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Environ Sci Technol. 2016 Apr 5;50(7):3852-9. doi: 10.1021/acs.est.5b05932. Epub 2016 Mar 23.

Uptake Mechanisms of Eu(III) on Hydroxyapatite: A Potential Permeable Reactive Barrier Backfill Material for Trapping Trivalent Minor Actinides.

Xu L1,2, Zheng T1,2, Yang S1,2, Zhang L3, Wang J3, Liu W1,2, Chen L1,2, Diwu J1,2, Chai Z1,2, Wang S1,2.

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School for Radiological and Interdisciplinary Sciences (RAD-X), Soochow University , 215123 Suzhou, P. R. China.
Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions , 215123 Suzhou, P. R. China.
Shanghai Institute of Applied Physics and Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Chinese Academy of Sciences , 201800 Shanghai, P. R. China.


The permeable reactive barrier (PRB) technique has attracted an increasing level of attention for the in situ remediation of contaminated groundwater. In this study, the macroscopic uptake behaviors and microscopic speciation of Eu(III) on hydroxyapatite (HAP) were investigated by a combination of theoretical modeling, batch experiments, powder X-ray diffraction (PXRD) fitting, and X-ray absorption spectroscopy (XAS). The underlying removal mechanisms were identified to further assess the application potential of HAP as an effective PRB backfill material. The macroscopic analysis revealed that nearly all dissolved Eu(III) in solution was removed at pH 6.5 within an extremely short reaction time of 5 min. In addition, the thermodynamic calculations, desorption experiments, and PXRD and XAS analyses definitely confirmed the formation of the EuPO4┬ĚH2O(s) phase during the process of uptake of dissolved Eu(III) by HAP via the dissolution-precipitation mechanism. A detailed comparison of the present experimental findings and related HAP-metal systems suggests that the relative contribution of precipitation to the total Eu(III) removal increases as the P:Eu ratio decreases. The dosage of HAP-based PRB for the remediation of groundwater polluted by Eu(III) and analogous trivalent actinides [e.g., Am(III) and Cm(III)] should be strictly controlled depending on the dissolved Eu(III) concentration to obtain an optimal P:M (M represents Eu, Am, or Cm) ratio and treatment efficiency.

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