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Author: Subject: MnO2 -> MnSO4; What is the best route?
Hilski
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[*] posted on 2-10-2006 at 08:49
MnO2 -> MnSO4; What is the best route?


I have about 1kg of MnO2 that I would like to try and convert to MnSO4, and I was wondering what the preferred method would be.
In all my searching, really the only way I have been able to find is (from the "Toluene -> benzaldehyde" thread) to heat the MnO2 with an excess of HCl to convert it to MnCL2, and then disolve the MnCL2 in conc. H2SO4. After evaporating the liquid, one should be left with MnSO4. Is this the best/most direct way to do it?

What would you end up with if you were to heat the MnO2 with conc. H2SO4?

Thanks in advance.

-Hilski
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gsd
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[*] posted on 2-10-2006 at 09:14


1) The direct reaction of H2SO4 with MnO2 does not happen

2) MnCl2 will not become MnSO4 if you heat it with H2SO4.

There are several ways of doing it.

1) Roast MnO2 at high temp ( above 750 Deg C) to get MnO and then react with H2SO4

2) Reduce MnO2 to MnO by mixing it with a heavy oil ( furnace oil etc) and then igniting the mixture in absence of Oxygen, and then react with H2SO4

3) Use MnO2 + H2SO4 as an oxidizing agent as in oxidation of Toluene to Benzaldehyde; However this reaction is very slow and yield are not good. Oxidation of p-Hydroxy Toluene to p-Hydroxy Benzaldehyde goes very smoothly.

4) Use MnO2 + H2SO4 for oxidizing aniline to Hydroquinone however the product is contaminated with Ammonium Sulphate.

5) Direct Reaction of MnO2 with SO2 ( if you can get hold of SO2)

6) Indirect method : React MnO2 with HCl ( careful ! Cl2 gas is evolved as a by-product) to get MnCl2 solution ; convert it to MnCO3 and then react with H2SO4 to ger MnSO4

gsd

[Edited on 2-10-2006 by gsd]
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12AX7
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[*] posted on 2-10-2006 at 09:32


MnCl2(anh.) + H2SO4 = MnSO4 + 2HCl. Heat drives to the right. Mind fumes.
More completely, MnO2 + 2HCl(aq) + H2SO4 = 2H2O + Cl2 + MnSO4.
You can even do it with salt, at the expense of sulfuric acid; MnO2 + 2NaCl + 2H2SO4 = Na2SO4 + Cl2 + MnSO4.

I don't know if MnO2 + 2NaCl = Na2O + Cl2 + MnO occurs. Probably not, at least without oxygen to produce the manganite or manganate (MnO2 + 2NaCl + O2 = Cl2 + Na2MnO4).

Manganese can be reduced with carbon mildly exothermically as 2MnO2 + C = Mn2O3 + CO and Mn2O3 + C = 2MnO + CO. The first reaction occurs easily (spontaneous ignition when the mixture is heated to dull redness, reaching orange to yellow heat in the process), but the second needs higher heat to drive.

Come to think of it, the spinel Mn3O4 may also be involved. Spinels are generally very stable crystal structures. (For instance, the iron equivalent Fe3O4 is produced from FeO by disproportionation on cooling.)

FYI, direction reaction of MnO2 + H2SO4 yields little or nothing, however impurities of Mn(III) in e.g. pottery grade MnO2 may dissolve in strong acid to produce a pink to burgundy colored solution which hydrolyzes very easily when diluted.

Anyone know if easier reducing agents than SO2 (or equivalently, sulfites) will work? Reducing sugar for example, or ascorbic or citric acid, etc.

Tim

[Edited on 10-2-2006 by 12AX7]




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[*] posted on 2-10-2006 at 10:12


"1) The direct reaction of H2SO4 with MnO2 does not happen

2) MnCl2 will not become MnSO4 if you heat it with H2SO4."
Are you sure? I have just checked a couple of textbooks that say that MnO2 disolves in hot conc H2SO4 to produce MnSO4 and I can't see why the displacement of HCl should be any different from MnCl2 compared to NaCl.

My personal choice would be to roast the MnO2 with carbon then disolve the (mixed lower) oxide(s) in hot conc acid or to use HCl if I had a use for the Cl2.
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[*] posted on 2-10-2006 at 12:22


MnO2 most definitely dissolves in hot conc. H2SO4 with vigorous evolution of oxygen. This is not debatable. This says nothing of the usefulness of drain cleaner and crap pottery MnO2 in producing good MnSO4, however.

