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cnidocyte
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[*] posted on 3-9-2010 at 15:09
Dissolving MnO2


What solvent can dissolve manganese dioxide? Petroleum distillates don't seem to dissolve this stuff at all.

[Edited on 3-9-2010 by cnidocyte]
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ScienceSquirrel
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[*] posted on 3-9-2010 at 18:46


Manganese dioxide is not really soluble in anything at all.
It will react with hydrochloric acid to form manganese chloride, chlorine and water.
But you have gone from Mn IV to Mn II.
The hydrated salt is a light and quite pretty pink by the way!
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cnidocyte
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[*] posted on 4-9-2010 at 04:12


Ah right. So its going to be tricky cleaning up the mess I've made with this stuff lol.
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chemrox
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[*] posted on 4-9-2010 at 20:45


I've added it to refluxing chloroform...



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[*] posted on 5-9-2010 at 07:19


You can cleanup a mess made of MnO2 with a mix of hydrochloric acid and sodium sulfite. It does react with this mix, leaving behind almost colorless Mn(2+) which can be rinsed away with water.



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Methansaeuretier
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[*] posted on 5-9-2010 at 07:31


Quote: Originally posted by cnidocyte  
Ah right. So its going to be tricky cleaning up the mess I've made with this stuff lol.

It does dissolve very well and fast in a solution of sodium sulfite and any stronger acid (H2SO4, etc.). It will create dihydrogen sulfite in situ which is able to reduce MnO2 and create soluble MnSO4

But I think it may also dissolve in many other acids.

Btw. it does dissolve also in HCl/HBr but be careful using them... chlorine/bromine is generated because MnO2 is able to oxidise these acids to H2O and chlorine/bromine.

[Edited on 5-9-2010 by Methansaeuretier]
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[*] posted on 7-9-2010 at 08:47


Also, any mineral acid with H2O2, which acts as a reducing agent in this case, producing excess O2 gas. This works nicely for producing colorless MnSO4 and near-colorless MnCl2.

Solutions of Mn(II) tend to darken with exposure to air (forming Mn(III) species), a dash of H2O2 cleans this up.

If you are hard set on dissolving MnO2 per se, you might be able to find a salt which can. Examples are mixtures of sodium, potassium, magnesium, etc. nitrates, sulfates or chlorides. Finding a combination which does not react may be difficult (MnO2 is oxidized to MnO4(2-) by oxidizers like nitrate and chlorate, and it's reduced by chlorides, producing Cl2 gas and Mn2O3).

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franklyn
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[*] posted on 8-9-2010 at 08:04


For cleanup the methods already cited are adequate , for
true solvation without chemical reaction options are limited.

Metal oxides as in this case MnO2 are soluble to some extent
in a mixture of 1 part Choline Chloride to 2 parts of Urea. See
http://www.sciencemadness.org/talk/viewthread.php?tid=10529
Propylene Carbonate may also serve the purpose
http://www.sciencemadness.org/talk/viewthread.php?tid=8645#p...

.
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[*] posted on 17-1-2014 at 10:00


Hello,

I have 100# of Tantalum anodes coated with MnO2 and a layer of Ag on top. The material is 80% Ta and the remainder MnO2 and Ag

I want to remove the MnO2 and the silver in the easiest way possible.

I know that HCl will dissolve MnO2 and that HNO3 will dissolve the Ag. but some of the anodes are quite small so I am trying to reduce the chance of making AgCl.

My question is MnO2 will dissolve in a mineral acid and with H2O2. Do you think that HNO3 and H2O2 will accomplish this? If so what % H2O2 would I need to use.

My objective is to remove the MnO2 and reclaim the silver with Cu.

Eric




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[*] posted on 17-1-2014 at 11:23


Here is some background on the electrochemistry of some processes employing MnO2.

One source, "Electrochemical phenomena in MnO2–FeS2 leaching in dilute HCl. part 2 : studies on polarization measurements", by R.K. Paramguru1 at the Regional Research Laboratory (Council of Scientific and Industrial Research) Bhubaneswar, India, link: http://www.sciencedirect.com/science/article/pii/S0008443398... citing an electrochemical phenomena involving MnO2–FeS2 dissolution in dilute HCl.

I find this interesting given this equation:

MnCl2 + HOCl + H2O = MnO2 (s) + 3 HCl (see page 4 at http://www.ecs.umass.edu/cee/reckhow/courses/371/371l22/371l... )

as upon adding HCl to both sides, noting that HCl + HOCl = Cl2 + H2O:

MnCl2 + Cl2 + 2 H2O = MnO2 (s) + 4 HCl

which is, of course, the reaction for the generation of Chlorine written in reverse. My point, the reaction is reversible.

Now, instead of adding HCl to each side, lets add FeS2 to each side:

MnCl2 + HOCl + FeS2 + H2O = MnO2 (s) + FeS2 + 3 HCl

Now, the author in the reference cited above claims dissolution for the right side of this equation. But, this implies that MnO2 and even FeS2 (generally a hard act) dissolves in a solution of MnCl2 and HOCl.

In fact, there appears to be a commercial process for the recovery of Gold contained in Iron pyrite based on chlorination (Chlorine or Hypochlorous acid and a chloride). See page 141 at http://books.google.com/books?id=QeDTeUalP0IC&pg=PA141&a...

