|MadSci Network: Chemistry|
Dear Mendel, Desalination of water using an electric current is not a straightforward proposition. First the key ions that you need to remove, namely sodium, potassium, magnesium and calcium, are very difficult to reduce by electrolysis. This way of removing ions from solution is based on making them react with an negative electrode, neutralizing their charge and resulting in the ions being "plated" onto the electrode. For the case of sodium and the ions mentioned above, this requires lots of energy. A cheaper mean of desalinating water is to boil the water a low pressure, this means that water will boil at lower temperature instead of 100 degree C thereby requiring less energy in the process. Another way is to use what they call reverse osmosis. In this process the water molecules are pushed are through a membrane leaving the ions on one side of the membrane and pure water on the opposite side. The water is forced from a region of high salt concentrationto a region of low salt concentration by applying a pressure in excess of the osmotic pressure of the solution. This process can also be driven by an electric potential on both side of the membrane. I hope this answer your question. Luis
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