The adsorption of U(VI) on chlorite: batch, modeling and XPS study

Author:

Jin Qiang12,Wang Yuxiong12,Zhao Xin12,Fan Ye12,Diao Xinya12,Chen Zongyuan12,Guo Zhijun12ORCID

Affiliation:

1. MOE Frontiers Science Center for Rare Isotopes, Lanzhou University , 730000 Lanzhou , China

2. Radiochemistry Laboratory, School of Nuclear Science and Technology, Lanzhou University , 730000 Lanzhou , China

Abstract

Abstract A mechanistic modelling of the adsorption processes onto individual minerals presenting in the near- and far-fields can greatly enhance the credibility of long-term safety assessments of granite-based geological repositories. In this study, the titration and U(VI) adsorption characteristics of chlorite, one of the major minerals of rock fractures, have been studied. Potentiometric titration curves at two ionic strengths (0.1 and 0.4 mol/L NaCl) are successfully interpreted by considering protonation/deprotonation reactions on generic edge sites (≡SOH) in the framework of a non-electrostatic surface complexation model (SCM). The adsorption of U(VI) on chlorite was reached after 24 h, the adsorption kinetics can be described by a pseudo-second-order model. A non-electrostatic SCM with three surface complexes (≡SOUO2 +, ≡SO(UO2)3(OH)5 and ≡SO(UO2)3(OH)7 2−) was set up based on pH edges of U(VI) at adsorption equilibrium in the absence of CO2. Additional, experimental data measured as a function of U(VI) concentration, solid-to-liquid ratio and carbonate concentration were well reproduced by the proposed model. Finally, parallel experiments were conducted using X-ray photoelectron spectroscopy (XPS) to analyze the variation of U(VI) surface species speciation at different pH values. The good agreement between SCM prediction and XPS analysis demonstrates the reliability of the model in predicting and quantifying the radionuclides retention by chlorite.

Funder

National Natural Science Foundation of China

Natural Science Foundation of Gansu Province, China

Fundamental Research Funds for the Central Universities

Publisher

Walter de Gruyter GmbH

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