| Coal is still and will be the mainly energy source in a long time for China. Resultant huge amount of coal consumption will result in serious environmental problem. China is one of the largest mercury emissions countries in the word and coal-fired power plants are considered as the largest anthropogenic sources of mercury pollution. Therefore the mercury emissions control of coal-fired power plants is reasonable and necessary. Sorbent injection is a promising mercury emissions control technique. It could well use the existing particulate matter controller and effectively removal mercury from flue gas. However, the application of activated carbons as the current mercury sorbents is limited by following two reasons. On one hand, the high price of activated carbons and a huge amount of sorbent demanded by coal-fired power plants result in a huge cost for mercury control. On the other hand, the application of carbon-based sorbents increases the carbon content in fly ash and affects the utilization of fly ash in cement. This is not only a waste of resource but also a cause of new environmental problems. Therefore, it is important to find out efficient and cost-effective mercury sorbents. In this paper, natural mineral materials were applied as alternative to activated carbons due to their low cost. Various of sorbents were synthesized and their mercury removal performances were evaluated. The mercury removal mechanism of mineral sorbents was also deeply discussed.Four types of natural minerals, bentonite (Ben), mordenite (Mor), attapulgite (Atp), and vermiculite (Ben), were selected as raw sorbents and thermal treatment were conducted. Characteristics of these sorbents were analyzed by an X-ray diffractometer (XRD), an accelerated surface area and porosimeter (ASAP) using the N2 isotherm adsorption/desorption method, and an X-ray fluorescence spectrometry (XRF). The sorbents performances on mercury removal were evaluated on a lab-scale fixed-bed system under a simulated flue gas condition (N2, O2, and CO2) and the mercury concentration was detected continuously using a VM3000 online mercury analyzer. The results showed that thermal treatment could not enhance mercury removal abilities of sorbents and increasing temperature benefited the mercury removal. Bentonite exhibited the best mercury removal performance in the four natural sorbents and a poor mercury removal performance was observed for the vermiculite. The Hg0 removal by natural mineral sorbents was mainly based on the chemosorption. The reason that the natural mordenite and attapulgite could oxidize elemental mercury should relate to the existence of active titanium.According to the experimental results of four silicate minerals, three minerals, Atp, Ben, and Mor, were selected as raw sorbents, and several chemical promoters were employed to enhance mercury removal abilities of these raw sorbents. The chemical promoters are element sulfur, sodium polysulfide, calcium thioglycolate,2-mercaptopydine, 2-pyridinethiol-l-oxide, (3-mercaptopropyl)trimethoxysilane, cysteine, cystine, copper chloride, sodium chlorate, potassium bromide, and potassium iodide. The Al-pillared montmorillonite was also synthesized. The results showed that the loading of promoters in the sorbents varied with the different sorbents materials. In general, the contents of organic promoters in Mor were the lowest and layer structure benefited organic promoters loading; The element S-modified sorbents performed well than the organic S-modified sorbents in mercury removal and increasing temperature promoted mercury removal for element S-modified sorbents; Single sulfhydryl group could not adsorbed Hg0, whereas the existing of different types of radical were propitious to mercury removal based on chelation; The mercury removal efficiency of Cu-Mor was lower than that of Cu-Atp and Cu-Ben dut to the poor capacity in ionic copper adsorption for Mor; Cl-Atp showed an average Hg0 removal efficiency more than 90%at 120℃. Iron oxide in natural Atp could promoted Hg0 oxidation by weakening the Cl-O bond in the chloride; For KI-modified sorbents, I2 was generated from the oxidation of KI during the drying process and it effectively promoted the Hg0 removal; The three natural minerals presented poor adsorption abilities for bromine, which resulted in the disappointing mercury removal efficiencies; The physical characteristics of montmorillonite was improved after Al-pillared modification and the value of BET surface area increased from 61 m2/g to 209 m2/g. However, the mercury removal efficiency of the sorbent was still poor. Generally, the sorbents with more than 80%average Hg0 removal efficiency are element S-modified Ben (S-Ben), CuCl2-modified Atp (Cu-Atp), CuCl2-modified Ben (Cu-Ben), NaClO3-modified Atp (Cl-Atp), and three Kl-modified sorbents (I-Atp, I-Ben, and I-Mor)。 After the comparison of the different sorbents, Cu-Atp was selected as the most promising sorbent for further study. Two methods (using a VM3000 online mercury analyzer, and Ontario Hydro Method) were applied for mercury detecting. The experiment was conducted on a lab-scale fixed-bed system under a nitrogen gas condition and the various factors affecting mercury removal efficiency were studied. SO2 and H2O slightly inhibited mercury removal respectively. There was insignificant effect on mercury removal efficiency in the presence of NO. Both the forms of copper compounds and the solvents used in sorbent synthesis process could affect mercury removal efficiency of sorbents. The copper chloride in Cu-Atp would be hydrolyzed when Cu-Atp was heated at 150℃, and it could reduce the sorbent ability of mercury removal. The kinetic model simulation results were in good agreement with the experimental results. To improve the mercury removal ability of Cu-Atp at high temperature, Mn-doped Cu-Atp was synthesized. The experimental results showed that the mercury removal efficiency of Mn-doped Cu-Atp could retain at 80%in a long time at 150℃. It means that Mn doping effectively improved the sustained mercury removal ability of Cu-Atp.
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