removing sodium ions from a sodium salt solution

just want to clarify what you are asking. Basicaly you have a salt solution from which you want to remove the sodium only. Obviously that would leave either a different salt solution or an unstable and heavily ionized cloride solution. substition of the metal is not an available option. Is nonmetalic substitution possible? and have you tried using mechanical means such as electrostatic or magnetic fields to drag the sodium to one location - out of the process area?

You can't chemically precipitate out sodium due to its high solubility in water. You didn't state what your salt concentration is. If it's 10,000ppm & below, you can try using electrodialysis. This process will separate the cations and anions from the water. Since you want to retain the cations, you can recombine them back into the purified water stream at the outlet.

An added advantage of using this process is that you will also recover valuable NaOH as a byproduct, thus reducing your operational costs.

Try a EDI system. (electronic de ionization). You will have very heavy solution left over and there will be a chance for hydrogen gas to form so you will need a scrubber to reclaim the gas loss or to vent it.

Ammonium carbonate, or sulfide????