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  • Open Access

Factors determining ion rejection and one-step freeze desalination

Dachuang Shi*, Le Zhou*, Yixiang Wang, Yanguang Zhou, and Zhigang Li†

  • *These authors contributed equally to this work.
  • †Contact author: mezli@ust.hk
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Phys. Rev. Research 7, 033196 – Published 27 August, 2025

DOI: https://doi.org/10.1103/s77l-lvl4

Abstract

Freeze desalination is an emerging, membrane-free desalination method that utilizes the ion rejection phenomenon during the freezing of seawater, where salt ions tend to be rejected by ice. However, it requires the ion rejection rate to be higher than 98.2% to generate drinking water; i.e., at least 98.2% of the salt ions remain in the liquid phase. This poses a challenge for one-step seawater freezing due to the trapping of salt ions in ice. In this work, we first reveal that the ion rejection phenomenon is governed by the competition between two factors: ice growth and ion diffusion, which can be described by two characteristic timescales, τice and τion, respectively. To enhance the ion rejection rate, the ratio τice/τion should be increased. Based on this criterion, we propose a freeze desalination method by freezing flowing seawater, where τion is reduced due to the enhancement of the ion diffusivity caused by flow shear, to obtain potable water through a single cycle of seawater freezing with the ion rejection rate exceeding 98.2%. With additional temperature control, the productivity of drinking water can be further improved. The proposed freeze desalination method shows great potential for commercialization.

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Phys. Rev. Research 7, 033196– Published 27 August, 2025
  • Received 6 March 2025
  • Accepted 8 August 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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