Work

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

Year: 2026

Type: article

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 percentage points and RMSE was 0.587-0.660 percentage 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.

Source: Desalination and Water Treatment

DOI: 10.1016/j.dwt.2026.101998

Authors: Kagiso S. More, Ravi Rangarajan, Johannes P. Maree

Institutions: University of Doha for Science and Technology, University of South Africa

Language: English

Topic: Freezing and Crystallization Processes

Subfield: Filtration and Separation

Field: Chemical Engineering

Domain: Physical Sciences

SDG: Responsible consumption and production

Open Access status: gold

Estimated APC paid: $1,000