Electrokinetic removal of aluminum from water potabilization treatment sludge

Abstract

Electrokinetic extraction is an emerging technology that can be used to remove in situ contaminants from soils or industrial sludge by application of an electric field. Hydrogen evolution at the cell cathode can adversely affect removal of ionic contaminants by formation of non-conducting, solid Al(OH)3: acidic or complexing agents have to be used to avoid this phenomenon. The technique has been investigated for the remediation of potabilization water treatment sludge with a high Al (III) content in a discontinuous three-compartment cell. First tests were achieved with acetic or citric acid introduced in the cathode chamber for neutralization of OH− generated at the electrode, and Al (III) could be recovered near the cathode. The effect of the cell voltage was investigated. In a second series of experiments EDTA was introduced also in the sludge bed. Interpretation of the profiles of pH and Al concentration in the cell after treatment was made considering the speciation diagram of the (Al (III)–chelating agent) systems. Best results were obtained by using 0.1M acetic acid: up to 80% of the initial Al was recovered near the cathode, with an energy demand close to 7kWh per kg Al.