Characterization of Adsorption Capacity of Phenol Using Groundnut Husk-based Activated Carbon

Equilibrium adsorption studies of phenol onto activated carbon prepared from groundnut husk was investigated for effectiveness. Groundnut husks were washed, dried at temperatures between 110°C and 160ºC, pulverized and finally activated at 200°C for 3 hours. Optimum conditions of carbon dosage, pH, contact time and influence of concentration of phenol on carbon were investigated. Several analyses of isotherm data were tested by fitting them into different isotherm (Temkin, Langmuir, Dubinin-Kaganer-Rushkevich and Freundlich) models. The results of the optimization studies indicated an optimum adsorption of phenol with carbon dosage of 2.2 g; pH = 5 and contact time = 5 hours. Temkin, Dubinin-Kaganer-Rushkevich and Freundlich had high correlation coefficients in the range of 0.853 – 0.9501. The experimental data fitted adequately into these models but not into the Langmuir isotherm model with extremely low regression coefficient of 0.0038. The high correlation coefficients connoted strong interactions between the adsorbate and the adsorbent and a good interpretation of the adsorption behaviour of phenol. However, the Temkin and Dubinin-Kaganer-Rushkevich models showed indications of chemisorptions with high heat of adsorption of 1531.39 J mol-1 and mean energy of 5227.1 Jmol-1 respectively and the value of the separator factor RL­­­ (0.1805) that was less than unity obtained from the Langmuir model indicated favourable adsorption. The value of 1/n = 0.9277 that was less than unity from the Freundlich model depicted strong adsorption intensity. The adsorption of phenol by the activated carbon was best described by Freundlich model with the highest regression coefficient of 0.9501. It was evident from the Freundlich adsorption isotherm that adsorption capacity increased as the initial concentration of phenol was increased until a possible removal efficiency of 100% could be achieved. The adsorbent was found to be suitable and effective in the treatment of wastewater laden with phenol.