Direct Blue ۷۱ Removal from Aqueous Solutions by Adsorption on Pistachio Hull Waste: Equilibrium, Kinetic and Thermodynamic Studies

Background and Purpose: Azo dyes including Direct Blue ۷۱ (DB۷۱) are toxic, mutagenic and carcinogenic contaminants in effluents of industries. This study aimed to investigate the adsorption of DB۷۱ from aqueous solution onto pistachio hull waste (PHW) as a low-cost adsorbent. Materials and Methods: A series of experiments were performed via batch adsorption technique to examine the effect of the process variables such as contact time ۰-۲۱۰ minutes, initial dye concentration ۱۰-۱۰۰ mg/l, pH ۲-۱۲, adsorbent ۰.۰۵-۱ g/l, and the processing temperature of ۲۵, ۴۰, and ۵۰° C. The concentration changes of DB۷۱ were measured using the colorimetric method by the spectrophotometer T۸۰ ultraviolet/visible at the ۵۸۷ nm wavelength. Moreover, The PHW was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, Freundlich and Langmuir isotherm model, pHpzc and Brunauer–Emmett–Teller (BET) surface area analysis. Results: Maximum adsorption capacity was ۹۰.۴۸ mg DB۷۱ per ۱ g adsorbent at pH ۲, DB۷۱ ۱۰۰ mg/l, temperature ۵۰° C, and time ۲۱۰ minutes. In general, by increasing the adsorbent dosage, time, and processing temperature, the removal efficiency was increased; however, incrementing pH and dye concentration had a reverse effect. Maximum BET specific surface and total pore volume on the adsorbent were ۱.۰۴ m۲/g and ۰.۰۰۰۲ cm۳/g, respectively. The Freundlich isotherm (R۲ = ۰.۹۹۱۲) model fits the equilibrium data better than the Langmuir isotherm (R۲ = ۰.۹۰۲۴) model. The adsorption kinetic was found to be well described by the pseudo-second-order model. Thermodynamic analysis indicated that the adsorption process is a spontaneous and endothermic process. Conclusion: PHW can be used well as a low-cost surface adsorbent in the treatment of DB۷۱ from aquatic environments.

Keywords:

Direct Blue ۷۱ , Adsorption , Pistachio Hull , Aqueous