Adsorptive properties of sulfolignin-polyacrylamide graft copolymer for lead and uranium: Effect of hydroxilamine-hydrochloride treatment

Sulfolignin-polyacrylamide graft copolymer (PAAm-SL) was synthesized and its adsorptive features were compared with those of PAAm and PAAm-SL modified to their hydroxamic acid and amidoxime forms for Pb2+ and UO22+ ions. The increase in adsorption with increasing pH inferred that the main adsorption mechanism could be complex formation between electron donor terminals of lignin and the metal ions via proton exchanger. The modification of PAAm-SL significantly increased the adsorption capacity for UO22+. The adsorption kinetics of both ions was well compatible to second-order model. The enthalpy and entropy changes were positive, and the negative Gibbs free energy change was the proof for the spontaneity of adsorption. Sulfolignin as a water soluble lignin derivative was reusable after its grafting on PAAm having inert feature for metal ion adsorption.