ABSTRACT Chelate extraction using ethylenediaminetetraacetic acid (EDTA) and other chelates has been demonstrated to be an effective method of removal of Pb from many contaminated soils. However, column leaching of Pb from alkaline soils with EDTA has been problematic due to extremely low soil permeability. The purpose of this study was to determine the effect of the addition of KOH and Ca(Cl)2 to K2H2EDTA extraction solution on Pb removal and hydraulic conductivity. A Pb-contaminated soil was sampled from an abandoned lead-acid battery recycling facility. Both batch shaker extractions and column leaching experiments were completed using five different EDTA extract solutions. Addition of Ca(Cl)2 only to K2H2EDTA did not change the amount of Pb removed by batch extraction, and Pb solubility was only slightly decreased by the addition of both Ca(Cl)2and KOH. Lead solubility was observed to decrease as pH was increased by the addition of KOH. The amount of time required to leach 6.0 l of extraction solution through the soil columns varied from 2 to 33 days. The addition of Ca(Cl)2 and/or KOH resulted in increased soil hydraulic conductivity. However, Pb removal was diminished with the addition of Ca(Cl)2 and KOH because of decreased Pb solubility and also a shorter residence time of the extract solution in the column. The hydraulic conductivity was related to residual calcium carbonate content, suggesting that dissolution of CaCO3 and subsequent production of CO2 gas in soil pores was partially responsible for the observed reductions in soil permeability.
KEYWORDS: remediation, lead, soil, EDTA
This paper is from the Proceedings of the HSRC/WERC Joint Conference on the Environment, May 1996, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.
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