Characterization of pine-needle activated carbon and testing its heavy metals removal efficiency

Abstract

The current work investigated the chemical and physical characterization of an activated carbon prepared by physical and chemical activation of a low cost, widely available precursor, pine needles. Of the physical properties of the pine-needle AC, bulk density (158 g-L), ash (21percent) and volatile matter content (45percent), proved to be on the weak side when compared to other ACs. But the studied AC proved to possess high surface area (854 m2-g), and iodine (962 mg-g) and methylene blue (443 mg-g) numbers, which are good indicators to the adsorptive abilities. The pine-needle AC proved to have low removal capacities for arsenic, reaching a maximum of 0.29 mg As- g AC. On the other hand, the AC’s capacity for the other tested heavy metals was high, and was found to be very competitive with what is reported in the literature. The pine-needle AC’s capacity for Cd was at 17.5 mg-g in column scenarios and 43.5 mg-g in batch experiments. While that of Cr reached 26.8 mg-g and 54 mg-g respectively. Capacities for adsorbing Pb was at 44 mg-g in column testing but almost negligible in batch experiments. For Ni, the capacities reached 21 mg-g in column testing and 87 mg-g in batch experiments. And finally for Zn, the capacities reached 18 mg-g and 27 mg-g in the respective scenarios. pH of solution proved to have a big impact on the capacity of the AC. Generally, the increase in pH lead to an improvement in the removal capacity of the pine-needle AC, except for Cr which was best removed in the acidic range because as opposed to the other metals it form negative anions in solution, and Zn which was best removed at pH 6. The initial concentration of heavy metals in solution was found to have a clear effect on the adsorption capacity of the AC. In batch experiments higher concentrations always resulted in higher removal and higher capacity for all metals. But in column testing high concentrations (40-50 mg-L) overwhelmed the capacity of the AC for removal and resulted in lower capacities. The effect of the presence of