Kinetics, Isotherm, and Thermodynamics Study for the Adsorption of Basic Fuchsin on Cocoa Pod Husk Activated Carbon

Abstract

Aim: To prepare Activated carbon (AC) from local agro-forestry wastes, and apply it in dye adsorption in order to assess its efficiency in wastewater treatment. Study Design: Laboratory analysis for various parameters. Place and Duration of Study: Department of Chemical Engineering, Nnamdi Azikiwe University and Springboard Laboratories, Awka, Anambra State, Nigeria. The study was carried out from November, 2013 to May, 2014. Methodology: Batch adsorption study was conducted to determine the effects of pH (2–10), initial concentration (50–500 mg/L), contact time (3–90 mins), adsorbent dose (0.5–2.5 g), and temperature (303-333 K) on the adsorption of Basic Fuchsin (BF) from aqueous solution using activated carbon prepared from cocoa pod husk. Results: The adsorption of Fuchsine basic was dependent on pH, initial concentration, contact time, adsorbent dose, and temperature. CPAC adsorbed 99.99% from an aqueous solution of 50 mg/L Basic Fuchsin (BF) at pH 4.0, with the contact period of 1h and a dose of 2 g/L. Adsorption data of Basic Fuchsin (BF) removal on CPAC from aqueous solution was best fitted by pseudo-second order kinetic model among the three studied models, as gathered from the regression coefficient (R2 = 0.999), and the rate constant (k2 = 4.996 g/mg/min). The adsorption isotherm was best described by Langmuir model as gathered from the regression coefficient (R2 = 0.996). In the studied temperature range of 303-333 K, the Gibbs free energy (ΔG) was negative. The enthalpy (ΔH) of the adsorption process was -32.90 kJ/mol, while the entropy (ΔS) was -7.325 J/mol/K. The negative values obtained for the thermodynamic properties showed that the adsorption of BF onto CPAC was exothermic, spontaneous and feasible with a decrease in the degree of freedom of the adsorbed species. Conclusion: Significant amount of Basic Fuchsin can be reduced up to 99.99% from an aqueous solution using CPAC; an effective and low cost adsorbent.