Alteration of Sediments by Hyperalkaline K-Rich Cement Leachate: Implications for Strontium Adsorption and Incorporation

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• 作者：Sarah H. Wallace ; Samuel Shaw ; Katherine Morris ; Joe S. Small ; Ian T. Burke
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2013
• 出版时间：April 16, 2013
• 年：2013
• 卷：47
• 期：8
• 页码：3694-3700
• 全文大小：383K
• 年卷期：v.47,no.8(April 16, 2013)
• ISSN：1520-5851

文摘

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 ⁹⁰Sr 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 掳C. Scanning electron microscopy analysis of sediment samples reacted at room temperature showed surface alteration and precipitation of a secondary phase, likely a K-rich aluminosilicate gel. The presence of Sr鈥揝i(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 掳C, EXAFS analysis revealed clear evidence for 6 Sr鈥揝i(Al) backscatters at 3.45 脜, consistent with Sr incorporation into the neoformed K-chabazite phase that was detected by X-ray diffraction and electron microscopy. Once incorporated into chabazite, ⁹⁰Sr was not exchangeable with Mg²⁺, and chemical leaching with pH 1.5 HNO₃ was required to remobilize 60% of the ⁹⁰Sr. 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.