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 Mn3O4.
potassium manganate
Manganates. These salts are derived from manganic acid H2MnO4. 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);
MnO2+2KOH+O2 __> K2MnO4+H2O
In the absence of air the reaction proceeds slightly differently, some manganese sesquioxide being formed;
3MnO2 + 2KOH __> K2MnO4 + Mn2O3 + H2O
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:
3K2MnO4+2CO2 __> 2K2CO3+2KMnO4+MnO2
potassium permanganate
Permanganates are the salts of permanganic acid, HMnO4. The potasssum salt, KMnO4, 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:
2KMnO4+3H2SO4 __> K2SO4+2MnSO4+3H2O+5O;
2KMnO4+3H2O __> 2MnO2.H2O+2KOH+3O.
It completely decomposes hydrogen peroxide in sulphuric acid solution
2KMnO4+5H2O2 +3H2SO4 __> K2SO4 +2MnSO4+8H2O +5O2.
It decomposes when heated to 200-240°C:
2KMnO4 __> K2MnO4+MnO2+O2;
and when warmed with hydrochloric acid it yields chlorine:
2KMnO4+ 16HCl __> 2KCl +2MnCl2+8H2O+5Cl2.
Additional Useful Information: MnO2 is best freshly prepared but can be refreshed by treating with very dilute hydrochloric acid. When fresh or refreshed it is a mild oxidizer.
MnCO3 preparation from potassium permanganate is available at Manganese(III) Acetate (https://www.thevespiary.org/rhodium/Rhodium/chemistry/manganous.acetate.html)
(https://www.thevespiary.org/rhodium/Rhodium/chemistry/manganous.acetate.html)
MnCO3 and MnO2 are readily available.
500g containers of KMnO4 for ~$25 from local chemists, may be expensive if your looking at large qty's but how much do you want? its easily sourced from chem suppliers in larger qty's if need bee, no q's asked.
Whats the big problem?
AC, check your facts before giving advice to people. (...and preferably do it, with this kind of info, via PM).
Potassium Permannganate is a category 3 "illicit drug precursor" in Oz.
https://www.thevespiary.org/rhodium/Rhodium/chemistry/law/illicitdrugcode.au.pdf (https://www.thevespiary.org/rhodium/Rhodium/chemistry/law/illicitdrugcode.au.pdf)