Influence of selected amides and adsorbent particle size on the adsorption ofp-nitrophenol on granulated activated carbon

In this paper, the influence of selected amides on the adsorption ofp-nitrophenol was investigated. Commercial granulated activated carbon DARCO was used as an adsorbent. Granulations of 20-40 and 12-20 mps were used in the experiments. The presence of N-benzylbenzamide and N-methylbenzamide in the system lowered the adsorption capacity ofp-nitrophenol, while N-methylpropionamide did not show influence on the adsorption capacity. The equilibrium adsorption capacities forp-nitrophenol were 46.8 mg g(-1)for the smaller granulation (20-40 mps), and 45.4 mg g(-1)for the larger granulation (12-20 mps). The presence of the amide in the system reduced the adsorption capacity ofp-nitrophenol to as much as 6.7 mg g(-1). Weber-Morris model showed two distinct phases in the adsorption process, and they were attributed to the external (film) and intraparticle diffusion. For the estimation of the adsorption mechanism external mass transfer coefficient and effective intraparticle diffusivity coefficient were obtained. Obtained Biot number values are in the range of 0.17-0.50 for the smaller granulation, and 0.03-0.29 for the larger granulation. The external diffusion is the rate-limiting step, however, both steps in the diffusion process should be considered for describing the mechanism of adsorption. Freundlich and Dubinin-Radushkevich adsorption isotherms were used for the equilibrium investigation. Freundlich adsorption isotherm showed to be better suited for describing experimental results.