A composite strong-acid cation exchanger was developed for use in high-flow-rate metal recovery systems by coating a porous silica support with a styrene-divinylbenzene copolymer and subsequently introducing sulfonic acid groups. The purpose of this study was to clarify how structural factors of the composite exchanger affect adsorption-desorption performance under dynamic flow conditions relevant to compact and high-throughput recovery processes. A series of samples with different crosslinking ratios, sulfonation feed ratios, and particle sizes was prepared, and their adsorption properties were evaluated using Ni(II) and Cu(II) as model metal ions. Batch adsorption tests were carried out to examine adsorption rates and distribution behavior, while column experiments were performed to investigate breakthrough behavior, elution characteristics, recovery efficiency, scale-up performance, and cyclic stability. The results showed that the sample prepared with a crosslinking ratio of 15%, a sulfonation feed ratio of 2 equiv., and a particle size of 250-500 μm exhibited the most favorable overall performance among the materials examined. This sample showed rapid adsorption, sharp breakthrough and elution behavior, high recovery rates for both metal ions, and stable operation in scale-up and repeated adsorption-elution cycle tests. In addition, under high-flow-rate conditions, the optimized composite exchanger exhibited superior recovery behavior compared with the reference commercial resin. These findings demonstrate that systematic optimization of the resin structure and particle size is essential for maintaining efficient ion-exchange performance at high flow rates, and that the developed composite cation exchanger is a promising separation material for compact metal recovery systems.

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The effects of Cl^-, gelatin and Sb(Ⅲ) additions on the current efficiency and crystal morphology of Zn electrodeposition from the electrowinning solutions were investigated. When Cl^- (300 mg/L), gelatin (1 mg/L) and Sb (5 μg/L) were added individually, the current efficiency increased by 1–1.5% compared with the additive-free case. When two of these additives were used in combination, the current efficiency also increased compared with the additive-free condition, with the largest improvement observed for the combination of Cl^- and gelatin. This is attributed to the complementary effects of Cl^-, which promotes Zn deposition, and gelatin, which suppresses hydrogen evolution. When Cl^- coexisted with either gelatin or Sb, the grain size of the deposited Zn became larger than in the cases where gelatin or Sb was added alone. Since the addition of Cl^- reduces the overpotential for Zn deposition, it is considered that the nucleation rate decreases, leading to an increase in grain size. The number of bubble marks on the deposited Zn increased with the addition of Cl^-, but decreased when gelatin or Sb was present together with Cl^-. These results suggest that an increase in the nucleation rate of Zn reduces the formation of bubble marks.

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The objective of this study was to develop a method for quantitatively characterizing tetravalent Ru complexes, namely [RuCl₆]²⁻ and [Ru₂OCl₁₀]⁴⁻, in concentrated hydrochloric acid by ultraviolet-visible absorption spectroscopy. To obtain the standard spectra of each complex, measurements on K₂RuCl₆ and K₄[Ru₂OCl₁₀] dissolved in hydrochloric acid containing an oxidizing agent were performed. Test solutions were prepared by fusing Ru with NaOH and Na₂O₂, followed by dissolving in hydrochloric acid. Using cuvettes with appropriate pass lengths for each solution, the spectra were measured over a wide range of Ru concentrations, from 0.000323 to 0.0321 mol･dm⁻³. Then the spectra of the test solutions were separated into the contributions of [RuCl₆]²⁻ and [Ru₂OCl₁₀]⁴⁻ to quantify the Ru complexes. Among the tests conducted, [RuCl₆]²⁻ was mainly formed in hydrochloric acid when the amount of Ru added was relatively small, whereas [Ru₂OCl₁₀]⁴⁻ was more likely to be formed when the amount of Ru was large. [RuCl₆]²⁻ and [Ru₂OCl₁₀]⁴⁻ coexisted at comparable concentrations at the intermediate condition. Heat treatment on the Ru solution to improve the accuracy of the analysis was also demonstrated.

