I found this little tidbit of information (1911 encyclopedia) that might be useful to someone somewhere. I didn't find this information posted anywhere on the hive or rhodium. I cleaned it up a good bit to make it readable, hopefully I didn't make any errors.
manganese dioxide - also called pyrolusite
Exists naturally as pyrolusite or by heating manganese carbonate to 260°C in the presence of air and washing the residue with very dilute cold hydrochloric acid. It is a hard black solid which readily loses oxygen when strongly heated, leaving a residue of Mn
3O
4.
potassium manganate
Manganates. These salts are derived from manganic acid H
2MnO
4. Those of the alkali metals are prepared by fusing manganese dioxide with sodium or potassium hydroxide in the presence of air or of some oxidizing agent (nitre, potassium chlorate, ect);
MnO
2+2KOH+O
2 __> K
2MnO
4+H
2O
In the absence of air the reaction proceeds slightly differently, some manganese sesquioxide being formed;
3MnO
2 + 2KOH
__> K
2MnO
4 + Mn
2O
3 + H
2O
The fused mass has a dark olive-green color, and dissolves in a small quantity of cold water to a green solution, which is, however, only stable in the presence of an excess of alkali. The green solution is readily converted into a pink one of permanganate by a large dilution with water, or by passing carbon dioxide through it:
3K
2MnO
4+2CO
2 __> 2K
2CO
3+2KMnO
4+MnO
2potassium permanganate
Permanganates are the salts of permanganic acid, HMnO
4. The potasssum salt, KMnO
4, may be prepared by passing chlorine or carbon dioxide through an aqueous solution of potassium manganate, or by the electrolytic oxidation of the manganate at the anode. It crystallizes in dark purple-red prisms, isomorphous with potassium perchlorate. It acts as a powerful oxidizing agent, both in acid and alkaline solution; in the first case two molecules yield five atoms of available oxygen and in the second case, three atoms:
2KMnO
4+3H
2SO
4 __> K
2SO
4+2MnSO
4+3H
2O+5O;
2KMnO
4+3H
2O
__> 2MnO
2.H
2O+2KOH+3O.
It completely decomposes hydrogen peroxide in sulphuric acid solution
2KMnO
4+5H
2O
2 +3H
2SO
4 __> K
2SO
4 +2MnSO
4+8H
2O +5O
2.
It decomposes when heated to 200-240°C:
2KMnO
4 __> K
2MnO
4+MnO
2+O
2;
and when warmed with hydrochloric acid it yields chlorine:
2KMnO
4+ 16HCl
__> 2KCl +2MnCl
2+8H
2O+5Cl
2.
Additional Useful Information: MnO
2 is best freshly prepared but can be refreshed by treating with very dilute hydrochloric acid. When fresh or refreshed it is a mild oxidizer.
MnCO
3 preparation from potassium permanganate is available at
Manganese(III) Acetate
(
https://www.thevespiary.org/rhodium/Rhodium/chemistry/manganous.acetate.html)
MnCO
3 and MnO
2 are readily available.