For both samples, the evolution of [EDTA]free vs. time (Fig. 2)
is characterized by a fast decrease at the first minutes of the
leaching reaction (about of 20% of initially introduced EDTA is
consumed in less than 10 min) followed by a slowly decrease
for Grimault sample (about 50% of initial EDTA) or a very slow
decrease for Bierry sample. The initial fast decrease may be related
to the very fast release of calcium while the slow decrease
is likely more related to the slow leaching of Fe. Conclusively,
for non-calcareous soils, [EDTA]free may be considered quasiconstant
all over the reaction time. Moreover, the stoichiometric
ratio of EDTAfree/TM varied between 80 for EDTA/Pb in Grimault
sample to 10 377 for EDTA/Cd in Bierry sample over a 300-min
reaction period. EDTA could therefore be considered in excess
with respect to target TM’s in both samples. If a large excess
or constant concentration of EDTA is maintained, the leaching