Study Of Synthesis And Hg~0Removal Properties Of Metal Oxides Modified Fly Ash Adsorbent

Mercury air emissions come from coal combustion may cause great harm to both environment and ecology. The BET surface area of FA is relatively high and the primary chemical components in FA are rich, which allowed FA to be suitable for the application in mercury capture. In this paper, Co, Mn and Fe were loaded on FA, and experiments were carried out and the heterogeneous mercury reaction was speculated, which will apply some theoretical basis for the control of mercury.Firstly, the mercury removal ability of FA was improved after the nitric acid modification. BET, SEM, XRD showed that the BET surface area was increased after the modification. But there was no obvious advantage in nitric acid modified FA from the application and economic considerations. When under the experimental conditions of GHSV34000h-1, Calcination temperature at500℃, water bath temperature of50℃, reaction temperature of120℃, Hg0removal efficiency was about22%. And finally FA had no adsorption capacity after160min.Secondly, a series different Co loading of Co/FA were prepared by impregnated method. When under the experimental conditions of9%Co-FA, GHSV34000h"’, Calcination temperature at500℃, water bath temperature of50℃, reaction temperature of120℃, Hg0removal efficiency was about85%. The mechanism of elemental mercury captured by Co3O4/FA under air may be described as:Hg0was firstly adsorbed on the surface of Co3O4/FA, the adsorbed Hg0could be then oxidized by Co3O4, CoxOy-1was oxidized by O2to keep stable.Furthermore, a series different Mn and Fe loading of Mn-Fe/FA were prepared by impregnated method. When loaded Mn to Mn-FA, it was remarkable that the activity of Mn(1)-Fe(3)-FA showed good stability and Mn may be the main active site. When under the experimental conditions of9%Co-FA, GHSV34000h-1, Calcination temperature at500℃water bath temperature of50℃, reaction temperature of120℃, Hg0removal efficiency was about98%.Finally, the mechanism of elemental mercury captured by Mn-Fe-FA under air may be described as:elemental mercury was physically adsorbed on the cation vacancies, which was incorporated during the interactions between Mn oxide and ferrites; the adsorbed Hg0then was oxidized to HgO by Mn4+; Under air, the reoxidization of the reduced Mn3+and Fe2happened. During reoxidization. some cation vacancies may also be recovered. Therefore, when Mn-Fe-FA was exposed in air, its capability of removing mercury was kept stable within8h. Furthermore, HgO was very stable at120℃, it adsorbed on the catalyst, and finally removed from the flue gas.