Abstract
Electromagnetic fields are used in water treatment and desalination to regulate scale formation and extend the lifetime of membranes. External electric and magnetic fields can promote or suppress mineral nucleation and growth. However, the molecular-scale mechanisms of such processes remain unknown. Computing the free energies needed to form ion pairs under external fields provides important insights into understanding the elemental steps during the initial formation of mineral scales. In this paper, we used molecular dynamics combined with metadynamics simulations to investigate the free energies of forming the [Ca-CO3]0 ion pair, a fundamental building block of carbonate scales, under a range of magnetic (up to 10 T) and electric (up to 10 V m−1) fields in water. The presence of constant magnetic or electric fields favored the ion pairing reaction and lowered the free energies by up to 3% to 6%. The internal energy and entropic components of the free energy showed significant changes and exhibited non-linear behavior with increasing field strength. The [Ca-CO3]0 ion pairing is an entropy-driven process in the absence of an external field, but the mechanism shifts to an internal energy-driven process under selected external fields, suggesting possible changes in the nucleation pathways.
| Original language | English |
|---|---|
| Journal | Physical Chemistry Chemical Physics |
| DOIs | |
| State | Accepted/In press - 2024 |
Funding
This material is based upon work supported by the National Alliance for Water Innovation (NAWI), an Energy-Water Desalination Hub funded by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE), Industrial Efficiency and Decarbonization Office, under Funding Opportunity Announcement DE-FOA-0001905. A. G. S. provided insight on ion pair dissociation constant calculations using support from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. This research used birthright cloud resources of the Compute and Data Environment for Science (CADES) at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under contract no. DE-AC05-00OR22725. The authors thank Dr Tomasz Panczyk (Polish Academy of Science) for sharing packages in simulating the magnetic field in LAMMPS. This manuscript has been authored in part by UT-Battelle, LLC, under contract DE-AC0500OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( https://energy.gov/downloads/doe-public-access-plan ). The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government.
| Funders | Funder number |
|---|---|
| Basic Energy Sciences | |
| Data Environment for Science | |
| U.S. Department of Energy | |
| National Alliance for Water Innovation | |
| Office of Science | |
| Polska Akademia Nauk | |
| Chemical Sciences, Geosciences, and Biosciences Division | |
| Office of Energy Efficiency and Renewable Energy | DE-FOA-0001905 |
| CADES | DE-AC0500OR22725 |
