Sciencemadness Discussion Board - Changing salt water (sea water) drinkable (or less poisonous) by replacement reaction or acid

Changing salt water (sea water) drinkable (or less poisonous) by replacement reaction or acid

RogueRose - 14-2-2017 at 10:14

I was thinking about how sea water can't be drunk unless run through a RO system or boiled and distilled. Both can be next to impossible while traveling light like hiking (or military missions).

I was wondering what the possiblities would be to adding a compound or acid to the sea water to change the salt to a less harmful substance, one the could be filtered out or one that could be gassed off by boiling.

I've looked at something like sulfuric acid to change the salt to sodium sulfate but that would leave HCl which I guess might boil off as the concentration would be pretty low and it might lower the BP (as I've seen in some other reactions).

I'm sure this has been looked into in the years past in the military (well at least they should have I would think).

Is there anything that can be added to precipitate out anything harmful and either allow remaining compounds (if safe) to stay in solution, or boil them off?

DraconicAcid - 14-2-2017 at 10:18

There are personal-sized reverse osmosis devices.

zwt - 14-2-2017 at 10:37

There is another technology for producing a potable liquid from seawater, which meets your requirements of being lightweight and simple:
Foward osmosis bag
The catch is that the liquid produced is not pure water, but a Gatorade-like carbohydrate/electrolyte beverage.

Incidentally, I question their claim "...drink any water found on the ground, no matter how contaminated." It seems like the bag would cease to operate if the concentration of soluble contaminates approached the concentration of the syrup, and even at somewhat lower concentrations of contaminants, the "drinkable" liquid produced might be too concentrated to hydrate whoever drinks it.

[Edited on 14-2-2017 by zwt]

Amos - 14-2-2017 at 11:02

Even if you were to precipitate the sodium and other ions (which only a very small handful of compounds are able to do), this could only be done by dumping more ions in, effectively making the process useless.

No acid is going to remove sodium from solution. And any sodium at all at the concentration found in seawater, regardless of the anion, will cause dehydration after a short time due to the extra water needed by the kidneys to dispose of it. The sulfate ion tends to have a laxative effect, by the way. So sodium sulfate is likely even worse to be ingesting in those amounts.

Quote:

I've looked at something like sulfuric acid to change the salt to sodium sulfate but that would leave HCl which I guess might boil off as the concentration would be pretty low and it might lower the BP (as I've seen in some other reactions).

A hydrochloric acid solution with a concentration below that of the azeotrope (20.2%, which you're not going to survive long drinking) will become more concentrated as it evaporates, since the vapor pressure is lower than that for normal water.

Scalebar - 15-2-2017 at 07:56

Quote: Originally posted by zwt

There is another technology for producing a potable liquid from seawater, which meets your requirements of being lightweight and simple:
Foward osmosis bag
The catch is that the liquid produced is not pure water, but a Gatorade-like carbohydrate/electrolyte beverage.

[Edited on 14-2-2017 by zwt]

When we demoed them at a science festival we used urine and made damn sure we 1. used our own bags not anyone elses and 2. drank out of the correct side...

PHILOU Zrealone - 15-2-2017 at 13:55

Maybe hydroxy anion exchange resins and proton cation exchange resins may be a solution to scavenge all cations and anions and replace them by water (H(+) + OH(-)).

Any precipitation reaction will generate worst problem or displace the saline problematic.
There are only a few reactions when precipitation leads to a purer water...but then there must be coprecipitation like BaS and FeSO4 yielding BaSO4 and FeS precipitates...and thus reducing strongly the amount of anions and cations into the water.
Such case will never happen with sodium since most/all of its salts are solubles...so if you precipitate the chloride, you will replace it by something else... another anion...so no gain.

A Halogenated Substance - 15-2-2017 at 14:05

This reminds me of a particular straw they are using in areas that have little to no access to fresh water. Perhaps you could inspire a design off of it?

07E50C05-47FB-4D50-B766-659FFAA75BB9-3375-00000464090269AF_tmp.png - 115kB

Ouch. The words are hard to see. But from top to bottom it says "activated charcoal, iodine crystals, and membrane filters".

Here it is in use:

5264FF7F-5698-4DB4-A979-19854C12034B-3375-0000046587BB4619_tmp.png.jpg - 58kB

pneumatician - 19-2-2017 at 15:22

asked the military? if you live in the usa, exist a law called "freedom act of info" or something like this.

[Edited on 19-2-2017 by pneumatician]

BromicAcid - 20-2-2017 at 04:45

PHILOU Zrealone is correct in mentioning ion exchange resins. Theoretically it's easy, a cation exchange resin replaces Na+ (and others) with H+ and an anion exchange resin replaces the Cl- with HO-, effectively replacing all cations/anions with water. In practice it can be difficult since the cation exchange resins are themselves acid/basic so the discharge water ends up skewed in pH and not a perfect 7. I have seen these setups used industrially with banks of exchange resin so they are practical but I am not sure if they are practical on the small scale.

PHILOU Zrealone - 20-2-2017 at 14:27

Quote: Originally posted by BromicAcid

PHILOU Zrealone is correct in mentioning ion exchange resins. Theoretically it's easy, a cation exchange resin replaces Na+ (and others) with H+ and an anion exchange resin replaces the Cl- with HO-, effectively replacing all cations/anions with water. In practice it can be difficult since the cation exchange resins are themselves acid/basic so the discharge water ends up skewed in pH and not a perfect 7. I have seen these setups used industrially with banks of exchange resin so they are practical but I am not sure if they are practical on the small scale.

Thank you for pointing this out

Also to be noted that it is best that the water is not completely desionized if it has to be used for drinking...so even if process is uncomplete it is not a bad thing.

About the final pH...if it remains into the range of 6-8 it is physiologically fine (many drink water are into that range depending onto their origin...some are even outside this but those are special water for cures/special diets).

macckone - 20-2-2017 at 16:55

I use a prefilter and reverse osmosis filter when camping.
I also carry iodine and chlorine dioxide tablets.
The prefilter is important for really turbid water.
UV pens will kill most bacteria if prefiltered.
Ps. Military uses prefilter then RO.
The personal kits are a couple of ounces.

[Edited on 21-2-2017 by macckone]

symboom - 20-2-2017 at 17:40

Sea water
Adding Silver nitrate to form silver chloride and Sodium nitrate
to the sodium nitrate adding urea citrate to form urea nitrate
Calcium ascorbate to form insoluble calcium sulfate from the magnesium sulfate present in water

The ions left are magnesium ascorbate and sodium citrate both are need when at sea for prevention of scuvy
Would this work as a safe ion removal technique the salts present

A Halogenated Substance - 21-2-2017 at 14:24

Quote: Originally posted by symboom

The ions left are magnesium...

Doesn't the magnesium ion act as a sort of laxative? I'm not sure if constant laxative use is exactly great for one's bowels...

If you wanted to rid of this, you could try to add an alkali metal hydroxide or carbonate to precipitate out the majority of the magnesium and leave it as a trace; you would also then be left with sodium absorbate instead.

PHILOU Zrealone - 22-2-2017 at 14:53

As exposed above it is only displacing the problem...the water contains too much ions and its osmotic pressure makes it non drinkable in medium to large amount...