Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Alteration of sediments by hyperalkaline K-rich cement leachate: Implications for strontium adsorption and incorporation
Results are presented from 1 year batch experiments where K-rich hyperalkaline pH 13.5 young cement water (YCW) was reacted with sediments to investigate the effect of high pH, mineral alteration, and secondary mineral precipitation on Sr sorption. After reaction with YCW, Sr sorption was found to be greater than 75% in all samples up to 365 days and 98% in a sample reacted for 365 days at 70 °C. Scanning electron microscopy analysis of sediment samples reacted at room temperature showed surface alteration and predpitation of a secondary phase, likely a K-rich aluminosilicate gel. The presence of Sr - Si(Al) bond distances in Sr K-edge extended X-ray absorption fine structure (EXAFS) analysis suggested that the Sr was present as an inner-sphere adsorption complex. However, sequential extractions found the majority of this Sr was still exchangeable with Mg2+ at pH 7. For the sample reacted for 1 year at 70 °C, EXAFS analysis revealed dear evidence for ∼6 Sr - Si(Al) backscarters at 3.45 Å, consistent with Sr incorporation into the neoformed K-chabazite phase that was detected by X-ray diffraction and electron microscopy. Once incorporated into chabazite, Sr was not exchangeable with Mg2+, and chemical leaching with pH 1.5 HNO3 was required to remobilize 60% of the Sr. These results indicate that, in high pH cementitious leachate, there is significantly enhanced Sr retention in sediments due to changes in the adsorption mechanism and incorporation into secondary silicate minerals. This suggests that Sr retention may be enhanced in this high pH zone and that the incorporation process may lead to irreversible exchange of the contaminant over extended time periods.
Alteration of sediments by hyperalkaline K-rich cement leachate: Implications for strontium adsorption and incorporation
Results are presented from 1 year batch experiments where K-rich hyperalkaline pH 13.5 young cement water (YCW) was reacted with sediments to investigate the effect of high pH, mineral alteration, and secondary mineral precipitation on Sr sorption. After reaction with YCW, Sr sorption was found to be greater than 75% in all samples up to 365 days and 98% in a sample reacted for 365 days at 70 °C. Scanning electron microscopy analysis of sediment samples reacted at room temperature showed surface alteration and predpitation of a secondary phase, likely a K-rich aluminosilicate gel. The presence of Sr - Si(Al) bond distances in Sr K-edge extended X-ray absorption fine structure (EXAFS) analysis suggested that the Sr was present as an inner-sphere adsorption complex. However, sequential extractions found the majority of this Sr was still exchangeable with Mg2+ at pH 7. For the sample reacted for 1 year at 70 °C, EXAFS analysis revealed dear evidence for ∼6 Sr - Si(Al) backscarters at 3.45 Å, consistent with Sr incorporation into the neoformed K-chabazite phase that was detected by X-ray diffraction and electron microscopy. Once incorporated into chabazite, Sr was not exchangeable with Mg2+, and chemical leaching with pH 1.5 HNO3 was required to remobilize 60% of the Sr. These results indicate that, in high pH cementitious leachate, there is significantly enhanced Sr retention in sediments due to changes in the adsorption mechanism and incorporation into secondary silicate minerals. This suggests that Sr retention may be enhanced in this high pH zone and that the incorporation process may lead to irreversible exchange of the contaminant over extended time periods.
Alteration of sediments by hyperalkaline K-rich cement leachate: Implications for strontium adsorption and incorporation
Wallace, Sarah H. (Autor:in) / Shaw, Samuel (Autor:in) / Morris, Katherine (Autor:in) / Small, Joe S. (Autor:in) / Burke, Ian T. (Autor:in)
Environmental Science and Technology ; 47 ; 3694-3700
2013
7 Seiten, 5 Bilder, 2 Tabellen, 43 Quellen
Aufsatz (Zeitschrift)
Englisch
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