A novel low cost way to desalinate water

Someone wise once told me that oil is a replaceable convenience but water is life. The sad fact is that we are running out of fresh water, so we will become increasingly dependent on desalination to meet our needs. Israel already has to use desalinated water for crops. The current technologies for desalination are distillation and reverse osmosis, with some plans for solar evaporation in warmer areas. The issue with these technologies is they require a lot of energy.While partial vacuum distillation in combination with cooling of nuclear or coal plants is efficient most distillation desalination methods are inefficient. RO while it is more efficient than distillation requires expensive membranes that are quickly destroyed by contact with seawater.My idea is to use ion exchange to desalinate or at least reduce the total dissolved solids in the water. When most people think of ion exchange they think of water softening, where resins trade Ca and Mg ions for Na ions. But desalinization is a totally different problem, since you have to get rid of the NaCl, and this is normally a deionization problem. Ion exchange resins have been used for direct desalination but to do this they exchange H for Na and OH for Cl, so they be regenerated with expensive chemicals and the salt quickly destroys the delicate resins needed for deionization.

My suggestion is indirect desalinization, where the Cl is replaced with CO2 and Na replaced with Ca. As long as there is an excess of CO2 present the Calcium Bicarbonate will remain in solution. This will prevent fouling. Then the magic happens, the water is purged of CO2 and the insoluble Calcium Carbonate (limestone) falls out of solution. The once the water is mostly de-ionized it can be used for non-drinking applications, or further polished and made potable. The limestone and CO2 are then mixed with a small amount of fresh water and pumped back into the resins to recharge them. The concentrated brine is flushed out and the resins can be used again. Since the Ca and most of the CO2 is recovered the system could be very efficient. The resins are exchanging the ions of solids they do not have to be that high grade, and can be designed to allow acid/base regeneration to restore them. It is possible that clays or minerals could be used in place of synthetic resins. However, I did some quick back of the envelope calculations and it should be possible to chemically modify recycled plastics for this application. I believe it should be possible chemically treat shredded HDPE and PP to serve as ion exchange resin. By using a very low cost resin this process could be a viable large desalination method. Someday old soda bottles could provide us clean drinking water.