Four alummosilicate sorbents (montmorillonite, bentonite, raw perlite, and expanded perlite) were employed for retention of the cationic dye C.1. Basic Blue 41. Interactions between the clay and the dyestuff were investigated at several temperatures and clay:dye ratios. The mechanism behind the adsorption involves the formation of H-aggregates of the dye on both clays, followed by dye migration into the interlayer in the case of montmorillonite. Time-dependent absorbance spectra revealed the presence of various dye species in montmorillonite. Introduction of the dye molecules into the interlamellar space occurs more rapidly in bentonite than in montmorillonite. The dye molecules inserted between the clay leaves adopt different orientations and, eventually, stack in layers at increased dye loadings for both montmorillonite and bentonite. Higher dye aggregates are then present as suggested by diffuse reflectance spectroscopy. Dye sorption on both raw and expanded perlite proceeds via H-aggregate formation as well. (c) 2005 Elsevier Inc. All rights reserved.