Adsorption from aqueous solutions of selected heavy metal cations on chemically modified activated carbon

The adsorption of selected cations (chromium/III/, iron/III/, copper/II/, and silver/I/) from aqueous solutions on modified activated carbons was studied. Carbon-oxygen and carbon-nitrogen surface species were formed on the activated carbon (previously de-ashed) by treating it with concentrated nitric acid or ammonia. The modification procedures differentiated the chemical nature of carbon surface rather, than its porous structure. The surface chemistry of the carbons was characterized by selective neutralization techniques and the XPS method. The number of adsorbed ions depends on the surface acid-base functional groups and the pH equilibrium in the aqueous external solution. The adsorbed species were eluated with water, dilute nitric acid, and ethanol and then identified (in bulk solution). The form of the metal bond to the carbon surface was studied by XPS. The adsorptive behaviour of these modified carbons is explained on the basis of their surface acidity and/or basicity and their redox properties.