Adsorption of toxic metals from water using commercial and modified granular and fibrous activated carbons
Commercial granular and fibrous activated carbons have been studied for the removal of heavy metals from aqueous solutions. A wood based activated carbon (AUG WHK) and an activated carbon cloth (KoTHmex TC-66 C) based on polyacrylonitrile fibre as a precursor, were oxidised for different periods of time using nitric acid, ozone and electrochemical methods to introduce various acidic groups at the surface, thereby, enhancing metal binding capacity. Modified samples were subsequently studied for the specific removal of cadmium and mercury ions in solution and compared with the performance of a commercially available weak acid fibrous exchange material (Ecofil-Deco Ltd. K-4). Carbonaceous adsorbents were physically characterised by scanning electron microscopy, surface area and porosimetry (using N2 adsorption at 77K). There was a decrease in BET surface area betweenu ntreateda nd oxidised samples. Acid and electrochemically oxidised samples were completely stable although there was clear evidence of physical damage to ozone-oxidised carbons. Samples were also chemically characterised by pH titration, direct titration, X-ray photoelectron spectroscopy and elemental analysis. A significant increase in oxygen content was obtained after oxidation, which increased the total ion exchange capacity by a factor of approximately 3.3 compared to commercial as-received carbonaceous adsorbents. As the degree of oxidation increased, the point of zero charge was shifted to lower pH values, i. e. from 4.5 to 3.6. (Continues...).