Carbon containing refractories such as MgO-C and Al₂O₃-C have progressed remarkably as the lining refractories for steelmaking furnace owing to good resistance to slag corrosion and thermal shock. The refractories are constructed from oxide, graphite and antioxidant which are bonded by binder such as phenolic resin. The present paper is concerned with a role of and interaction among each component and change of microstructure in the refractories during heating. Antioxidant such as metal, alloy, carbide, etc. contributes to not only suppression of oxidation but self-repair of the refractories.

View full abstract

To estimate the methane gas emission from the mining panel during coal minimg operation, we proposed a numerical model. The values of methane gas content of coal which were measured by the special device were used in the finite difference calculations. From the comparison of estimation of the methane gas emission from the mining panel by using the numerical model with the actual observed results, following things became clear.
The numerical model which was used in the calculations is suitable for estimation of methane gas emission from the mining panel of Taiheiyo Coal Mine. When the maximum value of measured methane gas content of coal is used for the initial condition in the numerical calculations, the estimated values of methane gas emission are best fitted to the actual observed results.

View full abstract

The combination of the 16-elements conical-ended borehole technique and the compact overcoring method is an excellent method to measure the three dimensional state of stress by means of stress reliving in hard rock. In the present paper, this method has been applied to the discontinuous rock and the characteristics of stress distribution on the periphery of faults have been examined by the systematic stress measurement at multipoints in a single borehole. Subsequently, it has been discussed that numerical simulation is indispensable to grasp macroscopic initial stress field.
Firstly, it has been shown that the in situ stress measurement performed at 18 adjacent points by means of the combination of the 16-elements conical-ended borehole technique and the compact overcoring method within diorite and granodiorite, and it has been discussed that the present method is promising method to measure the absolute stress. Moreover, it has been clarified that the number of measuring points can be drastically increase by this method.
Secondly, from comparison of the measured value with the results by the displacement discontinuity method (DDM) analysis, it has been clarified that the faults are the geological primary factor controlling the initial stress distribution and the cracks are the secondary cause of disturbance of the initial stress distribution.

View full abstract

This paper describes a method for estimating the directions of the elastic principal axes and the coefficients of compliance of rock which is assumed to be an orthotropic elasticity.Prior to preparation of the rock specimen, the hypothetical coordinate system (x', y', z'), of which the axes are perpendicular mutually, is supposed in the rock sample. The rock specimens are collected at every 15° from 0° to 90° with respect to the axis of the hypothetical coordinate system on three planes containing two coordinate axes. Uniaxial compression tests are done on the specimens, and the coefficients of compliance on each specimen are obtained from uniaxial compressive stress-strain curves. Then, on three planes, the equations expressing the relationships between coefficients of compliance and direction of applied load with respect to the hypothetical axis are calculated by the non-linear least square method on a basis of elastic theory. From these relationships, the rotation angles of the hypothetical coordinate system with respect to the coordinate system (X, Y, Z) whose axes correspond to the elastic principal ones of the rock are calculated and the directions of the elastic principal axes are determined. Finally, using the rotation angles, the coefficients of compliance in the rock are determined.
By the procedure mentioned above, the directions of the elastic principal axes and the coefficients of compliance are estimated on granodiorite.

View full abstract

In order to investigate the deterioration mechanisms influenced by water and the physical properties of WAKANABE shale, we conducted two groups of experiments for the shale specimens. One is both AE (acoustic emission) measurements in the process of water permeation into the specimen, and in the moisture controlled circumstances. The other is mechanical experiments for the dry shale specimens including triaxial compression, fatigue and creep tests.
Results from these experiments are as follows; 1) WAKANABE shale which has dark gray stripes parallel to bedding plane, was sensitive material for the permeation of water and the change of moisture circumstances. That is, the chemical reaction of water and illite as one of the clay components of shale induced the initiation and the growth of micro cracks with AE activity. Especially, by the experiments of water permeation, it was confirmed that the AE source was migrated from the surface to the inside of the specimen with the water permeation front.
2) From the AE measurement under moisture controlled circumstances, the frequency of AE events increased drastically when the humidity changed rapidly. After that, the AE activity was depressed with the lapse of time.
3) Then, the AE sources were located along the bedding plane of the specimen, and corresponded to the macro cracks caused by tensile stress.
4) Through a series of mechanical experiments for the shale specimen, it was found that the dry specimen approximately kept the uniaxial compressive strength as much as the sandstone produced at the neighbor layer of WAKANABE shale.
5) The mechanical behaviors of the dry shale under the confining pressure, fatigue and creep tests indicated the similar tendency of the other kinds of rocks obtained by the experiments in the past.

View full abstract

Transmission and dissipation of stress wave at a percussive-drill rod-joint of the coupling sleeve type are discussed with special attention to the effects of wave length and rod diameter.
At first, a simple model proposed by Okubo et al, which consists of two rods and a spring, is analytically examined. It is found that dissipation of stress wave at a model sleeve depends on non-dimensional parameter t₁/τ: larger dissipation for smaller value of t₁/τ. t₁ and τ=Z/2k are wave length and retardation time, respectively, and Z is characteristic impedance of rod.
Experiments are carried out with five combinations of rod and sleeve ranging from 32 to 51 mm nominal diameters. Also, five kinds of hammer are used to impact rod end and generate elastic wave. The experimental results show that dissipation increases with rod diameter or Z, and decreases with hammer weight or t₁. It is found that fairly well agreement can be obtained between theoretical and experimental results.
Also, dissipation during drilling by a rock drill is measured. It is found that amplitude of elastic wave decreases by 2.9% per sleeve. This result can be also explained by the model.

