Isotherms, kinetics and thermodynamics of industrial dye acid red 27 adsorption on Sugarcane Bagasse Ash.

Abstract

In this study, sugarcane bagasse ash (SCBA), obtained as residue from the sugar mill, was used as an adsorbent for Acid Red 27 (AR27) removal from aqueous solutions. The ash characterization data showed 23.63% of organic compounds and silica (α-SiO2) as the most expressive inorganic compound (confirmed by X-ray diffractogram), the BET surface area had a value of 62.79 m2.g-1 and the pHpzc was 8.45. Regarding the adsorptive tests, the optimal initial pH to the dye removal was 2.0. The adsorption equilibrium reached in about 4h contact time and optimum SCBA dosage was found to be 4g.L-1. The pseudo-second order model best represented the adsorption kinetics. The Freundlich equation presented the best fit to the equilibrium data for the removal of AR27 by ash, with maximum adsorption capacity of 15mg.g-1 at pH 2.0. Thermodynamic study indicate that AR27 adsorption on SCBA occurs through a physisorption mechanism, with ΔHºads < 15kJ.mol-1. The ΔHºads evaluated by Vant' Hoff equation was explained as a combination of water desorption enthalpy, ΔHºW and isosteric like enthalpy, ΔHºD for the dye adsorption in liquid environment. The ΔHºD = 9.2kJ.mol-1 was calculated from Clausius-Clapeyron approach. The effects of coexisting anions on the adsorption and regeneration and reuse of the adsorbent were also investigated. This study suggests that SCBA, which was used without any pretreatment, has the potential to be applied as a low-cost adsorbent to mitigate effluents contamination with AR27 dye at low concentrations.