70.
The kinetics of the exchange between
56Mn-labelled manganese dioxide and cations in aqueous solution was studied by measuring the β
− activity acquired by the solution. The results of the exchange between a chemical γ MnO
2 and a divalent M
2+ ion (M=Mn, Co, Cu or Zn) or a trivalent M
3+ ion (M=Ga, Fe, In, Rh or Al) indicate a fast initial process followed by a diffusion—controlled exchange. It is assumed that
M
2+ ions exchange with Mn
2+ ions and M
3+ ions exchange with Mn
3+ ions in MnO
2. The process depends on the radii of the host and substituent ions and on consideration of crystal field stabilisation energies.
It seems that the γ MnO
2 studied contains more Mn
3+ than Mn
2+ ions. The possibility of the exchange between Mn ions and cations of a different charge cannot be ruled out. The exchange
between Co
2+ ions and MnO
2 was enhanced in presence of pyrophosphate, which stabilises Mn(III) as a complex. The fraction of Mn in different samples
of MnO
2 exchanged with a given cation depends on the type and not on the surface area of the sample.
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