Plutonium(IV) and (V) Sorption to Goethite at Sub-Femtomolar to Micromolar Concentrations: Redox Transformations and Surface Precipitation

详细信息    查看全文

• 作者：Pihong Zhao ; James D. Begg ; Mavrik Zavarin ; Scott J. Tumey ; Ross Williams ; Zurong R. Dai ; Ruth Kips ; Annie B. Kersting
• 刊名：Environmental Science & Technology
• 出版年：2016
• 出版时间：July 5, 2016
• 年：2016
• 卷：50
• 期：13
• 页码：6948-6956
• 全文大小：578K
• 年卷期：0
• ISSN：1520-5851

文摘

Pu(IV) and Pu(V) sorption to goethite was investigated over a concentration range of 10^–15–10^–5 M at pH 8. Experiments with initial Pu concentrations of 10^–15 – 10^–8 M produced linear Pu sorption isotherms, demonstrating that Pu sorption to goethite is not concentration-dependent across this concentration range. Equivalent Pu(IV) and Pu(V) sorption Kb>db> values obtained at 1 and 2-week sampling time points indicated that Pu(V) is rapidly reduced to Pu(IV) on the goethite surface. Further, it suggested that Pu surface redox transformations are sufficiently rapid to achieve an equilibrium state within 1 week, regardless of the initial Pu oxidation state. At initial concentrations >10^–8 M, both Pu oxidation states exhibited deviations from linear sorption behavior and less Pu was adsorbed than at lower concentrations. NanoSIMS and HRTEM analysis of samples with initial Pu concentrations of 10^–8 – 10^–6 M indicated that Pu surface and/or bulk precipitation was likely responsible for this deviation. In 10^–6 M Pu(IV) and Pu(V) samples, HRTEM analysis showed the formation of a body centered cubic (bcc) Pub>4b>Ob>7b> structure on the goethite surface, confirming that reduction of Pu(V) had occurred on the mineral surface and that epitaxial distortion previously observed for Pu(IV) sorption occurs with Pu(V) as well.