ELECTROSORPTION OF CHROMIUM IONS ON CARBON AEROGEL ELECTRODES AS A MEANS OF REMEDIATING GROUND-WATER

An electrically regenerated separation process has been developed for removing unwanted ions from aqueous waste streams as a minimally pollu ting, energy-efficient, and potentially cost-effective alternative to ion exchange, reverse osmosis, electrodialysis, and evaporation. Groun d water containing various anions and cations is passed through a stac k of carbon aerogel electrodes, each having a very high specific surfa ce area (400-1100 m(2) g(-1)) and exceptionally low electrical resisti vity (less than or equal to 40 m Omega . cm). After polarization of th e stack, impurity ions are removed from the electrolyte by the imposed electric field and adsorbed on the electrode surfaces. Field tests ha ve shown that hexavalent chromium in the form of HCrO4-/CrO42-/Cr2O72- can be selectively removed from contaminated ground water with a 530 ppm total dissolved solids (TDS) background. The concentration of Cr(V I) can be lowered from 35 to 2 ppb, well below the acceptable level fo r the regulatory surface water discharge limit of 11 ppb. The mechanis m for Cr(VI) separation involves chemisorption on the carbon aerogel a node, a process that can be reversed by cathodic polarization. Cr(VI) removal is not based upon simple double-layer charging.