Removing Salt from Water By Other Means Than Evaporation?

If you mean salt as 'sodium chloride' then there is no way except evaporation since

sodium chloride is highly soluble in water at room temperature . But your question is

ambiguous .You did not mention the application for this need .Little quantity of water

may be removed by sodium metal ,anhydrous calcium chloride etc.

Ashraf

Could you give me a lot of research and experiments on the evaporation of salt water vs. fresh water

o ya

This is commonly done by reverse osmosis, in sea water deslinization plants.

Also you could probably form a precititate if you added something like silver nitrate (in which case silver chloride would preciptate out of solution). There are probably other ways of precipitating compounds out of salty water -- maybe googling will turn something up.

There are some ion exchange methods but I think they're hard to use and expensive.

Well, it depends on the relative cost of low-grade energy from an engine cooling system, as might be found in an evaporator, or the value of electricity, which depends upon the circumstances of operation.

4kWh per m³ produced is relatively easy for a seawater reverse osmosis plant, depending on size. With a pressure-exchanger fitted at the back end of the plant, much lower electrical consumption figures can be produced. The plants on the island of Cyprus are good examples.

600kWh per m³ is about the going rate for seawater evaporation. Then, if there's loads of free cooling water available, one might as well use it and save the electricity bill....

If we assume you are using the general meaning of "salt", i.e. NaCl and you do not care what other chemical elements remain in the water, then there are several methods. An Ion Exchange column will substitute one element for another including Na and Cl. Adding a chemical that will form an insoluble precipitate such as AgNO3 (Silver Nitrate) will remove the Chloride from solution.

If you want to remove any chemical impurities, then either membrane filtration or reverse osimosis will work. These are physical methods not chemical, but they are not evaporation. This method can "clean" water until essentially only water molecules, hydronium and hydroxyl ions remain.

I haven't taken the time to find a reference, but you should be able to pass current through the solution and evolve the Chloride off as Chlorine gas and plate the Sodium onto an electrode. The conditions, anodic and cathodic material, and power consumption would have to be well controlled but should be do-able.

If you are simply interested in de-salination then this website has some good information: http://www.zenon.com/

This website also has information on companies that treat water and wastewater and is an interesting read: http://pubs.acs.org/cen/coverstory/8046/8046water.html

Hope this helps.

Wouldn't passing a current through the solution also evolve H2 and O2 while enriching your solution in NaOH? i.e. this removes the Cl but not the Na.

Chlorine producers use diaphragm electrolytic cells to seperate brine into chlorine gas and concentrated sodium hydroxide. If a diaphragm cell is not used, electrolysis of salt water converts to sodium hypochlorite and hydrogen gas.

aqua doc, thank you for the support on my comment.

The sodium hydroxide is formed due to the reactivity of metallic sodium with water. To remove the sodium from the cell without forming sodium hydroxide and hydrogen gas, one uses a mercury electrode. As the metallic sodium is formed it immediately forms an amalgam with the mercury and is effectively removed from the cell.

without Hg electrode: 2Na° + 2H₂O → 2NaOH_(aq) + H₂↑

with Hg electrode: Na° + Hg° + H₂O → Amalgam + H₂O

You are correct about the gas evolution if you use platinum electrodes in a simple cell. I am not even sure you would remove chlorine with this set-up, just increase the salt concentration.

As I stated in my comment, "The conditions, anodic and cathodic material, and power consumption would have to be well controlled...". This is the key to selectively electrolyzing solution components.

Yes, the products of the electrolysis of water is H2 and O2. The products of NaCl solution electrolysis would evolve Cl2 as well. I don't believe NaOH has to be the other product. That is why I included selecting the proper electrodes and conditions so that the Na would plate (it would also have to be isolated from the water to prevent an explosion).

Concur with 'habib'. One is left with a concentrated NaCl solution, and H₂ and O₂ gases.

<concentrated NaCl solution>

Typo spotted. That should read concentrated NaOCl solution, i.e. sodium hypochlorite.

A dual ion exchange column will do this. one type of resin bead removes the Na+ and exchanges it with H+ and the other one removes the Cl- and replaces it with OH-.

These are use once types.

For reuseable you need two columns You recharge one with KOH and the other with HCl.

......and this is widely done in industry to generate boiler feed water. Good point.

"Can salt, totally dissolved in water, be removed by anything other than evaporation?"

YES

Why isn't 0 deg F the lowest possible temperature for salt/ice/water, mixture?

Besides evaporation, there's reverse osmosis (RO), ion exchange (IE) and electrodialysis (ED) as well. Chemical precipitation is only possible if the salt you are trying to remove has insoluble compounds as well e.g. CuCl2 + 2NaOH = 2NaCl + Cu(OH)2 ppt. If you're trying to remove sodium or potassium salts, or nitrates, sulfates or chlorides, you'll have to use RO, IE, ED or evaporation; it's almost impossible to chemically preciptate out any of these compounds.

Depending on the salt concentration, several methods of removal can be employed. At low concentrations a mixed bed of anion and cation ion exchange resins will work just fine. At high concentrations one is talking about membrane processes; reverse osmosis [RO] is the one commonly employed on seawater, and many ocean-going vessels from yachts to cruise liners to aircraft carriers to oil-and-gas platforms have been fitted with this process equipment.

The recent cross-Atlantic rowers had a small RO plant built into the vessel, powered by a solar cell with battery storage, to generate a potable water from seawater.

This is the process of a Desalination plant - but from what I know, these plants are expensive to run and DCROR is very low. Also, consider reverse osmosis.

You guys hit all of the major ones, but nobody mentioned freeze / thaw separation. Using ambient temperatures (in an area with winter temperatures that are regularly below freezing) one can produce a cycle of freezing and thawing to create a relatively pure stream of water and a brine concentrate. This is done with produced well waters in the Northern US and Canada.

I prefer RO since that is what I design, but several of the above methods also work. I should note that RO is only good to about 99.7% removal and produces a brine stream that must be delt with.

Stephan

www.bradleyventures.com

How pure do you want the water?

purity is immaterial to me.

Now imagine we have continuous solution of water with HCL in traces present.specially when we use in HCL scrubber.Waste contains HGL, we mostly treat with NAOH , which gives salt of NACL inw ater.It is totally soluble. authorities accept TDS not exceeding 350 ppm.how doI release waste water when NACL in water wille xzceed 1500 PPm.?

Only solution I have ( non technical- aadd lot of fresh water tor educe TDS%)

Dinkar Vora

info@motivepowers.com

Freeze/thaw is commonly used on large scale applications. Salt water is partially frozen, the ice filtered out, the ice washed with fresh water to remove residual salt water entrained in the crystals, then melted to produce fresh water. Feed water is used to do the melting to recover energy.

RO is another application commonly used. It is energy intensive.

Ion exchange resins can be used as well, but salt water requires a lot of regeneration and that is expensive.