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Clay Minerals; September 2007; v. 42; no. 3; p. 329-339; DOI: 10.1180/claymin.2007.042.3.06
© 2007 Mineralogical Society of Great Britain and Ireland
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Polycation adsorption on montmorillonite: pH and T as decisive factors for the kinetics and mode of chitosan adsorption

J.-H. AN* and S. DULTZ

Institute of Soil Science, Leibniz University of Hannover, Herrenhäuser Str. 2, D-30419 Hannover, Germany

* E-mail: an{at}ifbk.uni-hannover.de

(Received 11 October 2006; revised 30 April 2007)

Adsorption of the polycation chitosan on montmorillonite was studied at different pH values from 4.5 to 6.5 and at temperatures of 25, 50 and 75°C. The amount of chitosan adsorbed increased with temperature, indicating that temperature is a decisive factor. At pH 5.0 and 25°C the amount adsorbed was 1.18 molc kg–1, whereas it was 1.5 times higher (1.79 molc kg–1) at 75°C. The uptake of chitosan increased significantly at higher pH. This can be attributed to the decrease in the degree of protonation. Surface charge and X-ray diffraction measurements indicate that most of the chitosan is adsorbed in the interlayer, where mono- and bilayer structures are formed.

The kinetics of chitosan adsorption also depend on temperature and pH. At <=50°C, the adsorption mechanism of chitosan on montmorillonite is closest to the intraparticle diffusion model, whereas at lower temperature (25°C) the adsorption process is closer to the pseudo-second order model. The pH of the solution affects the protonation degree of chitosan and the mode of adsorption on montmorillonite, but not the adsorption rate.

For chitosan-montmorillonite prepared at pH 5.0 and 75°C, the effective anion exchange capacity (AEC) was found to be 80% (0.36 molc kg–1) of the calculated value. The relatively large AEC and the location of most of the anion exchange sites in the interlayer make chitosan-montmorillonite an interesting prospect as an adsorbent for water-purification procedures.

KEYWORDS: organo-clay mineral, chitosan, montmorillonite, adsorption kinetics, anion exchange capacity






JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
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