The liquid-solid type reaction encountered in this study is usually complicated by the presence of resistances as a result of film diffusion across the external solid surface and particle diffusion through the pores of solid. Therefore, it became necessary to establish the operating conditions that minimized the influence of film and particle diffusion. This investigation was an attempt to eliminate these diffusional effects and determine the kinetics of the removal of orthophosphates from the aqueous solutions by activated carbon using a differential bed reactor approach. The reaction kinetics studied in this experiment may be summarized as follows :
r = 0.0240C_e-0.0379C_i^0.28q_e^0.80 at pH 4.0
r = 0.0179C_e-0.0361C_i^0.28q_e^0.80 at pH 8.0
r = 0.00619C_e-0.0136C_i^0.28q_e^0.80 at pH 12.0
A comparison of these equations indicates that the reaction kinetics at pH 4.0 is much faster as compared to those at pH 8.0 and 12.0. The equilibrium adsorption studies support the existence of this adsorption isotherm which fits the empirical Freundlich isotherm, comparatively. For activated carbon, maximum orthophosphates adsorption occured at pH 4.5-7.0 with decreasing amounts of adsorption at lower and higher pH.