Optimization of the adsorption of methyl green dye on almond shells using central composite design

Almond shells, known as the agricultural industry’s waste, were utilized to adsorb methyl green dye from aqueous solutions. The effects of initial concentration (2–10 mg/L), the adsorbent dosage (0.1–0.5 g), shaking speed (150–250 rpm), pH (4–7), temperature (20°C–50°C), and particle size (137–892 μm) on methyl green adsorption on the almond shell were examined. The response surface methodology was used to optimize the methyl green dye’s adsorption process using the almond shell. The central composite design was utilized to obtain optimum experimental conditions. Performed experiments obtained the isotherm data, and it was analyzed by utilizing the Langmuir, Freundlich, and Temkin isotherm models. The isotherm data can be fitted well by the Langmuir model. The pseudo-second-order model can anticipate the adsorption kinetics. The thermodynamic parameters such as ΔG° ΔH°, and ΔS° were calculated and found to be –2.878, 42.12 kJ/mol, and 0.151 kJ/mol K, respectively. These values demonstrated that the present adsorption process was feasible, spontaneous, and endothermic in the temperature scope of (20°C–50°C). This study indicates that almond shells were considered an efficient adsorbent to remove from the aqueous solutions. The maximum adsorption capacity of the almond shell (1.1 mg/g) was obtained. In this system, the almond shell’s pre-activation process was not preferred because it will create an extra cost. Adsorption kinetics studies showed that the model is represented as a pseudo-second-order of adsorption data.