In This paper, the author tries to discuss on the development and finiteness of natural resources on the basis of the present state of their supply and demand. The natural resources are classified into several categories i.e. mineral resource as solid raw materials, fossil fuels, nuclear power and new natural resource of energy. The finiteness and exhaustion of natural resources are one of the most important problems, in near future, because they are indispensable for production of various industrial materials as well as fuel of power plants, industrial plants, transport facilities, and home use. Then, the effect of increasing concentration of CO2 on the global warming is critically discussed from scientific and long term point of view. Furthermore, it is indicated that the nuclear power is one of the most important energy resources in the future, although there remain some severe technical problems to be solved, at present. Next, the author discuss on the technical features and possibilities of such new natural energy resources as solar panel, wind power plant, geothermal energy, etc. And, the features of various storage facilities of electric power are discussed from technical and ecological point of view, because most of new natural energy are transformed into electric power for transmission and tentative storage. Finally, the author indicates that is most important to discuss on the interaction amongst new natural energy, mineral resources, and global environment from scientific and long term point of view.
A new algorithm is implemented to represent formation and decomposition of methane hydrate particles during operation of the production system in the Discrete Element Method with the Coarse Grid Thermal-Fluid Coupling Scheme, which is developed by one of the authors. The phase of discrete particles changes at interface between the particles and continuous phase. The phase-change rate depends on the fugacity from the Pressure-Temperature diagram around the circumstance. The scheme is also enable one to simulate the process of agglomeration from hydrate particles and bonding to equipments of the production system by devising a bonding model. Several simulations were conducted to verify the scheme on the momentum and the thermal energy exchange between particles and continuous phase. Also parametric studies are conducted to examine the algorithm of phase-change by changing phase-change rate constant and the Pressure-Temperature diagram. Further, particles agglomeration in a duct is expressed using the bonding model. It was verified that the momentum and the thermal energy between particles and continuous phase are exchanged correctly with phase-change. Also the scheme was able to represent phase-change of methane hydrate and particle agglomeration. As a result, it was found that the scheme is able to be a useful tool to examine the flow assurance without blockage by methane hydrate in the production system if the parameters used in simulations are tuned up.
Strength and deformation of frozen rocks were investigated by uniaxial compression test and cyclic loading test at -20°C. Failure processes of Shikotsu welded tuff and Bibai sandstone were considered based on their deformation behaviors. Larger deformation of wet specimen was found than that of dry specimen in both rocks due to pore ices plastic deformation. However, effect of water content on strength depends on type of rocks. UCS of wet specimens of Shikotsu welded tuff was greater than that of dry specimens. In contrast, UCS of wet specimens was smaller on Bibai sandstone. The former phenomenon can be interpreted by inclusion effect of pore ice. The latter phenomenon can be explained due to stress corrosion by unfrozen water or reduction in friction coefficient of crack planes by pore ice.
Si dissolution rate and mechanism of the ferro nickel slag with different mixing ratios of scallop shell and cooling rates have been investigated to apply ferro nickel slag as soil improvement agent. Slag with slow cooling rate was consisted of crystalline materials such as forsterite and enstatite. On the other hand, the slag with rapid cooling rate was amorphous material. Different constituent crystalline materials were obtained by addition of scallop shell. After addition of 30wt% the scallop shell, Ca-bearing crystalline materials such as monticellite, akermanite, wollastonite and augite were generated in the molten slag. The results obtained by batch dissolution experiment and SEM/EDX observation are summarized as follows. (1) The amorphous slag has a faster Si dissolution rate than crystalline slag. However, Si dissolution rate of the crystalline slag become faster after addition of scallop shell. Si dissolution rate of the molten ferro nickel slag after addition of 30wt% scallop shell has the same with that of the amorphous slag with rapid cooling rate. (2) Ca-bearing crystalline materials such as monticellite, akermanite, wollastonite and augite were easily dissolved than Mg-bearing materials such as forsterite and enstatite which were originally contained in the slag with slow cooling rate. (3) Among the crystalline materials in the slag, dissolution of the part consisted mainly of monticellite were distinguished. It was followed by wollastonite, akermanite and augite. Marked dissolution did not observed in the part consisted mainly of forsterite and enstatite. (4) Difference in dissolution behavior of the crystalline materials was due to the Ca content and degree of silica tetrahedron polymerization. (5) Release of the nutrient elements such as Si and Mg can be promoted by the selection of rapid cooling rate and addition of scallop shell as Ca source in the production of slag.
Soil contamination by heavy metals including hexavalent chromium is a worldwide environmental issue. The objective of this study was to evaluate zero-valent iron, magnetite, and activated carbon as potential reductants used in the electrokinetic-PRB hybrid system for the treatment of soils contaminated by hexavalent chromium. The batch experimental results showed that the reduction of hexavalent chromium by these reductants was consistently enhanced by acid, which was a desirable result because PRB in the electrokinetic-PRB hybrid system is strongly acidified by the acid generated at the anode via water electrolysis. However, zero-valent iron and activated carbon were concluded not to be suitable reductants for our objective because of the following reasons. For zero-valent iron, acid dissolution of zero-valent iron released a significant amount of ferrous ion which migrates toward the cathode and as a result, high recovery of chromium in the PRB cannot be expected because ferrous ion reduces hexavalent chromium outside the PRB. For activated carbon, it was found that the generated trivalent chromium was dissolved in the aqueous phase meaning positively charged trivalent chromium migrates toward the cathode without remaining in the PRB. On the contrary, magnetite did not release ferrous ion under the acid exposure. Additionally, the generated trivalent chromium was sorbed to the magnetite without being released in the aqueous phase. Thus, it was concluded that magnesium is a suitable reductant for the electrokinetic-PRB hybrid system providing a high recovery of trivalent chromium in the PRB.