[Edited on 2-10-2006 by S.C. Wack]
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[*] posted on 2-10-2006 at 12:34


hydrogen peroxide and acid will very quickly reduce MnO2 to Mn2+.



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Elawr
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[*] posted on 2-10-2006 at 19:10


What if you were to fuse the MnO2 with Na2HSO4 and powdered charcoal?



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Hilski
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[*] posted on 2-10-2006 at 19:56


Quote:

6) Indirect method : React MnO2 with HCl ( careful ! Cl2 gas is evolved as a by-product) to get MnCl2 solution ; convert it to MnCO3 and then react with H2SO4 to ger MnSO4


That's actually the reaction I intended to describe, MnO2 -> MnCO3 after converting the MnO2 to MnCl2, and then precipitating with sodium carbonate . Somehow I managed to leave that part out though.

But this one looks easy enough:
Quote:
You can even do it with salt, at the expense of sulfuric acid; MnO2 + 2NaCl + 2H2SO4 = Na2SO4 + Cl2 + MnSO4.


Yeah it uses more H2SO4, but then you don't have to do the reaction with HCl. I may give this one a shot.
Has anyone tried this reaction, or have any more details like how to separate the MnSO4 from the Na2SO4?

Thanks for all the replies



[Edited on 3-10-2006 by Hilski]
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[*] posted on 2-10-2006 at 21:18


Since I am at work right now, I cannot confirm this will work as a one-step procedure. However, based on other experiments I have done, I suspect that it just might. I know that NaS can be had by fusing NaHSO4 with powdered charcoal. The sulfate ion is a better oxidizer at high heat, and we're tallking dull red or hotter - 700-800 degrees C or more. No aqueous chemistry here - this is anhydrous molten salt. Sulfides in aqueous mileu will easily reduce MnO4- straight to Mn++. So the next chance I get, I gonna melt down some Na2SO4 anhydrous and add a little MnO2 and then charcoal. If I am right, I should see effervescence from the melt, and then be able to recover MnSO4 from the cooled melt. That is, unless somebody beats me to it! Should be easy enough to precipitate the Mn++ as the carbonate by adding baking soda to the solution and decanting.
]:)

[Edited on 3-10-2006 by Elawr]

[Edited on 3-10-2006 by Elawr]




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[*] posted on 2-10-2006 at 22:18


Quote:
Originally posted by S.C. Wack
MnO2 most definitely dissolves in hot conc. H2SO4 with vigorous evolution of oxygen. This is not debatable. This says nothing of the usefulness of drain cleaner and crap pottery MnO2 in producing good MnSO4, however.

[Edited on 2-10-2006 by S.C. Wack]


Haven't tried it but have read it before, so I'm guessing its true. Manganese is a weird materal due to all its various oxidation states... doesn't help that there isn't very much material on the net about it.

And yeah, I would think pottery grade MnO2 and drain cleaner would suck. I'd recommend using some Mn metal from skylighter and excess concentrated sulfuric acid in the right proportions so you don't have to seperate the MnSO4.

Heat, dissolve, dilute, charge and your ready to go.
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[*] posted on 2-10-2006 at 22:19


If you want reasonably pure MnSO4, avoid routes that will result in Mn and Na ions in solution together.

If you need chlorine for anything, then the
MnO2 + HCl (or NaCl + H2SO4) => Cl2 + MnCl2,
MnCl2 + 2 OH(-) => Mn(OH)2 or MnCl2 + CO3(2-) => MnCO3
Mn(OH)2 + H2SO4 => MnSO4
would do well. The toluene to benzaldyhde route if you want that, the low yield is of benzaldehyde, there's no loss manganese. Otherwise MnO2 + H2SO4 + alcohol or sugar to get MnSO4

You might even try mixing ammonium sulfate in excess and MnO2, heating that until it melts, hold at around 300-350 C for awhile, then increase the hea until all the excess ammonia and sulfuric acid/SO3 are driven off. Go all the way up to 700 C, when the MnSO4 fuses.

