Adsorptive removal of the azo dye Direct blue 2 onto agriculture waste corncob

• Published in: Desalination and water treatment 2021-06, Vol.224, p.421-432
• Main Authors: Gómez, Luis M., Hormaza, Angelina
• Format: Article
• Language: English
• Subjects: Adsorption; Agricultural by-product; Design of experiments; Dye-bearing effluents; Kinetic equilibrium and thermodynamic
• ISSN: 1944-3986; 1944-3986
• DOI: 10.5004/dwt.2021.27191

Lignocellulosic agricultural by-products have been used as non-conventional and inexpensive adsorbents for treating different pollutants. In this work, the uptake capacity of corncob (CC) was evaluated in the removal of Direct blue 2 (DB2) dye, a diazo dye widely used in the textile industry. A 23 full factorial design led to 88.3% DB2 removal under a CC dosage of 6.0 g L–1, an initial DB2 concentration of 60 ppm, and a particle size range of 0.3–0.5 mm. A subsequent optimization of the process through a central composite surface design allowed to achieve an efficiency of 89.81% by increasing the dosage to 8.0 g L–1 and keeping the initial DB2 concentration and particle size range of the previous design. Under these optimized conditions a maximum adsorption capacity of 158.085, 132.043 and 101.841 mg g–1 at 298, 308, and 318 K was respectively obtained. The evaluation of the kinetics showed the best adjustment with the Elovich equation at 298 and 308 K with a correlation coefficient R2 = 0.95 and 0.97 correspondingly, whereas at 318 K the second-order model exhibited the best fit with a R2 = 0.97. Regarding process equilibrium, the Langmuir-Freundlich equation was found to present the best fit over the four evaluated models with an average adjustment coefficient R2 = 0.99. Further, the assessment of the RL value in a concentration range of 5–4,000 ppm for all temperatures led to values between 0 and 1.0 which support the favorability of this adsorption process. Finally, the thermodynamic parameters with negative values for Gibbs free energy (ΔG = –1,435.41 J mol–1) and enthalpy (ΔH = –14,813.54 J mol–1) pointed out the spontaneity and exothermic feature of the process, while entropy described a slight randomness at the interface of the solution (ΔS = –44.87 J mol–1 K–1). Thus, the obtained results suggest CC as a novel and promising adsorbent for a feasible scaling up of this process.