In the long term, worldwide consumption of nonferrous metals is steadily rising as a result of improvements in economic growth accompanied by an increasing population. In particular, consumption in Asia is following a trend of rapid growth which is expected to far exceed the world average. Under the current state of overseas ore dependence in Japan, to secure the stable supply of mineral resources is one of the key issues facing the Japanese nonferrous metals industry. We are encouraging those responsible in the Japanese mining industry to positively conduct overseas exploration activities, in order to locate promising deposits, strengthen international competitiveness and expand their contribution to the international mining sector.

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It is the purpose of this study to clarify long-term stability of a circular roadway subjected to inner pressure σr (ri)together with rock pressure σr (r0). Circumferential stress at the wall σθ(ri ) obtained by the elastic analysis is equal to {2σr(r0) -σr (ri)}. Therefore, it is natural to consider that tensile failure possibly develops into the surrounding rock starting at the wall if σr (ri ) is larger than 2σr(r0). A question arises whether it can be properly applied to a circular roadway where large visco-elastic deformation is expected.A non-linear rheological model proposed by this authors was used to simulate time-dependent behaviour of rock around a circular roadway. It was assumed that inner pressure gradually increases. Results of computer simulation indicate that, at first, the failed region develops and the roadway converges. As time goes by, inner pressure gradually increases, then convergence ceases and finally the roadway diameter starts to increase. We obtained interesting results as follows；1. Even if σr(ri) is larger than 2σr (r0), σθ(ri) is still remained in compression provided that Poisson's ratio increases with failure of rock.2. Post-failure characteristics of rock, that is, slope of descending portion of stress-strain curve in the post-failure region is not so important.3. Time-dependency of rock is very important, and affects long-term stability of a circular roadway. Right now, we have only limited information concerning time-dependent behaviour of rock. It is especially important to obtain accurate knowledge concerning Poisson's ratio and behaviour of rock in tension.

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Rapid solid/liquid separation from dilute colloidal dispersions is one of the most difficult techniques and effective method has yet to be established so far. But by using the electro-interfacial properties of colloidal particles, effective fine particle removal from dilute suspensions was made possible in a simple way. In this experiment, rapid separation of ultra fine silica particles (mean diameter of 200 nm) crystallized from geothermal water were investigated by using a column bed method packed with ferro-nickel fibrous slag wool, which was made as waste material from Fe-Ni electrosmelting process. Collection efficiency of silica particles was highly dependent on chemical characteristics of suspension, that is, pH and ionic strength：better separation was attained in more acidic condition and higher KNO3 electrolyte concentration. These experimental results were generally in agreement with the heterocoagulation theory. It could be concluded that surface interactions between particle and collector virtually determined the total removal capacity of collector bed.

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The rapid separation of fine silica particles (mean diameter of 200 nm) deposited from geothermal water were investigated by using a column bed packed with ferro-nickel slag wool. If repulsive double-layer interaction prevented particle adhesion on collector wool surface, collection efficiency greatly improved by modifying the slag wool surface with ferric hydroxide, aluminium hydroxide or aluminium silicate. In the experimental results, silica collection in 1 mM KNO3 electrolyte at pH 5 reached 17 % at dimensionless time 2 by Fe-Ni slag wool collector. On the other hand, silica recovery prominently increased up to 80 % by ferric hydroxide modification wool, 100 % by aluminum hydroxide modification wool and 85 % by aluminum silicate modification wool. These results were interpreted by the heterocoagulation theory, estimating surface interaction energy between silica particle and collector surface.

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Hydrochloric acid leaching of Co, Ni, Cu, Mn and Fe from the cobalt-rich ferromanganese crust under reducing conditions was performed using hydrogen peroxide and sodium sulfite as reducing agents. Hydrochloric acid concentration more than 3.0 mol/dm3 is required to obtain the high extraction of Co and Ni without reducing agents at ambient temperature. The high extraction of Cu in dilute hydrochloric acid solution without reducing agents at ammbient temperature explains the different form of Cu from other metals present in cobalt-rich ferromanganese crusts. When hydrogen peroxide or sodium sulfite was used as reducing agent, the high extraction of Co and Ni was obtained with dilute hydrochloric acid at ambient temperature. In particular, hydrogen peroxide extracts metals in stoichiometric amounts. The extraction of Ni depends significantly on the leaching temperature, regardless of the presence or absence of reducing agents.

