j paul
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not dehydration
Desalination
not dehydration
most so called desalination systems involve taking a volume of sea water and removing part or all of the water.
A commonly used demo in school chemistry lessons is the addition of silver nitrate solution to a sodium chloride solution, to give a sodium nitrate
solution and a precipitate of silver chloride. Silver is expensive and sodium nitrate can be used to prevent unwanted erections. So this is not a
practical process for precipitating salt to make drinking water, and the only reason for mentioning it is to remind you of the types of chemical
precipitations that will be needed to remove most of the salts from sea water.
note<br> Most of us get get our drinking water from rivers. River water has an average of approximately 118.2 mg per litre of dissolved salts.
Roughly 300 times less salty than sea water, but 16.6 times more salty than rain water.
Although sea water contains measurable amounts of over 80 of the known elements, and probably contain most of the other natural elements in lesser
amounts. 99.9% of the salinity of sea water comes from.
<br>Chloride 18,980 grams per litre<br>Sodium 10.556 grams per litre<br>Sulphate 2.649 grams per litre<br>Magnesium 1.272
grams per litre<br>Calcium 0.400 grams per litre<br>Potassium 0.380 grams per litre<br> Bromide 0.065 grams per
litre<br>Borate 0.026 grams per litre<br>Strontium 0.013 grams per litre<br>Fluoride 0.001 grams per litre.<br>
What follows are four atempts on the idea of how it might be possible to remove the salt from a volume of sea water, leaving behind potable water.
one<br>First the calcium and magnesium are precipitated as hydroxides, by adding 2.7 grams per litre of sodium as sodium hydroxide. This used
to be the way that magnesium was extracted from sea water Then the chloride and sulphate are removed by adding lead fluoride. Giving a solution of
sodium / potassium fluoride and precipitate of lead chloride / sulphate / oxychlorides etc. This solution is then passed through a bed of alumina,
the sodium fluoride reacts with the alumina to form cryolite, sodium aluminium fluoride, an insoluble mineral that will remove the fluorine and half
of the sodium from the solution. The rest of sodium forms sodium aluminate, a soluble mineral, that is used as a water softener. The sodium aluminate
becomes less soluble as the water is cooled, and can be used to regenerate the sodium hydroxide. Filtering trough chalk will remove any excess
fluorine<br>the area of doubt here is with regards to the potassium, is there a potassium cryolite. And can enough of the aluminate be removed
without using to much energy for cooling
two<br>Remove the; calcium, magnesium, as above. Follow this by adding lead acetate. This will precipitate the lead chloride / sulphate /
oxychlorides leave a sodium and potassium acetate solution. Sodium and potassium acetates are the food additives E262 and E261. The sodium and
potassium can be removed by passing it through an aerated bed containing; alumina, silica and an aerobic bacteria that will consume the acetate. The
potassium and sodium will react with the alumina and silica to form insoluble zeolites and clay minerals. This water would need conventional treatment
to remove the clay and bacteria<br>the area of doubt here is that the sodium can not be easily recycled.
three<br>Remove the; calcium, magnesium, chloride and sulphate as above, this time using metallic lead electrodes, and a low current AC supply.
At the anode a coating of lead sulphate and lead chloride starts to form, but this flakes of when the current reverses. As the lead electrodes are
eaten away, the solution becomes more caustic and the calcium and magnesium precipitate out. The sodium / potassium hydroxide solution that is left
can be filtered through a mixed bed of low grade bauxite and sand.<be> draw backs here are the cost of electricity. and the fact that the
magnesium and calcium will be mixed in with the lead salts, possibly making recovery of the lead more complex
four<br>for use on life boats etc.<br>part of the standard safety equipment could be two large foldaway water tanks, that can be filled
with sea water as needed. And a box containing 100 pre measured doses of powders A & B. powder A is silver citrate and powder B is a finely ground
mixture of alumina and silica. Add A leave a couple of hours then add B, the next day you have a tank of drinking water.
NaCl and H2O are chemicals. So why should it be left to the physicists to turn sea water into potable water. There has to be a good chemical solution,
even if these meagre efforts are not it, and there is hopefully enough brain power on this site to find it.
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elementcollector1
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...Why was this suddenly brought up?
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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unionised
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Just for a start, lead chloride is rather soluble in water (about 1%w/w) and also toxic.
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Pyro
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sodium nitrate might be useful for my next ME at school 
all above information is intellectual property of Pyro. |
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blogfast25
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And so is Ca(OH)2...
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bbartlog
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Your proposed methods are not competitive with existing desalination technology in any way that comes to mind. And to second blogfast: Ca(OH)2 is not
*that* insoluble, and drinking a saturated solution would be very bad for you indeed (I think the pH is over 13).
Depending on your goals, you could simplify the problem by trying only to reduce the sodium and chlorine load by 90%. The levels of magnesium,
sulphate etc. are not harmful even if they likely make for a less pleasant drinking experience.
The less you bet, the more you lose when you win.
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j paul
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As you may have guest I am not a chemist, and I’m just putting together things that I have read. So if I have been misinformed about lead forming a
white curdy precipitate and that Mimetite and Pyromorphite are not insoluble lead minerals, I’m sorry.
Forget about lead, use Silver, or is there a better way to remove the chloide?
As for the economic argument, it is impossible to make the case either way until you know; what the process is, what useful bi products come out of
it( Zeolite cryolite or gold ), and how much of the reagents can be recovered and reused it will be impossible to say.
But for now there aught to be a set of chemical processes to make sea water drinkable? What are they???
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smaerd
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Forgive my ignorance but whats wrong with the reverse osmosis technology?
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bbartlog
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In the sense that one can't fully prove a negative, I suppose that's technically true. However, extremely strong arguments can be made against the
economic feasibility of chemical desalination. Consider that current costs for other technologies are about US $0.50 per ton of water. You would have
to find a way to precipitate about 30 kg of salts while using less than $0.50 worth of reagents in order for chemical purification to be on the same
footing as flash desalination.
| Quote: | | There has to be a good chemical solution |
Not necessarily.
The less you bet, the more you lose when you win.
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Poppy
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So comes with a vitamin rich and also improved, flavoured, sweetened water! 
Bubbling exhaled CO2 through the solution would cause a lot of stuff to precipitate.
Put on this, the reasoning promotes some interesting thought experiment: what if we drinking salted food everyday, and that salt contains trace
ammount of lead, fish and sushi would pose a major risk accounting for magnification of lead levels retained in living organisms.
We are all prone, rather slowly, of acquiring dementia, which may point out the causes of the cultural disorder experienced by the modern
civilizations.
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