Speciation Analysis Of Arsenic And Selenium In The By-products From Coal-fired Power Plants

Coal is the main primary energy source in China.While China's power generation ranks among the world's leading position,it also results in some environmental problems such as toxic trace elements emission.Some volatile elements such as arsenic and selenium can be released into atmosphere along with flue gas or concentrated in fly ash.The toxicity of heavy metals relate with their species.In this thesis,the pretreatment and analytical methods for total amount and species of As and Se by high performance liquid chromatography-atomic fluorescence spectrometry coupling system(HPLC-HG-AFS)were established.Arsenic and selenium species in coal,fly ash and gypsum samples from several power plants were analyzed and verified by the developed methods.30 mmol/L(NH₄)₂HPO₄(pH 6.0)was used As the mobile phase,and Hamilton PRP-X100 anion exchange column was used as the separation column for arsenic species,which could separate As(III)and As(V)on baseline within 7 min.The two arsenic forms showed good linearity in the concentration range of 10-200 g/L,and the correlation coefficient was better than 0.999.The detection limits of the coupling system for As(III)and As(V)were 1.8 and 4.6 ng/g,respectively.Sample pretreatment methods were also developed in this study,phosphoric acid and ascorbic acid were used as the extraction solution.Most of the arsenic in the samples was in the form of As(V),while a small part was in As(III).80 mmol/L(NH₄)₂HPO₄(pH 6.0)was used As the mobile phase for selenium speciation analysis.Hamilton PRP-X100 anion exchange column was used the separation column,which could separate Se(IV)and Se(VI)on baseline within 8 min.Under the optimized conditions,the linear relationship of two selenium species was good,and the correlation coefficient was greater than 0.999.The detection limits of the coupling system for Se(?)and Se(?)were 1.6 ng/g and 3.5 ng/g,respectively.The sample pretreatment methods for selenium species in coal and its burning products were also develped.The optimal extraction solution for fly ash is 0.1 M sodium hydroxide solution,while the optimal extraction solution for gypsum is 0.2%hydrochloric acid solution.Microwave assistant extraction was effective for improvement of pretreatment.The sample analysis results indicated that selenium in the samples was mainly in Se(IV).