on the effective confining pressure and the surface roughness. From these results, we expressed the maximum friction as a function of the effective confining pressure and the surface roughness.

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The motion of a single MH-bubble in quiescent fluid was examined experimentally. If a methane-gas bubble is placed under the condition that hydrates nucleation can initiate, typically at high pressure and low temperature, a thin methane hydrate film is formed on the bubble surface and it alters the motion of the bubble in the fluid drastically. It behaves as if solid did.To clarify the fluid dynamics of MH-bubbles, we devised the special apparatus which enabled us to observe the three dimensional behaviours of the MH-bubbles under high pressure condition. The three dimensional motions of the MH-bubbles were captured by two high-speed cameras whose resolution was 1024*1024 pixel at 500Hz. To analyze the motions of the MH-bubbles, Direct Linear Transformation Method was adopted.Equivalent diameter of the MH-bubble was altered from 3.8 to 7.8 mm, which corresponded to the range from 555 to 1155 in Reynolds number, by replacing the nozzles with different diameters.The MH- bubbles in this range exhibited the zigzag motion, while methane bubbles the spiral motion. Main findings in this research are as follows:(1) The aspect ratio, the height to width ratio, decreased linearly with the increment of the equivalent diameter of a MH-bubble. This reflects the fact that the shape of the MH-bubble shifts from spherical to ellipsoidal. (2) Strouhal number which characterizes the zigzag motion of the MH-bubbles increased with Reynolds number. (3) The drag coefficients were measured up to the Reynolds number of about 1000. The drag coefficient of a MHbubble departs from the standard drag curve when the shape deformation become notable. After that, it rise in accordance with the progress of the deformation. These phenomena also have been observed in the behaviour of a bubble with a surfactant.

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Removal of fluorine in effluent with low concentration is difficult technique and an effective method has not been established. This paper describes a novel fluorine-removal process that composed the following processes, addition of Al(III) source to feed water, conditioning of the slurry with magnesium oxide (MgO), neutralizing reaction, returning the settled slurry, and gravitational settling of the solids. This process allows the formation of a mixed Mg(II)-Al(III) hydroxide precipitate, which gradually develops into Layered Double Hydroxides (LDH) compound. MgO, which serves as both the neutralizer and the Mg(II) source, contributes to both the excellent settling and dewatering characteristics of the resulting solids. The sludge returning technique, well-known as High Density Sludge (HDS) method, is employed to prolong the sludge retention time to dissolve as much MgO as possible. Repeated batch-wise fluorine-removal tests showed that the residual fluorine concentration gradually decreased according as the number of batch test increased. Optimum fluorine removal ratio reached 96 %, where initial fluorine concentration 20 mg/L decreased below the national environmental standard, 0.8 mg/L. Powder X-ray diffraction analysis indicated the presence of both LDH phase and Periclase phase in the formed solids. Considering the good settling and dewatering characteristics of solids, the proposed process served as alternative treatment technique for low concentrated fluorine-containing effluents.

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