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.

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 multitask-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

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.

o r 7 4 4 , M o t o o k a , N i s h i -k u , F u k u o k a 8 1 9 -0 3 9

Extensive rainfall can lead to the discharge of untreated mine drainage from abandoned mines. The Ministry of Economy, Trade and Industry aims to promote environmental impact assessments in scenarios where untreated mine drainage discharges may occur due to extensive rainfall. This study aims to develop a risk assessment method for these events, focusing on 26 abandoned mine drainages without responsible parties. We estimated metal concentrations at discharge points under the assumption that untreated drainage is released. A tiered system was used for the risk assessment: Tier 0 evaluates risks using river flow rates during droughts, while Tier 1 uses simulated post-rainfall river flows via AIST-SHANEL.

Numerical simulations are widely used to analyze the mass transfer in a cell with the aim of improving the efficiency of electrolysis processes. In this study, galvanostatic electrolysis with CuSO4–H2SO4 aqueous solution as the electrolyte and pure copper as the anode in laboratory scale was modeled in order to examine how to simulate the transport phenomenon of ions in the copper electrorefining. A galvanostatic electrolysis test using an electrolysis apparatus with similar dimensions to the model was also performed, and the measured cell voltage was compared with that estimated by the simulation. In the simulation, Cu2+, H+, HSO4− and SO42− were assumed to move according to the Nernst–Planck equation while satisfying the electrical neutrality condition in the electrolyte, and the local equilibrium for the dissociation of HSO4− was also taken into account. The dependence of the diffusion coefficient and mobility of ions on the electrolyte composition was also incorporated into the calculations, aiming to obtain the potential gradient and ion concentration distribution that are close to the actual values.