Freezing Saltwater to Remove Salt: A Model for Efficient Desalination

What is it about?

This study explores a smart way to turn salty water into fresh water by freezing it, focusing on how salt behaves during the process. Usually, when you freeze saltwater, the water turns into ice, and the salt gets pushed out into the remaining liquid (called brine). But sometimes, salt gets trapped in the ice, making it hard to separate and get pure fresh water. We created a mathematical model that predicts how salt moves based on temperature changes and salt concentration differences. By controlling the freezing speed and temperatures, we can "push" more salt into the brine and leave the ice cleaner. This method uses much less energy than boiling or filtering water through membranes, as freezing only needs about 30% of the energy compared to evaporating water. We tested the model with sodium chloride solutions (like table salt in water), which mimic seawater. The goal is to make desalination cheaper and more eco-friendly, especially since fresh water is scarce and demand is high. Unlike other methods that rely on expensive equipment or chemicals, this freezing approach is simple, reduces corrosion, and has a low environmental impact. Our calculations show how to adjust conditions like cooling rates to optimize salt removal, potentially leading to better designs for desalination plants.

Featured Image

Photo by Aaron Burden on Unsplash

Photo by Aaron Burden on Unsplash

Why is it important?

This work is unique because it provides a detailed theoretical model that links heat transfer and salt diffusion in real-time during freezing, addressing a key challenge in freeze-desalination: preventing salt from getting trapped in ice. While freezing desalination has been known since the 1960s, it's underused due to separation difficulties. Still, our model uses precise calculations at the ice-brine interface—where most studies disagree on salt levels—to predict and improve outcomes. It's timely amid global water shortages, with over 44 million cubic meters of desalinated water produced yearly, mostly via energy-intensive methods like multi-stage flash or reverse osmosis that consume fossil fuels and harm the environment. Our approach could cut energy use by up to 70%, making it viable for remote or low-resource areas. The impact? It could boost adoption of freeze-desalination, reducing costs, minimizing chemical use, and enabling scalable, sustainable fresh water production—potentially transforming industries like agriculture, food processing, and coastal communities facing salinity issues.

Perspectives