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In decades, various studies on passive treatment methods of acid mine drainage (AMD) have been actively conducted in order to reduce the cost of AMD treatment. Open limestone channel is one of the most common methods and has already been implemented mainly in overseas. On the other hand, it is difficult to secure large channels in Japan due to its topography, we need to consider the use of alkaline materials with higher acid neutralization potential which enables successful treatment with narrower space. In this study, therefore, PAdeCS, a cement-derived environmental remediation agent, was used to remove the harmful metal elements by neutralization treatment. Then, we developed a simulation model assuming a combined system of open limestone channel and alkaline material (PAdeCS) channel and predicted the behavior of harmful metal elements within the combined channel. The simulation results showed that PAdeCS has extremely high acid neutralization potential, that high temperature is advantageous for neutralization treatment of harmful metal elements, and that the channel design needs to be changed depending on the initial drainage composition. Finally, a new flowchart for selecting the appropriate passive treatment method was proposed, which consists of three steps of the preferential removal of Fe, neutralization by limestone, and additional treatments.

This paper takes a case-based approach to describe the dynamic processes inherent in digital transformation (DX). Using a theoretical modeling approach, Fujikawa, Kondo, and Imai (2022) proposed a dynamic process model in the form of a two-dimensional matrix with two axes (platform and stakeholder), four quadrants (stages) and two transitions (paths). Based on a theoretical sampling approach, the current study identifies four cases (Askul, Pioneer, Komatsu, and Nihon Kotsu) as “DX cases that went through different stages and paths” and analyzes these examples as revelatory and longitudinal cases. The paper explores the possibility of integrating new insights and logic detected in the case analyses back into the conceptual model.

The present study investigated the applicability of constructed wetlands (CWs) filled with oyster shells (OSs) for removing heavy metals from acid mine drainage (AMD). Lab-scale CWs consisted of columns (ID 12.5 cm, H 50 cm) packed with OSs or limestone, which were left unplanted or planted with cattails. Synthetic and real AMD containing 7.3 mg/L of Zn, 38.0 mg/L of Fe, and other minerals (pH = 4.0) were fed to the CWs (1 L/column) under a hydraulic retention time of 7 days in a sequencing batch mode. The effluent pH values of the CWs reached 6.9–8.3. Results show that OSs with high CaCO3 contents had higher neutralizing capability for AMD than limestone had. During 7 months of operation, all CWs were highly effective for removing Zn (88.6–99.2%); Fe (98.7–99.7%); and Cd, Cu, Pb, As, and Mn (48.2–98.9%) from both real and synthetic AMD. The mass balance in the CWs indicated accumulation in OSs or limestone as a main pathway for removing heavy metals, representing 44.8–99.3% of all metals, followed by biomass (8.8–29.9%) in the planted CWs. Other processes examined for this study only played a minor role in removing heavy metals. The higher metal treatment performance of OS CWs demonstrated the value of this aquaculture byproduct as a CW substrate.

We performed a three-dimensional (3D) analysis of ferrite grains recrystallized in low-carbon steel during annealing. Cold-rolled specimens were heated to 723 K and held for various periods. The 3D morphology of ferrite grains recrystallized during the annealing process was investigated. The progress of recovery in low-carbon steel was more inhibited than that in pure iron. However, ferrite recrystallization in low-carbon steel was more rapid than that in pure iron. The Avrami exponent was inconsistent with the 3D morphology of the recrystallized ferrite grains in pure iron but consistent with that of the grains in low-carbon steel. Thus, the Avrami exponent depends on the recovery and recrystallization behaviors. Furthermore, the recrystallized ferrite grain growth was virtually 2D. Three types of recrystallized ferrite grains were observed: recrystallized ferrite grains elongated along the transverse or rolling direction; plate-shaped recrystallized ferrite grains grown in the transverse and rolling directions; fine and equiaxed recrystallized ferrite grains. These results suggest that the recrystallized ferrite grains did not grow in the normal direction. Thus, we concluded that the 3D morphology of recrystallized ferrite grains depends on the kinetics of recrystallization and the initial microstructure before recrystallization.