View full abstract

Among the deep ocean manganese nodule mining technologies, the sea floor collector design is the most complicated and insoluble one. Manganese nodules are distributed on the surface of the vast and low strength pelagic sediments, which compose mainly of biogenic siliceous material and clay minerals. The sea floor collector will be supported by the deep ocean sediment layer and travel on it with steering to avoid obstacles. It will pick up and collect manganese nodules from the sea floor and reject undesirable materials such as sediment and oversize objects. Geotechnical properties of the deep ocean sediment layer play a very important role in the design of the sea floor collector.
Several important physical and geotechnical properties, such as water content, particle size, consistency, vane shear strength, sensitivity, uni-axial compressive strength, and tri-axial strength, of the Pacific deep ocean sediment layer were measured on board and in laboratory on land using box core samples collected from the ocean floor where the manganese nodules distribute. Then, its dynamic geotechnical properties were measured by newly proposed method in which a fallen collider was applied onto the test-specimen surface and they were compared with the static properties. It is concluded that the vane shear strength can be a representative indicator of the geotechnical properties of the deep ocean sediment layer for the collector conceptual design.

View full abstract

It is known that silver ions accelerate the dissolution of copper in the bacterial leaching of chalcopyrite. The enhancement effect of silver ions is attributed to the formation of silver sulfide on the surface of chalcopyrite. The presence of chloride ions would affect the enhancement effect of silver ions because silver ions precipitate as silver chloride with chloride ions. The purpose of this work was to study the effect of chloride ions on the bacterial leaching of flotation concentrates of chalcopyrite and sphalerite using Thiobacillus ferrooxidans with the addition of silver ions. Results obtained are summarized as follow,
(1) The addition of up to 100mg/l chloride ions enhanced the bacterial leaching of copper from a chalcopyrite flotation concentrate at the initial silver concentration of 50mg/l. The copper dissolution was accelerated with the addition of silver chloride powder.
(2) The yield of zinc from a sphalerite flotation concentrate after the bacterial leaching of 20 days decreased with increase in the initial silver concentration. The addition of silver ions hindered the oxidation of sphalerite with ferric ions. Chloride ions weakened the negative effect of silver ions on the bacterial leaching of sphalerite.

View full abstract

The authors have studied pulverization of limestone by the Tower Mill to develop more valuable uses of this resources. In the process of this study, the Tower Mill KD-3, a modified version of the Tower Mill KD-2, was used as equipment. As for the KD-2, this type is composed of three parts: comminuting, classifying and collecting part. But in the KD-3 classified coarse particles are settled in the bottom of the classifying part for another products. It is worth noticing that the air flow through the nets set improved classification of ground particles. In each experiment, to investigate the factors affecting the weight and the particles size of pulverized products, the weights of steel balls, limestone and the number of revolutions of screw were kept constant, while the grinding part and the air flow rate (U_m) in the classifying part were varied.
The results obtained are summarized as follows: 1) The fine particles classified in the classifying part flow into the cyclone smoothly with the air while the coarse particles are settled in the bottom of the classifying part for another products because of the modified structure of this classifying part and the set nets.
2) The weight of products were affected by the dead space in the comminuting part, the inlet surface area and the number of spirals in the cyclone.
3) The ratio of secondary particles influenced the weight of the-10μm particles and the 50% particles diameters in the product.
4) The maximum values of the particle diameter (D_max) in the product collected by the cyclone were found to be in accordance with the Stokes's law.
5) The decrease and uniformity of the flow rate made the D_max values smaller.
6) The minimum value of Dmax was: 8.2μm for products collected by the cyclone; 14.7μm for another products settled in the bottom of classifying part.

View full abstract

Ozone oxidation-precipitation reaction was investigated in strongly acidified solutions of MnSO₄ with/without added sulfate.
The rate of the oveall reaction was determined by chemical analysis on manganese ion species in the solution and the variation of oxidation-reduction potential (ORP) was continuously measured to follow the ozonation process in MnSO₄ solutions of initial Mn concentration of 0.10 mol/l and sulfuric acid concentration of 1.0 to 5.0mol/l over a temperature range between 25 and 80°.
The behavior of 15 elements (18 ionic species of metal ions and oxonium complex ions) added to the MnSO₄ solution (0.1mol/l in Mn and 1.0mol/l in acid) during ozone oxidation at 25 and 70° was examined by ORP measurement and chemical analysis of the precipitates.
The results are summarised as follows: 1) The rate of ozone oxidation-precipitation is strongly affected by acid concentration. An increase in acid concentration resulted in elongated induction period for the precipitation of MnO₂, the reduced overall reaction rate and also higher minimum concentration of manganese remaining in the solution.
2) A rise in reaction temperature favors the ozonation reaction. At 70°, precipitation of MnO₂ took place even at sulfuric acid concentration of 4 or 5.0mol/l.
3) Li, Na, K, Al and Mg ions added to the solutions caused only a little change in ORP during ozonation and the content of these ions of the precipitates was fairly low.
4) Co, Ni and Cu in the solution were incorporated at about 2% in the precipitate without a significant change in ORP.
5) ORP measurement showed that As (III), V (IV) and Fe (II) were oxidized prior to the oxidation of Mn (II). These ions and Ti (IV) are incorporated in the precipitates to a considerable extent of 7 to 10 wt % of the dried samples. None of the added metal ions is precipitated alone from their single acidic solution.
6) Zn and Cd were incorporated in the precipitate at about 1 wt %. More than 70% of the added mercury was eliminated with manganese from the solution of an initial mercury concentration of 0.001mol/l.

View full abstract