# dissolving manganese without chlorine generation



## drifter (Jan 21, 2012)

Hi all, is there an acid / alkaline / chem that will get manganese in solution without releasing chlorine into the solution?


Ive got a heap of manganese laden cons that i want to strip away from the good stuff. 


Cheers


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## Geraldo (Jan 21, 2012)

What form is the manganese in? Sulfides? Oxides?

If it is an oxide, you can leach it with dilute sulfuric acid, but you need a reductant. In the zinc industry, they use SO2, or zinc concentrate (nominally ZnS) or lead concentrate (PbS). Ferrous iron (Fe2+) in solution also works.

Regards, Gerald


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## drifter (Jan 21, 2012)

Thanks mate, I assume its manganese oxide (dioxide??) just the common stuff found on quartz ,pyrolusite??. It causes h2O2 to bubble away.

What is the reductant needed for? sorry for the questions


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## Geraldo (Jan 22, 2012)

drifter said:


> Thanks mate, I assume its manganese oxide (dioxide??) just the common stuff found on quartz ,pyrolusite??. It causes h2O2 to bubble away.
> 
> What is the reductant needed for? sorry for the questions



As far as sulfuric acid is concerned - manganese (II) is fairly soluble, while manganese (IV) isn't. The reductant is there to reduce the Mn4+ to Mn2+ (in the solid state) so that it will dissolve. 

Manganese likes to be oxidized, so it is generally in the IV (4+) state in nature...or at least more so than the II (2+) oxidation state.

If you were refining manganese ore pyrometallurgically, you would use coal or coke to reduce the Mn4+ to Mn2+ in a furnace, but since you asked about hydrometallury - - it requires a liquid-active reductant. So, ferrous (2+) iron is very good, because it is already in solution. The sulfide minerals (like lead or zinc concentrate) work by generating small amounts of H2S and similar polysulfides that can react with the MnO2. SO2 works if it is mainly dissolved (as sulfurous acid) - it is a decent reductant, especially in a sulfuric acid solution (and the result of reaction is just more sulfuric acid).

Hopefully that is clearer than mud?

Best Regards, Gerald


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## drifter (Jan 23, 2012)

Thanks 8) 

Another quick question..

so the iron is there to steal two oxygen atoms from each mnO4 molucule? If so, I'm guessing i'd need twice as much iron as mnO4 by volume as each iron atom will only pinch one oxygen atom?

would placing the required amount of steel wool into the sulphuric acid put it into solution in a form that would work?

thanks again, appreciate your time 8)


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## Geraldo (Jan 23, 2012)

drifter said:


> Thanks 8)
> 
> Another quick question..
> 
> so the iron is there to steal two oxygen atoms from each mnO4 molucule? If so, I'm guessing i'd need twice as much iron as mnO4 by volume as each iron atom will only pinch one oxygen atom?



Not by volume. By molarity. In the ideal case, two moles of ferrous iron in solution will react with one mole of MnO2 to produce two moles of ferric iron and one mole of "MnO", which dissolves in sulfuric acid to create manganic acid or manganese sulfate. The source of your Fe2+ ions will ultimately determine the "volume" added (or more precisely, the mass added).

Break out the periodic table, recall "molar mass to mass" calculations from high school, and you will be alright!



drifter said:


> would placing the required amount of steel wool into the sulphuric acid put it into solution in a form that would work?



Using steel wool or scrap iron is very slow. It will probably work eventually (weeks? months?). Metallic iron powder has been tested (by me, and possibly others who also didn't publish it out of embarrassment) and it was also very slow - - some 3-4 days before I gave up. The iron rusts of course (which you would think is the point) but it forms a slime layer that slows the reaction. It also makes a gelatinous mess. It works well in an autoclave with pure oxygen, but that is out of realm of practical for something like this. And if you DO have an autoclave, leach pyrite and make Fe2+ cheap.

The classic source of ferrous iron for a sulfuric acid-based solution is ferrous sulfate (chemical). I can't think of a hardware store source of ferrous sulfate, but I am not very good at that sort of thing. I am a lot better at ordering chemicals from the chemical supply catalog...sorry.

There are a lot of other methods for manganese leaching - I just spouted the one I am familiar with. I am also more comfortable with sulfuric acid than most of the other acids (HCL is stinky and Nitric is stinky, produces toxic brown clouds and burns the heck out of you if you splash any on your skin). You might consider a Google search for manganese leaching if you want to pursue other acids, avenues, etc.

As an aside, hydrogen peroxide can also be a reductant, even though most think of it as a strong oxidizer. I have seen papers on leaching MnO2 from alkaline batteries using H2O2 - the reaction mechanism is (roughly):

MnO2 + H2SO4 + H2O2 = MnSO4 + O2 + H2O

The MnSO4 is soluble in H2SO4. Since you mentioned H2O2 in your original post, it might be something that is easier for you to acquire?

Best Regards, Gerald


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## drifter (Jan 23, 2012)

:shock: you sure know alot about manganese 8) 

I'm not so much trying to leach mn, more trying to strip it away from mid table cons so i can do a traditional leach for Au.


Got any theories on nugget formation in gold ores that have secondary manganese deposits through them? Could meteoric water cause the mn to generate chlorine and thus insitu leach disseminated fine gold to be deposited elsewhere in high concentration (nuggets / large specs / crystals)? 

cheers
Simon


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## Geraldo (Jan 24, 2012)

drifter said:


> I'm not so much trying to leach mn, more trying to strip it away from mid table cons so i can do a traditional leach for Au.
> 
> 
> Got any theories on nugget formation in gold ores that have secondary manganese deposits through them? Could meteoric water cause the mn to generate chlorine and thus insitu leach disseminated fine gold to be deposited elsewhere in high concentration (nuggets / large specs / crystals)?
> ...



Hi Simon,

Yeah, I understood that you were trying to remove the Mn so it isn't in the way of gold recovery. Reductive leaching in sulfuric acid is probably the safest way to remove MnO2, and also some iron species. It won't touch gold or silver. One danger, now that I think about your case, is silicates - in weak acid they tend to leach and form silicic acid, which is a snotty-looking gelatinous goo that prevents settling, filtration and makes life miserable in general. Stronger hot sulfuric acid will tend to convert silicates to silica (or perhaps it just dehydrates the silicates, I am not sure) and avoids that problem.

Sorry, I cannot offer useful theories on the geological origins of your concentrate. I took geology way back when, but basically what I got out of it was how to tell orthoclase from plagioclase feldspar...sometimes.

Good luck!

Best Regards, Gerald


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