chief
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MgCO3 from MgSO4 + Na2CO3
Can I use stoechiometric amounts of MgSO4 and Na2CO3 to precipitate/ react _all_ the MgSO4 ==> MgCO3 (100% efficiency) ?
Does it need to be cooked, and how long ?
Main question: Is the reaction 100 % or is there some equilibrium ?
I want to get the Na2SO4, without the MgSO4.
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12AX7
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99% or so. MgCO3.(a couple hydrate) isn't completely insoluble (Ks ~ 10^-6).
Since Na2SO4 and MgCO3 have widely different solubilities, it would be easy to get arbitrarily good isolation through recrystallization.
Tim
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woelen
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Precipitation reactions are not the best way to obtain pure compounds. You will suffer from coprecipitation. So, you will have Na(+) ions and SO4(2-)
ions, encapsulated in the MgCO3 precipitate, and it will be quite hard to remove these ions (they can be encapsulated very well, i.e. caged).
The efficiency, however, is high. I think that 12AX7 with his 99% gives a very reasonable estimate, maybe it even is somewhat better. Efficiency is
not the problem, purity of the end-product is the problem. VERY good rinsing after precipitation helps cleaning the end-product, but you will not get
is totally free from Na(+) and SO4(2-).
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Eclectic
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If you boil the mixture a bit, you will get a denser product that settles faster. Then you can decant the excess liquid and boil with clean water
several times to remove solubles. Vacuum filtration will make a filter cake that dries faster than gravity filtration.
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not_important
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If you want true MgCO3, then you can't use Na2CO3 which will give a basic carbonate of one sort or another : X MgCO3 . Y Mg(OH)2 . Z H2O, for some
actual minerals X=1, Y=1,Z=3 and X=4,Y=1,Z=4 or 5.
I you just an insoluble magnesium compound for making other magnesium salts from than a basic carbonate will do just fine. If you want true MgCO3 the
you either you a solution of NaHCO3 saturated with CO2, or a suspension of Mg(OH)2 or a basic magnesium carbonate that you saturate with CO2. The
mix must be not be hotter than 50 C or so, the MgCO3 will precipitate out as the CO2 is allowed to slowly escape.
The commercial magnesium carbonates are basic carbonates, if done with cold dilute solutions you obtain the "light magnesium carbonate", hot
concentrated solutions give the "heavy magnesium carbonate". Most commercial applications use the basic carbonate, true MgCO3 is pretty much a lab
chemical.
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chief
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Very interesting. But I want to get some Na2SO4, and if possible: clean from any MgSO4.
The carbonate is a byproduct, to be stored and forgotten. How clean is then the Na2SO4 (99 % too ?) ? Or is it any NaHSO4 ? In the moment I have
cooked stoechiometric amounts of the MgSO4 * 7H2O and Na2CO3, and the precipitate is setting ...
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YT2095
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Hmmm... I`m curious about something here are you Sure you want NA2SO4 and not NaHSO4?
the reason I ask is that Na2SO4 is really quite boring for most reactions but you can do plenty with NaHSO4.
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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chief
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I just want an melt of salts, within the melt the SO4, and Na has to be in it. Main thing: It behaves as an sulfate, and does no strange things at
temperatures up to at least 400 [Celsius]
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Antwain
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easiest way to Na2SO4 is OTC caustic soda + OTC battery acid. The method you are proposing will work, but it will be a royal pain in the arse, believe
me. Once, in my more inexperienced days, long before I could get nitric acid, I wanted nitric acid, and figured correctly that if Na+ ions weren't
going to be a problem I could use NaNO3 + H2SO4 to make it in situ, and it worked quite well. Problem was that I could only buy Mg(NO3). 6 (IIRC) H2O.
I experimented with both Na2CO3 and NaOH to precipitate the Mg2+. The carbonate was far inferior to the hydroxide, it made an EVEN MORE voluminous and
gelatinous precipitate, and fizzed when heated. Even using NaOH it was a pain. For 500g of the nitrate I needed to use ~5L of water, which had to be
boiled down and took more than a week per batch because it takes forever to settle down, even in a 2.5L jug (which needs to be filled and decanted
several times). So it can be done, but I would strongly recommend finding another way.
if you have H2SO4, use NaOH or Na2CO3, if not, buy NaHSO4 as pool acidifier and add Na2CO3 to that.
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YT2095
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ok cool, I`m sure you have your reasons, I was just making sure 
can you get your hands on Sodium Hydroxide (Lye) at all? if you can get that and make the Hydroxide of magnesium, it`s a whole order of magnitude less
soluble 
makes cleaning up and purification just that little bit easier!
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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woelen
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Oh chief!! You really want to MAKE Na2SO4? This is so boring and so common in most places of the world. It can be purchased as a mild laxative (not to
be confused with MgSO4.7H2O).
