| Coal combustion is the primary source of mercury emission, as one of the most toxic pollutants and can easily be released into the atmosphere without control, mercury severely threats environment and human health due to high physiological toxicity and biological accumulation. Research on the control of Hg0 emission has become a major environmental concern after the particulate matter (PM), NOx, and SO2 control. As an effective mercury-control method, removing mercury with sorbents especially activated carbons has been subject to greater attention in recent years and become the current focus worldwide.In this paper, iron-based nano-sorbents were used for elemental mercury removal in flue gas. Nano-Fe2O3 powders and Fe2O3/SiO2 nanocomposites with high surface area,pore volume and controlled pore distributions were synthesized by hydrothermal method and sol-gel method respectively. The performance of mercury removal on the synthesized nano-sorbent were evaluated in simulated flue gas. Based on all the related researches, the main results are summarized as follows:The hydrothermal method was selected for the preparation of nano-Fe2O3 on the basis of compare of a variety of synthesis method, which is low-cost, effective and easily operated. The optimal conditions confirmed by experimental analysis were as follows : calcination temperature =300℃, solution pH =12, initial concentration of Fe3 + =0. 5 mol / L.The adsorption characteristics of nano-Fe2O3 for elemental mercury were evaluated in a fixed-bed reactor. The effects of particle size and surface area of nano-Fe2O3, reaction temperature and contact time on the removal of mercury were studied. Meanwhile the contrast test with normal-sized Fe2O3 was conducted, and XPS was used for the mechanism study. The results showed that nano-Fe2O3 has excellent adsorption characteristic than normal-sized Fe2O3. The increase of bed temperature can promote mercury adsorption. And elemental mercury is mainly chemically adsorbed by nano-Fe2O3. The XPS analysis showed that 85% of the adsorbed mercury on the surface of iron oxide are oxidation state. The acid gases in flue gas could play an important role for elemental mercury adsorption. Both the presence of NO and HCl could enhance the mercury adsorption, while with HCl addition the efficiency is obviously higher. The inhibiting effect of SO2 on Hg capture was detected which could compete for adsorption sites with mercury. The inhibitory effect is proportional to SO2 concentration.The catalytic characteristic of nano-Fe2O3 for elemental mercury especially the effects of particle size of nano-Fe2O3, reaction temperature, crystalline phase and flue gas components on the catalytic removal of mercury were studied. From the oxidation test results, it was founded that the decrease of the power size, as well as the increase of temperature could enhance elemental mercury oxidation, while exorbitant temperature could result in sintering, which could destroy the pore structure and damage the activity. The difference of crystal structure betweenα-Fe2O3 andγ-Fe2O3 nanoparticles plays a prominent role in mercury oxidation. Due to the oxygen in theγ-Fe2O3 has higher thermodynamic chemical potential and activity thanα-Fe2O3,γ-Fe2O3 nanoparticles show much higher activity for mercury catalytic oxidation and more sensitive to condition changes. The presence of oxygen is the basis for catalytic reaction .The presence of water vapour shows different effect on mercury oxidation depending on its concentration. The lower content of water vapour can promote mercury oxidation slightly, which results from the hydroxyl produced on the surface of nano samples. while the higher content of water vapour inhibits mercury oxidation. The addition of NO, NO2, SO2 and HCl could enhance the mercury oxidation with the tendency HCl> NO2> SO2> NO; to the effect of combination of acid gas, the highest oxidation efficiency was achieved under NO2 + HCl condition.The sol-gel process was used for the process of Fe2O3/SiO2 nanocomposites preparation with citric acid as active agent. And the process was optimized with orthogonal experimental method.The experiments of element mercury removal using Fe2O3/SiO2 nanocomposites has been conducted under simulated flue gas,and the effects of temperature, Fe2O3 loading and SO2 has been discussed. Experimental results show that compared with nano-Fe2O3 powders, nano-Fe2O3/SiO2 has much stronger performance for mercury removal. The optimal conditions wich were confirmed by experimental analysis were as follows : temperature =350℃, Fe2O3 loading =10%.To the nano-Fe2O3/SiO2 composites, high concentration SO2 is not conducive for mercury removal. To obtain the best results, the concentration of the SO2 in the flue gas environment should be less than 1000×10-6. Temperature programmed desorption (TPD) results show that the mechanism for the removal of mercury by nano-Fe2O3/SiO2 is mainly chemisorption, and the oxygen is beneficial concluded from the higher efficiency and mercury oxidation present in air condition.The experimental results of adsorbent regeneration show that the nano-Fe2O3/SiO2 composites still remain good pore structure and high mercury removal performance after several recycling experiments.
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