RogueRose
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MnO2 purification or production from KMnO4
I've seen that pure or reagent grade MnO2 is pretty expensive ($35 for 4 oz or $80 for 500g) and it is pretty hard to find in quantities at
"affordable" prices. While there is pottery grade available, I question the purity and especially the potential contaminates which may be anything
including something which may be nasty. Another option is from batteries but I'd have to think this might be even less pure than pottery grade but
IDK about that.
Now since MnO2 isn't soluble in water (or anything else I've found so far) IDK how one would go about purifying it. I guess SO2 could be bubbled
through it to give MnSO4 which is very soluble and could be recrystallized and has a BP of~ 1500F. It does decompose to MnO2 via electrolysis (does
it gas off SO2 in this case?) so this cold give a route to pure MnO2 I suppose.
Another option would be to make Mn(NO3)2 (and recrystallize till pure) then heat to 300C to yeild MnO2 and NO2 which could be another source. Mn
nitrate is also very soluble (much more so than sulphate) in water.
MnCO3 (found this for $9.35/lb for pottery grade - not bad though) may be made by "Treatment of aqueous solutions of manganese(II) salts with alkali
metal carbonates leads to precipitation of this faintly pink solid." (source wiki) which is negligibly soluble in water. This can be done with Na or K carbonate (or lithium, cesium, rubidium or francium, but these
are much more expensive I would suspect). So I guess the MnO2 could be sulphated then a replacement reaction with K or Na carbonate to give the MnCO3
- which then could be nitrated to give the Mn(NO3)2.
Finally I'm wondering about using KMnO4 as it can be purified by recrystallizations and can often be obtained pretty pure at good prices. Decomp at
464F. KMnO4 + Heat -> K2MnO4 + MnO2(s) + O2 (don't know if the K2MnO4 is solid or not...? probably liquid at the decomp temp?) From there the
K2MnO4 can be decomposed by adding water by this equation: 3 K2MnO4 + 2 H2O → 2 KMnO4 + MnO2 + 4 KOH. With MnO2 being the only substance not
soluble in water. So there should be MnO2 from both decomposition steps if this path works out. This seems a little questionable as I might be
missing something here and the process of making KMnO4 is pretty close to the opposite of the last decomposition step I mentioned. Will this process
work or is there a better way?
So, what would be the best way to make reagent grade MnO2?
One reason for looking at these steps is that I would probably make some of each of the salts as I prepared the pure MnO2 so that has a benefit in and
of itself, so there is value in that and even greater value in doing this process all myself!
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Sulaiman
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ebay.uk has 99.9% MnO2 at £7.99 for 500g with p&p,
and 99.99%, 250g for £9.
PM me if you want me to help.
CAUTION : Hobby Chemist, not Professional or even Amateur
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j_sum1
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Nurdrage has a couple of good videos on purifying battey gunk to end up with pretty good MnSO4. From there to MnO2 is not tricky.
Round here it is possible to buy high purity MnSO4 as a trace element additive for fertiliser. Worth looking into.
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RogueRose
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Wow! That is quite a bit different in price from the amazon and Aldrich prices I saw! That could be worth looking into and save a lot of time!
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woelen
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Those numbers must be fake. Pure MnO2 is very difficult to make. The best MnO2 available in the world still has less than 99% purity.
MnO2 can be made very pure in the sense that the solid does not contain any other elements besides Mn and O. But even those most pure materials are
deficient in oxygen, e.g. MnO1.95 instead of MnO2 (so there is 1.95 oxygen for each Mn). It also is possible to make material with an exact Mn : O
ratio equal to 1 : 2, but in that case, the material also must contain a little of another cationic species. Then you get something like K0.1MnO2 or
Na0.1MnO2 or Ca0.05MnO2. The average oxidation state of the manganese in all these materials is a little bit below 4. (around 3.9).
There are eBay sellers who are not real chemical sellers, but sellers of minerals or industrial oxides or something like that. These people claim
purities of 99.99% or so, but beware of that. Such figures are nonsense. If you look at the figures supplied by companies like Aldrich, Merck and so
on, then you see figures like 98% or 99% and those figures are realistic. If Aldrich says that something is 99.99% pure, then it is believable, but
then quite sure the price will be high, very high.
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