Surface complexation modeling of uranyl ion sorption on mesoporous silica K. S ˇ tamberg a, *, K.A. Venkatesan b , P.R. Vasudeva Rao b a Department of Nuclear Chemistry, Faculty of Nuclear Science and Physical Engineering, Czech Technical University, Br ˇehova ´ 7, 11519 Prague 1, Czech Republic b Fuel Chemistry Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India Received 10 June 2002; accepted 26 March 2003 Abstract Sorption of uranium on MCM-41 was studied as a function of pH, time, [U(VI)] and [CO 3 2 ]. In the absence of carbonate the sorption edge occurs at pH 2 and the percentage sorption increased to 95% when the pH of the solution is 6. Further increase in pH results in complete sorption (99%) of uranium. In the presence of carbonate the percentage sorption decreased from 94 to 75% when the pH was varied from 6 to 11. The acid  /base property of MCM-41 was investigated by titration of the sorbent with HNO 3 /NaOH at constant ionic strength. Three surface complexation models, namely, the constant capacitance model (CCM), diffuse layer model and non-electrostatic chemical equilibrium model (CEM) were employed to simulate the amphoteric behaviour of MCM-41 and uranium sorption on it. Various model parameters used for describing the sorption property of the sorbent were obtained from the non-linear regression of the experimental data. The sensitivity analysis and goodness-of-fit indicated that only CEM and CCM could be used to the description of the experimental data. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Mesoporous silica; Adsorption; Uranium; Surface complexation; Modeling 1. Introduction With the discovery of mesoporous molecular sieve (MCM-41), by Kresge and Beck et al. [1,2], considerable efforts have gone in the way to develop this new family of material and employ them for the removal and separation of various metal ions from aqueous solutions [3  /6]. The striking features of MCM-41 such as very large BET surface area, large pore volume and fast kinetics of sorption attracted many researchers to utilise them as sorbent and study its sorption behaviour towards chemical and radio toxic metal ions from various waste streams. Mobil corpora- tion [6] patented a sorption separation process for the purification of water using modified MCM-41. Feng et al. [3] have developed highest capacity thiol functionalized monolayers on mesoporous silica, FMMS, for trapping Hg 2 from aqueous solution. Grun et al. [7] investigated the properties * Corresponding author. Tel.:  /420-2-243-58205; fax:  / 420-2-223-20864. E-mail address: stamberg@br.fjfi.cvut.cz (K. S ˇ tamberg). Colloids and Surfaces A: Physicochem. Eng. Aspects 221 (2003) 149  /162 www.elsevier.com/locate/colsurfa 0927-7757/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0927-7757(03)00139-0