C.I. Acid Black 1 transfer from dilute solution to perlite framework in organic waste management.

Dyes, considered as toxic and persistent pollutants, must be removed from organic wastes prior to their composting and application in sustainable agriculture. Azo dyes, capable of altering the physicochemical properties of soil, are difficult to expel by conventional wastewater treatments. C.I. Acid Black 1 (AB 1), a sulfonated azo dye, inhibits nitrification and ammonification in the soil, lessens the nitrogen use efficacy in crop production and passes substantially unaltered through an activated sludge process. The retention of C.I. Acid Black 1 by raw and expanded perlite was investigated in order to examine the potential effectiveness of this aluminosilicate material toward organic waste cleanup. Dye adsorption proved spontaneous and endothermic in nature, increasing with temperature for both perlites. Expanded perlite having a more open structure exhibited a better performance compared to the raw material. Several of the most widely recognized two-parameter theoretical models, i.e., Langmuir, Freundlich, Temkin, Brunauer-Emmett-Teller (BET), Harkins-Jura, Halsey, Henderson, and Smith, were applied to reveal physicochemical features characterizing the adsorption. The Langmuir, Freundlich, Temkin, BET, Henderson, and Smith equations best fitted experimental data indicating that the adsorption of anionic dye on perlites is controlled by their surface, i.e., non-uniformity in structure and charge. This heterogeneity of surface is considered responsible for promoting specific dye adsorption areas creating dye "islands" with local dye supersaturations.

Interactions between C.I. Basic Blue 41 and aluminosilicate sorbents.

Four aluminosilicate sorbents (montmorillonite, bentonite, raw perlite, and expanded perlite) were employed for retention of the cationic dye C.I. 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.