Toshifumi Igarashi’s research while affiliated with Hokkaido University and other places

This study investigated the hydrogeochemical characteristics of a tailings storage facility (TSF) from an abandoned copper (Cu) mine, where circumneutral drainage is observed. Surface drainage streams of the tailings, tailings pore water, and seepage were analyzed to determine the TSF water chemistry. The mineralogy and chemical composition of the tailings were characterized using X-ray diffraction (XRD) and X-ray fluorescence (XRF). The tailings contain elevated Cu, up to 2530 mg/kg, and zinc (Zn), up to 2390 mg/kg. However, Cu and Zn were not leachable from the tailings bored cores and remained undetected in the tailings pore water. Mineralogical analysis of the bored cores identified pyrite, calcite, chlorite, and goethite, while pore water revealed elevated concentrations of calcium (Ca), up to 485 mg/L and sulfate (SO42−), up to 1720 mg/L. Thermodynamic modeling suggests pyrite oxidation and calcite dissolution are controlling the Ca–SO42− dominated water chemistry, maintaining a circumneutral pH ranging from 6.1 to 7.3. These conditions promote the precipitation of ferrihydrite and goethite, which may sequester the potentially toxic elements in the pore water. Sequential extraction confirmed the limited mobility of Cu and iron (Fe), which were strongly partitioned in the oxidizable and residual phases. Although acid–base accounting (ABA) indicates that the tailings remain susceptible to acid generation, the findings suggest the historical use of artificial neutralizing agents containing calcite during tailings disposal. This is derived from the correlation between the mineralogical compositions in the bored cores and the solubility controlling phases in the tailings water. Subsequently, the tailings indicate neutral drainage, leading to decreased potentially toxic element mobility; the predicted lifespan of the inorganic carbon in the calcite is estimated to last several hundred years before depletion.

Excavated rocks generated during tunnel construction may pose an environmental hazard due to the release of acidic leachate containing potentially toxic elements (PTEs). Addressing this concern requires strategic countermeasures against mitigating the release of PTEs. This study investigated the efficacy of a novel approach for managing altered excavated rocks that generate acidic leachates with elevated arsenic (As) by utilizing the finer altered rock as a base material for the sorption layer. The proposed method involves classifying the altered excavated rocks into coarse (9.5–37.5 mm) and finer (<9.5 mm) fractions, with the finer fractions incorporated with iron (Fe)-based adsorbent to form a bottom sorption layer for the disposal of coarser rock samples. Leaching behavior and As immobilization efficiency were assessed through shaking, stirring leaching tests, batch sorption tests, and column tests under varying particle size fractions of the rock samples. Results indicate that altered finer rock fractions exhibit increased As leaching under shaking conditions due to enhanced dissolution. The addition of >1% of Fe-based adsorbent to the finer rock in the sorption layer effectively suppressed As leaching concentration, meeting the management criterion of <0.3 mg/L for specially controlled contaminated soils in Japan. Batch sorption tests using the finer rock samples with the Fe-based adsorbent confirmed their efficacy as effective adsorbents. This efficacy was further elucidated in column experiments consisting of the coarse rock samples and fine altered rock samples mixed with the Fe based adsorbent at the bottom as a sorption layer. Results showed that the sorption layer effectively decreased the As leached from the rock layer, utilizing the altered excavated fine rock as a base material in the sorption layer. This approach highlights the potential for repurposing excavated rocks as sorption media, enabling sustainable management strategies for As-contaminated rocks. This study provides an innovative framework for integrating adsorption-based remediation, contributing to sustainable countermeasure strategies for excavated rocks.

