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To investigate the effect of current density and pH in solution on the lightness and surface morphology of deposited Ni, Ni electrodeposition was performed at current density 100 to 500 A･m -2 and the amount of charge 7.2×10 5 C･m -2 in unagitated chloride solution of pH 1 to 3 at 333 K. The composition and structure of the surface of the deposits were analyzed by radio frequency glow discharge optical emission spectroscopy and three dimensional SEM. The lightness of deposited Ni decreased with increasing pH, and became to be minimum at 300 A･m -2 . The concentration of the surface oxide of deposits increased with pH, and became high at 300 A･m -2 , which shows that the surface oxide of the deposits causes the decrease in the lightness. On the other hand, the surface of the deposited Ni was composed of both the pyramid microcrystals of several micrometers and the hill formed by the aggregations of pyramid microcrystals. To separate the two structural units of the pyramid microcrystals and the hill, the deposits were cut every 200 nm from the top to the thickness direction in three dimensional SEM, and the number and area of deposits in the cutting plane were measured, as a result, it was found that the lightness of the deposited Ni depended on the surface structure. The lightness of deposited Ni seems to depend on both the surface oxide and the microstructure of deposits.

The roles of As 2 O 3 and Cu 2' in the cementation of Co by Zn dust were studied in synthetic Zn leach solutions by polarization measurements, scanning micro-electrode technique, ESCA and EPMA analyses. It was confirmed that Co had an inherent property of not beginning to deposit at its equilibrium potential and that the potential at which Co began to deposit was polarized in Zn sulfate solution almost to reach the equilibrium potential of Zn. These properties peculiar to Co were directly responsible for the extremely small removal rate of Co in the cementation using Zn dust alone. The partial polarization curves of Co were significantly shifted to more noble direction in the presence of As 2 O 3 and Cu 2' in Zn sulfate solution, indicating that these additives acted as a catalyst which promoted the kinetically suppressed deposition rate of Co in the presence of large amounts of Zn 2' . Considering the fact that Cu, which began to electrodeposit at its equilibrium potential, was reduced to metallic state by Zn dust immediately, the deposited Cu on the initial Zn dust surface would offer active cathode area on which Co can deposit easily. On the other hand, As 2 O 3 was also reduced by Zn dust in preference to Co and deposited in the forms of metal and oxide. The metallic As acted as an inhibitor for hydrogen evolution on the deposited Co, while As oxide worked as a catalyst to reduce the inherent deposition overpotential of Co and promoted the cementation rate of Co.

The copper refinery process produces Se(VI)-bearing wastewater with a high content of Cl ¹ and SO 4 2¹ ions. To overcome the negative effect caused by Cl ¹ and SO 4 2¹ ions on Se(VI) reduction and its following removal, this study investigated the possible synergistic effect of the combination of Se(VI)-reducing bacterium, Thaurea (T.) selenatis and zero-valent iron (ZVI). In the presence of SO 4 2¹ (200 mM) and Cl ¹ (300 mM), the following was observed: (i) ZVI alone was unable to remove Se both under strictly aerobic and micro-aerobic conditions.(ii) Se(VI) reduction by T. selenatis alone was severely inhibited under anaerobic conditions (and thus no microbial growth was observed).(iii) On the other hand, T. selenatis was capable of growth and Se(VI) reduction under micro-aerobic conditions. (iv) Combining T. selenatis and ZVI under micro-aerobic conditions showed a synergistic effect on Se(VI) reduction, readily facilitating Se removal. This synergistic effect was optimized by adjusting the pH to near neutral (optimal for T. selenatis growth), but by adjusting the temperature to 35°C (sub-optimal for T. selenatis growth): Se removal of 55% by T. selenatis alone, was significantly improved to 98% by combining T. selenatis and ZVI. The proposed key process to display the synergistic effect on Se removal under micro-aerobic conditions is as follows: (i) Using the remaining dissolved O 2 (DO) during the first hours, T. selenatis can overcome the inhibitory effect of Cl ¹ and SO 4 2¹ by growing with more energy-gaining aerobic respiration, (ii) ZVI indirectly serves as a reducing agent to maintain low DO levels, consequently readily switching from aerobic to anaerobic Se(VI) respiration by T. selenatis. (iii) ZVI may also be acting directly for Se deposition by reducing microbially-produced intermediate Se(IV), which is more reactive than original Se(VI). The present findings could be used as a basis for developing an economically feasible and environmentally harmless bio-treatment technology for Se(VI) containing copper refinery wastewaters.