Yasumasa Ogawa's research while affiliated with Akita University and other places

... The arsenic concentrations in the studied sediment samples vary between 0.02 and 875 mg/kg. Most of the concentrations are below or around the Bulgarian soil normal (10 mg/kg) and Romanian alert (15 mg/kg) values (Figure 2 (Nikolic et al., 2011;Adamovic et al., 2022). The pollution is confined to the Danube right bank in bottom and suspended sediments, while arsenic concentrations are low in the Pristol floodplain sediments (Figure 2). ...

... While the mobility of U in the ecosystem depends on redox conditions (IRNS, 2012) and complexation by organic matter (Bone et al., 2020), with the most stable and mobile form being U(VI), the mobility of Th in soil is very limited due to strong sorption to soil particles (Torstenfelt, 1986). In contrast, the content of REEs in soil is related to redox potential and pH as well as to the presence of clay, carbonate, organic matter, and Al, Fe, and Mn oxides and oxyhydroxides (Aide and Aide, 2012;Felipe-Sotelo et al., 2017;Mihajlovic and Rinklebe, 2018;Aide, 2019;Tang et al., 2020;Ogawa et al., 2021). Their content generally decreases with the decrease of pH, redox potentials, and Al-Mn-Fe contents (Aide and Aide, 2012;Mihajlovic and Rinklebe, 2018;Aide, 2019). ...

... Ogawa et al. also reported that an extremely low-cost process in which FA is mixed with approximately 30 wt% of water and aged for a week is effective in inhibiting the leaching of boron, arsenic, chromium, and fluorine [29,30]. In contrast, Seki et al. reported that the aging treatment reported by Ogawa et al. promoted the leaching of toxic elements for some types of FA samples [31]. Furthermore, in the leachabilities of elements from concrete or cement containing coal ash, Mahedi et al. reported the leaching characteristics of calcium, magnesium, sulfur, manganese, barium, and chromium from cement activated soil-fly ash [32]. ...

... Nieto et al. [22] and Adamovic et.al. [23] noted pollutant transport over significant distances from AMD [22,23]. The total amount of pollutants from mine outflow from the Kizel Coal Basin (for the catchment areas of the Yaiva, Kosva, and Chusovaya Rivers) is 21,455 tons per year of iron, 1128 tons per year of aluminum, and 217 tons per year of manganese [24]. ...

... The leaching behavior of arsenic and selenium over time was examined using three representative R-FAs (R-FA1, R-FA2, and R-FA3) and their C-FAs (C-FA1, Table 2, and their densities, BET-specific surface areas, and particle size distributions are shown in Table 3 and Figure 3. According to the chemical compositions shown in Table 2, the pH of FA samples depends on the content of CaO [41]. The density changed minimally with or without cement mixing. ...

... Several comprehensive reviews of surficial weathering of iron sulfide ore-derived mine tailings in a semi-arid environment have been published over the past decades (Blowes and Jambor, 1990;Jambor, 1994;Jambor and Blowes, 1998;Lindsay et al., 2015). Previous studies have also investigated the geochemical mobility of metals, aqueous rare earth elements, and actinides (i.e., U and Th) in the natural aquatic system (Ogawa et al., 2021;Ogawa et al., 2019). The REEs patterns in groundwater result from complex solid-water interactions and can be applied as process indicators of a post-mining area (Grawunder et al., 2018). ...

... Kashiwakura et al. revealed the removal of boron and arsenic from FA by washing with acid [26,27], and Bhattacharyya et al. demonstrated their stabilization for arsenic, boron, chromium, molybdenum, selenium, and vanadium by adding ferrous sulfate [28]. Ogawa et al. also reported that an extremely low-cost process in which FA is mixed with approximately 30 wt% of water and aged for a week is effective in inhibiting the leaching of boron, arsenic, chromium, and fluorine [29,30]. In contrast, Seki et al. reported that the aging treatment reported by Ogawa et al. promoted the leaching of toxic elements for some types of FA samples [31]. ...

... We hypothesize that the LMCT process plays a role in As(III) oxidation under neutral pH conditions, but with a different contribution and mechanism from that under alkaline pH conditions because of the inadequate formation of Cu(OH) 2 colloid. Since acidic water or wastewater co-contaminated with arsenic and copper is often discharged downstream of copper smelters (Matschullat, 2000), copper mines, and gold mines (Camm et al., 2004;Đorđievski et al., 2018;Milu et al., 2002), the environmental significance of Cu(II) photochemistry may increase with a decrease in the acidity of the medium in natural or engineering systems. ...

... Sorption onto hydrous Al or Fe oxy-hydroxides (HAO or HFO) is an important process for natural attenuation of many elements in acidified aquatic systems (e.g., Gammons et al., 2005aGammons et al., , 2005bGammons et al., , 2005cWood et al., 2006;Schemel et al., 2007;McCleskey et al., 2009;Ogawa et al., 2014;Carrero et al., 2015;Ayora et al., 2016). Sorption onto HAO and HFO is largely dependent on pH and thus aqueous speciation of target metals and their fractionation (Ogawa et al., 2018(Ogawa et al., , 2019. It is also reported that REE fractionation are also caused by differences in the stability of aqueous REE complex with various anions (e.g., Grawunder et al., 2014;Olías et al., 2018;Lozano et al., 2019Lozano et al., , 2020aMunemoto et al., 2020). ...

... After the tsunami disaster of the Great East Japan Earthquake 2011, As contaminated marine sediment that came from the tailing of the abandoned gold mine was brought back to the coast of Kesennuma City, Miyagi Prefecture, located in the subarctic area of Japan. Risk assessments of As in tsunami sediments was conducted, and it was revealed that the water-soluble As concentration in the sediment was higher than Japan Environmental Quality Standard of As as 10 μg/L restricted by Japan Soil Contamination Countermeasures Law (Tsuchiya et al., 2012). ...