But if you really want to make it, then either use NaOH + H2SO4, in molar ratio 2:1 or Na2CO3 + H2SO4 in a 1 : 1 molar ratio. Adjust, such that the pH
is slightly over 7. Then boil down. Also the use of NaHSO4 as pH-minus for pools is a nice option. Antwain really is right, these methods are much
easier than the precipitation method, which also surely will leave amounts of magnesium in the solid.
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chloric1
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Cheapest way
If you add sodium bicarbonate continuously to battery acid eventualy a cake of fine crystals will settle. This can be recrystalized from distilled
water and cooled to give the decahydrate which can be dehydrated in a 200 degree oven to anhydrous salt. The pH minus is even cheaper than battery
acid and you will get huge amounts. Just remeber bicarbonate until fizzing stops. Chemistrystore.com sells 3 lbs CHEAP. It is not hazmat.
Fellow molecular manipulator
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not_important
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| Quote: | Originally posted by chief
Very interesting. But I want to get some Na2SO4, and if possible: clean from any MgSO4.
The carbonate is a byproduct, to be stored and forgotten. |
So you title your thread after the byproduct you don't care about, rather than the product you want.
| Quote: | | How clean is then the Na2SO4 (99 % too ?) ? Or is it any NaHSO4 ? In the moment I have cooked stoechiometric amounts of the MgSO4 * 7H2O and Na2CO3,
and the precipitate is setting ... |
Because the precipitate is not MgCO3 but a basic carbonate, your stoichiometric proportions aren't necessarily stoichiometric. You won't have any
NaHSO4, the basic carbonate would react with it, but you might have some magnesium left in solution.
As other have said, you would have done better to start with NaHSO4 and avoid having any magnesium to worry about. Alternatively boiling a solution of
equal molar amount of ammonium sulfate and sodium carbonate will result in the loss of NH3 and CO2, leaving sodium sulfate.
BTW, washing soda - sodium carbonate heptahydrate - loses water to form the monohydrate. Unless you've done the proper treatment you have some
variable and unknown amount of water, somewhere between the monohydrate and the heptahydrate; this is why it's better to use soda ash, the fully
dehydrated sodium carbonate, if you're going by weight and not titrating to the end point.
[Edited on 27-9-2007 by not_important]
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smuv
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Sodium bisulfate can be obtained from pool supply stores as pH down, and upon neutralization with sodium carbonate will also yield sodium sulfate.
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chief
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I have about 20 _old_ car-batteries in the basement: How good will be that acid for the purpose ?
They are not charged and probably have 0 voltage.
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woelen
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That acid is perfectly useful for the purpose of making raw Na2SO4. Just add Na2CO3 or NaOH, as suggested. Work slowly, because of strong bubbling
with Na2CO3 and strong production of heat with NaOH.
Recrystallization once will make the material sufficiently pure for all practical purposes.
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Mr. Wizard
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| Quote: | Originally posted by chief
I have about 20 _old_ car-batteries in the basement: How good will be that acid for the purpose ?
They are not charged and probably have 0 voltage. |
You can increase the strength of the acid in the old car batteries by charging them up as much as possible, before dumping the acid from them. Be sure
all the cells are filled with distilled water first. If lead or other heavy metal contamination is a problem with you resulting Sodium Sulfate, you
may want to use another source of acid. The Lead Sulfate is "insoluble " but still enough is present at 1.7 x 10-8 to be concerned with. Battery
electrodes can contain Calcium, Antimony and other metals. That solubility constant may vary when in a very low pH electrolyte.
[Edited on by Mr. Wizard]
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chief
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"Battery electrodes can contain Calcium" ? Whatfor calcium ? As what sort of compound ?
As I understand the charging would use up the lead-lulfate and generate H2SO4; has anyone tried to manufacture H2SO4 like that ? Generate the
lead-sulfate somehow and then do the elctrolysis.
Maybe it could be as easy as alternatingly putting different electrolytes into such a lead-battery:
H2O for H2SO4 - generating; then maybe Na2SO4 + electrolysis for re-generating some lead-sulfate (NaOH would be generated: If it harms the electrode
one might insert additional Iron-electrodes during that part of the reaction; then again the H2O + SO4 ==> H2SO4 electrolysis and so on.
Industrially that process would, of course, be inferior to the direct SO2 ==> SO3 oxidation, but for experimentation it might be a simple way ????
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not_important
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Metallic calcium as an alloy with the lead. Improves some the operational characteristics, including resistance to corrosion, overcharging, gassing,
and self discharge.
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Mr. Wizard
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The Calcium is there , but I don't know it's exact purpose, possibly to strengthen or preserve the integrity of the plates. I do know it can cause
problems for casting lead bullets or others using batteries for their Lead. The dross, or floating crud that is removed from a pot of molten Lead
batteries will contain Calcium and Antimony. If this dross or even the finely divided alloy comes in contact with water or acid it will generate
Hydrogen, and also Stibnine and Arsine gas as a result. Many sources of shooter's Lead contains Arsenic as a hardening agent for Lead shot. These
gases are very poisonous. The Lead and the Sulfuric Acid in batteries are not their only hazard.
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