Application of Modified Agricultural Waste in the Adsorption of Bromocresol Green Dye

Abstract

Background: The adsorptive removal of anionic dye (Bromocresol green) from aqueous solution was investigated using activated carbon prepared from rice husk. Place of Study: The research work took place at Nnamdi Azikiwe Univeristy Awka, Nigeria. Methods: The rice husk which was obtained from rice mills in Awka was activated with tetraoxophosphoric acid and carbonized in a furnace. The adsorption process was investigated by varying the contact time, temperature, dosage, pH and initial concentration in a batch process. Five isotherm models (Langmuir, Freundlich, Temkin, Halsay and Harkin-Jura) were employed in the equilibrium studies. Thermodynamics and kinetics of the adsorption were carried out. Results: The result indicated that increase in contact time, adsorbent dosage and temperature increased the percent uptake of the Bromocresol green dye. Maximum percentage adsorption of about 93% was obtained. Langmuir and Harkin-Jura isotherm models best described the equilibrium data of the adsorption process. Pseudo second-order kinetic model best correlates the kinetics of the experimental data. The thermodynamic study showed that the Gibbs free energy (ΔG), enthalpy change (ΔH) and entropy change (ΔS) were –2.541 kJ/mol,  -7.401 kJ/mol and –15.52 kJ/mol K respectively. Conclusion: This work has shown that activated carbon prepared from rice husk can be used in adsorptive removal of bromocresol green dye from solution and that the adsorption process was spontaneous and exothermic.