Enhanced electrokinetic removal of cadmium from sludge using a coupled catholyte circulation system with multilayer of anion exchange resin

• Processes improved, traditional and no circulation were studied.
• Multilayer ion exchange resin assisted in the improved circulation system.
• The transportation of reducible and oxidizable Cd was enhanced.
• The circulation process showed higher removal efficiency than others.
• The Cd ions in liquid have been prevented from re-entering sludge.

A bench-scale study was conducted to enhance the electrokinetic (EK) processes in the sludge remediation with an improved catholyte circulation system (improved EK-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 EK-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 EK process. Removal efficiency of Cd has increased 60%. The current and electroosmosis rates of improved EK-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 EK-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.