Adsorptive Removal of Zn(II) and Crystal Violet into Phosphoric Acid Activated Corncob

The use of activated lignocellulose-based biomaterial for wastewater treatment has gained more and more attention due to its availability, efficiency, and low cost. In this study, corncobs were activated using phosphoric acid, and the adsorptive efficiency of the obtained adsorbent was tested by crystal violet (CV) and Zn(II) ion removal from an aqueous solution. The Central composite design methodology was applied for phosphoric acid activation of corncobs (experimental ranges: H3PO4 0.68-3.32 mol/L; contact time 1.08-3.32h). The results show that the activated corncobs of the highest surface area (130m²/g) and highest iodine value (150mg/g) were obtained for an initial phosphoric acid concentration of 2.12 mol/L and a contact time of 5.8 hours. Central composite design was used for the assessment of simultaneous removal of CV and Zn(II) (experimental ranges: mass of adsorbent 0.04-0.35g; pH 1.08-6.78; molar ratio Zn (II)/CV 0.24-1.76). It was found that maximum adsorption of CV (0.0082mg/g) and Zn (II) (0.0036mg) was obtained at pH 4.5 for activated corncob mass of 0.12g and Zn (II)/CV molar ratio of 1.3. Kinetic studies reveal that pseudo-second-order kinetic models perfectly describe the adsorption process with kinetic constants of 0.004min.g. µmol⁻¹ and 2.653min. g.µmol⁻¹ for CV and Zn (II), respectively. Adsorption data fit both Langmuir and Freundlich adsorption models, this implied that the Zn (II) and CV are adsorbed in the form of a monolayer and that there are different types of adsorption sites uniformly distributed over the activated corncob surface. The adsorption mechanism proposed is pore filling for the Zn (II) ion and surface bonding for CV.