The objective of this study was to understand the instantaneous ignition and combustion reactions of CuFeS₂/silica mixture by preheated oxygen gas blowing. The ignition initiation position of CuFeS₂ was controlled by installing a coiled heater inside the reaction tube of the drop furnace, and the ignition and combustion reactions of the CuFeS₂/silica mixture were evaluated by blowing preheated oxygen gas. The sample was mixed at a mass ratio of Fe/SiO₂ = 1.1. The combustive sample was observed by a high-speed camera. The microstructure of reaction products in water-quenched samples was evaluated using scanning electron microscopy-energy dispersive spectroscopy. Based on particle temperature measurements by a two-color temperature method, bright particles observed by ignition and reaction were classified into the following four types: (1) ones with a surface temperature of at ≥2000℃, (2) ones including two different temperature regions of 1600 and 1900℃, (3) ones with a uniform temperature at around 1500°C, and (4) ones at lower temperatures of ≤1300°C. The microstructural analysis revealed that the Cu/S ratio of the matte phase had an average composition of 3.6 near Cu₂S. The ratios of Cu/S and Fe/SiO₂ had no change within experimental errors in all collected particles consisting of slag and matte phases.

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.

In the Tier 0 assessment, two mine drainages (No. 5 and No. 8) exhibited Cd, Pb, As, Cu, Zn, Fe, and Mn concentrations below environmental standards, indicating that high dilution effect contributed to a low-risk discharge even after a certain period following extensive rainfall. In the Tier 1 assessment, even for mine drainages assessed as high-risk in the Tier 0 assessment, some mine drainages, which initially assessed as high-risk in Tier 0, showed metal concentrations below environmental standards for up to 7 days following peak rainfall, suggesting that high flow rates can mitigate discharge risks. For practical application, simulating river flow during extensive rainfall would allow predictions of heavy metal concentrations at discharge and water use points. Our approach would enable the setting of appropriate discharge periods and volumes, even in situations where untreated discharges are unavoidable, contributing to minimize environmental impacts downstream.

This study investigates the mineral diversity in placer platinum-group minerals (placer PGM) purportedly collected from the Onnebetsu area in Shibetsu City, Hokkaido. Placer particles consist primarily of native elements and alloys and can be broadly categorized into two groups, iridium-group and palladium-group. The iridium-group placer is predominantly composed of rutheniridosmine, osmium, ruthenium, and iridium, with each occurring as both primary and secondary phases. In contrast, the palladium-group placer consists primarily of isoferroplatinum as the primary phase, accompanied by tulameenite, tetraferroplatinum, and ferronickelplatinum as secondary phases. Notably, the iridium-group placer may also contain PGM typically associated with the palladium-group placer in subordinate amounts. In addition to the primary and secondary phases, other PGM occur as inclusions, within the outermost layers of particles, and in exsolution textures. A total of 41 PGM species were identified in this study, along with six unnamed species. The Onnebetsu area stands out as the region in Japan with the highest diversity of PGM discovered to date. This remarkable variety is largely attributed to the palladium-group placer, which is originated from cumulate rocks formed by partial melting of a mantle.