Electrosorption of Chromium Ions on Carbon Aerogel Electrodes as a Means of Remediating Ground Water

Abstract

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.

Evaluating hexavalent chromium reduction and electricity production in microbial fuel cells with alkaline cathodes

“…3d), indicating that another Cr(VI) removal pathway was present at lower pH. With Cr(VI) at the pH range studied being mainly in the negative chromate ion (CrO 4 2-) form, Cr(VI) cannot be electrostatically removed by the also negatively charged cathode (Farmer et al 1997). A more possible mechanism which explains this decrease in Coulombic efficiency would be that of chemical Cr(VI) reduction by lactic acid (Deng and Stone 1996).…”

Developing Nano-Structured Carbon Electrodes for Capacitive Brackish Water Desalination

“…He has published several comprehensive papers analysising the use of new carbon materials in the CDI process as well as fundamental electrochemical double layer issues of the electrodes [9][10][11][12][13]. In the mid-1990s, Farmer and co-workers [14][15][16][17] from the Lawrence Livermore National Labs (LLNL), developed a new kind of high specific surface area material which was called carbon aerogel for their CDI device and at the same time rekindled interest in CDI within the scientific community.…”

“…In recent years, most reports in terms of CDI typically utilized various carbons, such as carbon aerogels [14][15][16], carbon cloth [18][19][20], carbon sheets [21], carbon nanotubes [22][23][24][25][26][27][28][29][30]and mesoporous carbon [31][32][33][34] etc as electrode materials because these materials have the advantage of high specific surface area, easy large scale production and environmental-friendly. I n a d d i t i o n t o C D I , m e m b r a n e c a p a c i t i ve deionization technology (MCDI) as an modification of CDI has attracted great attentions.…”

Desalination with carbon aerogel electrodes. Revision 1

“…,For example, dissolved heavy-metal ions can be removed by reversible electrosorption [27] or by electrodeposition [28][29][30][31], in contrast to simple double-layer charging. In the specific case of carbon aerogel C.DI, LLNL.…”

“…In the case of a 1:1 electrolyte in water at 25"C, the characteristic thickness of the diffise layer ranges from 1 nm at a concentration of 0.1 M to 30 nm at 104 M [26,27]. Though BET surface areas are frequently quoted, the electrosorption capacity, given as equivalents adsorbed per gram of carbon is believed to be a more relevant measure of electrode performance (7,8].…”