Study On The Speciation Of Trace Elements In FGD Gypsum From Coal-fired Power Plant

Coal is dominant in China's energy mix,with more than half used for coal-fired power generation.The trace element mercury,arsenic,chromium,cadmium and lead in the coal are mainly enriched in the FGD gypsum and fly ash after combustion,and some of which are discharged into the atmosphere in the form of gaseous phase harmful to the environment.Desulfurization gypsum and fly ash are two main by-products of coal-fired power plants,which are widely used in production process.Since 1990 s,many scholars have proposed different chemical extraction methods for the speciation of trace elements in coal,ash,slag and FGD gypsum.With focusing on the speciation of trace elements in fly ash or desulfurization gypsum,the possible environmental effects of trace elements in the re-utilization of FGD gypsum were investigated.In this paper,by analyzing trace elements in coal-fired power plants in the distribution of inputs and outputs track the distribution of trace elements in a power plant.The speciation of five trace elements in FGD gypsum from four power plants were analyzed by the Community Bureau of Reference(BCR).The distribution and speciation of different volatile trace elements were compared,and the effective speciation and residual speciation in FGD gypsum and fly ash were compared to understand the environmental stability of the trace elements in FGD gypsum.This study shows that Hg,As,Cr,Cd and Pb were mainly distributed in the fly ash and desulfurization gypsum,in which more than 60% of the mercury is distributed in gypsum,80% of chromium,lead and arsenic in fly ash,cadmium is evenly distributed in the fly ash,FGD gypsum and bottom ash.The speciation analysis of trace elements in the desulfurization gypsum shows that mercury,arsenic and lead are mainly in the form of residual speciation,while chromium and cadmium are mainly in the form of effective speciation.Chromium and cadmium are more easily released into the environment than mercury,arsenic and lead.The distributions of trace elements' speciation in fly ash and FGD gypsum from the same power plant show that the affective speciation of Hg,As,Cr,Cd and Pb in the four FGD gypsum increase greatly,especially Cr and Cd elements,up to 70%.From the above analysis,we can infer the relationship of mobility between five trace elements in FGD gypsum: Hg> Cr,Cd> As,Pb.Moreover,the trace elements in the FGD gypsum is weaker than it in fly ash about the environmental stability.