Printed circuit boards (PCBs) are difficult to recycle because of the layered structure of non-metal (i.e., epoxy resin, glass fiber) and copper. In this work, we conducted a systematic investigation to effectively recover copper from PCB. A thermal treatment was employed for improving the crushing performance of PCB and conducted by varying the temperature and the gas. Then, the mechanical strength, degree of liberation (DL), and copper separation efficiency of the heat-treated and untreated PCBs were investigated. After heat treatment under a 300 °C air atmosphere, the mechanical strength of PCB decreased from 386.36 to 24.26 MPa, and copper liberation improved from 9.3% to 100% in the size range of a coarser size fraction (>1400 μm). Accordingly, when electrostatic separations were performed under these conditions, a high-Cu-grade concentrate and high recovery could be obtained. The results show that the change in the physical properties of the PCBs leads to an improvement in the DL following thermal decomposition at 300 °C in air. Our study elucidates the physical properties of PCBs and the DL under various heat treatment conditions. Furthermore, it shows that the heat treatment condition of 300 °C in air is ideal for recovering copper from the PCB.

In this study, the grinding characteristics of waste printed circuit boards (PCBs) were evaluated using a population balance model (PBM). The grinding characteristics under various conditions (hammer rotational speeds of 1600, 2000, and 2400 rpm; screen aperture sizes of 0.71, 1.0, and 1.40 mm; and maximum feed sizes of 4, 6, and 8 mm) were identified. A PBM for a continuous hammer mill was used to quantitatively demonstrate the grinding characteristics. No significant difference was observed in the particle sizes of the products for various hammer rotational speeds. Nevertheless, the specific rate of breakage increased with the hammer rotational speed. As expected, a narrow screen aperture yielded a fine product. The mean residence time was increased in this case to comminute the particles to a finer size. Furthermore, a finer feed was predicted to yield a finer product; however, a coarser feed was observed to yield such a product instead. Each hammer milling condition should be controlled with respect to the hammer milling performance and target particle size of the product.

서 론 달은 지구에서 가장 가까운 천체로, 지구와 비교하여 중 력이 1/6 수준으로 낮아 로켓을 이용해 궤도를 벗어나기 용 이하여 우주 개발의 거점으로 주목받고 있다. 우주 진출의

Charging of the lunar surface induced by solar radiation can potentially threaten in situ resource utilization. Associated issues include dust adhesion and material degradation. Photoelectric currents are the primary cause of surface charging. This work reports on the development of a unit capable of measuring photoelectric currents in a vacuum chamber, which can simulate surface charging under conditions similar to those on the moon in daytime. The main components of the unit are a mesh grid, a photocathode specimen, and a ring collector. Photoelectric currents from an aluminum sample were measured by adjusting the electric potential of these components, and the impact of the electric potential of each component is discussed. Calculating the expected electric current within the experimental setup allowed validation of the current measurements: the measured and calculated values agreed well with an error of ~5.5%. Finally, the photoelectric currents for various metals (aluminum, nickel, and copper) were measured using the same experimental setup. The results showed consistent measurement of photoelectric current values across all metals. This study offers insights into the development of units for measuring photoelectric current and methodologies to validate their results.