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This study examines the effects of rock spalling on support elements in order to prevent cracking and to ensure the integrity of the support system and safety during shaft sinking. When the ventilation shaft at the Horonobe Underground Research Center reached a depth of more than 250 m, severe rock spalling occurred, and cracks developed in the concrete lining immediately above the spalling zone. Therefore, a three-dimensional numerical analysis of the shaft was conducted to estimate changes in the stress distribution within the concrete lining caused by the spalling. The simulation results indicated that the vertical tensile stress in the concrete lining increased as the spalling progressed. By integrating the analytical results with field observations and considering various support patterns to prevent further rock spalling, a flowchart for selecting the optimal support pattern was developed. Shaft sinking was subsequently completed to a depth of 500 m without significant damage to the concrete lining or excessive spalling. The flowchart developed in this study will contribute to the selection of optimal support patterns for future shaft sinking projects.

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Methane hydrate (hereafter, “MH”) is expected as an alternative energy resource to traditional fossil fuels. Further, rare-earth elements-rich mud, polymetallic nodules, cobalt-rich crust, and seafloor hydrothermal deposits are highly attractive mineral resources for exploration and development. These are located in the seabed of Japan’s Exclusive Economic Zone. A multi-task-type vertical transport system using an air-lift pump is proposed as a common system to transport these mineral and energy resources from the seabed in deep sea. The authors conducted a numerical analysis in the previous study for a shallow-type MH production system using a gas-lift pump, adopting the one-dimensional drift-flux model, and a numerical model for phase change, to examine the multi-phase flow characteristics, and predict the performance of practical ones. In this study, air is used instead of methane gas to apply the system for transporting MH as well as mineral resources. A new scheme, called “the multi gas-phase scheme”, is developed and devised in the program to account for flows of both air and methane gas in the lifting pipe. The numerical results of 0 MPa(G) back pressure, 273.15K(0℃) temperature explained the system’s flow characteristics in practical operation well, compared with those of 0.2 MPa(G) back pressure, 283.15K(10℃) in the previous study. The MH production rate: 6912t/d, volume concentration of MH: 14.4 – 11.3 %, slurry flux: 4.85 – 6.18 m/s, power requirement: 1019 – 1995 kW are predicted under the dimensions; length and water depth of lifting pipe: 940 and 900 m, water depth at air injection point: 300 m, pipe diameter below and above air injection point: 0.4 and 0.5 m, respectively, and operational conditions; back pressure: 0 MPa(G), volume concentration of mud in slurry: 3%, air flow rate: 4 – 8 kg/s. We demonstrated that the program could derive useful information and know-how for designing and operating the system.

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Rock excavators equipped with cutting functions, such as roadheaders, surface miners, and various coal mining machinery, are widely used in civil engineering and mine operations. In the design and development of these machines, numerous researchers have conducted theoretical, experimental, and numerical studies to understand the rock cutting mechanisms using bits. This review article summarized research trends and future challenges concerning rock cutting mechanisms, focusing on theoretical and experimental studies. First, the technical terminology for cutting processes of a chisel bit or a point attack bit was introduced, and various equations for calculating cutting resistance based on the two- or three-dimensional cutting theory were described in detail, including their background, derivation processes, and relationships. Then, recent experimental studies on the factors affecting cutting resistance of a point attack bit were reviewed while mentioning key achievements with a chisel bit. The law of similarity and the cutting processes of multi bits mounted on a rotating drum were also explained since they are essential for the design and development of actual rock excavators. Studies on cutting hard rocks and mining deep seafloor mineral resources are ongoing, and hence it will be necessary to clarify the rock cutting mechanisms under these complicated severe conditions with utilizing accumulated knowledge introduced in this review article.

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This paper provided an overview of recent advances in simulation technologies for comminution processes, focusing on analysis techniques based on the Discrete Element Method (DEM), categorized into grinding media behavior and material particle behavior. Regarding the simulation of grinding media behavior, we explained that engineering-important physical quantities such as power consumption, grinding rate, mechanochemical reaction rate, and wear amount have strong correlations with indicators calculable from simulations, such as dissipated energy and collision energy. This indicates that a part of the design of comminution processes, which has long relied on experience and intuition, is transitioning toward theory-based design. Additionally, regarding the simulation of material particle behavior, we explained the remarkable evolution of fracture models, in addition to the analysis of grinding and agglomeration mechanisms through coupled analysis with fluids. In particular, addressing the conventional challenge of arbitrariness in parameter determination, the establishment of methods that link experimentally measurable physical quantities with model parameters represents a significant step forward in enhancing the practical utility of simulations. This enables the reproduction of real phenomena in virtual space, even for comminution processes involving complex fracture phenomena, and is expected to contribute to eliminating the black box nature of grinding.

