For thermodynamically understanding copper or nickel smelting processes using oxygen or oxygen-enriched air as a blowing gas, a series of the authors' experimental studies of the phase equilibrium and distribution of minor elements between the copper matte or the nickel matte and the FeOX-SiO2 base slag under the SO2 partial pressures of 0.1, 0.5 and 1 atm at 1,300 °C are reviewed in this paper. The solubility of copper was found to be independent of pSO2 when the matte grade was specified and it was considered that this behavior was ascribable to the constancy of (pO2 /pS2 ) against pSO2 . On the other hand, it was clarified that the solubility of nickel in the slag increased with increasing pSO2 at a given matte grade. The difference in the dissolution behavior between copper and nickel was considered to be ascribable to the difference in the chemical formulas of the mono-metallic sulfides in which one copper atom combines with 1/2 sulfur atom while one nickel atom with 2/3 sulfur atom. When the distribution ratio of a minor element, X, between the slag and matte phases was defined as LXs/m = (mass % X in slag)/{mass % X in matte}, LXs/m for arsenic, antimony and bismuth at a given matte grade increased with increasing pSO2. This behavior was explained reasonabley by assuming a mutual reaction between a metallic species in the matte and an oxidic species in the slag. On the other hand, the distribution ratio of silver at a given matte grade was almost constant against pSO2. This was considered to be ascribed to the sulfidic species of AgS0.5 prevailing in the matte phase as well as the constancy of (pO2 /pS2 ) against pSO2.

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At first, study on loading-rate dependency of strength was briefly summarized. It is well known that uniaxial (unconfined) compression strength increases with loading rate. Though only limited data are available, some authors reported that confined strength increases with loading rate. Also, tensile strength obtained by uniaxial tension, indirect tension and bending tests increases with loading rate. Based on the summarized experimental results, a failure criterion in which loading-rate dependency of strength is considered was proposed；high criterion for high loading rate and low criterion for low loading rate. As an extreme case, long-term strength or failure criterion at extremely low loading rate can be obtained. The simplest form of the long-term strength is σ1 = a·σ3 where σ1, σ3 are major and minor principal stresses, and constant `a' varies from 2 to 6 depending on rock. For validation of the proposed failure criterion, rock stresses were plotted on σ1 vs. σ3 diagram. It was found that all data except one were plotted under the line σ1 = 4σ3. It is reasonable to consider that, in relatively stable rock mass, rock stress is maintained at a certain value or condition lower than a long-term strength. If so, this result supports the validity of the proposed failure criterion.

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This paper describes the simulation model of in-situ cuttings concentration change due to lost circulation in horizontal and inclined drilling. The mixture flow of cuttings and mud fluid is regarded as the solid-liquid two-phase flow in the annulus and the numerical simulation model is developed based on the equation of motion of cuttings. The numerical simulation of in-situ cuttings concentration change due to lost circulation was carried out, and the simulated results were compared with the previous research related to the cuttings velocity change due to lost circulation. As simulated results agreed with the experimental results in the previous research, it was confirmed that the model developed here is reasonable. Therefore, by using this model, numerical simulation was carried out again under several conditions. From the simulated results, it was found that the effect of lost circulation on the change of in-situ cuttings concentration and height of moving bed becomes significant according to the decrease of the inclination angle of the drilling well.

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The adsorption of dialkyl di- and mono-thiophosphinates on gold, silver and gold-silver alloys has been studied in the present work. These reagents, which are selective collectors for sulfide flotation, are known to improve noble metals recovery from ores. Voltammetric studies have indicated that dithiophosphinate adsorbs on gold at much higher potentials than on silver, while monothiophosphinate adsorbs only on silver. However, both adsorb on gold-silver alloys with the adsorption potential decreasing with increasing silver content. Using FTIR spectroscopic measurements, the surface species formed during the interactions of these collectors have been identified. The results of the electrochemical and spectroscopic measurements have been compared with the contact angle data obtained at controlled potential conditions.

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Natural organic acids, such as tannic acids (TA), wood vinegar (WV), fulvic acids (FA), and humic acids (HA), were investigated as suppressants of microbially mediated dissolution of pyrite with Thiobacillus ferrooxidans and Thiobacillus thiooxidans in acidic media at pH 2∼4, and the suppression mechanism is discussed. The suppression occurs by adsorption of natural organic acids on pyrite, inhibition of cell growth, as well as reduction and complexation of Fe(？) ions. Most of these factors are affected by pH：the suppression by FA was stronger at pH 2 than at pH 3∼4, because the affinity between pyrite and the aromatic groups in FA is stronger below the isoelectric point (iep) of pyrite (around pH 2.5). Cell growth was more strongly inhibited by natural organic acids at lower pH. The order of suppression was WV > TA >> FA > HA at all pHs here, and dependent on the number of functional groups, such as phenolic and carboxylic groups in the natural organic acids. The pKa of WV was ∼5.0, and the acid-base titration and elemental analysis suggested that WV contains acetic acid and large amounts of other organic acids. Wood vinegar was found to suppress and retard pyrite dissolution over a wide pH.

