A bench-scale study was conducted to enhance the electrokinetic (EM) processes in the sludge remediation with an improved catholyte circulation system (improved EM-C). Three layers of replaceable anion exchange resin were set in the system to prevent cadmium ions migrated into liquids from re-entering the sludge. Results indicate that the improved EM-C treatment was more stable and efficiently prevented Cd ions to re-enter the sludge which is necessary for providing better assurance and had positive effects on Cd removal, especially in a long period of EM process. Removal efficiency of Cd has increased 60%. The current and electroosmosis rates of improved EM-C increased rapidly. The pH in sludge and the cathode reservoir were between 7.1 and 8.7. Sequential extraction analysis reveals that the reducible and oxidizable Cd had higher removal efficiencies after improved EM-C. The increased potential availability indicates that the attached Cd was desorbed and transformed to a more readily migratory form (exchangeable), which was the reason of Cd removal enhancement. (C) 2013 Elsevier B.V. All rights reserved.