Adsorption of hazardous crystal violet dye by almond shells and determination of optimum process conditions by taguchi method

Almond shells are classified as an agricultural waste of the food industry. In this study, almond shells were prepared as efficient adsorbents for removing Crystal Violet (CV) dye. The effects of adsorbent dosage, pH, initial concentration, shaking speed, temperature and particle size were studied. The Taguchi L25 experimental design method was used to obtain the optimum experimental condition. The data were analyzed using the signal to noise (S/N) ratio and analysis of variance (ANOVA) for removal of CV from aqueous solutions. The isotherm data were obtained from the experiments performed. The obtained isotherm data were analyzed via the Langmuir, Freundlich and Temkin isotherm models of which the Langmuir isotherm model fitted the best. Thermodynamic parameters such as ΔH°, ΔS° and ΔG° were calculated and the results were 18.5 kJ/mol, 0.057 kJ/mol K and –1.514 kJ/mol at 25°C, respectively. The results of this study indicate that almond shells are efficient adsorbents for removing Crystal Violet (CV) from aqueous solutions. The maximum adsorption capacity was found to be 1.075 mg/g on the almond shells. Adsorption kinetics studies showed that adsorption data can be modeled by a pseudo-second-order model. The optimum conditions for the adsorption on almond shells were found to be: adsorbent dosage = 0.5 g, concentration = 4 ppm, pH = 6, shaking speed = 200 rpm and shaking time = 180 min.