The objective of this project was to develop novel functionalized carbon aerogel electrodes that are integrated in an electrochemical cell for selective removal of heavy metals. Treatment of large amount of aqueous wastes containing heavy metal ions at many U.S. Department of Defense (DoD) and Department of Energy (DOE) facilities requires considerations of wide ranging technologies with flexible and, sometimes, customized capabilities. One example is the need to remove radioactive Cs+ from a large background of Na+ and K+. Another example is the removal of Resource Conservation and Recovery Act (RCRA) metals from brackish groundwaters or plating shop effluents.

The technical approach involves three integrated major tasks. The primary task is to develop functionalized carbon aerogels that would have a specific affinity for a targeted metal. Four types of carbon aerogel electrodes will be prepared and studied. The conventional resorcinol-formaldehydebased carbon aerogel electrodes and three modified types of materials treated by thermal activation and chemical modifications (2 methods). Acidic carbon-oxygen complexes can be introduced on carbons by thermal treatment with oxidizing agents (O₂, CO₂, steam) or by chemical treatment in solutions with KMnO₄, HNO₃. Chemical treatment via silanization and amidization to introduce compounds such as porphyrin compounds (tetra(p-aminophenyl)porphyrin) will be studied. These modified electrodes are expected to have special affinity for metal cations such as Cr, Co, Cu, Ni and Zn. These novel materials will then be incorporated (second task) in an electrochemical separation cell. The cell dimension will contain active electrode surfaces of 2 inch x 4 inch. The cell is undivided and uses no membranes. The cells are polarized by programmable power supplies that have a voltage range of 0 to 1.2 V with a current range between 0 and 60 A. The third task is to investigate selective removal of 35 ppb Cr(VI) [Lawrence Livermore National Laboratory (LLNL) contaminated source level] from an aqueous solution containing other non-toxic components such as Na+, K+, and Ca2+. Total dissolved solids (TDSs) in these solutions are about 500 ppm. The effects of selective removal of Cr and another heavy metal (Co, Cu, Pb, Zn and Ni) will be investigated. The primary risk would be the complicated phenomena associated with competitive electrosorption of a heavy metal and other ions. The fabrication of and the selective separation with functionalized electrodes has not been investigated in the past.

In FY97, LLNL researchers focused their efforts on finding solutions to the specific needs of DoD and DOE facilities to treat large amount of aqueous wastes containing heavy metal ions. This integrated experimental program has worked toward developing tailored carbon aerogel electrode materials that are modified chemically and physically to enhance the selective separation of a targeted metal from an aqueous stream. The research has begun to demonstrate and/or identify factors affecting selective removal of a model species, Cr. Other metal ions such as Co, Cu, Pb, Zn and Ni and selected mixtures will be considered. Researchers have also initiated the study of the effects of interfering phenomena such as side reactions, poisoning, and preferential removal of concomitant undesired species.

This project will provide DoD and DOE a novel and promising technology for efficient waste remediation. It has significant implications and applications in a wide range of areas besides metal separation. The project also leveraged SERDP investment in capabilities and knowledge on Capacitive Deionization and its three successful demonstration projects at one DOE and two DoD sites.

This projects will transition its result directly DoD and DOE sites, providing a novel and promising technology for efficient waste remediation.