Alizarin Red Removal Using Epichlorohydrin-Modified Walnut Shells

This study investigated the adsorption of alizarin red (AR) from aqueous solutions using Epichlorohydrin-Modified Walnut Shells (EMWS). Through static adsorption experiments, the impact of contact time (tc), initial pH of the solution, solution concentration (c0), and temperature (T) on the adsorption of AR onto the EMWS was examined. The optimum values of tc and pH were determined to be 360 min and 3.51, respectively. The adsorption capacity of the EMWS for AR increased when c0 and T were increased. Non-linear fitting of the equilibrium data was performed using the Langmuir, Freundlich, and Temkin isotherms. AR adsorption was well explained by the Langmuir isotherm with the qm of 81.44 mg/g at 323 K. To simulate the adsorption kinetics, various models including pseudo-first-order, pseudo-second-order, intra-particle diffusion, and Elovich models were employed. The results indicated that it followed the PSO kinetic model (k = 4.56 × 10 -4 g / (mg·min), qe = 18.84 mg/g and R2 = 0.9808). Moreover, the Elovich model confirmed the occurrence of chemisorption. According to thermodynamic investigations, the adsorption of AR is found to be spontaneous (ΔG﹤0) and endothermic (ΔH = 12.24 kJ/mol) while exhibiting an increase in entropy (ΔS = 58.5 J / (mol.K)). The results indicated that EMWS showed great potential as an affordable and efficient adsorbent for treating AR wastewater.