J. Ikhsan, B. B. Johnson, John D. Wells, M. J. Angove. (000), 'Surface Complexation Modeling of the Sorption of Zn(II) by Montmorillonite', Colloids and Surfaces A: Physicochemical and Engineering Aspects, (submitted), 000.

ABSTRACT

Adsorption of Zn(II) motmorillonite samples K+-Wyoming (SWy-K), K+-Texas (STx-K) and Ca2+-Texas (STx-Ca) was studied at pH 25 o C in the presence of 10 mM KNO3 for SWy-K and STx-K or 3.3 mM Ca(NO3)2 for STx-Ca. X-ray diffraction measurements showed no change in the interlayer-spasing of the montmorillonite samples on adsorption of Zn. Data from adsorption edges, adsorption isotherms, and potentiometric titrations were modeled with an extended constant capacitance surface complexation model (ECCM). All data were fitted closely by the model which included two dominant surface reactions: cation exchange at the permanent negatively-charged sites on siloxane faces, including interlayer regions of montmorillonite, and inner-sphere surface complex formation at variable-charge surface hydroxyl groups on the edges. Generally the best fit parameters of the ECCM for the three samples agreed well. The exception was the concentration of permanent-charge sites, which was about 4-times greater for Wyoming sample.

Key Words: adsorption; zinc; montmorillonite; extended constant capacitance model; surface complexation model.