Tracer tests are often performed to obtain hydraulic parameters and to model geothermal reservoir systems. The Advection-Dispersion Equation (ADE) based on Fick's law has generally been used to describe the mass transport in the underground. However, this conventional model cannot describe mass transport correctly in the highly complex media such as fractured reservoirs. In this study, the fractional Advection-Dispersion Equation (fADE) has been utilized to calibrate tracer curves instead of the classical ADE. We investigate the relationship between flow parameters involved in the fADE and fractal dimension to explore the feasibility of predicting fractal dimensions of fractured rock masses based on the fADE. We simulate tracer transports employing fracture network models where the fractal dimensions are in the range of 2.0-3.0. It is shown that the fADE parameters correspond closely to the characteristic properties of the fracture networks. This indicates the fADE model based on fractal geometry is capable of capturing key aspects of flow and transport in fractured reservoirs and of predicting fractal dimensions of fractured rock masses by tracer tests.

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To improve the performance and efficiency of rock drills, it is essential to understand the penetration behavior of a bit into rock. However, studies on the impact penetration with a button bit, which is commonly used for percussive drilling of hard rock recently, are insufficient. In previous studies, large fluctuations were observed in a force-penetration curve calculated from rod stresses measured during percussive drilling, and therefore precious force-penetration curves could not be obtained. In this study, a calculation method was examined to preciously obtain a force-penetration curve from impact penetration tests. The results of numerical simulation showed that the fluctuations can be caused by the mismatch between the product and calculation model, and that the precious forcepenetration curve may be obtained with subtracting the bit force in a free end test from that in an impact penetration test. The suggested method was applied to the measured results of impact penetration tests with granite conducted by Fukui et al. (2010), and improved force-penetration curves were obtained. The method proposed in this study can be adopted to in-situ rock drilling, and contribute to the development of the bit suited to each rock type.

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The practical application of the rock cavern storage of liquefied fuels (such as natural gas, liquid hydrogen or dimethyl ether) requires stability analysis of the cavern in question with regard to thermal stress; and an understanding of strength parameters (cohesion and angle of internal friction) of rock mass is essential for such analysis. In our research, we conducted an oblique shear test to dice for determining the strength parameters with sandstone from room temperature down to ultralow temperatures. Next, we attempted a method for estimating the strength parameters from the results of uniaxial compression and indirect tensile tests, and compared the estimated strength parameters with the measurement values. Here are our findings below. Rupture envelope of Kimachi sandstone agreed with Coulomb's failure criterion independent of water content and specimen temperature. Cooling barely changes the cohesion and angle of internal friction of the dry sandstone. On the other hand, the cohesion of saturated sandstone increases from room temperature down to －170℃ broadly in a linear manner. The angle of internal friction shows interesting behavior of increasing after having decreased from room temperature to －50℃ one time. The estimated strength parameters using general Mohr's failure criterion curves are not consistent with the shear test results. This means that it is difficult to estimate the strength parameters of the saturated sandstone by results of uniaxial compression and indirect tensile tests in an environment with low temperatures. However, we can almost estimate the strength parameters of the saturated sandstone in temperatures down to －100℃ by using a compound envelope curve proposed in this paper.

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A copper ore containing mixture of tetrahedrite (Cu₁₂Sb₄S₁₃) and tennantite (Cu₁₂As₄S₁₃) as main copper bearing minerals were used in the current study to investigate antimony (Sb) and arsenic (As) leaching into the NaHS–NaOH solution and precipitation behaviors of these metals from the solution. In leaching test, effect of temperature, NaHS concentration, pulp density and leaching time were investigated to evaluate leaching of Sb and As impurities into the solution and recovering a clean Cu ore containing Sb and As less than 0.5 mass%. At leaching tests, temperatures ranging from 90–95ºC and NaHS concentration from 600 g/L (10.8 M), both Sb and As contents in the solid were reduced to <0.5 mass%. A two-step alkaline leaching tests were performed at high pulp density up to 1,000 g/L and high dissolution result in the solution was obtained for both Sb and As leaching, respectively. In the precipitation, elemental sulfur with S/(As+Sb) mass ratio of 0.25 was added to leachate contains high amount of As and Sb and kept the temperature at 90ºC for 1-2 hours. The solution prepared cooled quickly up to 30ºC with moderate stirring and maintained the condition for 3-5 hours. As a result, over 90 % of Sb and As were recovered from the leachate, respectively. The recirculation of process filtrates for re-use in tennantite/tetrahedrite leaching continued to give reproducible leaching results.

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