The performance of EDTA for the treatment of calcareous soils contaminated
with heavy metals from mining and smelting activities was evaluated in this
study. Soil samples containing variable levels of contamination, from 500
to 35 000 mg kg(-1) Ph and 700 to 20 000 mg kg(-1) Zn, were subjected to ED
TA treatment and the extraction of heavy metals was found to vary, ranging
between 50 and 98% for Pb and 50 to 100% for Zn. Total residual concentrati
ons were above the limits set by regulatory authorities; leachable metals,
however, were efficiently removed and treated soils were all acceptable in
terms of toxicity. The effect of EDTA concentration and pulp density was st
udied on a soil sample containing 12 000 mg kg(-1) Pb and 10 000 mg kg(-1)
Zn. Heavy metals removal was improved at low pulp densities and when EDTA c
oncentration was increased from 0.025 to 0.25 M. The tetrasodium salt Na-4-
EDTA was found to be less effective for metals removal compared to the diso
dium salt Na-2-EDTA, though applied at higher concentrations. This experime
ntal work has also demonstrated the great importance of soil matrix for the
overall evaluation of the EDTA leaching as a cost effective remedial optio
n. The simultaneous dissolution of calcite was found to consume approximate
ly 90% of the available EDTA. It was thus concluded that for the treatment
of calcareous soils the design criteria and cost estimations should be base
d on the calcite content of the soil.