Chelating-Agent-Enhanced Heavy Metal Extraction from a Contaminated Acidic Soil

An acidic soil was deliberately contaminated with lead (Pb), cadmium (Cd), and chromium (Cr). The heavy metal speciation in the aged soil sample was analyzed using a sequential extraction procedure. A single-step extraction procedure was then employed to remove the heavy metals from the soil using sodium ethylenediaminetetraacetic acid, sodium nitrilotriacetic acid, and calcium trisodium diethylenetriaminepentaacetic acid. The extraction parameters were the type and concentration of chelating agent and the duration of extraction time. All the extractions that involved chelating agents were carried out at pH 7.0. The heavy metal extraction efficiencies of chelating agents were compared to those of HNO3,CaCl2, and deionized water. The extraction results showed that the chelating agents were more efficient in extracting Pb and Cd from the acidic soil than HNO3. The extractable Pb and Cd were removed from the soil within 15 min of extraction time with the chelating agents. However, the chelating agents demonstrated a poor Cr extraction. The extraction efficiency seemed to be dependent on the heavy metal speciation in the solid phase. The extraction with a low chelating agent: metal molar ratio and short extraction time was proven to be optimal for Pb and Cd extractions. In contrast, an effective Cr extraction would require a high dosage of chelating agent and a long extraction time.