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Peer-reviewedCC BYDesalination and Water Treatment

An open-source mathematical–thermodynamic framework for freeze crystallization of seawater RO reject-brine

  • Kagiso S. More1
  • Ravi Rangarajan2
  • Johannes P. Maree3
  1. 1Centre of Excellence for Sustainability and Food Security, University of Doha for Science and Technology, Doha, Qatar; Corresponding author.
  2. 2Centre of Excellence for Sustainability and Food Security, University of Doha for Science and Technology, Doha, Qatar; Department of Environmental Health and Safety, University of Doha for Science and Technology, Doha, Qatar
  3. 3Institute for Nanotechnology and Water Sustainability, College of Science, Engineering and Technology, University of South Africa, Private Bag X6, Science Campus, Johannesburg, FL, 1709, South Africa
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Abstract

Freeze crystallization (FC) offers a low temperature pathway for simultaneous water recovery and selective salt crystallization from concentrated desalination brines. This study developed a coupled PHREEQC-Python framework for sequential FC of two seawater reverse osmosis brines using FREZCHEM thermodynamics, Pitzer activities, direct ice-liquid equilibrium, and fractional removal of crystallized phases. Simulations were conducted from 25 to −25 °C at 1 °C intervals and independently benchmarked against OLI. Ice formation commenced between −3 and −4 °C, mirabilite between −6 and −7 °C, and hydrohalite between −22 and −23 °C. At −25 °C, predicted ice recoveries were 85.69% and 90.37%, compared with OLI values of 86.35% and 90.05%. Across 11 common temperatures, ice recovery MAE was 0.386–0.405 %age points and RMSE was 0.587–0.660 %age points. Mirabilite recovered 80.81–90.82% of initial SO 4 2- , while hydrohalite recovered 54.37–67.29% of Na and 44.56–59.59% of Cl. Maximum component and water mass balance errors remained below 0.013%. Experimental validation against an industrial leachate FC test reproduced ice and mirabilite formation at −6 °C, where 118.7 kg of ice was recovered from 273 L of leachate. Simplified refrigeration energy requirements were 50.35–51.42 kWh/m³ recovered ice equivalent. The framework therefore quantitatively identifies distinct water, SO 4 2- , and NaCl-bearing salt recovery windows while providing a reproducible basis for thermodynamic screening and staged FC process design.

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Cite

BibTeXRIS
BibTeX
@article{more2026opensource,
  title = {{An open-source mathematical–thermodynamic framework for freeze crystallization of seawater RO reject-brine}},
  author = {Kagiso S. More and Ravi Rangarajan and Johannes P. Maree},
  journal = {Desalination and Water Treatment},
  year = {2026},
  month = oct,
  doi = {10.1016/j.dwt.2026.101998},
  url = {https://doi.org/10.1016/j.dwt.2026.101998},
  note = {CC BY},
}
RIS
TY  - JOUR
TI  - An open-source mathematical–thermodynamic framework for freeze crystallization of seawater RO reject-brine
AU  - Kagiso S. More
AU  - Ravi Rangarajan
AU  - Johannes P. Maree
PY  - 2026
DA  - 2026/10/24
JO  - Desalination and Water Treatment
DO  - 10.1016/j.dwt.2026.101998
UR  - https://doi.org/10.1016/j.dwt.2026.101998
AB  - Freeze crystallization (FC) offers a low temperature pathway for simultaneous water recovery and selective salt crystallization from concentrated desalination brines. This study developed a coupled PHREEQC-Python framework for sequential FC of two seawater reverse osmosis brines using FREZCHEM thermodynamics, Pitzer activities, direct ice-liquid equilibrium, and fractional removal of crystallized phases. Simulations were conducted from 25 to −25 °C at 1 °C intervals and independently benchmarked against OLI. Ice formation commenced between −3 and −4 °C, mirabilite between −6 and −7 °C, and hydrohalite between −22 and −23 °C. At −25 °C, predicted ice recoveries were 85.69% and 90.37%, compared with OLI values of 86.35% and 90.05%. Across 11 common temperatures, ice recovery MAE was 0.386–0.405 %age points and RMSE was 0.587–0.660 %age points. Mirabilite recovered 80.81–90.82% of initial SO 4 2- , while hydrohalite recovered 54.37–67.29% of Na and 44.56–59.59% of Cl. Maximum component and water mass balance errors remained below 0.013%. Experimental validation against an industrial leachate FC test reproduced ice and mirabilite formation at −6 °C, where 118.7 kg of ice was recovered from 273 L of leachate. Simplified refrigeration energy requirements were 50.35–51.42 kWh/m³ recovered ice equivalent. The framework therefore quantitatively identifies distinct water, SO 4 2- , and NaCl-bearing salt recovery windows while providing a reproducible basis for thermodynamic screening and staged FC process design.
SN  - 1944-3986
SN  - 1944-3994
ER  -