(254z) Sorptive Removal of Cationic – and Anionic Dyes By the Acid Activated Red Mud from Aqueous Solutions

Sinem Ortaboy^1,2, Elif Turker Acar¹, Elif Tuzun¹, Gulten Atun¹

¹Chemistry, Istanbul University, Engineering Faculty, Istanbul, Turkey

²University of California at Berkeley, Berkeley, CA, United States of America

In recent years, many attempts have been made to use bauxite waste red mud (RM) for wastewater treatment to remove both cationic^1,2 and anionic colorants³. It has been shown that acid treatment improves surface properties of the RM sorbents.¹

In this study, the RM was treated with HCl according to Shiao and Akashiâ??s procedure before use in sorption experiments.⁴ The diffusion coefficients of the MB and NB on the RM were estimated as 6.4 Ã? 10^-11 and 4.0 Ã? 10^-11 m²/s, respectively, by using the Vermeulen approximation based on homogeneous surface diffusion.

Experimental equilibrium data obtained in the initial concentration range of 0.5 â?? 20 mmol/L were fitted to the Langmuir and Freundlich isotherm models. The monolayer capacities for MB increased from 0.019 to 0.056 mmol/g in the temperature range of 288â??318 K. Thermodynamic calculations showed that spontaneity of the endothermic sorption process was entropy controlled. The sorption capacity of ~0.021 mmol/g for NB was not influenced by temperature but the sorption equilibrium constants were significantly decreased indicating that sorption process was exothermic in nature. The pH change during the sorption process showed that NB^- anions are adsorbed on positively charged surface hydroxyl groups while sorption of MB⁺ cations takes place on the negatively charged surface sites. The diffuse reflectance infrared Fourier transforms (DRIFT) spectral analysis of the bare and dye loaded RMs were also used to elucidate sorption mechanisms.

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