Research On Rapid Fractions Analysis Methods Of Lead In Coal Combustion And Its Products

Coal-fired power plants are one of the major anthropogenic sources of lead emission,and most of lead in coal can be transferred into its combustion products(fly ash,desulfurization gypsum,and slag)after combustion.The toxicity of Pb not only depends on the total amount,but also closely related to its fractions and bioavailability.Revealing the fractions distribution of Pb in coal,fly ash(FA),desulfurization gypsum and slag can more scientifically assess its transport capacity and environmental stability.However,the conventional sequential extraction(CSE)method,which is based on a vibratory approach,suffers from a long experimental cycle and poor reproducibility.Ultrasound and microwaves can be used as intensified means to stimulate the rapid release of the various bound fractions in solids,which is expected to greatly reduce the extraction time of lead.In this thesis,two methods capable of rapid determination of lead forms in coal combustion and its products were established using ultrasound and microwave,respectively,and the reproducibility,analytical parameters and uncertainties of these two methods were analyzed.The microwave method was selected to rapidly extract the lead fractions from coal combustion,fly ash,desulfurization gypsum and slag from 20 power plants to explore their bioavailability.The specific studies are as follows:(1)To investigate the degree of dissolution of experimental samples by wet dissolution method,dry ash dissolution method and microwave dissolution method,the methods were compared.The microwave dissolution method was selected as the optimized method for its short dissolution time,simple operation and high recovery rate.The method was applied to screen out coal,fly ash,desulfurization gypsum and slag samples with high lead content.(2)Using the traditional method(BCR)for sequential extraction,we screened the samples with high contents of Pb,and established two methods for rapid extraction of Pb fractions in coal combustion products using ultrasound and microwave as auxiliary means.The rapid methods reduced the extraction time from 48 h to 20 min while guaranteeing the satisfactory recoveries of Pb(88.3%-108.2%).(3)The developed ultrasonic and microwave methods were applied to coal,fly ash,desulfurization gypsum and slag from six power plants to verify the reproducibility of the methods,and the limits of detection,limits of quantification,linearity,precision and uncertainty of the methods.The results demonstrated that the factors were acceptable.(4)Rapid extraction of lead from coal,fly ash,desulfurization gypsum and slag of20 power plants by microwave method showed that lead in coal and desulfurization gypsum mainly existed as the mobile fraction,with average percentages of 68.23% and77.03%,respectively.Lead in coal and desulfurization gypsum had high bioavailability and high environmental risk.Lead in fly ash and slag mainly existed in the residue fraction,with average percentages of 88.65% and 77.71%,respectively.Lead in this fraction is more stable and with low environmental risks.And the health risks of the four products were assessed.According to the bioavailability factor method(i.e.,considering the metal forms that solid substances can leach in the environment),the lead in coal and gypsum is a bioavailable element with high risk to the environment,and the lead in fly ash and slag is a non-bioavailable element,which is more stable in the environment and has low risk to the environment;according to the risk assessment index method(i.e.,considering metal forms that are easily leached in the environment),the risk level of fly ash is no risk,the risk level of coal and slag is low risk;the risk level of gypsum is medium risk.