Effect Of The Modified Methods On Adsorbing Gaseous Mercury With Vermiculite

China is one of the world’s largest nations for mercury emissions, and the burning coal is a major source of atmospheric mercury pollution. In recent years, elemental mercury, as a worldwide pollutant, has been given more attention due to its highly toxic, volatile, persistent and bio-accumulative. In this paper, we introduced the adsorption control technology of elemental mercury, and then choose vermiculite as elemental mercury adsorbent material because of its low prices and abundant amount. Following, synthesized a series of vermiculite adsorbents use different modification methods, and the affect of vermiculite modification methods to adsorbing capacity of elemental mercury have studied.First, the vermiculite was expanded using different methods, including microwave, calcination, hydrogen peroxide and microwave/hydrogen peroxide. Expansion conditions are optimized based on the previous studies. The results show that: high fire and processing time 1 min for microwave modified; calcinations temperature 1000℃ and calcinations time 1 min for muffle modified; concentration 20%, soaking temperature 60℃ and soaking time 3 h for hydrogen peroxide modified; concentration 20%, high power, processing time 3 min for hydrogen peroxide/microwave modified. The results shown that expanded vermiculite favor adsorption of elemental mercury, especially, the adsorbing capacity of expanded vermiculite with microwave is maximum for absorb of elemental mercury（12 mg/g）, and increased by 22% than activated carbon. The morphology and structure of the expanded vermiculite was characterized by BET, SEM, XRD, TEM, confirming that after the expansion process vermiculite layered structure has not changed too much, and with the increase of vermiculite interlayer distance, the adsorption properties of vermiculite to elemental mercury is gradually increased.To further enhance the ability of vermiculite adsorption for elemental mercury and make vermiculite into a skeleton with many holes. In this paper, the acid-modified vermiculite experimented based on microwave expansion vermiculite. According to the effect of adsorption experiments, the suitable hydrochloric acid solution was selected as acid modifier from three kinds of acid modifying agent of hydrochloric acid, sulfuric acid and nitric acid. According to adsorption of elemental mercury, with the single factor and orthogonal experiments to optimize the conditions of to synthesized the hydrochloride modified vermiculite, the results show that: the concentration of HCl was 2 mol/L, hydrochloric acid solution and expanded vermiculite solid-liquid ratio was 1 g/25 mL, modified temperature was 70℃, standing time was 2 h. Hydrochloric modified vermiculite to adsorbed elemental mercury can reached 30.74 mg/g under this experiment condition, adsorption capacity also enhanced markedly compared with microwave expanded vermiculite. BET, XRF, XRD and other characterization analysis showed that hydrochloric acid solution did not destroy the structure of vermiculite, it just dissolved the organic and inorganic impurities in vermiculite interlayer to formed an adsorbent material with high surface area and high porosity, these characteristics are conducive to the adsorption of mercury.FeCl₃, CuCl₂, ZnCl₂, NH₄ Cl, NaCl, zinc powder and sulfur powder was selected to modify hydrochloric modified vermiculite to improve mercury removal capability. The result shown that the vermiculite with FeCl3 modified showed the better adsorption of elemental mercury. The amount of adsorption for elemental mercury is 18.80 mg/g when FeCl₃ capacity was 5%. But the rate of adsorption of elemental mercury is slow. Doped zinc and sulfur in vermiculite were able to provide many active sites.The studies shown that the modified vermiculite could improve adsorption properties of elemental mercury. As well as, low cost price of vermiculite make it has a wide range of applications in industry.