Adsorptive removal of cationic and anionic dyes from aqueous solution by utilizing almond shell as bioadsorbent

Abstract

Almond shell is a food waste that is utilized as bioadsorbent for the uptake of Eriochrome Black T (EBT) and Malachite Green (MG) dyes from aqueous solutions. The biomaterial was characterized by specific surface area (BET), scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, and X-ray diffraction. The effects of the initial pH of solutions, particle size, adsorbent dosage, initial dye concentration, contact time, and temperature on the EBT and MG adsorption were studied using batch contact mode at 22 °C. Rapid sorption dynamics following a second-order kinetic model were shown by kinetic studies. The adsorption equilibrium data were fitted well to the Freundlich isotherm for EBT and MG as anionic and cationic dyes, respectively. The adsorption of pollutants was exothermic (ΔH0 = −1.7 kJ mol−1 for EBT and −32 kJ mol−1 for MG). The reaction was accompanied by a decrease in entropy (ΔS0 < 0 for EBT and MG). Negative values of ΔG0 showed the spontaneity of the MG adsorption process. However, positive values of ΔG0 showed that the EBT uptake by almond shell is not a spontaneous reaction. The results indicate that almond shell is a promising alternative for the biosorption of anionic (EBT) and cationic (MG) dyes from aqueous solutions.