The extraction of mineral deposits is often associated with the occurrence of acid mine drainage (AMD), which can persist even after mine closure due to remaining sulfide minerals. This study investigates a 200-year-old abandoned mine and its impacts on nearby water resources. The study area is well known for Kuroko ore deposits located upstream of spring and river water resources. To elucidate the impacts of the abandoned mine site, mine water and spring and river water samples were collected, and their geochemical properties were monitored between 2021 and 2022. Groundwater, seepage, and surface water at the mine site showed AMD characteristics with Ca²⁺–SO4²⁻/Mg²⁺–SO4²⁻ type. AMD-affected mine water showed a low pH range of 3.40–4.84, with elevated SO4²⁻ of up to 326 mg/L. At the downstream of the mine site, one of the groundwater samples showed pH of 3.55 and average concentrations of 5.03 mg/L of Al, 2.06 mg/L of Cu, 2.06 mg/L of Fe, 0.42 mg/L of Pb, and 8.04 mg/L of Zn, inferring the contaminant transport. Saturation indices of the mine water also indicated that the solubility controlling phases, anglesite, gibbsite, ferrihydrite, and jarosite influence the concentrations of Al, Fe, and Pb at the mine site. Meanwhile, spring and river water samples showed Ca²⁺–HCO3⁻, Ca²⁺–SO4²⁻, and Na⁺–K⁺–HCO3⁻ type with a circumneutral pH range of 5.59–8.02 and they were unaffected by AMD. The principal component analysis (PCA) of the spring and river water samples also showed higher loadings for Ca, Mg, NO3⁻, and Cl⁻ reflecting the abundance of carbonate and evaporite minerals while the mine water and groundwater downstream showed higher loadings of Cl⁻, Fe, SO4²⁻, and Zn. The results suggest that the past mining activities only influenced the mine site and groundwater downstream. Consequently, the fate and migration of contaminants in the downstream of the mine site should be evaluated in the near future. Graphical Abstract

A thiosulfate-oxidizing bacterium, Thiomicrospira sp. strain V2501, was isolated from groundwater collected in a terrestrial deep subsurface environment. This strain was capable of chemolithoautotrophic growth on CO2 and thiosulfate. Here, we report the 2,240,851 bp complete genome sequence of strain V2501.

Large clastic dykes (the Harutori‐Taro and Harutori‐Jiro dykes) and smaller dykes are exposed in the underground Kushiro Coal Mine (KCM), Japan. This study examines these dykes as a case study to investigate the geological conditions and fluid flow history that lead to the development of large clastic dykes in basins. The composition of the dykes indicates the Beppo and/or Harutori formations as their parent unit. Crystallite size distribution (CSD) analysis reveals Ostwald ripening of the kaolinite in the kaolinitised feldspar from the dykes, suggesting stagnant conditions in the parent unit before the dyke was formed. In contrast, smectite CSDs and the high carbonate content of the dykes suggest that large volumes of fluid flowed through the dykes along the established hydraulic gradient, which was triggered by the breaking of the upper seal. The isotopic and chemical compositions of the calcite and aragonite in the dykes, with moderate siderite and rhodochrosite content, indicate the fluid was a warm (>30°C) mixture of freshwater and saltwater, which was transferred from deeper levels of the parent unit towards the crest of an anticline. Immediately after sand injection, the semi‐closed system of the parent unit near the root of the large dyke was transformed into a major flow channel for overpressurised fluids. Subsequently, a large volume of fluid flowed along the vertical conduit (or dyke) over a long period of time (>1 Myr), which removed fluid from a widespread area (i.e., several hundred square kilometres) of the basin. The results show that thin parent units, poor lateral continuity of the upper seal, and spatially heterogeneous overpressurisation do not preclude the formation of large dykes.

To estimate the lifetime of an immobilizer used for countermeasures for disposing of excavated rocks containing hazardous trace elements such as arsenic, the appropriate method for evaluating the solubility of the immobilizer is required. In our previous study, the solubility-limiting solid phase that governs the solubility of the immobilizer, was assumed based on the saturation index (SI) of each mineral calculated using water chemistry of the leachate obtained by batch immobilization experiments. In this study, the formation of the solubility-limiting solid phases was confirmed by electron microscopic (EPMA) observation and elemental mapping analysis by using the residues of batch immobilization experiments. The results observed by EPMA showed that brucite as a solubility-limiting solid phase of Mg-bearing immobilizers, formed surrounding magnesium oxide. In case of using Ca-bearing immobilizers containing Mg, Mg ion was sorbed on calcite and dolomite-like secondary mineral was formed, which could behave as the solubility-limiting solid phase. These results indicate that the prediction of the solubility-limiting solid phase by SI based on the results of batch immobilization experiments was also consistent with and supported by the results of microscopic observations and elemental mapping analysis of the solid phase.