FMF - Friends of Minerals Forum, discussion and message board

[Darryl]

In my initial post under the heading "cleaning quartz" I made the comment that I had used solutions of hydrogen peroxide ranging in concentrations from 3% - 30% to dissolve manganese oxide cements from sandstones. As unreasonable as this sounded when I was first told it would work, I tried it and it did work. The only thing I could ever figure out was that the oxygen from the peroxide was combining with that of the metalic oxide and going off as O2 (and was the source of the strong bubbling action) while the manganese ions combined with the OH that was left from the peroxide. Does anyone have any thoughts on whether or not this is what happened?

[alfredo]

Hydrogen peroxide by itself won't dissolve manganese oxides, it needs an acidic environment to work, which doesn't necessarily imply a lot of acid - just a few drops of almost any cmmon acid to slightly acidify the solution will work.

[Montanpark]

Hi all,
please don´t forget that manganese oxide only catalyses the decomposition of H2O2 to water ond oxygen. What is dissolving the Mn-Oxide is the acid .. and you should be careful to do this with muriatic as the reaction produces toxic chlorine gas. The decomposition of the peroxide only loosens the particles in more or less amorphous Mn oxides as it can soak the material well and the small gas bubbles 'blast' off the stuff. The chemical solution with HCl for instance reacts like this:
MnO2 + 4 HCl -> MnCl2 + Cl2 + 2 H2O (with MnO2 as given oxide)

cheers
Roger

[Darryl]

Hello group,

Many thanks to Roger and Alfredo for their input. Their mention of the role acids play in the reaction I observed brought to mind some details I did not put in my earlier posts because I thought them irrelevant, now I see they are not. I am afraid my procedues will appear very sloppy to many but my only interest in breaking down the sandstones was to see if I could find bits of precious metal in them so I wanted to get them stripped as quicklly, cheaply, and safely as possible. I did use various acids including HDL, sulfuric, nitric and aqua regia under a fume hood on some small samples but over 95% were done with hydrogen peroxide from one source or another.

I I used hydrogen peroxide from 3 sources: 3% solutions purchased at various retail stores; 30% lab grade peroxide that I obtained from the chemistry department at the college where I was teaching at the time; and a solution I purchased by the gallon at a swimming pool supply company. While the peroxide from the later source had a distinct vinegar smell to it I didn't think about the acid in it being what was doing the dissolving. I am unaware of the acidity of the 3% strore purchased peroxide but it may be acidic. As for the 30% solution I obtained from the chem lab, I don't see how it could have been an acidic solution BUT since it produced a dangerously vigerous reaction when I first tried it, I dilluted it with tap water for subsequant dissolution trials. Could the tap water have provided the required acidity to which you referred? Thanks for any additional information you can provide since I plan to return to this project in the future.