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Physicochemical speciation change in Fe as well as pH and water temperature variations in the Tamagawa field in (a) November 2010, (b) July 2010 and (c) June 2009. NB values were used to subdivide total Fe into mobile (sum of dissolved, colloidal and suspended species) and precipitated species. Successive filtration results were used to divide mobile species into dissolved, colloidal and suspended types. Data of pH, water temperature and concentrations of Fe are cited from Ogawa et al. (2013). Due to no determination in November 2010, Fe²⁺ data are cited from Ogawa et al. (2012)
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This work assessed both the fractionation and the seasonal mobility variations of Ga and In in systems impacted by acidic thermal waters. This was accomplished by performing thermodynamic calculations using the PHREEQC algorithm and by assessing the activity of acidophilic iron-oxidizing bacteria. The pH of the Kusatsu thermal waters in Gunma Prefe...
Citations
... 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). ...
... The Yukawa River was examined during three sampling periods (December 2015, and March and September 2019). The geochemical behavior of As and rare metals, such as Ga and In, in this area in February 2009 have been reported previously (Ogawa et al., 2013(Ogawa et al., , 2018. ...
... Thorium was transported to the reservoir (site K-5) without significant precipitation on the riverbed, and then about 80% of Th originating from the thermal waters settled onto the reservoir bed. This mobility is quite similar to those for As, Ga and In (Ogawa et al., 2013(Ogawa et al., , 2018, meaning that the reservoir acts as an effective sink for these elements. ...
Acidic thermal water originating from the Kusatsu geothermal area of Gunma Prefecture, Japan is introduced into rivers, where there are many anthropogenicobjects such as a neutralization plant, a dam and water channels for hydroelectric power plants. We have investigated changes in the physico-chemical nature and fractionation mechanisms of rare earth elements (REEs) including Y and actinides (Th and U) by artificial and natural neutralization processes during river transport.
The geochemical behavior of these elements and fractionation among them are mainly controlled by pH-dependent sorption and/or precipitation, once the pH increases up to 5.5. Dissolved Th is nearly completely removed, and hydrous Fe and Al oxides (HFO and HAO) sorbing Th or Th(SO4)2s settle onto the reservoir's bed. On the other hand, REEs and U remain as dissolved species. The effect of temperature on removal of these metals is limited.
At pH values of ~5.5, REEs and U are removed by HFO and/or HAO, resulting in less fractionation among them. As pH increases to greater than 6.5, dissolved REEs continue to be removed by HFO and/or HAO, whereas U largely remains as a dissolved species in river water. Formation of UO2‑carbonate complex species prevents removal of dissolved U. When pH approaches 8, U is desorbed from suspended materials.
Fractionation of REEs including Y occurs during sorption onto suspended materials and is strongly pH-dependent. REEs are less fractionated, when sorption occurs under pH less than ~6.2. As pH increases, heavier REEs tend to be removed by sorption onto suspended materials, and lighter REEs tend to remain in river water. Compared to fractionation between MREE and HREE, fractionation between LREE and MREE is larger. Yttrium is sorbed more effectively than LREE but less effectively than HREE. REE fractionation may occur significantly under pH 6.2–7.5.
... Recent studies of the mobility of Ga and In in rivers acidified by thermal waters reveal that physico-chemical speciation changes (chemical state of target elements such as dissolved species and sorbate on HAO and HFO) are strongly influenced by aqueous speciation changes (such as free ions or complex species with some anions) (Ogawa et al., 2013), and thermodynamic calculation can accurately predict the sites (or times) at which sorption reactions onto HFO begin, as well as the semi-quantitative amounts sorbed onto HFOs (Ogawa et al., 2018). However, although there are many reports of REE and U sorption experiments involving aqueous REE species (e.g., Walter et al., 2003;Davranche et al., 2004), research on clarifying the relationship between physico-chemical and aqueous speciation of REEs and actinides in natural aquatic systems is very rare. ...
... (3) Dissolved Th is nearly completely removed and dissolved U also decreased, under the conditions at which hydroxyl species are predicted to become significant. So, aqueous speciation changes of actinides are important for their sorption reaction, similar to Ga and In (Ogawa et al., 2018). On the other hand, geochemical behaviors of REEs are simply controlled by pH. ...
In the Tamagawa geothermal area of Akita Prefecture, northern Japan, Obuki spring discharges a large amount of thermal water (∼9000 L/min), which is chloride-rich and acidic (pH 1.2). We have investigated changes in the physico-chemical nature and fractionation mechanisms of rare earth elements (REEs) including Y and actinides (Th and U) in the Shibukuro and Tama rivers into which acid thermal water from the Obuki spring discharges. The geochemical behavior of these elements is shown to be mainly controlled by pH-dependent sorption onto ferric and/or aluminum oxy-hydroxides (HFO and HAO). HFO is formed around pH > 3. In the upstream region, where pH is less than 4, dissolved Th is removed due to precipitation of Th(SO 4 ) 2(s) . Whereas, under pH condition greater than 4, remaining dissolved Th is nearly completely sorbed onto suspended HFO, where hydroxyl species of Th are thermodynamically significant. Then, the Th(SO 4 ) 2(s) and HFO-sorbed Th are nearly completely removed in an upstream man-made lake. Dissolved U is also removed mainly by sorption onto HFO, where hydroxyl species of UO 2 are predominant. A considerable portion of U is also trapped in the sediments of this lake. On the other hand, removal of REEs is nearly negligible until the lake. This is the first fractionation among REEs and actinides caused by pH-dependent sorption, and the order of removal from river water is Th > U ≫ REEs. The remaining dissolved U and REEs in the river waters are transported farther downstream. At pH values of >6, suspended HAO is effectively formed, and the second fractionation among REEs and U occurs. During the second fractionation, REEs are removed by HAO, whereas U largely remains as a dissolved species in river water under higher pH conditions. Lighter REEs, such as La and Ce, tend to remain in the river waters compared to the other REEs including Y. The predominant chemical species for UO 2 during the second fractionation are carbonate complex species, and relative proportions of hydroxyl species drastically decreases, resulting in prevention of U sorption onto HAO.
