Freeze desalination is a low energy consuming way to remove salts from water. As the water freezes the cristaline structure it adopts pushes out ions resulting in fresh water ice. Ice floats on water so the fresh water ice can be separated from the remaining salt brine, and the brine can be cooled to lower temperatures ensuring the ice does not melt into it.
Water that freezes pushes out salts and other pollutants
The most common way to desalinate today is RO, or Reverse Osmosis, which alludes to natural osmosis (water moving towards higher salt concentrations). It has nothing to do with osmosis, it is simply filtering out salt ions. Because these ions are small and are bound by water this takes a lot of energy, which the fossil credit economy deems a good thing because it generates cashflow and allows you to sell expensive water. What is good for the economy is not good for human survival though.
Another common way to desalinate is to evaporate water. This can be done with heat but also by pulling a vacuum. The heat method is preferred because again it uses a lot of energy and it makes water high cashflow. Water can be heated up to 100 Celsius but to get to steam you need to put in extra energy. This is because water is polar and kind of snugs into itself. As you can see in the graph above as you put more energy in water (horizontal axis) the water temperature rises (vertial axis). You see that you need a lot of energy (twice as much to get from 0 to 100 Celsius!) to get from 100 Celsius water to 101 Celsius steam! This means steam desalination of ice cold ocean water can take up to three times more energy than freeze desalination!
There are two main challenges : first to cool the water most efficiently, second to remove the fresh water ice from the brine with the least amount of loss. You can do decades of research on this topic, and it is being done, but the solution to both problems are quite easy to bring to a reasonable level.
There are many ways to cool, one is to create a vacuum, the other is to use compressors to compress a gas that can then extract heat (like ammonia). This requires energy, which can come from any source, wind, solar, or from the grid.
Diving into patents for desalination I came across this one, using metal redox reactions to power removal of salts. The interesting aspect is that the voltage is low and power consumption is low as well. The idea is simply to react the ions away, which because they form chains of ‘charged’ molecules will precipitate out of the liquid. This aspect of behaviour of ions in fluids is a largely unknown field of research. Water for instance being polar should chain up if a current is applied over a distance.
It is surprising how hard it is to find examples of freeze desalination processes. It seems to have gotten harder. I read the below in this publication. Very little detail is shared, and all searches also yield a lot of RO information.
“The HybridICE™ technology was shown to be a better option than other desalination technologies currently in use, in terms of energy utilization and cleaner by-products.”
Some studies lead to combining freeze desalinaton with RO, which seems like a big waste, kind of a cruch of sorts..
Freeze desalination can easily remove the worst of water pollution, which can be helpfull to make industrial processes less damaging.
“Freeze desalination by crystallization seems to be successful
mainly due to its ability of producing high quality product with
much lower energy requirement as compared to other available
“The proposed method had a theoretical energy consumption of only 58% of that needed for -contact freezing methods-. With gravity filtration separation of the produced ice–water mixture for 20 min or centrifugal dehydration for 1 min, a 0.5% salt content standard for freshwater and a 60% freshwater yield were attained. In addition, the method produced ice crystals with minimal impurities, after brine attached to the surface was removed through centrifugal dehydration, a 0.05% salt content standard for drinking water was achieved.” (source)
It would be a challenge to build a freeze desalination device myself, as it only seems to require a freezer and salt water. I do have a salinity measuring device.
Mata Hari (welcome to Greencheck.nl)