If you make Mn(OH)2, set a little aside before dissolving the rest in H2SO4. If you go for oxidising some organic compound with MnO2 + H2SO4, take a bit of the solution and precipitate out some Mn(OH)2 or MnCO3. You want to neutralise excess H2SO4 with Mn(OH)2 or MnCO3, and have a bit of excess of the base. Boil for a few minutes, let cool and settle, filter off the remaining Mn(OH)2 or MnCO3. This removes some impurities as carbonates or hydroxides absorbed on the excess MnCO3.

Heating solid MnSO4(some water) until it dehydrates and then more strongly until it just melts (say 720-730 C), hold there for a few minutes, then cool, dissolve in water, add a little ammonium carbonate or MnCO3, boil, cool, settle, filter will remove even more d-block metals. MnSO4 is more heat stable than most of the d-block sulfates, they break down into oxides or basic sulfates, when taking the MnSO4 into solution the added or formed MnCO3 again traps those impurities and makes it easier to remove them.

The ceramic MnO2 I've purchased appears to be fairly pure, a little iron seems to be the main impurity. But the recrystallization of manganese sulfate can be difficult, there are a number of hydrates and some have lousy cold/hot solubility ratios; that's why it's best to try to get as many impurities out early as you can. and not have a lot of sodium in solution with it.
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[*] posted on 3-10-2006 at 09:51


"hydrogen peroxide and acid will very quickly reduce MnO2 to Mn2+. "
Sure about that ?
Last time I checked, MnO2 decomposed H2O2 so fast there would be very little chance for a reduction.
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[*] posted on 3-10-2006 at 11:08


Quote:
Originally posted by unionised
"hydrogen peroxide and acid will very quickly reduce MnO2 to Mn2+. "
Sure about that ?
Last time I checked, MnO2 decomposed H2O2 so fast there would be very little chance for a reduction.


Yes I'm very sure. This is how I extracted MnO2 from batteries for my Mn experiments. You mix MnO2 and acid first then add H2O2.

MnO2 + 4H + 2e----> Mn2+ + 2H2O

H2O2 ----> 2H+ + O2 + 2e




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[*] posted on 3-10-2006 at 12:55


Are you sure about this?

Last time I checked MnO2 was simply a catalyst for the decomposition of H2O2 and was not reduced by the reaction.
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[*] posted on 3-10-2006 at 15:07
Thanks


This is very informative. Thanks for all the replys.

My intentions are to combine any MnSO4 that is yielded, with the proper ammounts of (NH4)2SO4 and 60% H2SO4 to make mangano-ammonium sulfate. Then manganese-ammonium alum will be made using electrolytic oxidation per US patent 808095.
I'm sure most of you have already seen the great writeup Cyclonite posted in the Toluene -> Benzaldehyde thread. If you haven't, you should definately check it out.

I will probably go the MnO2 + HCl (or NaCl + H2SO4) => Cl2 + MnCl2, MnCl2 + NaHCO3 => MnCO3 route to make the MnSO4, simply because it is more feasible for me to do so.

Does anyone have any more detailed info on the actual process for MnO2 + 2NaCl + H2SO4 => Cl2 + Na2SO4 + MnSO4 ?

Thanks again



[Edited on 3-10-2006 by Hilski]
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[*] posted on 3-10-2006 at 15:13


from what I undertstand MnSO4 is used as a fertilizer just buy some and save yourself the trouble.
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[*] posted on 3-10-2006 at 17:05


Quote:
Does anyone have any more detailed info on the actual process for MnO2 + 2NaCl + H2SO4 => Cl2 + Na2SO4 + MnSO4 ?


Add heat...

Incidentially, why is this thread under organic...still?

Tim




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[*] posted on 3-10-2006 at 17:40


Quote:
Originally posted by evil_lurker
Are you sure about this?

Last time I checked MnO2 was simply a catalyst for the decomposition of H2O2 and was not reduced by the reaction.


not in acid...!!!




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[*] posted on 3-10-2006 at 19:01


Quote:
Incidentially, why is this thread under organic...still?


Yeah, sorry about that. I realized after I started the thread that it was in the wrong forum.

Quote:
Add heat...

Yeah, but how do I get rid of the Na2SO4? MnSO4 and Na2SO4 are both soluble in water, although MnSO4 is about 3 times more so than Na2SO4.
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[*] posted on 3-10-2006 at 22:50


Quote:
Originally posted by Hilski

Yeah, but how do I get rid of the Na2SO4? MnSO4 and Na2SO4 are both soluble in water, although MnSO4 is about 3 times more so than Na2SO4.