In the future, larger-scale and more detailed simulations are anticipated to become possible with further improvements in computational capabilities. Furthermore, by integrating such advanced simulation technologies with AI (Artificial Intelligence) and IoT (Internet of Things) technologies, the digital twinning of comminution processes is expected to accelerate. If systems can be constructed that instantaneously search for optimal operating conditions in virtual space and provide feedback for autonomous control of actual equipment, maximization of energy efficiency and realization of nano-level precision grinding can be reasonably expected. We hope this paper serves as a useful resource for understanding the technological progress in comminution and the current state of simulation technologies.

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Carbon dioxide capture and storage (CCS) is expected to be a key decarbonization technology for achieving carbon neutrality. Sensitivity analyses using an energy system model on CCS costs and storage capacity indicate that increasing domestic CO₂ storage capacity is economically rational. To increase CO₂ storage capacity, we have devised a method of subseafloor CO₂ storage using clathrate hydrates (hereinafter referred to as CO₂ hydrate storage). CO₂ hydrate storage is a method of storing CO₂ by forming an artificial hydrate seal within the subseafloor strata, utilizing the property of CO₂ to generate hydrates under the low-temperature and high-pressure conditions of the deep-sea around Japan. Numerical simulations of CO₂ hydrate generation show that more than half of the injected liquid CO₂ dissolves into formation water, while the remainder is ultimately stored in the formation by the hydrate seal. Regarding storage costs, estimation performed with QUE$TOR 2020 indicates that CO₂ hydrate storage is less expensive than aquifer storage, because even though the depth from sea-surface is greater, the injection location beneath the seafloor is shallower, resulting in lower well drilling costs.

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To promote the recycling of lithium-ion batteries, it is essential to develop pretreatment technologies that can efficiently delaminate and recover electrode layers containing active materials. In this study, we investigated the applicability of an underwater ultrasonic delamination technique, proposed by the authors, to used cells and commercial batteries. Ni–Co–Mn (NCM) ternary oxide cathodes were used to compare delamination behavior before and after charge/discharge cycles. After cycling, delamination was facilitated by the formation of aluminum fluoride (AlF₃) at the interface between the aluminum (Al) current collector and the cathode material. Furthermore, underwater ultrasonic treatment was applied to cathodes from four types of commercial cylindrical cells. While some electrodes were difficult to delaminate by ultrasonic treatment alone, delamination rates exceeding 95% were achieved when combined with a preheating step at 200–400°C. Analysis of the polyvinylidene fluoride (PVdF) binder content and cutting strength of the cathode material revealed that preheating reduced binder adhesion strength. Under these conditions, cavitation impacts generated during ultrasonic treatment effectively acted on both the internal structure of the cathode material and the cathode material/Al foil interface, thereby promoting separation and delamination. Overall, these results demonstrate that underwater ultrasonic treatment, when combined with appropriate pretreatment conditions, can be applied to various commercial spent electrodes with different structures, materials, and degradation states. The technique is expected to offer high adaptability in actual recycling processes, contributing to the expansion of applicability and improved efficiency of the overall recycling workflow.

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In secured landfill sites, accurate prediction of leachate volume is essential for stable operation and environmental management purposes. In this study, a tank model was developed using meteorological and operational data to predict seasonal variation in leachate volume. To improve estimation accuracy, the model also incorporates snow accumulation and snowmelt processes. Although the tank model is relatively simple, it demonstrates good performance in simulating leachate volume trends based on weather data. By incorporating snow-related hydrological processes, the correlation coefficient between the estimated and measured leachate volumes during winter and early spring improved significantly, from 0.15 to 0.72. The annual leachate volumes estimated using the model showed over 90% agreement with the measured values, confirming the model’s validity. The results also indicate that refining the estimation of evapotranspiration could further enhance prediction accuracy. This approach provides a practical and accessible tool for the daily management of landfill operations under varying climatic conditions.

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