Colloids and Surfaces A: Physicochemical and Engineering Aspects 170 (2000) 65 – 77 Copper – gibbsite interactions: an application of 1-pK surface complexation model R. Weerasooriya * , B. Dharmasena, D. Aluthpatabendi Chemical Modeling Project, Institute of Fundamental Studies, Kandy, Sri Lanka Received 17 August 1999; received in revised form 8 January 2000; accepted 19 January 2000 Abstract Copper and proton adsorption on gibbsite were determined at differing experimental conditions. The pH zpc of gibbsite was 8.70. As determined by the basic Stern-layer model (BSM), the optimized binding constants of electrolytic ions were K Na =-0.31 and K NO 3 =7.94. These parameters were coupled with the charge-distribution multi-site ion complexation (CD-MUSIC) model in quantifying copper adsorption by following reaction stoichiome- try. (AlOH -1/2 ) 2 +Cu 2 + =[(AlOH) 2 z Cu w ] +1 log K =7.15 90.7 © 2000 Elsevier Science B.V. All rights reserved. Keywords: Gibbsite; Charge distribution multi-site ion complexation model; 1-pK model; Surface complexation; Copper www.elsevier.nl/locate/colsurfa 1. Introduction A wide array of heterogeneous complexants such as dissolved organic matter (e.g. humic sub- stance, HS), mineral surfaces (e.g. metal hydrous oxides, clays), and bacterial ex-polymers is ubiqui- tous in natural aquatic environments [1]. When compared with the anomalous metal binding ca- pacity of HS, the transport, toxicity and removal of trace metal ions in aquifers and natural waters are controlled in part by sorption/desorption on hydrous metal oxides and clays. Hither to date, substantial chemical information is available about trace elements binding on various iron hy- droxides [2]. However, the relevant data on alu- minum hydrous oxides, gibbsite in particular, are comparably low [3–8]. The overall aim of this investigation was to determine copper adsorption behavior on gibbsite over a range of physico- chemical conditions that are significant from the environmental viewpoint. The selection of Cu 2 + was made primarily due to its contrasting chem- istry and potent biological significance. The cop- per deposited in human brain, skin, liver, pancreas and myocardium may cause ‘Wilson’s disease’ [9]. Thus the EPA promulgated in 1991 that the maximum contaminant level goal is 1.3 * Corresponding author. Tel.: +94-8-232002, ext. 24; fax: +94-8-232131. E-mail address: rw130@usa.net (R. Weerasooriya) 0927-7757/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0927-7757(00)00453-2