Sciencemadness Discussion Board

Isolating manganese metal from potassium permanganate

Upsilon - 7-11-2013 at 15:24

I want to obtain a sample of manganese metal, and I want to know how to go about doing so. I have a theory in mind but I'm not sure if it will work. First I would pass chlorine gas through a solution of potassium permanganate, which I hope causes the MnO4- ion to dissociate into MnO2 and O2:

2KMnO4 + Cl2 -> 2MnO2 + 2KCl + 2O2

I would then filter off the insoluble MnO2, and reduce it with aluminum powder:

3MnO2 + 4Al -> 2Al2O3 + 3Mn

Any ideas on this?

DraconicAcid - 7-11-2013 at 15:34

I'm sure you can find a better reducing agent than chlorine gas.

Upsilon - 7-11-2013 at 16:05

Quote: Originally posted by DraconicAcid  
I'm sure you can find a better reducing agent than chlorine gas.


Any suggestions? Chlorine gas really isn't hard to generate and work with, since it can be easily made with common household chemicals. If I reduce it with any kind of acid, it would create manganese heptoxide, which is a liquid that decomposes in contact with water and is very explosive.

DraconicAcid - 7-11-2013 at 16:23

It takes very concentrated acid to make Mn2O7. Take your KMnO4, and add aqueous methanol or isopropanol to it, with a small amount of acid.

Upsilon - 7-11-2013 at 16:31

Quote: Originally posted by DraconicAcid  
It takes very concentrated acid to make Mn2O7. Take your KMnO4, and add aqueous methanol or isopropanol to it, with a small amount of acid.


Yes it would, but if I didn't use concentrated acid, it would make permanganic acid which only exists in aqueous solution. Either way I can't make a thermite reaction work with liquids.

Anyway, I'm not too big on organic chemistry; could you please explain how that reaction would work?

DraconicAcid - 7-11-2013 at 16:54

No, you can't do the thermite reaction with liquids. What you will do is to react potassium permanganate with a weak reducing agent such as an alcohol (in aqueous solution) to get a precipitate of MnO2, which you can collect by filtration, dry, and then use for the thermite reaction.

Upsilon - 7-11-2013 at 17:00

Interesting, could you please post the equation for this reaction?

halogen - 7-11-2013 at 17:11

Don't waste KMnO4. Use batteries. Can't find batteries, ship anyone of us here permanganate and we'd send you the batteries.

Thermite can be messy if you want a "sample" and MnO2 is known for violence andrapidity. Coarse particles slow that down, and how much simpler than Al and MnO2. But... you might be able to prepare a Mn salt eutectic and electralyze it. That too sounds fun, road less traveled. Doing it in water is possible but apparently difficult.

[Edited on 8-11-2013 by halogen]

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Upsilon - 7-11-2013 at 17:39

KMnO4 really isn't that expensive, from the right person you can get 500g for around $20. I'd rather buy it then have to deal with tearing apart batteries. If you don't recommend a thermite reaction, I could at least use a better method than electrolysis. It would take far too long. If I add HCl to the MnO2, it would make water-soluble MnCl2 and water, correct? Using a solution of this MnCl2, I could throw in some aluminum foil and it will make manganese metal over time.

[Edited on 8-11-2013 by Upsilon]

halogen - 7-11-2013 at 18:03

Couldn't hurt. Technically Mn reacts a little bit with water, check the activity series, so i don't know but sure, I'd give it a whack.

Well what how much you trying to make, butchering one/two battery no big deal, plus carbon electrodes if you ever need 'em and a bit of zinc.

Thermite IS recommended, just if you're looking for a big erudite block you know? You get a messy lump, and scattered bits. As is common knowledge larger particles slower burn, plus, a lower oxide like Mn2O3 would be easier to control.

You'll do fine. Just don't get lots in you - manganism.

[Edited on 8-11-2013 by halogen]

MrHomeScientist - 8-11-2013 at 11:57

Quote:
If I add HCl to the MnO2, it would make water-soluble MnCl2 and water, correct? Using a solution of this MnCl2, I could throw in some aluminum foil and it will make manganese metal over time.


I don't think this will work. I've never heard of manganese being produced with aqueous chemistry; I think it will react with the water as it is produced.

If you do try it, remember that dissolving MnO2 in HCl goes according to the equation:
MnO2 + 4HCl --> MnCl2 + 2H2O + Cl2
And note that this produces chlorine gas, so do this outside or in a fume hood. This reaction tends to be a lot harder than you'd think, at least when dealing with commercial grade dioxide. Freshly precipitate MnO2 should react much better.

