A review of studies of subcritical crack growth in rock is presented. First, theoretical background of subcritical crack growth is presented. It has been considered that the main mechanism of subcritical crack growth in silicate materials is stress corrosion under low homologous temperature and pressure. Next, theoretical background of stress corrosion is presented. Especially, the theoretical relation between the crack velocity and the stress intensity factor is described. Then, progress of the study of subcritical crack growth in silicate materials is presented by reviewing previous studies for glass, quartz, and silicate rocks. It has been clarified that the reactive species of stress corrosion is water and hydroxyl ion. For anisotropic rock, the crack velocity was dependent on the propagation direction and opening direction even at the same stress intensity factor. Finally, recent results of subcritical crack growth in rock are presented. It was clarified that the relation between the crack velocity and the stress intensity factor was decided by the crack opening direction. The crack velocity was higher when the temperature and the humidity were higher. It was shown that the activation energy became smaller when the crack path was smooth from the observation of the crack path.
To estimate long-term stability of deep underground structures, it is important to investigate the time-dependent behavior of rock. Loading rate dependency, creep and relaxation have been well examined under uniaxial stress state conditions, however, less in known of the effects of confining pressure. In this paper, recent experimental and theoretical studies on the time-dependency of rock were reviewed primarily focusing on the effects of confining pressure. Firstly, time-dependent behavior under confining pressure was compared to the uniaxial stress state, and the effects of confining pressure were discussed. Loading rate dependency, creep and the relation between them were examined with the aid of recent theoretical studies. The close relations among time-dependency, probability distribution of rock properties and scale effect were explained theoretically. Finally, equipment and practical testing methods used to investigate the time-dependent behavior under confining pressure were reviewed.
Revising the method proposed by Vasco et al., we developed a new method for more accurately estimating groundwater flow by an inverse analysis of tilt data on the surface. The features of this method are that 1) a region (V) where groundwater flow occurs is divided into elements in which the volume change in groundwater per unit volume of rock (Δν) and the Skempton coefficient B are assumed to vary in a linear or quadratic manner with the coordinates, that 2) the values of Δν are set to zero at the boundaries of the region V and that 3) as constraining conditions which are weighed and added to a squared error in tilt, the sum of squared second derivatives of Δν are used. We call the method using linear interpolation Inversion-1 and that using quadratic interpolation Inversion-2. First, analyses by these methods were conducted for two flow models of water injection to know the applicability of the methods. It was shown that both Inversion-1 and Inversion-2 can evaluate the volume change in groundwater much more accurately than the method by Vasco et al. when Δν varies relatively gently with the distance from the injection point (Model 1). However, when Δν varies steeply with the distance from the injection point (Model 2), either Inversion-1 or Inversion-2 cannot produce good results. This was considered to be caused by the fact that the measured data are much fewer than Δν to be determined. Furthermore, the effect of the size of the region V on the estimation of Δν was analyzed since it is usually difficult to accurately estimate the size of a region where water flow occurs. The results showed that the effect of the size of the region V is relatively small for both Inversion-1 and Inversion-2 unless the size is much smaller than the real one and that Inversion-2 produces a smaller error than Inversion-1. Thus, it can be said that it is better to perform an analysis by Inversion-2 with a large size of the region V in the beginning.
Groundwater flow at the site of MIU (Mizunami Underground Research Laboratory) in the Tono district, Japan, was evaluated by a new inverse method using tilt data measured by four tiltmeters during excavation of shafts. The features of the method are that 1) the fluid volume change per unit volume of rock (Δν) is assumed to vary in a quadratic manner with the coordinates in elements within a region of groundwater flow, that the values of Δν are set to zero at the boundaries of the region and that the sum of squared second derivatives of Δν are adopted as constraining conditions which are weighed and added to a squared error in the tilt. An inverse analysis was performed by assuming three sizes for a whole region of groundwater flow. It was shown that there are three regions where the volume of groundwater decreases and two regions where the volume of groundwater increases regardless of the size of the whole region of groundwater flow and that groundwater came mainly from the sedimentary rocks lying between two faults. The latter is consistent with the previous prediction that these faults have a low permeability and may act as a flow barrier. Furthermore, the results of the inverse analysis predict that there may be other hydrogeological structures which prohibit groundwater flow. Thus, the inverse method proposed by the authors for evaluating groundwater flow from tilt data has proved to be reliable in spite of the assumption that the rock mass is a homogeneous half-space.
