Removal of mercury (II) from aqueous solution with three commercial raw activated carbons

In order better to comprehend the fundamental kinetics and adsorption mechanism of raw activated carbon, three typical commercial raw materials, including peach stone based activated carbon (PSAC), coal based activated carbon (CAC), and coconut husk based activated carbon (CHAC) were employed to remove mercury (II) from aqueous solutions in static batch adsorption experiments. The adsorbents were characterized by Fourier transform infrared spectrometry, X-ray diffraction analysis, surface area and porosity analysis, scanning electron microscopy, point of zero charge, isoelectric point, and X-ray photoelectron spectrometry, respectively. Four types of adsorption kinetic models and seven adsorption isotherm models were used to simulate the adsorption process. Initial solution pH, adsorbent dose, initial mercury (II) concentration, and soaking time were analyzed. The results show that theoretical maximum adsorption capacities in Langmuir monolayer model were 59.5, 48.9, and 44.9 mg/g for PSAC, CAC, and CHAC, respectively, at room temperature with initial mercury (II) concentrations of 40-450 mg/L and a pH of 4. Removal efficiencies of 94.1-99.5 % were achieved by the three absorbents. The pseudo-first-order kinetic model represented high correlations for the three adsorbents. The XPS spectra of mercury, fitting of intra-particle diffusion model and the calculation of the adsorption heat in Temkin model all indicated that the physisorption for mercury (II) was the predominant process for the three activated carbons.