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COMPETITIVE ADSORPTION OF Cd AND DYES TO KAOLINITE

Rodney G. Harris, Bruce B. Johnson and John D. Wells^*

Colloid and Environmental Chemistry Laboratory, La Trobe University, PO Box 199, Bendigo, Victoria 3552, Australia

^* E-mail address of corresponding author: j.wells{at}latrobe.edu.au

The competitive adsorption to kaolinite between Cd(II) and four polyaromatic dyes (9-aminoacridine, 3,6-diaminoacridine, azure A and safranin O) was studied in 5 mM KNO₃ at 25°C. Under these conditions, Cd adsorbs to the silica face of kaolinite between about pH 4 and 6.5, but at higher pH, adsorbed Cd is progressively relocated to the crystal edges. In the presence of dye, less Cd adsorbed to kaolinite below pH 7. If sufficient dye was added to saturate the kaolinite surface, Cd adsorption was totally suppressed up to ~pH 6. At higher pH, Cd followed the characteristic pattern for edge adsorption. In separate experiments 9-aminoacridine and azure A displaced pre-adsorbed Cd from kaolinite. The displacement curves were initially linear, with one Cd ion being displaced for every 13 dye molecules adsorbed at pH 5.5, and one Cd ion for every 35 dye molecules at pH 7.5. The interpretation of these results is that the dyes bind to kaolinite much more strongly than Cd(II) does, but only to the silica face.

Key Words: • 9-aminoacridine • 3,6-diaminoacridine • Azure A • Clay • Displacement • Dye • Isotherm • Kaolin • Safranin O

This article has been cited by other articles:

				R. G. Harris, B. B. Johnson, and J. D. Wells STUDIES ON THE ADSORPTION OF DYES TO KAOLINITE Clays and Clay Minerals, August 1, 2006; 54(4): 435 - 448. [Abstract] [Full Text] [PDF]

				R. G. Harris, J. D. Wells, M. J. Angove, and B. B. Johnson MODELING THE ADSORPTION OF ORGANIC DYE MOLECULES TO KAOLINITE Clays and Clay Minerals, August 1, 2006; 54(4): 456 - 465. [Abstract] [Full Text] [PDF]