InfroductionA process for the capacitive deionization (CDI) of water with a stack of carbon aerogel electrodes has been developed by Lawrence Livermore National Laboratory.Aqueous solutions of NaC1 or NaNO3 are passed through a stack of carbon aerogel electrodes, each having a very high specific surface area (400 to 1100 m2/g). After polarization, nonreducibie and nonoxidizable ions are removed from the electrolyte by the imposed electric field and held in electric double layers formed at the surfaces of electrodes, as shown in Fig. la. As desired, the effluent from the cell is purified water. This process is also capable of simultaneously removing a variety of other impurities. For example, dissolved heavy metals and suspended colloids can be removed by electrodeposition and electrophoresis, respectively. CDI has several potential advantages over other more conventional technologies. Unlike ion exchange, no acids, bases, or salt solutions are required for regeneration of the system. Regeneration is accomplished by electrically discharging the cell. Therefore, no secondary waste is generated. In contrast to thermal processes such as evaporation, CDI is much more energy efficient. Since no membranes or high pressure pumps are required, CDI offer operational advantages over electrodialysis and reverse osmosis (RO).

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An electrically regenerated separation process has been developed for removing unwanted ions from aqueous waste streams as a minimally polluting, energy-efficient, and potentially cost-effective alternative to ion exchange, reverse osmosis, electrodialysis, and evaporation. Ground water containing various anions and cations is passed through a stack of carbon aerogel electrodes, each having a very high specific surface area (400−1100 m2 g-1) and exceptionally low electrical resistivity (≤40 mΩ·cm). After polarization of the stack, impurity ions are removed from the electrolyte by the imposed electric field and adsorbed on the electrode surfaces. Field tests have shown that hexavalent chromium in the form of HCrO4 -/CrO4 2-/Cr2O7 2- can be selectively removed from contaminated ground water with a 530 ppm total dissolved solids (TDS) background. The concentration of Cr(VI) can be lowered from 35 to 2 ppb, well below the acceptable level for the regulatory surface water discharge limit of 11 ppb. The mechanism for Cr(VI) separation involves chemisorption on the carbon aerogel anode, a process that can be reversed by cathodic polarization. Cr(VI) removal is not based upon simple double-layer charging.

This is a preprint of a papcr inknded for publication in a journal or proceedings. Since changes may bc made before publication, this preprint is ma& available with the undcrstanding that it will not bc citcd or reproduced without the permission of the author. DISCLAIMERThis document was prepared as an m u n t of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any wmranty, express or implied, or assumes any l g a l liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or prdisclosed, or represents that its use would not infringe privately owned rights. ABSTRACTCapacitive deionization with carbon aerogel electrodes is an efficient and economical new process for removing salt and impurities from water. Carbon aerogel is a material that enables the successful purification of water because of its high surface area, optimum pore size, and low electrical resistivity. The electrodes are maintained at a potential difference of about one volt; ions are removed from the water by the imposed electrostatic field and retained on the electrode surface until the polarity is reversed. The capacitive deionization of water with a stack of carbon aerogel electrodes has been successfully demonstrated. The overall process offers advantages when compared to conventional water-purification methods, requiring neither pumps, membranes, distillation columns, nor thermal heaters. Consequently, the overall process is both robust and energy efficient. The current state of technology development, commercialization, and potential applications of this process are reviewed.

Boron containing stainless steels are used in the nuclear industry for applications such as spent fuel storage, control rods and shielding. It was of interest to compare the corrosion resistance of three borated stainless steels with standard austenitic alloy materials such as type 304 and 316 stainless steels. Tests were conducted in three simulated concentrated ground waters at 90°C. Results show that the borated stainless were less resistant to corrosion than the witness austenitic materials. An acidic concentrated ground water was more aggressive than an alkaline concentrated ground water.