Work

Electric field-assisted freeze desalination: Effects on ion transport, water structure, and ice growth rates

Year: 2025

Type: article

Abstract: • DC fields enhance ion diffusivity via directional drift in saline solutions • Mild dipole polarization at low fields promotes mobility and accelerates ice growth • Salt rejection improves up to 97% at field strength above thermal energy threshold • Field-induced ion diffusion dominates over crystallization-driven diffusion • Strong Na⁺–SO₄²⁻ ion pairing is observed in multicomponent saline systems Freeze desalination (FD) has emerged as a promising low-energy alternative to conventional desalination methods, particularly in cold or renewable-energy-integrated environments. However, its efficiency is often hindered by incomplete salt rejection and limited control over crystallization kinetics. This work investigates the influence of an externally applied static electric field on ion transport and ice growth dynamics in saline systems, using molecular dynamics (MD) simulations. Pure water and two saline solution models were explored: a binary NaCl–water system and a multicomponent seawater system containing Na⁺, Cl⁻, SO₄²⁻, Mg²⁺, Ca²⁺, and K⁺, both at an overall salinity of 45 g/L. Under isothermal, no phase change conditions, electric fields enhanced diffusivity via drift and partially aligned water dipoles along the direction of the field, particularly at field strengths exceeding the thermal energy threshold ( k B T ) . At high field strengths (i.e., E≥0.03 V/Å), the diffusivity of Na⁺ in the multicomponent system surpassed that in the binary system due to disrupted Na + -SO 4 2− ion pairing. Ice crystallization analysis of the binary NaCl-water system revealed that electric fields improve salt rejection rates from 88.7% at no-field to 97% at 0.03 V/Å, without significantly suppressing crystal growth rates. A dimensionless diffusion metric confirmed that field-induced ion transport dominates over crystallization-driven separation. These findings demonstrate how electric fields can be tuned to enhance FD efficiency, offering broader potential for field-assisted separation technologies.

Source: Energy Nexus

DOI: 10.1016/j.nexus.2025.100585

Authors: Khadije El Kadi, Sohail Murad, Isam Janajreh

Institutions: Khalifa University of Science and Technology, Illinois Institute of Technology

Language: English

Topic: Freezing and Crystallization Processes

Subfield: Mechanics of Materials

Field: Engineering

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $2,200

Funder: Khalifa University of Science, Technology and Research