Generally, in eddy current testing (ECT), magnetic field variations generated by induced eddy currents are detected using a pickup coil. However, according to Faraday’s law of electromagnetic induction, the sensitivity of a pickup coil decreases significantly at low frequencies, making the detection of low-frequency magnetic fields difficult. As a result, conventional ECT often have limited capability for detecting deep flaws in conductive materials. In this study, we propose an eddy current testing system based on an optically pumped magnetometer (OPM) with low-frequency excitation. The proposed method aims to improve the detectability of not only surface flaws but also deeper flaws that are difficult to detect using conventional ECT. To enable measurements under geomagnetic field conditions, the magnetic signal detected by the probe was transferred to an OPM inside a magnetically shielded box via a flux transformer. Furthermore, to suppress the effects of external magnetic noise and environmental disturbances, the probe was covered with an aluminum alloy magnetic shield. Experiments were conducted using a 12-mm-thick aluminum alloy plate containing artificial flaws with a diameter of 3 mm and depths ranging from 2 to 6 mm. The experimental results demonstrate that the proposed OPM-ECT system successfully detected all backside flaws in the specimen, indicating the potential of this method for deep-flaw inspection in conductive materials.

When recycling scrap iron, impurities that are difficult to remove, called trump elements, become a problem. Among them, tin (Sn) has many opportunities for contamination and affects the processability of steel, so new removal methods are needed. Sn is highly reactive with iodine(I) and becomes a metal iodide gas at high temperatures. The purpose of this was to remove Sn from iron scrap using I. We prepared Carbon-saturated iron containing 2 mass% Sn as a sample, weighed 0.1 g, and put it into the furnace. I₂ gas was then injected into the furnace. The Sn concentration and Sn removal rate were calculated by dissolving the sample after the experiment and performing analysis by ICP-OES. As a result, the Sn concentration in the sample was reduced to 0.008%, and the removal rate was up to 99.5%.

Blast furnace slag is generated in large quantities as a by-product of ironmaking and is mainly utilized in bulk applications such as cement production. However, high-value utilization focusing on the functional properties of individual components included in the slag remains insufficient. Using a low-concentration citric acid aqueous solution, selective separation and recovery of silica from blast furnace slag could be performed but some impurities remained. Cation-exchange resin treatment reduced impurity metal ions such as Ca and Mg so effectively that the SiO₂ purity increased to approximately 95%. Water vapor adsorption measurements revealed type-IV isotherms with hysteresis that indicated the development of mesoporous structures. Practical desiccation performance was evaluated under closed vessels in comparison with a commercial silica gel. The recovered silica exhibited moisture adsorption behavior comparable to that of the commercial one and demonstrated its applicability as a desiccant material for humidity control applications. The proposed method enables efficient recovery of functional silica from blast furnace slag under relatively mild conditions and has potential as a sustainable resource-recycling utilization process.

Copper removal from ferrous scrap by a Metal-Immersion (MI) process using a molten Pb bath was investigated using a simulated scrap sample and Cu-clad steel. The specimens were immersed in molten Pb at 973-1273 K for 1 or 10 min under Ar atmosphere. In the simulated scrap sample, complete removal of Cu was achieved at 1173 and 1273 K for 10 min, whereas residual Cu remained after immersion at 1173 K for 1 min and at 1073 and 973 K. This behavior is attributed to a decrease in the dissolution rate of Cu with increasing Cu concentration in the Pb bath. In the Cu-clad steel sample, the Cu layer was completely removed by immersion at 1273 K for 10 min. Cross-sectional SEM-EDS observation showed negligible dissolution of Fe into the Pb bath, no intermetallic compound formation, and little diffusion of Pb into the steel phase. These results indicate that the Pb-bath MI process enables selective removal of Cu with minimal influence on the steel substrate, even for Cu-clad steel, which is difficult to separate by conventional physical methods.