"Natural analogues" can be defined as the processes or materials analogous to those operating in the geological disposal system of radioactive waste. Natural analogue studies provide the only means by which long-term data can be obtained under the real natural conditions, and also the most convincing support to the long-term performance assessment of the geological disposal system.
The framework of our natural analogue studies concerning the stability of the engineered barrier materials for geological disposal system of high-level radioactive waste is reviewed. One of the results is that the volcanic glass included in a clay bed did not alter during the past one million years.
The Tono Uranium Deposits are studied as geochemical analogues of radioactive waste disposal in Japan. We conclude that although the deposits have been subjected to a variety of geological processes and events such as faulting, erosion and uplift/subsidence, the reducing condition has been maintained and uranium has not migrated for at least the past ten million years.
Application and further development of the natural analogue studies are also discussed.

抄録全体を表示

Cobalt-rich manganese crusts on seamounts and manganese nodules on deep ocean floor have both been received attention as future resources for Co, Ni, Cu, and Mn. Lack of information on cobalt-rich manganese crusts has precluded comparisons between the two sources in terms of their technical and economical advantages. In the past 15 years, Japan has surveyed the cobalt-rich manganese crusts; therefore, it seems the proper time to compare the two. In this paper, we consider distribution features and R&D results to develop a method for examining and comparing the economical potentials of manganese nodule and cobalt-rich manganese crust mining. Through the preliminary evaluation of the two, the effectiveness of the method is confirmed.
Cobalt-rich manganese crust development seems a risky but high return venture because of its high sensitivity to cobalt prices. Manganese nodule development, on the other hand, is considered to be a stable and good for a long-term venture. One of the application fields will be the selection of suitable metallurgical processing. A lower substrate ratio in excavated ore is clearly required for the economy of the crust development. In order to improve the evaluation, detailed technical information for the recovery efficiencies in the subsystems and units is necessary.

抄録全体を表示

Core discing occurs due to tensile stress induced by boring within or below a core stub. To determine effects of the length of core on the magnitude and direction of tensile principal stress, a finite element analysis was carried out for an HQ core with different lengths for 77 in-situ stress conditions. We analyzed the semi-axial tensile principal stress, which is inclined from core axis by less than 45°, and the maximum semi-axial tensile stresses were determined with respect to the core axis for each position of the cross-section of the core. The minimum value and the mean inclination relative to the core axis of the maximum semi-axial tensile stresses were analyzed to determine the stress condition under which core discing is likely to occur. As a result, 30 in-situ stress conditions were identified as the stress condition under which core discing is likely to occur and the necessary condition for the in-situ stresses was proposed. The critical tensile stress, which is the maximum tensile stress that can produce a tensile fracture propagated throughout a cross-section, was analyzed for these stress conditions and a new criterion for core discing, which can be applied to any length of core, was proposed. Stress conditions estimated by the criterion were consistent with previous experimental results for a long core and for discs with small thickness. According to the criterion, the relationship between the length of core and the in-situ stress necessary for core discing was discussed, which showed that the stress field can be divided into three regions and that core discing with small length mostly occurs at great depth. The relationship between the length of core and the thickness of disc was determined by assuming that the position of a fracture is given by the mean position of the maximum semi-axial tensile stresses. Theoretical estimation reproduced previous experimental results on the effects of stress magnitudes on the thickness of disc.

抄録全体を表示

An analysis of tensile principal stress below an HQ core stub was carried out with a finite element method for eleven lengths of core in 25 stress conditions under which core discing is likely to occur. The direction of the semi-axial tensile principal stress, which has an inclination angle relative to the core axis of less than 45°, was analyzed in detail for the central part of the core. Based on the results, a method for estimating three-dimensional directions of in-situ stress from the height at the periphery of the end-surface of a disc was proposed. Main results obtained in this study are summarized as follows:
1) The direction of the semi-axial tensile principal stress is fairly uniform in a wide area of the central part of the core and does not depend on the length of core appreciably. Accordingly, the direction of the semi-axial tensile principal stress is considered to govern the geometry of the end-surface of a disc.
2) The azimuth of the semi-axial tensile principal stress in the central part of the core approximately coincides with that of the minimum principal stress, while the inclination relative to the core axis (φ_m) is smaller than that of the minimum principal stress (φ₃). A method for estimating φ₃ from φ_m was proposed, which gave an error of less than 25 %.
3) When the difference between the normal stresses perpendicular to the core axis (σ_x-σ_y) is great, a saddle-shaped disc is formed and the shape becomes more distinct with the increase in the stress difference. However the saddle shape becomes less distinct as the length of core decreases.
4) By assuming that the end-surface of a disc is inclined in the direction of the semi-axial tensile principal stress in the central part of the core, a method for estimating three-dimensional directions of in-situ stress from the height at the periphery of the end-surface of a disc was proposed.

