A Kinetic and Thermodynamic Study of Cationic Thiazine Dye Removal From Aqueous Solution by Date Stones Variety Ghars

Abstract

Date stones represent an unused resource that is often incinerated or disposed of directly as waste. Therefore, great attention has been paid to transforming it into useful products. This study was conducted to evaluate the ability of activated carbon prepared from the stones of one of the date varieties, called “Ghars,” as an agricultural waste to remove a basic dye, methylene blue (MB), from aqueous solutions. The surface characteristics of prepared activated carbon Ghars stones (ACGS) were characterized using scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. Physical and chemical factors affecting MB adsorption, such as contact time, the mass of adsorbent, potential of hydrogen (pH) value, and initial concentration of the solution, were studied in a batch system. Isotherm equilibrium data are well described by the Freundlich model (R2 = 0.98), and the experimental adsorption capacity was found to be (qe.exp = 130.3 mg/g) at 298 K. The kinetic study indicates that the adsorption process of MB follows the pseudo‐second‐order (PSO) model. ΔH° (19.94 J/mol) and ΔG° (−1.101, −1.127, −1.430, and −1.546 kJ/mol) values revealed that the adsorption of MB on ACGS was endothermic nature, feasible, and spontaneous. The positive value of ∆S° (15.67 kJ/mol) confirmed the increased in the randomness at the solid‐solution interface during the adsorption process of MB on ACGS. MB adsorption/desorption experiments demonstrated the reusability of ACGS for five consecutive cycles. The results showed that ACGS developed from agricultural waste could be successfully used to remove cationic organic pollutants from wastewater.