Dynamic dissolution of Cm ions incorporated at the calcite-water interface: an molecular dynamics simulation study

• Published in: Physical chemistry chemical physics : PCCP 2024-02, Vol.26 (9), p.7545-7553
• Main Authors: Chu, Zhao-Qin, Zhu, Ru-Yu, Su, Jing
• Format: Article
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d3cp05611b

The stability of actinide-mineral solid solution in a water environment is critical for assessing the safety of nuclear-waste geological repositories and studying actinide migration in natural systems. However, the dissolution behavior of actinide ions incorporated at the mineral-water interface is still unclear at the atomic level. Herein, we present metadynamics simulations of the reaction pathways, thermodynamics and kinetics of trivalent curium ions (Cm 3+ ) dissolving from calcite surfaces. Cm 3+ ions incorporated in different calcite surfaces ( i.e. , terrace and stepped surfaces) with distinct coordination environments have different reaction pathways, free energy barriers and free energy changes. We found that Cm dissolution from a stepped surface is more favorable than that from a terrace surface, both thermodynamically and kinetically. In addition, water molecules seem to promote the detachment of curium ions from the surface by exerting a pulling force via water coordination with Cm 3+ and a pushing force via proton migration to the surface layer and water diffusion in the vacant Cm site. Thus, the findings from this work prove to be a milestone in revealing the dynamic dissolution mechanism of trivalent actinides from minerals and would also help predict the dissolution behaviors of other metal ions at the solid-water interface in chemical and environmental sciences. The Cm 3+ ions incorporated at different surfaces of the calcite bulk have different dissolution behaviors. The Cm dissolution from a stepped surface is more favorable than that from a terrace surface, both thermodynamically and kinetically.