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A major problem with water-based cutting fluids is bacterial propagation that can quickly ruin the fluid's effectiveness and cause rancid smell. Effects of copper triethanolamine (Cu-TEA) and copper ethylenediaminetetraacetic acid, disodium (Cu-EDTA) on the colony forming activity of sulfate-reducing bacteria (SRB) have been investigated. The copper complexes were prepared by direct addition of TEA or EDTA to the copper sulfate solution, or by electrolysis with copper electrode in complexing agent solutions. In the copper complexes, the mole ratio of copper ions to TEA or EDTA was 1：1, respectively. The growth of SRB was affected by the addition of Cu-TEA or Cu-EDTA and inhibited strongly at 0.1 mmol dm-3 copper concentration. From the data available, no obvious difference was observed between the copper complexes regarding the colony formation of SRB.

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To obtain basic knowledge on supercritical water chemical recycling of polyethylene, engineering parameters such as reaction temperature, reaction time and reaction pressure were studied to determine how they affect the conversion of polyethylene into oil in a supercritical state. Targeting on this, the study also focussed on discriminating the recovered oil (non-volatile) from the cracked oil (volatile and non-volatile) and the reaction mechanisms. The base conditions were a reaction temperature of 425 °C, reaction time of 120 min, water fill rate of 30 % and a water/PE ratio of 5 : 1. At reaction temperatures of 415 °C and 425 °C, the non-volatile oil rate was about 90.2 wt %. Above 425 °C the rate lowered and the rate of volatile components increased. At up to 425 °C, the major components were l-alkenes and n-alkanes, and, at higher temperatures, the l-alkenes decreased. Above 435 °C, aromatic hydrocarbons were produced. With a longer reaction time of 180 min, the recovered oil rate decreased, resulting in a non-volatile oil rate of 77.7 wt % and volatile oil rate of 8.1 wt %. With an increase in the water fill rate, the non-volatile oil rate rose and was 90.2 wt % at a rate of 30 %. As the water fill rate was increased, the products in the aqueous phase after the reaction increased, with 2-propanol, 2-butanol and 2-propanone as the major components. Also, as the rate increased, the compositions of the recovered oil and gas resulted in a decrease in l-alkenes with n-alkanes as the major component following the increase in hydrogen production. This implies that the increase in the water fill rate, as a reaction mechanism, strengthens the ionic character of water. There is a consequent increase in water-soluble substances such as 2-propanol, which when further oxidized to 2-propanone, liberates hydrogen, and this hydrogen participates in the cracking of hydrocarbons.

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The distributions of trivalent rare-earth elements such as lanthanum, cerium, praseodymium, neodymium. samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium between hydrochloric acid solutions and solutions of di-(2-ethylhexyl)-phosphoric acid (DEHPA) + pyridine (py) or its derivatives in kerosene have been examined under different conditions. Infrared and nuclear magnetic resonance spectra were made for the organic extracts. As a result, the addition of pyridine or its derivatives gave the synergistic effect on the extraction of rare-earth elements from hydrochloric acid solutions by DEHPA. In those extraction systems, however, the variation of the distribution coefficients for rare-earth elements plotted as a fuction of their elements in the atomic numbers revealed the curve in tetrad effect similar to the extraction by DEHPA alone. It was found that the seperation factors of adjacent elements resemble each other.

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In order to develop the analysis of various pyro-metallurgical processes, thermodynamic properties related to CaO, the most important component of slag or flux, at 1,773 K were determined by conducting the following experiments： (1) Equilibration of molten copper with solid SiO2 under controlled oxygen partial pressure. (2) Equilibration of molten copper with the CaO-SiO2-CaS slag saturated with CaS in a CaS crucible. From the results of the experiment (1), the Raoultian activity coefficient of silicon at infinite dilution in molten copper at 1,773 K, was determined as： log = -1.45 (±0.03). Based on the results of experiment (2) and the previously determined value of , the activities of SiO2 and CaO in the CaO-SiO2-CaS slag saturated with CaS at 1,773 K were calculated by application of the Gibbs-Duhem integration techniques. And then, the standard free energy of formation of CaO at 1,773 K were determined to be： Ca(g) + 1/？ O2(g) = CaO(s)：ΔG / ？J·mol-1 = -430 (±10).

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As a fundamental study to control compositions of the slag in the oxidation zone of a QSL lead smelting furnace, phase equilibrium between the metallic lead and the PbO-FeOx-CaO-SiO2 or PbO-FeOx-CaO-SiO2-ZnO slag was investigated at 1,323∼1,523 K and a composition region of the homogeneous liquid slag phase and the composition and chemical formula of solid phases in the slag coexisting with the liquid phase were determined. The PbO-FeOx-CaO-SiO2 slag with Q (= mass % CaO/(mass % CaO + mass %SiO2)) of 0.4 is completely fusible at 1,423 K when the mole fraction ratio of FeOx , R, defined as R = NFeOx /(NFeOx NCaO + NSiO2 ), is around 0.4, and departure from this value gives rise to a solid-liquid two phase region in the range of the low PbO content. This result indicates that the QSL process, which is operated practically with R of about 0.4, is quite reasonable. Solubility of ZnO in the PbO-FeOx-CaO-SiO2-ZnO slag with Q = 0.4 and R = 0.4 at 1,423 K decreases with increasing PbO content in the composition range between 0 and 18 mol % PbO, then increases in the range between 18 and 33 mol % PbO, and finally becomes stagnant at about 18 mol % ZnO in the composition range above 33 mol % PbO. This result has an important meaning for the QSL operation using a charge with a high content of zinc. Hence, it is considered that precautious control of the PbO content in the slag is required for avoiding formation of a solid phase in the slag.

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