Effects of Extracting Reagents and Metal Speciation on the Removal of Heavy Metal Contaminated Soils by Chemical Extraction

Abstract

Chelating agents and acids were evaluated for removing heavy metals from contaminated soils. Two soils, latosols soil and sandatone-shale alluvial soil, artificially contaminated with Cu, Zn, and Pb were investigated. The removal efficiencies of Cu, Zn, and Pb from both soils for various chelating agents and acids followed the descending order EDTA > DTPA > Citric Acid > HCl. Heavy metals were associated in latosols soil with 34, 40, and 33% in the exchangeable fraction for Cu, Zn, and Pb, respectively. However, heavy metals were associated in sandatone-shale alluvial soil in stronger adsorbed forms with 40, 55, and 42% in the Fe–Mn oxides fraction for Cu, Zn, and Pb, respectively. Effect of EDTA concentration on the removal efficiency of heavy metals was examined for a wide range of 1 × 10−4 to 5 × 10−2 M. When EDTA concentration was low in the range from 1 × 10−4 to 1 × 10−3 M, the removal efficiencies of all the heavy metals from latosols soil were higher than those from sandatone-shale alluvial soil. The higher removal efficiencies of heavy metals observed in latosols soil than those in sandatone-shale alluvial soil is proved due to that the heavy metals in latosols soil were associated in weaker adsorption forms than heavy metals associated in sandatone-shale alluvial soil.