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Hashimoto, Yohey,Takeuchi, Satoshi,Mitsunobu, Satoshi,Ok, Yong-Sik Elsevier 2017 Journal of hazardous materials Vol.322 No.1
<P><B>Abstract</B></P> <P>This study investigated how silver nanoparticles (AgNP) and ionic silver (AgNO<SUB>3</SUB>) undergo phase-transformations in soils under aerobic and anaerobic conditions using extended X-ray absorption fine structure (EXAFS) spectroscopy. After 30 days of aerobic incubation, 88% of AgNP added to the soil remained persistent, whereas AgNO<SUB>3</SUB> was completely transformed into Ag associated with humus and clay minerals. In the anaerobic soil, 83% of the spiked AgNP was transformed into Ag<SUB>2</SUB>S, accompanied by significant decrease in water- and acid-extractable Ag fractions. About 50% of AgNO<SUB>3</SUB> spiked to the anaerobic soil underwent transformations into metallic Ag and associations with clay minerals. Oxide (Ag<SUB>2</SUB>O) and carbonate (Ag<SUB>2</SUB>CO<SUB>3</SUB>) forms of Ag were not predominant in aerobic and anaerobic soils. The redox potential of soil had a profound effect on determination of the phase-transformation pathways for AgNP and ionic Ag.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We investigated how AgNP and ionic Ag undergo phase-transformations in soils. </LI> <LI> 88% of AgNP remained persistent after 30 day of aerobic soil. </LI> <LI> In the anaerobic soil, 83% of the spiked AgNP was transformed into Ag<SUB>2</SUB>S. </LI> <LI> Ionic Ag was sorbed with soil colloids or reduced to metallic Ag. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Stabilization of arsenic and lead by magnesium oxide (MgO) in different seawater concentrations
Kameda, Kentaro,Hashimoto, Yohey,Ok, Yong Sik Elsevier 2018 Environmental pollution Vol.233 No.-
<P><B>Abstract</B></P> <P>Ongoing sea level rise will have a major impact on mobility and migration of contaminants by changing a number of natural phenomena that alter geochemistry and hydrology of subsurface environment. In-situ immobilization techniques may be a promising remediation strategy for mitigating contaminant mobility induced by sea level rise. This study investigated the reaction mechanisms of magnesium oxide (MgO) with aqueous Pb and As under freshwater and seawater using XAFS spectroscopy. Initial concentrations of Pb and As in freshwater strongly controlled the characteristics of the reaction product of MgO. Our study revealed that i) the removal of aqueous Pb and As by MgO was increased by the elevation of seawater concentration, and ii) the removal of As was attributed primarily to (inner-sphere) surface adsorption on MgO, independent on seawater concentrations, and iii) the retention mechanism of Pb was dependent on seawater concentrations where formations of Pb oxides and adsorption on the MgO surface were predominant in solutions with low and high salinity, respectively. The release of As fixed with MgO significantly increased in seawater compared to freshwater, although the amount of As desorbed accounted for <0.2% of total As.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Initial concentrations of Pb and As in freshwater controlled the characteristics of the reaction product of MgO. </LI> <LI> Removal of aqueous Pb and As by MgO was increased by the seawater concentration. </LI> <LI> Surface adsorption of As on MgO is predominant in 0–3.6% seawater. </LI> <LI> The retention mechanism of Pb was dependent on seawater concentrations. </LI> <LI> Release of As fixed with MgO significantly increased more in seawater than freshwater. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>