Adsorption Of Gaseous Elemental Mercury With Activated Carbon Impregnated With Ferric Chloride

Mercury is the only metal which is liquid at room temperature and atmospheric pressure; it has become an increasingly environmental concern due to characteristics of its persistence, neurological toxicity, volatility, bio-accumulation. The coal-fired power plant was the major source of the gas phase mercury, which was mainly in elemental form and not readily removed by existing air pollution control devices. The effective mercury controlling way is to transfer the elemental mercury to more soluble bivalent form, which is easily to be removed then. Activated carbon injection technology is the most widely used method to capture mercury, the adsorption properties could be strongly affected by physical and chemical properties of activated carbon. Many study focus on the mercury of the coal-combustion flue gas, but there is a few study on it of lead and zinc smelting gas. In this thesis, the research will be developed into it. Study the adsorption effect of activated carbon modificated by chemical modification.The influence of carrier, active ingredient, calcinations temperature, reaction temperature, elemental mercury concentration, volume space velocity, chlorine metal salts were analyzed. The industrial coal activated carbon (AC) is decided to be the carriers for mercury by multiple carriers screening experiment. The "breakthrough time" of pure active carbon is 330min min, the breakthrough adsorption capacity is 1.4840 mg/g. The results of active component screening experiments found that FeCl3 is the best modified components. The activated carbon impregnated with ferric chloride is 2.454 times the breakthrough capacity of the pure AC, the breakthrough adsorption capacity is 3.642mg/g. Five transit metal salts, such as FeCl3, ZnCl2, NiSO4.6H2O, Ce(NO3)3.6H2O, C4H6CoO4. 4H2O) were investigated, and the adsorption capabilities were in the trends below:Fe/AC> Zn/AC> Ni/AC> Ce/AC> Co/AC. As concentrations of FeCl3 solution changes over breakthrough adsorption capacity. The adsorption efficiency of modified activated carbon was influenced by the concentration of FeCl3, in the sequence 0.15mol/L> 0.10mol/L> 0.20mol/L> 0.30mol/L>AC. The adsorption effect dependence of calcinations temperature is complicated. It is an unfavourable for adsorption of Hg0 when the temperature gets too high or too low, the best calcination temperature is 300℃. The adsorption capacity of Hg0 increases with elemental mercury concentration; in can improve adsorption driving force to some extent, thus promotion adsorption rate, it has a positive effect. It can shorten the exposure time between Hg0 and the surface of adsorption bed when increasing volume space velocity, leading to reduce the performance of mercury.Studies have found that change common active carbon by loading chloride and other elemental in its surface can make the activated carbon surface form a new activity. The affinity of these substances with mercury is stronger than the affinity of carbon with mercury which can react with mercury to generate more stable HgCl2, etc, these substances are prior to chemical adsorption of mercury which can greatly improve the efficiency for removing gaseous elemental mercury.Characteristics of these sorbents were characterized by scanning electron microscope (SEM), N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). It was observed that AC sorbent exhibited highest activity, highest special and surface area. Therefore, this sorbent was the optimum support for Hg0. The important observation of the XPS analysis for the AC samples, Fe/AC-300 has two obvious peaks of Fe2p centered at 711.4 and 725.22eV respectively. After reading a large number of literature, we know that Fe existing as mixed valence of+2, +3 valence form in modified adsorbent. The important observation of the XRD analysis for the AC samples is that these are the characteristic diffraction peaks of C, indicating the crystal form of modified activated carbon remained intact. It is more beneficial to adsorbent Hg0 because of the highest special and surface area and more active sites. It is more beneficial to promote the formation of the carbonyl group when calcinations temperature is 300℃. These functional groups are favorable mercury oxidation to a certain extent. We proposed the mechanism of mercury adsorption on the base of the study of experiment and characterization.On the whole, activated carbon impregnated with ferric chloride have high adsorption efficiency, which have the potential for business application because of the low cost.