Experimental Study On Mercury Removal Performance And Leaching Characteristics Of Fly Ash Modified By H₂S Non-thermal Plasma

Mercury from coal-fired power plants is harmful to the ecological environment.Activated carbon injection technology has been widely applied in coal-fired power plants,but the high-cost limits its applications in China.In addition,activated carbon injection technology increases the carbon content in fly ash.This makes it difficult to use fly ash in the cement production industry.Therefore,fly ash was selected as raw material and it was modified by non-thermal plasma in the presence of H₂S for better performance.Mercury adsorption experiments were carried out in a fixed bed to investigate mercury removal performance.Then,the effect of treatment time,adsorption temperature and flue gas components on mercury removal performance was investigated.Finally,the environmental effects of mercury adsorbed on adsorbents were evaluated by standard toxicity leaching experiments.In this research,the specific surface area?BET?,scanning electron microscopy?SEM?,X-ray diffraction?XRD?,thermogravimetric analysis?TGA?and X-ray photoelectron spectroscopy?XPS?were employed to character fly ash.It is concluded that H₂S non-thermal treatment has little influence on specific surface area,pore size,pore volume,the crystal structure and micro-morphology.XPS results show that the forms of active sites on the surface of modified fly ash are mainly elemental sulfur and adsorbed sulfur.The mercury adsorption experiments were done by fixed bed for investigating the mercury removal performance of raw and modified fly ash.The results show that H₂S non-thermal plasma treatment increased the mercury removal efficiency of fly ash.The mercury removal efficiency was enhanced with the increase of treatment time.The mercury removal efficiency of modified fly ash was 88%during the first 10 seconds in simulated flue gas.O₂,NO and HCl promoted mercury adsorption,while SO₂ inhibited the adsorption of mercury.The presence of oxygen enhanced the promotion of NO and HCl whereas weakened the inhibition of SO₂.The results of temperature programmed mercury desorption experiment,TG test and XPS test showed that the elemental sulfur on the surface of modified fly ash reacted with Hg⁰ to form HgS.The results of standard toxicity leaching test showed that the mercury concentration in leachate of modified fly ash was lower than that of detection line.Liquid-solid ratio,pH value and leaching time had no effect on the mercury leaching characteristics of modified fly ash.The mercury leaching characteristics of modified fly ash was not related to leaching methods.In conclusion,fly ash modified by non-thermal plasma in the presence of H₂S is an efficient and economical adsorbent for mercury removal.