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Ion Exchange of NaCl from H2O

  1. Jan 2, 2009 #1
    Leaving the physics out of this, I'm working on an idea for an in home MHD generator. I'm trying to figure out a conductive fluid to use. I'm back to the idea of salt water, or H20 + NaCl. I know this is a very conductive solution, but I'm no chemist. What I plan to do is put a MHD generator and use the water pipes leading into a home, to provide the flow of the fluid, since it's already a pressurized system with decent flow when anyone uses any water in the home.

    I've read though that the basic result of adding NaCl to H2O is that it forms two ions, Na- and Cl+ along with H+ and OH-. Is this correct? What is one just adds Na or just Cl to water (H2O)? What is formed? One main concern is removing the additives from the water after it's passed through the generator, so how does one go about quickly, and effectively removing the Na and Cl from water? I know off reverse osmosis, electrodialysis, and ion exchange that do not involve boiling the water. Ion exchange seems like the best option. Electrodialysis would work but it's a very slow process it seems. I'm looking for something that can remove the sodium and chloride from the water and would not effect the pressure or speed of your basic shower head, or faucet. With an ion exchange though, seeing as both H+ and OH-, how does an ion exchange work to only change out the Na- and Cl+?

    I am thinking that I could use two ion exchanges, one before the generator and one after the generator. The basic idea would be to replace any ions (fluoride, calcium, potassium) in the water with Na and Cl (salt) before the generator, then after the generator take the NaCl back out of the water and put the original ions in. Is this design feasible?

    I previously had a partner working with me on this project and he was the chemistry guy but I've had to take over the whole thing for a while here, and I'm just not too well versed in chemicals/molecules and exactly how it all interacts.

    Thanks
     
  2. jcsd
  3. Jan 2, 2009 #2

    Borek

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    Staff: Mentor

    Not doing any calculations one can easily predict that amount of energy consumed for retrieving NaCl from water will be many times higher than amount of energy gained through MHD.
     
  4. Jan 2, 2009 #3
    I understood the bases for ion exchange though to be passive not requiring any energy (from the outside) for the actual exchange. It's simply diffusion of the atoms. Correct me if I am wrong, but thinking back to the biology classes I've taken, and I remember that the kidney and I believe it was neurons use this technique of passive diffusion to work. I know in the kidney there are parts that are actively transported via ATP, but I though most was done passively. In the same respect I was under the impression that ion exchange in this case would be passive too.

    Perhaps NaCl is not idea, maybe simple Na- ions? Then to take it out of the water via ion exchange you would just need a substance with a strong + ion concentrations, if the membrane is only permeable to Na-, the the sodium would diffuse out of the water.
     
  5. Jan 3, 2009 #4

    Borek

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    Staff: Mentor

    No such thing as Na- ions (Na+ it is).

    Simple diffusion ends with a uniform distribution. What you want to do is to obtain non-uniform distribution. That always requires some energy input.
     
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