Remediation of Heavy Metals Contaminated Silty Clay Loam Soil by Column Extraction with Ethylenediaminetetraacetic Acid and Nitrilo Triacetic Acid

Ethylenediaminetetraacetic acid (EDTA) as traditional chelating agent and nitrilo triacetic acid (NTA) as biodegradable chelating agent were used to evaluate the efficiency of leaching in silty-clay-loam soil contaminated with Pb, Cd, and Zn. Three concentrations of NTA and EDTA, 0.1, 0.01, and 0.005 M, were used in column leaching and each was set up in triplicate. Results demonstrate that the highest efficiency of heavy metals extraction was obtained in treatments with a concentration of 0.1 M EDTA and NTA. The extraction efficiency in first, second, and third pore volumes of 0.1 M EDTA were 41.92, 70.35, and 81.63% of Pb, 19.26, 44.28, and 77.58% of Cd, and 41.24, 56.14, and 65.8% of Zn, respectively. Also the extraction yields in first, second, and third pore volumes of 0.1 M NTA were 6.44, 14.72, and 16.78% of Pb, 47.68, 59.4, and 66.85% of Cd, an 11.44, 15.45, and 18.84 8% of Zn, respectively. Statistical analysis showed that EDTA concentration and pore volume have significant (p<0.05) effects on heavy metal leaching efficiency. At a washing solution pH of 4.5, the Pb, Cd, and Zn extraction efficiencies at the fifth pore volume were 87.25, 81.23, and 70.05% for the 0.1 M EDTA and 79.7, 59.8, and 60.12% for the 0.1 M NTA, respectively, when multiple heavy metals were used. The Pb, Cd, and Zn extraction efficiency for reuse of EDTA from leached solution were 99.12, 99.71, and 99.33%, respectively, for Na2S and 99.66, 99.74, and 98.59%, respectively, for Na2S/Ca(OH)2 treatment. The acidity of the environment has a significant impact on heavy metals removal for both chelating agents. The overall orders of metal extraction efficiency for EDTA and NTA that resulted from this study are Pb>Cd>Zn and Cd>Zn>Pb, respectively.