Electrosorption of arsenic on DARCO 12×20 from dilute aqueous solution

Adsorption, electrosoroption and electrodesorption of g.l-1 levels of arsenic from aqueous solutions has been investigated using Darco 12×20 GAC as the sorbent material. Electrolytes containing 500 mg.l-1 of a supporting electrolyte (NaCl or Na2SO4) spiked with 100 g.l-1 inorganic arsenic have been studied. The effects of the presence of Cr, Cu, Fe and Ni at the g.l-1 level have also been investigated. Darco 12×20 GAC was shown to be ineffective as an arsenic adsorbent in the range of conditions studied. The ability of Darco 12×20 to remove inorganic arsenic from aqueous solution was found to be significantly enhanced by the application of an electrochemical potential. Application of a suitable cathodic potential to the carbon working electrode was found to result in almost 100% desorption of the adsorbate. The presence of 100 g.l-1 chromium resulted in the removal of arsenic and chromium at similar linear rates suggesting the formation of an insoluble compound such as CrAsO4 via an electrochemically enhanced precipitation. Increasing the concentration of chromium from 100 g.l-1 to 347 g.l-1 (6.67 mol.l-1) resulted in first order arsenic removal in adsorption and electrosorption at 1.00 V, 1.25 V, 1.50V, 1.75 V and 2.00V anodic with ~50% of the arsenic being electrodesorbed at 2.00 V cathodic. The presence of 6.67 mol.l-1 Cu(II) was found to have a detrimental effect on arsenic adsorption and electrosorption. Electrosorption was found to proceed in the presence of 6.67 mol.l-1 Ni(II) with 125 mg of sorbent reducing the concentration of 500 ml of electrolyte from 100 g.l-1 arsenic to below the USEPA MCL of 10 g.l-1 at a potential of 1.75 V anodic. The presence of 6.67 mol.l-1 Fe(III) resulted in almost 100 % arsenic removal at 1.25 V anodic with almost complete arsenic desorption at a potential of 1.75 V cathodic.