Among the properties for controlling radionuclide migration of bentonite, used as a buffer material composing engineered barriers for the geological disposal of high-level radioactive waste, studies on the water penetration, swelling, chemical buffering and nuclide migration retardation properties were reviewed. For water penetration properties, the effects of bentonite dry density, silica sand mixture, temperature and salinity are approximately clear, and a model, applicable for various dry densities, silica sand contents and montmorillonite contents also has been developed. For swelling properties, the effects of bentonite dry density, silica sand mixture, salinity, interlayer cation, montmorillonite content and saturation degree are approximately clear, and a thermodynamic model, applicable for various dry densities, silica sand contents, salinities and montmorillonite contents has been developed. For chemical buffering properties, although data acquisition by a batch method and studies to directly measure pH and chemical component of the porewater of compacted bentonite have been conducted, data acquisition in compacted system and geochemical analysis have just started. Finding accumulation and data acquisition for various conditions such as high pH and saline groundwater are still needed. For nuclide migration retardation properties, the effects of bentonite dry density, salinity, silica sand mixture, montmorillonite content, particle size, interlayer cation, the charge of diffusion species and temperature on diffusion have been comprehensively studied. Data on the effect of interlayer cation on diffusion coefficient and activation energy and data on diffusion coefficient and activation energy for effective diffusion coefficient are however still insufficient. Inconsistency between batch sorption and retardation in diffusion should be additionally considered together with data setting method for safety assessment analysis. After the year 2000, studies for saline groundwater conditions have been powerfully conducted, and it is understood that saline groundwater conditions affect all properties described above. Continuing these studies, studies on the long-term behaviour considered the effect of alteration are necessary.
There are fewer basic data with respect to percussion drilling than those of rotary drilling, because the measurement of data such as percussion energy is difficult for percussion drilling. These basic data are necessary to implement percussion drilling and to design percussion drills. A calibration curve between the input energy into the percussion drill and the percussion energy was first made to estimate the percussion energy from the input energy while drilling. Next rotary-percussion drilling and rotary drilling were conducted using a roller cone bit with 4 in. diameter. Rocks used for the tests are Sori granite, Shinkomatsu andesite and Sanjome andesite whose uniaxial compressive strength is 223, 184 and 100 MPa, respectively. Analyses of drilling data revealed that the minimum value of the specific energy roughly coincides with the uniaxial compressive strength of each rock for both drilling methods. It was also revealed that variation of the specific energy with the bit weight in rotary-percussion drilling is small when compared to rotary drilling. In addition, the penetration rate and the rotary energy of rotary drilling which composes rotary-percussion drilling were estimated to be roughly equal to those of pure rotary drilling.
The smelting performance of a flash smelting furnace in the copper smelting process depends on the efficient premixing of concentrate particles and reaction air in the concentrate burner. When the concentrate particles and reaction air in the burner are well-premixed, the flowing pressure shows an additional pressure drop due to the interaction between the particles and the gas flow. In this study, the flow profile of the reaction air and the dispersion behavior of the concentrate particles in the concentrate burner are simulated by using numerical models in order to reveal the particle dispersion mechanism in the reaction air. When the concentrate particles are not fed into the burner, the reaction air mainly flows down along the inner wall of the burner cone and a large circulation flow is formed inside the main flow. The upward flow of the circulation flow formed below the concentrate chute prevents the concentrate particles fed through the chute from flowing down in the axial direction, and the particles consequently spread in the radial direction.
A comprehensive mathematical model was developed to describe the combustion phenomena of the copper concentrate particles in a flash smelting furnace, and then we try to improve its accurancy by changing the number of particle diameter groups of concentrate particles. This model incorporated the fluid flow, heat and mass transfer, and chemical reactions of the copper concentrate and supplementary fuel particles. The gas flow and motion of the particles were calculated using the Eulerian and Lagrangian methods, respectively. This developed model had two remarkable characteristics that were based on our understanding of the combustion phenomena in the reaction shaft of the flash smelting furnace. One characteristic takes into consideration the reaction of the concentrate particles to produce magnetite (Fe3O4) . The other characteristic considers the effect of shielding the radiative heat transfer caused by a concentrate cloud. The copper concentrate was assumed to comprise mainly chalcopyrite (CuFeS2) . The CuFeS2 reaction was considered to occur in two steps, namely, the decomposition of CuFeS2 and the oxidation of the resulting sulfur (S) and pyrrhotite (FeS) . This model has made it possible to predict the combustion phenomena which are the trajectories and temperatures of concentrate particles, and the temperatures and mass fractions of the gas. The calculated temperatures of the concentrate particles were approximately consistent with the temperatures measured in a commercial furnace, which verified the predictive accuracy of the model.
Loy Yang brown coal from Australia with ion-exchanged iron or nickel was carbonized up to 1000°C to study the influences of the exchanged cations on the char structure. The iron- and nickel-exchanged coals carbonized at 1000°C were converted to amorphous carbon. On the other hand, the Ca-Fe- and Ca-Ni- co-exchanged coals carbonized at 1000°C were converted to turbostratic carbon (interlayer spacing of C (002) is about 3.43 Å and crystallite size along c-axis is 40-70 Å). Ratio of turbostratic carbon to total carbon increased from about 25 to 65 % with increasing nickel loading. Mechanism of the formation of the turbostratic carbon was discussed in terms of aggregation behaviors of loaded metal species and C1 gas evolution profiles.
In order to recover copper from waste printed wiring boards which were free of mounted parts, bioleaching experiments of the boards were carried out using Acidithiobacillus ferrooxidans in shaking flasks. The size fraction and the copper content of the sample mainly used were -3.5+8mesh and 34.1% respectively. In the preliminary study using metal copper powder, the dissolution of copper was accelerated with the addition of ferric iron in the bioleaching while not in the absence of ferric iron. Ferric iron oxidized metal copper to give copper ions, and Acidithiobacillus ferrooxidans oxidized ferrous iron, promoting dissolution of metal copper. The dissolution rate of copper increased with increase in the initial concentration of ferric iron in the bioleaching of the waste printed wiring board. After the bioleaching of 125 hours, 72% of copper was dissolved with initial ferric ion concentration of 600mg/L, which was approximately three times as much as that without ferric iron.
Abstract: In this study, we examined drying shrinkage and the water absorption characteristics of super-lightweight concrete having dry specific gravity of less than 1.0. The results show that the drying shrinkage characteristics including the change in length and weight reduction ratios became small for super-lightweight concrete having dry specific gravity of 0.95. Moreover, water absorption tends to increase remarkably in one minute for super-lightweight concrete having dry specific gravity of 0.95.