Sorption of Acid Black 1 dye onto bentonite - equilibrium and kinetic studies.

The present study shows sorption capacity of bentonite from the Slovak Jelšový Potok deposit for the anionic dye (Acid Black 1) from aqueous solutions and uses it as an effective and economical adsorbent for the removal of anionic dye. The laboratory experiments were carried out in batch method at 3 different sorbent doses (20, 10 and 5 g L) and an initial concentration of dye ranging from 1 to 1,000 mg L. The adsorption equilibria data were fitted by Freundlich, Langmuir, Dubinin-Radushkevich and Temkin isotherms. The Langmuir equation provided the best description for the sorption, indicating that adsorption occurred on a mono-layered surface. The maximum sorption capacity of bentonite has been estimated as 31.29 mg g. Moreover, the results showed that non-linear method could be a better way to obtain the isotherm parameters. The pseudo-first- and pseudo-second-order equations have been applied for the determination of time effect on sorption/removal of dye from solution. The highest determination coefficient values were observed for the pseudo-second-order model, suggesting chemical character of the adsorption process. Acid Black 1 was probably bound through chemisorption by forming hydrogen bonds between the Si-OH and Al-OH groups in the bentonite and the -NH, -NH2 and -OH groups in the dye.