Mass Transfer Resistance Considerations for Dye Adsorption on Activated Carbon

In this study, the adsorption of a textile dye from water onto activated carbon is considered and the results of our own experimental studies on adsorption equilibrium and kinetics are presented. The adsorption isotherm and kinetic curves were found to reflect the possibility of removing the dye from water by adsorption onto activated carbon. Kinetic studies were conducted using a fixed bed of adsorbent grains. The water and dye solution flowed through the column with the adsorbent. The main aim of this study was to determine diffusion coefficients and mass transfer coefficients. The values of the external mass transfer coefficient and external diffusion coefficient of the dye in water were calculated for different flow rates of the solution, i.e., for different external resistance values. The external diffusion coefficient was DAB = 2.21·10−10 m2/s and the external mass transfer coefficient was between kc = 4.813·10−8 m/s for the lowest solution velocity in the adsorber equal to 0.0693 m/s and kc = 5.623·10−8 m/s for the highest velocity equal to 0.185 m/s. The internal diffusion coefficient and internal mass transfer coefficient, i.e., the coefficients of the transfer from the external surface of a grain to its interior, were determined with the use of the analytical solution of the diffusion and adsorption equation For the apparent solution velocity of 0.0693 m/s the internal diffusion coefficient was Ds = 0.57·10−10 m2/s and the internal mass transfer coefficient was ks = 1.89·10−10 m/s. For the velocity of 0.163 m/s, the internal diffusion coefficient was Ds = 0.84·10−10 m2/s and the internal mass transfer coefficient was ks = 9.00·10−10 m/s. The results of the calculations presented are a measure of the efficiency of a given adsorbent in a given system. The values obtained for the mass transfer coefficients can be used as data for further calculations of this process.