Some other references that may be of interest:

"Kinetics and mechanism of MnO2 dissolution in H2SO4 in the presence of pyrite" in Journal of Applied Electrochemistry, February 1999, Volume 29, Issue 2, pp 191-200.

"Oxidation of FeS2 and FeS by MnO2 in Marine Sediments" by Axel Schippers & Bo Barker Jørgensen at Max Planck Institute, for Marine Microbiology, Celsiusstrasse, Germany.

"Electrochemical phenomena in MnO2–FeS2 leaching in dilute HCl. part 3: manganese dissolution from indian ocean nodules", published in Canadian metallurgical quarterly, 1998.

"Biogeochemistry of pyrite and iron sulfide oxidation in marine sediments", published in Geochimica et Cosmochimica Acta, Vol. 66, No. 1, pp. 85–92, 2002.

"Electro-generative mechanism for simultaneous leaching of pyrite and MnO2 in presence of A. ferrooxidans", link: http://www.ysxbcn.com/down/upfile/soft/200856/20085621187488...

"Galvanic interaction between sulfide minerals and pyrolusite", published in Journal of Solid State Electrochemistry, March 2000, Volume 4, Issue 4, pp 189-198
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[*] posted on 17-1-2014 at 14:43


Chemical equations are not mathematical equations

v = u + at

and;

u = v - at

But chemical equations do not obey the same rules.
For instance the equilibrium reaction between calcium oxide and carbon dioxide is dependent on temperature.
At room temperature and up to several hundred degrees the reaction favours calcium carbonate, as it gets hotter, the compound begins to disassociate until eventually carbon dioxide is driven off as a gas and we are left with calcium oxide.
Calcium oxide will react very slowly with carbon dioxide at room temperature.
This is an equilibrium but it is a slow and temperature dependent one.
Please stop 'adding HCl to both sides', and other pseudomathematical operations, they are in most cases, nonsense.
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[*] posted on 18-1-2014 at 16:25


The best chemical for the dissolution of MnO2 are Sodium metabisulphite, any weak acid + H2O2, or ascorbic acid.

I use the last frequently to remove MnO2 from delicate minerals such as calcite and aurichalcite
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[*] posted on 19-1-2014 at 06:17


i got approx 5L H2O2 12% with oleic acid added to it (stabilizer?)
i once realised that after i poured it together with abit of MnO2 that the MnO2 got more brownish, this was not what i expected to see, as i have been trying to destroy MnO2 with oxalic acid and 98% H2SO4

also after having a beaker standing around with 37% HCl and MnO2 for several months time i now have a yellow tinted solution and a brown slurry
manganese chemistry is confusing and extremely messy, please dont handle MnO2 anywhere you are not prepared to destroy the top layer of with sandpaper




~25 drops = 1mL @dH2O viscocity - STP
Truth is ever growing - but without context theres barely any such.

https://en.wikipedia.org/wiki/Solubility_table
http://www.trimen.pl/witek/calculators/stezenia.html
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[*] posted on 18-5-2020 at 20:56


"manganese chemistry is confusing and extremely messy, please dont handle MnO2 anywhere you are not prepared to destroy the top layer of with sandpaper"

I definitely agree with you on the messy part! After jarring mine out of a battery for several minutes, it was a pain to keep my workspace clean.
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[*] posted on 19-5-2020 at 01:08


If you don't want to mess with strong acids, solution of oxalic acid is very good for removing MnO2 stains
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[*] posted on 19-5-2020 at 01:32


Quote: Originally posted by ThoughtsIControl  
"manganese chemistry is confusing and extremely messy, please dont handle MnO2 anywhere you are not prepared to destroy the top layer of with sandpaper"

I definitely agree with you on the messy part! After jarring mine out of a battery for several minutes, it was a pain to keep my workspace clean.

Remember that battery paste is about 30% graphite. That adds a lot to the mess.

It is not clear from the OP (many years ago) whether the goal is to clean up or to get Mn in solution.
The answer to your problem however might be gloves, newspaper, and being tidy.
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[*] posted on 20-5-2020 at 00:59
Best solvent for MnO2


Which acid is most efficient in dissolving MnO2 precipitate residues?
Strong reducing acids:
H2SO3 could give MnSO4.
The problem here is that many sulphites are poorly soluble. You could just get MnSO3 precipitate instead.
H2C2O4
Same issue. Manganese oxalate can be itself poorly soluble.
HCl? But the problem is that it is weak reducer. Difficult to force the reaction through.
Should it be better to clean MnO2 with HI instead? Much stronger reducer than HCl. MnI2 is fairly soluble. And while I2 is poorly soluble in water, it dissolves much better in excess HI...
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mackolol
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[*] posted on 20-5-2020 at 01:07


I don't really know what's the point, are you trying to get rid of MnO2 stains or you just plan to clean aparature from it in future? HCl and oxalic acid are enough to clean MnO2 residue without problems. HCl is a bit better than oxalic but I've tested both and they do the job. Hot HCl is the best. There is no need to use expensive and rather useful HI.

[Edited on 20-5-2020 by mackolol]
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[*] posted on 20-5-2020 at 03:12


When you work in acidic solution, there isn't any precipitation of MnSO3 or MnC2O4.



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