Kinetics and equilibrium studies of adsorption of phenol in aqueous solution onto activated carbon prepared from rice and coffee husks

Activated carbons obtained from the chemical activation of rice and coffee husks using H3PO4 were used to remove phenol from aqueous solution. Batch adsorption experiments were carried out and the amount of phenol adsorbed was determined as a function of adsorption time, pH of solution, adsorbent mass and initial concentration of phenol. The activated carbon used as adsorbent was characterized for its moisture content, bulk density, CHNS analysis, pH of zero point charge (pHpcz) and pH of the phenol solution. Some kinetics parameters were calculated; from kinetic results, the initial rate (obtained by pseudo second order) of adsorption is greater for all the adsorbent. The applicability of pseudo-second order model showed that the rate limiting step was chemisorption, involving forces caused by sharing or exchange of electrons between sorbent and sorbate. An Equilibrium study of the adsorption process showed that Langmuir isotherm described the isotherm data with high correlation coefficients on CAH2 and CAMH, while that of Temkin described that on CAH1. The values of energy obtained from the Temkin isotherm are also positive, this show that the adsorption process is exothermic. The results indicate that chemical rice husk and coffee husk activated carbon is suitable to be used as an adsorbent for phenol adsorption from aqueous solutions.