Please find attach file, maybe usefull.

Article Preparation of chemical manganese dioxide from manganese sulfate

 Proceed as follows:

[1]  First convert  Mn powder into  manganese chloride  by treating manganese  powder and hydrochloric acid:

(Wikipedia)

Mn + 2 HCl → MnCl2 + H2

[2]  On  neutralising MnCl2 with NaOH, firstly Mn(OH)2.nH2O (off white) precipitates as:

 MnCl2+2NaOH--------- Mn(OH)2 + 2NaCl

  Becomes hydrated as Mn(OH)2.nH2O

[3]  Filter--- NaCl remains in solution while  Mn(OH)2.nH2O is Off white precipitate

 [4]  Upon contact with air quickly goes brown by oxidation:

Mn(OH)2 + ½ O2 === > MnO2 + H2O

[5] Given a little time , air and stirring, this reaction proceeds to completion.

 IMMEDIATE precipitation of something black;  freshly precipitated MnO2 is always very dark brown, rather than black .

Dear Mr Hadi Cheraghi , Thank for your kind reply.

Dear Mr Manohar Sehgal  , Thank for your kind reply.

I'll try this chemical process and  could you tell me if there is another way to oxidize Mn in furnace?

Thank you in advance

Thank you again Mr Manohar Sehgal for your clear explication.