Gel-Chemistry-Controlled Heavy-Metal Transport and Retention in Cementitious Gel Nanopores: A Molecular Dynamics Study
Abstract
Cementitious materials are widely used for hazardous-waste encapsulation, yet molecular mechanisms governing heavy-metal ion retention across gel chemistries remain insufficiently resolved. Previous MD studies have focused on individual gel systems and pore-averaged metrics, limiting direct comparison across gel chemistries. Here, classical molecular dynamics simulations were used to investigate adsorption-controlled mobility of Pb2+, Ba2+, and Cs+ in nanopores of C-S-H, C-(N)-A-S-H, and N-A-S-H gels. Combining pore-averaged and spatially resolved diffusivity, residence-time analysis, ion-density profiles, 2D adsorption maps, radial distribution functions, coordination analysis, and interfacial binding-strength descriptors establishes a framework linking gel surface chemistry to mobility suppression while distinguishing local mobility from spatial ion partitioning effects on pore-averaged transport. Ion mobility is reduced in all gel nanopores relative to bulk, but the extent and mechanism vary strongly with gel chemistry. C-(N)-A-S-H with higher interfacial Al/Si substitution exhibits the strongest retention, driven by ion accumulation around Al-linked oxygen species via an ion-exchange-like mechanism with charge-balancing Na+. C-S-H immobilizes ions primarily through surface hydroxyl oxygens and Ca-mediated linkages, whereas N-A-S-H exhibits more distributed binding environments. Pb2+ and Ba2+ show broadly similar immobilization mechanisms, whereas Cs+ exhibits more gel-dependent interactions with silicate and aluminosilicate oxygen sites. A relative total binding strength (rTBS) descriptor shows a strong positive correlation with ion immobilization across gel types, ion species, and pore sizes. These results clarify gel- and ion-specific retention mechanisms and link interfacial binding strength to pore-averaged mobility suppression in idealized cementitious nanopores.
Versions
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BibTeX
@misc{chen2026gelchemistrycontrolled,
title = {{Gel-Chemistry-Controlled Heavy-Metal Transport and Retention in Cementitious Gel Nanopores: A Molecular Dynamics Study}},
author = {Weiqiang Chen and Qiyao He and Kai Gong},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2605.11604},
eprint = {2605.11604},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.11604},
}
RIS
TY - UNPB
TI - Gel-Chemistry-Controlled Heavy-Metal Transport and Retention in Cementitious Gel Nanopores: A Molecular Dynamics Study
AU - Weiqiang Chen
AU - Qiyao He
AU - Kai Gong
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2605.11604
UR - https://arxiv.org/abs/2605.11604
AB - Cementitious materials are widely used for hazardous-waste encapsulation, yet molecular mechanisms governing heavy-metal ion retention across gel chemistries remain insufficiently resolved. Previous MD studies have focused on individual gel systems and pore-averaged metrics, limiting direct comparison across gel chemistries. Here, classical molecular dynamics simulations were used to investigate adsorption-controlled mobility of Pb2+, Ba2+, and Cs+ in nanopores of C-S-H, C-(N)-A-S-H, and N-A-S-H gels. Combining pore-averaged and spatially resolved diffusivity, residence-time analysis, ion-density profiles, 2D adsorption maps, radial distribution functions, coordination analysis, and interfacial binding-strength descriptors establishes a framework linking gel surface chemistry to mobility suppression while distinguishing local mobility from spatial ion partitioning effects on pore-averaged transport. Ion mobility is reduced in all gel nanopores relative to bulk, but the extent and mechanism vary strongly with gel chemistry. C-(N)-A-S-H with higher interfacial Al/Si substitution exhibits the strongest retention, driven by ion accumulation around Al-linked oxygen species via an ion-exchange-like mechanism with charge-balancing Na+. C-S-H immobilizes ions primarily through surface hydroxyl oxygens and Ca-mediated linkages, whereas N-A-S-H exhibits more distributed binding environments. Pb2+ and Ba2+ show broadly similar immobilization mechanisms, whereas Cs+ exhibits more gel-dependent interactions with silicate and aluminosilicate oxygen sites. A relative total binding strength (rTBS) descriptor shows a strong positive correlation with ion immobilization across gel types, ion species, and pore sizes. These results clarify gel- and ion-specific retention mechanisms and link interfacial binding strength to pore-averaged mobility suppression in idealized cementitious nanopores.
ER -