MadSci Network: Chemistry

Re: What are some ways to desalinate water?

Date: Mon Dec 15 12:51:19 2008
Posted By: Luis Sojo, Faculty, Chemistry, Simon Fraser University
Area of science: Chemistry
ID: 1228701014.Ch

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.


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