Bath composition and operating conditions were compared between the electrowinning in hydrometallurgical production of Zn and the electroplating of single Zn and Zn alloys with iron-group metals in the production of corrosion resistant steel sheets. Both electrochemical processes were equivalent in a sense that Zn deposition proceeded on the metal cathode using insoluble anode from the sulfate baths where Zn existed in its simplest form of hydrated ion although the acidity of the bath was greatly different from each other. The electrochemical meaning of the critical current density, at which Zn began to deposit, was clarified first on the basis of the requirement permitting the deposition of less noble Zn in the presence of more noble hydrogen ions in the bath. Then the codeposition behavior of secondary element, i.e. an impurity in electrowinning and an alloying constituent in alloy plating, was explained by the theory of regular and anomalous type alloy deposition. According to its electrochemical meaning, the effect of secondary element in the bath on the magnitude of the critical current density was predicted, which agreed well with the experimental results. Further, the dissolution behavior of deposited Zn was discussed in relation to the mechanism in which the critical current density was changed in the presence of impurity in Zn electrowinning bath.
In deciding upon a revegetation plan for ecosystem recovery of rock slope of mined-out quarry, it is necessary to evaluate the degree of ecosystem recovery from a viewpoint of an environmental impact assessment. Fundamental studies on evaluation of the degree of ecosystem recovery were carried out using revegetation simulation image with tree's height as an index of ecosystem recovery. First, the landscape evaluation experiments were carried out in the case of trees grow on the berm area only using revegetation simulation image with virtual reality system (VRS). Then the same experiments were carried out in case of tree growth on both berms and the slope area using revegetation simulation image with photomontage. Both experiments were carried out by using rating scale method. The main results obtained in this study are summarized as follows: 1) In case of tree growth on the berm area, the degree of ecosystem recovery increases when height ratio increases. It became clear that the height ratio at the state of almost ecosystem recovery was 1.2. 2) In the case of tree growth on both berms and slope area, the degree of ecosystem recovery increase in proportion to height ratio. It became clear that the height ratio at the state of almost ecosystem recovery was 0.6. 3) In both cases, the degree of ecosystem recovery increases when height ratio increasess. 4) In the case of tree growth on both berms and the slope area, it is possible to shorten the length for ecosystem recovery compared to the tree growth on the berm area only.
In recent year, it is necessary to treat imported ore in zinc hydrometallurgy because of stable demand of material and depletion of domestic mine. However, the imported ore often contains a lot of impurities. Among them, SiO2 complicates solid-liquid separation after leaching process. The cause of this degradation is understood that Zn2SiO4 produced in roasting process is leached in leaching process, and then supersaturated silica solves in solution. In previous research, it was reported that solid-liquid separation was improved by increasing of pH and temperature, and seed method was effective for reducing SiO2 concentration. However, mechanism of the solid-liquid separation improvement hasn't been well understood. The purpose of this paper is to obtain the knowledge for the effects of temperature, pH and impurities on silica polymerization. (1) Solution temperature influences the colloidal silica polymerization, and the polymerization is promoted as the temperature is elevated. (2) In the solution of pH range from 1 to 3, the polymerization rate is almost the same. When pH is raised to 4, the polymerization rate has been promted. (3) Hydrolysis reaction of Fe and Al influences the decreasing of SiO2 concentration by rising pH in field test. (4) Addition of silica seed has greatly reduced the ionic and colloidal silica in the solution.
The synergistic effect of impurities on the dissolution behavior of Zn electrodeposited from the electrowinning solutions containing a different combination of impurities has been investigated by measuring the time-dependence of cathode potential during electrolysis and the polarization curves in the solutions. The impurities are classified into four groups ; group I (Ag, Cu, Cd) which changes inherent hydrogen overpotential η0H by depositing at limiting current density; group II (Ni, Co, Fe) which reduces η0H by partially depositing at lower current densities than limiting one ; group III (As, Sb, Ge) which catalytically reduces η0H ; and group IV (Al, Pb) which causes no change in η0H. In the solution containing both iron-group metal of group II and Cu of group I or Sb of group III as impurity, the dissolution of deposited Zn was more likely to occur than in the solution containing each impurity alone. Cu and Sb increase the kinetically suppressed deposition rate of iron-group metals, resulting in the increase in the critical current density for Zn deposition. The occurrence of dissolution of deposited Zn was closely related to the increase in critical current density for Zn deposition. Although the cycle of deposition and dissolution of Zn was repeated in the solution containing iron-group metal alone, no Zn deposited again after the dissolution occurred in the solution containing iron-group metal and Cu or Sb. This is ascribed to cathode surface replaced by Cu and iron-group metal during dissolution of Zn.
