Dicolouration of Congo red dye by activated carbon in aqueous medium

Congo red an azoique dye could be fixed on activated carbon. Batch experiments conducted in aqueous medium, at room temperature (20 +/- 2 degrees C) and pH 6.55, have showed a low affinity of this compound towards this adsorbent mainly at elevated concentrations (100 ppm and more). This fact might be attributed to its azoique structure. However, at relatively feeble concentrations, we noticed a better fixation since ca. 70 % of the substrate was retained over activated carbon (1 g/L) for a reaction time of 80 min. Change in initial concentration of dye has led to variation in the retention capacity. The influence of salt such as, NaCl, Na2SO4 and NaHCO3, at various concentrations have showed no significant effect on rate and capacity of adsorption. The experimental results indicated that temperature affect rate and retention capacity. Adsorption isotherms have been correctly represented by Langmuir and Freundlich. The kinetics of adsorption was found to obey to the Lagergrein model, demonstrating that there is a mass transfer at the interface liquid/solid which is however slow since the apparent rate constant was equal about to 40 min(-1).