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A pyrolysis-based technology was applied to recover high purity silica filler from epoxy resin compounds (molding resins) for electronic components, and to reuse it as a filler in the present paper. Molding resins mainly contain epoxy resin, harder, silica filler (70-85 wt %) and flame retardant consisting of brominated epoxy resin and antimony trioxide. Most effective conditions to reduce impurities in the recovered silica were found as heat around 1,000-1,100 °C and to keep oxygen concentration 5-10 vol. %. On the basis of these results, we have developed a practical process for recovering silica filler from molding resins using a roller kiln-type furnace. The recovered silica achieved a purity of C < 0.01 wt %, Sb < 0.4 wt %, and PO43- < 0.002 wt %. A jet-mil treatment was effective to grind the aggregates of recovered silica powder and to increase the reactivity of its surfaces. The recovered silica treated with the jet-mill showed good properties as a filler for a cast insulating epoxy resin compound. A secondary combustion method was successfully applied to the decomposition of the combustion gas. The treatment of the gas by heating at 1,100 °C decreased the toxic organic bromine compounds to a safe level and converted the antimony tribromide to diantimony trioxide, which could be collected by a dry recovery process at high recovery rate.

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The purification of raw iron oxide obtained from iron precipitation of the zinc leach residue using the recrystallization method with Na2B4O7 flux and their magnetic properties has been investigated. The main purpose of present study are to examine the effect of the prior water washing and decrease of amounts of Na2B4O7 flux on the purification of raw material. As a result, it was recognized that the prior water washing of raw material are undesirable, because of decrease of desulfurization in the purification by the sub-sequent recrystallization method,and the elimination of Zn, S and As in raw material is the best, when raw material/flux ratio is 70/30 and the prior water washing is not carried out. The magnetic properties is similar to that of α-Fe2O3 single crystal. The synthesis and magnetic properties of Mn-Zn ferrite from purified iron oxide were also examined.

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The solubility of oxygen in solid and liquid neodymium, were measured by the solid state electrotransport and metal-oxide equilibrium methods, are determined as follows: Solubility in solid neodymium; log (CO /mass %) Nd (α) = -1760 (± 20)T-1/ K-1) + 0.65 (± 0.02) (1,023 ∼ 1,123 K) log (CO /mass %) Nd (β) = -1850 (± 30)T-1/ K-1) + 0.70 (± 0.03) (1,173 ∼ 1,248 K) Solubility in liquid neodymium; log (CO/mass %) Nd (l) = -5580 (± 30)T-1/ K-1) + 3.30 (± 0.04) (1,373 ∼ 1,773 K) NdO was identified by the X-ray diffraction analysis as the oxide phase in equilibrium with neodymium from 1,023 to 1,248 K and Nd2O3 was identified as the oxide phase in equilibrium with neodymium from 1,373 to 1,773 K.

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Solid state electrotransport of oxygen in neodymium was studied. The effective valence Z* and the non-dimensional number δ (= uEL/D；u：mobility, E：electric field intensity, L：length of specimen, D：diffu-sion coefficient) of oxygen were measured by the tangent method under the following conditions；electric field intensity = 1.9∼2.5 Vm-1, temperature = 973∼1,223 K, initial oxygen content = 0.01∼0.11 mass %. The results can be summarized as follows： (i) The absolute values of the effective valence and δ of oxygen decrease with increasing either electric field intensity or temperature. (ii) The diffusion coefficient of oxygen in neodymium was determined as follows：DO /m2 s-1 = 0.26 exp (-196000/RT) (Nd(α)：973 ∼ 1,073 K)DO /m2 s-1 = 1.6 × 10-2 exp (-180000/RT) (Nd(β)：1,173 ∼ 1,223 K) (iii)Mobility of oxygen in neodymium increased with increasing temperature.

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It is well known that magnesium is capable of absorbing hydrogen and forming its hydride. The Mg-13 mol % Al alloy was picked up to produce a joining materials with a self-decomposition property as a new concept for metal recycling from the view points of the light metal and the low melting point. The hydrogen embrittlement behavior of this alloy was examined by using the cathodic electrolysis. The relation between the embrittlement behavior and the hydriding was investigated. The electrolysis was conducted in neutral, pH 6.0, or alkaline, pH 13.7, aqueous solution from 298 K to 353 K for 172.8 ks at potentials from the rest potential to -3.0 V (vs. Ag/AgCl sat. KCl). The following results were obtained: (i) At the lower potential in both solutions, the more Mg hydride was formed on the surface of the specimen. (ii) Many craters burst by the absorbed hydrogen were detected on the surface at the lower potentials because blisters of gaseous hydrogen were formed there. (iii) The additions of thiourea or gelatin to the neutral solution and of copper to the Mg-Al alloy accelerated the hydrogen embrittlement.

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