The effect of ammonia as a complexing reagent to enhance the efficiency of the in situ electrokinetic remediation is evaluated. Lab scale experiments with copper spiked kaolin were carried out to explore if the metal precipitation can be avoided at neutral and alkaline pH. Ammonia was added at the anode compartment and therefore delivered into the soil as ammonium by ionic electromigration. Two set of experiments have been performed, one using ammonia solution as anolyte and sodium nitrate as catholyte, and the other, combining the ammonia enhancement with the addition of acetic acid into the cathode (weak-acid enhancement). Results show that metal recovery with only ammonia was less than 40% removal whereas the combination of ammonia and acid enhancements achieved copper recoveries above 90%. A two-dimensional mathematical model was used to analyze the remediation with good reproducibility indicating that for this system the transport and chemical processes included in the model are the most important for the description of this experimental system. (c) 2006 Elsevier Ltd. All rights reserved.