Efficacy of impregnated active carbon in manganese removal from aqueous solutions

Adsorption is a chemical method for water purification. In the present study, native and impregnated active carbon was used for adsorption to evaluate the efficacy of the process in manganese removal from aqueous solutions. Impregnation reaction was performed using the precipitate colloids of manganese oxides onto the carbon surface. X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy confirmed that the process was appropriate for carbon impregnation. The experiments indicated that the highest adsorption of Mn2+ ions by impregnated active carbon occurred at the pH of 9 (Mn2+ removal: 67.19%). In addition, the reaction time, mixing rate, and adsorbent dosage affected the efficacy of adsorption, and optimal results were obtained at the reaction time of 100 minutes, mixing rate of 100 rpm, and adsorbent dosage of 4 mg/l. In all the test conditions, impregnated active carbon had better performance in Mn2+ removal from aqueous solutions compared to native active carbon (99% confidence level). The Langmuir and Freundlich isotherm models were also applied to evaluate the adsorption process. Accordingly, RL was 0.07 and 0.027 for raw active carbon and impregnated active carbon, respectively. RL magnitude confirmed the suitability of the Langmuir model for Mn2+ adsorption using impregnated active carbon. According to the results, impregnated active carbon exhibited the maximum adsorption capacity (qmax) of 20.53 mg/g, while this value was estimated at 6.62 mg/g in raw active carbon. On the other hand, the adsorption kinetic analysis indicated that the pseudo-second order mode and intra-particle diffusion model could be used for this process.