Simultaneous Removal Of NO And Gaseous Elemental Mercury By Tea Stem Biochar

Coal-fired power generation has always been the dominant position in China.Nitrogen oxides?NO_x?and elemental mercury?Hg⁰?in coal-fired flue gas have great harm to the environment,ecology,plants,and animals.The emission reduction of NO_x and Hg⁰ has become a hot spot in current research.Yunnan,as a major tea province in China,the abandoned tea stems byproducts are produced in the process of tea picking and making.The selected tea stems are discarded at will which would form solid waste environmental pollution and cause waste of resources.In this paper,the discarded tea stems were used for preparing a kind of novel,cheap,and transition metal oxides-loaded biochar adsorption catalyst by impregnation method.The purpose of this study was to remove nitric oxide?NO?and Hg⁰ simultaneously.The removal effect and adsorption catalytic reaction mechanism were explored to simultaneous removing the pollutants.The biomass and biochar adsorption catalyst were characterized using a variety of characterization methods to investigate their physicochemical properties.The adsorption of elemental mercury was fitted by means of dynamic and thermodynamic equations and the mechanism of simultaneous removal was determined.The results are as follows:?1?Unmodified and nitric acid-modified biochar have poor removal effect and need to be impregnated.The best impregnation ratio was 4%cerium dioxide?CeO₂?/4%copper oxide?CuO?and 4%CeO₂/4%manganese dioxide?MnO₂?,which were determined by separate NO removal experiments.Then the simultaneous removal experiments were performed at 100?-300?.The results showed that the highest NO conversions were 82.3%and 68.2%,respectively,and the highest Hg⁰ removal efficiencies were 93.0%and 98.1%,respectively.?2?The optimum volume fraction of oxygen?O₂?was 5%.The concentration of nitrogen dioxide?NO₂?was basically unchanged during the experiment and its volume fraction was always less than 5×10^-6.It could be known that NO was mainly reduced.?3?Through various physicochemical characterization analyses,it can be seen that there were mutual transformations of loaded metal ions in the modified biochar,which would promote the removal effect.?4?According to the dynamics fitting at 100°C,the adsorption of Hg⁰ was dominated by physical adsorption.It could be inferred that the main adsorption mechanism of Hg⁰ at 300?was chemisorption from XPS analysis.Thermodynamic analysis showed that the chemical adsorption of Hg⁰ was an exothermic reaction.The removal efficiency of Hg⁰ was low due to the increase of temperature and high NO conversion.