Transport and Speciation of Heavy Metals in Soils during Electrokinetic Remediation: Influence of Soil Type and Electric Potential

Abstract

This paper presents transport and speciation of heavy metals in soils during electrokinetic remediation. A series of laboratory electrokinetic experiments was conducted using two different clayey soils, kaolin and glacial till, to investigate the migration and removal of heavy metals Cr(VI), Ni(II), and Cd(II). In kaolin, the acid front advances towards the cathode faster than the base front towards the anode, leading to a development of an acidic condition in most of the soil. In glacial till, however, because of its high buffering capacity, the development of the acid front is hindered, which results in alkaline conditions throughout the soil during electrokinetic remediation. In both kaolin and glacial till, Cr(VI) migration towards the anode increases as the applied voltage gradient increases. However, Cr(VI) migration was higher in glacial till as compared to kaolin because of the high pH conditions that exist in glacial till. As the voltage gradient increases, greater migration of Cr(VI) was observed in glacial till as compared in kaolin. Some Cr(VI) was reduced to Cr(III) in both soils. The Cr(VI) reduction rate to Cr(III) as well as the Cr(III) migration are significantly affected by the applied voltage gradient, leading to different chromium distributions throughout the soil. In kaolin, the applied voltage gradient has a pronounced effect on the migration of nickel and cadmium. The Ni(II) and Cd(II) migration towards the cathode increases in kaolin as the applied voltage gradient increases. Unlike kaolin, in glacial till the applied voltage gradient has no effect on nickel and cadmium migration because of its high acid buffering capacity.