抄録全体を表示

The authors have established strict formulation of mathematical equations for permeability determination by transient pulse method and extended the formulation to the specified cases, i. e., the authors have applied the transient pulse method to the hollow cylinder specimen and extended it's application to the case where fluid leakage from the pressure cell is taken into account. In the hollow cylinder specimen, fluid leakage along specimen boundary can be easily prevented.
Intrinsic permeability k was given by the following formula:
k=ακμ log(R₀ / R_i) / 2πL V₁ V₂ / V₁ + V₂
where α is the value to be determined from test data, κ is fluid compressibility, μ is fluid viscosity, R₀, R_i and L are the outer radius, the inner radius and the height of the hollow cylinder specimen, respectively. V₁ and V₂ are capacity of the spaces communicating with the inside and the outside of the hollow cylinder specimen in the pressure cell.
The authors developed a simple apparatus for permeability measurement. Pneumatic permeability tests using the apparatus were carried out and the permeability of a specimen made of limestone was determined. The permeability test takes only a few hours even for a specimen made of low-permeability rock because of low viscosity of air.

抄録全体を表示

Fluid injection test using a borehole for permeability of rock mass, such as Lugeon test, is to evaluate the average permeability of rock mass around the borehole, as the Lugeon value or the coefficient of permeability, although those values do not directly represent the feature or characteristic of the fracture / joint in rock mass. However, a distinctive mark of the fracture is one of the significant factors, which reflect the apparent permeability, and it may be possible to find a distinctive fracture quality by observing the trend of test data.
In order to examine whether it is possible to evaluate a unique property of fracture in a solid, longitudinal percolation tests for fluid seepage in wooden samples, which contain longitudinal thin plane slit or slits were carried out. Characteristic evaluation of the fracture in the sample was tried through explanation of the flow rate-time curves under constant fluid injection pressure, which were obtained from the laboratory tests. The explanation is based on the numerical calculations of both the seepage analysis and elastic displacement analysis.
Possibility of simple and economical evaluation of fracture characteristic is suggested from the results and then, one method for evaluation of fracture characteristic by using the least in-situ data and comparing it with numerical simulation result, is proposed.

抄録全体を表示

Distinct noises are emitted when the PET flakes impinge on the walls of the zigzag air classifier during air classification. On-line monitoring of air classification was investigated by measuring the noises. The relative energy of the noises that are emitted at the feed or top part of the air classifier was found to be increased with feed rate or top recovery throughput rate, respectively. The label grade of bottom product was correlated with the bottom yield and the air velocity inside the air classifier. From these results, the technical feasibility of the on-line monitoring of the PET flakes yield and grade was demonstrated by measuring the relative energy. This monitoring system for air classification was successfully tested at a PET recycling factory.

抄録全体を表示

In this experiment, lithium cobalt oxide from a waste lithium ion battery (LIB) is recovered by flotation technique. At first, the waste LIB was classified by vertical cutting mill, air table and vibration screen. Referring to the result of a crushing, wasted LIB represented light materials (separator of anode and cathode of battery), metallic materials (aluminum, copper, etc) and electrode materials (a mixture of lithium cobalt oxide and graphite).
Electrode materials were thermally treated in a muffle furnace at 773 K, followed by flotation to separate lithium cobalt oxide and graphite. This is due to the fact that the surface of the lithium cobalt oxide particles were changed from hydrophobic to hydrophilic as for the binder removed from the surface at 773 K.
Referring to results that more than 97 % lithium cobalt oxide can be recovered from the mixture of 70 wt% lithium cobalt oxide and 30 wt% graphite, prior to the flotation test.
Considering the results, 92 % lithium cobalt oxide can be recovered from electrode materials, whereas the purity is higher than 93 % while the optimum conditions where : 0.2 kg / t kerosene, 0.14 kg / t MIBC and 10 % pulp density.

抄録全体を表示

This paper describes the upgrading of low rank coal by hot water drying (HWD), flotation, oil agglomeration and chemical coal cleaning. The coals used were Asam-Asam coal (3.4 db% ash, 73.7 dafb% C) and Beluga coal (8.0 db% ash, 71.5 dafb% C).
The HWD treatment was carried out at different temperatures such as 270, 300 and 330 °C. With increasing temperature water content and carboxyl content of the both coals were decreased and their floatability became higher. From the results of float-sink test for Beluga raw coal, it was estimated that a coal concentrate with 4 % ash and 92 % yield is effectively obtained by heavy medium separation for middle size coals(- 1,000 + 425μm) at a specific gravity of 1.45. Combustible matter recovery of the both HWD treated coals by flotation was 20-30 % higher than that of the both raw coals and the ash content of the froth product was lower for the treated coals than the raw coals. By 3 stage flotation of the fine HWD treated Beluga coal(53μm of average size), a clean coal product was obtained with less than 5 % ash and 76 % recovery of combustible matter.
Products containing 4.1-4.3 % ash were also recovered by oil agglomeration of the fine HWD treated Beluga coals (9 and 3μm of average sizes). This result is similar to that obtained by 3 stage flotation of 53μm average size coal and it indicated that removal of about 4 % ash is impossible by physical separation method alone. Chemical coal cleaning method of the HWD treated coals with aqueous caustic process leads to a drastic decrease in ash content with a high recovery of combustible matter than that of raw coal. The ultra clean coal with 0.5 % ash and 86 % recovery of combustible matter was produced by a combination of three treatments such as the HWD, 3-stage flotation and chemical cleaning.

抄録全体を表示