Movement of pertechnetate through soils: Hydrodynamic dispersion

Measurement of the hydrodynamic dispersion of pertechnetate (⁹⁹TcO^?₄) migrating towards the water-table complements other investigations of the partition of pertechnetate between soil solution and soil colloids. This study was performed on soil columns equilibrated with distilled water and through which a solution of ⁹⁹TcO₄NH₄ or ³⁶ClNa was percolated at constant rate. A theoretical elution curve was adjusted to the experimental points obtained from a sand column. An estimate could thus be made of the parameters characterizing the migration of pertechnetate. The model used here considered the presence of a ‘dead water’ zone in the column into which the solute penetrates by molecular diffusion only at a given rate. The elution curves obtained experimentally and theoretically have been compared with those for a non-reactive anion, ³⁶Cl^?. A simulationof the change of pertechnetate concentration in the eluate has been made for increasing values of the retention factor. The calculated curves confirm the very low mobility of this anion in soil.