Electrosorption/electrodesorption of arsenic on a granular activated carbon in the presence of other heavy metals

The adsorption, electrosorption, and electrodesorption of aqueous, inorganic arsenic on the granular activated carbon (GAC), DARCO 12 20 (Darco 1220) GAC, were investigated in solutions containing arsenic as the only contaminant, as well as with chromium, nickel, and iron. Darco 1220 was selected for these investigations primarily because it is relatively ineffective as a normal (unassisted) arsenic adsorbent in the chosen electrolytes at the low loadings used. It is shown that the application of anodic potentials in the 1.0-1.5 V range, however, result in enhanced uptake, most likely because of charging of the electrochemical double layer at the electrode surface. Regeneration (100%) of electrosorbed arsenic was achieved via electrodesorption at a cathodic potential of 1.50 V. The presence of metal ad ions was observed to have a significant and complex effect on arsenic adsorption, electrosorption, and electrodesorption. In particular, the Cr/As ratio was shown to have complex effects, decreasing adsorption uptake when present as 3:2 but enhancing adsorption when present as 5:1. Nickel was found to have less of an effect than chromium, except at the highest anodic potential used of 1.50 V, where it exhibited better performance than chromium. The presence of iron significantly enhanced uptake. With a 1.50 V anodic potential, the bulk arsenic concentration was reduced to less than detectable limits, well below the United States Environmental Protection Agency (U.S. EPA) maximum contaminant level (MCL) for drinking water. Regeneration efficiency by electrodesorption for the As-Fe system was greater than about 90%.