Fractional crystallization for the direct route. However, this can result in baldness through hair pulling; MnSO4 exists in anhydrous, mono, tri, tera, penta, hexa, and hepta hydrate forms depending on temperature during crystallization and other factors.

You could precipitate it out as the carbonate, filter and wash that, then dissolve in H2SO4.

Or you could do a little experimentation and try a direct route from heating MnO2 with excess (NH4)2SO4 and crystallizing the reaction product. The reaction is messy in the stoichiometry sense, as the 'NH4' goes off as water, nitrogen, ammonia, and sometimes a trace of NOx. You may need to add extra ammonium sulfate to the workup solution to have enough for the mixed Mn(II)NH4 salt (not an alum, that takes Mn(III)). The mixed Mn(II)NH4 sulfate can be isolate by crystallization; it is more soluble than ammonium sulfate hot, but less when cold, so concentrating until ammonium sulfate starts to crystallize, filtering hot, then cooling will let you get it out of solution. Yes, there's Mn left in solution, just let that evaporate and toss it into the next batch of MnO2 + (NH4)2SO4 before heating. Or you may be able to get away with just making sure there's enough ammonium sulfate in solution, as the procedure you mentioned says to use an excess of it, and taking the filtered solution of the cooled melt.
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[*] posted on 3-10-2006 at 22:56


Is the H2O2 method too expensive for you guys or something? Its the easiest cleanest method. I've tried it and it works perfectly and its quite rapid also.



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[*] posted on 3-10-2006 at 23:10


Peroxide in some areas is only available as the 3% solution for medical purposes, is fairly expensive in terms of cost per mole H2O2, and adds a lot of water. Fertilizer grade ammonium sulfate is a reais or two per kg, which is over 7 moles.

For some things H2O2 is perfect, for others I use MnO2 (ceramic grade) or NaClO3 (from herbicide), and for certain fusion reactions NaNO3 (ceramic grade); there's a few things dichromate is good at but the recovery of the chromium including reduction of excess Cr(VI) is a bit of extra work.
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[*] posted on 4-10-2006 at 07:23


Quote:
Originally posted by guy
Is the H2O2 method too expensive for you guys or something? Its the easiest cleanest method. I've tried it and it works perfectly and its quite rapid also.


I have been looking for some (stronger than 3%) H202 since I saw your post, but haven't been able to find it locally yet. I definately want to give that method a try, and experiment with several of the other suggestions made by the folks in this thread. What conc of H2O2 have you used sucessfully in this reaction?

Quote:
Or you could do a little experimentation and try a direct route from heating MnO2 with excess (NH4)2SO4 and crystallizing the reaction product. The reaction is messy in the stoichiometry sense, as the 'NH4' goes off as water, nitrogen, ammonia, and sometimes a trace of NOx. You may need to add extra ammonium sulfate to the workup solution to have enough for the mixed Mn(II)NH4 salt (not an alum, that takes Mn(III)). The mixed Mn(II)NH4 sulfate can be isolate by crystallization; it is more soluble than ammonium sulfate hot, but less when cold, so concentrating until ammonium sulfate starts to crystallize, filtering hot, then cooling will let you get it out of solution. Yes, there's Mn left in solution, just let that evaporate and toss it into the next batch of MnO2 + (NH4)2SO4 before heating. Or you may be able to get away with just making sure there's enough ammonium sulfate in solution, as the procedure you mentioned says to use an excess of it, and taking the filtered solution of the cooled melt.


I might try this one as well, although I will have to get (or make) a lot more (NH4)2SO4 than I have right now in order to do it.

Man this thread has really got me interested in all the different things one can do with Mn compounds.

Thanks.

[Edited on 4-10-2006 by Hilski]
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[*] posted on 4-10-2006 at 11:46


I used 3%. But looking at the scale of your experiment, it might be ineffecient. Though I can get it for about $0.99 a bottle.



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[*] posted on 4-10-2006 at 23:05


Quote:
Originally posted by guy
I used 3%. But looking at the scale of your experiment, it might be ineffecient. Though I can get it for about $0.99 a bottle.


Well, I can get 3% very cheaply also, in quarts or gallons even. Am I correct in assuming that MnO2 and H2O2 are used in equimolar amounts in 1M H2SO4? And is the Mn2+ converted directly to H2SO4? That would be nice as it would save steps in my case.

Thanks
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