The codeposition behavior of impurities such as Ag, Bi, Fe, Ni, Pb and Sb with Cu was investigated galvanostatically at 5-3000A/m2 using Pt cathode at 60 °C in acidic copper ( I ) chloride (cuprous chloride) solution of pH1-2 containing 1.0 mol/L of Cu+ and 4.9 mol/L of Cl-. The impurities were classified into two groups ; group I (Ag, Bi) which codeposits with Cu as metal ; group II (Fe, Ni, Pb, Sb) which is slightly involved in deposited Cu as nonmetal from electrolyte. Ag and Bi of group I behaved as more noble metal than Cu, which showed the typical feature of regular type codeposition. When Cu deposited dendritically, the content of Ag and Bi in deposit increased with increased duration of electrolysis by decreasing net current density due to increased cathode area. The current efficiency for Cu deposition in impurity-free solution was 95-100% over 100-1000A/m2 and abruptly decreased above 1000 A/m2 when the limiting current density of Cu was attained. Although Fe, Ni, Pb and Sb of group II were involved by 0.01-0.02mass% in deposit, they had no influence on the current efficiency and morphology of Cu.
The extraction of molybdenum (VI) from hydrochloric acid solutions by di-(2-ethylhexyl)-phosphoric acid (DEHPA, HX) in kerosene and benzene has been investigated under different conditions. The infrared, nuclear magnetic resonance and electronic absorption spectra measurements were made of the organic extracts. As the results, it is found that the extraction of molybdenum(VI) at low aqueous acidity ([HC1] ≤ 3 mol dm-3) is governed by a cation-exchange reaction and at higher acidity ([HC1] ≥ 3 mol dm-3) by a solvating reaction : at low acidity, MoO22+(aq) + 2(HX)2(org)↔MoO2X4H2(org) + 2H+ (aq) ; at higher acidity, MoO2Cl2(aq) + (HX)2(org)↔MoO2Cl2·2HX(org). Accordingly the monomeric complexes MoO2X4H2 and MoO2Cl2·2HX, indicating the coordination number of six for molybdenum as the octahedral structure, are formed in the extraction from aqueous solutions at low and higher acidities, respectively.
A series of treatment flow consisting of sulfuric acid leaching, precipitating separation and solvent extraction has been studied for separation and recovery of metal values from complex plating sludge containing iron, copper, nickel, chromium and zinc. The results obtained are summarized as follows. (1) More than 90% of copper, zinc and nickel are extracted by the mild leaching condition in which iron leaching is lower than 10%. Leaching of iron largely depends on the sulfuric acid concentration. Leaching efficiencies of iron and chromium decrease with increasing leaching temperature in dilute sulfuric acid. (2) Iron in the leaching solution is selectively precipitated at pH 4 by pH control with ammonia solution. Other elements except iron are not able to be separated by pH control. (3) Zinc is selectively extracted at pH 2.5 by PC-88A. Zinc extracted by PC-88A is perfectly stripped to the aqueous phase at pH lower than 1. (4) Copper is selectively extracted at low pH by LIX84-I, and the selective extractability of copper is perfect up to pH 5. Extraction of nickel starts at pH 5, and almost all nickel is extracted at pH 7 by LIX84-I. Chromium is not extracted by the solvent.
A Molten fly ash generated by direct melting process used in treating municipal solid waste (MSW) is designated as a specially-controlled waste in Japan due to the harmful heavy metals it contains. Proper detoxification before disposal in landfills is legally required, as in the case of fly ash produced by conventional MSW incinerators. As part of research and development of an incinerator fly ash treatment process using the sintering method, to date, the authors have clarified the removal mechanism of heavy metals such as lead (Pb) and cadmium (Cd), which are the main harmful heavy metals found in fly ash, and optimized the removal conditions based on thermodynamic and metallurgical approaches. Molten fly ash is more difficult to treat than incinerator fly ash. For research and development of a treatment process, a new pilot plant with a design capacity of 45kg/h was constructed in March 2004. Using this facility, we demonstrated that harmful heavy metals such as Pb in molten fly ash can be safely removed to trace levels which satisfy the Japanese environmental standard for soil, and the pellets obtained in the process can be recycled, for example, as artificial lightweight aggregate. And basic tests using the small-scale electric furnace were also carried out to collect data for elucidation of roasting mechanism. As the result, we confirmed that the influence of the hematite and lime concentration on pellet crush strength was very large and when the lime concentration was high, a lower hematite concentration was desirable.