Many electrode reactions have the mass change in addition to the charge transfer. In this study, a peculiar system was built and tested using a digital microbalance with the sensitivity of 10-5 g in order to measure in-situ the mass change of the active materials in a lead-acid battery during charge-discharge reaction. On close inspection by the Cu electrodeposition, the mass change in-site measured by the system, which was corrected on account of the buoyancy of the electrolyte to the electrode, was good agreement with the value obtained by the ex-situ measurement before and after the test. On the other hand, the higher the current density during electrolytic oxidation of Pb, the smaller the production rate of PbSO4 and the larger that of PbO2. High concentration of H2SO4 also brought larger amount of PbO2 for all the same quantity of electricity. Moreover, a part of the discharge product PbSO4 could not returned to the PbO2 during charge-discharge cycling, as the cycling proceeded. The difference of the electrode mass was eventually observed between the start of the cycling and the finish of the 3rd charging. The in-situ measurement also revealed that the reaction of PbSO4 to Pb and that of Pb to PbSO4 could start in the latter half of discharging and at the beginning of charging respectively.
Oxidation decomposition reaction of CN- ion was studied using two types of TiO2 photocatalysts and related nitrogen-doped photocatalysts. Although the oxidation products of CN- ion using TiO2 powder consisting 30% rutile and 70% anatase demonstrated CNO-, followed by NO3- and CO32-, the generation of CNO- was inhibited and the formation of molecular nitorogen was detected with TiO2 composed of 100% anatase. Doping nitrogen to TiO2 photocatalysts facilitates their use under visible light irradiation. Particularly, nitrogen-doped anatase type TiO2 photocatalyst oxidized CN- ion to N2 directly, while CNO- formation was greatly suppressed under the irradiation by sunlight. The use of nitrogen-doped anatase type TiO2 photocatalyst under sunlight irradiation is useful as a novel decomposition method for spent CN- solution. Redox potential determination is effective to monitor CN- ion decomposition reaction.
Chloroplatinic acid, for example hydrogen hexachloroplatinate (IV) (H2[PtCl6]), undergoes a ligand substitution reaction in aqueous solution. Rate of the ligand substitution was estimated from measurement of ultraviolet-visible (UV-Vis) absorption spectrophotometry and ion-exchange chromatography under different chloride concentrations, light conditions, and time frames. [PtCl4]2- in the PtCl2 solution of 20w% hydrochloric acid indicated absorption peaks on its spectrum, that was distinguished from Cl- and Pt (IV) complexes. Spectrum of [Pt(OH)2Cl4]2- in the PtCl4 solution diluted with ultra pure water changed with passage of time under normal fluorescent lighting. Absorbance at the wavelength below 380nm decreased with time, while that increased at the wavelength above. Simultaneously, the concentration of Cl- measured by ion chromatography decreased with time. These aging characteristics were referred from reaction pathway of the ligand substitution of OH- for Cl-. Drop of downward slop on the spectra at lower wavelength meant precipitation of hydrogen hydroxoplatinate (H2[Pt(OH)6]) induced by the substitution reaction. Hydrochloric acid was added to the diluted chloroplatinic acid solutions after that had reached equilibrium, and then prepared solutions also underwent measurement of UV-Vis spectra periodically. Characteristic of the spectra of above prepared solutions aged for several days, conformed with that of H2[PtCl6] solution. Spectra of the chloroplatinic acid solution with [PtCl6]2- had a specific peak at 260nm, and the peak area absorbance was in inverse proportion to Cl- concentration measured by ion chromatography. Thus, the change of this absorbance indicates the substitution of OH- for Cl-. Chloroplatinic acid diluted with hydrochloric acid or sodium hydroxide solutions showed above-mentioned change patterns not only under lighting but also in the dark. To the contrary, that of diluted with ultra pure water showed no changes in the dark. The reaction rate of the substitution was accelerated by lighting and increasing of amount of additions.
Shaft plays an important role in accessing or ventilating to deep underground, so it is necessary to assess its long-term stability. But little knowledge about the long-term behavior of shaft has been obtained from in-situ measurement, theoretical study and numerical simulation. In this study, time-dependent behavior and failure process of deep shaft was simulated with the aid of non-linear rheological constitutive equation of rock. This simulation focused on the effect of gravity and the deformation behavior parallel to the direction of excavation, which has hardly been examined with horizontal roadway or tunnel. Simulation with the model of 1000m deep shaft was carried out, and the effect of rock properties and rock stress conditions was examined. It was found that time-dependency, ductility, Poisson's ratio of rock mass and the ratio between horizontal and vertical rock stresses had an effect on failure process around the bottom of shaft. In addition, simulation with vertically and horizontally loaded disc-shaped model was carried out to investigate the effect of vertical rock stress and gravity in detail. It was found that the vertical deformation of shaft wall was much smaller than the radial one just before failure, but that the vertical rock stress and gravity had a large effect on failure process and long-term stability of shaft.