In order to better understand the mechanics of fracture propagation in rock, we have developed an analysis program based on the concept of the DEM (Distinct Element Method) and simulated a uniaxial compression test. Even at present, it is still difficult to measure all AE (Acoustic Emission) events generated during an experiment due to the limit of recording speed of a measuring device, and the influence of the noise. On the other hand, the DEM can simulate realistic, appropriate rock fracturing process, and makes it possible to consider generation of all microcracks including those difficulties in an AE measurement. Our simulation results are well in agreement with the fracturing process deduced from AE measurements in the previous laboratory experiments conducted by the other researchers. Moreover, they provide the new findings to solve the disagreement; the conventional theories and microscopic observations suggest that tensile cracks cause AE events, whereas an abundance of shear type AE events are observed in the experiments. Our simulation results indicate that the energy released from a tensile crack is very small compared with that from a shear crack, due to the tensile strength much smaller than compressive strength. Since it is thought that such a small AE is easily buried in a noise and hard to be measured in an experiment, shear AE would be observed dominantly in an actual AE monitoring experiment. These results, including the new finding to solve the conflict, indicate that DEM is an effective numerical analysis technique for studying the dynamics of microcracking in brittle materials like rock.
Loading-rate dependency of rocks in the post-failure region has been investigated by many researchers, but knowledge obtained in the previous studies is insufficient compared to that for the peak strength. In this study, loading-rate dependency of stress-strain curve at very low stress level in the post-failure region was investigated with three testing methods. A testing method, in which a single rock sample is loaded at alternating loading-rate, was applied to andesite and granite. Loading-rate dependency of stress-strain curve was clearly observed up to the very low stress level in the post-failure region, where failure progressed considerably. Next, unloading-reloading cycles were repeated in constant loading-rate test with these two rocks, and unloading curves at many points along stress-strain curve were obtained. Stress-strain curve at slow loading-rate obtained in alternating loading-rate test was shifted along the unloading curves, and then it overlapped on stress-strain curve at fast loading-rate. And percentage of change of stress in post-failure region was almost equal to that of the peak strength. A new testing method, in which alternating two loading-rates and unloading-reloading cycles were repeated with a single rock sample, was proposed and applied to andesite, granite and tuff. It was found that a new testing method is easy to conduct and suitable for practical use.
Dissolution rates of three basaltic rock samples from Japan (Fuji (sample1) and Hachijyojima (sample 2) fresh basaltic rocks, and Kitamatsuura (sample 3) altered basaltic rock) were experimentally determined in a pH range from 3 to 11 at 25°C. Initial dissolution rate constants are high (-9.9 ∼ -10.4 in logarithmic unit) . It is inferred that the initial dissolution rate is controlled by proton-cation (alkali, alkali earth and aluminium) ion exchange reaction and breakdown of Si-O bond in silicate. Long-term dissolution rate constants for Si determined are -11.5 ∼ -11.8 (in logarithmic unit) (sample1) and -11.3 ∼ -11.8 (sample 2) . These values are lower than those for artificial basalt glass previously obtained. The rate constant determined for sample 3 is consistent with those of feldspar previously studied. In future based on the present results on the dissolution rate of basaltic rocks, we will perform calculation on the temporal changes of the amount of carbonates precipitating from groundwater reacting with basaltic host rocks in order to estimate the amount of CO2 fixed by mineral trapping for underground CO2 sequestration in basaltic rock area in Japan.
The chemical leaching of chalcopyrite was carried out to investigate the effects of temperature, ferrous ions and pH values on the leaching rate. The copper extraction of chalcopyrite attained 94% after 11 days when the initial pH value was 0.7 and the extraction temperature was 60 centigrade, while it was under 5% at pH 2.0. If the temperature was over 40 centigrade containing sufficient sulfuric acid, the passivation was not taken place which indicates increasing in the reaction temperature is one of the efficient ways to prevent from passivation occurrence. When the ferrous ions with the amount of 1.8 g/l was added (as initial) , the copper extraction was 93% after 5days at pH 0.7 and 60 centigrade. The extraction rate was faster by 2.6 times than the case of the extraction without ferrous ions. This is considered that high concentration of ferric ions oxidized from ferrous ions by dissolved oxygen worked as an oxidant for concentrate leaching. However, the high concentration of ferric ions seems to be an inhibitor for chalcopyrite chemical leaching when both initial pH and the temperature are low. When the pH value was controlled constantly, the higher dissolution rate was obtained at the lower pH range at over 40 centigrade. This shows sulfuric acid concentration plays a significant role in the chemical leaching of chalcopyrite. Moreover, when the temperature is less than 30 centigrade, passivation was taken place at pH controlled below 1.0; passivation occurs easier in the higher range of initial sulfuric acid concentration. Concerning passivation, some more research is necessary. We also examined leaching behavior of several kinds of chalcopyrite concentrates. The IOCG chalcopyrite leaching behavior seems to be similar with our leaching results mentioned right above but we found that there was a difference like leaching rate .This is considered that iron minerals were contained as impure compounds in respective chalcopyrite samples.
In the copper smelting industries, it is important to increase the capacity of existing smelters in order to meet the increase in worldwide demand and to achieve cost cutting. With regard to flash smelting furnaces, an increase in the concentrate smelting capacity is required to achieve capacity expansion. It is necessary to examine the performance of the existing concentrate burners when the feed rate is increased. The authors have developed a mathematical model to describe the combustion phenomena observed in a flash smelting furnace. The fluid flow, heat and mass transfer, and chemical reactions of the copper concentrate were incorporated in this model. The copper concentrate was considered to mainly comprise chalcopyrite (CuFeS2) . The reaction of CuFeS2 was assumed to consist of two steps, namely, the decomposition of CuFeS2 and the oxidation of the resulting sulfur (S) and pyrrhotite (FeS) . The combustion phenomena observed in the furnace when the feed rate was increased and when accretion was formed on the burner tip were predicted using this model. It was found that the existing burner was capable of enhancing the smelting capacity. This has been attributed to the wide dispersion of the concentrate particles and its long residence time in the reaction shaft. However, the reaction in the reaction shaft became nonuniform with the increase in the feed rate. In order to improve the uniformity of the reaction, an increase in industrial oxygen supplied through the oxy-fuel burner and an increase in the diameter of the dispersing cone proved useful.
In a copper flash smelting furnace, collision of concentrate particles plays an important role in producing the desired slag and matte. Moreover, the collision of the particles and the resulting growth in the particle diameter are also very important in order to avoid the generation of a large amount of dust. The authors have developed a mathematical model incorporated the fluid flow, heat and mass transfer, chemical reactions, and collisions of the concentrate particles. Both the gas flow and particle motion were calculated using the Eulerian method. The copper concentrate was assumed to consist mainly of chalcopyrite (CuFeS2) . The concentrate reactions considered were the decomposition of CuFeS2 and the oxidation of the resulting sulfur (S) and pyrrhotite (FeS) thereby producing magnetite (Fe3O4) and sulfur dioxide (SO2) . Moreover, the oxidation-reduction reaction when concentrate particles collided was also considered. The particle collisions were assumed to occur according to a collision probability rule obtained by the model calculations. The growth in the particle diameter was described as a change in the volume fractions of the particle phases. When applied to a commercial flash smelting furnace, this model reproduced the particle diameter growth and the component transfer as observed in a pilot plant furnace.