Modeling of heavy metal ion binding by phosphoric acid activated carbon A.M. Puziy a,* , O.I. Poddubnaya a , V.N. Zaitsev b , O.P. Konoplitska b a Institute for Sorption and Problems of Endoecology, Medical Sorbents, Naumov St. 13, 03164 Kyiv, Ukraine b Taras Shevchenko Kyiv National University, Volodymyrska St. 62, 01033 Kyiv, Ukraine Received 16 April 2003; received in revised form 16 April 2003; accepted 24 July 2003 Abstract The adsorption of heavy metal ions (Cu, Cd, Co and Pb) onto oxidized synthetic activated carbon SP800-Ox modified with phosphoric acid has been investigated. It has been shown that metal adsorption order depends on solution pH and metal ion concentration. Metal ion adsorption was modeled by the surface complexation model (DDL) where carbon is represented as four independent monoprotic acid sites (super-acidic, phosphorus-containing, carboxylic and phenolic). Initial estimation of the surface group density and acidity were made on the base of single ion binding data (proton binding) analysis by a continuous distribution approach. Calculated metal ion binding constants suggest formation of only monodentate charged complex with composition (BBSOMe þ ), where BBSO  is deprotonated phosphoric, carboxylic or phenolic group. No other surface complexes were found to be significant. Super-acidic group did not participate in metal ion binding at all. # 2003 Elsevier B.V. All rights reserved. PACS: 68.45.D Keywords: Adsorption; Synthetic carbon; Heavy metals; Water treatment; Surface complexation model 1. Introduction The removal of heavy metals from aqueous solu- tions has become the major topic of water treatment research, recently. Several methods are commonly used (chemical precipitation, membrane filtration and ion exchange), but adsorption has been shown to be an economical alternative for removing trace of metals from water. Among the numerous materials applied in adsorption processes, activated carbons, primarily due to their low cost and high adsorption ability, are still the most widely used materials for adsorption of impurities. Despite a variety of com- mercially available carbons, advanced carbon adsor- bents for enhanced performance and lower cost are persistently requested. Understanding the adsorption mechanism is essen- tial for the development of new specialized activated carbons with enhanced properties tailored for specific liquid phase applications. Knowledge of the metal ion binding mechanism is necessary for description and prediction of the adsorption performance. The role of a particular surface group is crucial in designing of new advanced adsorbents with enhanced performance. Surface properties of activated carbon have been shown to play an important role in the adsorption Applied Surface Science 221 (2004) 421–429 * Corresponding author. Tel.: þ38-44-4529328; fax: þ38-44-4529327. E-mail address: puziy@ispe.ldc.net (A.M. Puziy). 0169-4332/$ – see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0169-4332(03)00956-5