The influence of different agitation techniques on the adsorption kinetics of 4-chlorophenol on granular activated carbon

Abstract

The influence of different agitation techniques on the adsorption of organic compounds, represented by 4-chlorophenol, onto granular activated carbon was investigated. The effect of the flask type and the type of agitator, including a laboratory shaker, mechanical agitator, magnetic stirrer as well as mixing with gas bubbles, was studied. The results of adsorption kinetics demonstrate that the adsorption process of 4-chlorophenol on the activated carbon follows a pseudo-second order kinetic model closely. The adsorption equilibrium was reached faster in the Erlenmeyer flask than in the round-bottomed flask. At the same agitation speed (200 rpm), the better adsorption rate and adsorption efficiency were observed using the mechanical and magnetic stirrers than the laboratory shaker. At the gas flow rate of 1.5 dm3 min-1, the mixing with the air or nitrogen bubbles was comparable with the agitation when using mechanical and magnetic stirrers at 200 rpm. The effect of the agitation speed on the adsorption of the 4-chlorophenol by the activated carbon was also tested. The kinetic experiments were carried out at 100, 200, 300 and 500 rpm and it was found that the adsorption rate increases with the increase in the agitation speed. As the stirring rate increased from 100 to 500 rpm, the adsorption rate constants increased from 0.577 to 1.264 g mmol-1 h-1 (mechanical agitator) and from 0.560 to 1.231 g mmol-1 h-1 (magnetic stirrer), respectively. The experimental results demonstrate that the agitation affects the adsorption kinetics significantly as well as the adsorption equilibrium of the organic compounds on the activated carbon, and should be taken into account in such studies.