Estimation of Trace Elements in Fly Ash Released from Coal Combustion

摘要

Qingshan Thermoelectric Plant located in Wuhan City, Hubei Province, China, and it uses coal as a fuel. Coal combustion generates not only gaseous pollutants like SO2 and NOx but also toxic and heavy metals to the atmosphere. From the environmental point of view, the determination and speciation of trace toxic and heavy metals released from coal combustion are very important. In this work, the atomic spectroscopic methods for determination of some trace elements were first established. Graphite furnace atomic absorption spectrometry (GFAAS) method was used to determine the trace Pb in standard reference material SRM 8322 (fly ash from combustion of pulverized coal). The hydride generation atomic absorption spectrometry coupled with flow injection analysis (HGAAS-FIA) was used to analyze the concentration of As in SRM 8322 and the ICP-AES for determination of trace elements Co, Ni, Cu, Cr, etc. For the laboratory research work, all the coal samples were digested with a mixture of acids (HNO3-HF-HCLO4) after burned at 650°C for one hour. Based on the establishment of atomic spectroscopic determination methods Tessier sequential speciation and separation methods were used in the studies of speciation distribution of some heavy metals in fine particles released from coal combustion of Qingshan Thermoelectric Plant. The transition elements in two samples from Qingshan Thermoelectric Plant (with different combustion condition) were extracted into five fractions by sequential extraction. In each fraction a suitable reagents with an optimum pH and time were used. Centrifugate separation of liquid part from the solid part was used after each fraction, the liquid part is taken for analysis and the solid part was extracted with a suitable reagents for the next fraction and the reaction continued for certain time. This procedure was done for the five fractions (exchangeable, carbonate bounded, Fe-Mn oxide bounded, organic matter bounded and residual). The experiment of the stimulant acid rain reacted with coal ash were also done in order to evaluate the transformation of these trace elements into water system after the fine particles of coal ash act with acid rain. The results showed that most parts of the metal in particles are stable. In order to study the distribution tendency of trace elements in coal, the separation of different coal particles were done using organic solvent extraction and gravity settlement method. The results showed that different trace elements had different distribution tendency in coal.