Removal of contaminants from fine-grained soils using electrokinetic flushing. Semiannual report, July 1 through December 31, 1992

摘要

This report details the status of work conducted on the use of electrokinetics (EK) to remediate a fine grained soil contaminated with lead. The experimental work entails soil collection and characterization, soil adsorption and desorption of lead, and experimental setup construction and testing. Test soil was collected from Northern Erie County, New York and underwent standard preparation and physical/chemical characterization. The soil is a silt loam with a low hydraulic permeability ((approx) 10(sup (minus)7) cm/s), a large amount of fine materials, moderate organic carbon content, and a moderately high cation exchange capacity (CEC). The soil has a low indigenous lead content and is slightly acidic. The soil was artificially contaminated with lead to concentrations of 95, 800, and 7,600 mg Pb/kg soil. Lead desorption experiments were conducted using several concentrations of HCl, HNO(sub 3), EDTA, CaCl(sub 2), acetic acid, and tap water. HCl, HNO(sub 3), and EDTA desorbed the majority of the soil-bound lead. Acetic acid and CaCl(sub 2) were less effective while tap water was ineffective. An experimental apparatus consisting of a consolidation unit and electrokinetic (EK) soil reactor to mimic EK flushing in the field was designed and constructed. The experimental unit underwent testing to determine if water could be moved through the soil under an applied electric current. Significant quantities of water were moved through soil. Based on limited results, water movement increased with increased conductivity. The pH and conductivity of the reservoir waters were monitored during the reactor testing. With time, the pH at the cathode dropped to less than 4 and at the anode was raised to about 10. Conductivities of the two reservoirs increased from their initial values because of ion migration from the soil into the reservoirs and the increase in either H(sup +) and OH(sup (minus)).