Removal of auramine-O dye from aqueous solutions using two natural adsorbents and process optimization using RSM

Document Type : Original Article

Authors

1 Department of Chemistry, Faculty of Basic Sciences, Ayatollah Boroujerdi University, Boroujerd, Iran

2 Department of Mathematics, Faculty of Basic Sciences, Ayatollah Boroujerdi University, Boroujerd, Iran

Abstract

The purpose of this study is to evaluate the applicability of two bio-adsorbents, tea waste and calcined eggshell, for the removal of auramine-O dye from aqueous solutions using the adsorption process. A comparison between the characterization of FTIR, XRD, and SEM for adsorbents before and after adsorption confirmed the adsorption of auramine-O on them. Effective parameters including initial solution pH, initial auramine-O concentration, adsorbent dosage, contact time, and temperature were optimized using response surface methodology with a central composite design. The highest removal efficiency was obtained under optimal conditions, predicting removal efficiencies of 97.68% for tea waste and 97.50% for calcined eggshell. Experimental results showed removal efficiencies of 96.50% and 96.20% for tea waste and calcined eggshell, respectively. The optimal pH close to a neutral medium and temperatures close to room temperature reduce the cost of scaling up the process. Adsorption isotherms, thermodynamics, and kinetics were also studied, revealing that the adsorption process follows the Langmuir isotherm, is thermodynamically exothermic and spontaneous and is kinetically a function of the pseudo-second-order model.
The adsorption amount of auramine-O on tea waste can vary depending on the type of tea and its processing method. Incomplete decomposition of calcium carbonate to calcium oxide during the calcination of eggshell and the prevention of the formation of a porous structure can affect adsorption efficiency.
Although the optimal conditions for achieving maximum adsorption are specific to these adsorbents and adsorbate, independent research can be conducted to industrialize the adsorption process.
Among the adsorbents in literature to remove auramine-O, NaX nanozeolites and multiwall carbon nanotubes have a higher removal efficiency than tea waste and calcined eggshell. However, they are not natural, abundant, are expensive and their preparation is difficult and costly. Therefore, the adsorbents used in this work are more suitable for removing auramine-O.

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Applied Chemistry Today
Volume 20, Issue 77
January 2026
Pages 73-92

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