Study On The Variation Of Mercury Existing States In Fly Ash During Thermal Treatment Process

Fly ash,a predominant solid waste of coal combustion by-products(CCBs),contains ahigher mercury concentration owing to its stronger adsorption capacity to gaseous mercury．During the fly ash cyclic utilization,enriched mercury in the fly ash will be easily releasedinto our environment to result into the secondary pollution In this study,the physicochemicalproperties of fly ash collected from Zhujiang Power Plant,Guangzhou w-as comprehensivelyanalyzed including its morphological features,specific surface area BET,porosity,residualcarbon concentration,chemical composition mad mineral composition On this basis,fourdifl~rent particle size grade(>150 m,75-150 m,54-75 m,<54 m)of fly ash wereseparated and the sorted samples were heated in difl'erent temperatures from 200 to 1200Celsius degree with each 200C intervals by tubular furnace Mercury species in the heatedsamples were extracted by sequential extraction procedure of EPA Method 3200 Theconcentration of various mercury species in the sorted mad heated fly ash were all determinedThe content and species of mercury in raw mad heated fly ash were important basis ofevaluation ofrisk on fly ash reuse process As the result,with the decrease ofthe particle size,the content of extractable mercury basically remained unchanged；the content of thesemi--mobile mercury mad non--mobile mercury increased slightly；but the content mad ratio ofthe mobile&semi-mobile mercury were decreased. Carbon content reduced with the decreaseof particle size of fly ash. There was a close relation between carbon and mobile&semi-mobile mercury,with the correlation coefficient of 0.8151. The surface area BETincreased with the decrease of particle size of FA,the correlation coefficient between the BETand the content of mobile&semi-mobile mercury was O.4354 There was a certain relationbetween non-mobile mercury content and Si02 content,with the correlation coefficient ofO 6746 The main material form of Si02 was glass microsphere. It indicates that non-mobilemercury mainly distributed in glass microsphere The<54 m particle size grade FA had themost glass microsphere through the SEM graphs This analysis results coincide with the testresults that non-mobile mercury increased with the decrease of particle size In the process ofheating,total content of mercury in the fly ash decreased continuously with the increase ofheating temperature. Two distinctive decrease rate was 20％mad 32％occurred at the heatingtemperature of 300C and 400C respectively．The content of non-mobile mercury had nosignificant changes in the heating process that dropped slightly about 5％.The content ofmobile & semi-mobile mercury changed greatly at 200C．300C mad 400C heatingtemperature Atthe heatingtemperature of 200C,the semi-mobile mercury decreased greatly, but the mobile mercury increased in amount and the total mercury remained unchanged Thisresult indicated that part of semi-mobile mercury was oxidated and retained in fly ash In thecondition of lower heating temperature．Hg。was catalytic oxidated into Hg(?) easily．At 300~Cand 400C．the content of mobile & semi-mobile mercury decreased greatly．At the heatingtemperature range of 600C-1200C,the content of mobile & semi-mobile mercury werealmost constant. As the heating temperature reached 1000C,particles of fly ash appearedcohesive phenomenon,and each mercury species remained unchanged...