# Cs+ Promoting the Diffusion of K+ and Inhibiting the Generation of Newberyite in Struvite-K Cements: Experiments and Molecular Dynamics Simulation Calculations

## TL;DR

This study shows how Cs+ improves the stability of struvite-K cements by reducing harmful byproducts and enhancing radioactive Cs+ immobilization.

## Contribution

The discovery of Cs+ promoting K+ diffusion and forming a new Cs-containing crystal phase in struvite-K cements is novel.

## Key findings

- Cs+ reduces newberyite and brucite formation by up to 60.81% in struvite-K cements.
- Cs+ achieves immobilization rates over 99% for radioactive Cs+ in different Mg/P ratios.
- A new crystal phase [CsPO3·H2O]4 was identified as a dominant Cs-containing phase.

## Abstract

Struvite-K cements, also called magnesium potassium phosphate cements (MKPCs), are applicable for particular applications, especially the immobilization of radioactive Cs+ in the nuclear industry. This work focuses on how Cs+ affects the hydration mechanism of struvite-K cements because newberyite and brucite in the hydration products are deemed to be risky products that result in cracking. Experiments and molecular dynamics simulations showed that Cs+ promoted the diffusion of K+ to the surface of MgO, which greatly facilitates the formation of more K-struvite crystals, inhibiting the formation of newberyite and brucite. A total of 0.02 M Cs+ resulted in a 40.44%, 13.93%, 60.81%, and 32.18% reduction in the amount of newberyite and brucite, and the Cs immobilization rates were 99.07%, 99.84%, 99.87%, and 99.83% when the ratios of Mg/P were 1, 3, 5, and 7, respectively. This provides new evidence of stability for struvite-K cements on radioactive Cs+ immobilization. Surprisingly, another new crystal, [CsPO3·H2O]4, was found to be a dominating Cs-containing phase in Cs-immobilizing struvite-K cements, in addition to Cs-struvite.