The 'usual' way to make manganese metal is via thermite, but it is actually extremely hard to get decent quality metal from this. The boiling point of Mn is less than the melting point of aluminum oxide, so much of your product metal will boil away in the thermite reaction. Any you recover will be in small nodules and likely contaminated with alumina. I've done this myself - the recommendations to use a lower oxide and coarse particle size are good ones. Blogfast25 is the resident thermite expert, and I know he's posted here a number of times about the troubles with Mn thermites, so a search along those lines would be valuable to you. Try google with the term "site:sciencemadness.org" if the local search engine fails you.

elementcollector1 - 8-11-2013 at 12:01

I've managed to electrodeposit manganese on copper in an aqueous solution of MnCl2. If anyone's interested, it was a concentrated solution, a blank PCB, a lead-tin anode straight out of a 60/40 solder tube, and 14V/2A power supply (car battery charger). Got a thin layer of bright silvery metal that had many dark spots, and required brushing frequently. This eventually darkened slightly. The only problem is removing copper from the equation to get a manganese foil - perhaps this might show some promising results? It doesn't affect zinc, which is more reactive than copper, and manganese is in the same boat.

DraconicAcid - 8-11-2013 at 12:02

Quote: Originally posted by MrHomeScientist  

The 'usual' way to make manganese metal is via thermite, but it is actually extremely hard to get decent quality metal from this. The boiling point of Mn is less than the melting point of aluminum oxide, so much of your product metal will boil away in the thermite reaction. Any you recover will be in small nodules and likely contaminated with alumina.

Manganese that is near boiling, exposed to air, will also oxidize.

Pyro - 8-11-2013 at 12:18

reflux toluene with the KMnO4 to get MnO2, that way you can also make benzoic acid.

then make a thermite, but cover it immediately with something to prevent oxidation of the Mn

Upsilon - 8-11-2013 at 13:30

Would a CO2 or N2 filled environment prevent any oxidation of the Mn? Magnesium will still be able to burn in either to start the thermite reaction, and they are less reactive than oxygen.

Pyro - 8-11-2013 at 14:06

You could initiate the reaction with KMnO4+glycerol, it's like a delayed fuse. as soon as you drip on the glycerol cover it.
you should see the youtube video on isolating B, he uses thermite.

Upsilon - 9-11-2013 at 06:03

I was shopping around and found that it's far cheaper just to buy MnO2 on its own.

Zephyr - 27-12-2013 at 15:54

Upsilon is right, its far cheaper to just buy Manganese dioxide on its, Seattle pottery supply sells a pound for $4.
http://www.seattlepotterysupply.com/Merchant2/merchant.mvc?S...

blogfast25 - 28-12-2013 at 06:42

A few points.

Apparently most Mn metal is now produced by electrodepositing, probably similarly to what EC1 did.

Pottery grades of MnO2 are almost always contaminated with Fe2O3. The separation of Fe and Mn is tedious. For quite pure MnO2 start from a reagent grade Mn(II) salt, dissolve it, precipitate as Mn(OH)2 with NH3 solution and oxidise the hydroxide carefully with hypochlorite (commercial thin bleach). Filter, wash and semi-calcine the resulting MnO2.

MnO2 thermites will not work very well unless you know what you’re doing. The main problem is that the boiling point of Mn (2061 C) and the melting point of alumina (2071 C) are very close together (the end-temperature of the post-reaction mix has to be considerably higher than the latter value). This results in much of the Mn being boiled off during reaction and in some cases to ‘empty crucible syndrome’. At a very minimum include fluorite or lime in your formulation to cool things down a bit. Also, don't waste money on the finest Al powder money can buy: coarser is better here because the mixture will burn slower and cooler.

It would also be better to start from the lower oxide Mn2O3 because less heat is generated during the reduction but Mn2O3 is harder to get.

Using permanganate as a source of Mn (as the title of the thread suggests) is really like putting the horse before the cart, considering just how hard producing commercial permanganate actually is (see sticky thread in general chemistry).


[Edited on 28-12-2013 by blogfast25]

eidolonicaurum - 3-1-2014 at 01:49

There is a very easy way of doing this, I have done it myself. If you heat potassium permanganate to about 300C, it might be hotter, it decomposes into potassium oxide, manganese dioxide and oxygen. The oxygen is very pure, it is difficult to get oxygen that is much purer, and by dumping the solid products left over into water and filtering, good quality manganese dioxide is obtained. This you can then do a thermite with.

Oscilllator - 15-2-2014 at 23:01

One other way you can do this is with a solution of hydrolysed sugar (sucrose -> glucose + fructose). Just make a concentrated solution of sugar, add a few ml of concentrated HCl and leave it somewhere hot for a while. My sugar solution has turned yellow over time. This is highly effective and cheap, since sugar is $1/kg for me at the supermarket.