title: Surface complexation modeling of Cu(II) adsorption on mixtures of hydrous ferric oxide and kaolinite.
abstract: BACKGROUND
  The application of surface complexation models (SCMs) to natural sediments and soils is hindered by a lack of consistent models and data for large suites of metals and minerals of interest. Furthermore, the surface complexation approach has mostly been developed and tested for single solid systems. Few studies have extended the SCM approach to systems containing multiple solids.
  
  
  RESULTS
  Cu adsorption was measured on pure hydrous ferric oxide (HFO), pure kaolinite (from two sources) and in systems containing mixtures of HFO and kaolinite over a wide range of pH, ionic strength, sorbate/sorbent ratios and, for the mixed solid systems, using a range of kaolinite/HFO ratios. Cu adsorption data measured for the HFO and kaolinite systems was used to derive diffuse layer surface complexation models (DLMs) describing Cu adsorption. Cu adsorption on HFO is reasonably well described using a 1-site or 2-site DLM. Adsorption of Cu on kaolinite could be described using a simple 1-site DLM with formation of a monodentate Cu complex on a variable charge surface site. However, for consistency with models derived for weaker sorbing cations, a 2-site DLM with a variable charge and a permanent charge site was also developed.
  
  
  CONCLUSIONS
  Component additivity predictions of speciation in mixed mineral systems based on DLM parameters derived for the pure mineral systems were in good agreement with measured data. Discrepancies between the model predictions and measured data were similar to those observed for the calibrated pure mineral systems. The results suggest that quantifying specific interactions between HFO and kaolinite in speciation models may not be necessary. However, before the component additivity approach can be applied to natural sediments and soils, the effects of aging must be further studied and methods must be developed to estimate reactive surface areas of solid constituents in natural samples.
authors.affiliation: Arizona State University, School of Earth and Space Exploration, AZ, USA. tlund@asu.edu
authors.forename: Tracy J
authors.initials: TJ
authors.lastname: Lund
authors.forename: Carla M
authors.initials: CM
authors.lastname: Koretsky
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Landry
authors.forename: Melinda S
authors.initials: MS
authors.lastname: Schaller
authors.forename: Soumya
authors.initials: S
authors.lastname: Das
references.citation: J Colloid Interface Sci. 2005 Feb 15;282(2):270-82
references.pmid: 15589531
references.citation: J Environ Qual. 2002 Jul-Aug;31(4):1129-36
references.pmid: 12175030
references.citation: J Environ Qual. 2002 Nov-Dec;31(6):1901-9
references.pmid: 12469840
references.citation: J Colloid Interface Sci. 1999 Sep 15;217(2):403-410
references.pmid: 10469549
references.citation: J Colloid Interface Sci. 2006 Mar 1;295(1):1-13
references.pmid: 16168423
references.citation: Environ Sci Technol. 2002 Feb 1;36(3):328-36
references.pmid: 11871545
references.citation: J Environ Qual. 2002 Jan-Feb;31(1):193-203
references.pmid: 11837423