EDTA extractability of trace metals in polluted soils: A chemical-physical study

The reactivity of a few trace metals (Cd, Pb, Zn,Cu) present in three polluted soils was studied using a classical extractant: EDTA. The effects of the concentration of this reagent (from 0.0001 M to 0.05 M) as well as those of the pH of the extracting solution (from 2 to 8) on the extracted amounts of metals have been determined. The behaviour of the cations seems to depend heavily on an excess or a lack of EDTA. In the case of an excess, concentrations of cations extracted are most of time pH-independent. On the contrary, when using a lack of EDTA, amounts of extracted cations show a complex behaviour versus pH which changes with the type of cation and with the degree of soil pollution A competition phenomenon between minor and major cations of the soil seems to be revealed. These major cations seen to be Fe3+ in acidic media and Ca2+ in neutral media. However, when in excess, this reagent reveals a powerful extractant of trace metals in soils: recovery rates greater than 60 % have often been observed.