Redistribution of fractions of zinc, cadmium and lead in calcareous soils treated with EDTA

摘要

The effect of EDTA (ethylene diamine tetra acetic acid) on the fractionation of Zn, Pb, and Cd in six calcareous soils was investigated. A total of 400 mg kg~(-1) Zn, 200 mg kg~(-1) Pb, and 8 mg kg~(-1) Cd was added to soils as chlorides. Both naturaland metal-amended soils were treated with Na_2 EDTA solution at amounts of 0, 1.0, and 2.0 g kg~(-1). Metals in the incubated soils were fractionated after 5 months by sequential extraction procedure, in which the metal fractions were defined as exchangeable (EXC), carbonate (CARB), Mn oxide (MNO), Fe oxide (FEO), organic matter (OM) and residual (RES) fractions. Increasing the amounts of EDTA significantly raised Zn concentrations in the EXC and CARB fractions in metal-amended soils. EDTA also increased Cd concentrations in the EXC fraction of the metal-amended soils. Increasing the amount of EDTA raised significantly Pb concentrations in the CARB and MNO fractions in metal-amended soils. In the metal-amended soils, EDTA removed some Pb from RES andOM fractions and redistributed them into CARB and MNO fractions. Based on relative percent in the EXC fraction, the order of solubility was Cd > Zn > f b for metal-amended soils, before and after adding of EDTA.