Study of the incorporation of carrier-free57Co in Fe(II) and Mn(II) oxalates by a double radioactive tracer method

The incorporation of carrier-free⁵⁷Co²⁺ by coprecipitation in Fe and Mn oxalato compounds is characterized by a double radioactive tracer method. This is achieved by labelling the host compound with a short-lived tracer,⁵²Fe or⁵²Mn. Activity ratios are measured at several stages, during the precipitation and, afterwards, during the dissolution of the solid. In any case, results indicate very large incorporation yields of⁵⁷Co in the precipitate, independently from the intrinsic precipitation yield of the host compound. The observation of a continuous distribution of dopant atoms in the matrix in coprecipitation and dissolution experiments allows to rule out the adsorption of the doping species on a pre-existing precipitate of the host compound and accounts for isomorphous replacement. Incorporation of⁵⁷Co in Fe(II) oxalate follows a logarithmic distribution law, giving rise to a concentration gradient of dopant species in the precipitate. Dopant atoms are found to be concentrated in the internal layers of the crystals.